Controlled flight into terrain (CFIT)

Investigation summary

What happened

On 5 January 2026, a Helicorp Leonardo Helicopters AW139 with 4 crew on board departed from its Canberra base in the Australian Capital Territory on a medical transport task to the Snowy Mountains, New South Wales. The task was the retrieval of a sick/injured hiker. While in the hover, after commencing to winch the paramedic down to the hiker’s location, the main rotors struck a tree, which had been previously identified by the crew as the nearest obstacle to the helicopter.

What the ATSB found

The crew positioned the helicopter with the nearest obstacle (a tree) in the pilot's blind spot prior to the pilot assuming sole responsibility for clearances to allow the air crew officer and paramedic to prepare for winching. Subsequently, the helicopter started to drift to the left prior to the air crew officer resuming responsibility for clearances.

The pilot did not detect and correct the helicopter’s drift towards its nearest obstacle while in the hover, which resulted in the main rotor striking the tree.

What has been done as a result

Following this occurrence, the operator: 

• released an operations manual bulletin to provide additional guidance on helicopter clearance limits and included an increased minimum lateral clearance of 20 ft (6 m) for the main rotors under all conditions 
• initiated a working group with the tasking agency to improve their operations 
• undertook post-incident assurance activities with the flight crew prior to their return to operations 
• conducted an updated refresher session on verbal escalation during sterile cockpit procedures
• included methods and terminology for escalation in its current human factors training program.

Safety message

Always consider and plan for escape path options in mountainous terrain wherever practicable. In preparation to conduct the winch, the crew positioned the helicopter facing downslope, in the opposite direction to the approach. This provided the pilot with an escape path option for the helicopter, which they used immediately after the main rotor strike occurred.

In addition, the use of minimum clearances in confined areas should be limited to those occasions when the nearest obstacle(s) can be actively monitored by appropriately trained crew. If this is not achievable, then use greater margins wherever practicable. 

The investigation

The occurrence

On 5 January 2026, at 1616 local time, a Helicorp (Toll Helicopters) Leonardo Helicopters AW139 with 4 crew members on board departed from its Canberra base in the Australian Capital Territory on a medical transport task to the Snowy Mountains, New South Wales. The task was a likely winch retrieval of a sick/injured hiker. The crew consisted of the pilot in the front right seat, air crew officer (ACO) in the front left seat, paramedic in the forward right cabin seat, facing rearwards, and doctor in the forward left cabin seat, facing rearwards.

En route to the reported location, the pilot assessed the helicopter’s performance and estimated that they would be 200 kg overweight for a winching operation. Consequently, the crew decided to conduct a search first, to confirm the hiker’s location and burn fuel, before conducting a power check and deciding if the doctor could remain on board for the winching. About 30 minutes after take-off, the paramedic detached from their harness and transitioned to a wander lead¹ to prepare for the winching. The pilot also cleared the ACO to transition from the front left seat to the cabin and onto a wander lead.

On approach to the reported location, the low flying checks were completed, and the ACO opened the right cabin door for the search. The pilot then saw a flare appear below them on the right side of the helicopter and the ACO identified the hiker near a waterfall in a re-entrant,² which was the reported location. They assessed that the helicopter would need to be flown slowly up the re-entrant towards the waterfall and then turned around prior to winching, to provide an escape route down the valley.

The crew conducted their winch checks and then the pilot conducted the power check and confirmed that the helicopter had sufficient power margin to keep the doctor on board for the winching. The helicopter then descended into the re-entrant and transited up the left side at slow speed (Figure 1). Before they reached the hiker’s location, the pilot momentarily stopped the transit as they experienced a ‘power-suck’³ and assessed that they had a tail wind. When the power stabilised, the pilot turned the helicopter around and reversed the helicopter into the re-entrant for the final 200 m to the hiker’s location. 

Figure 1: Entry and exit tracks to the hiker’s location and rotor strike

Source: Toll Group and Google Earth, annotated by the ATSB

After turning the helicopter around, the left cabin door was opened to facilitate the ACO providing obstacle clearances to the pilot who reported that abort options were now down the valley. The crew took about 5 minutes to position the helicopter, assess the power and confirm that they were ready to winch. During this period, the ACO alternated between the open left and right cabin doors and announced clearances to the pilot, identifying the respective door from which they were provided. 

The ACO briefed the pilot that the nearest obstacle was 20 ft away in the 8–9 o’clock position (left side) and directed the paramedic to the right cabin door to assess the ground below and plan the winching operation. The pilot subsequently asked if they could descend further and the ACO moved to the left door and instructed the pilot to descend 20 ft and move back 10 ft. This reduced the risk of a conical spin developing, due to the wind conditions in a narrow insertion point. After descending and backing further into the re-entrant, the pilot reported to the crew that they were starting to experience recirculation⁴, which was increasing the power requirements. Once all indications were normal and within limits, the pilot confirmed the winch operation could proceed. The paramedic and ACO then agreed on their winching location.

Prior to starting the winching, the left door was closed for cabin security. Before the ACO closed the left door, they briefed the pilot that the nearest obstacle was now a tree, 10 ft ‘above and to the left’ (this was 10 ft laterally in the 7–8 o’clock position and above the main rotor disk), and that there were also treetops about 35 ft below on the left. After the ACO closed the left cabin door, they pointed to the nearest obstacle through the window while instructing the doctor ‘that’s yours [name], keep an eye on that’, which the doctor acknowledged.

The ACO asked the pilot if they had a good hover reference, to which the pilot responded in the affirmative. The ACO then announced they were bringing the winch in to get the paramedic ready and that their ‘eyes are inside’, to which the pilot responded, ‘I’ve got the scan’. The ACO and paramedic conducted their pre-winch checks, and the paramedic was brought outside the right door on the winch, at which point the ACO confirmed with the pilot that they were clear to winch. However, before they started to winch, the ACO announced they needed to do the pre-winch brief and aircraft performance brief.

While the ACO was conducting the brief, the doctor was becoming concerned about the obstacle clearance on the left side but did not want to interrupt the ACO during safety‑critical checks. As soon as the ACO completed the briefs and started to winch the paramedic down, the doctor announced they had moved left ‘slightly’, and the ACO immediately cleared the pilot to move right ‘10’. This was followed by escalating calls from the ACO to the pilot to move right. As the pilot attempted to correct to the right, the main rotor struck the tree, and the calls from the ACO immediately changed to ‘move forward’. The pilot then transitioned the helicopter to forward flight while the ACO recovered the paramedic on the winch back into the cabin.

After the helicopter transitioned to forward flight, the pilot conducted a control check, and the ACO detected a clicking noise. The pilot announced that Perisher was the closest pad and requested confirmation of what struck the tree. The ACO and doctor confirmed it was the main rotor that struck the tree in the 7–8 o’clock position and not the tail rotor. The pilot made a PAN call to air traffic control, and the paramedic notified their base of the incident and that they would land at Perisher. The helicopter landed at Perisher at 1737 with minor damage. The hiker subsequently walked out and declined medical assistance.

Context

Personnel information

Pilot

The pilot spent 17 years in Army aviation as a line pilot and instructor. They held an Air Transport Pilot Licence (Helicopter), a class 1 medical certificate without restrictions, and had accumulated 6,880 hours flight experience, which included 2,065 hours on the AW139 with 84 hours in the previous 90 days. They joined the operator in 2016, completed the AW139 type rating in Italy, and started on the helicopter emergency medical service contract in 2017.

Air crew officer

The ACO spent 6 years in Army aviation before joining the operator about 4 years prior to the incident. They had accumulated about 1,700–1,800 hours flight experience, which included 800–900 hours on the AW139. The ACO’s 4 years with the operator included 1 year as a human factors instructor at their previous base.

Retrieval doctor

The doctor started with the emergency medical service 5 years prior to the incident as a registrar. They completed 1.5 weeks of aviation training with the operator, which included winch training and assessment. They conducted cyclic training 3 times per annum, which included human factors and safety management systems discussions with an incident case study. Crew resource management was incorporated in the human factors training.

The doctor reported that the incident flight was their first experience of being asked to monitor an obstacle in a confined area. They were not trained to provide clearances in their aviation training but were taught the safety call ‘climb, climb, climb’ if they had an immediate safety concern. Leading up to the main rotor strike they thought about the safety call but considered it was not appropriate with the obstacles above them and instead alerted the crew to the movement left. 

Helicopter information

General information

The helicopter was a Leonardo Helicopters (formerly Agusta Westland) AW139, manufactured in Italy in 2015 and registered in Australia in December 2015. It was powered by 2 Pratt & Whitney Canada PT6C-67C gas turbine engines and fitted with 5 main rotor blades and 4 tail rotor blades. 

To simplify the pilot’s instrument scan, a power index (PI) indicator is presented on the primary flight display for each engine. The PI combines the torque, temperature and gas generator speed instruments into a single indicator. While the PI is in the green range, no engine limits are exceeded. Above the green range, there is a yellow cautionary range, which indicates the take-off power range and above that, there are 2 red lines indicating maximum take-off PI and maximum transient PI.

Damage

The operator reported minor repairable damage to 3 main rotor blade tips (Figure 2). In addition, there was minor damage to the horizontal stabiliser and tail boom, which were struck by debris from the tree struck by the main rotor.

Figure 2: Main rotor blade damage (left) and horizontal stabiliser damage (right)

Source: Toll Group, annotated by the ATSB

Recorded data

The aircraft was fitted with a Curtis-Wright Multi-Purpose Flight Recorder (MPFR), which contained the cockpit voice recorder and flight data recorder. The MPFR was provided to the ATSB and was successfully downloaded at the ATSB’s Canberra facilities on 7 January 2026. After download, the MPFR data was uploaded to the Flight Animation Software (FAS) program where the flight data and cockpit voice data were synchronised for analysis. 

The FAS program revealed that the PI was fluctuating between the green and yellow ranges while the helicopter was in the hover in preparation for winching. However, the vertical speed was steady with only isolated momentary fluctuations of 50 ft/min rate of climb recorded.

When the ACO cleared the pilot to move right, away from their nearest obstacle, the helicopter rolled level from its left wing low hover attitude, the PI for both engines exceeded the maximum take-off PI red line momentarily and the vertical speed recorded a 100 ft/min rate of climb, followed by the main rotor strike.

The helicopter was also fitted with video-audio recording equipment in several locations, which included the cabin. A copy of the recordings for the accident flight were provided to the ATSB for review and analysis of the sequence of events in the cabin.

Operational information

Operations Manual Volume 2 – Rotary Wing

Volume 2 of the operator’s operations manual provided the rotor clearance requirement of 20 ft (6 m) horizontally from all obstacles. However, the manual also stated that by day only, and once established in the hover, the clearance could be reduced to 10 ft if it allowed for a more suitable winching position.

Operations Manual Volume 6 – Winching Operations

Volume 6 of the operations manual provided the following information for winching operations:

• Once established in the hover the PF [pilot flying] will normally be able to maintain position within the target area. However, there is often a requirement for minor repositioning whilst winching. During this precision manoeuvring the PF is relying on instruction from the ACO to accurately position the aircraft whilst remaining clear of any obstructions.

• A check of the left side of the aircraft must be conducted to identify the closest obstacle and ensure clearances are adequate. If the left door is opened to achieve this clearance, it must be closed prior to committing to the winch. At any time the ACO has their scan / eyes inside or checking the left, they are to advise this and receive acknowledgment from the PF.

• Once the ACO is back on the right side of the aircraft cabin, they are to ask the PF 'HOW IS YOUR HOVER REFERENCE?' If suitable references are available, the PF will respond with ‘HOVER REFERENCES ARE GOOD’ or request manoeuvring to improve references.

• WARNING: If suitable error tolerant hover references cannot be achieved by the PF, winching is not to be commenced.

The winching emergencies section of the manual included the emergency keywords ‘climb, climb, climb’ with the following caveat:

If not appropriate due to obstacles or terrain to call “CLIMB, CLIMB, CLIMB” a call for immediate aircraft movement is to be used in the required direction. For example: “LEFT, LEFT, LEFT”, “RIGHT, RIGHT, RIGHT” OR “MOVE FORWARD NOW.”

Safety analysis

The winch location was in a re-entrant near a waterfall, which required the pilot to turn and reverse the helicopter in for an assessment, before descending to a lower hover height for the planned winching operation. This provided the pilot with an escape route downslope and reduced the risk of a conical spin developing from a high winch but resulted in the nearest obstacle in the 7–8 o'clock position being in the pilot’s blind spot. 

This obstacle was a tree with the nearest branch located above the main rotor disk and laterally clear of it by about 10 ft, which complied with the operator’s minimum clearance requirements. However, the proximity and height of the surrounding trees resulted in recirculation disturbing the helicopter from a stable hover position, which increased the control inputs required by the pilot compared with their initial higher hover height. 

The ACO provided the pilot with obstacle clearances behind the helicopter until it was time to conduct their pre-winch checks with the paramedic, at which point nobody qualified was available to provide clearances to the rear of the helicopter. While the ACO and paramedic prepared for the winching, the doctor was monitoring their nearest obstacle to the rear left. When the ACO moved onto the pre-winch and aircraft performance briefs, the pilot was aware the ACO had returned to the right door, and the doctor started to sense the helicopter was drifting left towards their nearest obstacle. However, the ACO had not resumed providing clearances and the doctor’s training had reinforced the importance of not interrupting safety‑critical checks. 

Due to the risk of a person descending on the winch snagging on the airframe, the ACO would not resume their scan to provide clearances until after the paramedic had descended below the airframe. However, when the ACO started their pre-winch brief at the right door, it was possible that either the pilot anticipated the ACO resuming their scanning role and relaxed their own scan, or that their attention was diverted from their external scan by the briefs, such that they did not detect and correct the helicopter’s drift.

The doctor alerted the crew to the fact that they appeared to be drifting to the left as soon as the ACO started to winch the paramedic down, which triggered a ‘move right’ call from the ACO to the pilot. In response, the pilot applied a small roll input to the right combined with a small increase in collective and the main rotors struck the nearby tree.

Findings

From the evidence available, the following findings are made with respect to the main rotor strike involving Leonardo Helicopters AW139, VH-TJF, 42 km south-east of Corryong Airport, New South Wales, on 5 January 2026. 

Contributing factors

• The crew positioned the helicopter with the nearest obstacle (a tree) in the pilot's blind spot prior to the pilot assuming sole responsibility for clearances to allow the air crew officer (ACO) and paramedic to prepare for winching. Subsequently, the helicopter started to drift prior to the ACO resuming responsibility for clearances.
• The pilot did not detect and correct the helicopter’s drift towards its nearest obstacle while in the hover, which resulted in the main rotor striking a nearby tree.

Safety actions

Safety action by Helicorp

The operator released an Operations Manual Bulletin in response to the incident, which addressed the following points:

• increased their rotor clearance limit to 20 ft (6 m) in all circumstances
• provided additional guidance on determining spacing from overhanging obstacles
• provided additional guidance on the requirements for error tolerant references
• emphasised the need to prioritise error tolerant hover reference(s) selection over escape and downwash considerations.

A working group was initiated between the operator and tasking agency to improve interagency operations. Additionally, post-incident assurance activities were undertaken with the flight crew prior to their return to operations and an updated refresher session on verbal escalation during sterile cockpit procedures was conducted. Methods and terminology for escalation have also been included in their current human factors training program.

Sources and submissions

Sources of information

The sources of information during the investigation included the:

• ACT Ambulance Service
• cabin video footage and audio of the incident flight
• operator, its head of aviation safety and quality, and its investigator
• pilot, air crew officer and retrieval doctor of the incident flight
• recorded data from the MPFR unit on the aircraft. 

Submissions

Under section 26 of the Transport Safety Investigation Act 2003, the ATSB may provide a draft report, on a confidential basis, to any person whom the ATSB considers appropriate. That section allows a person receiving a draft report to make submissions to the ATSB about the draft report. 

A draft of this report was provided to the following directly involved parties:

• Agenzia Nazionale Per La Sicurezza Del Volo (ANSV, Italy)
• air crew officer
• Civil Aviation Safety Authority
• Leonardo Helicopters
• operator
• pilot
• retrieval doctor.

Submissions were received from:

• air crew officer
• Civil Aviation Safety Authority
• operator
• pilot.

The submissions were reviewed and, where considered appropriate, the text of the report was amended accordingly.

Purpose of safety investigations The objective of a safety investigation is to enhance transport safety. This is done through:  identifying safety issues and facilitating safety action to address those issues providing information about occurrences and their associated safety factors to facilitate learning within the transport industry. It is not a function of the ATSB to apportion blame or provide a means for determining liability. At the same time, an investigation report must include factual material of sufficient weight to support the analysis and findings. At all times the ATSB endeavours to balance the use of material that could imply adverse comment with the need to properly explain what happened, and why, in a fair and unbiased manner. The ATSB does not investigate for the purpose of taking administrative, regulatory or criminal action. About ATSB reports ATSB investigation reports are organised with regard to international standards or instruments, as applicable, and with ATSB procedures and guidelines. Reports must include factual material of sufficient weight to support the analysis and findings. At all times the ATSB endeavours to balance the use of material that could imply adverse comment with the need to properly explain what happened, and why, in a fair and unbiased manner. An explanation of terminology used in ATSB investigation reports is available here. This includes terms such as occurrence, contributing factor, other factor that increased risk, and safety issue. Publishing information Released in accordance with section 25 of the Transport Safety Investigation Act 2003 Published by: Australian Transport Safety Bureau © Commonwealth of Australia 2025 Ownership of intellectual property rights in this publication Unless otherwise noted, copyright (and any other intellectual property rights, if any) in this report publication is owned by the Commonwealth of Australia. Creative Commons licence With the exception of the Commonwealth Coat of Arms, ATSB logo, and photos and graphics in which a third party holds copyright, this report is licensed under a Creative Commons Attribution 4.0 International licence. The CC BY 4.0 licence enables you to distribute, remix, adapt, and build upon our material in any medium or format, so long as attribution is given to the Australian Transport Safety Bureau.  Copyright in material obtained from other agencies, private individuals or organisations, belongs to those agencies, individuals or organisations. Where you wish to use their material, you will need to contact them directly.

Investigation summary

What happened

On 18 September 2025, the pilot of a Cirrus SR20, registered VH-TEL, planned to conduct a personal flight under visual flight rules (VFR) from Bankstown Airport, New South Wales, to Mount Kosciuszko (without landing) and return. The pilot was the sole occupant on board.

The pilot took off from Bankstown Airport and flew south to, and then around, Mount Kosciuszko. The pilot then flew to Mallacoota Airport, Victoria, tracking overhead various aerodromes.

Once passing Mallacoota Airport the pilot began to descend while tracking north towards Merimbula Airport, New South Wales. Recorded data indicated that the pilot began to receive warnings about a high engine cylinder head temperature in cylinder 4. Additionally, there was low cloud in the area ahead.

While descending towards Moruya Airport, the pilot contacted Melbourne Centre air traffic control stating an intention to land. There were no further radio calls from the pilot. The pilot continued to track towards Moruya Airport before diverting to the west, continuing north-west towards the Great Dividing Range.

The pilot continued north-west for 13 minutes at 2,500 ft. For the remainder of the flight, the pilot maintained an altitude between 2,000 and 2,700 feet above mean sea level (AMSL), with intermittent climbs and descents. The mountainous area had fluctuating terrain heights, with a maximum terrain height of about 2,900 ft.

At 1458 the aircraft collided with terrain in dense forest in the Budawang National Park. The aircraft was destroyed, and the pilot was fatally injured.

What the ATSB found

The commencement of an approach to land at Moruya was not part of the flight plan and most likely the result of the warning and/or cloud ahead. It is unclear why the pilot made the decision to continue the flight rather than land at Moruya, as poor weather was present ahead of the aircraft and the pilot would have been seeing fluctuating cylinder temperature warnings. However, with limited prior experience in cross-country flights and facing deteriorating weather conditions, the pilot would have been less able to objectively weigh the cumulative hazards of continuing into adverse weather. 

The decision to deviate inland from the initial planned track and toward higher terrain was likely influenced by the perceived presence of a clear area ahead in the cloud layer. This gap, evident at the approximate time the aircraft passed to the west of Moruya Airport, would have presented a visually clearer path to the pilot. Furthermore, there was cloud over Moruya Airport and the pilot may have considered that maintaining VMC throughout an approach and landing there might not have been feasible. The cylinder head warnings were likely spurious but, even if the pilot had understood this, the warnings would have been an ongoing source of distraction.  

Following the decision to continue, tracking data showed the aircraft proceeding into the mountainous area of the Great Dividing Range, then almost reversing course at low altitude along a valley within the Great Dividing Range, consistent with an attempt to avoid cloud. Once in the valley, it is likely that the pilot did not know what direction to take away from the mountainous areas and cloud or, if they did, became trapped between the rising terrain and the low cloud base.

It is therefore likely that the pilot inadvertently entered instrument meteorological conditions (IMC) and became unable to regain visual references, which led to a loss of terrain awareness and the subsequent controlled flight into terrain.

Safety message

Research and investigations by the ATSB continue to show that weather‑related accidents remain one of the most persistent accident types in general aviation. When operating under visual flight rules (VFR), pilots must always be prepared to make conservative decisions when weather conditions begin to deteriorate. If visibility is reducing or the cloud base is lowering, pilots should strongly consider landing at the nearest suitable location rather than continuing into worsening conditions. Making an early decision to land, delay, or turn back can prevent a situation where safe flight cannot be maintained.

Attempts to maintain visual contact with the ground in marginal weather, commonly referred to as ‘scud running’, significantly increase the risk of controlled flight into terrain (CFIT). Reduced visibility, low cloud, and poor contrast can quickly lead to disorientation or collision with unseen obstacles or terrain. Continuing flight in these conditions often provides little margin for error, especially at low altitude.

Pilots are reminded to maintain situational awareness and resist the pressure to continue to a planned destination (commonly referred to as ‘get-there-itis’) when conditions no longer support safe visual flight. Additionally, if VFR pilots find themselves in marginal weather and becoming disoriented or lost, they should seek whatever help is available. Air Traffic Services (ATS) may be able to provide assistance, especially if the aircraft is in ATS surveillance coverage. There have been a number of reported occurrences where this simple action has averted potential disaster.

The investigation

The occurrence

On 18 September 2025, the pilot of a Cirrus SR20, registered VH-TEL, planned to conduct a pleasure flight under visual flight rules (VFR)[1] from Bankstown Airport, New South Wales, to Mount Kosciuszko (without landing there) and return. The pilot would be the sole occupant.

The pilot arrived at Bankstown Flying School (BFS), from which the aircraft was being hired, at about 0900. The owner of the flying school recalled the pilot requested assistance in how to add locations with no designated waypoints (Mount Kosciuszko and Thredbo) into their flight plan. After assisting with their flight plan, the owner asked the pilot about the weather for their planned route and information about last light.[2] The pilot had reported the weather was good for the flight and that last light was at 1800, however they planned to be back by 1700. 

At 0910 the pilot took the aircraft out of the hangar and had it refuelled. The owner recalled the aircraft should have been filled to full prior to the flight.

At approximately 1113 local time, the pilot took off from Bankstown Airport. Recorded data from the onboard GPS showed that once airborne, the pilot tracked to waypoint CAMB (Campbelltown University), passing 2,500 ft above mean sea level (AMSL) at 1121. The aircraft continued climbing through 4,500 ft while passing waypoint PIC (Picton) and at 1131 the aircraft was levelled off at 6,500 ft (Figure 1).

At 1150 the pilot began climbing to 8,500 ft and levelled off just prior to flying over the former Braidwood aircraft landing area (ALA).[3] The pilot continued to fly to and then around Mount Kosciuszko before climbing again to 9,500 ft. The pilot then flew for approximately 40 minutes to (overhead) Mallacoota Airport, Victoria, tracking overhead various aerodromes.

Figure 1: Flight path overview

Source: Google Earth, annotated by the ATSB

Once passing Mallacoota Airport at 1342, aircraft flight data showed the pilot began to descend while tracking towards Merimbula Airport, New South Wales, and then continued further north. 

At about 1426, the pilot contacted Melbourne Centre air traffic control (ATC) stating:

Moruya traffic Cirrus Tango Echo Lima is one zero miles south inbound with a straight in approach runway 36 thanks

There were no further radio calls from the pilot. The pilot continued to track towards Moruya Airport at 2,000 ft before diverting left and climbing to 2,500 ft passing the airport to the west at 1431 (Figure 2).

Figure 2: Diversion from Moruya Airport approach track

Source: Google Earth, annotated by the ATSB

The pilot continued north-west for 13 minutes at about 2,500 ft AMSL. For the remainder of the flight, the pilot maintained an altitude between 2,000 and 2,700 feet AMSL, with intermittent climbs and descents (Figure 3). The mountainous area had fluctuating terrain heights, with a maximum terrain height in the area of about 2,900 ft. 

Approximately one minute prior to the collision, the aircraft’s speed decreased to 69 kt before rapidly increasing to 101 kts just prior to the collision with terrain.

At 1454 the aircraft collided with terrain in dense forest in the Budawang National Park at 2,800 ft AMSL. The aircraft was destroyed, and the pilot was fatally injured. 

The aircraft’s emergency locator transmitter (ELT) activated in the accident, alerting the Australian Maritime Safety Authority (AMSA) Joint Rescue Coordination Centre (JRCC).

A rescue helicopter located the wreckage at about 1700 on 18 September, however rescue crews were unable to access the site due to the weather. The site was first accessed the following day by winch at about 1300. Rescue crew and police confirmed the occupant was deceased.

Figure 3: Flight path of the last 15 minutes of the flight

The lower plot does not show the point of impact, because the data recording ceased prior to that point. Source: Google Earth, annotated by the ATSB

Context

Pilot information

License and endorsements

The pilot held a Civil Aviation Safety Regulation Part 61 Private Pilot (Aeroplane) Licence, single-engine aeroplane class rating, night VFR rating for single-engine aeroplanes, and endorsements for manual propeller pitch control and retractable undercarriage. The pilot had held a licence since 1979. Their last flight review was on 2 November 2023 in VH-TEL and was valid until 30 November 2025. 

Flying history

The pilot ceased flying between mid-1988 and early 2008. Between January 2008 and February 2021, 6 flights were recorded, all conducted as in command under supervision (ICUS).

The pilot had accumulated 306.5 hours experience through to 10 February 2021. On 19 October 2021, the pilot commenced a PPL refresher course with BFS for the purpose of completing a flight review.

The pilot’s logbook indicated flights beginning in June 2024 and noted that their prior logbook had been stolen. It recorded that at the time of the accident the pilot had approximately 443.7 flight hours, including 4.5 hours in VH-TEL in the last 90 days. 

Additional flight data retrieved from the flying school on the pilot’s flight prior to June 2024 indicated that, at the time of the accident, the pilot had accumulated approximately 515 total flight hours.[4] Of these, approximately 60 hours were on the Cirrus SR20 aircraft since the pilot’s initial flight in the Cirrus in June 2023. All of these flights were conducted in VH-TEL.

Flight review and training

In October 2021 the pilot completed a training area flight and circuits flight. Additionally, the pilot completed 3 navigation flights in November 2021, January 2022 and February 2022 with a BFS Grade 2[5] flight instructor, in preparation for the pilot’s flight review for the PPL refresher course. On completion of the third navigation flight, the instructor recommended the pilot fly with a Grade 1 instructor to assess their ability relative to the flight review standards required. 

The Grade 1 instructor conducted 2 navigation flights with the pilot and reported the flight review was successfully completed after the second navigation flight with the remark that the pilot needs to ease back into flying. This flight review was completed on 18 May 2022, which was the signatory date for the pilot’s application to transfer their licence from Civil Aviation Regulations 1988 (CAR) Part 5 to Civil Aviation Safety Regulations 1998 (CASR) Part 61. The flight review had been conducted in a Piper PA‑28 Archer II (VH‑NRM).

The pilot enrolled in the Cirrus SR20 Perspective Transition (VFR) course[6] on 13 May 2023. The flights were conducted in June and July 2023, which was prior to the pilot’s flight review in VH-TEL on 2 November 2023. None of the 5 flight lessons included instrument meteorological conditions (IMC) [7] recovery as a task.

In addition to the flights, the pilot completed the Cirrus SR Series Manoeuvres Course, which was a series of videos, which included the following topics:

• VFR into IMC

• Straight and Level

• Level Turns

• Climbs and Descents

• Find Your Way Out [of IMC]

• Flight Into IMC Demo.

Following the completion of their SR20 conversion training in November 2023, the pilot operated the SR20, specifically VH-TEL, on an average of 2 flights per month until March 2025. From March to June 2025, the pilot transitioned to flying the Piper PA-28 on a biweekly basis.

Due to the pilot’s recent absence from operating the SR20 during this timeframe, a currency flight was required in July 2025. This flight was conducted on 4 July 2025 in VH‑TEL, under the supervision of an instructor. The instructor recorded in the student progress record and advised the ATSB that several technique errors occurred during the flight, which resulted in the instructor assessing the pilot as not competent. The pilot returned to flying the PA-28, completing 2 flights in the Sydney area, both scenic.

On 6 August 2025, the pilot conducted a second currency flight in VH-TEL with a different flight instructor. This was a flight into the training area before returning for circuits. The instructor recorded on the progress record that the pilot’s groundwork was good, and radio calls were well executed. The departure was performed satisfactorily, the approach was adequate, and the landing was described as very good and smooth. The instructor noted that the pilot flew the aircraft satisfactorily but required further attention to airspace management. Following this flight, the pilot was assessed as competent to operate the SR20.

There was no record of the pilot having conducted or completing any other relevant instrument flying training or qualifications.

Medical information

The pilot held a valid class 2 aviation medical certificate which was approved in March 2025. The only limitation to the pilot’s medical certificate was for reading correction to be available while exercising the privileges of their licence.

The owner of BFS reported that the pilot looked healthy and displayed normal behaviour on the morning of the flight. 

Post-mortem examination and toxicology reports were not available to the ATSB at the time of publishing this report.

Aircraft information

The Cirrus SR20 is a low-wing general aviation aircraft with 5 seats. VH-TEL had a single, Continental IO-360-ES26B reciprocating piston engine driving a constant-speed propeller. The aircraft was certified for day and night VFR and instrument flight rules (IFR)[8] operations.

VH-TEL was manufactured in 2014 and was first registered in Australia on 5 September 2014. The aircraft had been registered with BFS since April 2020, and at the time of the accident had accumulated 1,725.8 hours total time in service.

The aircraft was fitted with the Cirrus airframe parachute system (CAPS). This was designed to lower the aircraft and its passengers to the ground in the event of a life‑threatening emergency and could be activated by the pilot. The CAPS system consisted of a parachute, a solid-propellant rocket used to deploy the parachute, an activation handle, and a parachute harness embedded within the fuselage structure.

Meteorological information

Bureau of Meteorology forecasts

The applicable graphical area forecasts (GAF) available to the pilot for the flight were both issued at 0804 local and valid for the periods 0900–1500 and 1500–2100. The location of the accident was in Area A on the GAF. Area A for the period 0900–1500 forecast broken cumulus/stratocumulus from 3,000–7,000 ft. 

The TAF[9] for Canberra was CAVOK[10] conditions. The TAF for Moruya[11] included light showers of rain and a broken cloud base at 3,000 ft AGL. The TAF for Jervis Bay was a broken cloud base at 1,600 ft AGL becoming scattered at 3,000 ft AGL from 1100–1300 but with TEMPO periods from 0700–1200 for visibility reduced to 4,000 m with a scattered cloud base at 600 ft AGL and a broken cloud base at 1,000 ft AGL. 

Bureau of Meteorology observations

At 1430, the meteorological aerodrome report (METAR)[12] for Moruya Airport reported wind from the east-north-east at 7 kt (60°), visibility greater than 10 km and cloud overcast at 4,900 ft AGL. The METAR at Jervis Bay Airfield reported wind from the west‑south-west at 8 kt (240°), visibility greater than 10 km and cloud scattered from 2,100 ft and overcast above 2,900 ft AGL.

At 1500, the cloud cover had changed at both locations (Table 1).

Table 1: Reported METAR/SPECI[13] cloud layers at nearest airports

BKN: broken; OVC: overcast; SCT: scattered

Bureau of Meteorology satellite images (Figure 4 – left) showed cloud covering the Budawang National Park mountains at 1430. At 1500 (Figure 4 – right) the satellite imagery indicated a reduction in cloud cover, with partial clearing evident and some breaks observed in the cloud layer. The images provided no information on cloud height, or density at a given height.

Figure 4: Satellite image showing cloud formation on 18 September at 1430 and 1500 local time

The flight path was overlaid on the satellite image to illustrate the route relative to the weather. The actual flight occurred below the cloud base. Source: Bureau of Meteorology, annotated by the ATSB

Witness observations of weather

A witness located approximately 3 km west of the accident site reported hearing the aircraft, however, was unable to locate it in the sky due to fog.[14] They reported that prior to the fog, low lying cloud had been covering the tops of the mountains in the area where the collision with terrain occurred from approximately 1130. 

Another witness who was in Wog Wog (10 km north of the accident site) stated that there had been low cloud and drizzle from 1100. They described the visibility to have been ‘okay’ at ground level but poor near the tops of the mountains. 

Additionally, the operator for the rescue helicopter reported they were unable to access the site due to low lying cloud (Figure 5).

Figure 5: Cloud over the accident site between 1640 and 1703 local time

Top left and top right: cloud coverage to the north of the accident site. Bottom left: overhead the accident. Bottom right: view of the accident site and surrounding weather from the east. Source: ACT Emergency Services Agency, annotated by the ATSB

Accident site and wreckage

The aircraft wreckage was located in heavily vegetated, steep, mountainous terrain (Figure 6).

Figure 6: Overhead view of accident site

Source: ATSB

The ATSB conducted an examination of the accident site and wreckage on 21 September. The aircraft impacted the side of the mountain and slid backwards from the direction of travel until supported on the slope by some small trees. Ground impact marks and impact marks on the trees indicated the aircraft entered the trees with wings and fuselage almost level.

All of the flight controls and surfaces were accounted for on site and no evidence of in‑flight break‑up or pre-impact control issues was identified.

Onsite examination of the engine did not reveal any pre-impact mechanical issues. The propeller assembly had separated from the engine crankshaft, with propeller deformation consistent with the engine producing power at impact. The left- and right-wing fuel tanks had both been compromised and a fuel odour was present.

Data cards from a Garmin G1000 electronic flight instrument system and the aircraft’s data recovery module (RDM)[15] were recovered from the accident site (see Recorded data).

Cockpit assessment revealed the fuel selector was on the right tank, the flaps were set at 50%[16] and the fuel pump was off.[17]

The CAPS had not been activated.

Recorded data

Garmin 1000

The aircraft was fitted with a Garmin G1000 electronic flight instrument system consisting of one primary flight display and one multi-function display (MFD). The G1000 had a 58‑channel flight and engine parameter data logging capability at a rate of one data point per second. A memory card was retrieved from the device, which contained recorded data from multiple flights, including the accident flight. 

The final recorded data point was 2 seconds prior to impact and indicated that the engine was producing normal power until impact. Additionally, the data indicated there was sufficient fuel flow to the engine and there was approximately 10.8 US gallons in the left tank and 7.4 US gallons in the right tank of fuel remaining. This was consistent with ATSB estimates of fuel usage, which also indicated that the aircraft would have had about 48 minutes endurance on landing if the flight had been able to continue to Bankstown Airport with the same engine power applied.

Cylinder head temperature

Recorded engine data indicated the number 4 cylinder head temperature (CHT) increased from the normal operating range into the caution range when the aircraft was about 33 NM (61 km) south of Moruya Airport. Approximately one minute later, the temperature increased into the warning range.

The MFD installed in the cockpit displays CHT information and cautions/warnings. The MFD typically displays individual cylinder CHT as a vertical bar graph scaled from 100°F to 500°F in 100°F increments on the left-hand side of the MFD (Figure 7). Additionally, an engine information page can be selected by the pilot displaying individual cylinder CHT as a vertical bar graph with the current temperature value displayed numerically above the bar. An upward or downward trend arrow is shown below the numeric value to indicate whether the temperature is rising or falling. The G1000 did not record which pages were selected by the pilot at any given time.

Figure 7: MFD engine indication system (EIS) panel, showing the vertical coloured bars indicating a CHT warning state for engine cylinder 4 temperature

Source: Garmin, annotated by the ATSB

The pilot operating handbook (POH) published limits for the CHT were as follows, with the bar graph coloured accordingly:

• Normal range < 420°F (green)
• Caution range 420–460°F (yellow)
• Warning range > 460°F (red)

According to the POH:

In the event CHT exceeds 420°F, the MFD will display “Check CHT” in a yellow advisory box in the lower right corner of the MFD. In the event CHT exceeds 460°F, the MFD will display “Check CHT” in a red advisory box in the lower right corner of the MFD.

Figure 8: Exemplar window showing the crew alerting system (CAS) location and text for a CHT warning, the highlighted alerts softkey, and related alerts window text

Source: Garmin, annotated by the ATSB

The emergency procedure for a high cylinder head temperature from the Cirrus SR20 Airplane Flight Manual (AFM) indicated that if the CHT is in the caution range to land as soon as practical, and if it is in the warning range to land as soon as possible.[18]

For the remainder of the flight, the CHT of cylinder 4 continued to fluctuate, repeatedly moving between the normal (green), caution (yellow), and warning (red) ranges (Figure 9).

Following the initial rise in CHT into the warning range, the recorded engine data showed the pilot commanded a reduction in engine power over an approximately 30 second period, maintaining the reduced power for about one minute further. This is consistent with standard practice for managing elevated CHT. Approximately one minute after the power was reduced, as the CHT decreased and stabilised within the normal (green) operating range, and the data indicated the pilot then restored engine power to the previous level.

Figure 9: Number 4 cylinder head temperature readings throughout the last 1.5 hours of the flight

Source: Google Earth, annotated by the ATSB

The ATSB compared the recorded CHT and exhaust gas temperature (EGT) data for cylinder 4 in order to determine whether the observed high CHT indications were consistent with an overheating cylinder or were more likely the result of a faulty CHT probe. In normal engine operation, a genuine rise in cylinder head temperature is typically accompanied by a corresponding rise in EGT for the affected cylinder, as both parameters respond to increased combustion temperatures and heat rejection. Conversely, a significant increase in indicated CHT with little or no corresponding change in EGT is characteristic of a failing or erratic CHT sensor.

The analysis indicated that the EGT for cylinder 4 remained relatively stable and within normal operating limits throughout the period when CHT repeatedly entered the yellow and red advisory ranges. This suggested that the anomalies were most likely caused by a faulty cylinder 4 CHT probe. The ATSB presented this information to Cirrus Aircraft which agreed that ‘the CHT sensor was giving faulty information as there were no other indications that there was an engine issue in the data.’

Other recorded data

AvPlan

The pilot was using AvPlan electronic flight bag (EFB)[19] software for the flight. The EFB recorded flight data up until and after the collision with terrain. This flight path data was consistent with the data retrieved from the Garmin G1000. AvPlan uses a device built‑in GPS or an external Bluetooth/wi-fi GPS source for the aircraft position.

Flightradar24, FlightAware and ADS-B Exchange

The aircraft’s track was independently corroborated using data from FlightAware, Flightradar24 and ADS-B Exchange. All 3 services provided consistent position reports, derived from received ADS-B transmissions, for the duration of the flight until the aircraft reached the Budawang National Park.[20] After this point the tracks from the 3 providers began to diverge slightly, primarily due to differences in receiver coverage, data processing and extrapolation algorithms[21] when direct ADS-B signals were no longer received. None of the 3 services recorded any further validated ADS-B positions corresponding to the final portion of flight leading to the accident site.

Operational information

General

The owner of BFS reported that the pilot had intended to conduct a flight to Mount Kosciuszko approximately 6 weeks prior to the accident flight and several times afterwards. However, on each occasion the flight was planned, the pilot either rescheduled or cancelled due to adverse weather conditions. The owner stated that these cancellations were typically attributed to icing conditions in the vicinity of Mount Kosciuszko. The owner noted that the pilot demonstrated a high level of weather awareness.

Prior to the accident flight, the owner confirmed with the pilot that the pilot had checked the weather conditions. However, the owner did not independently verify the weather, as the flight was not a training operation, and they considered the pilot competent in assessing weather conditions.

Previous flights

In the 12 months preceding the accident, the pilot had accumulated 31.9 hours of flight time between the Cirrus SR20 and the Piper PA-28 Cherokee. The pilot’s longest flight during this period was 1.9 hours in duration, with an average flight time of 1.4 hours. All flights were conducted within the Sydney area, with the furthest north being Gosford, the furthest south being Port Kembla, and the furthest west being the mountainous area around the Three Sisters landmark in the Blue Mountains (Figure 10). The accident flight was the pilot’s first flight of more than 4 hours since January 2023.

Figure 10: Previous flight data                                                                                 

Source: Google Earth, annotated by the ATSB

Flight plan

Flight plans are only required for a VFR flight under certain conditions. One of the instructors recalled that the pilot would routinely submit a search and rescue time (SARTIME) and not file a flight plan. The instructor recalled they had discussed with the pilot the benefits of lodging a flight plan, including that in the event the aircraft became overdue, a flight plan would provide search and rescue authorities with valuable information to assist in determining the intended route and location to commence search efforts.

Under the Civil Aviation Safety Regulations (CASR) Part 91 General Operating and Flight Rules Manual of Standards (MOS) 2020: 9.02 Flight notification requirements, a pilot in command must ensure that one of the following has occurred if flying into a designated remote area:

• the submission of a flight plan;

• the nomination of a SARTIME for arrival;

• the leaving of a flight note with a responsible person.

For this flight, the pilot had filed a VFR flight plan via the National Aeronautical Information Processing System (NAIPS) prior to departure as the planned route transited a designated remote area of the Snowy Mountains. 

The flight plan indicated the pilot would fly south to Mount Kosciuszko before turning towards the coast to Merimbula Airport (Figure 11). The pilot would then head north through a VFR lane, using VFR waypoints, over the coastline (east of the Great Dividing Range) back to Bankstown Airport. When reaching Merimbula Airport the aircraft would be at an altitude of 9,500 ft AMSL and begin a decent to 7,500 ft AMSL reaching the altitude at Moruya Airport before further descending to 2,000 ft when reaching Ulladulla. Pilots are required to notify air traffic services (ATS) if the route, cruising level, or cruising speed changes from a submitted flight plan. Although the actual flight varied from the plan, the pilot did not notify ATS of the changes. 

When the pilot’s instructor was asked what pilots are taught in such circumstances, they stated that pilots are instructed to notify ATS of any change in plan or if they intend to deviate from their planned route. However, the instructor noted that the pilot had obtained their private pilot licence in the 1980s and was unsure whether this topic had been recently discussed with the pilot, as they had never observed the pilot submit a flight plan during their conversion training.

Figure 11: Planned flight (blue) comparison to actual flight (yellow)

A. Bankstown Airport; B. Campbelltown University waypoint; C. Picton waypoint; D. pilot chosen waypoint using lat/long; E. Moruya Airport. Source: ATSB

Visual meteorological conditions

Visual meteorological conditions (VMC) are expressed in terms of in-flight visibility and distance from cloud (horizontal and vertical) as prescribed in the CASR Part 91 (General Operating and Flight Rules) Manual of Standards (MOS) 2020: 2.07 VMC criteria. These conditions allow pilots to operate the aircraft primarily by visual reference to the terrain and horizon, maintaining situational awareness and separation from other aircraft without reliance on instruments.

For flight below 10,000 ft AMSL, the Part 91 MOS prescribed that pilots maintain a minimum visibility of 5 km, and remain at least 1,000 ft vertically and 1,500 m horizontally clear of cloud. In areas below 3,000 ft AMSL or 1,000 ft above ground level (AGL), and within uncontrolled airspace, VFR flights may operate clear of cloud and in sight of the ground or water, provided visibility remains at or above the required minima. These criteria ensure that pilots have sufficient external visual references to maintain safe flight and effective traffic separation.

The CASA Visual Flight Rules Guide included the following notes for VFR flight:

Pilots should not initiate VFR flight on top of more than SCT [scattered] [22] cloud when weather conditions are marginal. Before committing to operate VFR flight on top of more than SCT cloud, pilots should be confident that meteorological information used is reliable and current, and clearly indicates that the entire flight will be able to be conducted in VMC.

and

Pilot decision-making, particularly regarding weather and flight, is often complex; however, the solution to avoiding VFR into IMC [instrument meteorological conditions] when weather is marginal before take-off is not to depart. During flight, it is to turn back or divert before it becomes impossible to do so.

Figure 12, taken from the CASA Visual Flight Rules Guide, provides a visual depiction of the VMC criteria for aeroplanes below 10,000 ft.

Figure 12: VMC criteria below 10,000 ft

Source: Civil Aviation Safety Authority

Pilot response to weather

When questioned about how the pilot typically obtained weather information for the flight, the instructor stated that the weather would have been checked prior to departure using TAFs and GAFs. The instructor expected that the pilot would also have been monitoring the automatic terminal information service (ATIS) while en route.

The instructor further recalled a previous flight (in May 2022) with the pilot during which the pilot descended to avoid entering cloud. At that time, the instructor questioned the pilot on the VMC requirements for the flight. The pilot became overwhelmed and elected to return to the departure aerodrome. The instructor recalled that there were no subsequent discussions between them regarding operations in adverse weather, and none of the remaining training flights were conducted in cloudy conditions. The instructor noted that the pilot avoided flying into or near clouds and had previously cancelled multiple flights due to weather.

Pilots can confirm destination weather in flight using multiple approved sources. The aerodrome weather information service (AWIS) is available on a published VHF frequency or by telephone. Review of the aircraft data indicated the radios were not changed to published AWIS VHF frequencies at any stage of the flight, and the pilot was not carrying a mobile phone that could have been used to obtain an AWIS broadcast by telephone. 

Where fitted with ADS-B In and a suitable display (such as an EFB),[23] pilots may receive real-time weather data including METAR, TAF, airmen's meteorological information (AIRMET),[24] significant meteorological information (SIGMET),[25] and GAF forecasts within coverage. An approved EFB can also provide these products via internet or satellite subscription. The pilot carried an EFB running AvPlan, which was capable of displaying current meteorological information however, there was no recorded data to confirm whether the pilot accessed this information at any stage of the flight.

Communication

The aircraft was equipped with 2 independent VHF communication transceivers (COM 1 and COM 2). Each transceiver could display and store 1 active frequency and 1 standby frequency simultaneously, resulting in a total of 4 frequencies available to the pilot. The instructor stated that at BFS they teach students to use COM 1 as the primary radio used for monitoring towers and ATS and COM 2 is used for secondary frequencies such as the common traffic advisory frequency (CTAF) and ground frequencies.

The pilot had configured COM 1 as the active radio and COM 2 as standby. Prior to departure, COM 2 was set to the Bankstown Airport ground frequency and left on this frequency for the entirety of the flight. COM 1 was initially set to the Bankstown Airport tower/CTAF frequency and changed throughout the flight. When flying south-east near Braidwood, the pilot changed frequencies multiple times within 9 minutes. They first selected an unknown frequency (125 MHz), then Sydney Tower (120.5 MHz), and then a second unknown frequency (120.15 Mhz), before selecting Melbourne Centre (120.75 MHz). The pilot then maintained 120.75 MHz (Melbourne Centre) as the active frequency after passing Braidwood ALA and continued using this frequency for the remainder of the flight.

The only recorded inflight radio transmission was made on the Melbourne Centre frequency with the pilot indicating a decision to land at Moruya.

VFR into IMC research

The ATSB, in conjunction with research published by CASA, has identified that VFR pilots continuing flight into IMC remains one of the most consistently fatal types of general aviation occurrence. These events are characterised by a loss of visual reference resulting in spatial disorientation, loss of control, or controlled flight into terrain. The onset of IMC during VFR flight is often sudden, and pilots without instrument training or recent instrument experience typically have little time to recover once visual cues are lost.

ATSB occurrence data showed that many VFR into IMC accidents follow a consistent pattern of decision‑making and flight progression. Pilots often either depart into marginal weather conditions and/or continue as conditions deteriorate, influenced by a strong ‘press-on’ mindset to reach their destination. A 2005 ATSB research publication – General Aviation Pilot Behaviours in the Face of Adverse Weather (B2005/0127) – concluded that the likelihood of encountering IMC increases significantly during the final stages of flight, particularly within the last 20% of the planned route. 

CASA’s associated AvSafety - Flying into bad weather card[26] supports these findings, noting that poor weather-related decision-making and underestimation of meteorological risks remain persistent issues across the VFR pilot population. The education programs, including CASA’s online Pilot safety hub[27] encourage pilots to establish and adhere to personal weather minima, obtain updated forecasts before and during flight, and avoid reliance on visual cues when conditions are near or below VMC limits.

Related occurrences

Recent examples of VFR into IMC accidents are provided below.

Collision with terrain involving Beechcraft 35-C33 Debonair, VH-KZK, 12 km east of Khancoban, New South Wales, on 15 July 2025 (AO-2025-040)

On 15 July 2025, a Beechcraft 35-C33 Debonair, registered VH-KZK, departed Wangaratta Airport, Victoria, for a private flight under the visual flight rules (VFR) to Moruya Airport, New South Wales. Soon after entering the Snowy Mountains area, it is very likely that the pilot, who did not hold an aircraft instrument rating, experienced spatial disorientation after flying into instrument meteorological conditions. The aircraft entered a spiralling descent to the right that continued until the aircraft collided with terrain. The pilot was fatally injured, and the aircraft was destroyed.

VFR into IMC, loss of control and collision with terrain involving Socata TB‑20, VH-JTY, 65 km west of Mackay Airport, Queensland, on 28 October 2023 (AO‑2023-052)

On the morning of 28 October 2023, a SOCATA-Groupe Aerospatiale TB-20, registered, VH‑JTY, departed Montpelier aircraft landing area, Queensland, for a visual flight rules private flight to Palmyra aircraft landing area, Queensland. After encountering cloud en route, the pilot elected to continue along the intended flight path through cloud instead of diverting around or remaining on top of it. Shortly after, it is very likely the pilot entered weather conditions not suitable for visual navigation, leading to spatial disorientation and a descent into mountainous terrain. The aircraft was destroyed and both occupants received fatal injuries.

VFR into IMC, loss of control and collision with terrain involving Airbus Helicopters EC130 T2, VH-XWD, near Mount Disappointment, Victoria, on 31 March 2022 (AO-2022-016)

On 31 March 2022, at about 0741 local time, 2 Microflite Airbus EC130 helicopters, registered VH‑WVV and VH-XWD, departed the Batman Park helicopter landing site in Melbourne, for the town of Ulupna, Victoria. Both helicopters were operated in accordance with the VFR and departed in VMC conditions. Cloud was forecast along the route, but the pilots elected to continue to the destination. The helicopters encountered IMC over Mount Disappointment and VH-WVV conducted a U-turn to avoid entering cloud. While also attempting to conduct a U-turn, VH-XWD entered cloud, developed a high rate of descent, and collided with terrain. The helicopter was destroyed, and the 5 occupants were fatally injured.

VFR into IMC and in-flight break-up involving Van's Aircraft RV-7A, VH-XWI, 90 km south of Charters Towers, Queensland, on 23 April 2021 (AO‑2021‑017)

On 23 April 2021, a Van’s Aircraft RV-7A, registered VH-XWI, was being operated on a private flight under the VFR from Winton to Bowen, Queensland. During the flight, the pilot most likely entered IMC and lost control of the aircraft several times. This led to the airspeed limitations for the aircraft being exceeded and the aircraft sustained an in-flight break-up. The pilot was fatally injured, and the aircraft was destroyed.

Safety analysis

Examination of the wreckage and flight data indicated that the aircraft’s engine was producing power until impact. All major sections of the aircraft were located at the accident site, and there was no evidence of an in-flight break-up or structural failure. The flight data and the presence of all major components at the scene indicate that the aircraft did not experience a pre-impact mechanical or airframe issue that would have contributed to the collision with terrain.

The flap setting of 50% would be used in low and slow manoeuvring such as looking for a landing site under deteriorating weather or manoeuvring through valleys. Flying slower reduces the radius of turns and the use of the flap gives the aircraft a buffer to the stall speed. This setting might be considered a compromise configuration between flying clean and flying full flap, giving these advantages while retaining a greater capability to climb at short notice without the drag of a full flap.

Cylinder temperature fluctuations and cockpit distraction

When passing Mallacoota Airport, the pilot commenced a descent from about 9,000 ft above mean sea level (AMSL). At that time, the pilot would have seen low cloud ahead and probably descended in order to fly below it or in preparation for an approach and landing at one of the aerodromes along the planned flight route.

Flight data showed fluctuating temperature indications from the number 4 cylinder throughout the latter part of the flight. These temperature fluctuations would have generated warnings displayed to the pilot on the multi-function display, alerting them to a potential engine issue. 

The first indications of this fluctuation occurred prior to the initial approach to Moruya Airport. The recorded engine data showed that the CHT rose to the caution range and subsequently progressed to the warning range. There was a reduction in engine power over an approximately 30‑second period, before maintaining reduced power for about a minute further. This was likely to have been initiated by the pilot in response to the high CHT warnings and was consistent with the appropriate response to a genuine warning. The engine was then returned to normal power after the CHT levels dropped back into the normal range.

Shortly thereafter, the CHT again increased, entering the caution range for a second time. After an 8‑minute period with the CHT in the caution range the pilot radioed ATC with their intention to land at Moruya Airport. Given that a landing at Moruya was not planned, it is most likely that the pilot initiated the approach as a result of the warning and/or cloud ahead.

The ATSB assessed that these warnings were very likely spurious, and an attentive pilot with a good understanding of engines could doubt their validity based on the engine instruments. The pilot may have thought the warnings were genuine or spurious, and this understanding could have changed throughout the flight. 

In any case, the persistence of these warnings throughout the remainder of the flight would have been a continuing source of distraction, potentially increasing workload and reducing their capacity to monitor other operational factors such as navigation, weather conditions, and terrain clearance.

Decision to continue flight past Moruya Airport

After commencing an approach to Moruya Airport, and making a radio broadcast to that effect, the pilot discontinued the approach and continued the flight below the cloud base. Satellite and meteorological data indicated areas of low cloud around the Moruya area, with instrument meteorological conditions (IMC) present as the pilot approached the airport. Additionally, poor weather was observed along the planned route of flight (along the east coast) beyond Moruya. There were no further radio transmissions or position reports from the pilot following the initial call indicating their intention to land at Moruya. Given that poor weather was present ahead of the aircraft and the pilot would have been seeing fluctuating cylinder temperature warnings, it is unclear why the pilot made the apparent decision to continue the flight rather than land at Moruya.

This decision may have been influenced by the perceived presence of a completely clear area in the cloud layer ahead. Analysis of satellite imagery revealed a temporary gap or break in the extensive cloud cover extending from Moruya Airport towards the Great Dividing Range. This gap, evident at the approximate time the aircraft passed to the west of Moruya Airport, would have presented a visually clearer path to the pilot. There was cloud over Moruya Airport and the pilot may have considered that maintaining VMC throughout an approach and landing there might not have been feasible. 

In any case, the decision to deviate inland from the initial planned track and towards higher terrain was likely influenced by this break in cloud. Given previous observations from the instructor indicating an aversion to flight near conditions of reduced visibility, it is probable that the pilot elected to manoeuvre towards this apparent break in order to remain in VMC. However, this deviation towards rising terrain significantly increased the risk of controlled flight into terrain, particularly in the prevailing low-visibility environment where visual assessment of terrain clearance could not be assured.

The pilot may have elected to continue the flight partly due to ‘get-there-it is,’ which describes a mindset in which a pilot becomes fixated on reaching the destination, often disregarding deteriorating weather, aircraft anomalies, fatigue, or other risk factors (ATSB, 2011). This self-induced pressure can lead to continued operation into conditions that a more objective assessment would deem unsafe, as the perceived pressure to complete the trip overrides sound aeronautical decision‑making.

The pilot’s limited experience with long distance flights may have exacerbated the effects of this phenomenon. Having completed only the second flight of approximately 4 hours duration in their flying career, the pilot had minimal exposure to the progressive challenges associated with extended cross-country operations, including the management of fatigue and evolving weather systems over prolonged periods, and in‑flight technical anomalies. 

With limited prior experience in calibrating risk in deteriorating conditions, the pilot would have been less able to objectively weigh the cumulative hazards of continuing into adverse weather while managing the fluctuating indicated engine cylinder head temperature (or being distracted by the spurious warnings, depending on how the pilot understood them). This increased their susceptibility to get-there-itis, such that their established safety decision-making processes were outweighed by the perceived attainability of the destination.

Continued flight into poor weather

Following the decision to continue the flight, tracking data indicated that the aircraft proceeded into the mountainous area of the Great Dividing Range, then almost reversed course at low altitude along a valley, consistent with the pilot attempting to remain below the cloud base and/or avoid cloud ahead. It is therefore likely that the pilot misjudged the extent and density of the cloud or the height of the cloud base. While continuing at low level, with an altitude lower than the surrounding terrain, the aircraft likely entered IMC. The subsequent flight path was consistent with attempts to avoid cloud, and it is probable that the pilot did not know what direction to take away from the mountainous areas and cloud or, if they did, became trapped between the rising terrain and the low cloud base. 

Findings

From the evidence available, the following findings are made with respect to the VFR into IMC and controlled flight into terrain involving Cirrus SR20, VH-TEL,12 km east of Braidwood/Percheron aircraft landing area, New South Wales, on 18 September 2025.

Contributing factors

• After commencing an unplanned approach to Moruya Airport, likely due to an engine warning and/or observed cloud ahead, the pilot discontinued the approach for undetermined reasons. The pilot, with limited cross-country experience, then continued the flight underneath the cloud base towards rising terrain.
• The pilot very likely entered weather conditions not suitable for visual navigation, leading to a loss of situational awareness and collision with terrain.

Other factor that increased risk

• The aircraft’s number 4 cylinder fluctuating temperature warnings, likely resulting from a faulty sensor probe, occurred prior to the pilot electing not to land and continued until the collision with terrain. The ongoing warnings likely distracted the pilot, increasing workload and reduced their capacity to monitor and respond to other operational factors.

Sources and submissions

Sources of information

The sources of information during the investigation included:

• two instructors
• Bankstown Flying School
• Civil Aviation Safety Authority
• New South Wales Police Force
• maintenance organisation for VH-TEL
• Airservices Australia
• AvData
• AvPlan
• witnesses
• Garmin G1000
• Cirrus Aircraft. 

References

ATSB (2005). General Aviation Pilot Behaviours in the Face of Adverse Weather. Aviation Research Investigation Report B2005/0127. 

ATSB (2011). Accidents involving Visual Flight Rules pilots in Instrument Meteorological Conditions. Aviation Research Investigation Report AR-2011-050.

Submissions

Under section 26 of the Transport Safety Investigation Act 2003, the ATSB may provide a draft report, on a confidential basis, to any person whom the ATSB considers appropriate. That section allows a person receiving a draft report to make submissions to the ATSB about the draft report. 

A draft of this report was provided to the following directly involved parties:

• Bankstown Flying School
• Civil Aviation Safety Authority
• Cirrus Aircraft
• maintenance organisation for VH-TEL.

Submissions were received from:

• Civil Aviation Safety Authority
• Cirrus Aircraft.

The submissions were reviewed and, where considered appropriate, the text of the report was amended accordingly.

Purpose of safety investigations The objective of a safety investigation is to enhance transport safety. This is done through:  identifying safety issues and facilitating safety action to address those issues providing information about occurrences and their associated safety factors to facilitate learning within the transport industry. It is not a function of the ATSB to apportion blame or provide a means for determining liability. At the same time, an investigation report must include factual material of sufficient weight to support the analysis and findings. At all times the ATSB endeavours to balance the use of material that could imply adverse comment with the need to properly explain what happened, and why, in a fair and unbiased manner. The ATSB does not investigate for the purpose of taking administrative, regulatory or criminal action. About ATSB reports ATSB investigation reports are organised with regard to international standards or instruments, as applicable, and with ATSB procedures and guidelines. Reports must include factual material of sufficient weight to support the analysis and findings. At all times the ATSB endeavours to balance the use of material that could imply adverse comment with the need to properly explain what happened, and why, in a fair and unbiased manner. An explanation of terminology used in ATSB investigation reports is available here. This includes terms such as occurrence, contributing factor, other factor that increased risk, and safety issue. Publishing information Released in accordance with section 25 of the Transport Safety Investigation Act 2003 Published by: Australian Transport Safety Bureau © Commonwealth of Australia 2025 Ownership of intellectual property rights in this publication Unless otherwise noted, copyright (and any other intellectual property rights, if any) in this report publication is owned by the Commonwealth of Australia. Creative Commons licence With the exception of the Commonwealth Coat of Arms, ATSB logo, and photos and graphics in which a third party holds copyright, this report is licensed under a Creative Commons Attribution 4.0 International licence. The CC BY 4.0 licence enables you to distribute, remix, adapt, and build upon our material in any medium or format, so long as attribution is given to the Australian Transport Safety Bureau.  Copyright in material obtained from other agencies, private individuals or organisations, belongs to those agencies, individuals or organisations. Where you wish to use their material, you will need to contact them directly.

Investigation summary

What happened

On 7 July 2025, a Kavanagh Balloons G-450, registered VH-FGC, was conducting a morning scenic flight near Beaudesert, Queensland, carrying 20 passengers and the pilot.

Shortly after launch when climbing above a ridge, the pilot identified a change in the expected wind direction and the presence of fog. The pilot considered the safest option available was to proceed to an alternate landing site in reduced visibility. However, on approach to land, a low-level wind shift changed the balloon direction. The pilot elected to conduct a landing at a different landing site rather than continue flight over populous areas.

On landing, the balloon basket was carried forward with momentum, it skipped several times before it came to a stop. However, the balloon envelope made contact with a dead tree, resulting in minor damage to the envelope. No injuries were reported.

What the ATSB found

The ATSB found that the pilot reassessed operational and safety decisions as unexpected weather impacted the flight (wind direction and fog). Ultimately the pilot was unable to avoid contact with a dead tree in the final stages of landing in reduced visibility.

However, comprehensive passenger safety briefings meant that passengers adopted brace positions prior to landing which likely prevented injury.

Safety message

The formation, movement and depth of fog is difficult to predict with accuracy, which can lead to pilots inadvertently flying into reduced visibility. 

If contemplating ballooning operations in conditions conducive to fog development, even if it is not forecast, pilots are strongly encouraged to not only be aware of the possible formation of fog, but to plan for its likely effect on their flight. 

This accident highlights the importance of effective safety briefings and how passengers adopting the correct body position during landing substantially reduces the likelihood and severity of injury. The pre-flight briefing is critical in ensuring passenger preparation, particularly as opportunities to reinforce this information during flight may be limited. 

Pilots should use all available resources (such as passenger demonstrations and safety briefing cards) to ensure that each passenger understands the landing position and its importance.

The ATSB SafetyWatch highlights the broad safety concerns that come out of our investigation findings and from the occurrence data reported to us by industry. One of the safety concerns is Reducing passenger injuries in commercial ballooning operations.

The investigation

The occurrence

On 7 July 2025, a Kavanagh Balloons G-450, registered VH-FGC, operated by Hot Air Pty Ltd was conducting a morning scenic flight near Beaudesert, Queensland. 

The pilot conducted multiple weather assessments prior to the flight (see Pre-flight observations), and the balloon was set-up with the assistance of ground crew at The Overflow Estate (Figure 1).

At approximately 0623 local time, the balloon departed The Overflow Estate, at Wyaralong Dam in a north-easterly direction, carrying 20 passengers and one pilot. Based on their pre‑flight weather assessment, the pilot originally intended to land in a south-east landing site near Bromelton (Figure 1) and the ground crew had been instructed to make their way via car to assess the wind conditions near the intended landing site. However, after take‑off the balloon maintained a north-east flight path towards Woodhill and Cedar Grove.

Figure 1: Flight path overview

Source: Google Earth, annotated by the ATSB

About 13 minutes after launch, the balloon had passed over the dam when the pilot climbed the balloon over a ridge line. At about 500 ft above ground level (AGL), the pilot described encountering fog in the direction of travel (Figure 2). The pilot discounted nearby options for an early landing and considered that the safest option available, in the reduced visibility, was to select a new landing site clear of hazards in the north-east (Figure 3).

Figure 2: Fog visible after climbing a ridge at 0636

Source: Operator, annotated by the ATSB

Figure 3: Flight path details

Source: Google Earth, annotated by the ATSB

While en route to that preferred landing site, the fog thickened, before the pilot climbed the balloon above the fog (Figure 4).  

Figure 4: Fog conditions below the balloon at 0640

Note: Two other balloons from a separate (unidentified) operator were visible above the fog at this time. Source: Operator

At about 0703, while on approach to the preferred landing site (Figure 3), the balloon encountered a low-level wind change at about 200 ft, increasing in strength from 4–6 kt. The wind change tracked the balloon 90 degrees left, and made landing unfeasible due to a dam and trees. 

The wind shift was unexpected to the pilot as they described that surface conditions looked calm, with the fog not appearing to move. Due to ground crew traveling back from the first intended landing site, the pilot did not have information usually available via a surface wind assessment on the ground.

The pilot reconsidered the safest options available considering the reduced visibility and selected a different landing site further north, which was used infrequently by the operator, was closer to a populated area and isolated trees, but with no identified powerlines (Figure 3). The pilot burned[1] to lift the balloon over a wet area before descending towards the new landing site. 

On approach, the pilot burned again to lift the balloon over a boundary fence (Figure 5) before they commenced deflation to descend for landing and instructed the passengers to adopt their pre-briefed brace positions. While approximately 5 m from the ground, the pilot visually detected a dead tree (Figure 5). In response they rapidly deflated the balloon in an attempt to stop short of the tree. The pilot further reinforced the brace instruction to the passengers. At 0709, the balloon basket touched down, however was carried forward with the balloon’s resultant air mass momentum. The basket skipped 4 times before it stopped moving (Figure 5), however the balloon envelope inertia continued until the envelope contacted a dead tree (to the left of the basket), resulting in minor damage. 

Figure 5: Onboard video of the approach (left) and the final approach flight path (right)

Source: Operator and Google Earth, annotated by the ATSB 

The pilot and passengers were uninjured, and due to the delayed arrival of the ground crew, the pilot sought the help of 3 volunteer passengers to recover the envelope from the tree. There was no resultant damage to the basket, however envelope damage included 15 large tears due to contact with the dead tree.

Context

Personnel information

The pilot held a commercial pilot licence (balloon), with 1,253.2 hours total flying time, of which 1,174 hours were flown as pilot in command. In the previous 90 days, the pilot had flown 40.2 hours as pilot in command, including 7.2 hours on the G-450.

The pilot held a current CASA class 2 aviation medical certificate with no conditions.

The pilot reported starting work at 0430 on the day of the occurrence, having obtained about 6 hours of sleep the night before, and an additional 30‑minute nap the previous morning. They recalled feeling fully alert at the time of the occurrence. 

Aircraft information

VH-FGC was a Kavanagh Balloons G-450 manned free balloon, manufactured in 2017 by Kavanagh Balloons Australia Pty Ltd. The aircraft was certified in the manned free balloon category and operated with a valid certificate of airworthiness.

The G-450 balloon has an envelope capacity of 450,000 cubic feet and a maximum take‑off weight of 3,700 kg. At the time of the occurrence, the balloon envelope had accumulated a total time of 662.6 hours in service, while the basket had accumulated 1,614.1 hours. The basket was designed to carry a maximum of 24 passengers per basket (6 per passenger compartment).

The balloon was fuelled with 358 L of liquid petroleum gas propane at the start of the flight, with 135 L remaining at landing. 

Operator information

Hot Air Pty Ltd operates in the Scenic Rim area of South East Queensland and also the Atherton Tablelands in north Queensland. The organisation has agreements in place with landowners to access several launch and landing locations in a circular pattern near Beaudesert, referred to as the operator’s flying area. The locations include private and commercial properties. 

Recorded information

The balloon was equipped with the following equipment capable of recording:

• a GPS which records the flight track
• a ‘flight tablet’ which included an electronic Google Earth satellite map (Figure 6). The satellite map was overlaid with the operator’s flying map layer which was maintained/updated via an electronic register. The flying map included the following operational information:
  • launch and landing areas / property boundaries (dark blue)
  • sensitive zones (SZs), with restricted operation (red)
  • powerlines (yellow)
  • other relevant landowner information (white text).
• An onboard camera recording the front facing view of the flight.

Figure 6: Operator flying map showing the balloon flight path 

Note: Property names were blurred to maintain landowner privacy. Source: Operator, modified by the ATSB

The final landing site was designated an ‘emergency landings only’ area on the Operator flying map (Figure 6) in Woodhill. The operator occasionally used this site when necessary, but it was not used frequently. 

Meteorological information

Observations for surrounding area

The Beaudesert automatic weather station (AWS) provided the air temperature (°C), dew point temperature (°C), and relative humidity (%) along with other information and showed conditions conducive to fog formation (Table 1), that is: 

• temperature and dew point less than 1°C difference
• winds were calm
• high relative humidity (above 95%)
• no significant weather movement.

Table 1: Beaudesert AWS information for 7 July 2025

Forecast for surrounding area

A local graphical area forecast was valid for a six-hour period from 0300–0900 which indicated visibility of about 300 m with scattered fog.

At 0503, the Bureau of Meteorology (BoM) issued an updated aerodrome forecast (TAF)[2] for Amberley, which indicated fog and reduced visibility of 500 m up until 0700 at which time the conditions could be expected to improve. 

At 0607, the BoM issued a further update to the TAF, which forecast shallow fog with visibility of 8,000 m, and a 30% probability of fog reducing visibility to 800 m and scattered cloud at 200 ft, until 0900 that day. 

Satellite imagery

Satellite imagery was obtained from the BoM, valid as of 0500. The imagery depicted areas of fog or low cloud around, but clear of the original intended area of balloon operation (see Appendix A – satellite images).

Pre-flight observations

The pilot also reviewed several sources of weather information in the preceding hours prior to launch, as required by the operator’s exposition[3] (Version 1, 11 November 2024) and CASR Part 131[4] (Table 2).

Table 2: Pilot weather observations 

Based on the observations the pilot decided to depart from The Overflow Estate launch site (west of Beaudesert) with the plan to fly in a south-east direction back into their operational flying area (and towards Beaudesert). 

Regulatory requirements and guidance

Balloon pilots and operators must also comply with Part 131 of the Civil Aviation Safety Regulations (CASR), pre-flight weather assessment rules in section 12.02 of the Part 131 Manual of Standards (MOS).[5]

Balloon operations can occur in Class G airspace with at least 100 m visibility below 500 ft AGL when outside 10 NM from an aerodrome (such as in the case of Beaudesert). However, CASA highly recommends that pilots and operators exercise this significant reduction in the visibility requirements with caution and only if sufficient flight preparation has taken place. Further balloon guidance is available at Advisory Circular 131-02 v4.0.

Survivability

Pre-flight passenger safety briefing

One consideration in balloon accidents is the basket tipping during landing, which can increase the risk of injury. Tipping is more likely if a basket contacts, or lands on, a tree or fence. 

Passengers were provided with safety briefings and instructions prior to boarding as required by the operator’s exposition. These included:

• entry/exit to the basket
• remaining in the basket until instructed by crew
• securing and stowing personal items
• prohibited dangerous goods
• use of rope handles
• landing/brace positions (for normal/upright landing and emergency/hard landing).

The passengers included several foreign tourists from non-English speaking backgrounds. Verbal information was supported by physical demonstrations (of the required landing position) and graphical briefing cards with basic diagrams and translations in simplified Chinese, Japanese, Korean, and German. 

One passenger reported receiving pre-flight safety information via email at multiple points leading up to the flight, which was then supported by the safety demonstration on the day of the flight.

Related occurrences

A search of the ATSB occurrence database found that in the 10 years to July 2025 there were 37 balloon hard landings, ground strikes, or collisions with terrain in Australia, resulting in 17 injuries. Of these, 13 occurrences involved contact/collision with trees.

Further information on some of these occurrences can be found in Appendix B – Related occurrences.

Safety analysis

As is often required in balloon operations, the pilot was required to reassess operational and safety decisions at multiple points before and during the flight. 

This analysis will explore the assessment of weather, launch location, contingency options, and landings in reduced visibility.  

Fog encountered in flight

Fog was forecast for a wide area that included the operator’s flying area and the local conditions were conducive to fog. Satellite images support the pilot’s report by confirming that fog was likely not visible in the immediate flying area when the pilot travelled to the launch site before the flight. Based on their visibility assessment and pre-flight observations, the pilot determined it was safe to fly. 

However, after take-off and on climbing above the ridge line over the dam, the pilot identified fog in the direction of flight, and the balloon subsequently entered fog.

Approach to land

Once lined up and on approach to land at the preferred landing site, the balloon was affected by an unexpected low-level wind shift and tracked about 90 degrees to the left. 

Subsequently, the pilot considered other landing locations and associated risks, and selected an emergency landing site, used infrequently by the operator.

Reduced visibility

Once committed to landing in the final landing area in significantly reduced visibility, the pilot visually detected a tree through the fog in front of the balloon. In an attempt to take avoiding action, they rapidly deflated the envelope to land the balloon, however due to inertia, the balloon envelope made contact with the tree and was damaged. 

Comprehensive safety briefings

The passengers were provided with comprehensive safety information leading up to, and before the flight. The ground crew and pilot also ensured understanding of the brace positions prior to launch.

As a result of the proper brace position, effective briefing and re-enforced communication during landing, no injuries were sustained.

Findings

From the evidence available, the following findings are made with respect to the controlled flight into terrain involving Kavanagh Balloons G-450, registration VH-FGC, 12 km north‑north-west of Beaudesert, Queensland, on 7 July 2025. 

Contributing factors

• After clearing a ridge line, fog was encountered in the direction of the flight path.
• During the approach to land in low visibility, an unexpected low-level wind shift diverted the balloon away from the preferred clear landing area, and required the pilot to select an alternate unplanned landing site in the final stages of landing.
• Due to reduced visibility, the pilot was unable to see hazardous obstacles in the final landing area and therefore unable to take timely avoiding action.

Other findings

• Comprehensive passenger safety briefings meant passengers adopted brace positions prior to landing which likely prevented injury.

Sources and submissions

Sources of information

The sources of information during the investigation included:

• the pilot of the accident flight
• the chief pilot of the operator
• Civil Aviation Safety Authority
• Bureau of Meteorology
• accident witnesses
• video footage of the accident flight and other photographs and videos taken on the day of the accident
• recorded data from the GPS unit on the aircraft.

References

CASA (Civil Aviation Safety Authority), (2025), Part 131 Aircraft – Operations, Advisory Circular AC 131-02v4.0, CASA

CASA (Civil Aviation Safety Authority), (2025), CASR Part 131 – Guide for balloons and hot air airships, v1.2, CASA

Submissions

Under section 26 of the Transport Safety Investigation Act 2003, the ATSB may provide a draft report, on a confidential basis, to any person whom the ATSB considers appropriate. That section allows a person receiving a draft report to make submissions to the ATSB about the draft report. 

A draft of this report was provided to the following directly involved parties:

• the pilot
• the operator
• Civil Aviation Safety Authority
• Bureau of Meteorology.

Submissions were received from:

• Civil Aviation Safety Authority
• Bureau of Meteorology.

The submissions were reviewed and, where considered appropriate, the text of the report was amended accordingly.

Appendices

Appendix A – satellite images

High resolution visible satellite imagery

Satellite imagery was obtained from the Bureau of Meteorology and was valid at 0500 (Figure A1) showing fog/low cloud as light blue areas.

Figure A1: High resolution visible satellite imagery from 0500

Note: This imagery was not available to the pilot at the time of the event. Source: The Bureau of Meteorology, annotated by the ATSB

Appendix B – Related occurrences

Hard landing involving balloon, VH-EUA, near Yarra Glen, 8 February 2018 (AO-2018-016)

On 8 February 2018, a Kavanagh B-350 hot-air balloon, registration VH-EUA, departed Glenburn, Victoria, for a scenic charter flight with a pilot and 15 passengers on board. About 45 minutes into the flight, over the Yarra Valley, the balloon experienced a sudden wind change with associated turbulence. The pilot decided to land immediately rather than continue over rising and heavily vegetated terrain. The resulting landing was hard and fast and 11 passengers were injured, with 4 of them receiving serious injuries. 

Collision with terrain involving Kavanagh E-240 Balloon, VH-LUD, near Yamanto, Queensland, on 8 October 2021 (AO-2021-042)

On 8 October 2021, a Kavanagh Balloons E-240 balloon, registered VH-LUD and operated by Floating Images Aust. Pty Ltd was conducting a morning scenic flight about 45 km south‑west of Brisbane, Queensland. On board were a pilot and 9 passengers. About 55 minutes into the flight, the pilot commenced a descent to locate a suitable landing area. During the descent, the balloon entered an area of localised fog where visibility reduced to 10 m.

The pilot continued the descent into the fog until a tree was observed in the path of the balloon. The pilot attempted to avoid the tree by initiating a climb, but the balloon collided with, and came to rest on the side of, the tree, damaging the lower part of the balloon envelope. The pilot subsequently climbed the balloon off the tree and above the fog. The flight continued to an uneventful landing in a nearby paddock that was clear of fog. There were no injuries.

Controlled flight into terrain involving Kavanagh Balloons G-525, VH-HVW, Pokolbin, New South Wales, on 30 March (AO-2018-027)

At about 0710 Eastern Daylight-saving time on 30 March 2018, a Kavanagh Balloons G‑525 balloon, registered VH-HVW (HVW) and operated by The International Balloon Flight Company (Australia), launched from a site near Pokolbin, New South Wales, for a planned 1-hour scenic flight. HVW was one of three balloons launched by the company from the same site. After climbing through fog to about 2,000 ft and realising how far the fog layer extended, the pilot of HVW, along with the other 2 pilots, decided to abort the flight and descend for a landing at the nearest suitable site. On approach to land in low‑visibility conditions, HVW collided with trees, which caused the basket to rotate 180 degrees. It then landed heavily, resulting in injuries to 16 of the 24 passengers, 3 of them serious. The pilot was uninjured and 74 of the balloon’s panels required patching or repair. 

Purpose of safety investigations The objective of a safety investigation is to enhance transport safety. This is done through:  identifying safety issues and facilitating safety action to address those issues providing information about occurrences and their associated safety factors to facilitate learning within the transport industry. It is not a function of the ATSB to apportion blame or provide a means for determining liability. At the same time, an investigation report must include factual material of sufficient weight to support the analysis and findings. At all times the ATSB endeavours to balance the use of material that could imply adverse comment with the need to properly explain what happened, and why, in a fair and unbiased manner. The ATSB does not investigate for the purpose of taking administrative, regulatory or criminal action. About ATSB reports ATSB investigation reports are organised with regard to international standards or instruments, as applicable, and with ATSB procedures and guidelines. Reports must include factual material of sufficient weight to support the analysis and findings. At all times the ATSB endeavours to balance the use of material that could imply adverse comment with the need to properly explain what happened, and why, in a fair and unbiased manner. An explanation of terminology used in ATSB investigation reports is available here. This includes terms such as occurrence, contributing factor, other factor that increased risk, and safety issue. Publishing information Released in accordance with section 25 of the Transport Safety Investigation Act 2003 Published by: Australian Transport Safety Bureau © Commonwealth of Australia 2025 Ownership of intellectual property rights in this publication Unless otherwise noted, copyright (and any other intellectual property rights, if any) in this report publication is owned by the Commonwealth of Australia. Creative Commons licence With the exception of the Commonwealth Coat of Arms, ATSB logo, and photos and graphics in which a third party holds copyright, this report is licensed under a Creative Commons Attribution 4.0 International licence. The CC BY 4.0 licence enables you to distribute, remix, adapt, and build upon our material in any medium or format, so long as attribution is given to the Australian Transport Safety Bureau.  Copyright in material obtained from other agencies, private individuals or organisations, belongs to those agencies, individuals or organisations. Where you wish to use their material, you will need to contact them directly.

Executive summary

What happened

On 6 February 2023 at about 1532 local time, a Coulson Aviation Boeing 737-3H4 large air tanker (LAT), callsign Bomber 139 and registered N619SW, departed from Busselton Airport, Western Australia (WA) on a firefighting task to Fitzgerald River National Park, WA. There were 2 pilots on board, the aircraft captain in the left seat as the pilot flying and a co‑pilot in the right seat as the pilot monitoring. At about 1614, during the go-around from a second partial retardant drop, the aircraft impacted a ridgeline at an elevation of about 222 ft. The pilots suffered minor injuries and the aircraft was destroyed.

What the ATSB found

The ATSB found that the accident drop was conducted at a low height and airspeed downhill, which required the use of idle thrust and a high descent rate. The delay in the engines reaching go-around thrust at the end of the drop resulted in the aircraft’s height and airspeed (energy state) decaying as it approached rising terrain, which was not expected or detected by the pilot flying. Consequently, the aircraft’s airspeed and thrust were insufficient to climb above a ridgeline in the exit path, which resulted in a controlled flight into terrain. The operator’s practice of recalculating, and lowering, their target drop speed after a partial load drop also contributed to the low energy state of the aircraft leading up to the collision with terrain.

The ATSB also found that the operator and tasking agency had not published a minimum drop height, which resulted in the co-pilot, who did not believe there was a minimum drop height, not making any announcements about the low energy state prior to the collision. The ATSB found the operator’s pilot monitoring duties were reactive to the development of a low energy state and did not include call-outs either before or at the minimum target parameters to reduce the risk of a low energy state developing.

The ATSB benchmarked the WA, New South Wales and National Aerial Firefighting Centre standards against the United States Forest Service and United States National Wildfire Coordinating Group standards and found inconsistencies between the Australian agencies’ standards but not among the United States agencies’ standards. This was likely a result of each Australian state participating in the LAT program independently producing their own standards.

What has been done as a result

As a result of this accident, the operator developed a master corrective action plan to address the following topics:

• minimum drop speed and height
• recalibration of airspeed during partial load drops
• pre-drop planning and familiarisation
• pilot situational awareness
• flight training exercises
• exit flight path
• communication and coordination with Birddog
• adherence to standard operating procedures
• crew resource management
• human factors
• continuous training and proficiency assessment.

The Birddog operator reported that as part of their continuous improvement they removed their Lead Plane procedures from an annex in their Company Operations Manual and introduced a Lead Plane Standard Operating Procedures manual with expanded procedures in October 2023.

In November 2023, the WA Department of Fire and Emergency Services, and Department of Biodiversity, Conservation and Attractions released the Western Australian Aerial Fire Suppression Procedures 2023-2024. The draft version of this document was reviewed by their contracted operators and included a chapter for Large Air Tanker (LAT) Operating Procedures. The document included standard drop heights for all the aircraft types employed, procedures for task rejection, standdown and reinstatement of aviation resources after a safety incident, and a section on tactical flight profiles with the addition of the Lead and Chase-Position profiles. 

In response to the draft report, the WA Department of Biodiversity, Conservation and Attractions reported they would review the 2024‍–‍25 published drop heights with the intent of prescribing a ‘minimum’ safe drop height, noting the actual drop height to safely achieve the objective is the pilot-in-command’s decision.

In response to the draft report, the Australasian Fire and Emergency Services Authorities Council committed to develop a national standard for LAT Operating Procedures. This was delegated to the Aviation Safety Group through the National Aerial Firefighting Centre Strategic Committee within the purview of the Consistent Doctrine working group.

Finally, the ATSB has issued a safety recommendation to Coulson Aviation to take safety action to address their crew resource management procedures for retardant drops to reduce the risk of the aircraft entering an unrecoverable state before the pilot monitoring alerts the pilot flying.

Safety message

The history of aerial firefighting includes collisions with terrain accidents during the descent, retardant (or water) drop and go-around that have primarily manifested as controlled flight into terrain and loss of control accidents. The history of accidents needs to be understood within the context of the effect of drop height and speed on the firefighting effort, and the environmental conditions at the fireground, which may lead to an elevated level of risk tolerance. 

The lessons from this accident indicate that standard operating procedures and crew resource management should be implemented with the intent to prevent an unsafe situation from developing. While they should also include recovery actions, there may be insufficient safety margin available for a successful recovery and therefore the safety standards should not be solely dependent on the performance of the pilot flying and recovery call-outs. 

At a large fireground, it is likely there will be personnel and assets from multiple organisations and jurisdictions interacting. In this scenario, non-standard procedures and practices may result in unforeseen risks emerging. It is therefore important for tasking agencies to take the lead, with the support of stakeholders, in developing the quality and safety standards they require for the firefighting effort to mitigate operational risks.

The occurrence

On 6 February 2023 at about 1532 local time, a Coulson Aviation Boeing 737-3H4 large air tanker (LAT), callsign Bomber 139 and registered N619SW, departed from Busselton Airport, Western Australia (WA) on a firefighting task to Fitzgerald River National Park, WA (Figure 1). There were 2 pilots on board, the aircraft captain in the left seat as the pilot flying and a co‑pilot in the right seat as the pilot monitoring.[1]

Figure 1: Bomber 139 flightpath from Busselton to Fitzgerald River National Park

Source: FlightAware, annotated by ATSB

Earlier in the day, at 1015, and then again at 1215 and 1310, the WA Department of Biodiversity, Conservation and Attractions (DBCA) submitted aerial fire suppression requests to the State Operations Air Desk (SOAD). The request was for fixed-wing assets to the location of a fire 24 km west-north‑west of Hopetoun, WA under the criteria of ‘known high fuel loads and likelihood of excessive ROS [rate of spread] and/or extreme fire danger’. In response, the SOAD:

• identified the aerial assets available
• established a fire common traffic advisory frequency (F-CTAF)
• spoke to the pilots
• sent tasking messages at 1012, 1127, 1407 and 1505.

Bomber 139 was included in the 1127, 1407 and 1505 taskings. The SOAD LAT SARWATCH log[2] recorded that Bomber 139 departed from Busselton on these taskings at 1208 and 1330 and returned to Busselton each time before departing on the accident flight at 1530.

At 1519 the Birddog[3] (BD) responsibility for the LATs at the fireground transferred from Birddog 125 (BD125) to Birddog 123 (BD123) due to BD125 refuel requirements, with Birddog 682 (BD682) stationed above as the primary air attack aircraft.[4] Before BD125’s departure, a familiarisation flight of the fire zone was conducted in company with BD123 to discuss the layout of the fire, tactics, retardant drops, and objectives for the drops. The pilot of BD123 reported that no hazards were discussed. Bomber 139’s captain contacted BD123’s crew when they were 15 minutes from the fireground, and the Birddog pilot acknowledged their call and advised an altimeter QNH[5] setting of 1003 hPa. The captain acknowledged the altimeter setting and informed BD123’s pilot they would contact BD682 when they were 5 minutes from the fireground.

The pilot of BD682 subsequently cleared Bomber 139 to enter the F-CTAF not above an altitude of 2,500 ft and the captain notified BD682 they would be working with BD123 on an altimeter setting of 1003. The crew of BD123 queried BD682 if the line was clear and were advised that no ground personnel had been sighted and that they were not expected for about another hour. At this stage, Bomber 139’s co-pilot advised the captain of their drop speeds, which included a target drop speed (V_DROP) of 133 kt (1.25 Vs[6]).[7] When the captain reported BD123 in sight, the Birddog pilot asked Bomber 139 if they wanted a Show-Me[8] run or to follow BD123 straight to the drop, which would be a Lead profile.[9] The captain responded that they would follow BD123 straight to the drop. BD123’s pilot then obtained confirmation from the captain that right-hand circuits would be acceptable to avoid reduced visibility in smoke. 

BD123’s pilot briefed Bomber 139 that the plan was to use a road (Figure 2) as the start point and tag and extend the existing line of retardant, while keeping the smoke off to the left side, and that the line for the drop was clear of ground personnel. Bomber 139’s captain subsequently reported to BD123 that they were in position and the captain called for the co-pilot to complete the pre-drop checklist, which included:

• confirming coverage level[10] 3 was set
• disconnecting the autothrottles
• arming the retardant aerial delivery system.

The captain notified BD123 that their target speed would be 135 kt for final and then set the flaps to flap-40 (full flap). BD123’s crew then briefed Bomber 139 on the drop, which included advice of:

• a straight exit
• no hazards
• a downhill approach
• target altitude initially of 500 ft descending to 400 ft. 

Bomber 139’s co-pilot subsequently reported to the captain that the checklist was complete. The captain then queried the co-pilot about the flightpath BD123 was leading them on to the target and commented that their approach appeared to be high.

BD123’s pilot reported turning onto final for the drop, which was on a heading of 155º, and that visibility would be good after they cleared the smoke. About 15 seconds later, the captain queried the co-pilot where the road was for the start of the drop and the co-pilot responded that it was just ahead of them. BD123’s pilot then briefed Bomber 139 to ’start at the road and keep all smoke to the left, 3, 2, 1, start, your target altitude is 500 descending to 400’. The captain then confirmed sighting the road.

Bomber 139 descended to a minimum height[11] of 78 ft and completed a 9-second partial drop[12] of three-quarters of their tank at about 70% N1[13] with a minimum computed airspeed[14] of 124 kt before the captain stopped the drop because their retardant line was starting to enter area that was already burnt. The captain reported the partial drop to BD123, and another Lead profile was set up to tag and extend the first drop with the remaining retardant, with the captain remarking to the crew of BD123 ‘…and head down off the hill’.

The captain instructed the co-pilot to conduct the pre-drop checklist for the second drop and the co‑pilot recalculated and reported that 118 kt would be their revised drop speed. On the second circuit the captain again queried the co-pilot about the flightpath they were taking to the final approach. The captain requested BD123 slow to 120 kt for the next drop, which was acknowledged. The Birddog pilot then briefed Bomber 139 to ‘tag and extend all existing retardant, it is start at the hill as it pushes down, target altitude 500 descending 400’. 

The co-pilot reported that flap-40 was set, and the pre-drop checklist was completed. The captain again reported uncertainty to the co-pilot about the approach path BD123 was taking. The Birddog pilot then provided the following commentary, ‘this is final, fully retardant drop out here in a second, standby, [pause], retardant’s right at our 12 o’clock, [pause], 3, 2, 1, tag and extend existing retardant’. The captain reported at interview that the second approach was conducted through drift smoke from the fire, and they were unable to identify the target until they exited from the smoke, which was at the start of the drop. The co-pilot reported not being able to see the target on final until BD123 deployed smoke over the location.

During the second drop, Bomber 139 descended to a minimum height of 57 ft at 110 kt and about 30% N1 (engines at high idle)[15] as the retardant line was extended downhill. The aircraft recovered to a height of 81 ft at 107 kt at the end of the drop at which stage the captain had started to advance the thrust levers as the rate of descent peaked at about 1,800 ft/min. The co‑pilot had their hand on the flap lever in anticipation of the flap retract call from the captain as soon as they started to climb for the go-around.

The engines did not immediately respond to the movement of the thrust levers and the captain started to pitch the nose up, which resulted in a reversal of the rate of descent and a decay of the airspeed. The captain then announced ’fly airplane’ followed immediately, at about 1614,[16] by the activation of the stick shaker[17] and an abrupt vertical acceleration associated with the aircraft impacting a ridgeline at an elevation of about 222 ft at 104 kt with the engines at 85‍–‍89% N1. 

The co-pilot did not announce any deviations during the drop and accident sequence and later reported their focus of attention was likely on the airspeed indicator and radio altimeter, monitoring for any adverse trends. After the impact with the ridgeline, the aircraft cleared a small line of foliage before impacting the ground a second time and then sliding to rest (Figure 2). In response to the collision, BD123’s pilot broadcast an all-stations MAYDAY[18] call.

Figure 2: Bomber 139 retardant drops and accident site

Source: Department of Fire and Emergency Services, annotated by ATSB

After motion had ceased, the co-pilot started the evacuation checklist. Both pilots were unable to open the cabin door as it had buckled and the co-pilot was unable to open the right-side window. The captain observed out of the left side window that a post‑impact fire had started and managed to open that window on their second attempt. Both pilots then exited out of the left window and moved clear of the wreckage and fire. They were subsequently rescued by a helicopter involved in the fire control activities after 2 single-engine air tankers had dropped water with foam on the aircraft fire, believing the crew were still inside. The crew suffered minor injuries and the aircraft was destroyed. Figure 3 depicts Bomber 139’s recorded accident flightpath.

Figure 3: Bomber 139 recorded accident flightpath at Fitzgerald River National Park

Source: Google Earth, annotated by ATSB

Context

Personnel information

Aircraft captain

The aircraft captain joined the operator, Coulson Aviation, in 2016 with a United States Department of Agriculture Forest Service (USFS) Air Tanker Training Pilot qualification. The captain became their director of fixed-wing operations in 2017, having flown several multi-engine airtanker types over about 20 years. The captain held an airline transport pilot certificate, reissued by the US Federal Aviation Administration (FAA) on 6 October 2020 with a rating for Boeing 737 (B737) and a current first class medical certificate with no limitations. The captain had accumulated 8,233 hours of flying experience, which included 1,399 hours on the B737 and about 5,500 hours aerial firefighting experience. In the previous 90 days the captain had accumulated 84 hours, all on the B737.

The captain’s last pilot-in-command proficiency check on the B737 (in accordance with the FAA regulations) was on 30 November 2022, with a satisfactory result. The captain conducted 2 company check flights on 11 May 2022, which were simulated initial attack mission training flights for a new co-pilot. These flights were part of the operator’s annual northern hemisphere spring season training program. Both reports indicated no assistance was required and no deficiencies were recorded. 

Co-pilot

The co-pilot joined Coulson Aviation on 18 April 2022 with prior aerial firefighting experience flying the air tactical group supervisor, but no previous low flying or large air tanker (LAT) experience. The co-pilot attended the operator’s 2022 spring season ground training and occupied the jump seat as an observer in the B737 for the flying training. Between 1‍–‍7 June 2022, the co-pilot completed a B737 type rating course with a satisfactory result recorded for the check on 7 June 2022. The co-pilot was issued with their USFS qualification on completion of their B737 type rating, which was an administrative process for co-pilots and did not require an evaluation flight.

The co-pilot held an airline transport pilot certificate, reissued by the FAA on 7 June 2022, with a rating for B737 and a current first class medical certificate with no limitations. On 12 September 2022, the co-pilot participated in an initial attack evaluation flight as the co-pilot on the B737. The co-pilot had accumulated 5,852 hours of flying experience, which included 128 hours on the B737, about 500 hours aerial firefighting experience and 36.9 hours on the B737 in the previous 90 days. 

Crew work-rest history

The captain reported they had 6 and 14 hours sleep in the previous 24 and 48 hours respectively. They self‑assessed that their level of mental fatigue at the time of occurrence was 2 - Very lively. Responsive, but not at peak.[19] The co-pilot reported they had 8 and 18 hours sleep in the previous 24 and 48 hours respectively and a self‑assessed mental fatigue level at the time of occurrence of 2 - Very lively. Responsive, but not at peak. 

The crew’s tour of duty started on 20 January 2023. They had flown 7.3 hours and conducted 13 drops (including partial drops) on the current tour prior to the day of the accident. The accident occurred on their third flight and fourth retardant drop of the last day of their tour after flying about 3.3 hours that day. The pilots’ self-assessments and work-rest history did not indicate that mental and physical fatigue were likely to have been contributing factors to the accident.

Aircraft information

General information

The aircraft was a Boeing 737-3H4, serial number 28035, registration N619SW, issued with a certificate of airworthiness in the transport category^[20] by the FAA on 9 November 1995 and fitted with 2 CFM56-3 turbofan engines. It entered service with a US airline on 12 November 1995 and accumulated 69,016 hours before transfer of ownership to Coulson Aviation on 8 August 2017. The latest certificate of registration was issued on 14 November 2017 and was valid until 30 November 2023.

Tanker modification

On 10 November 2018, Coulson Aviation were issued with a supplemental type certificate (ST04050NY) by the FAA for the installation of the Coulson Aerial Firefighter Tanker Modification (retardant aerial delivery system – RADS) to Boeing model 737-300 series aircraft, which limited passengers to persons related to firefighting mission‑essential activities. The RADS modification was completed on 30 May 2022. At the time of the accident, the airframe had accumulated 69,187.6 hours.

The RADS incorporated 2 tanks on either side of the centre fuel tank with a total capacity of 36,000 pounds (lb).[21] The cockpit had a primary and secondary user interface installed and push button drop switches on both the pilot and co-pilot controls. According to the flight manual supplement:

When the flight crew activates either switch, the primary user interface software will produce a door position command based on the predefined Coverage Level (CL) requirement, drop quantity, tank levels, ground speed and aircraft height above the ground.

The RADS design included an emergency dump switch that provided full system hydraulic pressure to dump the full load in less than 2 seconds. To avoid nuisance audio alerts during a retardant drop, the RADS modification incorporated an audio inhibit switch, which inhibited the landing gear configuration, ground proximity warning system and traffic collision avoidance system for 5 minutes.

Flight instruments

The captain and co-pilot instrument panels were fitted with radio altimeter indicators to display the aircraft height above terrain when below 2,500 ft above ground level. A decision height (DH) could be set on each of the radio altimeters, which activated a DH light on the respective attitude indicator when that height was reached, but did not include an audio alert.

The altimeters and airspeed indicators incorporated bugs that could be set to reference altitudes and airspeeds. The operator reported that the orange airspeed bug was used for the target drop speed. The altimeter bug was not used because the retardant drop was conducted at a height above terrain and not at an altitude. Figure 4 illustrates the co-pilot’s instrument panel with the radio altimeter DH set at 50 ft.

Figure 4: Co-pilot’s partial instrument panel

Source: Operator, annotated by ATSB.

Head-up guidance system

Under previous ownership, the aircraft was fitted with a Rockwell Collins flight dynamics model 2300 head-up guidance system (HGS) for the left seat pilot (captain’s seat), which was approved for use as a supplemental display. The HGS permitted the flying pilot to scan the airspeed and radio height, while maintaining an external visual scan of the environment during the retardant drop. Consequently, the captain reported that they considered the DH light on the instrument panel to be of no benefit while flying the retardant drop with the HGS.

The HGS had 4 modes of operation. All 4 modes could provide an airspeed error symbol, to indicate the difference between the aircraft’s actual airspeed and the reference airspeed set by the pilot on the mode control panel. A DH annunciation was also available in the mode used by the captain. The captain set the target drop speed on the mode control panel to provide a reference airspeed during the retardant drop but did not use the DH setting.

Boeing 737-300 engine acceleration requirements

According to the engine manufacturer, CFM (GE and Safran partnership):

An acceleration check is defined in Boeing 737-300/400/500 AMM Task 71-00-00-715-015-C00. This demonstration test requires the engine to accelerate from high idle to the fan speed corresponding to approximately 95% of static take-off thrust within 7.4 seconds.[22] The target fan speed is corrected for pressure altitude and outside air temperature. However, there are multiple factors that can impact the expected engine acceleration time during flight, including but not limited to:

1) The 7.4-second requirement is for a rapid throttle movement (1 second or less) from idle to take-off power. Slower throttle movements may result in a longer acceleration time.

2) The 7.4-second requirement is with engine bleeds and electrical loads OFF. Engine bleeds ON can extend the acceleration time.

3) Mach number can impact the acceleration time, but an airspeed of 110 kts at low altitude would likely have an insignificant impact.

Meteorological information 

On the day of the accident there was a low-pressure trough crossing southern WA, resulting in thunderstorms and wind direction changes from the north-east to the south-east to the south-west. The graphical area forecast for the accident site included moderate turbulence from the surface to 10,000 ft with thermals. A SIGMET^[23] was issued at 1400 for frequent thunderstorms associated with the trough (Appendix A – SIGMET thunderstorm activity). While the north-western boundary of the SIGMET was close to the accident site, satellite and radar imagery indicated there were no thunderstorms in the vicinity of the accident site at the time of occurrence. 

The Hopetoun North weather station, located about 24 km east‑north‑east of the site, did not record any rainfall and the 10-minute weather data from the station is provided in Table 1. With reference to Figure 2, the smoke from the fire and accident site indicated the retardant drops were conducted into wind, which the Bomber 139 captain reported was about 10‍–‍15 kt.

Table 1: Hopetoun North weather station recordings

Pre-flight risk assessment

The aircraft captain completed the operator’s flight risk assessment tool (FRAT) at 1015. The FRAT score was 14, which was an acceptable level of risk with no mitigation or escalation required. If the FRAT had been reviewed between each flight, the SIGMET issued at 1400 would have added 8 points, resulting in a FRAT score of 22 for the accident flight that departed from Busselton at about 1530.

A score greater than 21 required mitigation or escalation, noting the operator’s procedures prohibited an elevated FRAT from being approved by the aircraft captain. While the weather conditions, including the thunderstorm activity advised in the SIGMET, were not considered to be a factor in this accident, this has been included in the report to raise awareness of how a risk management process could miss a developing flight hazard.

Wreckage and impact information

The aircraft’s approach to the ridgeline left 2 distinct jet-blast lines, evidenced by trees broken in the opposite direction of travel (Figure 5). Closer to the ridgeline, trees were broken in the direction of travel, likely from contact with the aircraft’s engines and airframe with evidence of retardant transfer from the airframe to the foliage just below the ridgeline. The length of the jet‑blast lines were about 74 m and 62 m respectively for the left and right engines. After contacting the ridgeline, the aircraft became airborne for about 69 m, shedding engine, wing, and fuselage debris before impacting a second time in a slight nose down attitude on a heading of about 140º.

Figure 5: Jet-blast corridors and ridgeline impact

Bulldozer fire tracks constructed after the accident. Source: ATSB

The aircraft came to rest about 176 m from the ridgeline and yawed left to the direction of travel onto a heading of about 080º. The fuselage had a main fracture near the tail and the left engine had separated from the left pylon and was resting adjacent to the forward fuselage (Figure 6). The left engine pylon exhibited a 70º upward bend, which was likely from the impact with the ridgeline, noting the left engine debris field started from the ridgeline and there was no evidence of left engine drag marks. The aircraft was consumed by fire, but there was no evidence of:

• fire trail^[24] or fuel spill before the aircraft came to rest
• any debris separating from the aircraft before it impacted the ridgeline. 

Figure 6: Second impact and main wreckage

Bulldozer fire tracks constructed after the accident. Source: ATSB

The flight data recorder (FDR) and cockpit voice recorder (CVR) were recovered on the first day of the site and wreckage inspection and retained by the ATSB for examination and download. Due to the extensive fire damage, only a limited inspection of the aircraft was achievable. This included establishing the positions of the leading-edge flaps, trailing-edge flaps, and horizontal stabiliser, with no anomalies found. The trailing-edge flap ballscrews were in the fully extended position, consistent with a flap-40 setting. 

The left main landing gear was found adjacent to the aircraft and part of its support structure was in the debris field indicating it was torn from the aircraft prior to it coming to rest. The nose and right main landing gear were retracted in place. The extent of the fire damage precluded an inspection of the cockpit and flight instruments. Figure 7 depicts the horizontal distances and elevations (measured with a differential global positioning system), and the angles presented by the foliage damage associated with the accident sequence.

Figure 7: Accident sequence distances and elevations

Source: ATSB

Recorded information

The CVR (Honeywell SSCVR P/N 980-6022-001) and FDR (Honeywell SSFDR P/N 980‑4700‑001) were transported by a recorders specialist from the accident site to the ATSB’s Canberra technical facility. The condition of the CVR prior to disassembly is depicted in Figure 8. The condition of the FDR prior to disassembly is depicted in Figure 9.

Figure 8: CVR prior to disassembly

Source: ATSB

Figure 9: FDR prior to disassembly

Source: ATSB

As a result of fire damage to the recorders the data recovery process required disassembly, inspection, and repair of the memory boards inside the crash survivable memory unit. The FDR memory board exhibited discoloration, melting and flow of the conformal coating with multiple controller pins desoldered. The CVR exhibited discoloration of the heat indicator, several controller pins had separated from the memory board and multiple short-circuits were identified. 

Following repairs to both memory boards, successful downloads of data were achieved. The FDR provided 25.5 hours of flight data and the CVR 30 minutes of audio on 4 channels (pilot, co-pilot, public address, and cockpit area microphone). The FDR plot of the final 30 seconds before the impact with the ridgeline, with the approximate position of the accident retardant drop inserted, is shown at Figure 10. The time parameter in the figure (UTC)^[25] is an approximate calculation based on the aircraft’s auxiliary telemetry unit global positioning system recording of the retardant drops. Appendix B contains the FDR plot of the last 5 minutes of flight with the 2 drops conducted on the accident flight.

During the final low-level retardant drop the thrust levers were positioned at high idle (0°) while at a radio height above the ground of less than 100 ft. As the engine N1 speed decreased to about 30%, the rate of descent increased to 1,800 ft/min before the thrust levers were advanced while the aircraft continued to descend. About 2 seconds prior to impact, at a radio altitude of about 28 ft with the flaps at 40°, an increasing aircraft nose-up pitch attitude resulted in both angle of attack vanes exceeding 20° (maximum 23.6°), which triggered the stick shaker. The aircraft attained a positive rate of climb just before impact with terrain.

Boeing provided the ATSB with a copy of their preliminary flight data analysis report of the accident, which was used to validate ATSB flight data output. Noting the aircraft attained a positive rate of climb with high engine N1 speed just prior to impact, Boeing reported in their preliminary findings that ‘Had there been sufficient altitude remaining, the airplane would have likely climbed away without impacting the ground.’

Figure 10: FDR plot of final 30 seconds of accident drop

Final 30 seconds of flight data showing corrected altitude, radio height, pitch angle, angle of attack (same scale), thrust lever angle, engine N1 speed, computed airspeed, groundspeed, vertical speed, stick shaker and approximate position of the retardant drop. The vertical acceleration spike indicates the initial impact. Source: ATSB

Engine acceleration performance and drop times

According to the FDR data, the captain started to advance the thrust levers about 7 seconds before the collision and took about 5 seconds to advance them from 0° to 30° thrust lever angle. The engines started to accelerate from 30% N1 (high-idle) about 1 second after the captain started advancing the thrust levers and reached about 85‍–‍89% N1 in a 6-second acceleration period that coincided with the first impact. The acceleration performance depicted by the recorded data was consistent with the Boeing 737-300 engine acceleration check requirements, discussed previously.

According to the operator’s flight crew operations manual (FCOM) take-off procedure, after the pilot flying has aligned the aircraft with the runway, the thrust levers are initially advanced to 40% N1 and the engines allowed to stabilise, then TO/GA [take-off / go-around] is selected and thrust levers advanced to take-off N1. The accident FDR plots depicted a distinct change in the engine acceleration curve from about 40% N1 (at 0813:46 in Figure 10). The engines took about 4 seconds to accelerate to 41‍–‍43% N1 and another 3 seconds to accelerate to 85‍–‍89% N1.

Noting the FCOM take-off procedure and the distinct engine acceleration profile, the ATSB asked the operator if the take-off procedure was related to engine acceleration time and how this was managed during a retardant drop. The operator clarified that the FCOM take-off procedure to allow the engines to momentarily stabilise at 40% N1 before advancing to take-off thrust was in accordance with the Boeing 737 flight crew training manual, which provided the following explanation:

Allowing the engines to stabilize provides uniform engine acceleration to take-off thrust and minimizes directional control problems. This is particularly important if crosswinds exist or the runway surface is slippery. The exact initial setting is not as important as setting symmetrical thrust.

For the management of engine acceleration during retardant drops, the operator reported that if the terrain at a drop site was level, then the engines would likely be set at 60‍–‍65% N1 and they would quickly accelerate to the go-around thrust at the end of the drop. However, to control the airspeed during a downhill drop, they could not prescribe a minimum N1 setting, and the pilot flying may need to use flight idle thrust to control the drop speed.

In this situation pilots were trained to advance the thrust levers about halfway through the drop so that the engines could quickly accelerate to go-around thrust at the end of the drop. The operator acknowledged that if the pilot was late advancing the thrust levers from idle, it would result in a delay of about 3 seconds before the engines could be accelerated up to the go-around thrust setting.

On the accident drop, the FDR recorded that the captain advanced the thrust levers about halfway through the drop. However, the accident drop was a quarter load, which took 5 seconds to release. In comparison, the first partial drop of three-quarters of the load took 9 seconds to release. The 2 previous drops on the day of the accident were both full loads at coverage level 3 and took 12 and 15 seconds, respectively. Two days earlier, 7 full or partial drops were conducted at coverage levels 6 and 8. The full drops at coverage level 6 were released in 6‍–‍7 seconds and the full drops at coverage level 8 were released in 5 seconds. This indicated that, given the typical engine spool‑up time, either a partial drop or a drop at a high coverage level with the engines at idle could result in a post-drop delay in engine acceleration to go-around thrust.

Tactical flight profile

First and second flight taskings

The first retardant drop of the day for Bomber 139 at the fire ground was with BD125 and started with a left-hand circuit Show-Me profile about 500 ft above the subsequent drop height in a northerly direction on the western flank of the fire. The overfly of the target was followed by a close left-hand circuit with BD125 in the Chase-Position profile[26] and a full load release at coverage level 3 over 12 seconds. 

On the second drop, on the eastern flank of the fire, another Chase-Position profile left-hand circuit was flown with a tag and extend full load release in a southerly direction at coverage level 3 over 15 seconds but without a Show-Me profile. Figure 11 depicts the flight profiles and Figure 12 shows imagery of the first drop, which started at the same road as the accident flight, and the second drop tag and extend an existing line of retardant.

Figure 11: First and second drop flight profiles on 6 February 2023

Source: Google Earth, annotated by ATSB

Figure 12: First drop (left) starting at road and second drop (right) tag and extend

Source: Department of Fire and Emergency Services, annotated by ATSB

Accident flight tasking

When Bomber 139 returned to the fire ground for the third drop of the day, BD123 had replaced BD125. The BD123 pilot reported having prior experience working in terrain with more extensive vertical relief in Canada and considered the accident flight target and exit to be relatively flat. They further advised being aware of a 40‍–‍50 ft change in the elevation and, as a matter of practice, would not conduct uphill drops.

The Birddog pilot assessed the altitudes for the drop were about 450 ft at the start and 400 ft at the end, which they estimated would provide 100‍–‍150 ft height above terrain. However, the pilot provided the altitudes in hundreds of feet and therefore briefed 500 ft as the start altitude. At follow-up, the pilot confirmed they briefed a safe altitude(s) for Bomber 139 to transit through the run and that they levelled their aircraft at their briefed altitude over the target as a visual reference for Bomber 139’s captain. 

The Birddog pilot reported that it was not uncommon for the Show-Me profile not to be flown if the LAT had conducted previous drops in the area. A right-hand circuit was not their preferred option but they did not consider it would be a problem because they were providing a Lead profile to the target. However, they reported a ‘slightly longer final’ was conducted to ensure that they could line up on their visual cues and see the target. 

After the first partial drop, BD123 conducted a sharp right turn to assess the drop while Bomber 139 conducted the go-around. When Bomber 139’s captain reported the need for a second drop the Birddog pilot offered the captain the choice of either another Lead or Chase-Position profile. The captain had no preference and the Birddog pilot elected to conduct another Lead profile, which required Bomber 139 extend their circuit until BD123 could regain the Lead position. The Birddog pilot reported that this resulted in another ‘slightly longer final’.

The Coulson Aviation fixed-wing flight operations manual did not include detail of the setup and conduct of retardant drops and the Bomber 139 captain referred the ATSB to the US National Wildfire Coordinating Group (NWCG) aerial supervision standards for how they expected a Lead Plane (Birddog) would conduct operations in the US. The Birddog operator’s standard operating procedures (SOPs) for Lead Plane Operations (2009 and 2023) provided the same tactical flight profiles and descriptions as those published by the NWCG.[27] Their SOPs also stated that drops ‘should be downhill’, that they were to provide ‘the final heading for the run and the altitude for the drop start point’, the drop height ‘minimum is 150 ft above the top of the vegetation for heavy tankers’ and that ‘The airtanker pilot is responsible for maintaining safe drop heights.’

Bomber 139’s captain’s preference for the circuit, and what they reported teaching, was to fly a close circuit that kept the target in sight. To achieve this, the captain would initiate a descending base turn abeam the drop start point and maintain visual contact with the target through the first half of the base turn. About halfway through the base turn, the captain would extend their visual scan from the target to include the exit and on roll-out to wings level, the aircraft would be positioned on short final close to the start of the drop. 

On the first drop of the accident flight the captain reported the large circuit was due to the manoeuvring required to join up with BD123. The captain recalled that this resulted in a very wide base but final was flown clear of the smoke on the right side of the fire-line and at a normal angle of approach (Figure 13).

However, in the low ground of the depression the fire-line had extended further west, which resulted in a climbing right turn away from the fire before the downhill section of the drop and the captain did not see the exit before starting the second circuit. Subsequently, BD123 led them further east into the drift smoke for the next approach to turn the line in a more westerly direction. This resulted in Bomber 139 approaching the target through the smoke and the captain did not identify the target until they were at the start of the drop and had not seen the exit.

Figure 13: Accident flight first and second drops

Source: Google Earth, annotated by ATSB

Energy management

United States Federal Aviation Administration handbook

The FAA provided a description of aircraft energy management in their Airplane Flying Handbook (FAA-H-8083-3C) Chapter 4: Energy Management: Mastering Altitude and Energy Control. The introduction to the chapter described it as ‘about managing the airplane’s altitude and airspeed using an energy-centered approach.’ While this chapter was not written for a LAT rapid inflight weight reduction, it included 4 concepts of relevance to the accident. They were: Irreversible Deceleration and/or Sink Rate, Total Mechanical Energy, Energy Height or Total Specific Energy and Specific Excess Power, which were described as follows:

Irreversible Deceleration and/or Sink Rate

Unrecoverable depletion of mechanical energy as a result of continuous loss of airspeed and/or altitude coupled with insufficient excess power available under a given flight condition. Failure to recover above a certain critical AGL [above ground level] altitude results in the airplane hitting the ground regardless of what the pilot does.

Total Mechanical Energy

Sum of the energy in altitude (potential energy) and the energy in airspeed (kinetic energy).

Energy Height or Total Specific Energy

Measured in units of height (e.g., feet), it represents the airplane’s total energy per unit weight. It is found by dividing the sum of potential energy and kinetic energy by the airplane’s weight. It also represents the maximum height that an airplane would reach from its current altitude, if it were to trade all its speed for altitude.

Specific Excess Power

Measured in feet per minute or feet per second, it represents rate of energy change—the ability of an airplane to climb or accelerate from a given flight condition. Available specific excess power is found by dividing the difference between power available and power required by the airplane’s weight.

The FAA’s equation for specific excess power was Ps = (T-D) * V / W, where Ps = specific excess power, T = engine thrust, D = total drag, V = airspeed, and W = aircraft weight.

Flight data review

The ATSB reviewed the 4 retardant drops conducted by Bomber 139 on the day of the accident (including the third partial drop followed by the fourth accident drop), and analysed the height, vertical speed, airspeed, angle of attack and N1 parameters. The 2 states compared for each run were at the minimum drop height and at the go-around thrust lever setting on completion of each drop (based on the thrust levers reaching a stable setting after being advanced at the end of each drop). The data for the 4 drops was as follows:

• On the first drop, Bomber 139 reached a minimum height of 46 ft with 120 ft/min rate of descent at 113 kt and 61‍–‍66% N1. Minimum airspeed was 109 kt at 50 ft and maximum angle of attack was 19.7° at 64 ft.[28] On reaching the go-around thrust lever setting, the height was 64 ft with 360 ft/min rate of climb at 128 kt and 77‍–‍86% N1. Idle thrust was employed intermittently near the start of the drop, which resulted in a V-shaped airspeed trace during the drop (Figure 14) and in BD125 closing on Bomber 139 during the drop (Figure 15).
• On the second drop, Bomber 139 reached a minimum height of 69 ft with 120 ft/min rate of descent at 132 kt and 67‍–‍70% N1. Minimum airspeed was 129 kt at 77 ft. On reaching the go‑around thrust lever setting, the height was 140 ft with 480 ft/min rate of climb at 136 kt and 85‍–‍88% N1.
• On the third drop, Bomber 139 reached a minimum height of 78 ft with 600 ft/min rate of descent at 126 kt and 70‍–‍71% N1. Minimum airspeed was 124 kt at 82 ft. On reaching the go‑around thrust lever setting, the height was 153 ft with zero vertical speed at 129 kt and 87‍–‍88% N1.
• On the accident drop, Bomber 139 reached a minimum height (before initiating the go‑around) of 57 ft with 1,800 ft/min rate of descent at 110 kt and 30‍–‍31% N1. Minimum airspeed was 106 kt at 59 ft. On reaching the go-around thrust lever setting, the height was about 30 ft with 480 ft/min rate of descent at 105 kt and 55‍–‍60% N1.

Figure 14: FDR plot of first drop with minimum airspeed reference

Source: ATSB

Figure 15: Aspect change of Bomber 139 from start of first drop (left) to go-around (right)

Birddog 125 closing on Bomber 139 during the first drop. Source: Department of Fire and Emergency Services, annotated by ATSB 

The effects of the FAA‑specific excess power equation were evident in the 4 retardant drops on the day of the accident. The high engine thrust (N1) and large weight reduction on the first 3 drops resulted in a positive reversal of the vertical speed and airspeed at the end of those drops. However, the idle thrust and smaller weight reduction on the accident drop resulted in the airspeed and height decaying at the end of the drop as the captain arrested the aircraft’s significantly higher rate of descent.

This was consistent with a negative specific excess power (drag greater than thrust) and the FAA’s description of an Irreversible Deceleration and/or Sink Rate. Table 2 summarises the parameters from the flight data review of the 4 drops.

Table 2: Summary of parameters

After the accident, the operator informed the ATSB that they had increased their minimum drop height from 150 ft to 200 ft and their target drop speed to 1.3 Vs for downhill drops with flaps-40 and 1.35 Vs for flat terrain drops with flaps-30. They later reported to the ATSB that they believed the recalculation and lowering of drop speeds between partial drops was a ‘significant contributing factor to the accident.’ 

The Bomber 139 captain reported that reducing the target drop speed (1.25 Vs) following a partial drop provided them with the same stall speed safety margin at the start of each drop as the stall speed also reduced following a partial drop.

If a performance problem occurred in the go-around from the first drop of a split load, the crew could jettison the remaining load to gain an airspeed safety margin equivalent to the loss of the full load. However, if a performance problem occurred on the final drop of a split load, then the additional safety margin was reduced as it was limited to the weight of the remaining partial load. 

The release of the entire load on the first drop of the accident flight would have reduced the aircraft weight by about 28% (124,640 lb to 89,440 lb), whereas jettisoning the second drop reduced the aircraft weight by about 9% (97,850 lb to 89,440 lb).[29] In consideration of the implications of recalculating the drop speed between partial drops for a LAT, the ATSB used the FAA’s mechanical energy formulas to assess the potential gain in energy-height from higher drop speeds.

The drop speed at the end of the accident drop was used as the datum and compared with the target drop speed lower deviation limit (refer Figure 17), target drop speed, the previous end of drop speed, which was also the minimum airspeed during that drop, and previous target drop speed. The results are presented in the following table.

Table 3: Drop speed energy-height differences

From Table 3, the actual airspeed at the end of the accident drop resulted in a loss of about 90 ft in energy-height compared to the target drop speed. However, the recalculation of the target drop speed resulted in a loss of about 167 ft in energy-height from the full load target drop speed. Therefore, a comparison between the full load target drop speed and the accident drop speed found that about 65% of the energy-height loss was from recalculating and lowering the drop speed and about 35% of the energy-height loss was from flying slower than the target drop airspeed. 

The divergence in the go-around performance of Bomber 139 between the end of the third drop and the final drop is presented in the following FDR plot (Figure 16), in which the parameters are aligned with the end of each drop. The ATSB noted the following from the plot:

• the third drop (RETARDANT DROP 1) exits with a higher N1, airspeed, vertical speed, and lower angle of attack (AOA) than the final drop (RETARDANT DROP 2)
• the pitch attitudes and radio heights diverge at the exit, noting the third drop overflew the depression
• the airspeeds diverge as the vertical speeds and N1 converge.

Figure 16: FDR plot of the third (left labels) and final (right labels) drops

Source: ATSB

Crew resource management

Introduction

Crew resource management (CRM) and controlled flight into terrain (CFIT) prevention training were LAT contract requirements in Australia and the US. It was the responsibility of the contractor and not the contracting agency to deliver the training and provide evidence of completion. The operator, Coulson Aviation, delivered these training programs to their personnel during their northern hemisphere spring training in April 2022. The relationship between CRM and SOPs was described in FAA advisory circular AC 120‑71B (2017): Standard Operating Procedures and Pilot Monitoring Duties for Flight Deck Crewmembers, as follows:

Effective crew coordination and crew performance depend on the crew’s having a shared mental model of each task. That mental model, in turn, is founded on SOPs. 

Monitoring performance can be significantly improved by: (1) developing and implementing effective SOPs to support monitoring and cross-checking functions, and appropriate interventions, (2) by training crews on monitoring strategies, and (3) by pilots following those SOPs and strategies.

Coulson Aviation standard operating procedures

Target drop height

The Coulson Aviation B737 flight crew operations manual (FCOM Volume 1, July 2019) RADS flight pre-drop checklist, included a step to ‘Set the DH REF [decision height reference]/radio altimeter minimums to target drop height.’ However, their B737 Fireliner quick reference handbook normal checklist (QRH - FCOM Volume 3, August 2019) abbreviated this checklist item to ‘Altimeters set’, as per the FAA approved flight manual supplement for the Fireliner modification. The CVR revealed several instances of the pilots cross-checking their altimeter pressure settings with each other and other aircraft, and confirming their drop speeds to bug, as per their QRH pre‑drop checklist. However, there was no reference to a target drop height or decision height setting.

The aircraft captain confirmed that the decision height setting on the radio altimeter was not used because it did not provide an aural alert and because the pilot flying is predominantly ‘eyes-out’ during the drop and therefore not monitoring the decision height light on the attitude indicator. The co-pilot did not use the decision height on the radio altimeter and did not believe it was a SOP to use it because it could cycle on-and-off during a retardant drop over undulating terrain.

The operator confirmed that, despite the documented FCOM requirement, the decision height setting was not used. They further stated that it could be a distraction if it activated intermittently during a retardant drop.

According to the aircraft captain, 150 ft was the standard target drop height, with the caveat that ‘drifting down’ to lower drop heights was not uncommon at lighter coverage levels. The operator confirmed that while they used the USFS LAT minimum drop height of 150 ft as their standard target drop height at coverage level 3 (accident drop setting), it was not published in their fixed‑wing flight operations manual or their B737 and C-130 FCOMs. The operator also reported that pilots may be tempted to drop below the standard target drop height at light coverage levels as the retardant will be subjected to less wind interference and this will improve the accuracy of the drop. 

At their initial interview, the co-pilot stated they did not believe there was a minimum drop height, but also reported having limited industry knowledge.

At a follow-up interview, the co-pilot confirmed that none of the captains had briefed a target drop height and that they had flown with all the operator’s B737 captains. The co-pilot reported understanding that 150 ft was the standard drop height figure, but also stated that ‘150 ft is the highest you want to be for that coverage level [3] depending on wind drift.’ The co‑pilot also reported that the altitudes briefed by BD123 were for terrain clearance on the approach and exit and indicated it would be a downhill drop, and that they were not target drop heights. Finally, the co‑pilot advised that they felt confident about speaking up if something felt unsafe and, on that day, ‘there was nothing that seemed unsafe’. 

Monitoring duties

The aircraft captain reported the co-pilot’s duty was to scan inside and out and call deviations, such as airspeed, if different from what was briefed, and confirmed the 150 ft drop height published by the USFS was a minimum height. The CVR indicated that the target drop speed was the only parameter briefed and the last announcement from the co-pilot was about 70 seconds before impact to inform the captain that the pre-drop checklist was complete. The co-pilot reported their focus of attention was inside on the airspeed, which they recalled was on their target drop speed of 118 kt, and on the radio altimeter, which they could not recollect but believed ‘would have been about 100 ft’. The co-pilot was listening to the engine noise but was not monitoring engine thrust and couldn’t recall the thrust lever settings. 

A colleague of the co-pilot confirmed the operator’s CRM philosophy was not to overcommunicate – ‘brief first, then only communicate if there is a deviation from the brief’. Figure 17 depicts the operator’s B737 Fireliner FCOM Volume 1 Retardant drop procedure. With reference to the tolerances in Figure 17, the FDR data indicated that the aircraft descended below their standard target drop height deviation limit of -25 ft about 13 seconds before impact, and remained below it until impact. The airspeed was below their target speed deviation limit for about 11 seconds before impact and 4‍–‍5 seconds before the captain started to advance the thrust levers.

Figure 17: Retardant drop procedure

Source: Coulson Aviation

Crew resource management training

The operator’s CRM training package, delivered in April 2022, included material on the following topics:

• training objectives
• introduction to CRM
• current SOPs
• discussion
• roles and responsibilities.

The training objectives topic highlighted one of the challenges in their industry as follows:

Given the dynamic nature of fire, SOPs allow a relatively wide range of individual preferences among captains, this can and does lead to a level of confusion within the cockpit, especially among new/inexperienced crew members…

The introduction to CRM topic indicated that human error is a contributing factor to most accidents, and highlighted the following factors:

Problems are associated with poor group decision making, ineffective communication, inadequate leadership and poor task or resource management. 

The ‘current SOPs’ topic within the CRM training package included detail of the FCOM Volume 1 Retardant drop procedure (Figure 17) and the QRH Pre-drop checklist. The FCOM Volume 1 Pre‑drop checklist procedure, which included setting the radio altimeter decision height to the target drop height was not included. 

The ‘discussion’ topic listed the following items:

• callouts
• calling a go-around
• when and how to communicate discomfort
• identifying hazards
• when should FO/FE [first officer/flight engineer] hit the button [emergency dump]?

The ‘roles and responsibilities’ topic included, but was not limited to, the following:

• captain – Position aircraft on Show-Me to observe line and start/stop point
• co-pilot – Backup captain on configuration/altitude/airspeed/checklist/drop/escape. 

Controlled flight into terrain prevention training

The operator’s CFIT prevention training package, also delivered in April 2022, included material on the following topics:

• What is CFIT?
• Why does it happen?
• How can I avoid CFIT?
• What are some of the contributing factors to CFIT?
• CFIT accident reviews [which included a general aviation accident, an airliner accident and 3 airtanker accidents].

The first 3 topics were based on material from the FAA’s general aviation joint steering committee (GAJSC) that defined CFIT as follows:

CFIT is defined as an unintentional collision with terrain (the ground, a mountain, a body of water, or an obstacle) while an aircraft is under positive control.

The operator had highlighted several sections of the FAA’s material, which included the following:

…the General Aviation Joint Steering Committee (GAJSC) observed that a clear majority of the CFIT accidents in a typical year occur in daylight, and with visual conditions.

Other top causes of CFIT are…unrealistic aircraft performance expectations (e.g., high density altitude, tailwinds on approach).

While the operator’s accident case studies included multi-crew operations, their introductory material from the GAJSC was directed at single-pilot general aviation operations. Consequently, the avoidance strategies focused on assisting single-pilot operations, such as a FRAT and technological devices such as moving maps with terrain overlays. The slides in their CFIT training package did not include CRM and SOPs as prevention strategies in the retardant drop. 

The role of multi-crew CRM to prevent CFIT was described in FAA advisory circular AC 120-51E (2004): Crew resource management training, as follows:

Effective monitoring and cross-checking can be the last line of defense that prevents an accident because detecting an error or unsafe situation may break the chain of events leading to an accident. This monitoring function is always essential, and particularly so during approach and landing when controlled flight into terrain (CFIT) accidents are most common.

The FAA advisory circulars (AC 120-51E and AC 120-71B) were directed towards the commercial transport sectors to assist operators with the development and implementation of their CRM training, SOPs, and pilot monitoring duties. Consequently, they addressed the multi-crew environment and followed recommendations from a 1994 US National Transportation Safety Board safety study (NTSB/SS‑94/01): A review of flightcrew-involved, major accidents of U.S. air carriers, 1978 through 1990. The NTSB’s review found that 23% of the contributing errors were monitoring and/or challenging errors, which occurred in 84% of the accident sequences. They reported that ‘Most of the errors that were not monitored or challenged played very important roles in the accidents.’

Tasking agency standard operating procedures

National Aerial Firefighting Centre

The National Aerial Firefighting Centre (NAFC) was formed by the Australasian Fire and Emergency Services Authorities Council (AFAC) in 2003 through a partnership between the federal and state/territory governments to deliver cooperative national arrangements for the provision of aerial firefighting resources. The states and territories recognised that if they had one contract for operators to follow then they could easily be moved around the country as necessary to facilitate the sharing of the resource and associated cost. To support this process, the NAFC produced Operational Standards, which provided the minimum standards for a NAFC contract. These were procurement standards, with the respective state/territory emergency services having responsibility for operational policies and procedures. 

The NAFC contracted about 150 firefighting aircraft, including LATs, for use by state and territory emergency service and land management agencies across Australia. At the time of the accident, the NAFC Members participating in the LAT program were New South Wales (NSW), WA, Victoria, and Queensland.

The NAFC-contracted aircraft were assigned a nominated operational base where they were tasked by the NAFC Member’s emergency services. Each of the NAFC Members participating in the LAT program confirmed to the ATSB that they had developed their own SOPs for aerial firefighting, which included LAT SOPs.[30] A LAT service provider (such as Coulson Aviation) therefore operated under a NAFC contract, which required them to comply with the NAFC Standards and the Member state’s SOPs associated with their base.[31] However, their base could change throughout the season in response to the fire threat, which was acknowledged in the National Aerial Firefighting Strategy 2021‍–‍26 section on risk management and resource sharing, as follows:

During any single fire season, it is highly likely that risk factors will lead to Commissioners and Chief Officers wanting to redeploy assets within jurisdictions and potentially redeploy assets across jurisdictional borders. Aerial assets offer the greatest flexibility to redeploy both within and across jurisdictions. LATs and strategic mapping aircraft can operate in more than one jurisdiction on the same day.

To date all aircraft have been assigned to a state or territory in line with the co-contribution commitment which has been part of the NAFC Resource Management Agreement since its inception. The 2020 Royal Commission into National Natural Disaster Arrangements introduced the notion that national assets, particularly LATs and Type 1 Rotary Wing, be tasked according to ‘greatest need’ and their deployment and application would be considered on a national rather than jurisdictional basis.

The NSW Rural Fire Service (RFS), which had their own LAT and could have multiple additional LATs on contract in any season, reported that if one of their LATs was re-deployed to a non‑participating Member state or territory, then it would be operated in accordance with the NSW RFS LAT SOPs, but not inconsistent with local requirements. However, the RFS acknowledged that the non-participating Member state or territory would need to brief the LAT and Birddog operators on any differences, which would require that Member to be familiar with the NSW LAT SOPs.

The federal government contributed funding to the NAFC national fleet of firefighting aircraft but the primary responsibility for aerial firefighting remained with the states and territories and therefore, Member states produced their own SOPs. However, AFAC stated that their Member states and territories would be undertaking greater resource sharing in the future. Therefore, they concluded that the industry should develop national standards and that the NAFC business unit, under the AFAC banner, is a mechanism for this as they had existing areas of Member collaboration in contracts and innovation for aerial firefighting. 

Following the C-130 LAT accident in NSW on 23 January 2020 (AO-2020-007), a statement of intent for aviation safety by the NAFC led to the formation of the Aviation Safety Group (ASG). The ASG was supported by the NAFC and had Members from agencies in all jurisdictions, including New Zealand and a representative from the Civil Aviation Safety Authority. During the B737 LAT accident investigation, the NAFC advised the ATSB that the ASG had developed a list of priorities that included:

• airspace management, including cross-border operations
• human factors and CRM training – for agency personnel, especially those who interface with aviation
• consistent doctrine – review and national standardisation (where practical) of standards and operational procedures
• safety information framework – reporting and sharing of safety information and messaging
• common cross-border radio operations, including hardware innovations and frequency management
• a national LAT Lead Plane pilot training standard.

At the time of writing, the ASG had not identified a national LAT SOP as a priority item.

United States Forest Service standards

The USFS has managed wildland fires on national forests and grasslands for over 100 years, working with federal, state, tribal and local partners. In 1976 the National Wildfire Coordinating Group (NWCG) was established to provide national leadership for these partners. The NWCG had an Executive Board comprised of 12 member entities and their role was described as follows:

The Executive Board works in a collective, collaborative and consensus-seeking manner to accomplish the NWCG mission. NWCG develops the interagency standards that are core to implementing its mission, which the member agencies then choose to implement through their own directive systems.

The USFS reported that federally‑owned lands made up most of the western US and some states had adopted the USFS SOPs as their de facto standard where they had a small area of state responsibility. Local requirements were addressed with a briefing package at each airtanker base. In illustrating the multi‑jurisdictional nature of aerial firefighting, the USFS provided an example operational scenario where a LAT could be employed on a fire in Montana in the morning, in Southern California in the afternoon and end the day in Washington state on another fire.

They reported that these movements across geographical boundaries required national standards to be in place, and that most of the aviation standards were lessons learned from accidents. The national standards were accepted as a better way of operating and they considered the first 30 days after an operator moved between jurisdictions to be a high-risk period due to the change in rules. Therefore, given the movement of aerial firefighting aircraft and operating personnel between the US and Australia, they considered that closer harmonisation of standards would likely bring safety benefits across the industry.   

Benchmarking of tasking agency standards and procedures

Following the C-130 LAT accident in 2020, the ATSB obtained a copy of the NSW RFS LAT SOPs (Operating guidelines for air tankers operations 2018) for review. That review included benchmarking the NSW SOPs against the USFS SOPs, noting the accident aircraft was a US registered LAT and the operator was also contracted by the USFS during their fire season.

The ATSB found several procedures in the USFS SOPs, relevant to the C-130 accident, which were omitted from the NSW SOPs. They were a task rejection policy and procedure, known as a ‘turn down’ in the USFS SOPs under their policy of ‘Risk Refusal’, and procedures for deploying a LAT without aerial supervision. These omissions were raised as safety issues by the ATSB in August 2022 and directed to the NSW RFS for action. The safety issues were closed on 2 May 2023 as adequately addressed.

Following the B737 LAT accident, the ATSB reviewed the WA LAT SOPs (Large air tankers operational procedures 2021-22 version 3.3), current at the time of the accident. This was a joint publication between the WA Department of Fire and Emergency Services and the WA Department of Biodiversity, Conservation and Attractions. The ATSB compared procedures relevant to the C‑130 and B737 accidents from the WA SOPs with the 2018 NSW RFS LAT SOPs and the USFS airtanker SOPs (Standards for airtanker operations 2019) and NWCG aerial supervision SOPs (Interagency aerial supervision guide 2017).[32]^,[33] While the USFS airtanker and NWCG aerial supervision SOPs were separate documents, the WA and NSW LAT SOPs also incorporated the LAT aerial supervision procedures.

The WA SOPs included 3 target identification techniques (tactical flight profiles), but they did not include the Lead or Chase-Position profiles, which were employed on the day of the accident. They also did not include a drop height and there was no task rejection policy or procedure. However, they did include the following requirements:

The BRDG [Birddog] AAS [air attack supervisor] is to confirm the drop zone clear with the Primary AAS or Ground Controller prior to the LAT commencing the final drop run.

The LAT must not drop until DROP ZONE CLEAR has been confirmed.

The NSW SOPs included the same target identification techniques as the WA SOPs and therefore they also did not include the Lead or Chase-Position profiles. However, the NSW SOPs did include reference to a LAT drop height and stated the following:

The Birddog aircraft will assess the Air Tanker for drop height to ensure a height of approximately 150 feet above the canopy or bare ground is attained. Low drop heights should be avoided to minimise the risk during low level flight operations and ground crews in the vicinity of the drop.

The NWCG SOP tactical flight profiles consisted of the Show-Me profile, Chase-Position profile, and Lead profile. All 3 of these profiles were flown on the day of the accident. The USFS and NWCG SOPs both stated the drop height for a LAT was a ‘minimum’ of 150 ft above the top of the vegetation. Below the minimum drop height reference in the NWCG SOPs were the following notes:

It is important for the retardant to “rain” vertically with little or no forward movement. The airtanker pilot is responsible for maintaining safe drop heights. 

The preference for downhill drops was captured in the NWCG and WA SOPs. The NWCG SOPs stated that the approach should be ‘downhill, down canyon, down sun’. The WA SOPs stated, ‘implement where possible that all exits are downhill’. The NSW SOPs did not include an explicit statement to this effect but their flight safety considerations included ‘Terrain may limit firebombing run directions and the availability of exits.’ 

While not a factor in either the C-130 or B737 accidents, the NWCG SOPs included emergency overrun procedures (as did the Birddog operator). In the Lead profile (accident flight profile), the Birddog pilot cannot see the LAT and therefore there is a risk of the LAT overrunning the Birddog. The WA and NSW SOPs did not include procedures for how to mitigate the risks associated with an overrun, which include wake turbulence-induced loss of control for the smaller aircraft, mid-air collision and terrain collision associated with an avoidance manoeuvre. 

Development of the target drop height and speed

Background

The NAFC contract for the operator’s multi-engine airtankers required their aircraft to have US Interagency Airtanker Board (IAB)[34] approval in addition to any local NAFC Member approval requirements. Multi-engine airtankers were approved for use in the US by the IAB, which was a contract requirement of US government agencies at the federal, state, and local level. The current Interagency Airtanker Board procedures and criteria for evaluating aircraft and dispensing systems used in aerial firefighting were published in 2013. According to the USFS, the theory of aerial application of retardant was as follows:

For proper aerial application of retardant to the fuel (vegetation), all forward momentum of the retardant cloud should stop, and the liquid should rain down vertically. This allows an even coating and better vertical penetration into the tree or brush canopy.

Section 7 (B) of the IAB procedures on tank system criteria, described the retardant coverage levels as the gallons per 100 square feet (gpc) and that the flow rate from an aerial delivery system is ‘the most significant controllable factor’ in determining the level of coverage obtained. The USFS considered drop tests to be the most accurate means of measuring ground pattern performance. The IAB procedures defined a drop test as a ‘dynamic flying test of the aircraft retardant delivery system over a cup/grid matrix, which is used to determine the coverage level production of the system for each drop type.’ According to the USFS:

A balance of factors is required for airtankers to meet the coverage level requirements. This balance is established during the IAB testing and is done in a controlled environment with little to no wind on flat terrain. Multiple passes are made over a test grid at different tank controller settings, airspeeds, and heights. This establishes the flight profile and tank controller settings that produce acceptable ground pattern performance under test conditions.

Section 3 (H) of the IAB procedures on multi-engine airtanker requirements included a descent profile requirement as follows:

Aircraft shall be capable of descending at Board-approved maximum operating weight along a 13 percent (7.4°) slope for 30 seconds to 5,000 ft pressure altitude in the drop configuration without exceeding maximum drop speed. At the 25 second mark, a full load of water shall be dispensed at coverage level 6 and again at coverage level 8 and demonstrate no more than 7% difference in average flow rate from grid results.

Drop height requirements

Section 3 of the IAB procedures on multi-engine airtanker requirements did not include a minimum drop height. However, section 7 (B) of the IAB procedures on tank system criteria stated that the requirement was that drops ‘shall be made at a 200-foot drop height or the minimum safe drop height if greater than 200 feet.’ The operator had conducted IAB drop testing with their B737 Fireliner and described the process as follows:

The IAB grid test evaluates the performance of the drop tank in negligible wind conditions at various coverage levels, aircraft configurations, ground speeds, and drop heights. As part of that process, high speed video was evaluated to determine the optimal drop height which is the lowest height that allows the forward trajectory of the retardant to cease, thus minimizing shadowing effect so that the fuels are evenly coated.

As part of the grid test evaluation, the IAB provided the operator with a table of the recommended minimum grid test drop heights under the heading of ‘minimum altitude above the height of the fuel to eliminate the forward momentum, i.e. eliminate shadowing[35] (feet).’ Each drop height corresponded with a controller setting for the coverage level to be achieved. For the operator’s B737 Fireliner, the minimum drop heights were over the range of 150‍–‍200 ft for the controller settings 1‍–‍8 (150‍–‍185 ft for the C-130). For all the LATs listed in the table, the recommended minimum grid test drop height was 150 ft for controller settings 1‍–‍3 (setting 3 was used on the day of the accident). The operator reported that they adopted the heights in the table as their standard target drop heights for training and operations.

The USFS clarified that the table drop heights were for determining ground pattern performance during testing only and were not operational requirements. The operational drop heights were identified in the contracts, which may reference interagency operational handbooks. They reported that environmental variables, such as wind, terrain, fire behaviour and suppression tactics may require a drop height higher than was demonstrated during testing. 

The USFS Airtanker Services contract standards[36] stated a minimum drop height of 150 ft, which was consistent with their airtanker SOPs and the NWCG aerial supervision SOPs. Their contract standards also stated that ‘Retardant shall be dropped as accurately as possible on the designated target areas of the fire.’ The USFS confirmed that if an operator conducted drops below 150 ft, they would be non-compliant with the contract. However, they acknowledged that operators have dropped lower to improve their accuracy or with the assumption that it will assist the ground firefighters by providing a thicker line of retardant. 

In March 2000, the USFS published the results of a research project into safe drop heights for fixed-wing airtankers (Lovellette). The purpose of the project was to examine the cessation of the forward momentum of the retardant cloud, which served 2 purposes:

• prevent shadowing of the fuel (as discussed above)
• reduce the risk to ground personnel from flying debris struck by the retardant cloud.

Video analysis of drop tests from the project led to the development of a relationship between safe drop height, load size, and the peak flow rate (Lovellette, 2000). The danger to ground firefighters was minimised if the retardant lost its forward momentum and fell vertically (Lovellette, 2000). This provided a safe drop height that increased with higher controller settings that use a higher flow rate to achieve the required coverage level. 

Another review of drop patterns by the USFS found that lower coverage level patterns showed distortion under higher wind speeds while the higher coverage levels were relatively unaffected (Suter, 2005). Suter (2005) noted that higher drops increased the retardant cloud susceptibility to wind erosion and the maximum coverage levels tended to decrease as the drop height increased. While the analysis of drop patterns showed disadvantages to increasing drop height, Suter (2005) also noted that increasing drop height is ‘safer for flight crew and ground personnel.’  

The USFS confirmed that Lovellette’s (2000) safe drop height project was for the safety of ground personnel and not the airtankers. The focus on the safety of ground personnel was reinforced with their interagency aviation safety alert in 2019 (IASA 19-02)[37] on the subject: Retardant Safe Drop Height, area of concern: Safety of Ground Personnel. From the safety alert:

The force of the retardant dropped from too low of an altitude can topple trees up to 90 feet in height and a trunk a foot in diameter.

Pilots must remember that lower is not always better. Drops that are too low fail to provide retardant in an efficient manner with the desired coverage level. This is not only dangerous but fails to provide the support ground crews require.

Drop speed requirements

Section 3 (E*)[38] of the IAB procedures on multi-engine airtanker requirements included the following points about the effect on flight conditions from the release of retardant:

Release of retardant in all normal drop configurations and at all normal drop speeds does not result in dangerous or seriously objectionable flight conditions.  

1. The minimum drop speed is not less than the Vmc (minimum control speed), nor 1.25 Vs (stall speed), both speeds being evaluated in the drop configuration.

2. The maximum drop speed does not exceed Va (design maneuvering speed).

According to the USFS, environmental variables may require an increase in the drop speed of 10‍–‍20 kt, but excessive drop speeds could adversely affect the firefighting effort as per the following description:

At higher airspeeds, the retardant can shear at the tank opening and not drop in a column, thus reducing coverage levels. If the retardant cloud has too much forward momentum the retardant will coat only one side and create a shadowing effect, allowing fire spread. Forward momentum creates a hazard to ground crews if they are inadvertently in the path of the drop. Too slow of a release speed is a safety of flight issue.

The USFS reported the drop test airspeed requirements dated back to 1976 and the rationale for the prescribed parameters could not be found. However, they reported that the speed is not limited to the maximum load the applicant is seeking approval for and the relevant condition was ‘Release of retardant in all normal drop configurations and at all normal drop speeds does not result in a dangerous or seriously objectionable flight condition.’ They further stated that: 

Release can be one drop of the entire volume or split drops up to 4 drops so all normal drop configurations could be between the full volume down to a quarter volume. To produce the desired coverage level the speed may change but not go below the minimum drop Vmc nor 1.25Vs or above the maximum of Va.

The operator incorporated tables for weights and speeds in their B737 Fireliner QRH normal checklist. The weights column was based on 5,000 lb increments in the aircraft operating weight from 85,000 lb to 135,000 lb. There were 4 columns for airspeeds, which included a column for 1.25 Vs that was also annotated as V-drop (target drop speed). This table provided a quick reference for the crew to update their drop speed between partial drops and was consistent with the IAB minimum drop speed requirements for evaluating multi-engine airtankers. 

Emergency dump

Section 7 of the IAB procedures on tank system criteria required ‘features that enhance safety in the event of an in-flight emergency.’ These features included an independently‑controlled emergency dump system. The operator’s flight manual supplement for the B737 RADS indicated the emergency dump system could jettison a full load in 2 seconds.

Previous controlled flight into terrain accidents

The ATSB reviewed several LAT and multi-engine water-bomber CFIT accidents during the investigation. The following 3 LAT accidents from Canada and the US were discussed with various personnel during the investigation.

Canada

Cranbrook, British Columbia – 2003

On 16 July 2003, a Lockheed L-188 Electra (Tanker 86) collided with terrain, fatally injuring the 2 crewmembers, during the go-around from a first partial retardant drop (A03P0194). In the final seconds before impact there were 2 separate retardant drops into the trees and ground witnesses heard the engine noise level increase significantly. The Transport Safety Board (TSB) of Canada noted that the ‘ridge that the aircraft struck blended into the rising terrain and was not obviously separate from its surroundings.’ The TSB published the following findings as to causes and contributing factors:

For undetermined reasons, the Electra did not climb sufficiently to avoid striking the rising terrain.

Given the flight path and the rate of climb chosen, a collision with the terrain was unavoidable.

The characteristics of the terrain were deceptive, making it difficult for the pilots to perceive their proximity and rate of closure to the rising ground in sufficient time to avoid it.

Lytton, British Columbia – 2010 

On 31 July 2010, a Convair 580 (Tanker 448) collided with terrain, fatally injuring the 2 crewmembers, while crossing the edge of a ravine in the side of the Fraser River canyon before descending on the fire located in the ravine (A10P0244). The TSB findings as to causes and contributing factors included the following:

Visual illusion may have precluded recognition, or an accurate assessment, of the flight path profile in sufficient time to avoid the trees on rising terrain.

Visual illusion may have contributed to the development of a low energy condition which impaired the aircraft performance when overshoot action was initiated.

United States

Modena, Utah – 2012

On 3 June 2012, a Lockheed P2V-7 (Tanker 11) collided with terrain while following the Lead Plane onto final for its second retardant drop of the day at the same location (WPR12GA243), fatally injuring the 2 crewmembers. From their analysis of the 2 drops using the flight recorders, the NTSB made the following observation:

The most significant difference between the first drop approach and the accident drop approach was that Tanker 11's first approach into the drop zone was initiated from a higher altitude, about 1,000 feet above the ridge line surrounding the west side of the fire, and had a relatively steady rate of descent on to the final drop course. In comparison, the accident flight approached the final drop course from a lower altitude that approximated the elevation of the ridge lines surrounding the west side of the drop zone in level flight while it turned onto the final drop course.

The CVR revealed an ‘airspeed’ call from the first officer about 2 seconds before impact but no altitude or height calls. The NTSB determined the probable cause(s) of the accident to be:

The flight crew’s misjudgement of terrain clearance while maneuvering for an aerial application run, which resulted in controlled flight into terrain. Contributing to the accident was the flight crew’s failure to follow the lead airplane’s track and to effectively compensate for the tailwind condition while maneuvering.

The hidden hill visual illusion

The ATSB discussed previous LAT CFIT accidents and the topic of visual illusions in the low-level environment with the Bomber 139 captain. The TSB of Canada explored the problem of visual illusions during low-level flight in their reports of CFIT LAT accidents at Cranbrook, British Columbia (2003) and Lytton, British Columbia (2010). The Cranbrook accident was during the go‑around from a partial drop and the Lytton accident was during the approach to the drop zone. They concluded that visual illusion may have contributed to the accidents by delaying the crew’s recognition of the terrain. 

The Bomber 139 captain presented lessons learned from the NTSB’s report into the LAT accident at Modena, Utah (2012) at the US National Aerial Firefighting Academy for a period of 3‍–‍4 years. During this period, the captain developed a belief that the crew of Tanker 11 experienced the ‘hidden hill’ illusion, which occurs when the terrain in the foreground blends into the terrain in the background, consistent with the TSB reports. The captain reported that ‘hidden hill’ was a common industry term they used in their annual CFIT prevention training and the ATSB noted the Tanker 11 accident was one of the case studies in the operator’s CFIT prevention training package.

While the ATSB was at the B737 LAT accident site in WA, the Bomber 139 captain visited the site with senior management personnel from the operator. At the start of the visit, the ATSB escorted them to the location of the start of the accident drop, which provided them with a view of the accident site from across the depression. The captain later reported the following observation:

If you looked away from where the airplane hit to where the vegetation still existed. It was hard to see any depth or any descent throughout that at all or the fact that there was a rise on the other side.

Safety analysis

Introduction

On 6 February 2023, a Coulson Aviation Boeing 737 large air tanker (LAT), callsign Bomber 139, was tasked to conduct fire retardant drops in the Fitzgerald River National Park, Western Australia (WA). The aircraft was tasked by the WA Department of Fire and Emergency Services (DFES) at the request of the WA Department of Biodiversity, Conservation and Attractions (DBCA). The captain was the pilot flying, in the left seat, and the co-pilot was the pilot monitoring, in the right seat.

Bomber 139 conducted 3 flights on that day, which was the last day of the flight crew’s tour of duty. The first 2 flights each comprised a single full load drop at the fire ground with a return to Busselton. On the third flight, following an initial partial drop, the crew conducted a second drop, which released all the remaining retardant. The aircraft collided with terrain during the go-around from the second drop. The wreckage and site examination, meteorological information, flight data recorder (FDR), cockpit voice recorder (CVR) and flight crew interviews found no technical fault with the aircraft, evidence of flight crew fatigue or hazardous weather condition that contributed to the accident.

This analysis will discuss the operational and human factors at the fire ground that influenced the accident, in addition to the operator and tasking agency standard operating procedures (SOPs). It will also discuss the need for national LAT SOPs following this accident and a previous collision with terrain of a Lockheed C-130 LAT during the go-around from a partial load drop in New South Wales on 23 January 2020 (ATSB investigation AO-2020-007).

Accident sequence

On Bomber 139’s arrival at the fire ground on the first flight of the day, Birddog 125 (BD125) provided a Show-Me profile for Bomber 139 before Bomber 139 conducted a close left-hand circuit to the target with BD125 in the Chase-Position. The fire was burning on the right side of the drop line, which kept the circuit clear of smoke.

On arrival for the second drop, BD125 once again set Bomber 139 up with a left-hand circuit to the target for a drop flown by BD125 in the Chase‑Position, but this time without a Show-Me profile. The left-hand patterns clear of the smoke provided Bomber 139’s captain with a clear view of the drop zone and exit during the approach to the target. 

When Bomber 139 arrived at the fire ground on the third (accident) flight, BD123 had replaced BD125. In preparation for the drop, BD123 briefed Bomber 139 that the drop zone was clear of ground crew, there were no hazards, and that it was a downhill drop. The captain declined BD123’s offer of a Show-Me profile, consistent with the second flight. However, the captain accepted a Lead profile right-hand circuit, which was inconsistent with the earlier flights.

The right‑hand pattern was chosen to keep them clear of smoke, as the plan was to tag and extend an existing line of retardant downhill into a depression towards the south with the fire burning to the east of the line. It also meant that the captain, in the left seat, was sitting on the outside of the circuit, which made it more difficult to view the drop zone on the downwind and base legs. 

Bomber 139 then followed BD123 on a ‘wide’ right-hand circuit pattern with a final approach and descent to the target down the right side of the smoke. The captain, who preferred a closer circuit pattern to maintain visual contact with the drop zone and exit during the approach, had trouble identifying the start of the drop (a road crossing) on the first approach. The captain’s difficulty identifying the road was likely due to the wide right-hand circuit pattern and resulted in the captain’s attention becoming focussed on sighting it for the start of the drop.

During the drop the captain detected that they were not on the correct line to keep the retardant drop clear of the burnt area. Therefore, they stopped the drop and conducted a go-around from the high ground with the fire in the depression burning across their path. The elevation of the terrain beneath at the time of that go-around was higher than the elevation of the terrain at the accident site, which was on the far side of the depression. Therefore, the accident ridgeline remained below the horizon for the crew on the first drop, potentially obscured by smoke from the fire in the depression and likely indistinguishable from the surrounding terrain due to the relatively consistent vegetation coverage.

The captain’s decline of the Show-Me profile, wide right-hand circuit, Birddog brief of a downhill drop and subsequent go-around from the high ground, meant that the captain did not expect, or detect, rising terrain in the exit path prior to attempting the second drop.  

The operator had adopted 150 ft as their standard target drop height. However, a low drop height and speed would improve the accuracy of a drop at a low coverage level. The crew was using a low coverage level [3] throughout the day and on the 2 previous flights that day, Bomber 139 recorded minimum drop height parameters of 46 ft and 69 ft with the engines at 60‍–‍70% N1. When the thrust levers were advanced at the end of each drop, there was an immediate positive response in N1, airspeed and vertical speed. The minimum parameters on the first (partial) drop of the accident flight were 78 ft and 124 kt at about 70% N1. Following the partial drop, when the captain advanced the thrust levers for the go-around there was once again an immediate positive response in N1, airspeed and vertical speed. 

The performance response from the aircraft on the previous drops, expectation of a downhill drop with no hazards and no personnel on the ground, likely contributed to the captain’s confidence that the aircraft could be safely flown and recovered from a low drop height and speed. The minimum parameters recorded on the accident drop were 57 ft and 106 kt. However, this time, the captain used the idle thrust setting of 30% N1 at the start of the drop to control the airspeed for the downhill run, which required a relatively high rate of descent that peaked at about 1,800 ft/min. At this setting, the engines required 7‍–‍8 seconds after the thrust levers were advanced before they would reach go-around thrust.

The captain was aware of the need to advance the thrust levers before the end of a drop if idle thrust was used. However, the accident drop was a partial load that only took 5 seconds and encompassed a downhill section with rising terrain in the exit that the captain was not aware of. Consequently, when the captain advanced the thrust levers about mid-way through the drop, there was a delay in the engines accelerating to go-around thrust which resulted in a low and decreasing aircraft energy state at the end of the drop and the collision with rising terrain in the exit path.

Energy management

A comparison of the drops conducted by Bomber 139 on the day of the accident indicated that N1 was a key parameter for a successful go-around and no performance problems were evident when N1 was in the region of 60‍–‍70% at the end of the drop. Variation in the N1 acceleration profile data at about 40% on the accident drop indicated that a slower engine acceleration occurred below this point, which was consistent with an idle thrust setting. However, the industry preference was for drops to be conducted downhill and consequently, the operator reported it was not practical to prescribe a minimum N1. Instead, they trained their pilots to advance the thrust levers during the drop if idle thrust was required at the start of the drop.

During the accident drop, Bomber 139’s captain advanced the thrust levers about mid-way through the drop, which provided insufficient time for the engines to respond. The ATSB found this would likely be the case for partial drops and drops conducted at higher coverage levels, due to the shorter drop time. If idle thrust was used in these scenarios, a safe go-around would depend on the LAT having sufficient energy, in terms of height and airspeed, to maintain terrain clearance until the engines accelerated to go-around thrust.  

When considering the drop height parameter, the ATSB found that the US Interagency Airtanker Board (IAB) had investigated and determined that 150 ft was a LAT minimum safe drop height for their airtanker evaluation process. This was the reference drop height in the US airtanker and aerial supervision standards for a LAT.

Minimum drop heights were developed to reduce the forward momentum of the retardant cloud such that it would rain down vertically over the vegetation to prevent shadowing and minimise the hazard to ground personnel from falling debris. However, the retardant cloud can be subject to wind‑induced drift during the drop, which makes higher drop heights unsuitable due to the loss in coverage and incentivised lower drop heights over light fuel loads to improve accuracy.

Given the above factors, and noting that Bomber 139 was conducting drops significantly below 150 ft, there was no evident justification for changing the use of 150 ft as a LAT minimum drop height standard. Nevertheless, any increase in drop height would improve the aircraft energy state and therefore the safety of the flight crew.

The operator used a drop speed of 1.25 Vs for their drop configuration, which was based on the IAB minimum drop speed for their testing. The drop configuration was based on the flap setting and weight of the aircraft at the start of each drop. If a series of partial drops were conducted, then the flight crew would lower the target drop speed between each drop in accordance with the table of aircraft weights and speeds on their checklist.

While the IAB drop testing permitted drop speeds between 1.25 Vs and Va, the US Forest Service (USFS) explained that higher drop speeds can shear the retardant column at the tank opening and reduce the coverage level. Therefore, while an increase in the drop speed would improve the energy state of the aircraft, it would also require testing to ensure the required coverage level for effective fire suppression was maintained.

While the target drop speed was 1.25 Vs and the operator had published a lower deviation limit of ‑5 kt, the recorded data from the 4 drops on the day of the accident revealed that it was only on the second drop that Bomber 139 maintained the target drop speed within the tolerance. During the first drop, the airspeed decayed about 25 kt below the estimated target drop speed before recovering to within the tolerance at the end of the drop. On the third and fourth drops, the airspeed decayed about 9 kt below the target drop speed during the drops. 

The retardant drop is a manually flown contour flight manoeuvre in potentially rough air and over undulating terrain across a drop zone that has not been formally surveyed for obstacle clearance and gradient. Therefore, airspeed and height deviations could be expected. If a performance problem developed before the entire load was released, then the crew had the option to conduct an emergency dump to reduce the weight and increase the airspeed safety margin. However, if the drop speed was recalculated and lowered between partial drops, the safety margin for the go‑around was also reduced.

During the investigation, the operator reported to the ATSB that they believed the recalculation and lowering of the target drop speed was a ‘significant contributing factor to the accident.’ It was also noted by Boeing, from their analysis of the recorded data, that had Bomber 139 avoided the ridgeline, there was nothing to preclude the aircraft climbing away from the ground. 

The ATSB’s analysis of energy-height revealed Bomber 139 would have gained about 39‍–‍90 ft if the recalculated target drop speed lower tolerance of 113‍–‍118 kt was maintained during the final run. As such, even considering the low operating height of the final drop, if the aircraft had been flown at or above the lower deviation limit (113 kt) of the reduced target speed of 118 kt, the ground collision would probably have been avoided.

The energy analysis also identified that when the accident end-of-drop speed was compared with the previous drop, the recalculation of the drop speed was a greater proportion of the energy‑height loss (65%) than flying slower than the recalculated target speed (35%). The full load target drop speed would have provided them with +167 ft of energy-height to their target accident drop speed and +257 ft of energy height to their accident drop speed. Therefore, while the ATSB concluded that lowering of target drop speed between partial drops was not a contributing factor to the accident, it significantly reduced the terrain clearance energy‑height safety margin. 

Crew resource management

Analysis of the cockpit voice recorder (CVR) for the accident flight revealed the Bomber 139 captain and co-pilot were working cooperatively with a division of duties during the set-up for the first drop. Between the first and second drop, they were again working cooperatively to track the position of BD123, update their checks and set their aircraft up for the second drop. However, the CVR also revealed that the co-pilot was silent in the cockpit for about the last 70 seconds of the flight, during which Bomber 139 was flown below the operator’s standard target drop height and speed deviation limits published in their flight crew operations manual (FCOM) Retardant drop procedure and with the engines at idle. In accordance with the FCOM procedure, deviating outside of the limits of either of these parameters required a ‘call-out’ from the pilot monitoring, which was the co-pilot.

The co-pilot had been employed by the operator for less than a year and was aware of the 150 ft standard for drop heights, although they also expressed a belief that the accident drop height was about 100 ft. The co-pilot also believed there was no minimum drop height and indicated that they had interpreted the 150 ft standard as a maximum drop height to mitigate the potential adverse effects of the wind on the fall of the retardant. On the day of the accident, all 4 drops were conducted significantly below 150 ft, which likely reinforced the co‑pilot’s interpretation of 150 ft as a maximum height and was consistent with the idea that the wind could reduce the accuracy and coverage level at higher drop heights. 

The operator’s FCOM pre-drop checklist included setting the radio altimeter decision height bug to the target drop height. The 150 ft drop height was assumed knowledge in the operator’s organisation as they had adopted the IAB recommended minimum drop heights, which complied with their USFS contract requirements. However, the setting of the decision height bug to the drop height was not included in their quick reference handbook normal checklist and was not practiced by them.

Despite the published FCOM requirement, the operator believed that setting the decision height bug at their target drop height would result in a distraction if the decision height light cycled on and off over undulating terrain. Therefore, as the captain had not briefed a target drop height and the co-pilot had interpreted the 150 ft as a maximum drop height, the co-pilot did not have a minimum reference drop height to monitor against the deviation limits in the FCOM. This probably led to the co‑pilot’s silence about the low height during the accident drop.

The co-pilot reported the airspeed indicator was one of their primary flight instruments they were scanning during the drop, and that they believed it was indicating their target drop speed of 118 kt throughout the run. Recorded data indicated the airspeed went below, and remained below, the lower deviation limit about 2 seconds before the start of the drop after fluctuating intermittently above and below the lower limit during the approach. However, the co-pilot did not detect and announce the low and decreasing airspeed. 

The second approach was flown through the smoke and the CVR indicated the captain was having trouble identifying the start of the drop. As the co-pilot was also looking for the target and observed BD123 deploy smoke over the target, they were potentially distracted from the airspeed indicator during the approach.

Within 2‍–‍3 seconds of the start of the drop, the captain started to advance the thrust levers at which stage the co-pilot was anticipating the flap retract call for the go-around. The ATSB was unable to determine why the co-pilot did not recognise the low and decaying airspeed. However, it is possible that the short duration of the drop might have resulted in the co-pilot shifting their attention to the vertical speed indicator, altimeter and flap lever in preparation for the go-around once the captain started to advance the thrust levers. 

The operator reported their crew resource management (CRM) philosophy was to brief first and then only announce deviations as this minimised distractions during the retardant drop. However, this practice did not employ all the resources at their disposal to mitigate the risk of a low energy state developing. While they considered the decision height bug to be a distraction if it was set at the target drop height, they had not considered setting the bug at the lower deviation limit to assist the pilot monitoring duties. They also did not brief a target drop height if the captain planned to vary the drop height from their 150 ft standard, which resulted in the co-pilot being left ‘out‑of‑the‑loop’ in terms of their responsibility to monitor the target drop height. 

The pilot monitoring call-outs in the operator’s retardant drop procedure were reactive to exceeding the target drop height or drop speed deviation limits. They did not include proactive ‘approaching target height/speed’ or ‘on height/speed’ call-outs. Proactive announcements confirm to other crewmembers that the pilot monitoring is conducting their duties and alerts the pilot flying to the flight path and energy state of the aircraft.

The operator’s expectations of pilot monitoring duties were presented in their CRM training but their controlled flight into terrain prevention training package did not present their CRM and SOPs as prevention strategies. Retardant drops are conducted to unsurveyed areas, which may result in lower safety margins than an approach to, or departure from, an airport. Hence the application of CRM and SOPs to managing the energy state of the aircraft should be as important for a retardant drop as for a departure or an arrival.

According to the US Federal Aviation Administration’s (FAA) advisory circular on standard operating procedures and pilot monitoring duties for flightdeck crewmembers, effective CRM is founded on SOPs. Therefore, while the operator’s pilot monitoring announcements were reactive to a low energy state, the ATSB could not conclude that this CRM-related aspect contributed to the accident due to the conflict between the operator’s procedures and actual practice. However, the ATSB concluded that the reactive nature of the pilot monitoring duties in their retardant drop procedure increased the risk of their aircraft entering an unrecoverable energy state and therefore have assessed it as a safety issue for Coulson Aviation.

Standard operating procedures

During the ATSB’s 2020 C-130 LAT accident investigation, it was apparent that the crew had developed an elevated level of risk tolerance for hazardous weather conditions. While the loss of the crews’ lives and lack of CVR data limited the ATSB’s ability to explore their pre-flight and tactical decision-making, the ATSB did note that there were no ‘circuit-breakers’ in the system to mitigate the crews’ acceptance of a task in the prevailing conditions. The operator had not imposed weather limits or a pre-flight risk assessment and the tasking agency did not have a policy and procedure to manage the task rejections that unfolded throughout the day.

Following the Bomber 139 accident, the co-pilot reported to the ATSB that they did not believe there was a minimum drop height. The ATSB subsequently found that neither the operator nor the tasking agency had published a drop height. While the operator had adopted their USFS contract standard of 150 ft as their standard target drop height, this was assumed knowledge within the organisation and was not published as a SOP. Consequently, captains could exercise their own judgement to improve accuracy if there was no contractual limit imposed. Their contract for services with the National Aerial Firefighting Centre (NAFC) did not impose a minimum drop height but required the operator to comply with the Member SOPs for their nominated operational base. The WA LAT SOPs did not impose a drop height limit and therefore the Bomber 139 crew could conduct their drops below 150 ft without breaching their contract or published SOPs.   

The history of the development of airtanker drop heights revealed the primary aims were to minimise the risk to ground personnel from falling debris and prevent shadowing of the vegetation. The drop height safety requirement for ground personnel was published by the USFS in 2000 (Lovellette) and was later reiterated with a safety alert in 2019 following the fatal injury of a ground firefighter from a retardant drop in 2018. The WA LAT SOPs managed the safety risk to ground personnel by prohibiting drops before the drop zone was confirmed clear. This confirmation was communicated between the Birddog aircraft and Bomber 139 on the accident flight, which meant that the ground personnel safety requirement was not applicable to the drop height on this occasion.

The history of drop tests also revealed that wind speed and drop height affected the drop pattern and consequently the effectiveness of the drop. Greater wind speeds distorted the drop pattern at the lower coverage levels (Suter, 2005). When released from a sufficient height to stop the forward momentum of the retardant, Suter (2005) noted that the cloud was susceptible to wind erosion. Therefore, lower drop heights improve the drop pattern at low coverage levels. This knowledge may incentivise pilots to conduct lower drops, and operators and tasking agencies to accept this practice.

In this accident, the ATSB found that a low drop height was a contributory factor to the low energy state and collision with terrain during the exit from the drop. According to the FAA’s AC 120-71B (2017) Standard Operating Procedures and Pilot Monitoring Duties for Flight Deck Crewmembers, crew performance is founded on SOPs and pilot monitoring performance can be improved with the development of effective SOPs. Without a published SOP, the Bomber 139 captain could exercise drop height discretion and the co-pilot did not have a deviation parameter to monitor and call-out. Therefore, the ATSB has assessed the lack of a minimum drop height SOP as a safety issue for Coulson Aviation. 

Furthermore, the fireground is an area of operations where multiple operators are required to interact. This introduces the problem of non-standard procedures between operators and the potential for unforeseen risks to emerge. In this accident, the Birddog operator had published a minimum drop height SOP. However, neither the LAT operator, nor the relevant WA government tasking agencies— the WA Department of Fire and Emergency Services and Department of Biodiversity, Conservation and Attractions—had published a minimum drop height.

The tasking agency SOPs provide a mechanism for the integration and standardisation of their aerial firefighting operation and for them to take the lead on setting the quality and safety criteria they require from the aerial firefighting effort. Therefore, the lack of a minimum drop height SOP is considered to be a safety issue for the WA Department of Fire and Emergency Services and Department of Biodiversity, Conservation and Attractions.

National large air tanker standard operating procedures

Aviation is a federally regulated activity but there is no federal authority with the operational responsibility for aerial firefighting. In 2003, the National Aerial Firefighting Centre (NAFC) was formed by the Australasian Fire and Emergency Services Authorities Council with the support of federal, state and territory governments. Their state and territory Members agreed that a single contract for each operator would facilitate the movement of assets between jurisdictions. However, the operating procedures that applied in each jurisdiction remained each Member’s responsibility.

While this may not increase risk for aerial firefighting assets that remain within a single jurisdiction throughout the season, LATs have been identified as having the capability to operate in more than one jurisdiction on the same day. Furthermore, the 2020 Royal Commission into National Natural Disaster Arrangements identified LATs as assets that should be tasked according to ‘greatest need’ on a national rather than jurisdictional basis.

The LATs and their aerial supervision do not operate in isolation and must be integrated into each jurisdiction where they operate. Therefore, any inconsistencies or omissions between tasking agencies’ SOPs will increase the complexity of risk management activities as it will be more difficult to assess and manage the associated risks. On the day of the Bomber 139 accident, the LAT and Birddog aircraft were conducting tactical flight profiles at the fireground, which were consistent with the Birddog operator and US National Wildfire Coordinating Group SOPs, but were not reflected in the WA LAT SOPs. Bomber 139 was also conducting drops without a prescribed minimum safe drop height or emergency overrun procedures under their contract for services.

The WA LAT target identification procedures (tactical flight profiles) were consistent with the 2018 NSW LAT procedures published at the time of the C-130 accident. However, NSW had published a LAT drop height of 150 ft but WA had not published a drop height, and where WA had prescribed the drop exits should be downhill, NSW had not made this explicit. Consequently, a different standard or no standard existed in each agencies’ document, which indicated an inconsistent approach to the development and implementation of LAT SOPs. 

In contrast, the US standards for LAT and aerial supervision operations reviewed by the ATSB consistently reported a 'minimum drop height of 150 ft’ for LATs. The USFS reported that the move in 1976 towards the development of national standards was accepted as a better way of operating. They captured the lessons learned from accidents and facilitated the movement of airtankers across state borders to operate at multiple firegrounds on the same day.

The ATSB noted that the US aerial firefighting standards were a collaborative effort with multiple signatories on each document. One of the challenges in compiling a standard is understanding what should, and should not, be included. The current process of each NAFC Member developing their own standards hampers an inter-agency collaborative process with stakeholder consultation to develop a set of best-practice SOPs. 

The differences in the NAFC Members’ LAT SOPs, noted by the ATSB, were not based upon a complete review, only the circumstances surrounding the C-130 and B737 accidents. A comprehensive review of all Member LAT SOPs, while beyond the scope of this ATSB investigation, would likely find further inconsistencies and omissions. This work is best conducted by the key stakeholders, who are the NAFC Members, with input from the LAT operators, aerial supervision operators and air attack supervisors.

At the time of the C-130 and B737 accidents, there was no agency responsible for producing national aerial firefighting SOPs. Following the Royal Commission into the 2019/2020 bushfire season, a national Aviation Safety Group (ASG) was formed from the NAFC Members and a priority list developed, which included standardised doctrine. However, the ASG’s list of priorities did not explicitly identify LAT SOPs, despite the 2 recent LAT accidents and the intent for them to be deployed on a national ‘greatest need’ basis.

The ATSB considers the absence of national LAT SOPs a safety issue and considers the Australasian Fire and Emergency Services Authorities Council collaboration model through the NAFC Strategic Committee the most appropriate pathway to address this deficiency. The safety issue has been raised with the understanding that the LAT SOPs will either incorporate the LAT aerial supervision procedures or that the LAT aerial supervision procedures will be developed and implemented concurrently, noting the ASG has already prioritised a national LAT Lead Plane pilot training standard.    

Findings

From the evidence available, the following findings are made with respect to the controlled flight into terrain involving Coulson Aviation Boeing 737-3H4, registered N619SW, at Fitzgerald River National Park, Western Australia on 6 February 2023. 

Contributing factors

• During the retardant drop downhill, the aircraft descended significantly below the operator’s standard target drop height and airspeed and entered a high rate of descent with the engines at idle. While the engines were starting to accelerate at completion of the drop, the airspeed and thrust were insufficient to climb above a ridgeline in the exit path, which resulted in the collision with terrain.
• Prior to the retardant drop, the aircraft captain (pilot flying) did not detect there was rising terrain in the exit from the drop, which likely contributed to the captain allowing the aircraft to enter a low energy state during the drop.
• After arrival at the fireground, the aircraft captain (pilot flying) declined a ‘Show-Me’ run and was briefed by the Birddog pilot that it would be a downhill drop. Bomber 139 then conducted a go-around from the high ground after the first drop and was led to the target through the smoke on the second drop. These factors likely contributed to the captain not expecting or detecting the rising terrain in the exit path.
• The co-pilot (pilot monitoring) did not identify and announce any deviations during the retardant drop, which could have alerted the aircraft captain (pilot flying) to the low-energy state of the aircraft when it descended below the target drop height with the engines at idle.
• The flight crew did not brief a target retardant drop height and, contrary to published standard operating procedures, did not set it as a decision height reference on the radio altimeter. Subsequently, the co-pilot (pilot monitoring), who did not believe there was a minimum drop height, did not alert the aircraft captain (pilot flying) to the low-energy state of the aircraft.
• Coulson Aviation and the relevant Western Australian Government Departments had not published a minimum retardant drop height in their respective operating procedures for large air tankers. Consequently, the co-pilot (pilot monitoring), who did not believe there was a minimum drop height, did not alert the aircraft captain (pilot flying) to a drop height deviation prior to the collision. (Safety issue)

Other factors that increased risk

• The Coulson Aviation practice of recalculating the target retardant drop speed after a partial drop reduced the post-drop stall speed and energy‑height safety margins. (Safety issue)
• The Coulson Aviation crew resource management practice of limiting the pilot monitoring (PM) announcements to deviations outside the target retardant drop parameter tolerances increased the risk of the aircraft entering an unrecoverable state before the PM would alert the pilot flying. (Safety issue)
• Australian states and territories that engage in Large Air Tanker (LAT) operations have developed their own separate standard operating procedures (SOPs) for LATs and aerial supervision assets. This can result in safety requirements being omitted or misunderstood by the different tasking agencies, such as a minimum drop height, resulting in inconsistencies in the development and application of LAT SOPs. (Safety issue)

Safety issues and actions

Drop speed recalculation

Safety issue number: AO-2023-008-SI-01

Safety issue description: The Coulson Aviation practice of recalculating the target retardant drop airspeed after a partial drop reduced the post-drop stall speed and energy‑height safety margins.

Inadequate procedural requirements

Safety issue number: AO-2023-008-SI-02

Safety issue description: Coulson Aviation and the relevant Western Australian Government Departments had not published a minimum retardant drop height in their respective operating procedures for large airtankers. Consequently, the co-pilot (pilot monitoring), who did not believe there was a minimum drop height, did not alert the aircraft captain (pilot flying) to a drop height deviation prior to the collision.

Inadequate procedural requirements

Safety issue number: AO-2023-008-SI-03

Safety issue description: Coulson Aviation and the relevant Western Australian Government Departments had not published a minimum retardant drop height in their respective operating procedures for large airtankers. Consequently, the co-pilot (pilot monitoring), who did not believe there was a minimum drop height, did not alert the aircraft captain (pilot flying) to a drop height deviation prior to the collision.

Crew resource management practice

Safety issue number: AO-2023-008-SI-04

Safety issue description: The Coulson Aviation crew resource management practice of limiting the pilot monitoring (PM) announcements to deviations outside the target retardant drop parameter tolerances increased the risk of the aircraft entering an unrecoverable state before the PM would alert the pilot flying.

Safety recommendation description: The Australian Transport Safety Bureau recommends that Coulson Aviation takes safety action to address their crew resource management procedures for retardant drops to reduce the risk of the aircraft entering an unrecoverable state before the pilot monitoring alerts the pilot flying.

National Large Air Tanker standard operating procedures

Safety issue number: AO-2023-008-SI-05

Safety issue description: Australian states and territories that engage in Large Air Tanker (LAT) operations have developed their own separate standard operating procedures (SOPs) for LATs and aerial supervision assets. This can result in safety requirements being omitted or misunderstood by the different tasking agencies, such as a minimum drop height, resulting in inconsistencies in the development and application of LAT SOPs.

Safety action not associated with an identified safety issue

Additional safety action by Coulson Aviation

3 May 2023

Coulson Aviation increased the safety margins for large air tanker drops in Australia from 150 ft and 1.25 stall speed to 200 ft and 1.35 stall speed. This was promulgated on Operations Bulletin 2023-01 on 8 February 2023 and their B737 Fireliner normal checklist was amended accordingly.

October 2023

In October 2023, Coulson Aviation provided the ATSB with a copy of their master corrective action plan (CAP) document, which they had developed in response to the Bomber 139 accident. This comprised flight activities, ground activities, Operations Bulletins and Flight Operations Manual amendments under the following topics:

CAP 1: raise minimum drop speed and height

CAP 2: recalibration of airspeed during partial load drops

CAP 3: pre-drop planning and familiarization

CAP 4: pilot situational awareness

CAP 5: flight training exercises

CAP 6: exit flight path

CAP 7: communication and coordination with Birddog

CAP 8: adherence to standard operating procedures

CAP 9: crew resource management

CAP 10: human factors

CAP 11: continuous training and proficiency assessment.

Additional safety action by the Birddog operator

The Birddog operator reported that as part of their continuous improvement they removed their Lead Plane procedures from an annex in their Company Operations Manual and introduced a Lead Plane Standard Operating Procedures manual with expanded procedures in October 2023.

Additional safety action by the Western Australian Department of Fire and Emergency Services and Department of Biodiversity, Conservation and Attractions

In November 2023, the Department of Fire and Emergency Services, and the Department of Biodiversity, Conservation and Attractions released the Western Australian Aerial Fire Suppression Procedures 2023‍–‍2024. The draft version of this document was reviewed by their contracted operators and included a chapter for Large Air Tanker (LAT) Operating Procedures. The document included standard drop heights for all the aircraft types employed, procedures for task rejection, standdown and reinstatement of aviation resources after a safety incident, and a section on tactical flight profiles with the addition of the Lead and Chase-Position profiles.

Additional safety action by the Western Australian Department of Biodiversity, Conservation and Attractions

The Western Australian Department of Biodiversity, Conservation and Attractions advised that published drop heights for 2024‍–‍25 will be reviewed with the intent of prescribing a ‘minimum’ safe drop height, noting the actual drop height to safely achieve the objective is the pilot‑in‑command’s decision.

Glossary

Sources and submissions

Sources of information

The sources of information during the investigation included: 

• Australasian Fire and Emergency Service Authorities Council
• Birddog 123 pilot
• Bomber 139 captain and co-pilot
• Coulson Aviation
• General Electric Aerospace
• National Aerial Firefighting Centre
• New South Wales Rural Fire Service
• Queensland Fire and Emergency Services
• The Boeing Company
• United States Forest Service
• United States National Transportation Safety Board
• Victorian Department of Energy, Environment and Climate Action
• Western Australian Department of Fire and Emergency Services.

References

Australian Transport Safety Bureau (2022), Collision with terrain involving Lockheed EC130Q, N134CG, 50 km north-east of Cooma-Snowy Mountains Airport (near Peak View), New South Wales, on 23 January 2020 (AO-2020-007). Retrieved from https://www.atsb.gov.au

Federal Aviation Administration (2004), Crew Resource Management Training (AC 120-51E). Retrieved from https://www.faa.gov

Federal Aviation Administration (2017), Standard Operating Procedures and Pilot Monitoring Duties for Flight Deck Crewmembers (AC 120-71B). Retrieved from https://www.faa.gov

Federal Aviation Administration (2018), Flight Test Guide for Certification of Transport Category Airplanes (AC 25-7D). Retrieved from https://www.faa.gov

Federal Aviation Administration (2021), Airplane Flying Handbook Chapter 4: Energy Management: Mastering Altitude and Airspeed Control (FAA-H-8083-3C). Retrieved from https://www.faa.gov

Interagency Airtanker Board (2013), Procedures and Criteria for the Interagency Airtanker Board (IAB). Retrieved from https://www.nwcg.gov

Lovellette G (2000), Safe Drop Height for Fixed-Wing Airtankers. Retrieved from https://www.fs.usda.gov

National Aerial Firefighting Centre (2021), National aerial firefighting strategy 2021-26. Retrieved from https://www.nafc.org.au

National Transportation Safety Board (1994), Safety study: A review of flightcrew-involved, major accidents of U.S. air carriers, 1978 through 1990 (NTSB/SS-94/01). Retrieved from https://www.ntsb.gov

National Transportation Safety Board (2014), Low altitude operation/event involving Lockheed P2V-7, N14447, Modena, Utah, 3 June 2012 (WPR12GA243). Retrieved from https://www.ntsb.gov

National Wildfire Coordinating Group (2017), Interagency Aerial Supervision Guide (PMS 505). Retrieved from https://gacc.nifc.gov

New South Wales Rural Fire Service (2018), Operating guidelines for air tankers operations. RFS, Sydney.

Suter A (2005), Aerial Delivery Systems User Information: Wind speed and drop height. Retrieved from https://www.fs.usda.gov

Transportation Safety Board of Canada (2004), Collision with Terrain, Air Spray (1967) Ltd., Lockheed L-188 Electra C-GFQA, Cranbrook, British Columbia 2.5 nm south, 16 July 2003 (A03P0194). Retrieved from https://www.tsb.gc.ca 

Transportation Safety Board of Canada (2004), Collision with Terrain, Conair Group Inc., Convair 580 C–FKFY, Lytton, British Columbia, 9 nm SE, 31 July 2010 (A10P0244). Retrieved from https://www.tsb.gc.ca

United States Department of Agriculture Forest Service (2019), Standards for Airtanker Operations. Retrieved from https://www.fs.usda.gov

United States Department of Agriculture Forest Service (2019), Interagency aviation safety alert: Retardant safe drop height (IASA 19-02). Retrieved from https://www.fs.usda.gov

Western Australian Department of Fire and Emergency Services and Department of Biodiversity, Conservation and Attractions (n.d.), Large air tankers operational procedures 2021-22, v3.3.

Submissions

Under section 26 of the Transport Safety Investigation Act 2003, the ATSB may provide a draft report, on a confidential basis, to any person whom the ATSB considers appropriate. That section allows a person receiving a draft report to make submissions to the ATSB about the draft report. 

A draft of this report was provided to the following directly involved parties:

• Australasian Fire and Emergency Service Authorities Council
• Birddog 123 pilot
• Bomber 139 captain and co-pilot
• Civil Aviation Safety Authority
• Coulson Aviation
• National Aerial Firefighting Centre
• New South Wales Rural Fire Service
• United States National Transportation Safety Board
• Western Australian Department of Fire and Emergency Services
• Western Australian Department of Biodiversity, Conservation and Attractions.

Submissions were received from:

• Australasian Fire and Emergency Services Authorities Council
• Birddog 123 pilot
• National Aerial Firefighting Centre
• Western Australian Department of Biodiversity, Conservation and Attractions.

The submissions were reviewed and, where considered appropriate, the text of the report was amended accordingly.

Appendices

Appendix A – SIGMET thunderstorm activity

Figure 18: Lightning strikes (red) at 1600

Appendix B – Flight data recorder plot

Figure 19: FDR plot of last 5 minutes of the accident flight with the last 2 drops

Purpose of safety investigations The objective of a safety investigation is to enhance transport safety. This is done through:  identifying safety issues and facilitating safety action to address those issues providing information about occurrences and their associated safety factors to facilitate learning within the transport industry. It is not a function of the ATSB to apportion blame or provide a means for determining liability. At the same time, an investigation report must include factual material of sufficient weight to support the analysis and findings. At all times the ATSB endeavours to balance the use of material that could imply adverse comment with the need to properly explain what happened, and why, in a fair and unbiased manner. The ATSB does not investigate for the purpose of taking administrative, regulatory or criminal action. Terminology An explanation of terminology used in ATSB investigation reports is available here. This includes terms such as occurrence, contributing factor, other factor that increased risk, and safety issue. Publishing information Released in accordance with section 25 of the Transport Safety Investigation Act 2003 Published by: Australian Transport Safety Bureau © Commonwealth of Australia 2024   Ownership of intellectual property rights in this publication Unless otherwise noted, copyright (and any other intellectual property rights, if any) in this report publication is owned by the Commonwealth of Australia. Creative Commons licence With the exception of the Commonwealth Coat of Arms, ATSB logo, and photos and graphics in which a third party holds copyright, this report is licensed under a Creative Commons Attribution 4.0 International licence. The CC BY 4.0 licence enables you to distribute, remix, adapt, and build upon our material in any medium or format, so long as attribution is given to the Australian Transport Safety Bureau.  Copyright in material obtained from other agencies, private individuals or organisations, belongs to those agencies, individuals or organisations. Where you wish to use their material, you will need to contact them directly.

Executive summary

What happened

Late evening 29 May 2021, a Leonardo Helicopters AW139, registered VH-TJK, operated by Toll Helicopters, was tasked as single-pilot helicopter emergency medical service (HEMS) flight ‘Rescue 208’. Onboard the helicopter were 2 aircrew and 2 medical crew.

During the later stages of the approach into an unimproved helicopter landing site, the aircraft’s tail rotor struck a small tree. The contact was not identified by the crew. Having assessed the landing site as unsuitable, the crew discontinued the approach and diverted to a landing site about 1 km away. After shutting down, the flight crew conducted a walkaround inspection of the helicopter and identified evidence of foliage contact on the vertical fin.

What the ATSB found

The ATSB found that while manoeuvring to land within a confined area, unintended yaw and drift of the helicopter was not identified by the crew and stopped prior to the tail rotor striking a tree.

What has been done as a result

The operator has completed the following proactive safety actions:

• amended their operational guidance on minimum clearances from terrain when operating in confined areas
• issued guidance on site selection during primary missions
• a final internal safety report was provided to the ATSB and proactively shared among the emergency helicopter network
• installed the A800 Trakkabeam high‑intensity searchlights onto the fleet of aircraft.

Safety message

This incident highlights the need for flight crew to have a heightened situational awareness when operating into a confined area and unfamiliar location in the vicinity of obstacles, as there is very little to no margin to recover from any unexpected event(s).

Crew coordination plays a vital role in HEMS operations and ensures improved situational awareness, reduced errors, and the fostering of effective teamwork. Effective coordination and communication (including of concerns) minimises the risk of misinterpretation, ensures accurate transmission of information, and reduces the likelihood of mistakes.

The investigation

Decisions regarding the scope of an investigation are based on many factors, including the level of safety benefit likely to be obtained from an investigation and the associated resources required. For this occurrence, a limited-scope investigation was conducted in order to produce a short investigation report, and allow for greater industry awareness of findings that affect safety and potential learning opportunities.

The occurrence

On 29 May 2021, at about 2325 local time, a Leonardo Helicopters AW139, registered VH-TJK (callsign ‘Rescue 208’) and operated by Toll Helicopters, was tasked to conduct a helicopter emergency medical service (HEMS)[1] flight. The flight was planned under night visual flight rules (NVFR)[2] supplemented with the use of a night vision imaging system (NVIS).[3] The aircrew comprised a pilot and aircrew officer (ACO). The medical crew included a New South Wales health department (NSW Health) flight paramedic and an emergency specialist doctor.

The NSW Health aeromedical control tasked Rescue 208 to transit from Bankstown Airport to Shelly Beach (Figure 1) to assist with retrieval, stabilisation and transport of a patient to the Royal North Shore Hospital, NSW. After accepting the task, conducting pre-flight planning and briefing on the operation (including a planned winching retrieval), the pilot started the helicopter engines at about 2343.

Figure 1: Aircraft flight path

Source: Google Maps annotated by the ATSB

At about 2348, the aircrew and flight paramedic transitioned to using night vision goggles (NVG) and about a minute later, Rescue 208 departed Bankstown Airport, with the ACO in the rear cabin of the helicopter. While outbound at 1,500 ft, the paramedic was in contact the ground crew at the scene while the aircrew completed their checks. The aircrew had difficulties hearing the paramedic due to issues with the internal communication system.

The paramedic was informed by the scene commander on the ground at Shelly Beach that the plan had changed and was now for the crew to land in a playing field at Bear Cottage (Figure 2), instead of winching at the site. However, during that communication exchange, a second, closer landing option near the carpark at Shelly Beach was proposed, with the crew being advised that a HEMS helicopter had previously landed in the area (see the section titled Helicopter landing site).

Figure 2: Helicopter landing site options

Source: Google Earth annotated by the ATSB

Between 2352 and 2354, during the cruise, the doctor and flight paramedic discussed the equipment required for the rescue operation. A preparatory briefing was then conducted between the flight paramedic, the doctor and the ACO. At about 2355, the pilot acknowledged the briefing and subsequently briefed the crew on the weather, stating that there were light showers and the visibility was 5 km. Thirty seconds later, the pilot conducted the pre-landing checks, including lowering the landing gear, configuring and selecting the landing/search lighting system to ON (see the section titled Lighting and scan technique).

The aircraft arrived overhead Manly Beach at about 700 ft. The pilot then turned the helicopter south to parallel the beach and continued descent towards the proposed alternate landing area, while slowing the helicopter to an airspeed of 80 kt (Figure 3).

Figure 3: Aircraft flight path over Manly

Source: ATSB

At 2358, the pilot cleared the ACO to open the rear doors and continued descent while slowing to 60 kt. The ACO opened the right rear door and subsequently selected the winch power to ON, which also turned on the winch light. The pilot completed the pre-landing checks. The crew then received a radio call from the scene commander explaining the status of the patient, with a request that they land in the area near the Shelly Beach carpark if possible. The crew advised that they would assess that location and, if unable to land, they would reposition and land at Bear Cottage. About 30 seconds later, the helicopter was hovering at about 300 ft radio altitude (RA) adjacent to the proposed helicopter landing site (HLS).[4] From this position, the aircrew located the proposed landing area, primarily using the white search light rather than NVG.

At 0001, the pilot established the helicopter in a lower hover (between 100–130 ft RA) to assess the landing area. The ACO verbalised a description of the area, including the size, obstacles (advising that there were no power lines and that the trees were small), and available access. An approach plan was then discussed and the ACO then confirmed with the pilot and flight paramedic that they were happy to continue into the area. The pilot then handed over verbal control of the helicopter movement to the ACO, who then had responsibility for assisting the pilot by guiding them into the confined area HLS.[5]

The left rear cabin door was opened at about 0002 by the paramedic, who took up a position to ensure obstacle clearance to the left and rear of the helicopter. About 10 seconds later, the helicopter commenced an approach to the HLS on a heading of about 177°.

At 0003, as the helicopter descended, the ACO called ‘well clear of trees’ and guided the pilot through the movement of the tail through 20° right before stating ‘tail well clear’. The pilot then continued the descent, while undetected the helicopter yawed (see the section titled Helicopter movement) about 10° left to 145°. About 5 seconds later while at around 13 ft, the pilot asked the ACO about the slope of the site to which the ACO responded that it was ‘flat, or maybe a little bit nose to tail’. The flight paramedic responded to the comment of the slope stating it was ‘pretty heavy left’, this was not acknowledged by the other crew. During this conversation, the aircraft continued to gradually yaw further left.

Noticing the movement, the ACO told the pilot that they were drifting right and to move left. The ACO then advised that the tail was clear before again telling the pilot they were drifting to right. The ACO subsequently assessed that the helicopter was closer to the trees than they expected and called ‘climb climb climb’ and when the pilot did not respond, repeated the instruction. The pilot immediately responded to the second instruction and climbed the helicopter vertically to 100 ft (RA). Given the proximity of the trees, the ACO considered the possibility that the helicopter may have contacted them, however there had not been any indication of airframe contact (such as increased vibration).

Once out of the confined area, the pilot mentioned that they were happy to attempt another landing and the ACO agreed. The ACO did not mention the possibility the aircraft might have contacted the tree. However, the flight paramedic reiterated the increased slope on the left side of the aircraft and, after checking a second landing site in the car park, the crew diverted and landed at Bear Cottage.

After shutting down, the ACO and pilot conducted a walkaround inspection of the helicopter using hand-held torches. While inspecting the vertical fin, green material indicating contact with foliage was identified (Figure 4). The pilot then briefed the medical crew that the aircraft would be offline and notified the operator’s management of the incident.

Figure 4: Evidence of foliage contact on the vertical fin

Source: Toll Helicopters ACT/NSW

Context

Helicopter personnel

Pilot

The pilot had previously been employed by the operator for about 2 years from 2017–2019 and had recently returned to the role. They were cleared back to line flying on 29 April 2021. The pilot had a total of 4,594.8 flying hours, of which 1,219.7 were on the AW139. They had a total of 174.7 hours NVG flying time and since their return they had completed 16.1 NVG hours. An NVG/NVIS Capability Check Flight (CCF)[6] was completed 14 April 2021.

Aircrew officer

The ACO had 5,691 flying hours of which 2,001.1 were on the AW139. The ACO had 459 hours of NVG time at the time of the occurrence. They had completed an NVG/NVIS CCF on 19 May 2021.

Medical crew

The flight paramedic had previous experience in HEMS operations while working with another operator from mid-2015 to 2018. They started working with the operator in 2018 in road operations and in 2019 transitioned to flight paramedic. The flight paramedic was using NVG on the occurrence flight and had completed 3 hours of NVG flying within the last month.

The doctor had worked as an aeromedical doctor with another operator between August 2020 and February 2021 before joining the operator. At the time of the occurrence, they had about 10 months experience working in the HEMS operational environment. The majority of operations experienced during this time did not include night operations. The doctor was not using NVG on the occurrence flight.

Aircraft information

General

The Leonardo S.p.A AW139 is a medium-sized, multi-role helicopter, powered by two Pratt & Whitney Canada PT6C-67C turboshaft engines. The aircraft has a length of 16.66 m and a rotor diameter of 13.8 m. The AW139 aircraft is primarily used for emergency medical services (EMS) within Australia.

The tail rotor of the AW139 is a critical component of the aircraft’s flight control system, providing the necessary lateral force to counteract the torque generated by the main rotor system. Figure 5 outlines the aircraft dimensions and the area of foliage contact.

Figure 5: Area of impact with tree

Source: Leonardo Helicopters (Augusta Westland 139), annotated by the ATSB

Helicopter movement

Two important aspects of helicopter movement, especially in the context of hover operations are yaw and drift. Yaw refers to the rotation of the helicopter around its vertical axis. This is controlled by input to the tail rotor, which generates a lateral force to counteract the torque produced by engine/s driving the main rotor. The amount of yaw is adjusted by the pilot using the anti‑torque (tail rotor) pedals, which control the pitch (and therefore thrust) of the tail rotor blades. Yaw is important for controlling the heading of the aircraft and for maintaining balance in forward flight.

Drift refers to the (usually) unintended lateral movement of the aircraft as a result of wind/turbulence, flight control inputs and lateral tail rotor thrust (particularly in hovering flight). Drift can occur without the aircraft yawing and vice versa.

The Federal Aviation administration (FAA) Helicopter Flying Handbook (2019) Chapter 2 - Aerodynamics of Flight emphasises the importance of understanding and controlling both yaw and drift.

Active Vibration Control System

VH-TJK was fitted with an active vibration control system (AVCS). The system worked by sensing vibrations of the aircraft rotor system and using advanced algorithms to automatically adjust the pitch of the main rotor blades to reduce the amplitude of the vibration. The system could adjust the pitch of the blades up to 20 time per second, allowing it to quickly respond to changes in vibration levels.

External lighting

The aircraft was fitted with two pilot-steerable landing (search) lights mounted on the underside of the helicopter. Additionally, the aircraft was fitted with an ACO-steerable hoist light and each crew member had handheld torches available.

At low level, the operator required crews to make use of the external lights (white light), to assist the detection of wires and other obstacles and maintain terrain separation. This required the crew to conduct their scan with both the use of NVG and without.

Visual scan technique

Pilot

The pilot advised that during the approach their NVG goggles were in position, however they were also looking underneath and around them to use the white light to scan, and then doing a general scan through their NVG. To ensure they had adequate reference points, the pilot had one light directed to the front of the helicopter, with the second directed in the 3 o’clock[7] position.

The pilot also reported using lit houses in front and to their right, as reference points. During the descent, they used a dead tree in front of the helicopter and another identifiable tree to their right. They then transitioned to using ground references visible through the helicopter’s clear chin bubble. The pilot identified that the ground was sloping and decided they would assess the magnitude of the slope when they got to a low hover. The pilot also stated that they thought the inadvertent yaw occurred during a reduction in power associated with lowering the collective. They assessed this most likely happened when they brought their gaze down to the ground and were not using the identified trees as references. They did not believe that the unintended yaw was due to inadequate illumination of the confined area.

Aircrew officer

The ACO advised they used both NVG and the winch light to identify visual cues when descending into the HLS. They reported keeping the closest obstacle, being the contacted trees, to their right so they could observe and avoid them. They estimated the helicopter was 15‑20 ft away from the trees during the initial descent. The ACO moved from the right to left inside the helicopter and also lay on the floor to check underneath for clearance from obstacles. While monitoring the ground clearance, the ACO looked up and identified that the tail of the helicopter was significantly closer to the trees than expected, assessing that they may have misinterpreted yaw as drift when lying on the floor.

The ACO stated that they did not observe an excessive ground slope and were surprised by the paramedic’s assessment. They also advised that they were not relying on the paramedic to give advice on the helicopter clearance from objects. Finally, the ACO advised they did not consider visibility of the HLS was an issue, assessing the conditions as a relatively high visibility night.

Paramedic

The paramedic advised they were positioned on the left side of the helicopter during the approach to the confined area and, while they had NVG, they had better vision using the white light and a handheld torch. They advised that the role of the paramedic was to give negative clearances when asked, and to identify and call out potential hazards in the area. On the night, the paramedic recalled having a large clearance on the left side of the tail and they could see the ground dropping off behind the tail in the white light. They recalled that due to the references outside the aircraft they thought the aircraft had drifted.

The paramedic assessed that the underbelly lighting of the aircraft was not ideal for landing into the HLS and that with more white light the crew might have been able to identify more of the terrain.

Briefings

The crew arrived at the base at approximately 1930, for an overnight shift. They completed a shift hand-over, checked the local weather conditions and conducted a pre-flight inspection of the helicopter. The crew then went to bed at about 2200.

At 2325, the paramedic received a phone call for a priority job and woke the pilot. The pilot conducted a pre-flight operational risk assessment considering the:

• weather that included moderate to strong winds, turbulence and showers
• time of night
• moon illumination
• possibility of a winch.

The pilot determined the risk was within the appropriate levels to conduct the operation and woke the doctor and ACO.

The ACO completed an online reconnaissance of the area, to assess possible landing locations. The pilot completed the aircraft’s weight and balance and performance calculations and confirmed they allowed for an out of ground effect hover and winch, without the need for internal configuration changes.

During the transit to the scene a brief was completed, which included the crew duties, available equipment, possible landing locations, and weather.

The operator’s operations manual outlined that when a crew was operating to an unknown HLS, NVIS crews were required to conduct a thorough reconnaissance of the landing area with a white light prior to committing to an approach. This could be done either while conducting an orbit over the area or during a high hover over the site.

The crew completed 2 hovers, a high hover at approximately 300 ft and a low hover at approximately 100 ft (Figure 6).

Figure 6: Hover heights prior to entry into HLS

Source: ATSB

As a minimum, the reconnaissance and brief was required to assess the required power, wind, any obstacles and a plan for the approach and departure, typically based on the acronym PSWATP:

• P – Power available/required and therefore performance margin
• S – Size, shape, slope and surrounds
• W – Wind direction, strength and any turbulence
• A – Approach profile, departure and overshoot options
• T – Terrain, turbulence relevant to the area
• P – The plan, including crew duties, based on the reconnaissance

The pilot was to give a brief on the relevant information of the PSWATP briefing requirements and the ACO was expected to contribute to the reconnaissance.

Table 1 outlines the 6 sections of the PSWATP and at what point during the mission they were completed and by whom.

Table 1: Completion of Briefings

Section of PSWATP	Prior to departure	During flight	During reconnaissance hover
Power available/required and therefore performance margin	Pilot – completed the aircraft’s weight and balance and performance calculations. They also analysed the hover out of ground effect and confirmed it was acceptable for the mission.
Size, shape, slope and surrounds			ACO – discussed size, shape, and obstacles. Pilot and Paramedic – confirmed ACO observations.
Wind direction, strength and any turbulence	Pilot – conducted a pre-flight risk assessment based on the weather that included moderate to strong winds, turbulence and showers, time of night, moon illumination and a possible NVIS winch	Pilot – communicated information on wind and rain	Pilot – confirmed wind direction with crew
Approach profile, departure and overshoot options			Pilot and ACO – discussed initial approach into HLS
Terrain, turbulence relevant to the area	ACO – completed an online reconnaissance of the area, to assess possible landing locations		ACO – described the terrain to the crew
The plan, including crew duties, based on the reconnaissance		Paramedic & Doctor – Discussed crew duties and what equipment would be brought based on a winching	The crew – discussed the planned approach and the revised plan for each crew member after receiving an update on the patient’s condition

Helicopter landing site

The landing site was adjacent to Shelly Beach carpark and was an ‘unimproved’ or ‘non‑conforming’ HLS.[8] The open area was about 21.5 m wide and 41.5 m at its longest point (Figure 7).

The air crew and the flight paramedic recalled the area was a confined area and a ‘tight fit’, however after a low-level reconnaissance at 100 ft, they determined that although there were some obstacles (foliage and trees) in the area, it was a suitable place to land.

When manoeuvring into the landing site, the ACO did not communicate the proximity of the obstacles at the rear of the aircraft and as such both the pilot and the flight paramedic were unaware of the hazard they posed.

The HLS had a slope of 10° towards the west, which was undetected by the ACO (Figure 7). The pilot advised that slope was difficult to detect using both NVIS and white light. The operator’s operations manual indicated that the slope limitation for the helicopter was 10° in all directions. The pilot advised that they had intended to check the slope in a low hover and even if there had been no other concerns, they may not have landed in the HLS due to the slope.

The operator required a minimum safety distance of 10 ft laterally around the main and tail rotor disk, with aircraft fuselage to be maintained clear of obstacles however, 20 ft lateral separation was preferred. A minimum safety distance of 6 ft vertically below the rotor disk was recommended and landing with any obstacle under the rotor disk was to be avoided wherever practical. Under night operations, crews were asked to increase safety margins depending on the situation, aircraft configuration, operating crew and environmental conditions.

The operator stated that once the aircraft was in a low hover in a confined area, manoeuvring should be minimised as it was difficult to maintain adequate visibility and obstacle recognition in all directions, particularly rearwards.

Figure 7: HLS slope and obstacle location

Source: Toll Helicopters annotated by the ATSB

Figure 8 shows the approach and intended landing directions. The plan was that when the helicopter was established in a low hover over the landing site, the nose would be turned right so the tail would fit in the cut-out area.

The ATSB did not attend the site, however the operator’s report advised that:

At night, with an approach to the south, it would be difficult to land in the pad due to the slope at the south-eastern corner requiring the aircraft to be close to the obstacles on the non-active side of the aircraft (the side opposite to where the PIC [pilot in command] and ACO are operating). However, at the time of the incident, the crew believed that they could achieve the required minimum operating procedure of a 10-foot obstacle clearance. This assessment reduced the margins of any drift or yaw as experienced by the incident crew. Had the crew planned to achieve the preferred 20-foot obstacle clearance, it is likely that the contact with the tree may not have occurred.

The operator confirmed that the same confined area had been used for a task by day, in good conditions, on 26 January 2021, however it was approached from the reciprocal direction. The reciprocal direction allows a larger landing area with more obstacle clearance due to the reduced slope.

The pilot advised the operator that the decision to approach the HLS was influenced by the information that a company helicopter had landed at the site previously. However, they also advised the ATSB that they were not influenced by this information when assessing the HLS. The paramedic recalled that the information played a part in deciding to go to the HLS. The ACO, recalled there had been an aircraft in the HLS previously, however, they did not state if that affected their decision to whether to conduct the approach.

Figure 8: Approach and intended landing orientation

Source: Google Earth annotated by the ATSB

Weather

Prior to the flight, the pilot reviewed the weather using the Bureau of Meteorology (BOM) meteorological aerodrome report (METAR) and terminal aerodrome forecast (TAF) for Sydney Airport. At the time of the incident, the METAR showed the wind from the south-south‑west at 18 kt, 10 km visibility, showers of rain in the vicinity, few clouds[9] at 1,800 ft and broken cloud at 3,300 ft.

The astronomical conditions at the time of occurrence included moon illumination of about 87%. The moon angle was at 50.03°, which produced a shadow length of about 25 m when at 100 ft.  There was a possibility of reduced moon illumination due to the extent of the cloud and localised light rain in the area. The low angle of a rising or setting moon may reduce contrast detail and create strong shadowing effects which can mask hazards when operating under NVG. The crew reported ambient lighting generated from surrounding residential properties was present on approach to the HLS.

The operator’s operations manual states the minimum visibility for NVIS flight was 5,000 m and there should be no more than scattered cloud below 2,000 ft above ground level (AGL) within a 2 NM corridor either side of track. The weather at the time of this occurrence was above the minimum requirements for NVIS flight.

Flight data

The aircraft was fitted with a multi-purpose flight recorder (MPFR).[10] The MPFR data was found to contain the occurrence flight from Bankstown Airport to Bear Cottage, however the audio recording of the occurrence had been overwritten. Additionally, the operator provided the ATSB recorded rear cabin footage and the associated audio.

The MPFR data indicated that in the 30 seconds prior to the ACO instructing the pilot to climb, the aircraft experienced a 30° yaw to the left, a 2 ft lateral drift to the right followed by an 8 ft drift to the left, and a 3.5 ft longitudinal drift rearwards before a slight forward movement of 1 ft, as outlined in Figure 9.

Figure 9: Aircraft flight data

Source: ATSB

Training

Australian regulations required a minimum 6-month NVIS recency interval. However, the operator implemented a requirement for additional NVIS training, specifically ‘complex operations’ to confined areas, including winching in areas devoid of cultural lighting,[11] at least every 3 months. Further, 6-monthly recency flights were to be conducted with a training and checking pilot and/or ACO ‘to improve standardisation, enhance crews comfort levels and further develop the skills and knowledge required to operate on NVIS’.

The operator advised that the choice of NVIS training and checking locations was constrained by several factors, including proximity to the operator’s base (due required response time), the permission of various landowners, the presence of hazards, and to ensure sites were devoid of cultural lighting to maximise training effectiveness. As such, the operator also used simulators for recurrent pilot and ACO training and during clearance-to-line training. This included low level flying, winching, and manoeuvring into confined areas. Simulators were also used for ‘complex operations’ training for both pilots and ACOs.

Safety analysis

During the cruise, the crew were given 2 options for landing locations. The occurrence HLS was explained as a site where the operator had previously landed and had the advantage of being closer to the mission location. The advice that a company AW139 had previously landed at the site may have also influenced the crew’s decision to conduct the approach to that location.

The crew completed a reconnaissance in a hover, however they did not conduct an orbit of the site. Although not required by the operator’s procedures, an orbit would have allowed the crew to view the site from different angles and may have enabled them to identify the sloping ground, which was on the limits of the slope allowed for the helicopter type. It would also have provided an opportunity to fully assess the extent of the obstacles/available clearances. However, the crew advised that due to the prevailing weather conditions and avoiding the residential area close‑by they did not conduct an orbit.

Following the reconnaissance, the crew completed a briefing in the hover before approaching the HLS. They discussed the size and shape of the proposed HLS, they also discussed the approach and obstacles, ensuring all members of the crew were consulted. Although the non-standard HLS met the requirements of the operators 10 ft obstacle clearance, the crew were aware it was tight. As such, only small, controlled helicopter movements were allowable once established within the confined area.

During the approach, the communication between the ACO and the pilot was continual and clear. Additionally, once established inside the confines of the landing area, the ACO actively moved within the rear cabin to assess the lateral and vertical clearance to obstacles. Despite that, unintended movement of the helicopter – both yaw and drift (lateral and rearwards) was not identified by the crew and stopped prior to the tail rotor contacting foliage.

The crew did not identify the tail rotor strike until after the helicopter was shutdown at the alternate landing site. This may have been due to the relatively light foliage that was contacted, with the active vibration control system also possibly dampening any rotor vibrations from the collision.

The ACO suspected that the tail may have contacted the tree during the initial approach however, there was no physical confirmation in the aircraft airframe of this occurring. Despite this, if the ACO had advised the rest of the crew that a  strike may have occurred, it would have allowed discussion and informed decision making on subsequent actions.

Safety actions

Whether or not the ATSB identifies safety issues in the course of an investigation, relevant organisations may proactively initiate safety action in order to reduce their safety risk. The ATSB has been advised of the following proactive safety action in response to this occurrence.

Safety action by Toll Helicopters

The operator has completed the following proactive safety actions:

• The operator has amended their operational procedures stipulating aircrew maintain the following minimum clearances from terrain when operating in confined areas:
  • 20 ft from the main and tail rotors
  • by day only, 10 ft from main and tail rotors if operationally necessary
  • for obstacles below the main rotors, 6 ft vertically
  • 3 ft from aircraft fuselage including antennas and ancillary equipment.
• The operator issued guidance on site selection during primary missions outlining:
  • aircrew to prioritise lower risk landing and winching sites (i.e. large open areas, playing fields, parks etc.)
  • confined areas at or close to the scene should only be used if other options are not viable
  • recommended or directed sites from emergency services on scene are not mandatory and should be regarded as guidance information only
  • proximity to a scene should be regarded as secondary consideration.
• A final internal safety report was provided to the ATSB and proactively shared among the emergency helicopter network.
• Installed the A800 Trakkabeam high‑intensity searchlight onto the fleet of aircraft.

Sources and submissions

Sources of information

The sources of information during the investigation included:

• the crew of the occurrence flight
• Toll Helicopters (ACT/NSW)
• Bureau of Meteorology
• recorded data from the MPFR unit on the aircraft.
• cabin video and audio recordings

References

The Federal Aviation administration (FAA) 2019, Helicopter Flying Handbook Chapter 2: Aerodynamics of Flight

Submissions

Under section 26 of the Transport Safety Investigation Act 2003, the ATSB may provide a draft report, on a confidential basis, to any person whom the ATSB considers appropriate. That section allows a person receiving a draft report to make submissions to the ATSB about the draft report.

A draft of this report was provided to the following directly involved parties:

• Civil Aviation Safety Authority
• Toll Helicopters (ACT/NSW)
• Crew of VH-TJK
• Transportation Safety Board of Canada

No submissions were received.

Purpose of safety investigations The objective of a safety investigation is to enhance transport safety. This is done through: identifying safety issues and facilitating safety action to address those issues providing information about occurrences and their associated safety factors to facilitate learning within the transport industry. It is not a function of the ATSB to apportion blame or provide a means for determining liability. At the same time, an investigation report must include factual material of sufficient weight to support the analysis and findings. At all times the ATSB endeavours to balance the use of material that could imply adverse comment with the need to properly explain what happened, and why, in a fair and unbiased manner. The ATSB does not investigate for the purpose of taking administrative, regulatory or criminal action. Terminology An explanation of terminology used in ATSB investigation reports is available here. This includes terms such as occurrence, contributing factor, other factor that increased risk, and safety issue. Publishing information  Released in accordance with section 25 of the Transport Safety Investigation Act 2003 Published by: Australian Transport Safety Bureau © Commonwealth of Australia 2023 Ownership of intellectual property rights in this publication Unless otherwise noted, copyright (and any other intellectual property rights, if any) in this report publication is owned by the Commonwealth of Australia. Creative Commons licence With the exception of the Coat of Arms, ATSB logo, and photos and graphics in which a third party holds copyright, this publication is licensed under a Creative Commons Attribution 3.0 Australia licence. Creative Commons Attribution 3.0 Australia Licence is a standard form licence agreement that allows you to copy, distribute, transmit and adapt this publication provided that you attribute the work. The ATSB’s preference is that you attribute this publication (and any material sourced from it) using the following wording: Source: Australian Transport Safety Bureau Copyright in material obtained from other agencies, private individuals or organisations, belongs to those agencies, individuals or organisations. Where you wish to use their material, you will need to contact them directly.

 

Executive summary

What happened

On 11 March 2020, a Cessna 404 aircraft, registered VH-OZO, was being operated by Air Connect Australia to conduct a passenger charter flight from Cairns to Lockhart River, Queensland. On board were the pilot and 4 passengers, and the flight was being conducted under the instrument flight rules (IFR).

Consistent with the forecast, there were areas of cloud and rain that significantly reduced visibility at Lockhart River Airport. On descent, the pilot obtained the latest weather information from the airport’s automated weather information system (AWIS) and soon after commenced an area navigation (RNAV) global satellite system (GNSS) instrument approach to runway 30.

The pilot conducted the first approach consistent with the recommended (3°) constant descent profile, and the aircraft kept descending through the minimum descent altitude (MDA) of 730 ft and passed the missed approach point (MAPt). At about 400 ft, the pilot commenced a missed approach.

After conducting the missed approach, the pilot immediately commenced a second RNAV GNSS approach to runway 30. 

The occurrence

Overview

On 11 March 2020, a Cessna 404 aircraft, registered VH-OZO, was being operated by Air Connect Australia to conduct a passenger charter flight from Cairns to Lockhart River, Queensland. On board were the pilot and 4 passengers. The flight was being conducted under the instrument flight rules (IFR).[1]

Consistent with the forecast, there were areas of cloud and rain that significantly reduced visibility at Lockhart River Airport. After arriving at Lockhart River, the pilot commenced an area navigation (RNAV) global satellite system (GNSS) instrument approach to runway 30. The aircraft descended to an altitude of about 400 ft before the pilot conducted a missed approach. The pilot immediately commenced a second RNAV GNSS approach to runway 30, and during the descent the aircraft collided with terrain.

Planned flight

The passengers were contracted to carry out work at the local school at Lockhart River. The client arranged with the operator for the aircraft to depart Cairns at 0730 Eastern Standard Time[2] on 11 March 2020, wait on the ground at Lockhart River for about 5 hours, then depart at 1430 with the same passengers for the return flight. The operator assigned the pilot who regularly conducted the operator’s charter flights.

For the arrival at Lockhart River, the forecast weather was for light winds and rain and low cloud with periods of visibility reducing to 3 km in rain. There was also a 30% probability of thunderstorms. The pilot had submitted a flight notification, which specified IFR and capability for an RNAV instrument approach. The aircraft had sufficient fuel to conduct an approach at Lockhart River and return to Cairns and hold at Cairns for 1 hour if required.

Flight to Lockhart River

The aircraft departed Cairns at 0719 and tracked for the first planned waypoint on climb to its cruise level of 10,000 ft above mean sea level. Based on the forecast winds, the estimated time of arrival at Lockhart River was 0852. As the flight progressed, the pilot amended the estimated time of arrival to 0904. The aircraft’s track during the flight is shown in Figure 1.

Figure 1: VH-OZO recorded flight path from Cairns to Lockhart River, Queensland

Source: Google Earth overlaid with OzRunways data, annotated by the ATSB

At 0836, the pilot advised air traffic control that the aircraft was approaching top of descent, then tracking direct for the runway 30 RNAV GNSS instrument approach at Lockhart River, and the pilot requested traffic information. The controller responded there was no reported IFR traffic. At 0840, the pilot reported leaving 10,000 ft on descent and, at 0842, the controller advised the pilot of the very high frequency (VHF) and high frequency (HF) radio frequencies applicable to the rest of the flight. That was the controller’s last contact with the pilot and no further routine interactions with the controller were expected.[3]

During descent, the pilot transmitted on the common traffic advisory frequency (CTAF) for Lockhart River to activate the runway lighting for a period of 30 minutes. At 0852, the aerodrome frequency response unit (AFRU) broadcast ‘Lockhart River CTAF, runway lights are on’.

At about this time, the pilot very likely obtained weather information from the automated weather information service (AWIS) via VHF radio. Notes taken by the pilot indicated the wind was calm, visibility was at least 10 km, there was broken cloud[4] at 1,800 ft, broken cloud at 3,500 ft and overcast cloud at 5,300 ft, and the QNH was 1,008 hPa (see Automated weather information service).

At about 0857, the aircraft levelled off at 5,500 ft. At this time the aircraft was heading to waypoint LHREB, one of 3 initial approach fixes (IAFs) for the RNAV GNSS instrument approach to runway 30 (Figure 2). The weather information indicated that the conditions were better than the landing minima (which were a cloud ceiling of 730 ft and visibility 4,200 m).[5]

Figure 2: Lockhart River RNAV GNSS runway 30 approach chart

Source: Airservices Australia, annotated by the ATSB

First approach at Lockhart River

Figure 3 depicts the aircraft’s recorded flight track for the first approach and missed approach at Lockhart River. The altitudes described throughout the report are truncated to the nearest 100 ft. [6]

At 0859:38, the aircraft passed abeam LHREB, commenced descent from 5,400 ft and turned left to track to the runway in accordance with the RNAV GNSS procedure. At 0901:25, the pilot made a radio broadcast on the CTAF, advising the aircraft was 10 NM[7] to the south-east of the aerodrome, inbound to runway 30 and on descent passing 4,000 ft. Shortly afterwards, the aircraft passed the intermediate fix (IF) LHREI at 4,000 ft.  

Figure 3: Flight track of VH-OZO during first RNAV GNSS approach at Lockhart River Airport with times, feature labels, and approach parameters superimposed

Source: Google Earth overlaid with OzRunways data, annotated by the ATSB

At about 0903, one of the passengers sent a text message that contained an image of conditions outside the aircraft (Figure 4). At that time, the aircraft was over halfway between LHREI and the final approach fix (FAF) LHREF, at an altitude between 3,100 and 2,500 ft. The photograph had been taken through a passenger window on the right side of the aircraft cabin and, although there was significant cloud in the vicinity, some terrain/coastline was visible near the intersection of the wing’s leading edge and the engine cowl.

Figure 4: Image recorded by a passenger looking forward over the right engine and sent via text message at 0903

Source: Supplied, lower section of image cropped by the ATSB

The aircraft continued the descent on the approach track and passed LHREF on descent through 2,300 ft. At 0904:27, the pilot broadcast on the CTAF that the aircraft was at 5 NM and on final (approach) to runway 30.

The minimum descent altitude (MDA) was 730 ft.[8] The aircraft arrived at the missed approach point (MAPt) LHREM at 0906:17 on descent through about 600 ft. The descent continued to about 400 ft then, about 1,000 m from the runway, the aircraft started to climb. The aircraft was passing 600 ft as it crossed the runway threshold in the early stages of a missed approach. In accordance with the missed approach procedure, the aircraft was turned slightly right to track towards the turning fly-over waypoint LHREH.

At 0907:22, the pilot broadcast on the CTAF that they were conducting a missed approach for runway 30, tracking to the west then turning back to the east and climbing towards 3,500 ft (as specified for the missed approach procedure). After passing LHREH at 0907:43 on climb through 1,200 ft, the aircraft turned right to track east as prescribed by the approach chart.

At 0909, the pilot contacted Flightwatch[9] on HF and advised:

[VH-OZO] conducting a missed approach runway three zero [30] at Lockhart River, and we’ll be joining the approach on runway three zero [30], ops normal time two three three zero [2330]

The middle part of this radio transmission, as recorded by Airservices Australia, was unclear, which is not uncommon for HF radio communication.

Second approach at Lockhart River

The aircraft continued the climb to 3,800 ft before descending to level out at 3,500 ft, heading towards the closest IAF, LHREA. At 0912:51, the AFRU recorded runway lights on, consistent with the pilot reactivating the runway lights for another 30-minute period. About 2.0 NM prior to reaching LHREA, at 0913:53, the aircraft commenced a right turn towards the IF, and initially was right of the inbound track to LHREI (Figure 5).

Figure 5: Flight track of VH-OZO during second RNAV GNSS approach at Lockhart River Airport with times, feature labels, and approach parameters superimposed

Source: Google Earth overlaid with OzRunways data, annotated by the ATSB

At about 0914, while the aircraft was tracking towards LHREI on a south-westerly heading at 3,500 ft, an image was uploaded to social media by one of the passengers (Figure 6). The camera was oriented to the west, which was in the general direction of Lockhart River. An associated message indicated very low visibility and that the pilot was circling while waiting for a break in the weather. Another passenger sent a text message at 0914 stating that the first attempt at landing was unsuccessful, the runway was not visible and there was heavy rain. 

Figure 6: Image recorded by a passenger looking over the right wing and uploaded to social media at 0914

Source: Supplied

At about 0914:43, when about 2.7 NM from LHREI, the aircraft started descending from 3,500 ft. At this time, the aircraft was tracking towards the initial approach track between LHREA and LHREI (Figure 5).        

At 0915:50, the pilot made another inbound broadcast on the CTAF advising:

ten miles [10 NM] to the south-east on descent passing three thousand eight hundred [3,800 ft] correction two thousand eight hundred [2,800 ft], straight-in approach runway three zero [30], circuit area two one [time 0921].

The recorded height was about 2,800 ft at this time.

The aircraft continued descending and passed over LHREI and turned right to fly parallel to the intermediate approach track at about 2,800 ft. According to the recommended flight profile for a 3° approach (Figure 2), the aircraft should have descended from 3,500 ft at about 4.2 NM from the FAF (9.2 NM from the MAPt). At this point, the aircraft was at about 2,500 ft.

The descent continued at a similar gradient to the first approach although at about 1,000 ft lower than that approach. About halfway between LHREI and LHREF, the aircraft descended below the intermediate segment minimum safe altitude of 1,800 ft and continued to descend on the same descent profile.

When the aircraft passed LHREF at 0918:23, it was on descent through about 1,100 ft (below the 3° approach profile height of 2,160 ft). The aircraft was right of the final approach track and, shortly after passing LHREF, the aircraft started turning back towards the final approach track.

From LHREF to LHREM, the altitude limitation was the MDA of 730 ft and, at 09:18:55, the aircraft was approaching 700 ft. The aircraft then descended below the MDA and, soon after, the aircraft’s flight path crossed the final approach track (on a ground track about 20° left of the final approach track).

Collision with terrain

The aircraft’s track and descent continued until it impacted a sand dune on the coastline at about 0919:41. The pilot and 4 passengers were fatally injured, and the aircraft was destroyed. Due to the impact forces, the accident was not survivable.

Context

Pilot information

Qualifications and experience

The pilot held a commercial pilot licence (aeroplane) with an instrument rating and multi-engine aeroplane endorsement. They had recorded a total of 3,220 hours before the accident flight.

The pilot obtained the multi-engine endorsement in June 2014 (on a Cessna 310 aircraft), and had accrued 1,177 hours on multi-engine aircraft, including 399 hours on the Cessna 404 aircraft type. In June 2014, the pilot also obtained their initial (multi-engine) instrument rating, and their total instrument time was recorded as 148 hours.

The pilot operated as a commercial pilot in remote locations for about 5 years. Up until March 2016, they operated single-engine aircraft. In March 2016 they received training and were found competent on the Piper PA31 aeroplane type. Between March 2016 and February 2018, the pilot conducted flights for a charter company that operated Cessna 310 and Piper PA-31 aircraft, usually under visual flight rules (VFR[10]) with occasional instrument flights. They were approved by the Civil Aviation Safety Authority (CASA) as chief pilot of this operator in December 2016.

From October 2018, the pilot was employed by Air Connect Australia on a casual basis. Prior to joining the operator, the pilot’s recorded total flying time was 2,800 hours. The pilot completed induction then conducted a flight for type-specific training in a Cessna 421 from an independent CASA-approved flight examiner that the operator frequently used for proficiency checks. This flight was about 1.6 hours and the examiner recalled that the pilot managed the transition to the 400-series Cessna without any problems. Other than the pressurisation system in the Cessna 421, the examiner considered it was operationally equivalent to the unpressurised Cessna 404.[11]

Following this type-specific training, the chief pilot of Air Connect Australia supervised the pilot on 4 flight sectors in VH-OZO and conducted an operator proficiency check (OPC) over 2 further sectors on 29 October 2018. The chief pilot noted that the pilot’s planning was satisfactory, and operation of the aircraft was above standard.

From November 2018 to the accident flight, the pilot was based in Cairns and conducted most of the operator’s charter flights, normally in VH-OZO. In December 2019, the chief pilot organised for the pilot to undertake some supervised flying at night with an instructor in a Piper PA-44 Seminole in order for the pilot to maintain night recency. The operator rarely conducted night flights.

In the 90 days prior to the accident (11 March 2020), the pilot had conducted 59 flights (60 flight hours), all in VH-OZO. This included 4.5 hours recorded instrument flying time. In the last 30 days, the pilot had conducted 12 flights (13.5 flight hours), including 1.0 hour recorded instrument flying time. The most recent flights were on 18 February 2020.

Since joining the operator in late 2018, the pilot had logged 69 RNAV GNSS approaches to various aerodromes. These included 21 RNAV GNSS approaches in the previous 6 months, 12 in the previous 90 days, and 2 in the previous 30 days (with the last on 18 February 2020). Only one of the approaches in the previous 6 months was conducted to some extent in instrument meteorological conditions (IMC),[12] and this approach resulted in a missed approach (see Prior missed approach during an RNAV GNSS approach (22 January 2020).

Lockhart River experience

Since the start of 2019, the pilot had flown into Lockhart River 8 times, 6 of which were logged as RNAV GNSS approaches, with the most recent being on 14 October 2019.

The recorded data for previous RNAV GNSS approaches into Lockhart River were reviewed by the ATSB, with the details provided in Table 1. A review of recorded weather information indicated that none of these previous approaches at Lockhart River were conducted in IMC. For the 17 January 2019 approach, there may have been reduced visibility in the early part of the approach.[13]

Table 1: Pilot’s prior flights to Lockhart River 2019–2020

Proficiency checks and flight reviews

The pilot conducted initial instrument flight training in 2014. During training it was noted that the pilot needed to scan faster, improve situation awareness and improve radio phraseology. On one simulator training exercise it was noted the pilot was too high on the RNAV GNSS MDA and minimum altitudes.

The pilot did not pass their first attempt at attaining an instrument flight rating (in a Cessna 310) on 2 June 2014 for not maintaining altitude within +100 ft and -0 ft at the MDA, not using accepted navigation procedures, not being within half-scale deflection of glideslope, and not demonstrating sound command judgement. On the next day, 3 June 2014, the pilot passed on their second attempt.

Under Civil Aviation Safety Regulation (CASR) 61.650, pilots need to have completed an instrument proficiency check (IPC) in the previous 12 months to fly a multi-engine aircraft under the instrument flight rules (IFR). The IPC must also be done in a multi-engine aircraft of the same category.

The pilot undertook 6 IPCs with 3 different independent CASA-approved flight examiners between 2016 and 2019. These are detailed in Table 2.

Table 2: Pilot instrument proficiency checks 2016–2019

The pilot’s last 3 IPCs were conducted on 4 August 2018, 5 August 2018 and 7 August 2019, all with the same CASA-approved flight examiner (who also conducted the IPC in March 2016).

On 4 August 2018, the pilot did not pass the IPC due to misreading the altimeter. The flight examiner recalled that they were on descent to the minima on a circling approach and, when the aircraft was at 1,000 ft above the MDA, the pilot asked whether they were visual. It then became apparent that the pilot had misread the altimeter by 1,000 ft (that is, they thought the aircraft was 1,000 ft lower than it was). The pilot successfully passed the check the following day.

The pilot’s most recent IPC was conducted on 7 August 2019 and was valid until 7 August 2020. The flight examiner who conducted this check was selected by the pilot; it was not the flight examiner regularly used by the operator (and who was familiar with the Air Connect Australia operations manual and could also conduct OPCs).

For each of the IPCs in 2018 and 2019, the pilot conducted a training flight with an instructor prior to the test flight, using the same Cessna 310 aircraft as in the test flights. The instructor commented that the pilot flew significantly better in 2019. Between the 2 checks in 2018 and 2019, the Cessna 310 aircraft was fitted with a GPS/navigational system and electronic flight instruments comprising an attitude display indicator (ADI) and a horizontal situation indicator (HSI). The ADI displayed aircraft attitude information, together with a secondary display of air data information (airspeed, altitude and vertical speed). The ADI and HSI each provided course and advisory vertical guidance during RNAV GNSS approaches.[14]

As already noted, the pilot undertook an operator proficiency check (OPC) on 29 October 2018 before commencing line operations with Air Connect Australia. This was the last OPC carried out on the pilot (see also Operator proficiency checks).

Between February and June 2018, prior to joining the operator, the pilot undertook training with an airline in a multi-crew environment and high-performing (turboprop) aircraft. Although the pilot obtained high marks in theory and written tests, they did not obtain satisfactory ratings during 3 proficiency assessments in a simulator (with remedial training given after each of the first 2 assessments). A common identified problem was instrument approaches, with issues identified including inefficient instrument scan, fixation (on some parameters), speed control, workload management, insufficient situational awareness and ineffective profile management. The ATSB notes that the training and checking environment at the airline was different to the pilot’s previous experience and the operational environment at Air Connect Australia.

Observations of the pilot’s approach to safety

The chief pilot (and managing director) of Air Connect Australia described the pilot as being a good pilot who would not have gone into an approach if they thought the weather was going to be poor, and that there was never any pressure to fly in poor weather. The pilot was trusted to make safety decisions, which would be supported by the chief pilot. This was consistent with the recollection of a previous pilot who flew with the operator, who reported that there was never any operational pressure (from the operator’s key personnel).

Another pilot stated that the pilot of the accident flight had ‘good stick and rudder skills’ and that everything was done ‘by the book’. It was also reported that the pilot had not expressed any concerns about the operator, including its approach to safety.

Former colleagues from when the pilot was chief pilot at a previous operator described the pilot as smart, diligent, and methodical with good knowledge of the rules and regulations. They reported that the pilot did not take shortcuts or unnecessary risks and had good hand-flying skills.

With reference to instrument approaches, one pilot advised that they had many conversations with the pilot of the accident flight regarding aircraft accident reports and safety, and the pilot of the accident flight had stated that they would conduct instrument approaches using the published constant-descent profile and would not intentionally deviate below published segment minimum safe altitudes in order to get visual early in an approach.

During January 2020, the pilot spent a week conducting a series of charter flights between Aurukun and Weipa, Queensland, in VH-OZO with the same group of passengers (see also Prior missed approach during an RNAV GNSS approach (22 January 2020)). Their perception was that the pilot was a good, competent pilot who was diligent, professional, and responsible and that they never felt unsafe. They also advised that they observed the pilot reviewing forecast and actual weather conditions regularly and that the pilot would delay flights due to weather conditions if necessary. Some of the passengers reported observing the pilot make weather-based decisions and did not display any indications of external pressure to fly in poor weather. One of the passengers reported that the pilot had said they would only ever make 2 attempts at landing and, after that, would return to the departure aerodrome or divert to an alternate.

Recent history

The pilot had recently returned from annual leave, with their last flights before leave conducted on 18 February 2020. The 3 days prior to the accident flight were reported to be uneventful. It was described that the pilot ate and exercised regularly and had been sleeping well with a standard time to sleep about 2230 and wake time about 0700–0730. The night before the accident flight, the pilot went to bed at about 2230 and woke at about 0530. There was nothing of note from the pilot’s recent history to suggest they were experiencing a level of fatigue known to affect performance.

The pilot was notified about the 11 March 2020 flight a few days in advance. It was reported that the pilot had been in a good mood in the days prior to the flight and was looking forward to flying again. On the day before the flight, the pilot went to Cairns Airport and started the aircraft’s engines to re-familiarise themselves and ensure everything was ready for the next day’s flight.

Medical information

The pilot’s Class 1 Aviation Medical Certificate was renewed on 14 February 2020 and was valid until 14 February 2021. There were no indications of any significant medical problems in the pilot’s aviation medical records. There was no evidence to suggest the pilot had any current or ongoing medical issues at the time of the accident.

A post-mortem examination was conducted by a forensic pathologist on behalf of the Queensland Coroner. The pathologist found that there was ‘No obvious natural disease to contribute to the cause of death within limits of examination …’. Forensic toxicology screening returned negative results (that is, no alcohol or substances were detected). The sample was unsuitable for analysis for carbon monoxide.

Aircraft information

General information

The Cessna 404 Titan is an unpressurised, low-wing, twin piston-engine aircraft with retractable landing gear. The maximum take-off weight (MTOW) is 3,810 kg, and the aircraft was certified to be flown by a single pilot.

VH-OZO was manufactured by the Cessna Aircraft Company in 1980. It was reported that the aircraft was first operated in Australia before being transferred to Papua New Guinea and registered as P2-ALG. In December 2009, a CASA Certificate of Airworthiness was issued, and the aircraft was registered as VH-OZO. At that time, the aircraft’s total time in service was 28,193 hours.

Seating

The type certificate data sheet for the Cessna 404 stated the aircraft type had 11 total seats (2 pilot seats and 9 passenger seats). In 1980, VH-OZO was configured with a modified seating configuration with 13 seats (2 pilot seats and 11 passenger seats).[15]

During an audit of Air Connect Australia in June 2017, CASA identified that the Airplane Flight Manual stated a maximum of 9 passenger seats aft of the pilot seats but there was 11 on the aircraft. In its initial audit response, the operator stated that the seating change was approved many years ago and it was attempting to find supporting documentation. In a subsequent response, the operator stated that it had previously operated and would continue to operate with a maximum of 9 passengers. It noted that the extra seating would remain in the aircraft as it formed part of the aircraft’s current weight and balance data.

During the investigation, the chief pilot confirmed that the operator never operated the aircraft with more than 9 passengers and normally operated with significantly less than 9 passengers.

Photos taken during the accident flight indicated that no passengers were seated in the front right seat next to the pilot.

Aircraft instruments and systems

On arrival into Australia, the aircraft was fitted with aerial geophysical survey equipment and was operated in that configuration until the equipment was removed in March 2012. Concurrently, the aircraft were modified in accordance with an engineering order to install new types of avionics and integrate those with existing units. The post-modification avionics, including existing equipment, consisted of:

• Garmin GMA 340 audio panel
• dual Garmin GNS 430W GPS/Nav/Com units
• dual Garmin GI-106A GPS/VOR/LOC course deviation indicators (CDIs)
• Garmin GTX327 transponder
• Bendix/King KR87 automatic direction finder (ADF) and Bendix/King KI-227 ADF indicator
• Collins HF radio
• Cessna 400B Navomatic autopilot
• Bendix weather radar (monochrome display).

These units were still installed at the time of the accident except for the transponder, which had been replaced by an automatic dependent surveillance-broadcast (ADS-B) compliant unit in April 2017.

VH-OZO was not fitted with a terrain avoidance and warning system (TAWS), nor was it required to be under legislation in place in Australia at the time of the accident. Further information is provided in Terrain avoidance and warning systems.

An assigned altitude indicator was fitted to the aircraft, which was designed to be used as a reminder of the designated altitude. Altitudes could be manually set by means of individual thumb wheels and no aural or visual alerts were provided when reaching or leaving the set altitude. The aircraft did not have an altitude alerting system, nor was it required for the type of aircraft and operation.[16]

The 400B autopilot was one of the standard equipment options for the Cessna 404 type. It could provide pitch and roll control with heading and altitude hold (on command). A navigation function provided the autopilot with inputs from an associated CDI (the GI-106A), which in this case received data from the number‑1 GNS 430W.

For an RNAV GNSS approach, a pilot could ‘couple’ the autopilot for lateral navigation and manage vertical navigation by adjusting the autopilot pitch wheel to achieve the intended rate of descent. For a level segment, the pilot could select altitude hold on reaching the intended altitude. Several pilots who had flown VH-OZO advised that they routinely hand flew instrument approaches due to autopilot constraints.

The aircraft was fitted with the instrumentation required for operations under the IFR. These flight instruments were conventional analogue indicators and reflected the original specifications for the aircraft. The second artificial horizon/attitude indicator and altimeter were located on the right side of the co-pilot panel (far side of the instrument panel relative to the pilot) (Figure 7).

Figure 7: VH-OZO instrument panel

Source: Supplied, annotated by the ATSB

A closer view of the instrument panel is depicted in Figure 8. It had the standard 6 flight instruments directly in front of the pilot’s seat on the left. These include the attitude indicator, which depicts the aircraft’s basic roll and pitch attitude, and the primary performance instruments – altimeter, airspeed indicator and vertical speed indicator (VSI). Below those were 2 (GI-106A CDI) instruments[17] that provided course deviation indication provided either by the GNS 430’s digitally-tuned VOR/localiser and glideslope receiver or GPS input to conduct an RNAV GNSS approach. One CDI instrument was coupled to the aircraft’s number-1 GNS 430W GPS unit and the other to the number-2 GPS unit.

The basis of cockpit design is to have the primary instruments within a small arc of the pilot’s forward line of sight. Navigation systems such as the GPS units may be located next to the primary instruments, as was the case in VH-OZO. While conducting an RNAV GNSS approach, it is imperative that the pilot includes the GPS units in the scan.

Figure 8: Instrument panel of VH-OZO

Source: Supplied, annotated by the ATSB

Altimeters

VH-OZO was equipped with two 3-pointer altimeters (Figure 9), including one directly in front of the pilot. They had a 100-ft pointer (long and narrow), 1,000-ft pointer (short and wide) and 10,000-ft pointer (long and thin with a triangle at the end). The diagonal hashing indicated when below 10,000 ft and was gradually covered above that height.

These types of 3-pointer altimeters are very common in general aviation aircraft, including small aeroplanes used for passenger transport activities. Research has shown that such altimeters can be associated with misreading errors, including misreading the altitude by 1,000 ft, although accidents known to be associated with such errors seem relatively rare. Accordingly, such altimeters (and some other altimeter designs) are no longer allowed to be used on air transport certificated aircraft. Further information about requirements and guidance regarding altimeters is provided in Appendix A – Research and guidance regarding design of altimeters.

The aircraft was not fitted with a radio altimeter, nor was it required for the type of aircraft and operation.

Figure 9: Example of the 3-pointer type of altimeter fitted in VH-OZO

This altimeter shows an altitude of 1,210 ft (10,000 ft pointer indicating 0, 1,000 ft pointer indication 1,000 ft and 100 ft pointer indicating 210 ft.

Source: avioelectronica.com

GNS 430W overview

The Garmin GNS 430W is a panel-mounted unit that provides GPS navigation, instrument landing system or VHF omnidirectional radio range navigation, and VHF radio communication. It was approved for IFR operations, including RNAV GNSS approaches, and was used in conjunction with a CDI.

Although the ‘W’ designated wide area augmentation system capabilities[18] that facilitated GPS approaches with vertical guidance, Australia did not have the associated satellite-based augmentation system to enable this functionality at the time of the accident. As such, the GNS 430W was approved to provide distance and track information only for RNAV GNSS non-precision approaches.

Information was displayed to the pilot on an 8.4 cm by 4.6 cm (240 by 128 pixel) high-contrast colour LCD. A pilot could select the pages and menus to display relevant information during various flight stages. Those included the default navigation page and additional pages including:

• a 2-dimensional representation of terrain relative to the aircraft position
• information for vertical navigation of the aircraft
• a moving map display
• information about the status of the GPS satellite constellation
• information relevant for the navigation and communication functions of the unit.

When used for an RNAV GNSS approach, the navigation page would display a graphic CDI together with the active leg of the approach and 6 user-selectable data fields.[19] After passing the waypoint it was tracking to, the unit would automatically sequence to the next waypoint.

When approaching a waypoint such as an initial approach fix (IAF), if a turn was required, the unit would display the recommended flight path (turn) to intercept the next track segment. The unit would also display a flashing message about 10 seconds prior to the start of the recommended turn, alerting the pilot that a turn was required and the track to intercept.

To use the unit for RNAV GNSS approaches, it was a requirement that the NavData card[20] was valid and the approach procedure was loaded from the database. The operator subscribed to the Jeppesen NavData service that provided monthly updates. It was reported that the pilot updated the NavData card using a laptop computer in the 24 hours prior to the flight. There were no changes in the update that would have been relevant to the accident flight.

The terrain, obstacle and airport terrain database was loaded on a terrain data card. The operator did not subscribe to an update service for terrain/obstacle data. Obstacle data was updated on a 56-day cycle and updates to the terrain database were released on an ‘as-needed’ basis. There was no requirement to have current obstacle or terrain databases to use the GNS 430W for flight under the IFR and/or during an RNAV GNSS approach. A June 2018 photograph of VH‑OZO’s GNS 430W receivers indicated the obstacle database installed at that time was dated October 2011.[21]

Fault detection and exclusion was incorporated into the GNS 430W software to detect satellite failure and exclude failed satellites from usage.

In addition to their experience with VH-OZO, the pilot of the accident flight had experience using GNS 430 units during their time flying Cessna 310 and PA-31 aircraft with a previous operator, which included units with a terrain awareness function.

Garmin TERRAIN function

Garmin TERRAIN was a non-certified[22] terrain awareness system, provided as a standard feature of 400W-series units, to increase pilot situation awareness and help reduce the risk of controlled flight into terrain (CFIT). The functions required a valid 3D GPS position and a valid terrain and obstacle database. Terrain and obstacle information was advisory only and was not equivalent to warnings provided by TAWS. The Garmin 400W Series Pilot’s Guide & Reference manual stated:

CAUTION: The Terrain feature is for supplemental awareness only. The pilot/crew is responsible for all terrain and obstacle avoidance using information not provided by the 400W-series Terrain feature.

When the GNS 430’s terrain page was selected, it presented a 2-dimensional colour-coded display of terrain tiles and obstacles from its database, relative to the aircraft’s current position/altitude. Red (warning) indicated terrain/obstacles above and up to 100 ft below the aircraft’s current altitude, yellow (caution) between 100 ft and 1,000 ft below the current altitude, and black more than 1,000 ft below the current altitude. The terrain page would not normally be selected when conducting an RNAV GNSS approach.

Terrain advisory and alert messages were provided when flight conditions met specific parameters. The advisories/alerts comprised a visual annunciation in the lower left corner of the unit’s LCD display, accompanied by a larger pop-up advisory/alert on the current display page (except the page displaying terrain). To clear the pop-up advisory/alert, the pilot would either acknowledge the message to return to the selected page or acknowledge the advisory/alert and display the terrain page. The system did not provide auditory alerts.

A pilot could use an ’inhibit mode’ to deactivate the terrain advisory/alert message system and pop-up messages would not be generated. The terrain page was still selectable and would display colour-coded terrain and obstacle information relative to the aircraft’s position. Once inhibited, the terrain annunciator field displayed a ‘TER INHIB’ annunciation and the terrain alert system remained deactivated until reselected. The GNS 400W-Series manual stated that the terrain inhibit mode could be used when the advisories/alerts were deemed unnecessary by the pilot. The manual also stated:

Flying VFR into an area where unique terrain exists could cause the system to annunciate a nuisance alert. Pilots should use discretion when inhibiting the TERRAIN system and always remember to enable the system when appropriate.

According to the GNS 400W-Series manual, the terrain system issued a premature descent alert (PDA) when the aircraft was significantly below the normal approach path to a runway. The manual indicated that this alert would activate depending on the aircraft’s height above terrain and distance from the runway threshold (for example, it would be triggered if the aircraft was about 400 ft above terrain when 10 NM from the runway threshold, 350 ft at 5 NM, 320 ft at 4 NM, and 280 ft at 3 NM). PDA alerts were not provided when the aircraft was within 0.5 NM of the runway or less than 125 ft above terrain within 1.0 NM of the runway.

Based on this information and the recorded data for the accident flight (Recorded flight data), provided that the terrain advisory/alert function was enabled, a yellow and black ‘TERRAIN’ annunciation would be generated in the lower left corner of the LCD display, accompanied by a yellow and black ‘TOO LOW – TERRAIN’ PDA pop-up alert (Figure 10), about 15 seconds prior to the terrain collision.

Figure 10: Premature descent alert on the GNS 430W display

Source: Garmin GNS 400W Series Pilot’s Guide & Reference

The terrain system also provided forward-looking terrain avoidance (FLTA) alerts. Provided the terrain system was enabled, a FLTA terrain alert was generated when the predicted or present aircraft altitude above terrain or obstacles was below the minimum clearance value for that phase of flight. During an approach, the clearance value was 150 ft during level flight and 100 ft when descending.[23] The terrain/obstacle advisory alert comprised a yellow and black ‘TERRAIN’ annunciation in the lower left corner of the LCD display, accompanied by a yellow and black ‘TERRAIN ADVISORY’ or ‘CAUTION OBSTACLE’ pop-up message. The pop-up advisory alert would be displayed on all selectable pages (except the terrain page) and remained visible until the message was cleared/acknowledged by the pilot, or the minimum clearance value was no longer infringed.

If the minimum clearance value for terrain/obstacles remained, a terrain/obstacle ahead alert would be generated. The alert consisted of a flashing yellow and black ‘TERRAIN’ annunciation in the lower left of the LCD panel display and a flashing yellow and black ‘TERRAIN AHEAD’ or ‘OBSTACLE AHEAD’ pop-up alert. The pop-up alert would be displayed on all selectable pages, except the terrain page and remained visible until the message was cleared/acknowledged by the pilot, or the minimum clearance value was no longer infringed.

The GNS 400W-Series manual did not specify the warning period for FLTA alerts. However, an earlier version of the 430/430A-Series manual indicated the ‘TERRAIN ADVISORY’ or ‘OBSTACLE ADVISORY’ pop-up terrain alert would be displayed when approximately 60 seconds from potential impact and the ‘TERRAIN AHEAD’ or ‘OBSTACLE AHEAD’ flashing pop-up terrain alert when 30 seconds from potential impact.

On the accident flight, the descent rate when the aircraft reached 5 NM from the runway threshold (or 3.6 NM from the MAPt) is unclear (see Recorded flight data). However, soon after, the descent rate was about 1,200 ft/min and the predicted flight path would have resulted in an FLTA alert to be generated. Therefore, if the terrain awareness/alert system was enabled, an FLTA alert should have been generated about 30 seconds (or longer) prior to the collision.

Air Connect Australia did not have any operational guidance or procedures regarding the use of the terrain awareness function on the GNS 430W units. The chief pilot reported that, when they were the pilot flying VH-OZO, they would generally leave the function turned on, even though it could be annoying in some locations. However, they did not regularly fly the aircraft and had not conducted the most recent flights in the aircraft.

The ATSB spoke to several pilots who were familiar with GNS 430 units with a terrain awareness function. Some advised that the terrain awareness function would often be inhibited, whereas others would use the function on one 430 unit and inhibit it on the second 430 unit. None of the pilots were aware of operators having specific procedures and guidance for using the terrain function.

Pilots stated that the main reason for the terrain awareness function to be inhibited was the perception that it could issue nuisance alerts, with some of these pilots clarifying that this would only occur (or be a valid concern) when conducting visual approaches at non-licenced aerodromes. One pilot advised that they had heard of some pilots in one operator being concerned about using the terrain function if the terrain/obstacle database was not current. However, 2 experienced flight examiners advised that, in their experience, these databases were commonly not current on aircraft they encountered in their roles and that having a current database was not critical; the advantages of the terrain awareness function were more significant than any potential problem with a terrain/obstacle database not being current.

There was no information available regarding what the pilot of the accident flight normally did with the terrain awareness function when flying VH-OZO. Based on the available information, the ATSB could not establish if the terrain awareness function was enabled or inhibited during the accident sequence, or to what extent the pilot had previously encountered terrain alerts when conducting operations in the aircraft.

Configurations and speeds

The flap settings on the Cessna 404 included ‘UP’, ‘T.O. & APPR’ (take-off/approach) and ‘LAND’ (landing). The take-off/approach setting was often referred to as ‘approach flap’ and sometimes called ‘10° flap’.[24]  

According to the Cessna 404 Pilot’s Operating Handbook (POH), which included the Airplane Flight Manual approved by the US Federal Aviation Administration, the maximum landing gear extension speed (and operating speed) was 182 kt, the maximum speed to select approach flap was 182 kt, and the maximum speed to select landing flap was 152 kt.

The POH specified a recommended minimum approach speed (or V_ref[25]) at 50 ft of 91 kt (all engines operating, landing flaps, weight 8,100 lb or 3,6764 kg). For all aircraft weights of 7,500 lb (3,402 kg) and lower, the POH stated approach airspeeds (at 50 ft) of 88 kt. Consistent with the POH, the operator’s operations manual provided values for V_APP[26](approach speed) of 91 kt at 8,100 lb and 88 kt at 7,500 lb and lower weights.

The POH stated the minimum control speed (V_MCA) with approach flap selected was 78 kt. In addition, the one-engine inoperative best rate-of-climb speed for the aircraft type was 102 kt (flap in the take-off/approach position and gear up) and 109 kt (flap and gear up).

Aircraft maintenance

The aircraft logbook statement specified that VH-OZO was to be maintained in accordance with the system of maintenance developed by the aircraft owner and approved by CASA. The key elements of the system were:

• daily inspection in accordance with the Cessna 404 POH
• engine and airframe inspections every 100 +/- 10 hours in accordance with the Cessna 404 progressive care program (Operations 1 and 2 plus 3 and 4 completed within 12-month period)
• electrical and instrument inspections every 220 hours or 12 months in accordance with system of maintenance schedules
• IFR avionics inspections every 220 hours or 12 months in accordance with system of maintenance schedules
• special inspections, supplemental inspection documents, and corrosion prevention control program as required
• altimeter and pitot-static system inspection and test every 24 months
• maintenance release issue for a period of up to 220 hours or 12 months, whichever occurred first. 

Scheduled engine and airframe maintenance was carried out by the CASA-approved maintenance organisation associated with the aircraft owner. While the aircraft was based in Cairns, electrical, instrument, and radio maintenance as well as unscheduled maintenance was contracted to licensed aircraft maintenance engineers.

The most recent maintenance was the scheduled 100-hour inspection based on Operations 3 and 4 of the Cessna 404 progressive care program. That was completed on 16 February 2020 at 31,066 hours total time. A maintenance release was issued with the next scheduled maintenance being the oil/filter change after 50 hours operation and compass swing in July 2020. 

Other key maintenance was:

• 19 January 2020 at 31,050 hours: inspection of the electrical, instrument and IFR avionic systems certified as satisfactory
• 29 January 2019 at 30,750 hours: inspection and test of the pitot-static system and check of altimeters certified as satisfactory.

The current maintenance release was not found at the accident site. Operator records showed that the aircraft had been operated for 3.8 hours between maintenance release issue and the accident flight. The operator and aircraft owner both advised that no aircraft defects had been reported.

The ATSB identified that the vacuum pumps had been in service for a relatively long period and internal wear had not been inspected at the recent 100-hour inspection. Also, there was no record of testing or replacement of the vacuum manifold in the previous 10 years. Although these aspects increased the likelihood of a vacuum system failure, there was no evidence that the vacuum-powered instruments were adversely affected. Further information regarding the maintenance and serviceability of the vacuum system (associated with the attitude indicators and directional gyro) is provided in Appendix B – Vacuum system analysis.

Terrain avoidance and warning systems

General description

A terrain avoidance and warning system (TAWS) provides visual and aural alerting including a look-ahead terrain function. The aircraft’s height above terrain can be based on GPS or radio altitude information. TAWS is a generic term that also includes a ground proximity warning system (GPWS) with a forward-looking terrain avoidance function.

A TAWS is an important tool to help minimise the risk of controlled flight into terrain (CFIT). It provides an independent and unambiguous warning of proximity to the ground or obstacles, regardless of any navigational uncertainty or error such as mis-setting or misreading the altimeter.

Multiple levels or classes of TAWS are defined and internationally recognised. Class B TAWS (TAWS B) includes a minimum of the following alerts:

• reduced required terrain clearance
• imminent terrain impact
• premature descent
• excessive rates of descent
• negative climb rate or altitude loss after take-off
• descent of the aeroplane to 500 ft above the terrain or nearest runway elevation (voice callout ‘Five hundred’) during a non-precision approach.

Class B+ TAWS also has a terrain awareness display that shows surrounding terrain/obstacles relative to the aircraft. Class A TAWS (TAWS A) has all the requirements of Class B+ TAWS, plus 3 additional alerts. Both Class A and class B TAWS have a forward-looking terrain avoidance function.

To maximise its effectiveness, an aircraft operator should have standard operating procedures for the use of a TAWS and for actions to take in response to TAWS alerts.

Australian requirements

Civil Aviation Order (CAO) 20.18 (Aircraft equipment — basic operational requirements), which was in force at the time of the accident, stated that for Australian aircraft:

9.1C A turbine-engined aeroplane that:

(a) has a maximum take-off weight [MTOW] of more than 15 000 kg or is carrying 10 or more passengers; and

(b) is engaged in RPT [regular passenger transport], or charter, operations;

must not be operated under the I.F.R. unless it is fitted with

(c) an approved ground proximity warning system that has a predictive terrain hazard warning function…

(e) if the aeroplane has a maximum take-off weight of 5 700 kg or less, but is carrying 10 or more passengers – a TAWS-B+ system.

In effect, this meant that turbine-engine aeroplanes being used to conduct passenger transport operations under the IFR were required to have a TAWS if the aeroplane was carrying 10 or more passengers or it was a larger air transport aeroplane.[27] There was no requirement for a piston-engine aeroplane (such as VH-OZO) to be fitted with a TAWS.

International requirements for turbine-engine aeroplanes

The Australian TAWS requirements for turbine-engine aeroplanes were consistent with the standards included in International Civil Aviation Organization (ICAO) Annex 6 (Operation of Aircraft) Part I (International Commercial Air Transport – Aeroplanes), which included a standard[28] for all turbine-engine aeroplanes with a MTOW of more than 5,700 kg or authorised to carry 10 or more passengers to have a TAWS. In addition to Australia, this standard had been adopted by comparable countries, including the United States, Canada, New Zealand and Europe.

In 1996, the US National Transport Safety Board (NTSB) issued a recommendation to the US Federal Aviation Administration (FAA) to require that all turbojet-powered airplanes equipped with 6 or more passenger seats have an operating GPWS installed. In 1999 it also recommended that all turbine-powered aeroplanes of the same size be fitted with a TAWS. 

In response, the FAA commissioned a report that examined 44 CFIT accidents that occurred between 1985 and 1994 in the US involving turbine-powered aeroplanes with 6 to 10 passenger seats. Of the 44 aeroplanes, 11 were powered by turbojets and 33 were powered by turboprops. None were fitted with a GPWS system. Computer modelling techniques used to analyse the data showed that, had GPWS been fitted, 33 accidents could have been prevented; had enhanced GPWS been fitted, 42 accidents could have been prevented.

Accordingly, the FAA introduced a requirement for all turbine-powered aeroplanes with 6 or more passenger seats to be fitted with a TAWS B (in Federal Aviation Regulations 91.223 and 135.154). The requirement commenced in March 2002 for new aircraft and March 2005 for older aircraft.

The FAA did not propose to introduce the same requirement for piston-engine (or reciprocating-engine) aeroplanes. In its final rule summary in 2000, the FAA stated:

The General Aviation Manufacturers Association (GAMA) is against requiring TAWS on reciprocating-powered [piston-engine] airplanes because the costs would be high (e.g., “TAWS equipment would cost more than the hull value of the aircraft”), and the panel space for installing TAWS with a situational display is not available in these airplanes.

The FAA did not receive any comments that would justify undertaking a new rulemaking project to mandate TAWS for reciprocating-powered airplanes.

However, regarding the issue of panel space, the FAA knows of at least one manufacturer who has developed a complete TAWS unit that was designed to replace an existing panel instrument.

Following the US introduction, from November 2006, ICAO Annex 6 Part I included a recommendation that turbine-engine aeroplanes with an MTOW of 5,700 kg or less and authorised to carry 6–9 passengers should be equipped with a TAWS. This recommended practice was introduced as a regulatory requirement in other countries, including New Zealand (from 2007 for air transport operations under the IFR), Canada (from 2014 for operations other than day VFR flights), and in Europe (for such aeroplanes with an individual certificate of airworthiness issued after 1 January 2019).[29]

International requirements for piston-engine aeroplanes

Applicable from January 2007, ICAO Annex 6 Part I included a standard for TAWS B to be fitted to piston-engine aeroplanes with a MTOW greater than 5,700 kg or authorised to carry 10 or more passengers.

Subsequently, TAWS requirements were introduced in Canada (from 2014 for air transport operations other than day VFR flights), New Zealand (from 2007 for air transport operations under the IFR) and Europe (from 2012 for air transport operations) for piston-engine aeroplanes. No such requirements for piston-engine aeroplanes were introduced in the United States.

Canada also introduced the same requirement for piston-engine aeroplanes with a passenger seating capacity of 6–9 conducting air transport operations other than day VFR flights from 2014. As far as could be determined, no other countries had introduced a TAWS requirement for piston-engine aeroplanes with a passenger seating capacity less than 10.

In its notice of amendments about TAWS requirements in 2012, Transport Canada indicated that the cost for installing a TAWS B on small aeroplanes conducting air taxi (charter) operations in aircraft with a passenger seating capacity of less than 10 was about Can$23,000. It also noted that the expected benefits of TAWS (in terms of reduced fatalities, serious injuries and accidents due to CFITs) were significantly higher than the costs.[30]

Considerations of changes in Australia

In March 2006, the ATSB issued safety recommendation R20060008:

The Australian Transport Safety Bureau recommends that the Civil Aviation Safety Authority review the requirements for Terrain Awareness Warning Systems for Australian registered turbine-powered aircraft below 5,700 kgs, against international standards such as ICAO Annex 6 and regulations such as FAR 91.223, with the aim of reducing the potential for CFIT accidents.

CASA accepted the recommendation and stated that it would examine the capital/installation costs and benefits. This work was initiated as part of CASA’s notice of proposed rule making (NPRM) 0808OS (Passenger transport services and international cargo operations – Small aeroplanes) published in February 2009. The proposed requirements included that small aeroplanes (regardless of engine type) conducting passenger transport operations carrying 6 or more passengers under the IFR to be fitted with a TAWS B. In terms of benefits and costs, the NPRM stated:

The costs and benefits of mandating TAWS B equipment for IFR aeroplanes carrying 6 to 9 passengers has been assessed by CASA. Equipment and fitment costs are forecast to be approximately $23,000 per aeroplane. Options to offset these additional costs are under consideration by the Government. Benefits are expected to flow to the industry from increased public confidence with this equipment fit to small aeroplanes in which passenger operations are conducted, as the overall accident rate is expected to reduce.

Accordingly, the ATSB recommendation was closed.

Subsequently, CASA released a consultation draft of Civil Aviation Safety Regulation (CASR) Part 135 (Australian air transport operations—smaller aeroplanes) in 2012. This contained a requirement for a TAWS for aeroplanes conducting passenger transport operations with a maximum operational passenger seat configuration (MOPSC)[31] of 6 or more. The proposed requirement’s applicability had expanded to include all flights (not just IFR flights) and was based on the passenger seat capacity rather the actual number of passengers carried on a flight.

Following further consultation, the 2012 proposal was amended to a MOPSC of 10 or more. In the summary of proposed change for CASR Part 135 (published in August 2018), CASA stated:

CASA had originally proposed the fitment of a minimum of TAWS-Class B for aeroplanes with a MOPSC greater than 5 which aligned with the Federal Aviation Administration of the USA (FAA) and Transport Canada rules however this was changed after discussion with the Aviation Safety Advisory Panel Technical Working Group.

In the 2018 explanatory statement in for the introduction of CASR Part 135, CASA outlined the options it considered (in its regulatory impact statement) regarding the implementation of TAWS. It noted that the estimated cost of installing a TAWS was about $21,000 (including about $12,000 for the system and additional costs for installation and training). One option (named option 2) was to only require a TAWS for all aeroplanes with a MOPSC of 10 or more or a MTOW greater than 5,700 kg. It was determined that this would affect 18 aeroplanes (in addition to those that already had or required a TAWS). Another option (option 3) was to require a TAWS for all aeroplanes with a MOPSC of 6–9 as well. In terms of option 3, the statement noted:

The types of aircraft that are within this category include, the piston powered AeroCommander 680, Beech 95 and Cessna 421 and the turbine powered aeroplanes that include the Cessna 208, Fairchild SA 226 and Pilatus PC 12. CASA estimates that there are approximately 323 of these types of aircraft. Based on 323 aircraft within the six to nine seat range and the 18 aircraft with MTOW>5700kg of option 2 this would result in an estimated cost impact of $7.2m for 341 aircraft... [as well as $0.72m annually]

The statement noted that initially CASA had proposed option 3 to industry but, following initial consultation, it did not pursue this option. Feedback associated with the initial consultation on TAWS (and other proposed regulatory changes) included that charter businesses were operating in a difficult marketplace with many not being profitable.

As a result of this regulatory reform process, the Australian requirements for TAWS changed from December 2021, such that piston-engine aeroplanes with a MOPSC of 10 or more conducting air transport operations were required to have a TAWS, with the applicable date being December 2021 or December 2022 dependent on various factors (see Safety issues and actions).

For VH-OZO and its seating configuration at the time of the accident, CASA advised the MOPSC was 12.^[32]As such, if the operator had continued operating the aircraft for passenger transport flights with that seating configuration, the aeroplane would have been required to have a TAWS by December 2022 and, from December 2024, the operator would have had to operate the aeroplane under CASR Part 121 (and conduct all flights with 2 pilots under the IFR, as well as meet additional requirements compared to Part 135). Alternatively, the aeroplane would not have been required to have a TAWS or be operated under Part 121 if some seats were removed such that the MOPSC was 9 or less.^[33]

Aerodrome information

Lockhart River Airport had one sealed runway (12/30), which was 1,500 m long and 30 m wide. It was not serviced by an air traffic control (ATC) tower and it was outside of ATC radar coverage. The airport had a common traffic advisory frequency (CTAF), which was used by pilots to advise intentions and arrange separation with other traffic.  

The elevation of the runway was 76 ft at the threshold for runway 30 and 48 ft at the threshold for runway 12. The runway was equipped with low-intensity runway lights, and there was no visual approach slope guidance.

At the time of the accident there were 3 instrument approaches available at the airport:

• NDB approach to runway 30
• RNAV GNSS approach to runway 12
• RNAV GNSS instrument approach to runway 30 (Figure 2).

The airport was located on a coastal plain 4.5 km west of the Lockhart River township. The Great Dividing Range was nearby with the terrain rising to over 800 ft to the south-west and west within about 8 km of the airport.

Lockhart River was known to experience low cloud and poor visibility conditions. The average (mean) rainfall at Lockhart River is 2,058 mm. In the month of March, the average rainfall is 446 mm and 19.5 days have rainfall of more than 1 mm.

The ATSB interviewed several pilots with experience conducting RNAV GNSS approaches, including some who had conducted multiple approaches at Lockhart River due to poor visibility conditions. The pilots had several suggestions for reducing workload for a second approach, including holding or diverting to Coen or Weipa to wait for weather to pass.

Meteorological information

Weather forecasts - overview

The Bureau of Meteorology produced aviation forecasts, observations, warnings and advisories. As the official provider of the Aeronautical Information Service, Airservices Australia delivered the bureau’s aviation meteorological products to pilots through National Aeronautical Information Processing System (NAIPS).

For the flight from Cairns to Lockhart River, the meteorological forecast information consisted of aerodrome forecasts (TAFs), graphical area forecasts (GAFs), grid point wind and temperature charts (GPWTs) and any warnings (such as SIGMETs[34]). These could be supplemented by aerodrome weather reports (METARs), ground-based weather radar imagery, and satellite imagery.

According to the weather forecasts, the pilot would have expected mostly visual meteorological conditions (VMC)[35] during the day at Cairns with some periods of rain showers and low cloud. For the arrival at Lockhart River, the forecast weather was predominantly VMC but there were overlapping periods of rain and low cloud with 30% probability of thunderstorms.

Aerodrome forecasts

A TAF for Lockhart River was issued at 0449 EST[36] and was valid from 0600 to 1800. The expected weather conditions were:

• From 0600 to 1000: wind variable at 3 kt with visibility 10 km or greater. Light rain showers and cloud scattered at 1,000 ft.[37]
• Between 0600 and 1000: TEMPO[38] - visibility reduced to 3,000 m with rain and broken cloud at 500 ft.
• From 0600 to 0800: 30% probability of fog with visibility reduced to 500 ft and broken cloud at 100 ft.
• From 1000 to 1800: wind from the north-east at 5 kt with visibility 10 km or greater. Light rain showers with scattered cloud at 1,000 ft.
• Between 1000 and 1800: TEMPO - visibility reduced to 3,000 m with rain showers and broken cloud at 800 ft.
• For the whole forecast period, 0600 to 1800: 30% probability TEMPO - winds gusting 25 to 35 kt and visibility reduced to 1,000 m due to thunderstorms and rain. This was associated with broken cloud at 500 ft and scattered cumulonimbus cloud with the base at 1,000 ft.

Based on this forecast a pilot arriving at Lockhart River was required to plan for 60 minutes holding or diversion to an alternate aerodrome. The aircraft had more than sufficient fuel for that purpose (see Fuel calculations).

An amended TAF for Lockhart River was issued at 0925 (5 minutes after the accident) and was valid from 0900 to 1800. The expected weather conditions were:

• From 0900 to 1300: wind variable at 3 kt with visibility 10 km or greater. Light rain showers with cloud scattered at 1,000 ft and broken at 2,000 ft.
• For whole forecast period, 0900 to 1800: TEMPO – winds gusting from 20 to 35 kt and visibility reduced to 1,000 m due to thunderstorms and rain. This was associated with broken cloud at 500 ft and scattered cumulonimbus cloud with the base at 1,500 ft.

Graphical area forecasts

A GAF was issued at 0835 and was valid from 0900 to 1500 and applicable from surface to 10,000 ft. This covered the Queensland-North region, which was divided into 6 areas for this forecast. Most of the flight including the arrival at Lockhart River was within one area that was forecast to have the following conditions:

• Broken stratus 1,000 ft to 2,000 ft with broken cumulus/stratocumulus above that. Visibility reduced to 6,000 m in widespread rain.
• Isolated towering cumulus from 2,000 ft, broken stratus from 800 to 2,000 ft, and broken cumulus/stratocumulus from 2,000 ft. Visibility reduced to 2,000 m in scattered rain showers.
• Isolated cumulonimbus from 2,000 ft and broken status between 500 ft and 1,000 ft. Visibility reduced to 500 m in isolated thunderstorm rain showers.

A GPWT forecast was issued at 0538 and was valid to 1000. Lockhart River was located near the intersection of 4 data boxes and therefore roughly equidistant from 4 forecast locations. Taking 2,000 ft as a reference height for the approaches and coastal data as more relevant, the wind was forecast to be from the north-west at 9 kt increasing to 21 kt north of Lockhart River.

There were no significant weather warnings applicable to the flight.

Weather conditions - overview

The Bureau of Meteorology provided an overview to the ATSB of the actual weather conditions at Lockhart River on the day of the accident. It stated that a developing monsoon trough extended across Cape York Peninsula crossing the coast near Weipa and Lockhart River. A tropical low was embedded in the trough and was near Weipa at 1000, moving slowly eastward. The monsoon trough and low were causing scattered to widespread rain and isolated thunderstorms over much of Cape York Peninsula.

The surface winds at Lockhart River Airport were generally light and variable. Automatic weather sensors detected rain and heavy rain reducing visibility to 800 m and scattered to broken layers of cloud as low as 1,100 ft above ground level.

Aerodrome weather reports for Lockhart River

The METARs for Lockhart River were automatically generated every 30 minutes for routine reports and were issued as a special report (SPECI) at other times when one or more elements met specified criteria for degradation and improvement. For the period from 0830 to 0929 on 11 March 2020, the reports included:

• 0830: nil wind, visibility[39] 10 km or greater with rain and scattered cloud from 3,000 ft. Temperature and dewpoint were both 25 °C. Rainfall in the previous 10 minutes was 0.4 mm.
• 0900: nil wind, visibility 10 km or greater with rain and broken cloud at 2,000 ft, 3,500 ft, and 4,100 ft. Temperature and dewpoint were both 25 °C. Rainfall in the previous 10 minutes was 0.4 mm.
• SPECI 0910: nil wind, visibility 10 km or greater with rain and broken cloud at 1,800 ft and 3,400 ft then overcast at 4,200 ft. Temperature and dewpoint were 26 and 25 °C respectively. Rainfall in the previous 10 minutes was 0.4 mm.
• SPECI 0913: nil wind, visibility 3,800 m with rain and broken cloud at 1,800 ft and 3,400 ft, overcast at 4,200 ft. Temperature and dewpoint were 26 and 25 °C respectively. Rainfall in the previous 10 minutes was 2.2 mm.
• SPECI 0929: wind westerly at 5 kt, visibility 8,000 m with heavy rain and scattered cloud at 1,200 ft, broken cloud at 1,900 ft, and broken cloud at 3,600 ft. Temperature and dewpoint were both 25 °C. Rainfall in the previous 10 minutes was 0.4 mm and rainfall since 0900 was 3.8 mm.

The QNH remained at 1,008 hPa during this period.

Automatic weather station

The Bureau of Meteorology (BoM) provided data from the Lockhart River Airport automatic weather station (AWS) recorded at 1-minute intervals. Table 3 details 1-minute rainfall, 30-minute cloud and 10-minute visibility data for the period encompassing the aircraft’s first approach prior to the final approach fix (FAF) at 0904 to the accident at 0920. The last column in the table indicates the 1-minute visibility associated with the telephone message for the aerodrome’s automated weather information service (see following section section). More detailed information from the Lockhart River AWS for the period 0850 to 0930 is provided in Appendix C – Detailed 1-minute weather data Lockhart River 0850–0930.

Table 3: Extract of 1-minute weather data from Lockhart River Airport AWS

The first shaded area indicates when the aircraft was at the MAPt on the first approach and the second shaded area indicates the time of the accident on the second approach. The 1-minute visibility data was that recorded to be broadcast by the AWIS by telephone. The times have been displaced by 1 minute (back) to align with the 1-minute rainfall data provided by BoM. The cloud data was averaged over the previous 30 minutes (see description in report text).

Source: Bureau of Meteorology

The cloud information was derived using a sky condition algorithm. This involved taking a sample (using a ceilometer at the aerodrome) at least every 30 seconds and averaging the data over a 30-minute period, with samples taken in the last 10 minutes provided double weighting.[40] Although this algorithm provided more stable estimates of cloud than each sample, the reported cloud for any given minute did not necessarily reflect the cloud level at that specific point in time.[41]

The visibility meter estimated atmospheric visibility based on the continuous sampling of a single point, providing a measurement of the prevailing visibility at the sensor. However, it sampled a relatively small volume of air in the immediate vicinity of the instrument and, unlike a human observer, was not capable of estimating visibility in different directions or over longer distances. One-minute data was based on the last 60 seconds of sensor output, as an average based on a processing algorithm. The 10-minute data recorded each minute was the average value over the previous 10 minutes.

A number of factors can affect the accuracy of the reported visibility, including:

• discrete air masses, such as a shower of rain or a bank of fog, will not be identified unless the sensor is engulfed, and if the phenomenon is not of uniform density the visibility will be misreported
• stationary localised patches of fog will remain undetected if the sensor is clear of fog, or if the sensor is within the patch of fog the reported visibility may be less than actual.

The temperature and dewpoint were about 25 °C for the duration with the relative humidity at 99% (increasing to 100% from 0917).

The reported wind speeds and directions were the mean values at 10 m above ground level, averaged over the last 1-minute period. The recorded wind was 0 kt until 0914, with speeds of 3–4 kt from the west, between 0916 and 0921.

Automated weather information service

Lockhart River was equipped with an automated weather information service (AWIS) that transmitted AWS data in text-to-speech format on a discrete VHF frequency. A new AWIS message was generated every minute in a similar format to the METAR reports. To produce the reports from the AWS 1-minute data, some averaging and rounding of the information occurred. The broadcasts were not recorded.

In addition, AWIS data at Lockhart River could also be accessed by telephone. A different phone message based on the AWS data was produced every minute and this was recorded. However, the AWIS information available by telephone was processed differently to the AWIS information available by VHF, and therefore there could be slight differences in the information produced at the same time.

During the flight, the pilot recorded the following data in the space allocated for arrival weather information in the flight plan/log:

• calm (nil wind)
• 10 km (visibility)
• B1800 (broken cloud at 1,800 ft)
• B3500 (broken cloud at 3,500 ft)
• OV 5300 (overcast cloud at 5,300 ft)
• 1008 (QNH 1,008 hPa)
• 25 (temperature 25 °C).

This information closely matched the recorded AWS 1-minute data at 0854, which stated (with expected transmitted message in brackets):

• wind 0 kt at 023° (wind calm)
• visibility 10 km (visibility one zero)
• (present weather – rain)
• cloud 4 oktas[42] at 1,800 ft (cloud broken one thousand eight hundred)
• cloud 5 oktas at 3,500 ft (broken three thousand five hundred)
• cloud 7 oktas at 5,300 ft (broken five thousand three hundred)
• temperature 25.4 °C (temperature two five)
• dewpoint 25.2 °C (dewpoint two five)
• QNH 1,008.5 hPa (QNH one zero zero eight hectopascals)
• rainfall last 10 minutes 0.4 mm (rainfall last ten minutes zero decimal four millimetres). 

The pilot’s recorded weather information was also broadly consistent with the recorded AWIS messages available by phone for the period 0853­–0855. It did not closely match any of the other recorded AWS 1-minute data or the recorded AWIS messages available by phone during 0840–0920. Accordingly, it is very likely that the pilot wrote down the AWIS data accessed by VHF radio at about 0854. It could not be determined whether the pilot additionally accessed the AWIS data prior to this time and/or after this time.

The AWIS broadcasted the most recent 1-minute visibility data measured by the AWS (see Table 3, last column). This data indicated visibility below the landing minima (4,200 m) at the AWS site between 0911 and 0915, and at 0917.

BoM operated a network of weather watch radars around Australia that detected water droplets in the atmosphere. Information from the weather radar was displayed on a map, with different colours depicting the approximate rainfall/precipitation intensity.

The nearest weather radar was at Weipa, approximately 150 km west of Lockhart River. Coverage in the vicinity of Lockhart River was affected by the distance from the radar and terrain, reducing the radar’s ability to detect low-level showers. However, precipitation at higher altitudes would still produce radar echoes.

Figure 11 provides an indication of the weather around Lockhart River at 0918 on the morning of the accident (during the second approach), with Figure 12 displaying an extract of radar images from the time of the first approach and the time of the accident. The weather radar depicted areas of moderate precipitation in the vicinity of Lockhart River. In addition, an analysis of a sequential series of images showed precipitation moving through the area at a speed of about 30 kt (55 km/h) from the north-west.

The minute-by-minute data from the AWS around the time of the accident (see Automatic weather station and Table 3) recorded no significant surface wind. However, there was a short period of rainfall between 0910 and 0916, including moderate to heavy rainfall between 0912 and 0914. If this rainfall persisted and continued moving in a direction/speed consistent with the observed radar returns, it would have been in the vicinity of the accident site about the time of the accident.

Figure 11: Weipa radar image at 0918 EST (about 2 minutes prior to the accident) showing weather in Lockhart River area (circled, approximate radius 25 NM/46 km)

Source: Bureau of Meteorology, annotated by the ATSB

Figure 12: Extract of Weipa radar images at 0906 (time of the first approach) and 0918 EST showing rain rate on the approach path to runway 30 at Lockhart River Airport

Source: Bureau of Meteorology, annotated by the ATSB

Local weather observations

Two pilots were operating aircraft in the Lockhart River area before and after the accident. The first pilot, operating before the accident, tracked to Lockhart River from the south and conducted the RNAV GNSS runway 30 approach, landing at 0810. There were intermittent rain showers in the area and the pilot advised that the end of the runway was visible while descending through 1,000 ft. The pilot remained on the ground at Lockhart River until later in the day and heard an aircraft (VH-OZO) fly over at high engine power. They recalled that, at that time, there was scattered low cloud at 500–1,000 ft with reduced visibility in rain showers.

The following pilot, operating after the accident, tracked to Lockhart River from the south-west and diverted 15 NM to the right of track due to weather. On arrival, the pilot conducted the Lockhart River RNAV GNSS runway 30 approach and landed at 0953. The pilot reported that there was rain in the area and, although the conditions allowed visual navigation after the final approach fix (FAF) while descending through 1,500 ft, the runway was not visible until later in the approach.

A person who was near the airport at the time of the accident described the conditions as an unusual morning with mist coming from the rainforest, and that there was about 5 to 10 minutes of heavy rain at about the time the aircraft would have been in the area. At that time, there was low-lying cloud (north-west of the airport) and no wind.

Fishermen who were in the area at the time reported that, at about the time of the second approach, there was a ‘wall’ of heavy rain that came across from the north-west.

Instrument approach

Overview

An instrument approach is a published procedure that allows for safe navigation of an aircraft operating in instrument meteorological conditions (IMC) to descend from the lowest safe altitude to a specified position (missed approach point - MAPt) near the aerodrome. If the conditions are suitable, the approach can be continued to land. If the conditions are not suitable, the pilot must conduct a missed approach in accordance with the procedure.

There are 2 general categories of instrument approach:

• 2-dimensional (2D) – lateral/tracking guidance only, also known as non-precision approaches or LNAV (lateral navigation)
• 3-dimensional (3D) – lateral/tracking and vertical guidance, including precision approaches such as an instrument landing system (ILS) approach and a (non-precision) approach with vertical guidance (APV).

Both categories of instrument approaches were only conducted utilising ground-based navigation aids until RNAV GNSS[43] approaches were available in Australia from 1998.

An RNAV GNSS approach is a 2D instrument approach that utilises an on-board GPS receiver (or flight management system - FMS) to generate lateral/tracking guidance and distance information. These approaches are pre-programmed in a GPS/navigation system’s database. Other types of non-precision approaches use ground-based aids such as a non-directional beacon (NDB) or a VHF omni directional radio range (VOR).

The transition in Australia from navigation reliant on ground-based navaids to performance-based navigation is continuing. As part of that process, Airservices Australia has been implementing barometric vertical navigation (Baro-VNAV) APV approaches since 2016. These 3D approaches are restricted to runways with a validated (LNAV/VNAV RNP APCH) procedure and aircraft with the applicable avionics, typically an FMS. Although these approaches were available at Lockhart River from 3 December 2020, VH-OZO was not Baro-VNAV capable.[44]

RNAV GNSS approach design

RNAV GNSS approaches in Australia have a Y-pattern, runway-aligned design. The Lockhart River runway 30 RNAV GNSS approach uses this typical layout, as shown in Figure 13.

Figure 13: Extract from Lockhart River RNAV GNSS runway 30 approach chart showing layout of waypoints

Source: Airservices Australia, annotated by the ATSB

The approaches have 3 initial approach fixes (IAFs, in this case, LHREA, LHREB and LHREC), followed by an intermediate fix (IF, LHREI), final approach fix (FAF, LHREF) and missed approach point (MAPt, LHREM).

The segment between an IAF and the IF is the initial approach segment, the segment between the IF and the FAF is the intermediate approach segment, and the segment between the FAF and the MAPt is the final approach segment. Each segment is typically 5 NM.

The intermediate approach track is normally aligned with the final approach track. One of the IAF waypoints is also aligned with the intermediate/final approach track (in this case, LHREB) and the other IAFs are located 70° off the intermediate/final approach track (LHREAS and LHREC). A pilot can commence an approach by flying to one of the 3 IAFs within the capture region for that waypoint. The capture region is a 140° arc for the IAF on the intermediate/final approach track and a 180° arc for the IAFs not on the intermediate/final approach track (with the extreme points parallel to the intermediate/final approach track).

Instrument approach waypoints can either be fly-by waypoints (which require turn anticipation to allow tangential interception of the next segment) or flyover waypoints (at which the turn is initiated). For RNAV GNSS approaches, the IAFs, IF and FAF are fly-by waypoints and the MAPt is a flyover waypoint.

The approaches are recommended to be flown using a continuous descent angle.

The recommended profile published on approach charts consists of an initial approach altitude which then joins a constant descent to 50 ft above the runway threshold. The approach path angle of the descent is normally (and ideally) 3°. Depending on the approach, the initial approach altitude joins the constant descent profile at about the FAF or earlier.

For example, the approach chart for the Lockhart River runway 30 approach (Figure 14) had an initial approach altitude of 3,500 ft leading to an approach path angle of 3°, which commenced 0.8 NM after the IF (4.2 NM prior to the FAF and 9.2 NM prior to the MAPt).

Figure 14: Excerpt from Lockhart River RNAV (GNSS) runway 30 approach chart showing recommended vertical profile and segment minima safe altitudes

The full approach chart is provided in Figure 2.

Source: Airservices Australia, annotated by the ATSB   

Each segment of an RNAV GNSS approach has one or more specified segment minimum safe altitudes, depicted by shading on the chart’s profile diagram and the relevant altitude with a solid line underneath. For example, between the IF and the FAF on the runway 30 approach, the segment minimum safe altitude was 1,800 ft. The last segment minimum safe altitude, in the final approach segment, is the minimum descent altitude (MDA).

During an instrument approach, a pilot is able to descend below the recommended descent profile, but they are not allowed to descend below a segment minimum safe altitude, except for the MDA if certain conditions are met (as discussed below).[45] However, as stated in the Civil Aviation Advisory Publication (CAAP) 178-1(2) (Non-precision approaches (NPA) & approaches with vertical guidance (APV)):

While some pilots in the past have flown NPAs as a series of descending steps conforming to the minimum published altitudes, (a technique colloquially referred to as the ‘dive and drive’), CASA recommends a constant angle descent in a stabilised configuration. Many Controlled Flight into Terrain (CFIT) accidents have been attributed to the ‘dive and drive’ technique, due to human errors such as early descent before a step or failing to arrest descent. In addition, the aircraft’s descent is more difficult to manage due to changes in airspeed, rate of descent and configuration.

If the recommended descent profile starts prior to the FAF, the RNAV GNSS approach chart includes an advisory crossing altitude (or procedure height) at the FAF (and if required the IF) to assist pilots with maintaining the recommended descent profile (for example, 2,160 ft at the FAF in Figure 14). In addition, a pilot is provided with a distance/altitude scale on the approach chart that provides guidance for the recommended descent profile (see top of Figure 14). The distance specified is the distance to the next waypoint.

Approach waypoint naming convention

The waypoints documented on an RNAV GNSS approach chart are identified by a unique identifier comprising the airport identifier (in this case LHR), compass quadrant from which the approach is flown (E - east), and position on the approach (A, B, C, I, F, M or H).

During the investigation, some flight examiners stated that pilots occasionally misidentified waypoints (due to their similar names) and believed that they were on a different segment of the approach than they actually were. One flight examiner noted that this was more likely to occur when coming straight in via the IAF ‘B’ rather than when coming via one of the other 2 IAFs. This flight examiner also noted that one operator they worked with had introduced call-out requirement for pilots to annunciate that they were tracking from one waypoint to another in order to minimise this risk.

Conducting an approach

Before conducting the approach, the pilot must ensure they are qualified for RNAV GNSS approaches and satisfy the recent experience requirements. The aircraft must be equipped with an approved GPS receiver with a valid aeronautical database. It is also essential that the availability of receiver autonomous integrity monitoring (RAIM) is checked pre-flight and before entering the approach.[46]

To conduct the approach, the pilot selects the specific approach and IAF in the GPS unit (or FMS) and tracks towards the applicable IAF within the capture region. Prior to passing the IAF, a pilot must set the QNH to either the actual aerodrome QNH (from an approved source such as AWIS) or the aerodrome/area forecast QNH.

As the approach proceeds, the GPS (or FMS) will automatically sequence through the waypoints, displaying the next waypoint and distance to that waypoint. The pilot maintains the track with reference to the associated course deviation indicator (CDI).  

To maintain the recommended descent profile (without electronic vertical guidance), pilots are required to:

• establish a 3° descent by managing the descent rate proportional to the groundspeed (through engine power and pitch angle)
• with reference to the altimeter, monitor the aircraft’s altitude - relative to the distance from the next waypoint with reference to the table on the approach chart and/or when passing waypoints with advisory altitudes     
• adjust the descent rate and/or groundspeed as required to correct the profile
• level at the MDA and continue tracking to the MAPt unless the conditions are suitable for continuation of the approach.

The height of the MDA above the aerodrome elevation and the required visibility (in km) to complete the approach were included as bracketed figures after the MDA. If the minima label boxes on the approach chart were shaded, the MDA could be reduced by 100 ft when the actual aerodrome QNH was set. For example, for the accident flight, the pilot had noted the actual QNH so the 830 ft MDA could be reduced to 730 ft (Figure 15). At the lower MDA, the aircraft would be 653 ft above the aerodrome elevation and the minimum required visibility was 4.2 km. Practically, if the visibility was at the minima value, the pilot would see the runway threshold before the MAPt and, if the aircraft was on the recommended profile, by the MDA.

Figure 15: Excerpt from Lockhart River RNAV GNSS runway 30 approach chart showing minima table

The full approach chart is provided in Figure 2.

Source: Airservices Australia

The Aeronautical Information Publication (AIP) outlined several instructions or methods for pilots regarding the conduct of instrument approaches, in addition to those specified by an operator’s operations manual. CAO 20.91 (Instructions and directions for performance-based navigation, Instrument 2014) also applied to the operation of Australian aircraft using performance-based navigation (which included RNAV approaches during IFR flight), providing instructions/directions to operators and pilots conducting those operations. Relevant CAO and AIP requirements, instructions and methods are outlined in subsequent sections below.

Descent below the minimum descent altitude

After passing the FAF, a pilot is permitted to descend to the MDA (provided the aircraft is within navigational tolerances). Further descent below the MDA must not be made without the required visual reference. There may be different MDAs specified for a straight-in or circling approach. Descent below the straight-in approach MDA could only be conducted (AIP ENR 1.5, 1.8.2)[47] when:

• visual reference can be maintained;
• all elements of the meteorological minima are equal to or greater than those published for the aircraft performance category…; and
• the aircraft is continuously in a position from which a descent to a landing on the intended runway can be made at a normal rate of descent using normal flight manoeuvres that will allow touchdown to occur within the touchdown zone of the runway of intended landing.

The AIP also stated that, if visual reference is not established at or before reaching the MAPt, a missed approach must be executed (ENR 1.5, 1.10.1).

The competencies and standards required for an initial instrument rating and IPCs were specified in the CASR Part 61 Manual of Standards (MOS). For a 2D approach, the required tolerance was within +100 ft at the MDA but not below it.

Lateral tolerances

The AIP stated that instrument approach procedures were based on specific navigation aids, ‘with the applicable navigation tolerances associated with the aids being used in the development of the procedure’s obstacle protection surfaces.’ For an RNAV GNSS approach, CAO 20.91 stated that the lateral tracking tolerances were 1.0 NM (1,852 m) for the initial, intermediate and missed approach segments (terminal area operations) and 0.3 NM (556 m) for the final approach segment.

Navigational equipment could be designed so that full-scale deflection on the CDI represented the required navigation performance (RNP) lateral tracking tolerance during that phase of flight. For an RNAV GNSS approach, this would typically be represented as a lateral 1 NM displacement being represented as a full-scale CDI deflection during the initial segment and most of the intermediate segment, then transitioning from about 2 NM (3,704 m) prior to the FAF to a 0.3 NM displacement being full-scale deflection about 1 NM after reaching the FAF (Figure 16).

The GNS 400W-series manual indicated that the CDI full-scale deflection varied during the final approach segment.[48] When conducting an RNAV GNSS approach using a GNS 400W-series unit, the full-scale deflection was 350 ft (0.06 NM or 107 m) at the MAPt, diverging back to the FAF at an angle of either 2° to the final approach track, or an angle such to achieve 0.3 NM full-scale deflection at the FAF, whichever was less (Figure 16).[49] For 5 NM final approach segments, the angular 2° would always be less than the lateral 0.3 NM CDI full-scale deflection at the FAF.

Figure 16: Conventional transition from RNP 1.0 to RNP 0.3 NM during final approach segment (represented by full-scale CDI deflection) compared to the full-scale CDI deflection provided by the GNS 400W-series GPS

Source: ATSB, derived from information contained in ICAO Doc 8168 Procedures for Air Navigation Services-Aircraft Operations, Vol II − Construction of Visual and Instrument Flight Procedures and the Garmin GNS 400W-Series Pilot’s Guide & Reference manual.

For the 5 NM final approach segment for the runway 30 approach at Lockhart River, an angular 2° to the final approach track displaced 350 ft (107 m) at the MAPt equated to 0.23 NM (430 m) at the FAF. The transition from 1.0 NM full-scale deflection during the intermediate segment to the 2° automatic rescaling full-scale deflection for the final approach segment commenced 2 NM prior to reaching the FAF and was completed by the FAF. In other words, during the final approach segment, GNS 400W series units presented CDI full-scale defection that was less than the lateral tracking limit specified in CAO 20.91 for the final approach segment. This difference was relatively minor at the FAF (0.3 NM versus 0.23 NM) but increased significantly as the aircraft got closer to the MAPt.

When using the GNS 400-series units, if the CDI exceeded a full-scale deflection, a green arrow and distance was displayed on the default navigation page’s CDI, indicating the direction (left or right) and distance the aircraft was displaced (in NM) from the required track.

For a straight-in, area navigation-based approach (such as the RNAV GNSS approach to runway 30 at Lockhart River), the AIP (ENR 1.5, 1.21) stated that an aircraft was required to:

…pass the waypoint, and when established on the specified track, descend to not below the specified altitude….

Note: “Established” means being within half full scale deflection for the ILS, VOR and GNSS... [50]

The AIP (ENR 1.5, 1.10.1) also stated that a missed approach had to be conducted if:

…during the final segment of an instrument approach, the aircraft is not maintained within the applicable navigation tolerance for the aid in use…

CAO 20.91, Appendix 6, contained operating standards for conducting an RNAV GNSS approach, which included the requirement to commence a missed approach if the cross-track error/deviation equalled or was reasonably likely to equal the RNP for that segment of the approach (that is, 1.0 NM for the initial and intermediate segments and 0.3 NM during the final approach segment).

In other words, to comply with the AIP, after passing the FAF, the aircraft needed to be established within half full-scale deflection before descending below the previous segment’s MSA. If the aircraft was established within half full-scale deflection, the descent could continue to an altitude not below the segment minimum safe altitude, which in this case was the MDA.[51] In addition, to comply with CAO 20.91, a pilot was required to conduct a missed approach if the aircraft was laterally displaced 0.3 NM or more from the final approach track.

CASA advised the ATSB that there was, in the aviation community, a commonly held misconception that half full-scale deflection was the required tracking tolerance limit. This was potentially related to a number of factors, such as:

• CAO 20.91 included a note that stated ‘So far as practicable, the cross-track error/deviation for normal operations should be limited to 0.5 NM (½ x RNP) for the initial segment, the intermediate segment and a missed approach, and to 0.15 NM (½ x RNP) for the final approach segment. Brief deviations are acceptable during and immediately after turns where accurate cross-track information is not provided during the turn.’ This reference to half the RNP was providing a target level of safety rather than a minimum acceptable level of safety.
• The CASR Part 61 MOS required tolerance when assessing a pilot’s competency for a 2D approach was within half full-scale deflection.
• CAAP 179A-1(1) (Navigation using the Global Navigation Satellite Systems (GNSS)), issued in 2006, stated (erroneously) that for an RNAV GNSS approach that ‘The tracking tolerance is half of full-scale deflection regardless of the CDI scale’.[52]

CASA advised that operators could choose to specify a more restrictive lateral tracking requirement than that stated in CAO 20.91. If an operator specified a more restrictive limit (such as half RNP or half full-scale deflection), and included that in its operations manual, then that limit would be the applicable limit for that operator.

As discussed in Operator’s stabilised approach criteria, the operator of VH-OZO specified in its operations manual that a missed approach was required if an aircraft on an RNAV approach was not within ‘half scale deflection’ at the FAF. The ATSB is aware through its investigations that a number of other operators also specified a similar requirement for initiation of a missed approach.

Handling speeds

The AIP (ENR 1.5, 1.16) stipulated handling airspeeds for aircraft during instrument approaches based on the aircraft’s performance category. Aircraft performance categories were based on an indicated airspeed at the runway threshold (V_AT).[53]

The Cessna 404 V_AT was 91 kt. Therefore, the performance category for the Cessna 404 was category B, which applied to aircraft with a V_AT  of 91­–120 kt.

The relevant handling speeds for instrument approaches for category B aircraft were:

• 120 to 180 kt for the initial and intermediate approach segments
• 85 to 130 kt for the final approach segments
• maximum 150 kt for the missed approach.

A note in the AIP stated that a pilot was permitted to reduce the speed below the minimum in the initial/intermediate segments ‘to enable the final approach speed to be achieved prior to the commencement of the final segment’. In other words, for a category B aircraft, a pilot could operate below 120 kt prior to reaching the FAF but they could not operate above 180 kt.

The AIP handling speeds are broad speed bands used for purposes such as ensuring aircraft remain within the design tolerances for instrument approach procedures. Operators should provide more specific guidance regarding the appropriate speeds to use during instrument approaches for their aircraft types (see Flight profiles).

The AIP also stated that the descent rate after the FAF ‘should not normally exceed’ 1,000 ft/min.

Instrument flying and workload

Single pilot IFR operations are widely regarded to be among the most difficult and/or involve the highest workload. As stated by the US Aircraft Owners and Pilots Association (AOPA) in 2006:

No type of flying requires greater skill or longer periods of concentration than [single-pilot IFR] SPIFR…

Very simply, the problem is pilot workload, aggravated by the need for multi-tasking. A single IFR pilot also serves as navigator, radio operator, systems manager, onboard meteorologist, record keeper, and sometimes, flight attendant. En route flight in benign weather is usually not too stressful, but add high-density traffic in poor weather conditions or a significant equipment malfunction, and overload may not be far away.

In instrument flight, the pilot maintains an awareness of the aircraft’s spatial position by reference to instruments rather than outside visual references. The fundamental skills of instrument flight are instrument scanning and instrument interpretation. Instrument scanning is ‘the continuous and logical observation of instruments for attitude and performance information’ (FAA 2012).

In any phase of flight or manoeuvre, there are primary instruments that give the most pertinent information and supporting instruments that assist in their continued correct interpretation. For example, even when the aircraft is established in a constant-rate descent, and trimmed to remove control pressure on the yoke, it is necessary for the pilot to continuously check relevant instruments and make appropriate control adjustments to maintain aircraft performance and control. 

With proficiency, a pilot scans at an appropriate rate and is able to interpret the instruments to maintain an accurate mental picture of what is happening. An ineffective scan, such as fixation on one instrument or the omission of another, or misinterpretation of the displayed information, can result in a pilot having an incorrect mental model of the aircraft’s position or flight path.

More generally, workload is described by Wickens and others (2013) as follows:

Mental workload characterizes the demands of tasks imposed on the limited information processing capacity of the brain in much the same way that physical workload characterises the energy demands upon the muscles. In any resource-limited system, the most relevant measure of demand is specified relative to the supply of available resources...

People experience workload differently, based on their individual capabilities and the local conditions at the time such as training and experience in the situation at hand and the operational demands during that phase of flight (Orlady and Orlady 1999). When workload gets too high for the available resources task shedding occurs (Wickens and others 2013).

Dismukes and others (2007) discussed task shedding in this context, explaining that a pilot may move from a proactive assessment of the situation, commonly referred to in aviation as ‘being ahead of the aircraft’, to a reactive situation, where the pilot is responding to events as they occur without an overall strategy to manage the situation (that is, being behind the aircraft). Wickens and others (2013) further explained that task shedding can result in some tasks being shed altogether, and others being shed in a non-optimal manner. In addition, tasks such as internal and external communication are often shed during periods of high workload.

Holmes and others (2003) stated that distractions and high workload can result in a pilot scanning fewer instruments and checking them less frequently. High workload can also lead to a reduction in the number of information sources that an individual will search, as well as the frequency or amount of time these sources are checked (Staal 2004). Additionally, vigilance tasks, such as monitoring flight instruments, require sustained attention with the associated eye movements being fatiguing (Wickens and others 2013).

The United Kingdom Civil Aviation publication, Monitoring Matters, provided information regarding monitoring and stated:

… whilst you are ahead of the game, concentrating on the next event, keeping an eye on all the flight parameters, system modes etc, everything runs fairly smoothly. But as soon as something draws your attention away and you become out of the loop it becomes difficult to play catch up. 

Although it is possible to attend to more than one task using selective attention techniques, there is a limit to cognitive capacity. If tasks consume this capacity, that is when task shedding will occur. This publication further advised that under high workload, especially during approach and descent, attention capacity diminishes. This includes the ability to detect when the configuration of the aircraft is not correct, even when there is an aural or visual alert, particularly in the case of single-pilot operations as:          

…the processes and procedures will be equivalent to multi crew operation except there will only be one person in the cockpit and the systems may be less automated. Hence the need to monitor the flight profile, flight instruments, fuel state, engines, radios, etc. diligently. The instrument scan must be carried out very frequently, especially during departure and approach in order to monitor the aircraft state and planned profile.

In addition to being a complex skill to acquire, instrument flying skills needs to be maintained by frequent practice (Newman 2007). As stated by CASA in 2016 (Changes to instrument proficiency checks):

Conducting IFR operations is a relatively high risk activity and so requires dedicated knowledge and practical flight training… Skill-based qualifications, like the instrument rating, require the qualification holder to maintain their skills and operational knowledge. Skills and knowledge degrade over time. In the interests of safety, rules are put in place to ensure pilots are sufficiently competent conducting IFR operations.

Accordingly, there are requirements in place for pilots conducting IFR operations to regularly undertake proficiency checks (Proficiency checks and flight reviews) and have recent experience (Monitoring of pilot recency). In general, skill decay or skill degradation increases as the retention interval (or time since learning) increases, and it also increases depending on the quantity and quality of the initial and recurrent training and the amount of task exposure (Arthur and others 1998, Sanli and others 2018, Vlasblom and others 2020). Skill decay has various effects, such as preventing the development of further expertise and decreasing spare mental capacity. As noted by the European Aviation Safety Agency (2021):

Proficiency decay in only a few skills may lead to time management issues, reduced situation awareness, and the ability to keep ahead of the situation. In non-normal situations or emergencies, appropriate actions may not be taken due to one’s inability to analyse the situation as a result of the cognitive overload.

RNAV GNSS approach workload

There has been limited research that has compared different types of instrument approaches, and specifically looked at RNAV GNSS approaches. Research was conducted by the ATSB following a CFIT accident on an RNAV GNSS approach at Lockhart River in 2005 (Godley, 2006). The study found that, for pilots of smaller single-engine and twin-engine aircraft, pilot workload was perceived as being higher, and reported losses of situational awareness were more common, for RNAV GNSS approaches compared to other approach types except for NDB non-precision approaches.

In contrast, pilots of larger aircraft found that RNAV GNSS approaches were not as problematic, with the workload only being higher than ILS (precision) approaches. The different aircraft category responses were likely to have been due to high capacity aircraft having advanced automation capabilities and operating mostly in controlled airspace. Such aircraft were also more likely to have an FMS rather than a GPS unit.

The concern most respondents had regarding the design of RNAV GNSS approaches was that they did not use references for distance to the missed approach point on the approach chart and cockpit displays (in contrast to previous types of approaches). Other problems raised were short and irregular segment distances and multiple minimum segment altitude steps, that the RNAV GNSS approach chart was the most difficult chart to interpret, and that five letter long waypoint names differing only by the last letter can easily be misread. The most common incident reported with RNAV GNSS approaches was commencing the descent too early due to a misinterpretation of position.

It should be noted that at the time of this research, many GPS units displays only provided numerical data rather than a map view of the aircraft’s lateral position (such as with the GNS 430W). In addition, RNAV GNSS approaches have become more common and pilots have become more familiar with them, and the design of RNAV GNSS approach charts has improved.

Recorded flight data

General information

The aircraft was not fitted with a flight data recorder or cockpit voice recorder, nor was it required for the type of aircraft and operation.

The ATSB obtained data broadcast by the automatic dependent surveillance broadcast (ADS-B)[54] equipment fitted to the aircraft and GPS data from the pilot’s iPad with the OzRunways[55] application installed. The data included:

• timestamp
• latitude and longitude
• pressure altitude (from the ADS-B data) – rounded to the nearest 100 ft (for example, 498 ft would be rounded to 500 ft)
• GPS altitude (from OzRunways) – truncated to 100 ft (for example, 498 ft would be presented as 400 ft)
• groundspeed.

The lateral location (latitude and longitude) from OzRunways and ADS-B-based data were in close agreement. This indicated that the data from OzRunways was sufficiently reliable to show the aircraft’s lateral flight path.

The pressure altitude data from the ADS-B data was fairly consistently 100 ft higher than the OzRunways GPS height, which was partially due to the ADS-B data being rounded to the nearest 100 ft and the OzRunways data being truncated to the nearest 100 ft. In addition, the local QNH was 1,008.5 to 1,008.9 hPa during the period from 0900 to 0921, lower than the standard 1,013.25 hPa datum for pressure altitude. This would result in an altimeter set to the local QNH reading about 130–140 ft lower than the pressure altitude.[56] Thus, within the applicable errors, the altitudes from the 2 sources were consistent.

The OzRunways data points were provided at 5-second intervals, with some data points missing, and they covered the whole flight (including all of the 2 approaches), whereas the ADS-B data points were only available for parts of the approaches and/or were provided at less frequent intervals. As such, the OzRunways data is used in this report.

Figure 17 depicts the recorded data for the first and second approaches from the initial approach fix (IAF), through the intermediate fix (IF) and final approach fix (FAF) and to the missed approach point (MAPt). The top panel displays the aircraft’s altitude, the middle panel displays the lateral position, and the bottom panel displays the groundspeed. All distances on the horizontal axes are relative to the next waypoint, as would be displayed to the pilot on the GPS unit during the approach.

Figure 17: Recorded data for first and second approaches to Lockhart River

The upper panel shows altitude, the middle panel shows lateral deviation from the instrument approach path and the lower panel shows groundspeed. The purple bands on the groundspeed panel refer to the handling speeds (for indicated airspeed) specified in the Aeronautical Information Publication for a category B aircraft, such as the Cessna 404 (see Handling speeds).

Source: OzRunways data overlaid with Airservices approach information, annotated by the ATSB

Altitude during approaches

The top panel of Figure 17 shows the 3° approach path guidance (recommended descent profile) to the MAPt, which commenced from the initial approach altitude of 3,500 ft about 9.2 NM from the MAPt. As previously noted, the minimum descent altitude (MDA) was 730 ft unless the pilot had the required visibility. Key aspects regarding the recorded altitude data included:

• The first approach (in blue) was flown at or slightly above a 3° approach to the MAPt from significantly prior to the IAF until reaching 700 ft just prior to the MAPt. The average descent rate during the first approach from the IAF to the MAPt was about 720 ft/min.
• Although not indicated on the figure, the aircraft kept descending and reached a recorded altitude of 400 ft[57] at about 0.5 NM past the MAPt or 0.9 NM (1,700 m) before the runway threshold. It remained at that recorded altitude over 3 data points, or until it was 0.5 NM (900 m) from the runway threshold. The next 2 data points were not recorded, with the subsequent recorded data point indicating an altitude of 600 ft as the aircraft passed the runway threshold.
• ADS-B data was available for the latter part of the first approach, and this data indicated that the aircraft had still been descending when it reached the second of the 400-ft data points (0.7 NM or 1,300 m from the runway threshold), and had started climbing just before the third of the 400-ft data points (1,000 m from the threshold). The ADS-B data also provided recorded values of geometric altitude rate of change. This data indicated that just before and just after the MAPt the descent rate was about 900 ft/min, and at about the second 400-ft data point the descent rate was about 960 ft/min.
• The second approach (in red) was flown at about 3,500 ft prior to and after passing the IAF, with the aircraft starting to descend at about 0914:48 when about 2.7 NM from the IF. From about 1.6 NM prior the IF (at 0915:18 and an altitude of 3,300 ft), this descent was flown at about a 3° flight path, although about 1,000 ft below the recommended descent profile.
• The radio call commencing at 0915:50, when the pilot stated the position (10 NM) and altitude of the aircraft (3,800 ft then corrected to 2,800 ft), started about 0.4 NM prior to the IF. At 0915:58, about 0.2 NM prior to the IF, the aircraft was at a recorded height of 2,800 ft.
• For the second approach, the descent rate was about 700 ft/min during the descent from 3,300 ft to about 700 ft (at 0919:08 and 3.3 NM before the MAPt). From 700 ft until 100 ft, the descent rate was about 1,200 ft/min. Given this last part of the descent was over a 30-second period, it probably indicates an actual change rather than the effect of truncated data.
• During both approaches, there were several instances during descent where 2 data points in succession were at the same recorded altitude. There were also 2 occasions during the second approach where 3 data points in succession were at the same recorded altitude (at 700 ft and at 2,200 ft). Although this could indicate that the descent rate decreased to some extent at those altitudes, such patterns could also occur (at least in part) due to the data being truncated to the nearest 100 ft and the small amount of error associated with each GPS data point. A descent rate of about 700 ft/min would equate to about 60-ft difference every 5 seconds, whereas a descent rate of 600 ft/min would equate to about a 50-ft difference every 5 seconds.

Lateral position during approaches

Figure 17 depicts the lateral paths flown on the 2 approaches relative to the lateral track prescribed for the approach (shown as a dash-dot line). Dotted lines depict the full-scale CDI deflection on the Garmin GNS 430W and show the scale transitioning from 1 NM full-scale deflection during the intermediate approach segment to 0.23 NM full-scale deflection at the FAF, narrowing to 0.06 NM full-scale deflection at the MAPt. The aircraft’s position is based on GPS data; the actual CDI values displayed to the pilot were not recorded.

Key aspects regarding the lateral position data include:

• The flight paths for both approaches were consistent with the pilot hand-flying the aircraft, rather than the autopilot maintaining a programmed track.
• The first approach passed the IAF LHREB in the middle of the capture region for that waypoint. The whole approach was contained within half full-scale deflection of the CDI.
• For the second approach, the aircraft was just within the 180° capture region for the IAF LHREB when the pilot commenced the turn towards the IF LHREI (Figure 5). Prior to turning towards the initial approach track, the aircraft was on a track that was about 100° to the initial approach track.
• On the second approach, the turn onto the track between the IAF and the IF resulted in the aircraft initially being displaced full-scale CDI deflection to the right, which was corrected soon after. The aircraft was also turned slightly late at the IF and overshot the waypoint, before being corrected back to the intermediate approach track.
• About 3 NM before the FAF, the aircraft started deviating right of the intermediate approach track. About 2 NM before the FAF, the sensitivity of the CDI began increasing (as indicated by the dotted lines, see also Figure 17).
• When passing the FAF on the second approach, the aircraft was at about full-scale CDI deflection (0.23 NM to the right), and it continued deviating further right of the final approach track for 25 seconds before starting to return closer to the final approach track. The aircraft remained outside full-scale deflection in the final approach segment for about 55 seconds and outside half-full scale deflection for an additional 5 seconds. From about 17 to 32 seconds after passing the FAF, the aircraft’s deviation equalled or slightly exceeded 0.3 NM to the right of the final approach track (the lateral tracking tolerance specified in CAO 20.91 for the final approach track).
• The aircraft started to deviate left of the final approach track at about 2.5 NM prior to the MAPt and it continued left until the end of the recorded data. 

Groundspeed during approaches

Deriving an estimate of indicated airspeed from groundspeed involves considering several factors. In this case:

• The recorded wind at ground level indicated nil wind during the first approach and 3–4 kt from about 280° during the second approach. However, a review of wind and temperature forecast and analysis charts from multiple sources indicated that there would have been more wind at higher altitudes. Acknowledging that this was forecast and analysis data rather than recorded data, the ATSB estimated that there would have probably been about 10 kt headwind on the intermediate/final approach track at 2,300 ft and 5 kt at 1,000 ft. In addition, when the aircraft was heading towards the IAF on the second approach at 3,500 ft, and when the aircraft was heading from the IAF to the IF, there would have been a tailwind.
• Air pressure and temperature differences from a standard atmosphere meant that calibrated airspeed would have been lower than the true airspeed, with this difference increasing as the altitude increased. The difference was about 10 kt at 3,500 ft and 5 kt at 1,100 ft.
• The Cessna 404 Pilot’s Operating Handbook (POH) stated that the indicated airspeed at 140 kt was 1 kt higher than the calibrated airspeed with gear and flap up, 3 kt higher with gear down and flap selected to the take-off/approach position, and 5 kt higher with gear down and flap selected to the landing position. During the descent part of an approach, the operator’s flight profile stated the landing gear should be down and the flaps in the approach position (Flight profiles).[58]

Overall, the ATSB estimated that the indicated airspeed would have probably been close to (within 0 to +5 kt) of the recorded groundspeed during the 2 approaches while the aircraft was on or close to the intermediate/final approach track. For simplicity in this report, the groundspeed was considered to be equivalent to the indicated airspeed during these periods.

Key aspects of the recorded groundspeed (and estimated indicated airspeed) data for the 2 approaches include:

• The groundspeed (and estimated indicated airspeed) for the first approach was about 130–­140 kt for the whole approach between the IAF and the IF, and 130 kt at the FAF. It then increased to 140 kt before the aircraft reached 1,000 ft and then remained at about that speed as the aircraft passed through the MDA, passed the MAPt and passed the runway threshold.
• For the second approach, the groundspeed when the aircraft was heading toward the IAF was about 185 kt, but the indicated airspeed was about 160 kt. After making the turn towards the IF, the groundspeed was about 160 kt and the indicated airspeed was about 145 kt.
• Before commencing descent from 3,500 ft, at 0914:43, the groundspeed was about 150 kt and the indicated airspeed was about 135 kt. Soon after, there was a decrease in speed, which was probably associated with the pilot selecting approach flap and lowering the landing gear. The subsequent increase was probably associated with the aircraft’s descent.
• Between the IF and the FAF, the groundspeed (and estimated indicated airspeed) was about 135 kt. It increased to 140 kt soon after passing the FAF and, when the aircraft was 3 NM from the MAPt, the groundspeed increased to about 150 kt (associated with the aircraft’s increased descent rate).

Wreckage and impact information

The accident site was located on a sand bank adjacent to the beach, about 6.4 km (3.5 NM) south-east of the runway 30 threshold at Lockhart River Airport and 500 m to the south-west of the specified final approach track. This location was about 2.1 NM (3.9 km) from the missed approach point (MAPt).

The accident site was in line with the aircraft’s recorded track over the previous 3 data points. It was about 200 m beyond the last recorded data point (which had a recorded height of 100 ft), and its location indicated that the impact occurred less than 3 seconds after the last recorded data point.

The wreckage trail was spread over a distance of about 20 m from the initial impact point and the trail indicated that the aircraft was on a heading of about 280° (magnetic), with the impact point about 30 ft above mean sea level (Figure 18).

Figure 18: Overview of accident site

Source: ATSB

The ATSB’s on-site examination of the wreckage, damage to surrounding vegetation and ground markings indicated that at initial impact the aircraft was:

• upright and close to wings level
• at a flight path angle of about 5° nose down
• at relatively high speed.

An area of foliage around the aircraft displayed signs of chemical burn from avgas, indicating that the aircraft had a significant amount of fuel on board. There was no evidence of any structural or mechanical defects, but the examination was limited by the extensive damage.

The damage to the recovered propellor blades indicated significant rotational energy at impact consistent with both engines operating normally with substantial power.

The landing gear was extended at the time of impact. Other aircraft configuration information such as flap position, trim settings and switch selections could not be validated due to the impact damage.

The only components on the aircraft that may have recorded data were a digital fuel flow indicator/totaliser and a transponder, and the ATSB recovered these components. After consideration of the damage to these components and the potential value of any data, no further examination was undertaken.

Survivability aspects

Given the aircraft’s speed at impact (about 150 kt or 278 km/h) and the resultant impact forces (as evidenced by the nature of the wreckage), the accident was not considered survivable.

The aircraft was not fitted with a fixed emergency locator transmitter (ELT), nor was it required to be under the current regulations. A personal locator beacon (PLB) was in the pilot’s flight bag. Post-accident onsite examination noted it was within its expiry date and it passed a function test. PLBs do not have an inertial g-switch to automatically switch them on when an accident occurs, so the PLB did not activate during the accident sequence.

At 0934 and 0938, air traffic control (ATC) attempted to contact the pilot of VH-OZO after they had not cancelled or amended the SARTIME[59] of 0930. ATC also requested that the pilot of an inbound aircraft attempt to contact VH-OZO on the CTAF.

At 0939, an INCERFA was declared (which is a situation where uncertainty exists regarding the safety of an aircraft and its occupants) and soon after ATC transferred management of the situation to the Joint Rescue Coordination Centre (JRCC). At 1020, the JRCC advised ATC that it had declared a DETRESFA or distress phase (which is a situation where there is reasonable certainty that an aircraft and its occupants require immediate assistance). At 1251, the JRCC advised the ATSB that the wreckage at been located.

Organisational information

Air Connect Australia

Air Connect Australia was issued with an Air Operator’s Certificate (AOC) by the Civil Aviation Safety Authority (CASA) in March 2017 with an expiry date of 31 March 2020. It authorised the certificate holder to operate Cessna C310/340, C404, C402/421 and Raytheon Baron/Travelair twin piston-engine aeroplane types as well as single piston-engine aeroplane types with a MTOW not exceeding 5,700 kg on charter and aerial work operations.

At the time of the accident, CASA was assessing the operator’s application to renew the AOC, which was subsequently issued on 1 May 2020 with an expiry date of 30 September 2023.

From April 2017, the operator dry-leased VH-OZO from the aircraft owner, who was based in Western Australia. In this arrangement, the aircraft owner was responsible for the continuing airworthiness of the aircraft and the operator managed the operational aspects, such as fuel and flight crew.

Initially the operator’s personnel consisted of a chief pilot and the managing director, who was also the head of aircraft airworthiness and maintenance control. The chief pilot and managing director were the operator’s only line pilots. The chief pilot left in 2018, and the manager director became the chief pilot following an assessment by CASA.

In the 18 months prior to the accident, VH-OZO was the only aircraft operated and the operator employed one pilot (the pilot of the accident flight) additional to the chief pilot. As previously stated, the pilot of the accident flight conducted most of the operator’s flights.

Operator proficiency checks

To conduct IFR flights in a multi-engine aircraft, a pilot was required to complete an instrument proficiency check (IPC) every 12 months. The checks had to be conducted by a CASA-approved flight examiner. There were no additional requirements for proficiency checks for pilots conducting passenger charter operations under the IFR unless the operator had a check and training organisation as specified in Civil Aviation Regulation 217 (Training and checking organisation), which did not apply to operators such as Air Connect Australia.

CASR Part 135 (Australian air transport operations—smaller aeroplanes) was registered in December 2018 and commenced on 2 December 2021. It included a requirement for operators to conduct proficiency checks on pilots, with the requirements for such checks to be specified in the Manual of Standards (MOS). The draft Manual of Standards (MOS) for Part 135, publicly consulted in September 2018, included specific requirements for recurrent proficiency checks. For operators conducting IFR flights or flights at night, an operator proficiency check (OPCs) was required about 6 months after commencing unsupervised line operations for the operator and subsequently at intervals of 6 months. The MOS for Part 135 that came into effect in December 2021 had effectively the same requirements (with an OPC now called a ‘flight crew member proficiency check’).

Version 2 of the operator’s operations manual (February 2018) required an OPC to be conducted ‘every year’, with another section stating these needed to be completed ‘within the previous 12 months’. Version 3 of the manual (February 2020) required an OPC be conducted at the chief pilot’s discretion at periods not exceeding 24 months.[60] The manual stated that the OPC could be conducted by the chief pilot or a designated flight examiner.

The chief pilot noted that the flight examiner who regularly conducted IPCs for the operator (and was designated to conduct OPCs) would effectively conduct an OPC when they did an IPC. The change to every 24 months was done to provide more flexibility for scheduling checks.

In terms of the nature or content of the OPC, the operations manual stated that an OPC was required to be conducted

…on a flight encompassing all operations in which the pilot would normally be engaged. These flights will cover flight planning, refuelling, aircraft weight and balance, passenger briefing, forced landings and all emergency operations.

The manual also included an OPC form, which listed 23 items to be evaluated.

As previously discussed (Qualifications and experience), after the pilot of VH-OZO was cleared for line operations on 29 October 2018 (which included an OPC), the operator did not conduct any OPCs on the pilot. In addition, the chief pilot did not conduct any flights with the pilot after October 2018.

The pilot’s IPC in August 2019 was conducted with a flight examiner who was not familiar with the operator’s operations manual and therefore did not cover all aspects of an OPC, and the additional supervised training in December 2019 for night recency was done by an external provider and did not evaluate line operations.

Monitoring of pilot recency

CASR Part 61 outlined several different recency requirements. With relevance to the accident flight, these included a pilot not being able to:

• conduct a flight with passengers by day in a particular category of aircraft unless had conducted 3 take-offs and landings within the previous 90 days in that category of aircraft (CASR 61.395 (1))
• conduct a flight under the IFR unless had conducted at least 3 instrument approaches within the previous 90 days (CASR 61.870 (2))
• conduct a flight under the IFR in a particular category of aircraft unless had conducted at least 1 instrument approach in the previous 90 days in that category of aircraft (CASR 61.870 (3))
• conduct a 2D instrument approach unless had conducted at least one such approach in the previous 90 days (CASR 61.870 (4))
• conduct a flight under the IFR in a single-pilot operation unless had conducted at least one single-pilot flight under the IFR in the previous 6 months that had a duration of at least 1 hour and involved one instrument approach (CASR 61.875).

The CASA website stated:

We use recent experience requirements to maintain a pilots knowledge and skills when conducting instrument approach operations.

When conducting an approach to satisfy a recent experience, pilots should recognise the purpose of the approach is to maintain their competency to conduct such operations.

Simulating IMC, when safe to do so, will enhance the purpose of the approach. Conducting the approach provides some effective practice…

As previously noted, the pilot had been regularly logging the conduct of RNAV GNSS approaches (Qualifications and experience) as well as other types of instrument approaches. The pilot met all required recency requirements listed above.

The operator used the Aerotrack aviation management tool. The tool could be used to manage flight scheduling, fleet operations, and crew recency and rostering to meet regulatory requirements. It also created an online pilot logbook, as it tracked all flights conducted for the operator, and totalled recency requirements such as IFR flight time and instrument approaches.

The Aerotrack system correctly tracked all of the recency requirements except for CASR 61.875. The system tracked the total number of single-pilot IFR flight hours over a rolling 6-month period, calculated as a sum of all hours logged including partial hours (such as 0.5 hours).[61] However, it was not programmed to track if a single-pilot flight under the IFR (of at least 1 hour duration) was conducted.  

Regulatory oversight

In June 2017, CASA conducted a level-1 surveillance event on Air Connect Australia. CASA concluded that the operator was:

an overall compliant organisation with sufficiently equipped facilities and suitable qualified personnel conducting operations in accordance with its legislative authorisations and responsibilities.

The audit identified 5 non-compliance notices, including 3 relating to operations manual content regarding transponders, daily inspections and oil consumption records, and 2 relating to incomplete staff induction records for one pilot and the emergency proficiency checks for one pilot carried out by a person who was not the chief pilot. Other findings included 2 observations relating to job descriptions and one aircraft survey report finding. These findings were addressed by the operator.

In June 2018, CASA conducted a level-2 airworthiness and maintenance system surveillance activity relating to VH-OZO, prior to a flying operations inspector flying on the aircraft for the purpose of a chief pilot assessment. The surveillance report found there were no anomalies identified in either the technical documentation assessment or the physical inspection of the aircraft and the chief pilot assessment was then conducted.

In February 2020, CASA conducted a desk-top surveillance activity to determine if the AOC could be subsequently re-issued. The surveillance considered the organisation’s surveillance and compliance history, the management structure and operational oversight effectiveness. The review did not indicate any matter that would preclude a subsequent issue of the organisation’s AOC.

In May 2020, CASA conducted a post-accident regulatory and safety review. This review concluded that VH-OZO was correctly registered, certified for flight, maintained by qualified people, flown by a qualified person to a qualified aerodrome using a correctly validated approach. The review stated that past and current surveillance events had not detailed safety concerns with the operation of VH-OZO.

Operational information

Pre-flight planning and in-flight monitoring

Civil Aviation Regulation 239 (Planning of flight by pilot in command) stated:

Before beginning a flight, the pilot in command shall study all available information appropriate to the intended operation, and, in the cases of flights away from the vicinity of an aerodrome and all I.F.R. flights, shall make a careful study of:

a. current weather reports and forecasts for the route to be followed and at aerodromes to be used;

b. the airways facilities available on the route to be followed and the condition of those facilities;

c. the condition of aerodromes to be used and their suitability for the aircraft to be used; and

d. the air traffic control rules and procedure appertaining to the particular flight;

and the pilot shall plan the flight in relation to the information obtained.

AIP ENR 1.10 (Flight Planning) also stated these requirements. In addition, it stated a pilot was required to review NOTAMs[62] applicable to the flight.

At 1326 on the day before the accident flight, the pilot accessed a location briefing for Lockhart River from the National Aeronautical Information Processing System (NAIPS) via an electronic flight bag (EFB) application. This type of briefing typically displayed current forecasts, reports, and ‘notice to airmen’ (NOTAM) applicable to the nominated location.

Later that day, at 1830, the pilot requested grid point wind and temperature charts (GPWT) and a specific pre-flight information bulletin (SPFIB) from NAIPS via flight planning software. The SPFIB request was for Cairns to Lockhart River and return with the estimated time of departure nominated as 1930 the same day. This bulletin was valid until 1830 on the day of the accident.

A printout of the SPFIB found at the accident site showed aerodrome forecast (TAF) and weather reports (METAR) for Cairns. The weather for the next day (day of accident flight) at Cairns Airport was expected to be a visibility of 10 km or greater and showers of light rain with scattered cloud at 1,800 ft in the morning lifting to 2,500 ft. In addition, the forecast imposed a TEMPO for the next day to specify periods of visibility reduced to 2,000 m with showers of moderate rain and broken cloud at 1,000 ft.

On the printout of the SPFIB, a METAR for Lockhart River for 1800 (10 March 2020) showed light winds, visibility 10 km or greater and nil cloud detected. Since 0900 that morning, recorded rainfall was 1.8 mm.

No TAF was provided on the SPFIB for Lockhart River as the time of the request was outside the issue and validity period. There were no predicted outages of global positioning system/global navigation satellite system (GPS/GNSS) capability for Cairns or Lockhart River. NOTAM information included a change to Lockhart River runway distance and gradient data and no other notices with significance for the planned flight.

After the SPFIB was received, at 1942, the pilot submitted a flight notification for the planned departure from Cairns at 0730 the next morning to Lockhart River followed by a departure at 1430 for the return sector. Both sectors were planned under IFR with nominated capability for instrument approaches using GPS/GNSS equipment.

After the pilot requested the SPFIB and submitted the flight notification on the evening before the accident flight, there was no record of further requests for meteorological information from NAIPS. Such information was also available from the Bureau of Meteorology website and other sources without any user registration requirements. The ATSB was advised that the pilot was aware of the current weather forecasts for Lockhart River and Cairns on the morning before the flight.  

A damaged and partly illegible copy of the pilot’s flight plan/log was found at the accident site. This was a printout from flight planning software showing key navigational data and pilot notes on progress of the flight. There was no indication of any operational abnormalities.

Fuel calculations

On the morning of the flight, the pilot refuelled the aircraft with 650 L of avgas. A tabulated fuel plan showed 1,040 L on board at engine start at Cairns and expected fuel consumption of 285 L for the planned 94-minute flight to Lockhart River. The pilot had included provision for 45 minutes fixed reserve (124 L), 40 L variable reserve and 60 minutes holding (110 L) if required (consistent with the forecast TEMPO conditions in the TAF, see Aerodrome forecasts). If the variable reserve and holding allowance was consumed on the outbound sector (in addition to the calculated flight fuel), the remaining 605 L was sufficient to return to Cairns with allowance for 60-minutes holding on arrival.

In summary, the aircraft had sufficient fuel to conduct the flight from Cairns to Lockhart River and return, with additional fuel for holding on both sectors if required. The pilot was probably not intending to refuel at Lockhart River, although avgas was available if required.

Weight and balance

The pilot completed the operator’s passenger/cargo manifest form and calculated the aircraft’s weight and balance with reference to individual passenger weights and baggage. The take-off weight was recorded as 3,678 kg and nominal landing weight as 3,366 kg (7,421 lb). The aircraft’s maximum take-off weight was 3,810 kg and maximum landing weight was 3,674 kg. The graphical trimsheet showed the centre of gravity was within limits throughout the flight.

A copy of the operator’s in-flight monitoring form was found at the accident site. When the pilot completed the form in cruise at 10,000 ft, all of the recorded engine parameters for each engine were comparatively similar with no indication of any aircraft-related problems.

Communications during approaches

The AIP (ENR 1.1, 10.1) recommended radio calls at an uncontrolled aerodrome. These included:

• the pilot being inbound to an aerodrome (10 NM or earlier, commensurate with aeroplane performance and pilot workload, with an estimated time of arrival)
• during an instrument approach:
  • departing the FAF or established on the final approach segment (including details of position and intentions)
  • terminating the approach or commencing the missed approach (including details of position and intentions).

The Air Connect Australia operations manual stated the following for communications at non-towered aerodromes:

When operating within the vicinity of a non-controlled aerodrome, a known training area or authorised low flying area, Company pilots are to broadcast their intentions, listening out and communicate with any possible conflicting aircraft in accordance with the requirements of the AIP. 

Additionally, for straight-in approaches at non-towered aerodromes, the manual stated:

• Monitor / broadcast on CTAF shall be made by 10 NM and include aircraft type, position, callsign and include the intention to make a straight-in approach.
• Monitor / broadcast at 3 NM that the aircraft is established on the final approach.

During both of the approaches at Lockhart River, the pilot of VH-OZO made broadcasts when at 10 NM (that is, at about the IF). During the first approach, the pilot also made a broadcast at 5 NM (at the FAF) and during the missed approach. There was no call recorded when the aircraft was at 5 NM on the second approach.

Electronic flight bag and approach charts

During the flight, the pilot was using an iPad with an electronic flight bag (EFB) application (OzRunways) and was carrying a second iPad as a backup. The operator’s operations manual (section 2A1.3.2.2) stipulated that all EFB devices permitted for use were class 1 (portable electronic device) and functionality level 1, which meant that it could be one or more of the following:

1. held in the hand
2. mounted on an approved mount
3. attached to a stand-alone kneeboard secured to a flight crew member
4. connected to the aircraft power for battery re-charging
5. connected to an installed antenna intended for use with the EFB for situational awareness but not navigation.

Furthermore, unless secured in accordance with b or c above, the EFB was required to be stowed during take-off, landing, instrument approach and when flying less than 1,000 ft above terrain. It was also only to be used:

…as a source of navigational data e.g. Departure and Approach plates and airport information.

The operator did not have an approved mount for the iPad. Accordingly, the operator required paper approach charts to be used when conducting an instrument approach. The chief pilot stated that the pilot subscribed to the departure and arrival procedure charts published by Airservices Australia. There was a clamp on the control column where a paper approach chart could be placed (Figure 8). There were no paper approach charts identified at the accident site, although the flight plan/log was found. Due to the disruption of the wreckage, it could not be determined whether the pilot carried the paper charts on board.

A friend of the pilot stated that they had provided the pilot with a mounting device that could be used to mount an iPad on a control column. The pilot’s iPad EFB was on[63] during the approach, however there were differing reports about how the pilot used the iPad during previous flights and whether it was mounted on the control column, placed on their knee or placed on the vacant seat next to the pilot. Due to disruption of the aircraft in the accident, only the second (backup) iPad was found at the accident site.

Flight profiles

The operator’s operations manual included flight profiles to be used for various situations for the Cessna 404, and stated that the profiles were required to be used for all operations. The prescribed flight profile for an RNAV GNSS approach (and other straight-in instrument approaches) is shown in Figure 19.

The indicated airspeed was required to be below 180 kt at the IAF and at 130 kt (+ or - 5 kt) at the start of the descent after passing the IAF (with the landing gear down and approach flap selected). The airspeed was also required to be V_ref to V_ref +10 kt at the FAF. As noted in Configurations and speeds, the V_ref at maximum landing weight (8,100 lb) for the Cessna 404 was 91 kt and at weights 7,500 lb and below was 88 kt. In effect, the operator’s flight profile requirement to be at V_ref to V_ref + 10 kt at the FAF equated to an indicated airspeed of about 90–100 kt.

Figure 19: Flight profile for Cessna 404 RNAV GNSS approach

In another section titled ‘Final approach & threshold speeds’, the operations manual stated:

• The [pilot] shall conduct the final approach in accordance with the stabilised approach criteria… [see next section]
• CAT B: Speeds 91 – 120 kts. Initial / Intermediate 120 – 180 kts. Final app 85 – 130 kts. Visual circling 135 kts. Max speed for Missed Approach 150 kts.

These were the ‘handling speeds’ referred to the AIP for instrument approaches for a category B aircraft, such as the Cessna 404 (see Handling speeds). In effect, these speeds meant that the maximum allowed indicated airspeed after passing the IAF for the Cessna 404 was 180 kt and the maximum airspeed after passing the FAF was 130 kt.

The chief pilot recalled that the flight profiles were included in the operations manual by the previous chief pilot, who had based them on profiles used by another operator. The chief pilot stated that they advised the pilot of the accident flight to be at about 5,000 ft at the start of an approach (at the IAF) and then use a continuous descent to the runway from the IAF, and they demonstrated this to the pilot during their supervised flying in October 2018.

The chief pilot recalled that, when they flew the aircraft, they would select approach flap and landing gear early in the descent and be stabilised at a speed of 120 kt and a descent rate of 600 ft/min[64] well before the FAF. The chief pilot stated that the speed at the FAF should be about V_ref + 20 kt (which equates to about 110 kt) but that the 100 kt specified in the flight profile would be acceptable. They stated that 130 kt at the FAF was too fast.

The previous chief pilot also recalled that the operator’s flight profile was most likely obtained from another operator. They noted their recollection of speeds was limited given the time since they flew the aircraft, but they recalled that they would be at least at V_ref + 10 kt (that is, 100 kt) but not faster than 120 kt at the FAF, then slowing the aircraft down by 1,000 ft.

The flight examiner regularly used by the operator also worked with another operator of Cessna 404 aircraft (which was a different operator to that referred to by the previous chief pilot). The examiner stated that at the IF they would normally be at 130 kt with gear down and approach flap selected. The normal speed they used at the FAF was 110 kt (V_ref + 20 kt), and 100 kt would be a little slow at that point on the approach. The examiner advised that these speeds were also used by the other Cessna 404 operator.

In summary, the ATSB concluded that the operator’s published flight profile speed of 90–100 kt at the FAF was probably not the operator’s preferred speed during flight operations. Rather, it appeared that the preferred speed at the FAF was probably about 110 kt. However, the extent to which this was clearly communicated to the pilot of the accident flight could not be determined.

Stabilised approach criteria

Guidance regarding stabilised approach criteria

A stabilised approach is one in which all criteria specified in the operations manual are met, at or before the applicable height or reference point. The Flight Safety Foundation (FSF) has for many years recommended that operators have stabilised approach criteria. Detailed guidance was provided by the FSF in its approach and landing accident reduction (ALAR) briefing note 7.1 (Stabilized approach, 2000a). The recommended criteria were summarised in a list, as reproduced in Figure 20.

Figure 20: FSF recommended elements of a stabilised approach

Source: ALAR briefing note 7.1  (Flight Safety Foundation 2000a)

The FSF briefing note also stated:

The flight crew must “stay ahead of the aircraft” throughout the flight. This includes achieving desired flight parameters … during the descent, approach and landing. Any indication that a desired flight parameter will not be achieved should prompt immediate corrective action or the decision to go around.

The minimum stabilization height constitutes an approach gate on the final approach; a go-around must be initiated if:

• The required configuration and airspeed are not established, or the flight path is not stabilized when reaching the minimum stabilization height;
• The aircraft becomes unstabilized below the minimum stabilization height.

ICAO Annex 6 Part I applied to international commercial air transport operations in aeroplanes. Since 1998, it included a standard stating an operator’s operations manual had to include stabilised approach procedures.

ICAO document 8168 (Procedures for Air Navigation Services, Aircraft Operations, known as PANS-OPS) provided recommendations on procedures for flight crew. Since 2001, PANS-OPS included content on stabilised approaches and stabilised approach criteria. It stated:

Studies have shown that the risk of controlled flight into terrain (CFIT) is high on non-precision approaches. While the procedures themselves are not inherently unsafe, the use of the traditional step down descent technique for flying non-precision approaches is prone to error, and is therefore discouraged. Operators should reduce this risk by emphasizing training and standardization in vertical path control on non-precision approach procedures…

Operators should use the CDFA (continuous descent final approach) technique whenever possible as it adds to the safety of the approach operation by reducing pilot workload and by lessening the possibility of error in flying the approach…

This technique requires a continuous descent, flown either with vertical navigation (VNAV) guidance calculated by on-board equipment or based on manual calculation of the required rate of descent, without level-offs. The rate of descent is selected and adjusted to achieve a continuous descent to a point approximately 15 m (50 ft) above the landing runway threshold or the point where the flare manoeuvre should begin for the type of aircraft flown...

The guidance document also stated:

The primary safety consideration in the development of the stabilized approach procedure shall be maintenance of the intended flight path as depicted in the published approach procedure, without excessive manoeuvring.

PANS-OPS stated the types of information that should be included in stabilised approach criteria (such as speeds, minimum power settings, attitudes, crossing altitude deviation tolerances, aircraft configuration, maximum sink rate and competition of checklists and briefings). In addition, the document stated that an operator’s procedures should include, as a minimum:

a) that in instrument meteorological conditions (IMC), all flights shall be stabilized by no lower than 300 m (1 000 ft) height above threshold; and

b) that all flights of any nature shall be stabilized by no lower than 150 m (500 ft) height above threshold.

Although the FSF and ICAO guidance may be considered most applicable to larger air transport aircraft with multi-crew operations and turbine engines, similar guidance (with the same applicable heights of 1,000 ft for operations in IMC and 500 ft for operations in VMC) has also been widely recommended for operations in smaller aircraft (Appendix D – Guidance to industry regarding stabilised approaches). This guidance has emphasised the benefits of using a CDFA technique with stabilised approach criteria in terms of reducing workload and increasing the time to monitor, detect and react to problems.

In Australia, since 2014, the Civil Aviation Advisory Publication (CAAP) 215-1 (Guide to the preparation of operations manuals) stated that an operator’s manual should include stabilised approach criteria in its section on approach and landing procedures. Guidance regarding applicable heights or reference points for such criteria were not specified in the CAAP or other CASA guidance documents.[65]

CASA advised the ATSB that specific Australian guidance was not provided prior to 2021 since there was no direct legislative requirement for operators to use such criteria, and it was considered that there was readily available and significant global guidance on this topic available from a wide range of authoritative sources.

Operator’s stabilised approach criteria

The Air Connect Australia operations manual stated:

Stabilised Approach Criteria are as follows:

(a) All flights, other than training flights, must be stabilised by 300 feet above aerodrome elevation in both IMC and VMC.

(b) An approach is stabilised when the following criteria are met:

• The aircraft is on the correct flight path;
• Only small changes in heading and pitch are required to maintain the correct flight path;
• The aircraft is not more than V_ref + 20 kts and not less than V_ref indicated airspeed
• The aircraft is in the correct landing configuration;
• Sink rate is no greater than 1000 fpm [ft/min];[66] if an approach requires a sink rate greater than 1000 fpm, a special briefing should be conducted;
• Power setting is appropriate for the aircraft configuration and is not below the minimum power for approach as defined by the aircraft operating manual;
• All briefings and checklists have been conducted;
• Instrument approaches are stabilised by the final approach fix, if they also fulfil the tracking requirements – established within ‘half scale deflection’ for the ILS, VOR and GNSS, within + or – 5 degrees for the NBD; during a circling approach, wings should be level on final by 300 feet above aerodrome elevation;
• Unique approach procedures or abnormal conditions requiring a deviation from the above elements of a stabilized approach require a special briefing.

Missed Approach Procedure is as follows:

(a) Other than on training flights, an approach that is not stable below 300 feet aerodrome elevation in both IMC and VMC requires an immediate GO-AROUND. The procedure for a go around / missed approach is as follows:

• Should be flown as per the approach chart missed approach procedure, or as advised by ATC;
• The aircraft handling technique will be as per the relevant AFM for the appropriate aircraft…

The manual further stated:

If an approach does not meet the criteria for a stabilised approach…, the Pilot-in-Command shall conduct a missed approach.

To meet these stabilised approach criteria, the maximum indicated airspeed in a Cessna 404 needed to be V_ref + 20 kt or about 110 kt at 300 ft above aerodrome elevation.

The chief pilot advised the ATSB that the published applicable height of 300 ft was too low to be effective, as it was normally below the MDA. They believed approaches should be stabilised much earlier, ideally at height of about 1,000 ft or even earlier. The chief pilot also stated that all configuration changes should be done early in the approach, with only the selection of landing flap to be completed late in the approach at the pilot’s discretion. The flight examiner used by the operator noted that stabilised approach criteria for most piston twin-engine and single-engine aeroplanes needed to acknowledge that the last stage of flap (or landing flap) should generally not be selected until about 300 ft due to aircraft performance considerations.

The chief pilot also recalled that they had discussed the importance of being stabilised early in the approach to the pilot of the accident flight on multiple occasions, and they had stated the importance of conducting constant angle descents down to the MDA at 600 ft/min. The chief pilot also noted that they had emphasised to the pilot the importance of gradual reductions in power and therefore speed during approaches in order to minimise undesirable cylinder head temperatures, and use slow descent rates for passenger comfort. 

Additional information

During its investigation into the 2005 CFIT accident of a Metro aircraft at Lockhart River involving an operator that conducted passenger transport operations in Metro turboprop aircraft, the ATSB identified that that operator did not have stabilised approach criteria.[67] Of 5 other operators conducting operations in Metro aircraft, all had stabilised approach criteria, with 1 having an applicable height of 200 ft, 2 having an applicable height of 300 ft and 2 having an applicable height of 1,000 ft.

The ATSB also identified that an operator conducting passenger transport operations in a DHC-8 aircraft in 2012 had stabilised approach criteria based on an applicable height of 300 ft.[68] In addition, during another investigation commenced in 2021, the ATSB recently identified another operator of turboprop aircraft conducting passenger transport operations (charter) that had stabilised approach criteria with an applicable height of 300 ft. The ATSB has also identified that major airlines and some operators of single-pilot IFR operations in Australia have criteria based on 1,000 ft above ground level in IMC.

Prior missed approach during an RNAV GNSS approach (22 January 2020)

A review of the pilot’s logbook identified one other flight since the pilot joined the operator that involved 2 instrument approaches (and therefore a missed approach following an instrument approach). This occurred on a flight from Weipa to Aurukun, Queensland, on 22 January 2020, after which the pilot logged 2 RNAV GNSS approaches. Recorded data confirmed that the pilot conducted 2 approaches to runway 34 at Aurukun.

Analysis of the weather conditions and interviews with the passengers identified that there was a storm in the vicinity at the time, and interviews and recorded flight data indicated that the pilot was trying to avoid the weather. The passengers recalled observing the pilot using the onboard weather radar as well as an iPad with the weather on it to track the movement of the storm.

Passenger recollections regarding the weather during the first approach were varied; some recalled that they could not see the runway at times whereas others recalled the runway was still visible though restricted. The ground appeared to be visible most of the time. Images taken by a passenger during the first approach confirmed that there was significant cloud in the area though the ground could be seen to the left of the aircraft.

Review of the recorded flight data indicated that, on the first approach, the aircraft commenced descent on the recommended descent profile from about 1,600 ft, slightly below the initial approach altitude of 1,800 ft. The aircraft passed the FAF at an indicated airspeed of about 140 kt, and it was about 200–300 ft below the recommended descent profile when it passed the MDA at an indicated airspeed of about 145 kt. The aircraft descended to a recorded altitude of about 200–300 ft (at about 140 kt) before starting to climb.

The missed approach did not conform to the published missed approach procedure, with the aircraft flying to the right of the MAPt rather than maintaining the runway heading. However, the conditions may have been visual at this time. After the missed approach, the pilot circled for some time, remaining in VMC and waiting for the storm to pass, before conducting a second approach (about 31 minutes after the first approach). Images taken by a passenger during the second approach confirmed that the weather conditions were significantly better than on the first approach.

The exact reasons for the missed approach could not be determined (that is, whether it was due to reduced visibility of the runway or also due to the aircraft’s speed not meeting the operator’s stabilised approach criteria at 300 ft above aerodrome elevation).

Further details of these 2 approaches are provided in Appendix E – Aurukun incident flight – 22 January 2020.

Review of the pilot’s recent RNAV GNSS approaches

General aspects

The ATSB reviewed the available recorded data for the pilot’s flights in the previous 6 months for which the pilot had logged an RNAV GNSS approach (that is, 21 approaches). Recorded data was available for 16 of these approaches. Of these 16 approaches:

• 10 involved straight-in approaches to the runway
• 5 were flown to past the FAF and then a circling approach was flown from above the specified circling minima to the opposite (reciprocal) runway
• 1 was not an RNAV GNSS approach as it did not fly near the designated waypoints (and it was therefore not considered for further analysis).

Based on a review of available weather information, all 21 approaches were very likely conducted in VMC except for the first approach conducted at Aurukun on 22 January 2020 (which was potentially in IMC for a brief period). For those approaches conducted in VMC, the pilot was not specifically required to conduct an RNAV GNSS approach, except for the purpose of meeting recency requirements.

The published approach charts for all the approaches had 5 NM segments between the IAF and IF, IF and FAF, and FAF and MAPt. Most of the approaches were conducted at locations where the recommended descent profile commenced at about the FAF, except for one approach to runway 11 at Cooktown (where the recommended descent profile commenced at the IAF).

Vertical profiles

For most of the 15 RNAV GNSS approaches with recorded data available, the data showed the pilot typically descended to about 5,000–5,300 ft and then levelled out for a short period prior to the IAF. When passing the IAF, the pilot commenced a continuous descent to join the approach’s recommended descent profile on about a 3° approach.

The only exceptions to this method were the 2 approaches conducted at Aurukun on 22 January 2020 (when the pilot commenced descent on the approaches from close to the published initial approach altitude of 1,800 ft). As noted in Recorded flight data, the second approach at Lockhart River during the accident flight was also commenced at a lower altitude (that is, the published initial approach altitude of 3,500 ft) when the aircraft was between the IAF and the IF).

In general, the approaches were conducted close to the recommended descent profile. The only exception was the first approach at Aurukun on 22 January 2020, which reached the MDA about 200–300 ft below the recommended profile.

Lateral positions

The pilot generally entered each approach via the nearest of the 3 IAFs. In most cases, the aircraft passed the IAF from close to the middle of the capture region for that waypoint, or at least on a track that was less than 45° difference to the initial approach track. On one approach (at Cooktown), they entered from a similar position as the second approach at Lockhart River, although from about 65° right of the extended initial approach track to the IAF labelled ‘A’ (as opposed to about 100° at Lockhart River).

For all the straight-in runway approaches (except the second approach at Lockhart River), the aircraft remained close to the intermediate approach track and final approach track. In most cases, the aircraft also remained close to the initial approach track. The only exceptions were:

• the Cooktown approach (when the aircraft flew over the IAF then, while descending, deviated left of the initial approach track by 0.9 NM and remained left until close to the IF)
• the first approach at Aurukun on 22 January 2020 (when the pilot commenced the approach from slightly more than 1 NM west of the IAF and flew direct to the IF from that position, while remaining close to the initial approach altitude).

Indicated airspeeds

The ATSB reviewed the indicated airspeeds during the pilot’s 8 previous straight-in RNAV GNSS approaches to evaluate their consistency with the operator’s speed requirements and preferences, and these were compared with the 2 approaches at Lockhart River on the day of the accident (Figure 17). The 8 other approaches included the 2 approaches conducted at Aurukun on 22 January 2020 (Figure 25), and 6 other approaches that the pilot conducted from December 2019 to February 2020 and logged as RNAV GNSS approaches.

For the 10 approaches, the ATSB estimated the indicated airspeeds based on the recorded groundspeed, forecast and analysis wind charts and other relevant information. The actual wind speeds above the aerodrome on each occasion were not known, and as a result there could have been some differences between the estimated indicated speeds and the actual indicated airspeeds.

The results for key points on the approaches are shown in Table 4. In general terms:

• In all 10 cases, the approaches did not exceed (and were well below) the maximum AIP handling speed of 180 kt in the initial and intermediate approach segments.
• In all 10 cases, the approaches exceeded the operator’s preferred speed of 110 kt at the FAF. Most of the approaches were about 130–140 kt at the FAF, and 7 of the approaches appeared to exceed the maximum AIP handling speed of 130 kt at or after passing the FAF by 10 kt or more.
• In most cases, the approaches appeared to be close to the operator’s maximum stabilised approach speed of 110 kt at or approaching 300 ft. However, in 3 cases there was a significant exceedance. These included the first approach at Aurukun on 22 January 2020 (which was followed by a missed approach), and the 2 approaches at Lockhart River (with the first followed by a missed approach).

Table 4: Summary of estimated indicated airspeeds during the pilot’s recent RNAV GNSS approaches (in kt)[69]