Control issues

Investigation summary

What happened

On 20 September 2025, the pilot of a Cessna 208 aircraft, registered VH-DVS, was conducting parachute operations for Far North Freefall Club at Tully Airport, Queensland. After successfully completing 2 parachute drops that morning, at 0950 local time the aircraft took off for the third load of the day with 17 parachutists on board. The plan was for the parachutists to conduct a 16-way formation filmed by a parachuting camera operator.

After the aircraft climbed to about 15,000 ft, the pilot signalled to the parachutists to exit. The camera operator stepped out onto a small step and held on to the fuselage outside and aft of the cabin door. As the first parachutist (P1) stepped out the door to assume the most forward (front float) position, their reserve parachute inadvertently deployed, dragging P1 backwards and dislodging the camera operator into freefall, causing them a minor injury. P1’s legs were injured as they struck and damaged the aircraft’s horizontal stabiliser. The parachute wrapped around the horizontal stabiliser and the elevator, suspending P1 beneath it. 

Thirteen parachutists exited the aircraft and 2 remained in the doorway, watching as P1 used a knife to cut sufficient reserve parachute lines to enable the parachute to tear free. P1 then deployed their main parachute, which tangled with the remnants of the reserve parachute. P1 was able to untangle the lines and regain sufficient control of the main parachute to land without further incident.

Despite control difficulties due to substantial damage to the horizontal stabiliser and part of the reserve parachute wrapped around the tail, the pilot safely landed the aircraft at Tully Airport.  

What the ATSB found

The ATSB found that as the first parachutist climbed out of the aircraft and into the front float position, their reserve handle snagged on the aircraft's flap, resulting in deployment of the reserve parachute. The parachute wrapped around the now-damaged tailplane, resulting in aircraft control difficulties.

The ATSB also found that, although it did not contribute to the accident, the pilot and aircraft operator did not ensure the aircraft was loaded within its weight and balance envelope. 

Furthermore, the ATSB found that the parachutists opened the roller door and clipped it open before exiting the aircraft. As a result, the roller door remained open during the descent, increasing the ease with which the pilot could have exited the aircraft if needed. Although not mandatory at the time of the accident, the parachutist had a hook knife attached to their chest strap, enabling them to cut enough reserve parachute lines for the parachute to tear free of the tailplane. Finally, in difficult circumstances, the pilot managed to control the aircraft and return to land safely.

What has been done as a result

To ensure aircraft are loaded within their weight and balance envelope, and this is documented on a load sheet, Far North Freefall Club (FNFF) has:

• engaged with the current software distributor about including balance in the manifest system
• commenced investigation of alternative software
• implemented a proprietary interim system that calculates and graphically displays the centre of gravity position on the aircraft’s weight and balance envelope, indicating whether it is within or outside limits.  

Additionally, FNFF distributed a circular to all company pilots reminding them of the requirement to use supplemental oxygen when the aircraft is at or above flight level 140, and of the risks of hypoxia. FNFF also mandated parachutists carry a hook knife.

Furthermore, FNFF updated the loadmaster checklist within its safety management system. The checklist is displayed around the drop zone to raise awareness of loadmaster roles and procedures in the event of an emergency. A circular has also been sent to all current company loadmasters to reinforce familiarity with in-aircraft emergency procedures.

In addition, the FNFF safety team is reviewing its standard operating procedures manual to ensure all procedures, including those relating to loadmaster training and emergency response, are clearly documented and up to date. FNFF is also preparing a training slideshow incorporating footage from the incident. This presentation will be shared across the wider skydiving community for educational purposes.

Finally, at the time of writing, the Australian Parachute Federation was in the process of developing a guide for loadmasters. The guide will detail the role and responsibilities, including during an emergency. It will take into consideration the range of complexity of various operations, and aircraft type and size. Training and assessment material will also be developed.  

Safety message

This accident highlights the importance of parachutists being mindful of their handles particularly when exiting the aircraft. Additionally, this accident demonstrates that carrying a hook knife secured to the parachute container could be lifesaving in the event of a premature reserve parachute deployment. It is also a reminder for pilots conducting parachute operations of the importance of wearing an emergency parachute and knowing how to deploy it. Parachute aircraft operators should also ensure, where possible, that there is a suitable open door for the pilot to exit in the event of an irretrievable loss of aircraft control. 

Furthermore, as fatal parachuting accidents have occurred due to aircraft being loaded outside the centre of gravity limits, this is a reminder for pilots and aircraft operators conducting parachute operations to ensure aircraft weight and balance calculations are conducted prior to each load.  

Finally, altitude hypoxia is an insidious and potentially deadly hazard associated with operations at high altitude. Although there is limited research into hypoxia for parachuting operations, effects of mild hypoxia can impair performance and judgement, critical for safe operations. Pilots conducting parachute operations are required to use supplemental oxygen at or above 14,000 ft, and should also do so during holding or delays above 10,000 ft, or when experiencing mild hypoxia symptoms. 

Summary video

The investigation

The occurrence

On 20 September 2025, the pilot of a Cessna 208 aircraft, registered VH-DVS, was conducting parachute operations at Tully Airport, Queensland. The aircraft and pilot had been hired by Far North Freefall (FNFF) skydive club based in Tully. In accordance with company policy, the pilot was wearing an emergency parachute.

After successfully completing 2 parachute drop loads earlier that morning, at 0950 local time, the aircraft took off for the third load of the day with 17 parachutists on board. The plan was for the parachutists to conduct a 16-way formation filmed by a parachuting camera operator. The parachute jump was part of the annual ‘Big Ways at the Beach’ multi-day event, hosted by FNFF, in which experienced parachutists completed large group formations in belly-to-earth[1] freefall. 

At 0954 local time, the pilot requested and received a clearance from Brisbane Centre air traffic control (ATC), to conduct parachute operations within 5 NM (10 km) of Tully Airport, up to flight level (FL) 150.[2] 

At 0959, the pilot advised ATC they were ‘3 minutes to drop’ and requested clearance to drop and then descend, which they received 14 seconds later. About 3 NM (5.6 km) prior to the drop point, the pilot illuminated a red light on the rear wall of the aircraft cabin to alert the parachutists.

At 1001, the pilot illuminated an orange light, indicating there was about 1 NM (1.9 km) to the drop. The camera operator and the first parachutist exiting (P1) then moved to the doorway and opened the roller door. The roller door was clipped open and remained open until after the aircraft landed. On reaching about FL 150, the pilot slowed the aircraft to 85 kt indicated airspeed and extended 10° of flap, before illuminating a green light at 1002. On seeing the green light, P1 tapped the camera operator on the shoulder. The camera operator then stepped outside the doorway, with their right foot on the camera step, their right hand on the handle above and aft of the door and their left hand on the bar at the top of the door frame. 

Parachutist 1 then crouched down and stepped out at the front of the doorway facing forwards, into the ‘front float’ position, with their right foot in the front corner of the door frame and their left knee under the wing (Figure 1).  

Figure 1: Parachutist 1 stepping out the door

Source: Jarrad Nolan, annotated by the ATSB 

Parachutist 1 then stood up outside the door, reaching for a small post on top of the fuselage with their left hand and lifting their left knee under the wing and flap. During this manoeuvre, P1’s left handle (pud[3]) snagged on the wing flap and rotated (Figure 2). 

Figure 2: Left pud (outlined in red) snagging on the flap and rotating

Source: Jarrad Nolan, annotated by the ATSB 

That movement dislodged the pud from the parachute container, deploying its reserve pilot chute (Figure 3). 

Figure 3: Pilot chute deployment 

Source: Jarrad Nolan, annotated by the ATSB

The pilot chute then pulled the reserve parachute and lines out of the container. As the reserve parachute inflated and the lines became taut, P1 was pulled off the side of the aircraft towards the tail, dislodging the camera operator into freefall (Figure 4 and 5). 

Figure 4: Reserve parachute inflating and dragging the parachutist rearwards

Source: Jarrad Nolan 

The reserve parachute wrapped around the left horizontal stabiliser and elevator and deflated as P1’s lower legs struck the stabiliser (Figure 5). P1 was then suspended beneath the tailplane (Figure 6). 

Figure 5: Parachutist 1 striking horizontal stabiliser as camera operator falls free

Source: Jarrad Nolan 

Figure 6: Reserve parachute wrapped around horizontal stabiliser with Parachutist 1 suspended beneath it

Source: Jarrad Nolan

Initially unaware of what had occurred, the pilot recalled feeling the aircraft suddenly pitch up and observed the airspeed rapidly decreasing. Assessing that the aircraft had stalled, the pilot pushed forward on the control column and applied some power. At that time, a parachutist called out that there was a canopy[4] wrapped around the tail. The FNFF senior pilot (on board as a parachutist), who was seated beside the pilot but facing rearwards, felt the aircraft shudder, and relayed to the pilot that there was a skydiver hung up on the tailplane. 

The pilot then reduced power and felt the controls vibrating. The pilot reported having to use significant forward pressure on the controls and right aileron input to maintain straight and level flight. To reduce some of the control pressure, the pilot applied full forward trim, which then jammed in that position for the remainder of the flight. 

After an initial hesitation, the loadmaster directed the other parachutists to exit. Over the next 15 seconds, 13 parachutists left the aircraft. The last 2 parachutists (the FNFF senior pilot and the loadmaster) remained in the doorway watching as P1 began to cut themselves free using a hook knife, retrieved from a pouch secured by a lanyard to the left side of their chest strap. 

P1 reported that they found the lines harder to cut than expected but managed to cut 11 lines in 50 seconds. The reserve parachute then tore, releasing P1 from the aircraft with part of the reserve remaining on the aircraft’s tail. The last 2 parachutists then exited the aircraft. 

Figure 7: Reserve canopy torn and parachutist detached from aircraft

Source: Jarrad Nolan 

At 1003 while in freefall, P1 used their main pilot chute handle to release the pilot chute out into the airflow, deploying their main parachute. However, during the main parachute deployment, the remaining reserve parachute lines twisted around the main parachute lines. Additionally, during the opening sequence, the right brake toggle[5] of the main parachute released (Figure 8).

The main parachute fully inflated with line twists, and after initially turning right, commenced a rapid left turn. After several rotations, P1 grabbed and pulled on the right brake line above the line twists to arrest the turn. The parachute stopped turning, and P1 was able to unwind the line twists and release the left brake toggle. Passing about 8,000 ft, the main parachute lines fully unwound from the reserve parachute lines and functioned normally for the remainder of the descent.  

Figure 8: Main parachute opening, left brake stowed and right brake toggle released, twisted main and reserve lines

Source: Adrian Ferguson

The pilot assessed they had limited pitch[6] control and with forward pressure could achieve a gradual descent. The pilot retracted the flap, which then allowed slightly more rudder, aileron and elevator control. The pilot reported maintaining about 120 kt airspeed during the descent and assessed that with the limited elevator movement available, they would be able to conduct a gentle flare for landing. The pilot also looked over their shoulder and saw the parachute remnant wrapped over the tail and the damage to the leading edge of the horizontal stabiliser. The pilot radioed the FNFF ground control assistant and advised them of the situation. 

At 1005, the pilot declared MAYDAY[7] to Brisbane Centre ATC, advising they had a canopy wrapped around the elevator ‘with minimal control input’. The pilot then advised ATC that their plan was to assess the aircraft’s controllability and try to land it, but if ‘the tail fell off’, they would attempt to advise ATC and ‘bail out’. 

The controller clarified details with the pilot and directed another aircraft in the area to remain clear. The controller then declared a distress phase,[8] alerted emergency services, and transferred other aircraft to a different Brisbane Centre frequency. 

Descending through about 2,500 ft, the pilot assessed that they would land the aircraft rather than exit and parachute to the ground. The pilot elected to conduct a straight-in approach with a slight tailwind to runway 36,[9] to minimise manoeuvring the aircraft clear of high terrain either side of Tully Airport. The pilot also assessed there was insufficient elevator control to be able to safely extend landing flap. 

As the aircraft crossed the threshold, the pilot initially reduced power, but this led the aircraft nose to drop significantly. The pilot then reintroduced power and flew level with the runway before reducing the throttle to idle and using both hands to apply full backpressure on the controls. The aircraft landed at 1010, having sustained substantial damage to the horizontal stabiliser (Figure 9). P1 landed 9 seconds later with minor lacerations and bruising to their left lower leg and a deep gash to their right lower leg. After receiving phone confirmation that the aircraft had landed safely, at 1018 ATC cancelled the distress phase. 

Figure 9: VH-DVS after landing, showing damage to the horizontal stabiliser

Source: Jarrad Nolan

Context

Personnel information

Pilot

The pilot held a commercial pilot licence (aeroplane), a class 2 aviation medical certificate and an instrument rating. They completed their most recent single engine aeroplane flight review and gas turbine engine design feature endorsement, as part of their jump pilot[10] authorisation in a Cessna 208 aircraft, on 21 June 2024.

The pilot had accrued 800 flight hours, 410 of which were operating Cessna 208 aircraft. They had been conducting parachute operations at Tully Airport for about 11 months and last conducted emergency procedures training for parachute operations in April 2025. 

Parachutist 1

The accident jump was the parachutist’s (P1’s) 2,013th over a 21-year period. P1 held an Australian Parachute Federation (APF)[11] Certificate E, and achieved the Australian Star Crest in 2011, required for participation in skydive formations of more than 10 people.[12] 

The parachutist’s equipment included:

• Sunpath Javelin Odyssey harness and container, SN 25429, manufactured December 2003.
• Airtec CYPRES 2 Expert automatic activation device, SN 96270 manufactured July 2014.
• Icarus Safire 2 139 main parachute, which was royal blue, fluoro yellow with a white centre cell.
• Bottom of container throwaway main deployment type.
• Performance Designs Optimum 143 reserve parachute, SN 25632, manufactured in October 2021. The reserve was repacked on 13 August 2025 by Freefall Support and valid for 12 months.
• A hook knife in a pouch attached to their chest strap and secured with a lanyard (Figure 10).

Figure 10: Parachutist’s hook knife and lanyard

Source: Supplied

P1 used puds – soft handles held in place with Velcro – for their reserve deployment and main cutaway handles, in preference to ‘D’ handles, which they reported had previously been snag points (Figure 11). The reserve handle was a ‘Phat Daddy Tube Style’, described as ‘a soft handle with the bulk required to get a good grip in an emergency’. The APF assessed that the bulky handle design ‘may have increased the risk of snagging if not adequately protected’.

Figure 11: Pud ‘Phat Daddy’ soft reserve handle (left) and D handle (right)

Source: www.sunpath.com

P1 commented that having a bright orange reserve parachute that was visually distinct from their main parachute meant that it was immediately obvious that it was their reserve that deployed prematurely. The APF reported that this type of deployment occurred far less frequently than premature deployment of a main parachute. 

P1 conducted their normal gear check when the red light illuminated, which comprised checking:

• 3 handles (main pilot chute, cutaway of main chute and reserve handle)
• 3 straps (leg and chest straps properly routed and tucked away)
• 3 rings properly assembled on shoulders
• 3 things: altimeter on the back of left hand, altimeter inside of right wrist and helmet done up. 

The accident jump was the parachutist’s first jump that day. P1 had an altimeter with a recording function, which showed that the reserve parachute tore free of the tailplane at 13,720 ft. After a freefall time of 26 seconds, the main parachute deployed at 10,780 ft. 

The front float position is the most forward person in line and whose ‘exit’ is from outside the aircraft. P1 preferred the front float position. This was their third jump in that position out of the 6 jumps they had done at Tully that week. P1 also reported that out of the 20‍–‍22 jumps they did the previous year at the Big Ways at the Beach event, they had been in the front float position for about 8 of them.

All the event jumps were practised first on the ground as a ‘dirt dive’ using a mock-up aircraft at the airport. The mock-up had outer pegs and inner bars, but not a wing or flap to simulate their position (Figure 12). 

Figure 12: Tully mock-up aircraft for practising ‘dirt dives’

Source: Far North Freefall, annotated by the ATSB

Senior pilot

The FNFF senior pilot was approved by the APF. According to the APF Jump Pilot Manual (JPM), senior pilot responsibilities included:

• oversight of all aircraft related aspects of FNFF
• ensuring the safe and legal operation of aircraft. 

Drop zone safety officer

The Far North Freefall (FNFF) chief instructor (parachuting) was the drop zone safety officer (DZSO) for the day’s operations at Tully. Due to wet weather earlier in the week, participants in the event had attended safety seminars. One seminar included reinforcing to parachutists to always be mindful of their handles. The DZSO reported that the front float position had specifically been mentioned in the seminar, because it required being as far forward as possible, with an associated risk of snagging equipment on the aircraft while reaching to stand up. It was regarded as a relatively difficult position to hold. 

The DZSO was in the ground control assistant role (with a handheld radio) during the accident flight, when the pilot radioed and said there was a parachutist on the tail. The DZSO then started counting the parachutes they could see in the air. Another jump pilot on the ground came to help and asked the pilot whether they had declared MAYDAY, and the pilot replied that the jumper had got free of the aircraft’s tail. The camera operator was the first parachutist to land and pointed out to the DZSO that P1 was under their main parachute, with the reserve trailing. 

After P1 landed, the DZSO handed the radio to the FNFF senior pilot, sent a car to pick up P1 and arranged for a doctor (who was also a parachutist), to provide first aid. P1 was then driven to hospital. 

Loadmaster

The APF JPM detailed the loadmaster (LM) role as follows.

(a) Each parachute operation must have a nominated Loadmaster for each load.

(b) As per APF Operational Regulations (Part 6), the Loadmaster is responsible for:

(i) conducting a pre-jump briefing before any parachute descents are made, which covers all relevant aspects of the descent, and which includes all persons on-board the aircraft including pilot and parachutists;

(ii) ensuring the airspace and [drop zone] DZ below is clear of conflicting air traffic and any necessary drop clearances have been obtained; and

(iii) confirming the integrity of the exit point.

The LM on the accident flight reported being unaware they were the appointed LM for that load until after landing. There were 3 parachuting instructors on the load who were also approved and experienced LMs. About 5 minutes before departure, all parachutists on the load met at the mock-up, where they revised the exit and checked each other’s equipment (buddy checks). The load was displayed nearby on the manifest screen, showing who was the appointed LM for that load. The LM had not checked the screen. However, they reported that the LM role on the accident load was minimal, as it:

• only contained experienced parachutists
• was not the first load of the day (requiring confirmation of the spot position)
• only required one exit as all the parachutists were in the single formation. 

Normally, communications between the pilot and parachutists were via the LM. On this load, the FNFF senior pilot (also the most experienced parachutist) was seated next to the pilot and therefore more readily able to communicate.

The LM’s role in an emergency was not included in the APF Operational Regulations or Training Operations Manual. However, the JPM Section 9.6 Emergency exit, stated:

In an airborne emergency such as a structural failure or fire, the pilot may decide that the chances of surviving a landing in the aircraft are non existent, and decide to order the evacuation of the aircraft. Each load must have a loadmaster who will start the aircraft evacuation once the pilot gives the command.

At lower levels, the parachutists will open their reserve parachutes as soon as they are clear of the aircraft. These parachutes are designed and packed to deploy quickly and only require a couple of hundred feet. 

Note: Emergency procedures for structural failure are not discussed in manuals or safety publications because there are to [sic] many variables and little that can be effectively done. It is mentioned here because, with parachutes on-board, there is a chance that lives can be saved by exiting the aircraft. This applies equally to you as a pilot if you are wearing a parachute.

Additionally, the APF Safety management system continuous improvement package 4 2019, Aircraft emergency and evacuation procedures, was provided to APF member organisations to discuss in safety meetings. Regarding the LM role in an emergency, it included the section ‘Communication’: 

The Pilot is in command.  Wait for the Pilot’s instructions. You can make the situation worse for the Pilot, i.e. if you move closer to the door and cause a shift in the centre of gravity or asymmetric drag, by opening the door or everyone yelling and asking what to do.

Load Master to be ready to make the call if the Pilot does not respond (the Pilot may not be prepared for the emergency or may not provide instructions). The Load Master needs to be ready to give instructions. However, do not rush this decision (unless a catastrophic emergency) as the Pilot may be assessing the situation, e.g. if there is a small electrical fire the Pilot may try to put out this fire with the extinguisher before having a forced landing with a full plane load or instructing everyone to exit.

The APF and FNFF did not specify an emergency exit command. 

The LM reported calling ‘get out, get out, get out’ but that ‘exit, exit, exit’ was the command they should have used. The FNFF senior pilot recalled shouting ‘go, go, go’. Another parachutist nearer the door also yelled and pointed parachutists to exit when they had briefly paused in the doorway. That parachutist reported that in hindsight it was the LM’s role, not theirs, to give the command, but the chief instructor advised that in this case, it facilitated a quick exit, which was correct action at the time. 

The LM and FNFF senior pilot remained in the doorway until P1 was free of the tailplane, before exiting the aircraft. However, both later reported that, in hindsight, they should have gone back to the front of the aircraft and relayed the situation to the pilot, although they reported the pilot was probably aware that the parachutist was clear, as the aircraft ‘bucked’ when the parachutist tore free.  

During their discussions with the parachutists after the incident, the FNFF chief instructor (parachuting) identified that there had not been a plan as to what the parachutists would do in the event of an emergency to ensure they assisted and remained clear of each other’s parachute after exiting. Further, that there was no documented training for the LM role and the requirements in the event of an emergency were not well understood. 

Aircraft

VH-DVS was a Cessna Aircraft Company 208, manufactured in 1988, serial number 20800131, modified under a Texas Turbines Conversions supplemental type certificate with a Honeywell TPE331-12JR-704TT engine and a Hartzell Propellers 4-blade HC‑E4N-5KL propeller. At the time of the accident, the airframe total time in service was 10,270.60 hours. The aircraft’s tail assembly (empennage) consisted of a vertical stabiliser, rudder, horizontal stabiliser and elevator. VH-DVS was unpressurised and equipped with supplemental oxygen for the pilot’s use.

VH-DVS was modified for parachuting with bench seats and single point restraints. Handrails, posts, a step and a roller door were also fitted to facilitate parachutists to exit the aircraft, along with a ‘Baz clip’ to secure the door open (Figure 13). 

Figure 13: Baz clip securing the roller door open

Source: Far North Freefall, annotated by the ATSB

Following an accident involving another Cessna 208 in 2001 (see the section titled Previous similar occurrences), in which the pilot’s emergency egress was delayed by the roller door (blind) closing, the designer of the blind amended the design to include:

• a device to lock the door in the open position
• a placard warning that the blind must be locked open during parachuting.   

The aircraft was also fitted with a light system controlled by the pilot. In accordance with FNFF procedures, the pilot was to illuminate the: 

• red light 3 NM from the drop position
• orange light 1 NM from the drop position, at which time door could be opened
• green light to indicate pilot approval to commence exit. 

Following the accident, the following maintenance was conducted:

• inspection of the fuselage to horizontal stabiliser attach fittings; no defects found
• inspection of the elevator control cable assembly; no defects found
• left and right elevator control surfaces replaced
• horizontal stabiliser assembly replaced.

Weight and balance

The Civil Aviation Safety Authority (CASA) legislative instrument EX105/23 – Part 105 (Parachute Operators and Pilots) Instrument 2023, as amended and in force on 1 July 2025, exempted compliance with paragraph 91.095(2)(a) of the Civil Aviation Safety Regulations (CASR) regarding the maximum number of passengers that may be carried, the seating configuration and restraints stated in the airplane flight manual. For the exemption to apply, the instrument included in Section 9, among other requirements:

1) If the aeroplane has been modified in a manner that affects any of the following:

(a) the maximum number of passengers that may be carried on the aeroplane in accordance with the [airplane flight manual] AFM; or

(b) the passenger seating, or method of passenger restraint, in accordance with the AFM;

  then the modification must have been approved:

(c) by an authorised person or an approved design organisation under regulation 21.437 of CASR; or

(d) otherwise in accordance with a Part 21 approval; or

(e) by an approval continued in force, according to its terms, under regulation 202.054 of CASR.

(2) The pilot in command must follow the procedures designed to ensure that the aeroplane:

(a) remains within its MTOW; and

(b) remains within its centre of gravity limits and requirements at all stages of the operation; and

(c) complies with all limits, restrictions and conditions imposed by the approval mentioned in subsection (1).

Additionally, Section 10 of the instrument required the pilot to comply with the conditions of the exemption and for the operator, in this case FNFF, to ensure the pilot did so. 

Regulation 91.805 of CASR also required the pilot to ensure at all times that an aircraft was loaded and operating within its weight and balance limits. 

The CASR Part 105 Manual of standards (MOS), Chapter 7 – Weight and balance required both the aircraft operator and the pilot to ensure a load sheet was completed before flight, unless the aircraft was carrying the same load for multiple parachute drops. The load sheet was required to be carried in the aircraft and a copy given to the chief parachuting instructor or drop zone safety officer (and retained for 3 months). Among other things, the load sheet was required to include: 

(g) the weights and moment arms of: 

(i) the occupants of the aircraft; and 

(ii) any cargo carried on the aircraft; and 

(iii) any removable equipment carried on the aircraft; and 

(iv) fuel and consumables carried on the aircraft (for example, water or ethanol); 

(h) the calculated load weight, and total moment, that demonstrates that the centre of gravity is within the approved limits; 

(i) the maximum allowable weight for the flight, having regard to the prevailing environmental conditions; 

(j) a statement by the person who is responsible for planning the loading of the aircraft, that the load and its distribution are in accordance with the aircraft loading system;

FNFF used BURBLE manifest software. Parachutists were required to use an app to check in each morning, and their weight was included in their personal details. BURBLE then verified that APF members had signed the required waiver, the reserve parachute was within the repack date, and the parachutist intended to do an appropriate jump for their certificate/licence.

A manifest person then re-checked the information in BURBLE. After check-in, parachutists could be manifested on a load, along with a coach and/or camera operator as needed. A DZSO, ground control assistance (GCA) and loadmaster would be assigned for each load. 

As parachutists were allocated to a load, their weights were added to the aircraft weight. The manifest person would then update the quantity of fuel on board. The chief instructor (parachuting) advised that their normal process was to use a standard fuel weight based on sufficient fuel to conduct 3 parachute drop loads (and required reserves). If BURBLE flagged that the aircraft was overweight with that fuel quantity, the manifest person would then use a more precise fuel figure.  

The aircraft had an iPad as an electronic flight bag (EFB), which included a load sheet based on the BURBLE manifest. The pilot reported that they would review the load sheet on the iPad and ensure the aircraft was below the maximum take-off weight.

Although BURBLE performed a weight calculation, it did not calculate the aircraft centre of gravity or balance, or have any means to allocate parachutists to a particular (loading) zone of the aircraft. Several other Australian drop zones used IBIS software, which could perform weight and balance calculations. Under a Memorandum of Understanding, FNFF was required to operate the aircraft in accordance with Section 5 – Aircraft operational procedures of the Skydive Australia operations manual. This section of the Skydive Australia operations manual provided procedures for calculating weight and balance with IBIS or OzRunways.[13] VH-DVS’s OzRunways EFB included the aircraft’s skydive configuration, allowing pilots to enter fuel and passenger weights in order to determine the aircraft’s take-off weight and centre of gravity position for each flight.

Emergency procedures 

Knife 

Part 105 – Parachuting from aircraft – MOS 5.40 Emergency equipment carried on jump aircraft, required a knife suitable for emergency situations be carried on board the aircraft and to be readily available to the pilot or parachute instructor. This was also required in the APF Operational regulations, section 5.2 – Aircraft: 

5.2.5 Knife in Aircraft

A knife, capable of cutting parachute harness webbing, must be readily available and appropriately stored in the aircraft.

There was at least one knife on board VH-DVS as required by the APF JPM. However, in this occurrence, there was no practical means of getting the onboard knife to the parachutist hung up on the tail. 

Skydive Australia’s emergency procedures checklist, a copy of which was in VH-DVS, included actions in the event of a parachutist being hung up by their restraint, or their parachute snagging on exiting the aircraft (Figure 14).

Figure 14: Skydiver hang up checklist 

Source: Skydive Australia Operations Manual

Emergency parachute

The APF’s Operational regulations, section 5.2 – Aircraft, also required an emergency parachute be made available to pilots: 

5.2.6 Pilot’s Emergency Parachute Availability

A parachute that complies with APF Equipment Standards and training in the proper use of that parachute must be made available to pilots of aircraft used in making descents.

The Skydive Australia operations manual required the pilot to wear an emergency parachute when conducting skydiving operations. There was no requirement for a pilot to have conducted a parachute jump; they were trained in its use verbally and by demonstration. Emergency parachutes had one parachute, which was large and designed to open very quickly. The pilot was wearing an emergency parachute, had been trained in its use, and reported that they would only exit if they had no control of the aeroplane. 

The APF JPM section 9.7 Emergency pilot rig use stated:

In the event that you decide to use the pilot emergency parachute, you must be prepared to follow the procedures you’ve been briefed on by the DZSO for the particular rig in use. Pilot rigs normally contain a round canopy, which achieve minimal air speed (~5 to 8 knots) and glide ratios of up to 1:1. The general procedure for use is as follows:

(a) prior to leaving the aircraft, grasp the ripcord handle. It is easier to locate it prior to exit as it may move once in freefall, and the associated disorientation may make it more difficult to find.

(b) once clear of the aircraft, pull the ripcord to full arms length,

(c) once the parachute is open, reach up and grasp the two small steering toggles (handles), or the coloured lines, on the risers above your shoulders.

(d) to steer, pull down one side to turn in that direction.

(e) fly towards a cleared area and try to land into the wind to minimise landing speed.

(f) for landing, it is highly recommended that you perform a Parachute Landing Roll (PLR).

Premature parachute deployment

The APF JPM Part 9 Emergency procedures, included 9.3 In-aircraft parachute deployment:

There are a number of situations where a ripcord may be accidentally pulled or a pin dislodged resulting in a container opening in the aircraft, on climb‐out, or on the step. An extremely hazardous situation exists when the door has been opened and a pilot chute is suddenly deployed finding its way outside.

Further, it stated that parachutists ‘are taught to protect their handles and equipment while inside the aircraft and during climb-out’ (Figure 15).

Figure 15: Jump pilot manual extract 

Source: Australian Parachute Federation

The emergency procedures continued: 

An accidental opening in the aircraft with the door open is potentially disastrous. If a pilot chute escapes while the door is open, it can be out and into the slip stream before reaction is possible. The jumpers will do their best to ensure the person attached is able to be expedited out the door as quickly as possible. In the past, this has resulted in the parachutist attached to the parachute being pulled through the side of the aircraft!

Keep a close watch for any premature openings and if one occurs, immediately apply maximum rudder to swing the tail clear of the deploying parachute and the person attached.

The APF produced a safety poster, which was on the wall at FNFF. The poster stated that premature deployments can be prevented by:

- Proper equipment maintenance

- Using compatible equipment

- Buddy checks

- Minimising excessive movement in aircraft

- Checking handles, pins, etc before emplaning and before exit

- Taking care and being conscious of equipment during climb-out. 

Tully Airport

Tully Airport was an aircraft landing area with one sealed runway 18/36, 936 m long. The airport elevation was 47 ft, with terrain about 2,200 ft above mean sea level to the east and west. The drop zone was adjacent to the northern end of the runway. 

The drop position for the day was heading south (180°), running centrally overhead Tully Airport, with the pilot illuminating the green light at 0.8 NM (1.5 km) before (north of) the aerodrome reference point. 

The weather at Tully Airport on the morning of the accident included 6–10 kt south‑easterly winds, cloud covering about half the sky, and an ambient temperature of 21°C. The nearest Bureau of Meterology weather station was at Innisfail, about 42 km north.

At 1000, the Innisfail METAR[14] stated that the wind was from 170° at 3 kt, visibility greater than 10 km, QNH 1,014 hPa,[15] temperature 25°C. At 1010 (the time the aircraft landed), the 1‑minute weather data at Innisfail included: temperature 27°C, wind (which had been variable for the past 5 minutes) from 245° at 1 kt and QNH 1,014.6 hPa.

Supplemental oxygen 

CASR Part 105 MOS required unpressurised aircraft operating a parachute descent to have supplemental oxygen in accordance with the Part 91 MOS Division 26.11 – Oxygen equipment and oxygen supplies. The aircraft was required to be fitted with, or carry, supplemental oxygen, which was required to be used by:

• flight crew for any period exceeding 30 minutes when the cabin pressure altitude was continuously at least flight level (FL)[16] 125 but less than FL 140
• flight crew for any period when the cabin pressure altitude was at or above FL 140
• passengers for any period when the cabin pressure altitude was at or above FL 150.

CASA advised that this was incorporated in Part 91 between 2003 and 2011 to align with the United States Federal Aviation Regulations. The European Union Aviation Safety Agency required crew members to use supplemental oxygen when between 10,000 ft and 13,000 ft for more than 30 minutes, and at all times when above 13,000 ft.  

Aircraft conducting parachute drops from FL 150 were usually between FL 140 and FL 150 for about 2 minutes. In the occurrence flight, due to the premature parachute deployment, the aircraft was between FL 140 and FL 150 for closer to 3 minutes. For jump pilots, that is a high workload period, involving slowing and configuring the aircraft for the drop, confirming the drop position, and communicating with parachutists, air traffic control, the ground control assistant and on the common traffic advisory frequency. 

The APF operational regulations required adherence to the Part 91 MOS oxygen requirements. However, the pilot did not use oxygen on the accident flight. 

Hypoxia

Hypoxia is the absence of an adequate supply of oxygen to the tissues. Hypobaric hypoxia is the most common form in aviation and is associated with breathing air at low barometric pressure. A deficiency in alveolar oxygen exchange due to low oxygen tension (partial pressure) of inspired air leads to inadequate oxygen supply to the blood and reduced oxygen available to the tissues. In an aviation context, acute hypobaric hypoxia is the ‘most serious single physiological hazard during flight at altitude’ (Gradwell and Rainford, 2006). 

The risk of hypoxia increases with altitude and time at altitude. Additionally, multiple ascents to altitude may have a compounding effect on hypoxia. There is considerable variation between individuals in the effects of hypoxia. Hypoxia can occur in susceptible individuals below 10,000 ft. Between 10,000 ft and 15,000 ft, brain function is mildly impaired and hypoxic symptoms are common. Above 15,000 ft, brain function exponentially deteriorates (Shaw, Cabre and Gant, 2021).  

Physical activity, cold, illness and certain drugs increase the onset speed and severity of hypoxia. Additionally, jump pilots require a class 2 aviation medical certificate, which is less stringent than class 1 medical certification, and may allow underlying cardio‑respiratory conditions that increase hypoxia risks to go undetected. 

Those experiencing hypoxia may have no signs or symptoms and may be unaware of any cognitive impairment. In unpressurised aircraft, hypoxia can be prevented by breathing supplemental oxygen.

Limited research has been conducted into the effects of ascents to FL 140 and FL 150 for jump pilots or parachutists. An article in the United States Parachute Association’s publication Parachutist, described a small study of parachutists using pulse oximeters. They found that in ascents to 14,500–15,000 ft above mean sea level, blood oxygen saturation levels, normally 95–100%, dropped into the 80s (%) during ascent, and, into the 70s on one flight in which air traffic control holding resulted in an additional 10 minutes at altitude (Galdamez, 2024). Although individual responses vary to reduced oxygen saturation levels, a finger‑mounted pulse oximeter can alert pilots and parachutists to reduced blood oxygen saturation levels, prompting the use of supplemental oxygen. 

Previous similar occurrences

Premature parachute deployment

The ATSB investigated a parachuting accident involving Cessna 208 VH-MMV at Nagambie, Victoria, on 29 April 2001 (AAIR200101903). The aircraft climbed to FL 140 with 11 parachutists and the pilot on board. As the first 4 parachutists exited the aircraft, the middle parachutist’s reserve pin dislodged on the top of the door frame and the pilot chute deployed. The pilot chute pulled the reserve parachute over the horizontal stabiliser. The reserve parachute risers and lines tangled around the left elevator and horizontal stabiliser, with the parachutist hanging below them. Eleven seconds later, the empennage separated from the aircraft and the left elevator and parachutist separated from the empennage. The parachutist fell to the ground and was fatally injured.

The remaining parachutists exited the aircraft before it descended through 9,000 ft. The pilot transmitted a MAYDAY call, shut down the engine and left their seat. However, the rear roller door (blind) had closed. After several attempts, the pilot raised the blind sufficiently to exit the aircraft at about 1,000 ft above ground level and deploy their parachute before landing safely. The aircraft impacted the ground and was destroyed by impact forces and post-impact fire.  

Parachutists striking aircraft

The Nagambie report referenced 3 previous premature parachute deployments and 2 occurrences in which a parachutist struck the aircraft. Table 1 details occurrences since 2001 in which a parachutist struck and damaged the aircraft.

Table 1: ATSB occurrences since 2001 in which a parachutist struck the aircraft

Weight and balance

There were 2 accidents in Sweden investigated by the Statens Haverikommission (SHK) involving aircraft conducting parachuting operations, in which the aircraft’s weight and balance was not calculated. 

On 14 July 2019, 8 parachutists and the pilot were fatally injured in an accident in Sweden involving a GippsAero GA8 aircraft. The SHK investigation found that the parachutists moved to the back of the aircraft in preparation for the jump, which altered the weight distribution, resulting in the aircraft stalling, before breaking up in flight. The aircraft was found to have been overloaded. The SHK also found that as the load sheet did not contain the weights of the parachutists or the total mass of the load, the pilot was unable to complete weight and balance calculations. 

On 8 July 2021, the pilot and 8 parachutists were fatally injured when a de Havilland DHC-2 aircraft collided with terrain shortly after take-off. The SHK found that:

Control of the aircraft was likely lost in connection with the wing flaps being retracted in a situation where the stick forces were high due to an abnormal elevator trim position, while the aircraft was unstable due to being tail-heavy and abnormally trimmed. Due to the low altitude, it was not possible to regain control of the aircraft. 

The investigation also found that the pilot had no ability to perform a weight and balance calculation with the available information.

Safety analysis

As the parachutist climbed out of the aircraft and into the front float position, their reserve handle snagged on the aircraft's flap, resulting in deployment of the reserve pilot chute and parachute. The parachutist was highly experienced, had performed their gear checks before exiting the aircraft, and attended safety seminars in the days prior to the accident, which included being mindful of their handles.

The parachutist was also experienced in the front float position and had practised getting into that position several times in the mock-up on the ground before the jump. However, the mock-up did not have a flap to simulate its position, reducing the likelihood that the snagging potential would be recognised. 

As the parachutist was pulled rearwards, they struck the camera operator, who was dislodged from the aircraft sustaining a minor shoulder injury. The parachutist’s lower legs struck and damaged the leading edge of the horizontal stabiliser, which, combined with the parachute wrapped around the horizontal stabiliser and elevator, resulted in the pilot experiencing difficulties controlling the aircraft. Although not required to be carried, the parachutist had a hook knife, which enabled them to cut themselves free of the aircraft. Without access to the knife, separation from the aircraft may not have been possible. Additionally, although the pilot was wearing an emergency parachute and the roller door was clipped open to aid exiting if control was lost, the pilot was able to maintain sufficient control to land the aircraft without further incident. 

The parachuting club at Tully was using manifest software that calculated the aircraft’s weight including the parachutists. However, it did not perform balance calculations to ensure the aircraft was loaded within its centre of gravity envelope. Additionally, the pilot was not using the available electronic flight bag tool to calculate weight and balance for each flight, and the senior pilot was not ensuring this was done. There was no evidence that the aircraft was out of balance or that this contributed to the occurrence. However, fatal accidents have occurred involving aircraft conducting parachute operations, in which the aircraft were operated outside the aircraft’s balance limits. 

Hypoxia poses a risk to both pilots and parachutists when operating above about 10,000 ft, noting that its specific effects are highly variable between individuals. There is limited research into the effects of short, repeated exposure to altitude associated with parachuting operations, or of the magnitude of additional risk in operating for 2‍–‍3 minutes between 14,000 and 15,000 ft. However, given individual responses to altitude exposure, use of supplemental oxygen at and above 14,000 ft as required by legislation, reduces hypoxia risks and any compounding effects of multiple ascents associated with parachute operations.   

Findings

From the evidence available, the following findings are made with respect to the premature parachute deployment involving Cessna 208, VH-DVS, over Tully Airport, Queensland, on 20 September 2025. 

Contributing factors

• As the parachutist climbed out of the aircraft and into the front float position, their reserve handle snagged on the aircraft's wing flap, resulting in deployment of the reserve parachute and entanglement with the empennage. The parachute wrapping around the horizontal stabiliser, combined with damage from impact with the parachutist's legs, resulted in aircraft control difficulties.

Other factors that increased risk

• The pilot and aircraft operator did not ensure the aircraft was loaded within the weight and balance envelope.
• The pilot did not use oxygen when the aircraft was at or above flight level 140 as required by regulations to reduce the risks of hypoxia.

Other findings

• The parachutists opened the roller door and clipped it open before exiting the aircraft. As a result, the roller door remained open during the descent, increasing the ease with which the pilot could have exited the aircraft if needed.
• Although not mandatory at the time of the accident, the parachutist had a hook knife attached to their chest strap, enabling them to cut enough reserve parachute lines for the parachute to detach from the tailplane.
• In difficult circumstances, the pilot managed to control the aircraft and return to land safely.

Safety actions

Safety action taken by Far North Freefall 

To ensure aircraft are loaded within their weight and balance envelope and this is documented on a load sheet, Far North Freefall Club (FNFF) has:

• engaged with the current software distributor about including balance in the manifest system
• commenced investigation of alternative software
• implemented a proprietary interim system that calculates and graphically displays the centre of gravity position on the aircraft’s weight and balance envelope indicating whether it is within or outside the limits. 

Additionally, FNFF distributed a circular to pilots reminding them of the requirement to use supplemental oxygen when the aircraft is at or above flight level 140, and of the risks of hypoxia. FNFF also mandated parachutists to carry a hook knife.

Furthermore, FNFF updated the loadmaster checklist within its safety management system. Copies of the checklist are displayed around the drop zone to raise awareness of loadmaster roles and procedures in the event of an emergency. A circular has also been sent to all current FNFF loadmasters to reinforce familiarity with in-aircraft emergency procedures.

In addition, the FNFF safety team is reviewing its standard operating procedures manual to ensure all procedures – including those relating to loadmaster training and emergency response – are clearly documented and up to date.

FNFF is also preparing a training slideshow incorporating footage from the incident. This presentation will be shared across the wider skydiving community for educational purposes.

Safety action taken by the Australian Parachute Federation

At the time of writing, the Australian Parachute Federation was in the process of developing a guide for loadmasters. The guide will detail the role and responsibilities, including during an emergency. It will take into consideration the range of complexity of various operations, and aircraft type and size. Training and assessment material will also be developed. 

Sources and submissions

Sources of information

The sources of information during the investigation included:

• the pilot and parachutists
• the aircraft operator
• Australian Parachute Federation
• Civil Aviation Safety Authority
• Airservices Australia
• witnesses
• video footage of the accident flight and other photographs and videos taken on the day of the accident
• recorded data. 

References

Galdamez L (2024, December) Studying hypoxia in skydivers, Parachutist, Volume 65, Number 12, Issue 782, 58–59 

Gradwell DP, Rainford DJ (2006), Ernsting’s aviation medicine, Edward Arnold (Publishers) Ltd London, Chapter 3.

Shaw DM, Cabre G and Gant N (2021) Hypoxic Hypoxia and Brain Function in Military Aviation: Basic Physiology and Applied Perspectives. Front. Physiol. 12:665821. doi: 10.3389/fphys.2021.665821

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 aircraft operator
• the aircraft owner
• the pilot and parachutists
• Australian Parachute Federation
• Civil Aviation Safety Authority. 

Submissions were received from:

• the aircraft owner
• the aircraft operator
• a parachutist
• Civil Aviation Safety Authority
• Australian Parachute Federation.

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 25 June 2025, the flight crew of a Jetstar Airways Airbus A321-251, VH-OYF, were conducting a scheduled passenger transport flight, JQ38, from Denpasar International Airport, Bali, Indonesia, to Sydney, New South Wales. The first officer was the pilot flying and the captain was the pilot monitoring.

During the landing at Sydney Airport, the aircraft floated for a prolonged period along the runway, was subject to a right crosswind and drifted left of the runway centreline. The captain responded by commanding a go-round which the first officer executed. 

The crew proceeded to continue with the published missed approach procedure and subsequently landed without further incident. 

What the ATSB found

The ATSB found that after the first officer initiated the flare manoeuvre, their control inputs resulted in a lateral deviation from the runway centreline when the aircraft floated for a prolonged period in crosswind conditions. 

After the captain commanded a go-around, they inadvertently manipulated their sidestick control, which resulted in a brief period where simultaneous control inputs occurred. The crew were alerted by a ‘dual input’ generated voice message and the captain took control. There was a moment of preoccupation which resulted in the first stage of flap being retracted out of sequence, however, there were no associated flight envelope exceedances or negative effects on aircraft performance. 

Safety message

Sound go-around decision-making is an effective defence against the hazards associated with low-level manoeuvring during the landing phase of flight, such as lateral runway excursions. If adequate safety margins cannot be maintained during an approach and landing, the correct and expected response is to go around.

Being go-around minded improves crew readiness and supports timely, coordinated actions during a period of high workload. This should involve crew members reviewing potential go‑around scenarios, procedures and responses prior to conducting an approach. 

When flight crews are faced with the unexpected need to execute a go-around even at the final stages of landing, effective crew resource management, with clear communication between flight crew, is essential. This promotes effective teamwork when responding to disruptions and increased workload under stress, ensuring that the aircraft remains on a safe flight path and is correctly configured for the relevant phase of flight.

The investigation

The occurrence

On the evening of 25 June 2025, a Jetstar Airways Pty Limited Airbus A321-251 registered VH‑OYF was operating on a schedule passenger transport Jetstar flight, JQ38, from Denpasar International Airport, Bali, Indonesia, to Sydney, New South Wales. The flight was scheduled to arrive at Sydney Airport the following morning at 0630 AEST.[1] The operating crew included the captain, first officer, 6 cabin crew and 234 passengers. For the flight to Sydney, the first officer was the pilot flying (PF) and the captain was the pilot monitoring (PM).[2]   

After departing Denpasar, the aircraft climbed to flight level (FL) 330[3] and later descended to FL310 after reaching Australian airspace due to turbulence en route. Due to the turbulence en route, the captain elected not to take any controlled rest on the nearly 6‑hour flight, while the first officer stated they would not usually take controlled rest in flight. 

Prior to descent, the flight crew briefed for the arrival at Sydney, recalling that the turbulent conditions and the crosswind for the approach and landing were the main considerations. 

At 0554, the flight crew commenced their descent to the west-south-west of Sydney Airport and was cleared for the approach for runway 16R[4] which was conducted in day visual meteorological conditions[5] using the autopilot. The flight crew recalled there was a 30 kt crosswind down to about 500 ft above mean sea level (AMSL) and the approach up to that point was ‘pretty normal.’ Air traffic control (ATC) advised the crew to expect an 8 kt right crosswind for landing and the first officer chose to land in the flap 3 configuration,[6] which was consistent with guidance for landing in ‘rough’ conditions. (The first officer was procedurally restricted to a maximum crosswind landing component of 20 kt).

The aircraft reached 500 ft at 0621:14 and the captain called ‘stable’ (see Stabilised approach criteria). The first officer disengaged the autopilot 5 seconds later as the aircraft approached 400 ft and recalled encountering turbulence which placed the aircraft ‘a little higher’ on the approach. At 0621:45 at 90 ft, the first officer pitched forward, which they observed resulted in a 900 ft per minute rate of descent. 

At 0621:51, the first officer initiated the flare at 50 ft and reduced the thrust levers to idle at around the final approach speed (VAPP)[7] of 150 kt, which included a wind correction of 5 kt. At this point the first officer recalled they ‘over flared’. The captain also observed that the first officer applied the flare technique that was consistent with the technique for landing in the flap full configuration. The aircraft subsequently floated for a prolonged period along the runway after the first officer’s flare manoeuvre.

During the prolonged float, the aircraft was subjected to the crosswind conditions for a greater length of time. After observing the centreline deviation, the captain commanded a go-around approximately 600 m past the runway threshold, just prior to touchdown. The captain recalled they were ‘startled by the need to go around’ as the approach seemed ‘benign’ aside from the crosswind. They also reported a sudden stress response at this time as they had to rapidly transition from landing to commencing the go-around.

In response to the captain’s command, the first officer set take-off/go-around thrust at 0621:59 (Figure 1), which initiated the published missed approach procedure for the 16R GBAS landing system (GLS)[8] approach in the aircraft flight management system. The first officer also referenced their primary flight display (PFD) to command a target pitch attitude of 15° nose up.   

At this point, the captain recalled they instinctively applied control inputs via their sidestick while the aircraft was just above the runway, and the crew were alerted to this by the aircraft’s ‘dual input’ voice message (see Sidestick priority logic). 

The captain then engaged their sidestick pushbutton, and the first officer recalled hearing the ‘priority left’ voice message and the captain announce, ‘I have control.’ The captain subsequently took control of the thrust levers and the first officer relinquished control and became PM after the aircraft achieved a positive rate of climb. It was the role of the PM to retract the flap ‘one step’ at this point (see Go-around procedure). 

Figure 1: Overview of go-around 

Source: Google Earth, annotated by the ATSB

The captain announced the active flight modes on their PFD, which prompted the first officer to call ‘positive climb.’ The captain subsequently instructed the first officer to retract the landing gear, which was accomplished 42 ft above the runway at 0622:20. 

At this time, the captain looked up to the flight control unit located on the cockpit glareshield to engage the autopilot. After this was actioned, they looked back to their PFD and was ‘startled’ when they noticed that the aircraft suddenly banked right and responded by disengaging the autopilot at 0622:22. They subsequently realised that the aircraft flight director was providing commands for the published missed approach procedure and subsequently re-engaged the autopilot at 0622:29. 

The captain then requested flap 1, but the first officer noticed they were still configured with Flap 3 and retracted the flap by one step and announced, ‘flap 2.’ This occurred at 0622:32 when the airspeed reached 174 kt, which was below the maximum flap 3 speed of 195 kt.

They continued to follow the missed approach procedure, and the first officer advised ATC they were going around. The crew were given instructions to track for a right downwind for runway 16R at 4,000 ft. The captain recalled conducting a welfare check on the first officer, briefed the cabin manager via the interphone and made an announcement to the passengers through the public address system. 

The captain elected to remain as PF for the remainder of the flight, with the first officer acting as PM. The crew then conducted a second GLS approach for runway 16R, landing at 0638 without further incident.

Context

Flight crew information

The captain held an Air Transport Pilot Licence (Aeroplane), class 1 aviation medical certificate, and had accrued 5,921 hours total flying time, 1,480 of which were in the Airbus A320 and A321 aircraft types.

The first officer held a Commercial Pilot Licence (Aeroplane), class 1 aviation medical certificate, and had 2,212 hours total flying time, 551 of which were on the Airbus A320 and A321 aircraft types.

Fatigue

The captain reported that they felt 'moderately tired' during the go-around, likely due to the back-of-the clock[9] flight, which departed Denpasar at 0057 local time in Sydney. They also stated there was limited opportunity for controlled rest during the flight and their nap prior to the flight was disrupted due to noise at the hotel. The first officer reported feeling 'ok, somewhat fresh.’  

The flight crew also reported they had an adequate rest opportunity the evening prior to the flight and obtained around 6 hours sleep in the previous 24 hours and around 13‍–‍14 ‍hours in the previous 48 hours. Their sleep during the rest opportunity was reported to be good quality and the conditions at the hotel where they spent the night were suitable and therefore conducive to obtaining restful sleep. Biomathematical modelling[10] of the flight crew’s roster for the 2 weeks leading up to the flight indicated a low likelihood of fatigue.

The ATSB considered that fatigue was unlikely to have affected the flight crew’s performance at the time of the occurrence.

Aircraft information

General

The Airbus A321-251NX is a modern, fly-by-wire aircraft, powered by 2 CFM International LEAP-1A32 turbofan engines and had seating for 232 passengers in a single-class layout. 

All the flight controls are electronically actuated with the pilots using sidesticks to fly the aircraft in pitch and roll during manual flight. The 2 sidestick controllers are not coupled mechanically, and they send separate sets of signals to the flight control computers. 

Sidestick priority logic

Jetstar Airways A320-A321 Flight crew operating manual (FCOM) contains the following description of the aircraft sidestick priority logic: 

At all times, only one flight crewmember should fly the aircraft. However, if both flight crewmembers use their sidesticks simultaneously, their orders are algebraically added.

The flight control laws limit the combined order to the equivalent of the full deflection of one sidestick.

In this case the two green SIDE STICK PRIORITY lights on the glareshield come on and "DUAL INPUT" voice message is activated.

 A flight crewmember can deactivate the other sidestick and take full control, by pressing and keeping pressed the sidestick pb (Figure 2).

A “PRIORITY LEFT” or “PRIORITY RIGHT” audio voice message is given each time priority is taken.

Figure 2: Airbus A320/A321 captain's side sidestick and sidestick pushbutton

Source: Operator, annotated by the ATSB

Post-flight maintenance

The operator reported that there were no corrective maintenance actions that were required to be carried out in relation to the occurrence. The aircraft subsequently operated a scheduled passenger service the following day.

Meteorological information

The pre‑flight briefing package provided to the flight crew from the operator’s flight dispatcher included the aerodrome forecast[11] for Sydney Airport. The forecasted weather conditions for the scheduled time of arrival 0630 local time on 26 June indicated:

• wind direction of 240° at 15 kt with gusts up to 25 kt
• CAVOK[12]
• moderate turbulence[13] below 5,000 ft.

One-minute weather data for Sydney Airport from the Bureau of Meteorology indicated a wind direction of 255° at 17 kt with gusts up 20 kt at the time of the occurrence.

Airport information

Runway 16R at Sydney Airport is oriented on a magnetic heading of 155° and has a declared length of 3,962 metres with a width of 45 metres. A precision approach path indicator system is installed and set to 3° with a threshold crossing height of 64 ft. 

For daytime operations, the runway centreline, aiming point and touchdown zone markings provide visual references to assist pilots with approach and landing (Figure 3).

Figure 3: Sydney Airport runway 16R markings

Source: Google Earth, annotated by the ATSB

Recorded information

The aircraft’s quick access recorder data which captured the incident approach indicated that, as the aircraft descended below 1,000 ft, it maintained an appropriate speed and flightpath with no sustained exceedances of the stable approach criteria throughout the approach. 

At 0621:59, the recorded data captured the captain’s control inputs commencing concurrently with the initiation of the go-around, while the first officer was actively manipulating their sidestick control. Simultaneous control inputs lasted for a duration of 6 seconds (Figure 4), while the aircraft’s pitch attitude remained below the aircraft’s pitch limit of 11.5° until the aircraft had climbed through about 50 ft. 

The recorded data further indicated that the wind direction and speed varied following the flare manoeuvre, however the crosswind component remained well below the first officer’s operational limitation. The wind direction and speed was 315° at 13 kt with a crosswind component of 5 kt when the go-around was initiated.

Figure 4: Graphical representation of the recorded quick access data

Source: Quick access recorder from VH-OYF, annotated by the ATSB

Following the initiation of the go-around, the landing gear was retracted at 06:22:20 and 12 seconds later, the flap was retracted to the flap 2 configuration[14] at 174 kt.

Operational information

Stabilised approach criteria 

Jetstar Airways A320-A321 Flight crew operating manual (FCOM) defined a stabilised approach criteria as being established on the correct lateral and vertical flight path by 1,000 ft height above airport (HAA), configured for landing, and within the stated tolerances with the required checklists completed by 500 ft HAA. The FCOM also stated that if these criteria could not be met, or if the approach became unstable below 1,000 ft HAA, a missed approach was required. 

The crew reported the approach was stabilised against these criteria, which was consistent with the available recorded data.

Touchdown zone 

The FCOM provided the following operational information regarding the touchdown zone: 

The touchdown zone commences at 300 m (1000 ft) beyond the threshold and will not normally extend further than 600 m (2000 ft) beyond the threshold.

It is a requirement that the touchdown is planned to occur within the touchdown zone. Should it become apparent that the aircraft will touch down further than 600 m (2,000 ft) beyond the threshold, and the PIC believes that the landing is safe to continue, the PF must apply maximum reverse thrust and sufficient braking to ensure the aircraft stops within the landing distance available. If the PIC decides that a go-around is required, they will without delay, call “Go-Around”. In all cases this must be completed before the PF initiates reverse thrust.

The captain stated that runway 16R in Sydney was long enough to stop the aircraft on the runway if they had continued with the landing during the occurrence. This would have involved requesting maximum reverse and manual braking as necessary after the aircraft touched down. 

The FCOM did not specifically reference runway centreline tracking during a visual approach, however the captain stated that it was their personal expectation that a deviation from the runway centreline would lead them to calling for a go-around. 

Transfer of control  

The operator described procedures for transfer of control within the FCOM as follows:

The pilot relinquishing control of the aircraft shall say “You have control”. The pilot assuming control shall ensure that they have clear and unobstructed access to the flight controls and, when ready, say “I have control”. Only then is the pilot relinquishing control permitted to remove their hands and feet from the flight controls.

In critical phases of flight the PIC must be alert and positioned such that they can assume immediate control of the aircraft.

Following the occurrence, the captain stated the preferable method to conduct a go‑around at low level would have been to announce ‘I have control’ and initiate the go‑around themselves. They stated that their primary consideration when conducting a go‑around at low level was to avoid the risk of tail strike. 

Go-around procedure 

The FCOM defined the go-around procedure for the A320/A321, which specified the task sequence, memory-based crew actions and applicable guidance relating to techniques and navigation (Figure 5).

Figure 5: Jetstar Airway A320/A321 go‑around procedure below acceleration altitude

Source: Operator, annotated by the ATSB

Following the occurrence, the captain stated that although they could have taken over and landed, they believed that going around was considered the safest option. The first officer also stated, at about that time, that they were in the mindset of preparing to initiate a go-around themselves. 

Related occurrences

The following ATSB investigation highlights the importance of pilots maintaining their readiness for a go-around on every approach as it is typically a period of high workload requiring effective crew coordination. 

ATSB Investigation

On the morning of 18 May 2018, an Airbus A320 aircraft, registered VH-VQK, was being operated on a regular public transport flight by Jetstar Airways. The flight departed from Sydney for Ballina/Byron Gateway Airport, New South Wales.

The flight crew conducted a go-around on the first approach at Ballina because the aircraft’s flight path did not meet the operator’s stabilised approach criteria. On the second approach, at about 700 ft radio altitude, a master warning was triggered because the landing gear had not been selected DOWN. The flight crew conducted a second go‑around and landed without further incident on the third approach.

The flight crew did not follow the operator’s standard procedures during the first go‑around and subsequent visual circuit at 1,500 ft. In particular, the flaps remained at flaps 3 rather than flaps 1 during the visual circuit. This created a series of distractions leading to a non‑standard aircraft configuration for a visual circuit. Limited use of available aircraft automation added to the flight crew’s workload.

Safety analysis

During the approach to Sydney airport, with the first officer acting as the pilot flying (PF), the flight crew reported experiencing a crosswind of up to 30 kt until descending through about 500 ft above mean sea level. The crew were advised by air traffic control to expect a right crosswind component of 8 kt for landing, which was within the first officer’s operational crosswind limit of 20 kt. The captain confirmed the approach was ‘stable’ at 500 ft and the first officer continued the approach as PF.

At 50 ft, the first officer initiated the flare manoeuvre prior to landing. They recalled they ‘over flared,’ and the aircraft subsequently floated for an extended period along the runway. During this time, the first officer’s control inputs did not counteract the effect of the crosswind, and the aircraft drifted left of the centreline. After observing the lateral deviation from the centreline, the captain commanded the first officer to conduct a go‑around. 

This occurred just prior to the aircraft touching down when the flight crew would normally be focused on landing. The flight crew did not expect a go-around at the time and had to rapidly shift their focus to conducting the missed approach procedure. The captain recalled being ‘startled’ by the unexpected need to discontinue the landing, however they were more likely experiencing ‘surprise.’ Surprise is a cognitive-emotional response to something unexpected, which results from a mismatch between one’s mental expectations and perceptions (Rivera, Talone, Boesser, Jentsch, & Yeh, 2014). But their decision was consistent with the expectation that an approach be discontinued if the aircraft departed from the correct lateral flight path.

The unexpected change from landing to conducting a go-around close to the ground also resulted in the captain experiencing a sudden stress response at this time. When experiencing acute stress, people can respond quickly to a situation, but without conscious decision‑making (Wickens, Helton, Hollands, & Banbury, 2022). After the go‑around was commanded, there was a rapid increase in pitch attitude, engine thrust and airspeed, and in response the captain instinctively and inadvertently manipulated their sidestick while the first officer was flying, resulting in a dual-input alert. 

The captain reported they only realised they had manipulated their sidestick when they heard the dual input alert. Their primary consideration during the go-around was to avoid an excessive rotation rate to avoid a tail strike, which did not occur. Additionally, operator procedures directed captains to be alert and be positioned to ‘assume immediate control of the aircraft’ during critical phases of flight. 

Following the dual input alert, the captain took full control by engaging their sidestick push‑button and announced ‘I have control’, and the first officer assumed the role of pilot monitoring. A consequence of the control handover during the initial stages of the go‑around was the momentary interruption of sequential crew actions during the go‑around procedures. Interruptions typically disrupt the chain of procedure execution so abruptly that pilots turn immediately to the source of the interruption without noting the point where the procedure was suspended (Loukopoulos, Dismukes, & Barshi, 2009). 

Additionally, there was a further disruption (rapid task switching) associated with the first officer and captain exchanging pilot flying and pilot monitoring roles. As a result, some of the procedural items were completed out of sequence (flap 3 retraction occurred after gear retraction). 

Pilots are highly vulnerable to errors of omission when they must attend to multiple tasks. If one task becomes demanding, their attention is absorbed by these tasks demands and they can forget to switch their attention to other tasks (Loukopoulos, Dismukes, & Barshi, 2009). Although the flap retraction occurred out of sequence during the go-around, there were no associated flight envelope exceedances or negative effects on aircraft performance.  

Findings

From the evidence available, the following findings are made with respect to the control issues during landing and go-around involving Airbus A321, VH-OYF, at Sydney Airport, New South Wales, on 26 June 2025.

Contributing factors

• During the landing after crossing the threshold, the first officer’s control inputs resulted in a lateral deviation from the runway centreline during a prolonged float.
• After calling for a go-around, the captain inadvertently manipulated their sidestick while the first officer was the pilot flying, which resulted in a simultaneous control input and the go-around procedure being completed out of sequence.

Sources and submissions

Sources of information

The sources of information during the investigation included:

• Jetstar Airways Pty Limited
• Bureau of Meteorology
• the flight crew
• recorded data from the quick access recorder from VH-OYF.

References

Loukopoulos, L., Dismukes, R., & Barshi, I. (2009). The perils of multitasking. AeroSafety World, 4(8), 18-23.

Rivera, J., Talone, A., Boesser, C., Jentsch, F., & Yeh, M. (2014). Startle and surprise on the flight deck: Similarities, differences, and prevalence. In Proceedings of the human factors and ergonomics society annual meeting (Vol. 58, No. 1, pp. 1047-1051). Sage CA: Los Angeles, CA: SAGE Publications.

Wickens, C. D., Helton, W. S., Hollands, J. G., & Banbury, S. (2022). Engineering psychology and human performance, 5th edn. Routledge, doi: 10.4324/9781003177616.

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
• the flight crew
• Jetstar Airways Pty Limited
• Bureau of Meteorology.

Submissions were received from:

• the flight crew
• Jetstar Airways Pty Limited.

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

At 1021 on 7 April 2025, a Bankstown Helicopters Robinson R44 helicopter, registered VH‑EWM (EWM), with a pilot and 2 passengers on board, departed from Bankstown Airport, New South Wales, for a local scenic flight around Sydney Harbour. Shortly after 1028, as EWM was entering the Parramatta River helicopter lane behind an EC120 helicopter, the occupants of EWM experienced a sudden onset of turbulence followed by an uncontrolled descent. 

In response, the pilot applied full collective, which resulted in a low rotor speed condition as the helicopter descended towards the water. The pilot was able to manoeuvre the helicopter and complete a forced landing on the river shoreline.

What the ATSB found

The ATSB found that it is likely that EWM entered the rotor wake from a preceding heavier EC120 helicopter, which resulted in the control difficulties, an uncontrolled descent, low rotor speed warning and the forced landing. 

What has been done as a result

Following review of the draft report, the Civil Aviation Safety Authority undertook proactive safety action to improve existing guidance about helicopter wake vortices in Advisory Circular 91-16. The updated advisory circular was released on 17 July 2025 and can be found at the link: AC 91-16 v1.2 - Wake turbulence.

Safety message

Flight tests have demonstrated that helicopter wake turbulence is comparatively larger and less predictable in its behaviour than for aeroplanes of the same weight. Helicopter rotor vortices can descend, remain level or climb, and the duration of their persistence can increase significantly in conducive weather conditions. The United States Helicopter Safety Team website recommends remaining 3 rotor disks clear of a hovering or taxiing helicopter and allowing 3 NM and/or 2 minutes for the rotor wake from a preceding helicopter to dissipate.

The investigation

The occurrence

At 1021 local time on 7 April 2025, a Bankstown Helicopters Robinson R44 Raven 1 helicopter, registered VH‑EWM (EWM), with a pilot and 2 passengers on board, departed from Bankstown Airport, New South Wales for a local scenic flight around Sydney Harbour. Bankstown Tower air traffic control (TWR) cleared EWM to depart via ‘Choppers West’, which was a standard procedure for helicopters departing to the north when runway 29 was active at Bankstown. 

The pilot reported that they climbed to about 1,000 ft above mean sea level.[1] The pilot’s plan was to join the Parramatta River on the west side of the Ryde Bridge and descend to 500 ft to follow the helicopter lane[2] along the south side of the river to Sydney Harbour (Figure 1).

Figure 1: Key locations

Source: Google Earth, annotated by the ATSB

About 1 minute after EWM departed, an Airbus EC120B helicopter departed Bankstown, also following the Choppers West departure. Shortly after the EC120 departed, TWR advised the EC120 pilot that there was ‘R44 traffic 1 NM ahead’, to which the EC120 pilot reported that they had the traffic sighted. Bankstown TWR then advised the pilot of EWM that they were not receiving their transponder data, which the pilot acknowledged. The pilot of EWM then turned their transponder off and on in an attempt to transmit transponder information, but no data was received from it throughout the incident flight.

As the 2 helicopters tracked north towards the Parramatta River, the EC120 flew to the west of EWM and passed it before reaching the river. The EC120 then turned right to join the Parramatta River helicopter lane, tracking towards the Ryde Bridge and Sydney Harbour, and passed over the Ryde Bridge at a recorded radar altitude of 600 ft. 

The pilot of EWM reported that they descended the helicopter to 500 ft as they approached the river. Just before the pilot turned EWM right to join the helicopter lane, another larger helicopter (the EC120) suddenly appeared in front of them (Figure 2). The pilot of EWM estimated the EC120 was about 500‍–‍600 ft (150‍–‍180 m) in front of them and about 100 ft above them. While there was no recorded altitude for EWM, primary radar data indicated that EWM entered the lane about 9 seconds behind the EC120.[3] Primary radar data for EWM was lost about 10 seconds later, just after 1028, indicating it had descended below radar coverage.

Figure 2: Primary radar return (left) and loss of primary radar return (right) for VH‑EWM

Source: Airservices Australia, annotated by the ATSB

The pilot of EWM made a radio broadcast that they were entering the helicopter lane as they crossed the Ryde Bridge behind the EC120. They then experienced what they described as very strong turbulence from a vertical motion in the atmosphere. A passenger later described it as ‘like heavy turbulence … rolling left and right’ followed by ‘diving towards the water’.

The pilot noted that the helicopter was descending through 400 ft and responded by raising the collective lever.[4] However, the helicopter continued descending towards the water as it tracked behind and below the EC120. A passenger recalled the pilot announced ‘brace for impact’ as the helicopter approached the water. The pilot applied full collective to avoid the water, which caused the rotor speed to decay sufficiently for the low rotor speed warning horn to activate. They also reported feeling that they could not escape what they believed to be the rotor wake from the EC120. The pilot then sighted a suitable forced landing area at Cabarita Park and, using the helicopter’s remaining airspeed and rotor speed, manoeuvred the helicopter to the shoreline for a landing.

Following the landing, the pilot rolled the engine throttle back to idle and proceeded through their after‑start checks and confirmed normal operations on the ground. The pilot then conducted a hover check and again confirmed normal operations. The pilot attempted radio contact with their operations base but received no reply. They then conducted a return flight to Bankstown without further incident. 

Context

Pilot information

The pilot held a commercial helicopter pilot licence, issued on 26 November 2024, with a single‑engine helicopter class rating and low‑level rating. The pilot held a class 1 aviation medical certificate with no restrictions and expiration date of 30 May 2025. The pilot had accumulated about 112 hours flying experience and the incident flight was the pilot’s first commercial flight.

Helicopter information

The incident helicopter, EWM, was a piston‑engine 2‑bladed Robinson Helicopter Company R44 Raven 1 with a maximum take‑off weight of 1,089 kg. The weight and balance data provided by the operator indicated it was within limits for the flight. 

The Airbus EC120B was a turbine-engine 3‑bladed helicopter with a maximum take‑off weight of 1,715 kg. Therefore, the EC120 was about 57% heavier than EWM at their respective maximum take‑off weights.

The maintenance release for EWM indicated the helicopter was operated by Bankstown Helicopters in the operational category of Part 133 Air Transport. The maintenance release current at the time of the incident was issued on 3 April 2025 at 4,349 hours total time in service with an expiry date of 3 April 2026 or 4,400 hours. A maintenance test flight was certified on the maintenance release as conducted on 3 April with ‘nil defects evident.’ 

After the incident, the operator’s maintenance organisation inspected the helicopter and found no defects. As the flight hours remaining on the helicopter were close to the next overhaul, the operator elected to remove the helicopter from service and have the maintenance organisation complete the overhaul. 

Meteorological information

The METAR[5] recordings for Bankstown Airport at 1000 and 1030 indicated that the wind was westerly at a speed of 9 kt at 1000 and 7 kt at 1030. No cloud was detected. These conditions were consistent with the Bankstown Airport forecast for 8 kt westerly winds. The pilot reported their assessment of the weather was 5 kt of variable wind and CAVOK[6] conditions, but when they encountered the turbulence over the Ryde Bridge it felt like 40 kt of wind.

Rotor wake turbulence

In 1996, the United States Federal Aviation Administration (FAA) produced a report on the subject of Flight test investigation of rotorcraft wake vortices in forward flight. They used a laser doppler velocimeter to measure the vortices and small probe aircraft to test the actual flying conditions. Smoke generation was used to visualise the wake vortices for the probe aircraft. Their investigation concluded that:

• The measured vortex circulation diminished with decreasing airspeed for helicopter airspeeds below 40 knots. At these lower speeds, the wake vortex structure begins to break down and changes to a distinct downwash.
• Vortex duration depends strongly on ambient weather conditions and a variance of 300% was observed on those days most conducive[7] to vortex persistence and duration compared with those observed on typical days.
• Typically, helicopters with higher gross weight, larger rotor diameters, and larger numbers of rotor blades generated vortices of larger core diameters.
• Probe tests revealed that helicopter vortices did not descend in the same predictable manner as for fixed‑wing aircraft. Some vortices descended; some remained level; and some initially descended, levelled off, and then ascended above the altitude of the generating helicopter.

Figure 3: Rotor wake vortices visualised with smoke generators

Visualisation of the wake vortices behind an S‑76A helicopter in forward flight with smoke generators from the FAA (1996) flight tests. Source: Reddit

Meiris (n.d.) provided an article for the United States Helicopter Safety Team website, on the subject of Avoiding helicopter wake turbulence. The article referenced the FAA 1996 flight test report and provided the following recommendations:

As a result of these findings and the studies conducted regarding helicopter downwash in a hover, a few guidelines have been developed to increase awareness around helicopter wake turbulence:

• For hovering flight or a hover taxi, stay three rotor diameters away.

• For forward flight, a minimum of 3 nm [NM] separation is recommended, especially from larger helicopters. The investigation we discussed previously discovered that even at 3nm [NM], the planes encountered uncommanded pitch and roll oscillations.

• Leave 2 minutes for the rotor vortices to dissipate behind a helicopter in forward flight.

Related occurrences

The French Bureau of Enquiry and Analysis for Civil Aviation Safety investigation BEA2019-0234, Accident to a paraglider involving the Airbus - EC135 - T2 PLUS registered F-HTIN, examined a fatal paraglider accident in 2019. The paraglider’s wing collapsed after encountering the rotor wake from an Airbus EC135 helicopter, which drifted with the wind from the helicopter’s flightpath onto the paraglider (Figure 4).

Figure 4: Simulation of rotor wake drifting onto the paraglider

Source: YouTube – Bureau of Enquiry and Analysis for Civil Aviation Safety, annotated by ATSB

The 2022 United States National Transportation Safety Board investigation WPR22LA072 found that the pilot of a Cessna 120 attempted a go‑around about 20 seconds behind the passage of a Bell UH‑1H helicopter. During the go‑around the Cessna encountered wake turbulence, resulting in a loss of control and collision with terrain (Figure 5). The report indicated light wind conditions of 4 kt at the airport.

Figure 5: Loss of control accident from rotor wake

Source: YouTube – Aviation Safety Network, annotated by ATSB

Safety analysis

Primary radar data and the pilot’s report indicated that EWM entered the Parramatta River helicopter lane and passed over the Ryde Bridge about 9 seconds behind and slightly below the EC120 helicopter. At this point, EWM encountered heavy turbulence, an uncontrolled descent and a low rotor speed when the pilot applied full collective to avoid a collision with the water.

The uncontrolled descent and low rotor speed condition resulted in the pilot conducting a forced landing on the shoreline of the Parramatta River. 

The incident occurred under relatively calm wind conditions and EWM operated in a serviceable condition for the return flight. Subsequent maintenance inspections of the helicopter found no fault. Furthermore, EWM passed overhead the Ryde Bridge in sufficient proximity to a preceding heavier 3‑bladed helicopter to be subject to a rotor wake induced upset. Therefore, the ATSB concluded that the sudden onset of turbulence and uncontrolled descent were likely the result of EWM encountering rotor wake turbulence from a preceding EC120 helicopter. 

Findings

From the evidence available, the following findings are made with respect to the wake turbulence encounter and forced landing involving Robinson R44, VH-EWM, about 15 km north‑east of Bankstown Airport, New South Wales, on 7 April 2025. 

Contributing factors

• It is likely that the incident helicopter entered the rotor wake from a preceding heavier helicopter, which resulted in control difficulties, an uncontrolled descent, low rotor speed warning and a forced landing.

Safety actions

Safety action by the Civil Aviation Safety Authority

Following review of the draft report, the Civil Aviation Safety Authority undertook proactive safety action to improve existing guidance about helicopter wake vortices in Advisory Circular 91-16. The updated version of the advisory circular was released on 17 July 2025 and can be found at the link: AC 91-16 v1.2 - Wake turbulence.

Sources and submissions

Sources of information

The sources of information during the investigation included:

• Airservices Australia
• Civil Aviation Safety Authority
• the operator and maintenance organisation for VH-EWM
• the pilot and passengers of the incident flight

References

Bureau of Enquiry and Analysis for Civil Aviation Safety. (2021). Accident to a paraglider involving the Airbus - EC135 - T2 PLUS registered F-HTIN on 11 May 2019 at Le Conquet (Finistère). https://bea.aero/fileadmin/user_upload/BEA2019-0234.en.pdf

Federal Aviation Administration. (2023). Aeronautical information manual. http://www.faa.gov/air_traffic/publications

Federal Aviation Administration. (1996). Flight test investigation of wake vortices generated by rotorcraft in forward flight (DOT/FAA/CT-94/117). https://apps.dtic.mil/sti/tr/pdf/ADA318103.pdf

Meiris, J. (n.d.). Avoiding helicopter wake turbulence. https://ushst.org/avoiding-helicopter-wake-turbulence/

National Transportation Safety Board. (2022). Aviation investigation final report (WPR22LA072). Investigation docket https://data.ntsb.gov/Docket?ProjectID=104480

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
• the maintenance organisation for VH-EWM
• the operator and pilot of the incident flight.

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 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.

The occurrence

Prior to the occurrence flight

On 10 March 2025, a Bell 421EP, registered VH-VJF and operated by Coulson Aviation as HT204, was tasked with ground crew support operations on the Canning Peak fire, a sub‑fire of the West Coast fire complex in Tasmania. 

At about 0830, the Tasmanian Fire Service briefed pilots on the weather and taskings for the day while at Strahan Airport. The Air Attack Supervisor (AAS) reported that the 2 Bell 412 helicopters were tasked with the insertion of crews into the fireground (HT201) and then firebombing[1] in support of those crews with a 150-ft longline and bucket[2] (HT204).

At about 0900, both helicopters departed Strahan Airport for Tullah, which was the designated staging area[3] for the activities. Approximately 25 minutes later both helicopters arrived at Tullah. The pilot of HT204 reported shutting down the helicopter and waiting until they were required for firebombing operations. The pilot of HT201 reported picking up a crew and completing an insertion into the fireground before returning to Tullah and remaining on standby in case an extraction was required. 

First fuel cycle

At about 1215, HT204 was tasked with firebombing operations in direct support of ground crew who were undertaking hot and cold trailing.^[4] 

At 1226 local time the pilot departed Tullah for hotspots located west of the Murchison River on the south‑east end of the fire. The pilot was the only person on board. The pilot reported that the weather conditions on departure were calm, with a temperature of 22°C and light, variable winds. 

When reaching the dip site^[5] the pilot completed one fuel cycle, approximately 10 bucket loads, under relatively stable conditions. The pilot described the dip site as a narrow section of river, approximately 50–60 m wide, with tall trees lining the bank (see also Dip site). The drop zone was located approximately 1 km west of the dip site. 

The pilot then returned to Tullah to pick up an air crew officer (ACO) at 1400 and continued onto the designated air base in Zeehan, which had a sports oval being used as a refuel base (Figure 1).

Figure 1: First fuel cycle and return to Tullah

White line: flight path of the first fuel cycle and return to Tullah. Purple line: flight path from Tullah to Zeehan. Source: Google Earth, annotated by the ATSB

Zeehan air base

During the approach to Zeehan, the pilot noted a significant weather change, with winds shifting to a westerly direction at approximately 30 knots. 

While on the ground, the helicopter was refuelled for the next cycle. At about 1440 the pilot departed Zeehan and returned to the Canning Peak fireground. 

Second fuel cycle and occurrence

The pilot recalled that various dip sites along the river looked similar. Flight data (Figure 2) indicated the pilot initially conducted a descent into an incorrect dip site. The pilot recognised this and undertook reconnaissance to find the intended dip site. Once reaching the dip site, the pilot resumed bucketing operations. 

Figure 2: Second fuel cycle flight path

Source: Google Earth, annotated by the ATSB

The pilot reported that, at about 1525, while filling the third bucket load of water, the helicopter had been in a stable hover at about 150 ft above the water, when it unexpectedly sank. The pilot recalled the helicopter sinking approximately 50 ft. To recover control, the pilot applied forward cyclic and upward collective inputs to transition to forward flight and stabilise the helicopter, while aiming to avoid an over-torque event. 

Prior to this manoeuvre, the pilot reported they were unable to jettison the longline, which they attributed to pressing on the button’s ring guard instead of its centre, and the longline subsequently became taut. The helicopter then came to an abrupt stop and the pilot heard a ‘loud clunking noise’. The pilot then recovered the helicopter to a stable hover approximately 30 ft above the water and initiated rearward flight to release the water and retrieve the bucket from the river. The pilot observed an engine torque split[6] and once the bucket and longline were recovered they initiated a climb to clear the surrounding trees. 

The pilot reported that once they had cleared the trees, the torque split levelled back out. They conducted a range of tests to assess controllability and engine performance, including minor adjustments to engine torque. The pilot noted that the tail rotor control pedals felt stiff, however they continued to provide adequate input for sufficient helicopter control. 

The pilot contacted the AAS on the fire common traffic advisory frequency (FCTAF) stating they had a bucket issue and a flight control issue.  

The air attack pilot (who flew the helicopter with the AAS on board) oriented the helicopter to view HT204. The AAS recalled HT204 gaining altitude and tracking away from the Murchison River, over the fire, heading on a bearing south‑west uphill and back to Zeehan. They noted the helicopter was climbing slowly and appeared to be flying irregularly during this period. They reported they had not seen the occurrence as the dip site HT204 was using was beneath and behind the air attack helicopter. 

The AAS contacted the pilot on the FCTAF. The pilot of HT204 reported issues with the helicopter pedals and when asked what their intention was, the pilot reported they were heading back to Zeehan. The AAS acknowledged this and reported they would follow HT204 back. 

The pilot of HT204 assessed available landing options but elected to continue toward Zeehan rather than commit to an off-field landing. This decision was influenced by a previous experience where a potential landing site, assessed from approximately 500 ft, had appeared suitable but proved unsuitable upon reaching around 30 ft. The pilot considered that committing to a landing carried the risk of being unable to complete it safely.

The AAS and air attack pilot discussed possible landing options nearby. However, given the impaired controllability of HT204 and the smaller prepared landing areas on the fireground, they agreed the best action would be to return to Zeehan. 

Return flight

The pilot of HT204 reported that, during the return flight to Zeehan, airspeed was maintained between 65 and 70 kt[7] due to the tail rotor pedals feeling stiff. This would reduce strain on the tail rotor by operating the helicopter at a lower power setting.

The pilot reported continuing the flight toward Zeehan with a plan that, should the situation deteriorate further, the flight would be changed to Strahan Airport as an alternative. Throughout the remainder of the flight, pedal inputs were minimised in an effort to avoid exacerbating the condition.

The AAS described the helicopter’s flight en route to Zeehan as appearing abnormal. In addition to the notably reduced speed, HT204 appeared to be yawing from side to side and maintained an unusually low height above ground. They reported that due to the pilot sounding stressed they did not contact the pilot further.

The AAS recalled contacting the air base manager at Strahan and the air operations manager and advised them of an unknown mechanical malfunction with HT204. They reported that the pilot was still in control, and that they were following HT204 back to Zeehan.

Landing at Zeehan

At about 1548, the pilot conducted a shallow approach to set up a vertical descent to the oval in Zeehan with the bucket and longline attached. During the landing sequence, the ACO secured the bucket and longline and moved it away and forward of the landing zone. The pilot then released the line and allowed the helicopter to sink, utilising available power, which resulted in what they stated ‘appeared to be a satisfactory landing with minimal pedal input required’.

After landing, during the shutdown procedure, the pilot was unable to roll the engine throttles back to idle. While disconnecting the longline from the hook, the ACO observed significant damage to the helicopter’s fuselage structure aft of the external hook. 

The pilot of HT201 recalled that they landed and shut down their helicopter in Zeehan. They observed HT204 still running and the pilot underneath the helicopter assessing damage. They discussed the issue of not being able to roll the engines back and the pilot of HT201 suggested pulling the helicopter’s T-handles.[8] The T-handles were pulled to shut down the engines. 

Context

Pilot information

The pilot held a Commercial Pilot (Helicopter) Licence, with a single engine class rating for helicopters. They held type ratings for the Bell 212, 412 and 427. The pilot’s total aeronautical experience was over 3,000 hours of which 120.6 hours were on the Bell 412. In the previous 90 days the pilot had flown 50.3 hours, all on the Bell 412. 

The pilot was qualified to conduct helicopter firefighting operations and had low‑level and sling operation ratings.

The pilot last completed an aerial application proficiency check on 11 November 2024, which was valid for 12 months, and a low-level helicopter flight review on 4 December 2023. 

The pilot held a valid Class 1 aviation medical certificate, valid to July 2025. The certificate specified that the pilot was to wear distance vision correction while flying, which was being worn on this occasion.

Helicopter information

General information

The Bell Helicopter Company 412EP is a medium‑lift[9] utility helicopter commonly used for firefighting, search and rescue and transport operations. The helicopter had a 4-blade main rotor and 2‑blade tail rotor and was powered by 2 Pratt & Whitney PT6T-3DF turboshaft engines. The helicopter was manufactured in Canada in 2004 and first registered in Australia in 2020. The helicopter was owned by NSW Rural Fire Service (RFS) and operated by Coulson Aviation Australia. 

VH-VJF had accumulated about 4,819 flight hours total time in service and had a current certificate of airworthiness and registration. The helicopter’s technical log indicated no outstanding defects at the time of the accident. 

The helicopter’s multi-role configuration enabled it to be utilised in a range of aerial firefighting tasks, including reconnaissance, winching operations and firebombing using either a belly tank or external bucket system (Figure 3).

Figure 3: NSW RFS Bell 412 EP VH-VJF

Source: Lesley de Robllard, annotated by the ATSB

On the day of the accident, the helicopter was configured for firebombing operations and was fitted with an external load system, a vertical reference door, and a 150‑ft longline attached to a Bambi bucket[10] (see Bucket and longline information). In addition to these items, the helicopter also had a forward looking infrared (FLIR) camera mounted on the left‑hand side of the helicopter above the skids.

External load system

VH-VJF was equipped with an Onboard Systems International cargo hook suspension system. The system attached to an existing Bell hard point and hung at approximately the centre of gravity. It extended through an opening in the lower fuselage, which was fitted with a protective rubber ring around the edge (Figure 4). This protective ring was used to reduce the risk of damage if the hook hit the edge of the opening.

Figure 4: Onboard Systems International cargo hook suspension system on the Bell 412

Source: Onboard Systems International, annotated by the ATSB

The release of the hook could be initiated electrically or mechanically. Normal release was completed by pilot actuation of a push button on the side of the cyclic (Figure 5, left). The button is guarded by a small ring to prevent inadvertent pilot activation. When this button is pressed the latch of the cargo hook is opened. 

In addition to the electrical release, in an emergency a mechanical release can be completed by pushing a small pedal located between the 2 tail rotor pedals at the pilot’s feet (Figure 5, right). This activated a manual release cable attached to the cargo hook.

The cargo hook suspension system was required to be inspected annually or after 100 hours of external load operations, whichever came first. The system was last inspected on 20 February 2025. 

Figure 5: Electrical and mechanical external load release systems

Left: the electrical release found on the cyclic grip. Right: mechanical release between the 2 pedals. Source: Coulson Aviation, annotated by the ATSB

Coulson Aviation required pilots to test the electrical and manual release system prior to conducting flights for the day. The pilot recalled testing both the electrical and mechanical release the morning of the accident. They stated that both systems were in working order. In addition to the tests, the pilot recalled that when landing at Zeehan after the accident, the electrical release was used to drop the longline and bucket without issue. 

Coulson Aviation reported that both the electrical and mechanical releases of the hook were tested following the accident. Both were reported as serviceable. 

Vertical reference door

The Bell 412EP helicopters are usually flown from the right-hand seat. This configuration is used when pilots are conducting either winching or reconnaissance operations. The helicopters can be modified to include a vertical reference door, which is designed to provide the pilot with a side bubble window and instruments for longline operations from the left-hand seat.

VH-VJF was modified with a vertical reference door in accordance with the Transwest vertical reference door supplement type certificate. This included a bubble window, viewing slot, and instruments and warning lights installed in the door (Figure 6).

Figure 6: Instruments and warning lights installed in the vertical reference door

Source: Coulson Aviation, annotated by the ATSB

In addition to the instruments and warning lights, the type certificate required the installation of several systems to be placed on the left side of the helicopter. This included: 

• a force trim switch, cargo release switch and automatic flight control system (AFCS) release switch mounted on the left cyclic
• the torque meter and tachometer from the left-hand instrument panel moved to the vertical reference door
• an additional mechanical cargo release pedal between the left side pedals.

During the occurrence flight and other firebombing operations, the pilot was operating the helicopter from the left-hand seat, utilising the left cyclic and referencing the flight instruments through the vertical reference door. While conducting the water collection, the torque indicator was visible through the bubble window and could be monitored during the lift. 

Bucket and longline information

The bucket and longline were attached to the external load system via a bow shackle (Figure 7, left). 

The bucket was a Bambi Max bucket with a nominal capacity of 240 US gallons (910 L). The empty weight of the bucket was 137 lb (62 kg) and the maximum gross weight was 2,140 lbs (970 kg).

The collapsable bucket was equipped with multiple selectable drop valves. Pilots were able to use the bucket to split water loads into multiple drops (Figure 7, right) and had the capability to shed the load rapidly.

Figure 7: Longline attachment and Bambi Max bucket

Source: Coulson Aviation, annotated by the ATSB

The longline was constructed from high-strength synthetic fibre rope selected for its high tensile strength, low stretch characteristics, light weight, and resistance to heat and abrasion. The line incorporated an electrical cable along the line to control bucket release. The 150-ft length provided vertical separation between the helicopter and the load to reduce rotor downwash disturbance during water pick‑up. 

Forward looking infrared (FLIR) camera

FLIR cameras are used on aerial firefighting aircraft to provide thermal imaging of fire grounds, enabling crews to detect heat sources through smoke, darkness, or challenging terrain. This capability allows operators to identify fire hotspots, monitor fire spread, and support decision-making for resource deployment and suppression strategies.

On the Bell 412s, the FLIR camera was mounted on the left side, just above the skids. Coulson Aviation stated that although the cameras could be removed, they would generally be kept on the helicopters throughout all operations, allowing the ability for the crews to be re-tasked for reconnaissance missions. Some pilots indicated to the ATSB that the camera could partially obscure visibility during bucketing.

Helicopter damage

The ATSB did not examine the helicopter or equipment. Coulson Aviation conducted an examination of the helicopter the morning after the occurrence. The following damage was identified:

• The #1 engine control tube had sheared at the lower tube end bell crank, resulting in a complete loss of pilot input to the engine.
• The #2 engine control tube bell crank attachment bracket had detached from the helicopter structure’s securing rib, restricting pilot control of the engine.
• The tail rotor control rod on the right-hand side of the external hook’s bell crank airframe attachment had broken away, with the primary structure also separated.
• The main transmission oil cooler pressure line exhibited significant contact damage, however, no splits or leaks were identified.
• The fuel tank interconnect braided hoses sustained minor contact damage.
• Multiple aft fuselage drain lines were damaged.

Images of the helicopter indicated that the structural fuselage honeycomb aluminium skin, adjacent to and aft of the external hook, was deformed and had separated from the primary structure (Figure 8).

Figure 8: Helicopter aluminium skin damage

Source: Coulson Aviation, annotated by the ATSB

Images revealed indications consistent with contact between the longline and the rear cross tubes of the helicopter. In addition, inspection of the cargo hook and associated bumper stop components identified visible signs of impact damage (Figure 9).

Figure 9: External load system damage

Source: Coulson Aviation, annotated by the ATSB

In addition, the ring in the middle of the Bambi bucket spoke assembly was fractured in 4 places (Figure 10).

Figure 10: Bambi Max damage to spoke assembly

Source: Coulson Aviation, annotated by the ATSB

Multiple instances of cable bruising and stretching were reported to have been observed on the bucket cable wiring and attachment eye ends. The ATSB was unable to substantiate the presence of cable bruising and stretching based on the images provided of the cables.   

Weather data

On departure from Strahan Airport, the meteorological aerodrome report (METAR)[11] reported wind west‑north-west at 6 kt, visibility greater than 10 km and no cloud cover. 

The Tasmania Fire Service (TFS) incident action plan indicated that weather on the Canning Peak fire would change from north-westerly to west-south‑westerly by mid‑morning with winds reaching 10 kt by the afternoon (Table 1).

 Table 1: Canning Peak fire forecast

The AAS reported that on the day of the accident the wind was calm, there was no turbulence and ‘great’ visibility. A change in wind direction was noted from mid-morning changing from northerly to south-westerly, however this was expected based on the forecast. They recalled the area in which the aircraft were working in was protected from south‑westerly winds due to the topography. They reported no feedback from pilots regarding the weather or any other environmental conditions on the day. 

The pilot of HT201 reported there were blue skies and fairly light winds on the day of the accident. They recalled that although they were not bucketing on this day, during previous bucketing operations in the same valley, the wind conditions were variable and the wind would shift ‘back and forth’. 

 A weather station atop Mt Inglis, approximately 15 km north of the operating area (Figure 11), recorded south‑south-westerly winds at 5.7 kt gusting to 11.4 kt at the time of the accident. 

Figure 11: Canning Peak weather station location to dip site

Source: Google Earth, annotated by the ATSB

Fireground information

The West Coast fire complex originated from 24 individual ignitions sparked by dry lightning strikes on 3 February 2025, across Tasmania’s remote western and north‑western regions. These separate fires were grouped into a single complex for coordinated management due to their proximity, shared weather influences, and overlapping spread patterns. 

There were 4 primary firegrounds that accounted for the majority of the burnt area: the Canning Peak fireground, the Yellowband Plain fireground, the Mount Donaldson fireground, and the Corinna Road fireground. Each represented a distinct sector with unique terrain, vegetation types, and behavioural characteristics. These firegrounds collectively contributed to the complex’s total footprint of nearly 95,000 hectares.

Canning Peak fireground

The Canning Peak fireground was located in a more elevated and vegetated zone close to the Cradle Mountain area and in proximity to sections of the Overland Track. This sector featured rugged alpine-influenced terrain that complicated direct ground access, leading to heavy reliance on aerial suppression tactics. 

Figure 12: Canning Peak fireground

Black outline indicates area which has been burnt by fire. Source: Tasmania Parks and Wildlife Service, annotated by the ATSB

Day of accident

On the day of the accident HT201 was the designated winching helicopter and HT204 was part of the bucketing helicopters on the fireground. There were 6 helicopters (3 x AS350, 1 x Bell 412 (HT204), 1 x Bell 212, 1 x BK 117) bucketing within a 2 km proximity of each other intermittently. In addition, the air attack helicopter was on scene overhead.

The helicopters were distributed across 4 separate circuits, with 5 separate dip points, seperate individual and shared targets and some shared ground crew. 

Dip site

The pilot reported that the general location for a dip site was provided prior to commencing operations on the fireground, with selection of the specific section of river within that area being at their discretion. The pilot advised that they chose this dip site location on the river as it was relatively wider than other areas and they had used this section as a dip site on the days preceding the accident.

HT204’s dip site was approximately 700 m from the next nearest dip site with working helicopters. The dip site was approximately 1 km south‑east of the drop zone, along the Murchison River. Google Earth images indicate the river width at the dip point was approximately 20 m (Figure 13).

Figure 13: Dip site location on Murchison River

Source: Google Earth, annotated by the ATSB

The pilot described the dip site as a narrow section of river, approximately 50–60 m wide, with tall trees lining the bank. They reported that there were limited locations deep enough to operate the bucket, which constrained where they could dip and they stated they had used the same dip point on the days prior.

In addition, the river contained very little water at the time, allowing clear visibility to the riverbed. They stated that they could not recall whether any tree branches or rocks were present in the riverbed during the operation. Despite the presence of tall trees, the pilot indicated that the area was accessible to the aircraft and considered it one of the better dip sites along the river. They also noted that the turnaround time from the dip point to the fireground was approximately one minute. 

The AAS described the dip site as a section of river with trees approximately 30–60 m tall on either side. They recalled that the pilot was the only one using the dip point and the only helicopter in the circuit. In previous weeks, when different crews had flown the same helicopter on similar missions, no pilots had reported any problems with the dip point. Based on the dips that were observed, the occurrence pilot appeared to be performing them safely and adequately.

Recorded data

Multiple independent data sources, including TracPlus satellite-based tracking logs, FlightAware ADS-B derived positions, and OzRunways electronic flight bag recordings, were cross‑referenced and correlated to reconstruct the helicopter’s flights throughout the day and to approximate the entry and exit angles into and out of the bucketing site.

TracPlus

The helicopter was fitted with a TracPlus surveillance system, which provided real-time tracking through a satellite or mobile phone network. It reported position, altitude, and speed at set time periods, in this case every 15 seconds. 

OzRunways

The OzRunways application recorded the helicopter’s position at regular intervals of approximately 5 seconds throughout the day, capturing parameters including latitude, longitude, groundspeed, track, and truncated altitude (in 100 ft increments) where connectivity permitted. However, no position data was recorded during the bucketing operations (Figure 14). This absence of recorded data was likely attributable to the helicopter operating at very low levels, down to around 150 ft above ground level, while conducting repeated drops in mountainous terrain.

Figure 14: OzRunways flight data

Source: Google Earth, annotated by the ATSB

FlightAware

The FlightAware flight tracking data captured the helicopter’s en route flight to the bucketing site, as well as the subsequent low-level manoeuvres involving repeated water dips and drops. Position reports were recorded at irregular intervals ranging between approximately 8 seconds and 40 seconds[12] during these operations.

In addition to the TracPlus data, FlightAware was incorporated into the data analysis. The differing sampling rates and coverage characteristics of the 2 systems together produced a more complete reconstruction of the helicopter’s flight circuit during the second fuel cycle (Figure 15).

Figure 15: Second fuel cycle data from TracPlus and FlightAware

Pink line: TracPlus data. Blue line: FlightAware data. Source: Google Earth, annotated by the ATSB

Further investigation

To date, the ATSB has conducted the following activities:

• interviewed the pilot and other Coulson Aviation personnel
• interviewed the air attack supervisor from Tasmania Parks and Wildlife Service
• reviewed recorded aircraft information
• reviewed the forecast and observed weather conditions
• reviewed maintenance documentation for VH-VJF
• analysed recorded helicopter information
• reviewed pilot training delivered by Coulson Aviation.

The investigation is continuing and includes:

• review of Coulson Aviation’s risk controls for bucketing operations in the Bell 412
• review of Coulson Aviation’s operational and reporting procedures
• review of Tasmanian Fire Service operational and reporting procedures.

A final report will be released at the conclusion of the investigation. Should a critical safety issue be identified during the course of the investigation, the ATSB will immediately notify relevant parties so appropriate and timely safety action can be taken.

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.

Overview of the investigation

The ATSB commenced an investigation into a flight control issue involving a Virgin Australia Boeing 737-8FE aircraft, registered VH-VIE, which occurred near Perth Airport, Western Australia (WA) on the afternoon of 31 July 2021. The flight was a scheduled passenger service from Perth WA to Brisbane, Queensland.

During initial climb, the crew detected that the aircraft had commenced an uncommanded descent. The Captain disconnected the autopilot, leaving the autothrottle engaged while descending through 1,536 ft and manually trimmed the aircraft using the electrical stabiliser trim. Shortly afterwards, the crew received an enhanced ground proximity warning system (EGPWS) ‘DON’T SINK’ alert. The aircraft was re-established in a climb configuration.

At 2,144 feet, the Captain re-engaged the autopilot. Six minutes later, at 17,888 feet, the autopilot automatically disengaged. The autothrottle then also disengaged for reasons undetermined. To test if there was a problem with the A system autopilot, the crew engaged the B system autopilot and re-engaged the autothrottle. Shortly afterwards, air traffic control (ATC) queried the crew if their operations were normal. While responding to ATC, the crew detected the ‘STAB OUT OFF TRIM’ light illuminated and advised ATC to standby for further details. The crew then began the associated Quick Reference Handbook Non-Normal Checklist and while doing so, the B system autopilot automatically disengaged. The crew followed the checklist by not re-engaging the autopilots and autothrottle, and continued to manually fly the aircraft.

Once in cruise, the crew contacted ATC advising that they were unable to fly at reduced vertical separation minima (RVSM)^[1] and requested a block level ^[2] clearance of flight level (FL) 380 to FL400 due to stable atmospheric conditions. The crew then discussed the risks of continuing the flight to Brisbane. After liaising with company engineers, referring to company documentation and examining the weather at the departure, alternate and arrival airports, the crew decided to continue to Brisbane. The crew also assessed their fitness to fly, and distributed different phases of flight to each other to manage workload and fatigue. They communicated with their Chief Pilot and requested an off-duty company pilot, who was flying to Brisbane as a passenger, to join them in the cockpit to provide additional support if required.

A post-flight engineering inspection found that the circuit breaker for the automatic flight control system (AFCS) stabiliser trim was in the tripped position and the STAB OUT OF TRIM light was faulty. Engineers reset the circuit breaker, but were unable to replicate the fault during testing. The faulty light was replaced, but was considered unrelated to the tripped circuit breaker. The reason for the tripped circuit breaker was not established. A verification flight ensured that the AFCS was commanding the stabiliser without any issues. No further faults were detected.

As part of the investigation the ATSB:

• interviewed the flight crew
• examined the recorded flight data and the operator’s and aircraft manufacturer’s procedures
• examined the crew’s in-flight decision making.

The ATSB found that at all stages of the flight, the flight crew acted in accordance with operator’s and aircraft manufacturer’s procedures, and had considered and managed the risks associated with continuing the flight.

Reasons for the discontinuation

Based on a review of the available evidence, the ATSB considered it was unlikely that further investigation would identify any systemic safety issues or important safety lessons. Consequently, the ATSB has discontinued this investigation.

The evidence collected during this investigation remains available to be used in future investigations or safety studies. The ATSB will also monitor for any similar occurrences that may indicate a need to undertake a further safety investigation.

__________

1. Reduced vertical separation minima (RVSM): the reduction of vertical space between aircraft from 2,000 to 1,000 feet at flight levels from 29,000 feet up to 41,000 feet.
2. Block level: a section of airspace with specified upper and lower limits on a specific track, in which cleared aircraft are permitted to manoeuvre.

Safety summary

What happened

During the night of 25 March 2021, the pilot of a Leonardo Helicopters (formerly Finmeccanica) AW139 helicopter, registered VH-TJH, was performing aerial work near Katoomba, New South Wales, approximately 80 km west-north-west of Sydney. The task, conducted with the aid of night vision goggles (NVG), involved finding an injured bushwalker and winching in a paramedic and doctor.

While established in the hover at about 85 ft and facing cliffs near the Three Sisters, the aircrew officer started winching the paramedic down. The aircraft then stared drifting to the right towards rising terrain. The drift continued and a bank angle warning sounded as the aircraft rolled about 30° to the right. As the pilot corrected the drift the nose of the aircraft pitched up to about 51°. During the recovery manoeuvre an engine over torque occurred. After control of the aircraft was regained, the paramedic was retrieved, and the aircraft returned to Bankstown. None of the crew sustained injuries during the occurrence and a subsequent engineering inspection did not reveal any fault or damage to the aircraft.

What the ATSB found

The ATSB found that the external white lighting on the aircraft provided insufficient illumination for the pilot to maintain adequate visual references. It was also found that the lighting requirements specified by regulations provided no guidance or minimum requirements regarding the specifications or power output of the external white lights.

The ATSB also found that the operator provided insufficient guidance for the in-flight risk assessment specific to night vision imaging system (NVIS) winch operations. This led to the crew not evaluating or discussing components of the winch site that may have identified elements that made this winch site highly challenging.

It was also found that the operator’s currency requirements for NVIS winch operations did not provide the currency necessary to maintain competency in complex NVIS winch scenarios. The lack of recency in complex NVIS winch environments likely contributed to the pilot experiencing a high workload during the hover phase. This, in combination with the lack of visual cues probably led to the pilot becoming spatially disorientated and temporarily losing control of the aircraft.

It was also found that, despite being requested by the ATSB, the audio recording from the solid‑state multi-purpose flight recorder was not quarantined by the operator. This reduced the information available to the investigation team.

What has been done as a result

The operator advised the ATSB that they have updated their entire fleet with high powered Trakka searchlights, thus ensuring adequate lighting is available to illuminate the terrain at the required operating height during NVIS winching. Additionally, the operator has updated their NVIS winching recency requirements, with the addition of six-monthly recency requirement for NVIS winching in complex terrain, one of which is supervised by a Training and Checking pilot.

Furthermore, the operator has made significant changes to their winching procedures. The changes include additional guidance regarding risk management, pre-mission and pre‑winch risk assessment, as well as specific guidance to confirm and maintain adequate visual references during winch operations.

The Civil Aviation Safety Authority (CASA) have also advised that they will review the NVIS recency requirements. Consideration will be given to aligning with instrument flight recency (3 iterations in 90 days) and look at operational recency for winching and overwater SAR which will most likely require 3 iterations in 90 days. CASA have also made substantive changes to version 1.2 of the NVIS Multi-Part AC 91-13. These changes include guidance on the type of searchlight fitted and quantitative guidance regarding their capabilities. 

Safety message

Inflight decision making, particularly involving pilots flying with reduced visual reference remains an ongoing safety concern. While flying visually at night it is crucial that pilots have sufficient visual reference to see and avoid obstacles. Visual cues are also required to maintain orientation so pilots know which way is up and can maintain control of their aircraft.

NVG provide a useful tool to supplement visibility for flying in low light conditions, however it is important to understand their limitations. Pressing on into conditions of reduced visual reference carries a significant risk of severe spatial disorientation due to powerful and misleading orientation sensations with reduced visual cues. Disorientation can affect any pilot, no matter what their level of experience.

Operators are reminded that regulations only set out the minimum requirements. As such, they are encouraged to assess the risks of their operations and modify their procedures, manuals, and risk assessments accordingly. Operators are also reminded that it is a requirement under the Transport Safety Investigation Act 2003 to quarantine evidence, including flight data recorders and cockpit voice recorders, when requested by the ATSB. Flight data and audio recorded during an occurrence can often be some of the most useful and compelling evidence in an investigation and can assist in finding safety factors and ultimately benefitting safety.

The occurrence

On 25 March 2021 the crew of a Leonardo Helicopters (formerly Finmeccanica S.p.A) AW139 helicopter, registered VH-TJH (TJH) were performing aerial work near Katoomba, New South Wales (NSW), approximately 80 km west-north-west of Sydney (Figure 1).

Figure 1: Occurrence location

Source: Google Earth, annotated by the ATSB.

The helicopter operator had been tasked to locate and extract an injured bushwalker from the Blue Mountains National Park. The bushwalker had reportedly fallen near the base of the Giant Stairway near the Three Sisters rock formation (Figure 2).

Figure 2: Location of bushwalker at the base of the Giant Stairway near Katoomba, NSW

Source: Google Earth, annotated by the ATSB.

The task involved flying TJH from its base at Bankstown Airport, NSW, to the vicinity of Katoomba, NSW (about 65 km) to locate the injured bushwalker. The flight was conducted under the night visual flight rules, with the assistance of night vision goggles (NVG). On board was the pilot, an aircrew officer (ACO), a paramedic and a doctor. Once located, the paramedic, doctor and an equipment bag were to be lowered to the bushwalker in 3 individual winch insertions. The paramedic and doctor would then assess the patient and devise an appropriate extraction plan.

The crew shift started at 1930 on the evening on 25 March. The shift began routinely with a debrief and hand-over with the crew from the previous shift. This was followed by a check of the aircraft and equipment, including the NVG system and a review of weather conditions. Later in the shift, shortly before 2200, the pilot was notified of a possible task in the Blue Mountains, and they began some initial preparations. At 2241 the formal tasking for the job was received and preparations continued, including a pre-departure risk assessment. The helicopter departed from Bankstown Airport at 2329 and transited to Katoomba (Figure 3).

Figure 3: Flight data for VH-TJH on 26 March 2021

Source: Google Earth, annotated by the ATSB.

Approaching Katoomba at about 2355, the pilot identified the location of the bushwalker via a first responders’ strobe light. They then overflew the pre-determined staging point, a car park at Echo Point at the top of the mountain that could be used as a landing site if required (Figure 4).

Figure 4: Flight data showing VH-TJH overflying the bushwalker and staging point before approaching the winch location

Source: Google Earth, annotated by the ATSB.

The pilot then manoeuvred the aircraft into the winch position, initially placing the aircraft in a high hover at about 400 ft above ground level, abeam the strobe light with the nose of the aircraft pointing out towards the valley to aid emergency egress if necessary.

Prior to establishing the helicopter into the final winch position the pilot and ACO conducted a brief on-site risk assessment in accordance with the operator’s standard practice. It was identified that the pilot would have better visual hover references if the aircraft was placed with the nose towards the cliff. It was recognised that this orientation came at the cost of an emergency flyaway option down the valley, but it was assessed that improved hover reference was more desirable. After this conversation the pilot moved the aircraft to the right, towards the winch site, and descended to about 85 ft. The nose of the aircraft was also repositioned to face directly towards the cliff.

Concurrently, the ACO opened the rear right sliding door and the paramedic removed their NVG in preparation for winching. With the aid of a downward facing winch light and a handheld search light, the ACO sighted the bushwalker and gave voice commands to the pilot to guide them into position.

With the helicopter facing the cliff, the pilot positioned the 2 moveable landing lights to aid visibility. The right light was placed in the one o’clock position, and the left one was angled in the 11 o’clock position. They then used NVG to identify a large dead tree on the slope of the cliff directly in front of the aircraft to use as a hover reference point. Additionally, looking down underneath the NVG, the pilot identified a bush on the slope in the lower 2 o-clock position which was illuminated with the white light of the landing light. Using these 2 points as reference, the pilot scanned their eyes between the dead tree in the 12 o’ clock position (though NVG), the bush on the ground in the 2 o’clock low position (underneath the NVG) and then to the flight instruments (also underneath the NVG). These visual references were used to maintain the hover while the ACO provided verbal feedback and commands to the pilot to assist maintaining position.

Once established in the winch position, and after a final scan for obstacles, the ACO started winching the paramedic down. With about 12 ft of cable payed out, the paramedic’s head was just past the level of the flight step, underneath the rear sliding door. At this point, during one of their scans while checking the engine torque, the pilot detected movement of the helicopter and looked up. About the same time, the ACO also noticed the aircraft had moved out of position and called to the pilot ‘you’re drifting right, you’re drifting right’, ‘hold’, hold’. Despite this command, the helicopter continued moving to the right and forwards towards rising terrain. The ACO then called ‘You’re going to crash, you’re going to crash, move back and up’, and a ‘bank angle’ warning sounded.

The pilot recovered control of the aircraft and climbed away from the cliff as the paramedic held onto the flight step. During the recovery, an over‑torque warning illuminated. A subsequent review of recorded flight data (Figure 5) identified that during the initial drift out of position the aircraft was banked right up to approximately 30° and during the recovery manoeuvre it was pitched nose-up to about 51°.

Figure 5: Flight data for VH-TJH showing the hover, drift and recovery

Source: Google Earth, annotated by the ATSB.

Once clear of the cliff face and in stable flight, the ACO winched the paramedic back on board and closed the rear door. The aircraft then returned to Bankstown Airport for an uneventful landing. None of the crew sustained injuries during the occurrence and a subsequent engineering inspection did not reveal any fault or damage to the aircraft. The bushwalker was winched out by another helicopter crew the next morning.

Context

Personnel information

Pilot

The pilot had over 15 years of helicopter flying experience, including military and emergency medical services (EMS) operations. They also held an Air Transport Pilot Licence (Helicopter) that was issued on 16 January 2019.

The pilot’s logbook showed a total flying experience of 3,484.1 hours to the last recorded flight on 25 March 2021. This included over 600 hours using night vision goggles (NVG). The pilot’s total flying experience on the AW139 was 338.9 hours. In the previous 90 days, the pilot had flown 70.7 hours on type, and in the previous 30 days the pilot had flown 28.4 hours on type. The pilot’s licence indicated that they had completed an AW139 flight review on 21 October 2020.

The pilot also held a Class 1 aviation medical certificate valid to 21 December 2021.

Aircrew officer

The Aircrew Officer (ACO) had over 13 years’ experience crewing helicopters. In that time, they had accumulated nearly 3,000 total hours of which about 700 involved the use of NVG.

Paramedic and doctor

The paramedic’s role included rescue crew officer duties, down‑the‑wire duties and inter-hospital operations. Given the condition of the bushwalker and their medical history, a doctor was also tasked to provide additional medical treatment. Neither the paramedic nor doctor were expected to be directly involved in the operation of the aircraft.

Aircraft information

General

The Leonardo Helicopters AW139 is a medium-sized, twin-engine helicopter powered by two Pratt & Whitney PT6C-67C engines. The combined maximum power output of both engines is greater than the main gearbox’s allowable power limit. Therefore, over torque of the transmission can occur when a pilot demands excessive engine power with both engines operative. VH-TJH was certified and maintained for both Instrument flight rules (IFR) and night vision imaging system (NVIS) operations.

Flight crew configuration

Civil Aviation Order 82.6 was in force at the time of this incident and stated that the minimum crew for NVIS operations must not be less than the highest requirement for NVFR, or IFR, specified in either:

• the aircraft’s flight manual
• the operator’s operations manual acceptable to CASA
• Australian civil aviation legislation, including this Order, that applied to the aircraft.

Flight crew configuration for EMS helicopter operations was in accordance with the approved rotorcraft manual.

Supplement 24 of the AW139 rotorcraft manual detailed the minimum flight crew required for night visual flight rules operations as one pilot, unless otherwise required by operating rules.

Supplement 60 of the AW139 rotorcraft flight manual detailed the minimum flight crew required for night vision goggle operations and was to be read in addition to supplement 24 for EMS operations. This supplement allowed for the minimum flight crew to be a single pilot and an additional NVG‑equipped crew member during take-off and landing on unimproved sites to assist with obstacle identification and clearance.

Night vision imaging system

To improve vision during night operations, the helicopter crew utilised a night vision imaging system (NVIS). The operator was experienced in the application of this technology and trained their own crews and offered NVIS training to other operators.

The operator’s NVIS comprised:

• AN/AVS-9 green phosphor NVG
• NVG-compatible cockpit and cabin lighting
• ACO‑controlled steerable winch and handheld light
• Two pilot‑steerable white landing lights on the underside of the aircraft
• Additional airworthiness requirements and NVIS specific procedures and training.

Despite the advantages provided by NVG, their application has inherent limitations including:

• Optimal performance requires accurate set-up, including inter-ocular adjustment, tilt, vertical, horizontal (eye-relief), focus and dioptre.
• The image generated by NVG is monochromatic[1] (green), resulting in a degradation in the ability to recognise objects and perceive depth (RTCA 2001b). This can result in a lack of contrast, and therefore degradation of visual acuity.^[2]
• The field of view (FOV)[3] in NVG is limited to 40° horizontally and vertically (ITT Industries 2003). This compares to the FOV for normal unaided vision of about 200° horizontally and 120° vertically (Miller and Tredici 1992).
• The quality of the NVG image can be limited by environmental conditions, such as celestial illumination,[4] and weather conditions (e.g. humidity, fog, mist, cloud, precipitation) (RTCA 2001b).

For more information regarding operations with NVG see ATSB aviation research report: ATSB B2004/0152 - Night vision goggles in civil helicopter operations (April 2005)

External white lighting

Unlike military application, the use of white light was fundamental to the operator’s NVIS usage strategy. VH-TJO was fitted with the standard external AW139 lighting detailed above. The winch light pointed directly downward from the aircraft to illuminate the winch site, with illumination supplemented by the ACO’s handheld light. Low level operations (search and rescue/hover/winching) were conducted by the operator using a combination of references viewed both with and without NVG.

The pilot reported that the helicopter’s white lighting was ineffective in illuminating an area sufficient to maintain adequate visual references. The landing lights (which were also being used as search lights) were also described as being significantly less effective in comparison to the handheld light used by the ACO and also in comparison to other (purpose built) search lights used previously by the pilot with other helicopter emergency medical services (HEMS) operators.

Several other operators conducting similar night search and rescue, hover and winching operations, had modified their aircraft to include high‑powered search lights and additional external aircraft white lighting.

With regards to aircraft lighting, Civil Aviation Order (CAO) 29.11 – Air service operations – helicopter winching and rappelling operations, mandated that any helicopter engaged in winching over land by night was to be equipped with:

• 2 white lights, controllable by the ACO
• 2 white lights operable by the pilot and trainable in azimuth and elevation without removing their hands from the flying controls
• an approved inter-communication system permitting continuous communication between the pilot and ACO

Additionally, CAO 82.6 - Night vision imaging system — helicopters required that:

The operator and the pilot in command of an NVIS operation must ensure that the helicopter has a serviceable pilot-steerable searchlight, adjustable in both pitch and azimuth from the flight controls.

Finally, Appendix V of CAO 20.18 - Aircraft equipment — basic operational requirements required:

2 landing lights except that, in accordance with the provisions of regulation 308 of CAR 1988, aircraft engaged in private and aerial work operations and charter operations not carrying passengers for hire and reward are exempted from this requirement provided that 1 landing light is fitted. Note A single lamp having 2 separately energised filaments may be approved as meeting the requirement for 2 landing lights.

None of the three CAOs contained guidance or stipulation regarding the minimum intensity/performance capabilities required of the 2 white lights operated by the pilot.

The aircraft was fitted with two pilot‑steerable white landing lights on the underside of the aircraft (also being used as searchlights), as well as an ACO‑controlled steerable winch light and handheld light.

Meteorological information

Bureau of Meteorology forecasts

The flight from Bankstown Airport to the Katoomba area and return occurred in the Graphical Area Forecast NSW-E (GAF NSW-E). Within the GAF NSW-E there were 2 subdivisions affecting the flight. The departure and landing site was located in subdivision A1, and the occurrence location was in subdivision A. The GAF NSW-E was valid from 2200 local time on 25 March 2021 to 0400 on 26 March 2021, with forecast conditions including:

• average conditions of greater than 10 km visibility
• broken[5] stratocumulus[6] cloud 2,000 to 6,000 ft above mean sea level (AMSL) in A1
• scattered[7] stratocumulus cloud 2,000 to 3,000 ft AMSL
• moderate turbulence was implied in cumulous, stratocumulus and altocumulus cloud.

Automatic weather station observations

The Bureau of Meteorology’s routine report of the weather conditions at Bankstown Airport at 2330 local time (1 minute after take-off) showed a westerly wind at 4 knots, with an air temperature of 19°C and a dew point temperature[8] of 12°C. Visibility was observed to be greater than 10 km with nil clouds detected. It also showed that no rainfall had been recorded in the preceding 10 minutes and only 0.2 mm had been recorded since 0900 that morning. The QNH[9] was 1010 hPa.

Environmental observations

The pilot and ACO stated that before departure from Bankstown they had examined weather conditions en route and in the Katoomba area. No weather-related restrictions were identified. The clear skies and light variable winds were noted during the pre-flight risk assessment, as was the good visibility afforded by the roughly 80% moon phase.

Once on-site, conditions were initially observed to be good with very good visibility. However, once the aircraft was lowered into the winch position it was now positioned behind the cliff in the moon’s shadow. Additionally, the pilot reported that, with the aircraft’s nose pointed towards the cliff, they had no visual reference to the horizon. The pilot later estimated approximately a 60% reduction in overall visibility once they were in the winch position as compared to the conditions en route and at higher altitudes.

Additional information

Recorded data

VH-TJH was fitted with a Penny & Giles Aerospace Limited solid-state Multi-Purpose Flight Recorder (MPFR)[10]. The MPFR recorded over 900 flight data parameters and 2 hours of audio recordings on 4 channels.

The aircraft was also fitted with an additional video and audio recording system specifically introduced by the operator as part of the aeromedical fit out for the AW139. It consisted of 3 cameras, 2 of which were in the cabin and one fitted to the right-side fuselage below floor level and focused downward on the winch site. The rest of the system consisted of a power control module, an audio mixer and interfaces with the existing aircraft audio panels. Video and audio files were recovered from this system. Audio was recorded from several inputs, however the separate inputs were combined and recorded into one audio file.

As part of this investigation the ATSB requested both the flight data and audio recordings from the MPFR under the provisions of the Transport Safety Investigation Act 2003. Although the operator provided the flight data, the audio recordings had been overwritten. Additionally, while the operator provided video and audio from the incident from the onboard system, the operator isolated only a portion of the recordings, then reinstalled the memory card and the remaining data was overwritten. Although the audio data was not recovered from the MPFR, the recorded flight data information and time stamps from the MPFR have been used for analysis and throughout the report. Additionally, an animation was created using the flight data recorded by the MPFR.

 Video 1: Animation derived from flight data from the MPFR.

Source: Cesium, annotated by the ATSB.

Operational information – Operator flight manual

The operator’s manual included a volume relating specifically to winch operations (Vol 6L, Rev 7.1). The manual included guidance on the conduct of a pre-winch brief, to be conducted with the pilot before conducting any winch task. The brief was to include:

• Emergency procedures and intended actions for loss of power / control in the hover. The crew will be informed whether the aircraft is Safe Single Engine, Flyaway or Committed
• Helicopter performance
• Relevant mission information
• Safety considerations.

The manual also included a volume relating specifically to NVIS operations (Vol 6C Rev 7.1). The NVIS operations manual provided guidance regarding pre-flight Briefing and checklist. The NVIS flight planning was to include the establishment of a range of decision points for each NVIS flight that define go / no-go criteria. The decision points included to:

• minimum weather requirements for initiating NVIS flight (illumination, visibility, cloud base)
• statement of deteriorating conditions criteria for initiating an IMC recovery (visibility, cloud base)
• the NVIS Recovery Plan.

Neither of these volumes of the operations manual contained specific guidance pertaining to hazards associated with the combined operation of winching with NVIS in the form of an on-site risk assessment. However, overarching these volumes, the operators Volume 2 Rotary wing aircraft operations manual required the maintenance of visual references during a hover, stating:

Hovering is a visual manoeuvre that requires adequate references to maintain position. Where precision hovering is required, such as during live winching, hover exit/entry, fast roping, external load operations, etc, the operation is not to commence unless adequate visual references are available and can be maintained throughout the manoeuvre. If upon termination of an approach adequate hover references are not available, a go around is to be conducted as described in section 2D1.17.

Operational information - NVIS Recency

Operator requirements

At the time of the occurrence the operator’s recency requirements for a pilot to conduct NVIS operations included:

For a pilot with more than 50 hours of NVIS flight time:

• 3 hours incorporating at least 3 take-offs, circuits and landings within the last 6 months; or an NVIS operational proficiency check (OPC) in the last 6 months.
• NVIS proficiency check (NPC): Annually after the first NPC, subsequent NPCs could be conducted within the 90 days before recency would otherwise expire.
• NVIS winch: Conducted an NVIS winch in the preceding 6 months.

CASA requirements

Civil Aviation Order (CAO) 82.6 was in force at the time of this incident and established operational and airworthiness standards and approval requirements for the use of NVG in specialised helicopter aerial work operations.[11] CAO 82.6 and regulations 61.1010 and 61.1015 of Part 61 of the Civil Aviation Safety Regulations (CASR) 1998 stated that the minimum NVIS recency check requirements for a pilot with greater than 50 hours NVIS flight time included:

• completed at least 3 hours flight time at night under the VFR using NVG within the previous 6 months; and
• conducted at least 3 take-offs and at least 3 landings at night using NVG within the previous 6 months, or
• become authorised to pilot any type of helicopter using NVG within the previous 6 months, or
• by successfully participating in an operator's training and checking system for an operation at night using NVG, and the operator holds an approval under regulation 61.040.

International requirements

The United States (US) Federal Aviation Administration (FAA) stipulated 2-month currency requirements for NVIS Helicopter emergency service (HEMS) with passengers and 4 month currency without passengers. Additionally, within the previous 2 months for operations with passengers onboard the following were required:

• 3 take-offs and landings, with each take-off and landing including a climb out, cruise, descent, and approach phase of flight.
• 3 hovering tasks.
• 3 area departures and area arrivals.
• 3 tasks transitioning from aided night flight to unaided night flight and back to aided.
• 6 night vision goggle operations for helicopter operation.

The Transportation Safety Board of Canada, stipulated 3-month recency requirements, as did the European Aviation Safety Authority. The Civil Aviation Authority of New Zealand stipulated the minimum currency requirement for a NVIS crew member of 4 months.

Pilot recency

The pilot had over 600 hours NVIS flight time experience and satisfied both their operator’s and CASA’s recency requirements. However, their last NVIS winch was conducted on 2 February 2021 as part currency training, and it was noted that this was a very benign winch environment conducted in a local area. The last complex winch the pilot had conducted was on 3 February 2020, approximately 13 months before this incident.

During interview, the pilot reported that once on-site and in the hover, they felt a sense of unfamiliarity. They reported feeling rusty and cognisant that it was over a year since they had been in a similar situation. As a result, they felt they were ‘working really hard in an environment that used to be their bread and butter’. Having done one winch in the past 6 months, they felt ‘current but not competent’.   

Workload

There are 4 general factors that can directly affect workload (Jarvis 2010).

• difficulty of the task
• number of tasks running in parallel (concurrently)
• number of tasks in a series (switching from task to task)
• the time available for the task (speed of task).

Other indirect factors such as durations of task, fatigue and level of arousal can also contribute to workload (CAA, 2016). Factors affecting workload for pilots may additionally include stress, recency, and the use of NVIS.

Flying a helicopter is a cognitively complex task requiring developed psychomotor skills.[12] When manually hovering, the pilot needs to coordinate simultaneous control inputs of both hands and feet precisely, requiring constant attention. This is because helicopters are inherently unstable in the hover.

During interview, the pilot reported that they were experiencing a higher than normal workload in the lead up to the occurrence, stating that the ‘workload is high’ and they were ‘working really hard’.

Spatial disorientation

Spatial disorientation is a type of loss of situation awareness, and is different to geographical disorientation, or incorrectly perceiving the aircraft’s distance or bearing from a fixed location. Spatial disorientation occurs when pilots do not correctly sense their aircraft’s attitude, airspeed or altitude in relation to the earth’s surface. In terms of an aircraft’s attitude, spatial disorientation is often described simply as the inability to determine ‘which way is up’, although the effects can often be more subtle than implied by that description.

Spatial disorientation occurs when the brain receives conflicting or ambiguous information from the sensory systems. It is likely to happen in conditions in which visual cues are poor or absent, such as in adverse weather or at night.[13] Spatial disorientation presents a danger to pilots, as the resulting confusion can often lead to incorrect control inputs and resultant loss of aircraft control. The misperceptions can be so compelling that spatial disorientation accidents have had fatality rates of 90–91% (Gibb, Gray and Scharff 2010).

During interview the pilot reported that, while they were scanning their eyes from the 2‑o’clock low position to the engine instruments, they felt movement in the aircraft and brought their eyes up the 12 o’clock position. They then observed that the tree being used as a visual reference was no longer visible. In response, the pilot reported being both startled and confused. Additionally, they had no recollection of applying control inputs so the voice commands from the ACO announcing that they were drifting right, as well as the bank angle warning, were completely unexpected.

The pilot reported not comprehending why they were receiving the feedback from the ACO that they were drifting, nor the bank angle warning. They reported ‘the worst sense for the leans’, and a ‘horrible tumbling feeling’. Despite this, the pilot was still aware of their proximity to the cliff and the inherent danger that posed, but not their actual position in space. When the pilot pitched the aircraft up to avoid the cliffs, they caught a glimpse of a tree through the NVG on the right-hand side. At this point the pilot regained their orientation, enabling them to recover control of the aircraft.

Related occurrences

A review of Australia’s national aviation occurrence database for the 20 years leading up to this incident revealed 4 similar investigated occurrences involving the loss of control of a helicopter at night while using NVIS. Summaries of the 4 investigations are as follows.

Terrain awareness warning system alert involving Eurocopter BK 117C-2, VH-SYB, near Crookwell, New South Wales on 21 October 2016 (AO-2016-160)

On the evening of 21 October 2016, a Eurocopter BK 117 C-2 helicopter, registered VH-SYB, departed from the Crookwell medical helicopter landing site, New South Wales. The crew were returning to their home base at Orange, New South Wales, after conducting an emergency medical service task. The flight was conducted as a night visual imaging system operation under night visual flight rules, with the pilot and aircrew member both wearing night vision goggles.

Shortly after take-off, the helicopter unexpectedly encountered low cloud, and the pilot initiated the operator’s inadvertent entry into instrument meteorological conditions (IMC) procedure. While conducting the procedure, the momentum of the helicopter’s climb reduced. In response, the pilot lowered the helicopter’s nose to regain airspeed, but inadvertently overcorrected the pitch angle to 15° nose-down, as well as allowing a slight roll to the left. The resulting unusual attitude triggered a caution alert from the helicopter’s enhanced ground proximity warning system.

Loss of control in flight involving Leonardo Helicopters AW139 helicopter, VH-YHF, near Adelaide River mouth, 38 km east‑north‑east of Darwin, Northern Territory on 13 May 2018 (AO-2018-039)

At 2000 Central Standard Time on 13 May 2018, the crew of a Leonardo Helicopters AW139, registered VH-YHF, departed Darwin, Northern Territory, to search for an active emergency position-indicating radio beacon (EPIRB). The crew flew under night visual flight rules with support of a night vision imaging system.

During an approach to a potential EPIRB target, smoke from nearby bushfires affected visibility and the helicopter developed an uncommanded high rate of descent. The Aircrew Officer, in the rear of the helicopter, called ‘Climb! Climb! Climb!’, and the pilot regained control with a rehearsed recovery drill. During the recovery procedure, the power demand exceeded airframe limitations. This exceedance went undetected, and the helicopter was flown on a second sortie that same evening.

Main rotor blade strike involving Leonardo Helicopters AW139, VH-EGK, 21 km west‑south‑west of Caboolture Airport, Queensland on 20 June 2020
(AO-2020-031)

During night winching operations, the helicopter's main rotor blades struck a tree. The crew conducted a return to Archerfield. The post-flight inspection revealed the majority of the main rotor blades had sustained damage. One blade tip was substantially damaged. At the time of writing, this investigation was ongoing.

Loss of control and near collision with terrain, Leonardo Helicopters AW139, VH-TJO 
(AO-2020-038)

On 24 July 2020, the crew of a Leonardo Helicopters AW139, registered VH-TJO, departed Shellharbour Airport, near Wollongong, New South Wales, with 4 crew onboard (including a single pilot and aircrew officer). The flight was conducted under the night visual flight rules, with the assistance of night vision goggles, to recover 2 bushwalkers from the Bungonia National Park, New South Wales.

On arrival at the search and rescue location the helicopter was descended to approximately 240 ft above ground level and the airspeed was reduced. The aircraft was then tracked over high ground past the edge of an escarpment, where the terrain dropped away to the valley floor. During this time an uncommanded, and increasing, rate of descent and lateral drift developed. This was identified by the aircrew officer, with corrective instructions provided to the pilot. During the recovery, the engine power output exceeded airframe limitations, rendering the helicopter temporarily unserviceable.

Safety analysis

Introduction

While conducting aerial work near Katoomba, about 65 km west of Bankstown Airport, New South Wales, a Leonardo Helicopters AW139 registered VH-TJH, was hovered above an injured bushwalker near the base of the Three Sisters walking trail. The aircraft was lowered to about 85 ft AGL (above ground level), about 20 ft above the treetops with its nose facing the cliff in preparation for winching. As the Aircrew Officer (ACO) started lowering the paramedic on the winch line, the aircraft started drifting to the right and towards the cliff. The ACO alerted the pilot to the drift and a bank angle warning sounded as the aircraft banked to about 30° to the right. Aware of the nearby cliffs, the pilot pitched the aircraft up and away from the cliffs, pitching the aircraft to about 51° nose up. During this manoeuvre an engine over‑torque occurred. After control of the aircraft was regained, the paramedic was retrieved, and the aircraft returned to Bankstown.

Post flight engineering inspections by the operator did not identify any damage to the aircraft. Nor were any defects identified that could have contributed to the occurrence. Additionally, no evidence was found to suggest any medical, fatigue‑related or physiological issues that would have affected the pilot’s performance on the day of the flight. Therefore, this analysis will focus on the operational and environmental factors that led to an experienced helicopter pilot temporarily losing control of their aircraft during a complex NVIS winching operation.

External aircraft white lighting

Although Civil Aviation Orders (CAO) 29.11, 82.6 and 20.18 required the aircraft to be fitted with 2 white lights operable by the pilot, there was no guidance or minimum intensity/performance capabilities specified for these lights. As a result, the operator believed they were complying with the CAO requirements by using the 2 moveable landing lights as search lights. These landing lights were described by the pilot as being ineffective in illuminating an area sufficient to maintain visual references. It was also noted that they were significantly less effective when compared to the handheld light used by the ACO and to other search lights used previously by the pilot with other HEMS operators.

The limited illumination provided by the available lights likely influenced the crew’s decision to face the aircraft relatively close, and directly towards, the cliff in order to maximise the available hover references. However, even when operating close to the cliff, the lights were still ineffective at illuminating the search area sufficiently to provide adequate visual reference for the pilot. This significantly increased the pilot’s workload during the hover phase.

Inadequate external lighting has previously been found to be a safety issue on another ATSB investigation (AO-2020-038). This occurrence also involved a loss of control and near collision during NVIS HEMS operations. It also involved the same operator, aircraft type and lighting system. That investigation found:

The external aircraft white lighting was inadequate to illuminate the terrain below and to the side of the aircraft at the required operating height. This delayed the identification and recovery from the unsafe aircraft state resulting in the pilot not identifying the developing rate of descent during the incident, delaying the recovery from the descent.

In‑flight risk assessment

During the initial positioning of the aircraft, the pilot hovered the helicopter abeam the bushwalker at about 400 ft above the ground and positioned the nose of the aircraft out towards the valley to aid egress if necessary. Before manoeuvring the aircraft into the final winch position, the pilot and ACO conducted a brief in-flight pre-winch risk assessment. It was decided to reposition the aircraft towards the cliff as they descended to about 80 ft. This decision aided visual references for the pilot at the expense of ease of egress. It also resulted in the aircraft being in the moon’s shadow behind the cliff and the pilot not having any visible horizon. Both the pilot and ACO identified the significant degradation in available illumination at the site compared to what was briefed during pre-flight risk assessment however, the implication of this was not discussed. Egress actions in the event of a goggle failure were also not discussed, nor the aircraft external lighting limitations. As the pilot became aware that their workload was unusually high, there was also no communication about this to the ACO, however that may have been influenced by the focussed attention required to control the helicopter.

Had a more effective in‑flight risk assessment been conducted, it would likely have identified the elements that made this winch site a highly challenging one, such as the low illumination and absent visible horizon. This could have allowed the pilot to more accurately assess the likely workload associated with maintaining a steady hover in those conditions. This, in turn, may have led to a conclusion that the site was unsuitable for NVIS winching.

Although operator guidance was provided for both winching and NVIS operations, as well as pre‑flight and pre-winch briefings, there was limited guidance pertaining to the risk assessment of the combined activity once on site. The inclusion of a structured on-site risk assessment process/checklist specific to NVIS winching would have emphasised the requirement to identify and assess site‑specific hazards, such as the adequacy of visual references and a safe method of recovery in the event of NVG failure.

Recency

The pilot and ACO both met the company recency requirements, as well as CASA’s, for NVIS winch currency. Despite this, the pilot found themselves in a challenging operational situation that they had not been in for over a year. This resulted in the pilot feeling a sense on unfamiliarity when they found themselves in a complex NVIS winch environment. Specifically, they reported feeling rusty and felt ‘current but not competent’.  As a result, they felt they were ‘working really hard in an environment that used to be their bread and butter’.

Workload – spatial disorientation and loss of control

The pilot reported a higher‑than‑expected workload from the moment they got into the hover, combined with a feeling of unfamiliarity. In the past, the pilot had regularly flown in similar environments during military, search and rescue and HEMS operations however, at the time of the occurrence it had been over a year since their last complex NVIS winch. This likely contributed to the increased workload experienced by the pilot.

It is also likely that the lack of visual cues due to the moon’s shadow, the lack of visible horizon and the illumination provided by the external white lights as well as the pilot’s recency with complex NVIS winching, all contributed to the increased workload. These factors likely combined resulting in the pilot losing visual references during one of their instrument scans leading to the pilot becoming spatially disorientated and temporarily losing control of the aircraft. The engine over‑torque then occurred during the subsequent recovery manoeuvre.

Recovery of flight recorder audio

The ATSB requested that the multi-purpose flight recorder be quarantined for use in the investigation. Although flight data from the incident was recovered, the portion of the 2-hour audio recording that contained the incident was overwritten because power to the device was not removed while the aircraft was in transit.

Findings

From the evidence available, the following findings are made with respect to the loss of control and near collision with terrain, involving Augusta AW139, VH-TJH, near Katoomba, New South Wales on 26 March 2021.

Contributing factors

• The external aircraft white lighting was inadequate to illuminate the terrain below and to the side of the aircraft at the required operating height. [Safety issue]
• The pilot likely experienced a sustained higher than normal workload while operating in a reduced visual cue environment, causing a misidentification of hover references and disorientation, leading to a subsequent loss of control.
• Regulatory requirements did not ensure that aircraft lighting was adequate to conduct night vision imaging system winching operations safely. [Safety issue]
• Toll recency for night vision imaging system (NVIS) winching was insufficient to ensure that complex NVIS winching operations, such as in this occurrence, could be conducted safely. [Safety issue]

Other factors that increased risk

• Although the flight crew identified the degradation in available illumination at the winch site compared to what was briefed prior to departure, the risk posed by this hazard was not fully assessed on‑site.
• Although the operator’s procedures for winching and night vision imaging system operations included the need to have adequate hover references and a method of recovery in the event of a night vision goggle failure, there was limited guidance to ensure these requirements were confirmed by the flight crew on‑site before commencing precision hover operations. [Safety issue]

Other findings

• CVR was not recovered for this flight, however the company installed camera and audio were obtained for the period of the incident. This limited the ability of the investigation to ascertain specific information regarding the on‑site risk assessment conducted by the crew, which occurred outside the duration of the provided company footage.

Safety issues and actions

Aircraft lighting regulation

Safety issue number: AO-2021-018-SI-01

Safety issue description: Regulatory requirements did not ensure that aircraft lighting was adequate to conduct night vision imaging system winching operations safely.

External white lighting

Safety issue number: AO-2021-018-SI-02

Safety issue description: The external aircraft white lighting was inadequate to illuminate the terrain below and to the side of the aircraft at the required operating height.

TOLL recency requirements

Safety issue number: AO-2021-018-SI-03

Safety issue description: Toll recency for night vision imaging system (NVIS) winching was insufficient to ensure that complex NVIS winching operations, such as in this occurrence, could be conducted safely.

Operational in-flight risk assessment guidance

Safety issue number: AO-2021-018-SI-04

Safety issue description: Although the operator’s procedures for winching and night vision imaging system operations included the need to have adequate hover references and a method of recovery in the event of a night vision goggle failure, there was limited guidance to ensure these requirements were confirmed by the flight crew on‑site before commencing precision hover operations.

Glossary

Sources and submissions

Sources of information

The sources of information during the investigation included the:

• pilot of the occurrence flight
• the aircrew officer of the occurrence flight
• TOLL helicopters
• Civil Aviation Safety Authority
• Leonardo S.p.A Helicopters
• Bureau of Meteorology
• video footage taken from onboard the aircraft
• recorded flight data from the MPFR.

References

RTCA 2001b, Concept of operations: Night vision imaging system for civil

Miller, R. E. and Tredci, T. J. 1992, Night vision manual for the flight surgeon, USAF Special Report No. AL-SR-1992-0002, Armstrong Laboratory, Brooks Air Force Base.

Australian Transport Safety Bureau. (2007). An overview of spatial disorientation as a factor in aviation accidents and incidents. ATSB Aviation Research and Analysis Report B2007/0063.

Australian Transport Safety Bureau. (2005). Night vision goggles in civil helicopter operations. ATSB Aviation Research and Analysis Report B2004/0152.

Civil Aviation Order (CAO) 29.11

Civil Aviation Order (CAO) 82.6

Civil Aviation Order (CAO) 20.18

Part 61 of the Civil Aviation Safety Regulations (CASR) 1998

Jarvis S (2010). Workload. Proceedings of CAA RETRE Seminar, 2010. Flight-crew human factors handbook (CAA, 2016).

Gibb, R., Gray, R. & Sharff, L. Aviation Visual Perception: Research, Misperception and Mishaps. Ashgate, 2010

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:

• pilot of the occurrence flight
• the aircrew officer of the occurrence flight
• TOLL helicopters
• Civil Aviation Safety Authority
• Leonardo S.p.A Helicopters

Submissions were received from the Civil Aviation Safety Authority, TOLL helicopter and the aircrew officer. The submissions were reviewed and were 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. 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.

Safety summary

What happened

In the evening of 17 January 2018, a Professional Helicopter Services Robinson R44 helicopter, registered VH-HGX, departed the Yulara Town helipad, Northern Territory, for a 15-minute scenic flight with the pilot and three passengers onboard. Shortly after take-off, the rotor RPM began to decay and the low rotor RPM warning activated. The rotor RPM continued to decay to a level from which the pilot could not recover. The pilot attempted a forced landing, but was unable to arrest the rate of descent, resulting in a hard landing. The pilot and two passengers were seriously injured, and the remaining passenger experienced minor injuries. The helicopter was substantially damaged.

What the ATSB found

The ATSB found that the take-off was conducted at a high density altitude^[1] at near maximum weight. Therefore, a high engine manifold pressure (MAP) would be expected for the take-off. However, passenger video evidence indicated the rotor RPM (revolutions per minute) decay started at a relatively low MAP, and that the MAP increased slowly as the RPM steadily decayed. The ATSB found that the engine was producing the published rated take‑off power earlier on the day of the accident and that the pilot had flown the same departure with a full load of passengers on three previous flights. The rotor RPM decay was consistent with the low observed MAP. As such, the ATSB concluded the helicopter's rotor RPM steadily decayed due to a likely limited opening of the engine throttle during take-off. Fine-tuning of the engine throttle is controlled automatically by the engine governor, but it can be manually overridden by the pilot. The reason for the limited opening of the throttle could not be determined.

Following activation of the low rotor RPM warning, the pilot initially did not apply full throttle (for at least 5 seconds), and the helicopter maintained a positive rate of climb. At the time, the pilot was conducting the departure procedure low over the tree tops with an early left turn, which required visual attention outside of the helicopter for the majority of time. As a result, it was likely that the pilot had no spare attentional capacity at this time to immediately comprehend and respond to the deteriorating situation. In consideration of the potential power margin available at the time, if the pilot had applied full throttle in the first 5 seconds, and then lowered the collective lever sufficiently to prevent the helicopter from climbing, the low rotor RPM was likely recoverable.

The helicopter continued flight for about another 90 seconds, during which it climbed to about 200 ft at a low airspeed. This resulted in the rotor RPM decaying further to a level from which the pilot could not recover (likely below 80 per cent).

The ATSB further established that the pilot had inadvertently adopted a practice of conducting the rotors running turn-around (for passenger transfers) with the governor switched off. This was not in accordance with the Robinson Helicopter Company R44 checklist requirement for the governor to remain on from start until shut-down, nor the operator’s procedure for the governor to be selected on for the engine run-up. Although the pilot reported that the governor was selected on and checked before lift-off, this practice increased the risk of an inoperative governor not being detected before take-off.

The operator used individual passenger weights for their loading calculations, which was considered best practice. However, it was found that the operator’s passenger scales were not calibrated and were under‑reading the actual occupant weights. This resulted in the helicopter operating at a higher weight than planned, but less than the maximum weight. While the operating weight was within the published limits, the under-reading scales increased the risk of their helicopters not achieving their take-off performance.

The ATSB also found that the Robinson Helicopter Company’s R44 pilot operating handbook emergency procedure for low rotor RPM recovery did not include reference to the minimum power airspeed. Knowledge of this as a subsequent consideration to the immediate actions could assist pilots in the recovery from this safety-critical condition.

What has been done as a result

The operator temporarily suspended their tourist flights at their Uluru Base (including the Yulara Town helipad). Their chief pilot then conducted check flights with the local base pilots to ensure they could safely resume operations. In addition, the operator completed an audit of the helipad and updated their helicopter landing site register in accordance with the latest recommendations from the Civil Aviation Safety Authority (2014), and introduced a calibration schedule for their passenger scales.

The ATSB have issued a safety recommendation to the Robinson Helicopter Company to review the R44 pilot's operating handbook low rotor RPM recovery procedure for consideration to include a reference to the minimum power airspeed (Vy) for pilot awareness. Robinson reported that this will be reviewed by their engineering staff for possible revision to the pilot operating handbook.

Safety message

The intent behind checklist actions is not always apparent when learning procedures. Pilots should ensure they understand the purpose behind all checklist items, and if any doubt exists, seek clarification to reduce the likelihood of misunderstanding the requirements.

Low rotor RPM may develop in various flight conditions, but it is the low airspeed-low height condition, which is most likely to result in an accident. Helicopter pilots should ensure they are familiar with the power curve, the associated airspeeds for their particular helicopter, and be prepared to respond immediately to a low RPM warning.

Robinson Helicopter Company reported that pilots of their piston-engine helicopters should roll on throttle while lowering the collective lever, as per the low RPM recovery procedure, so that the throttle remains open. There is an overtravel spring in the throttle linkage that may, or may not, compress during the recovery. Pilots should not be concerned if the spring is, or is not, compressed, they should continue to roll the throttle on and lower the collective lever until the RPM is recovered.

In addition, the Robinson Helicopter Company website provides training videos for higher risk flight conditions that have resulted in fatal accidents. They include several presentations on energy management, tailored specifically for Robinson helicopter pilots, which could be beneficial to pilots during their initial training, upgrades and flight reviews.

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1. Density altitude is pressure altitude corrected for non-standard temperature. Pressure altitude is the altitude corrected for non-standard atmospheric pressure.

The occurrence

On 17 January 2018, at about 1828 Central Standard Time,^[2] a Professional Helicopter Services Robinson R44, registered VH-HGX, sustained a rotor revolutions per minute (RPM) decay on take-off from Yulara Town helipad, Northern Territory (NT), resulting in a hard landing about 0.63 km south of the helipad (5 km south of Ayers Rock Airport, NT) at about 1830.

Background

In the month of January 2018, the accident pilot became aware of an upcoming large charter group visit (115 people). The flights were scheduled to be from the operator’s Uluru Base^[3] Yulara Town helipad. On 17 January, the pilot started the day with ground duties until lunchtime. Ground duties included passenger safety briefings and bus driving. At 1300, the area manager and deputy area manager held a meeting with staff to brief them on the charter group operation, which was scheduled to start at 1500. The staff briefing included the passenger manifest and scenic route to be flown to separate the helipad departures with arrivals.

After the charter group arrived at 1500, the pilot conducted two short flights in another R44 and then about 40 minutes of ground duties. The pilot then took over VH-HGX from another company pilot, who had been operating the helicopter on scenic flights since about 1000. According to the run sheet, the pilot took one load of three passengers on the scenic flight before flying to Ayers Rock Airport to refuel. The helicopter departed the airport at 1727 with 100 L of fuel. The pilot reported that the fuel loading was predetermined from the staff meeting and believed the helicopter would be within the weight and balance requirements for the passenger manifest.

After returning to the Yulara Town helipad, the pilot took two groups of three passengers on the scenic flight. Ten litres of fuel consumption was recorded for the return flight from the airport and for each of the scenic flights.

Accident flight

At about 1827, the helicopter was loaded with three passengers from the Yulara Town helipad for a planned 15-minute scenic flight, with 70 L of fuel on board. This was the third scenic flight for the pilot in the accident helicopter since the last refuel earlier that afternoon. After the passengers boarded, the pilot accelerated the engine and rotor RPM from idle to 90 per cent, conducted a low RPM warning horn check (90 to 98 per cent RPM), selected the governor on (extinguishes the governor off light), and checked the engine and rotor indications were stable.

The pilot reported conducting a confined area^[4] take-off^[5] profile to clear some low trees in the departure path, which provided a headwind component for the departure. Passenger phone footage and helicopter tracking data indicated lift-off from the helipad was at about 1828. The departure consisted of the helicopter climbing about 17 ft vertically before the pilot applied forward cyclic^[6] about 5 seconds after lift-off to accelerate forwards for take-off while continuing to climb. Helipad surveillance camera and passenger phone cameras recorded the departure of the helicopter. The pilot reportedly checked the instruments were in the ‘green’ (normal operating range) in the hover prior to take-off, and the passenger videos indicated the ‘governor off’ light was extinguished for the departure.

About 3 seconds after take-off, and just prior to passing overhead the first trees in the departure path, the helicopter’s low rotor RPM warning horn and caution light activated (Figure 1). This indicated that the rotor RPM had decayed from 101–102 per cent (normal operation) to 97 per cent. The engine and rotor RPMs were matched and decreasing. The engine manifold pressure (MAP) was at 22.5 in Hg^[7] and the airspeed at 25 kt; both were increasing. Based on estimates from a combination of the helipad surveillance video and passenger video of the flight instruments, the low rotor RPM warning occurred at approximately 37 ft above ground level (20 ft climb above take-off height).

Figure 1: Activation of low rotor RPM warning

Source: Passenger, annotated by the ATSB

The helicopter continued to climb and increase forward airspeed, and the rotor RPM decayed to 90 per cent. A left turn was commenced shortly after take-off to avoid a no-overfly zone (Yulara Resort and Township) and join the scenic flight traffic pattern. During the left turn, the airspeed reached a maximum of about 38 kt before the helicopter pitched up slightly, resulting in a decay in airspeed as the helicopter continued to climb.

About 15 seconds after take-off, the engine and rotor RPM had decayed to 80 per cent, with a MAP of 26 in Hg, airspeed of 33 kt, height of about 87 ft above ground and vertical speed of 300 ft/min (Figure 2).^[8] The onset of vibrations became noticeable in the final seconds of the passenger video of the departure, which ended about 17 seconds after take-off. The helicopter continued to turn left onto a southerly track, instead of following the planned scenic flight departure pattern to the west.

Figure 2: Rotor RPM decay

Source: Passenger, annotated by the ATSB

The pilot initially reported that they applied full throttle in response to the low RPM warning horn, and that there was ‘not enough height to do much else’. This initial recollection was associated with the warning activating at a height of 300 ft, after the left turn, with 22–23 in Hg MAP. In response to the draft report, the pilot submitted that they had been taught to ‘open throttle and lower the collective’ in response to the low RPM warning, and that is what they would have done regardless of the height. Helipad footage indicated the helicopter was at a height of about 200 ft when it was abeam the helipad and in relatively level flight until it passed out of the camera view 42 seconds after take-off.

About 91 seconds after take-off, the pilot broadcast an emergency radio call ‘going down’. The deputy area manager immediately responded with a radio call to the pilot to ‘put it [helicopter] into wind’, and the pilot attempted a forced landing to what appeared to be a clear patch of sand. The pilot was unable to recall any other actions, but that there was a ‘couple of kicks’ of the helicopter just prior to the final descent. The front left seat passenger reported that the helicopter was climbing and descending during the flight, and then a ‘big shudder’. Both rear seat passengers reported that the helicopter started shaking from side to side (vibrations) at about 15 seconds after take-off and that the intensity of the shaking increased from moderate to extreme until the final descent.

During the descent, the rotor RPM was too low for the pilot to be able to arrest the helicopter’s rate of descent to a safe vertical speed, resulting in a hard landing. The landing area was a small knoll with a steep bank, which resulted in the helicopter rolling over. The pilot and two passengers were seriously injured, and the remaining passenger experienced minor injuries. The helicopter was substantially damaged.

The rear right seat passenger’s phone camera was activated intermittently in video mode several times during the flight. The low rotor RPM warning was audible throughout the recordings, which included the ground impact, and was reported by the passenger as sounding continuously throughout the flight. Figure 3 depicts the accident site. Figure 4 depicts the accident flight path, based on tracking data provided by the operator. The flight track was about 1.0 NM (1.85 km) at an average ground speed of about 40 kt.

Figure 3: VH-HGX wreckage

Source: Northern Territory Police

Figure 4: Accident flight path

Source: Google earth, annotated by the ATSB

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2. Central Standard Time (CST): Coordinated Universal Time (UTC) + 9.5 hours.
3. The Uluru Base included a maintenance facility at Ayers Rock Airport and helipad operations at Kings Canyon and the Yulara Resort, known as the Yulara Town Pad.
4. A confined area is an area where the flight of the helicopter is limited in some direction by terrain or the presence of obstructions, natural or man-made.
5. Lift-off refers to the helicopter rising from contact with the surface of the helipad into the air. Take-off refers to the helicopter accelerating forward for departure.
6. Cyclic: a primary helicopter flight control that is similar to an aircraft control column. Cyclic input tilts the main rotor disc, varying the attitude of the helicopter and hence the lateral direction.
7. The units for manifold pressure are inches of mercury (in Hg).
8. This was the last footage of the cockpit instruments.

Safety issues and actions

Passenger scales

Safety issue number: AO-2018-006-SI-01

Safety issue description: Professional Helicopter Services did not have a calibration schedule for their passenger scales, which were under-reading. This increased the risk of their helicopters not achieving their expected take-off performance.

Pilot’s operating handbook

Safety issue number: AO-2018-006-SI-02

Safety issue description: The Robinson R44 pilot’s operating handbook low rotor RPM recovery procedure did not include reference to the minimum power airspeed for the helicopter as a consideration, which may assist a pilot to recover from a low rotor RPM condition.

Safety recommendation description: The ATSB recommends that the Robinson Helicopter Company reviews the R44 pilot's operating handbook low rotor RPM recovery procedure for consideration to include a reference to the minimum power airspeed (Vy) for pilot awareness.

Safety action not associated with an identified safety issue

Professional Helicopter Services

As a result of this occurrence, Professional Helicopter Services has advised the ATSB that they have taken the following safety actions:

Check flights

They temporarily suspended commercial operations at their Uluru Base in order to enable the chief pilot to conduct several check flights with each pilot before resuming operations.

Helipad procedures

They completed an audit of the Yulara Town helipad and amended the published departure and approach procedures to align with designs recommended, but not mandated, by the Civil Aviation Safety Authority in Civil Aviation Advisory Publication 92-2(2): Guidelines for the establishment and operation of onshore Helicopter Landing Sites.

Safety analysis

Introduction

During the departure from the Yulara Town helipad, Northern Territory, VH-HGX experienced a rotor speed (revolutions per minute - RPM) decay at a point from which the take-off could not be safely aborted. The rotor RPM continued to decay to a level from which the pilot could not recover, resulting in a hard landing when the pilot attempted a forced landing. The pilot and two passengers were seriously injured, and the remaining passenger experienced minor injuries. The helicopter was substantially damaged.

This analysis will discuss the pilot’s running turn-around, the most likely reason for the rotor RPM decay, and the pilot’s response to the low rotor RPM condition. It will further discuss the increased risk to the flight associated with inaccurate passenger scales, an opportunity to improve the helicopter’s emergency procedures for a low rotor RPM recovery, and the benefits and limitations of the recordings.

Running turn-around

The operator reported that the governor would be turned off during the turn-around procedure for transferring passengers, and then selected on for the engine run-up. However, the pilot had adopted a practice of manually running the engine from idle, with the governor turned off, until completion of the low rotor RPM warning check at 98 per cent engine RPM. The ATSB considered that this practice could have inadvertently resulted in the pilot running the engine up into its green operating range (101–102 per cent engine RPM) before the governor was turned on.

The pilot submitted that they were confident the governor was on and working before take-off. However, any movement of either the twist grip throttle or the collective lever by the pilot after engine run-up that produced an RPM response could have been mistaken for a governor response. Therefore, an RPM indication in the green operating range, combined with the ‘governor off’ light extinguished, could have provided a false positive confirmation that the system was operating before take-off.

The extinguished ‘governor off’ light only indicated that the circuit for the light was open. This occurs when the governor switch is selected to the on position to provide electrical power to the controller but will also occur if the light’s circuit breaker trips. It did not provide an indication that the controller was operative. If the governor is not functionally checked from its low RPM operating range to 102 per cent, then a take-off may occur with an undetected problem.

Therefore, the pilot’s practice of engine run-up with the governor off increased the risk of an inoperative governor (either selected off or with a fault) not being detected prior to take-off. Since it was the operator’s procedure to turn the governor off during the running-turn-around, the ATSB considered it likely that the pilot had adopted this practice inadvertently.

Rotor RPM decay

The engine performance study used manifold pressure (MAP), engine RPM, the local environmental conditions and the engine manufacturer’s charts to determine the engine power and throttle movement. The passenger phone footage started at about the time of the take‑off (start of forward flight), at which time the RPM was at about 101 per cent. That review concluded that the engine throttle and power initially increased while the engine and rotor RPMs decayed during the departure.

The take-off was conducted at a high-density altitude at near maximum weight. Therefore, a high MAP would be expected on departure under these conditions. However, the passenger video indicated the RPM started to decay at a relatively low MAP, which increased slowly, as the RPM steadily decayed to 90 per cent over an 8 second time period. The decay continued to 80 per cent over the following 7 seconds.

The engine was operated in the maximum continuous power (MCP) to take-off power (TOP) range on the day of the accident. The pilot had flown the same departure with a full load of passengers on three previous flights (including one at a higher planned operating weight), which indicated it was capable of flying the departure. The decay in RPM at a relatively low MAP indicated that it was likely associated with insufficient airflow to the engine to enable it to produce the power required. Therefore, the ATSB evaluated the evidence against the scenarios of (1) overpitching, (2) air induction obstruction, (3) inoperative governor and (4) throttle mishandling. An inoperative governor or throttle mishandling were considered the most likely scenarios.

The increase in power during take-off indicated the engine was capable of producing more power than it did initially produce and found no evidence of a corrective throttle response from the governor system in the first 8 seconds of the engine and rotor RPM decay. Therefore, an overpitching event, in which the governor system would attempt to recover RPM, was considered unlikely.

The increase in MAP and power during take-off, as the RPM decayed, indicated the engine throttle was not stuck and that there was unlikely to be an obstruction of the air induction system preventing engine power from increasing. Therefore, an obstruction of the engine air induction was also considered unlikely to be the reason for the RPM decay.

Inoperative governor

The engine run-up and increase in power on take-off indicated there was mechanical continuity between the pilot’s controls and the engine throttle. The throttle opening is increased by the correlator when the pilot raises the collective lever and by the governor if it detects the engine RPM is low. Both inputs will result in an increase in MAP and power, but the correlator is an open loop process that does not monitor or manage engine RPM. It is the governor system that provides the closed loop process to correct for excursions in RPM by adjusting the engine throttle. Without a corrective input from the governor, as the pilot introduces control inputs via the collective, cyclic or tail rotor pedals, the engine throttle may not open to a position where the power produced is sufficient for the power required. This may produce an RPM decay at a low MAP, which was consistent with the observed indications.

The rise in MAP from 20.5 to 22.5 in Hg was in the same period that the vertical speed and airspeed increased, which was consistent with the pilot raising the collective lever for take‑off. The RPM decayed during this period from 101 to 97 per cent and engine power increased, which suggested the rise in MAP was a result of the correlator increasing the throttle opening as the pilot raised the collective lever. After the low rotor RPM warning, there was a continued decay in RPM from 97 to 90 per cent in the following 5 seconds, with only a small increase in MAP and engine power. This period provided no indication of a corrective throttle response from the governor in terms of a rise in MAP to a value equivalent to a full throttle setting.

The governor system was tested serviceable at the previous 100‑hour maintenance inspection 2 days before the accident, and it was reported to be working on the day. Robinson (RHC) testing of the governor controller found no fault and ATSB testing of the governor motor, friction clutch and pilot’s twist grip indicated that the governor system should have been capable of producing full throttle within the first 8 seconds.

Although, the ATSB and RHC found no faults with the components that were tested following the accident, the governor system could not be tested in its entirety under the accident conditions due to the damage sustained. Therefore, in consideration of the possibility that the governor operation was not verified before lift-off, the ATSB could not rule-out the possibility of a rotor RPM decay as a result of an inoperative governor.

Throttle mishandling

The pilot can inhibit the governor input to the throttle if the twist grip is held with a firm grip (known as ‘strangling the throttle’). This will provide the same instrument indications (and result) as an inoperative governor. The correlator will still increase and decrease the throttle when the collective lever is raised and lowered, providing a power response, but the pilot’s grip will inhibit corrective input from the governor to the throttle if an RPM excursion (over-speed or under-speed) occurs.

In consideration of the potential for mishandling the throttle, the ATSB reviewed the pilot’s training records and interviewed several of the pilot’s instructors. The phenomena of ‘strangling the throttle’ was well known, but there was no evidence of this problem in the accident pilot’s training records or from interviews. On review of the passenger video footage, the ATSB was unable to sight the pilot’s grip on the collective throttle twist grip, and therefore could not determine what technique was employed on take-off. However, as no individual governor system component was found to be unserviceable during post-accident testing, the ATSB could not rule-out the possibility that the pilot’s grip inhibited the governor input to the throttle.

Low rotor RPM response

The low rotor RPM warning activated when the helicopter was climbing over trees in the departure path. The RHC published low rotor RPM recovery procedure required the pilot to ‘immediately roll throttle on, lower collective and, in forward flight, apply aft cyclic’.

The pilot initially reported that when the low rotor RPM warning activated, they opened the throttle, but ‘could not do much else’. Although the pilot’s recollection was that this occurred at 300 ft, video evidence indicated the helicopter was at about 37 ft, and there was no significant increase in throttle for at least 5 seconds after the warning activated.

In the 5 seconds following activation of the low RPM horn, the MAP had only reached 24.0 in Hg and therefore the throttle position was likely still below the full throttle setting. The collective lever twist grip was found to be serviceable in post-accident testing. The engine run-up before lift-off, and the increase in power on departure indicated there was mechanical continuity from the pilot controls to the engine throttle. Therefore, it was likely that the pilot did not apply full throttle prior to the rotor RPM decaying to 90 per cent, as this action would have resulted in a rapid rise in MAP to a value in the vicinity of 25–26 in Hg.

The pilot later submitted that they would have applied full throttle and lowered the collective lever, irrespective of the height available. In addition, the operator submitted that the simultaneous action of opening the throttle and lowering the collective lever might have produced the observed MAP indications. However, the steady decay in RPM on departure indicated there was no significant change in the difference between power delivered and power required by the rotors.

If the power margin changes, then the RPM rate of decay will also change, reaching zero when the power applied to the rotors is equal to the power required by them. As there was no reduction in the engine power produced (as indicated by MAP) when the RPM decayed from 97–90 per cent during the departure, the steady decay in rotor RPM indicated that there was no significant reduction in the power required by the rotors. This, in combination with the continued climb to about 200 ft, suggested the collective lever was not lowered.

It is possible that during the early stages of the rotor RPM decay the pilot’s attentional resources were consumed with the departure over the treetops, and an early left turn to avoid a no-overfly area. This manoeuvre required the pilot’s visual attention outside of the helicopter for the majority of time. As a result, while the pilot may have perceived the low RPM warning, it was likely that they did not have the spare attentional capacity to immediately comprehend and respond to the warning in the early stages of the decay.

Allowing the helicopter to climb and lose airspeed during the take-off resulted in the power margin decreasing, at a time when the opposite was required. The passenger video of the take-off ended before the helicopter levelled off, and it continued flight for about another 70–80 seconds. This suggested the engine was continuing to produce power. As the rotor RPM had reached 80 per cent at about 87 ft above the ground, and the helicopter was still indicating a climb of 300 ft/min, it was likely that the rotor RPM continued to decay below 80 per cent, resulting in less engine power available for RPM recovery.

The front seat passenger’s report of the helicopter climbing and descending suggested the pilot may have lowered the collective lever in an attempt to recover rotor RPM. This section of the flight was not recorded, and the pilot had no recollection of it, so it could not be determined exactly what was occurring. However, it was likely that there was insufficient height, airspeed and engine power to recover from the low RPM condition that had developed on departure, resulting in the need for a forced landing.

With minimal height available above obstacles at the time the low rotor RPM activated, the optimum flight condition for RPM recovery was full throttle with the lowest collective lever position. For the R44, the lowest collective lever position in level flight is achieved at 55 kt, which would have provided a power margin of about 76 hp to the power produced on departure. In consideration of the potential power margin available, if the pilot had applied full throttle in the first 5 seconds and then lowered the collective lever sufficiently to prevent a climb, the low rotor RPM was likely recoverable.

Hard landing

Tracking of the main rotor blades and balancing of the main rotor system is conducted to minimise in-flight vibrations that occur at the normal operating speed of the main rotor. However, as RPM decays, the rotor blades will lose their rigidity, allowing them to flap up and down with greater amplitude. Excessive flapping of the main rotor blades may result in the blades rotating out‑of‑track and the rotor system operating out‑of‑balance. According to Kroes et al. (2013), incorrect tracking of rotor blades will produce a vertical vibration and an unbalanced main rotor system will produce a lateral vibration.

The development of low frequency vibrations (main rotor vibrations) associated with low RPM, as described by the passengers, may be a precursor to a main rotor blade stall event if corrective action is not taken immediately. Whether or not these vibrations precede a stall is situational dependent – a main rotor blade stall could occur without this warning if the RPM decay is rapid. According to the R44 pilot operating handbook, a main rotor blade stall will either ‘cut off the tailcone’ or the helicopter will ‘just stop flying and fall at an extreme rate’. A video review of other R44 low RPM incidents suggested the vibrations reported by the passengers were consistent with an RPM of 70–80 per cent.

Either due to the lack of identified suitable landing sites, a belief that the low rotor RPM was recoverable, or a combination of the two, the pilot continued to fly the helicopter for about 70–80 seconds after the RPM had decayed to 80 per cent. The continued decay of the RPM below 80 per cent at low height and airspeed meant that recovery was not going to be possible. At the time the pilot made a distress call and selected a forced landing site, the RPM was likely too low for it to be recovered and used to arrest the rate of descent before touchdown, resulting in a hard landing and serious injuries.

Passenger scales

On the day of the accident, the passengers were weighed on arrival at the helipad with the operator’s scales. Their weights were entered into a spreadsheet along with the helicopter empty weight, pilot weight and planned fuel load for each flight.

When the ATSB compared the recorded occupant weights on the accident flight with their actual weights, it was noted that the individual recorded weights for the accident flight were underestimated by about 9.6 per cent.

This discrepancy was also noted for passengers on other flights, in addition to those on the accident flight. Consequently, while the helicopter was likely operating below the maximum weight, it was operating at a higher weight than the planned weight and was potentially overweight on an earlier flight. The under-reading of the passenger scales was likely due to them not having a calibration schedule.

A high weight in favourable environmental conditions could result in a pilot incorrectly assessing the helicopter’s power margin in the hover as adequate for take-off. If unfavourable conditions subsequently develop during take-off, such as a change in the wind conditions, then the observed power margin from the hover could prove to be insufficient to safely continue.

The under-reading scales increased the likelihood that the helicopters would be operated overweight, which could have resulted in the power required being in excess of the power available. This condition increased the risk that the operator’s helicopters would not achieve their expected take-off performance.

Pilot operating handbook

The R44 pilot operating handbook emergency procedure for low rotor RPM recovery required the pilot to ‘immediately roll throttle on, lower collective and, in forward flight, apply aft cyclic’. These factors will maximise the likelihood of the pilot successfully recovering rotor RPM, but are dependent on the energy available, in the form of height or airspeed, to convert to rotor speed.

While these actions are listed in the handbook as immediate actions, lowering the collective lever may not always be practicable, such as low flying over obstacles. Further, the application of aft cyclic to use the forward airspeed as a driving force for the main rotor disc will also decelerate the helicopter. Therefore, the power required will increase if this is performed on the back-end of the power curve. In these situations, there is little energy available in terms of height or airspeed to convert to rotor speed. Consequently, there may be more benefit in allowing the airspeed to gently increase to the minimum power airspeed to reduce the power required for level flight, which will allow the pilot to progressively lower the collective lever and increase the power margin.

The minimum power required airspeed of 55 kt was published in the pilot operating handbook – normal procedures, as the recommended airspeed for maximum rate of climb. It was also included in the emergency procedures section of the handbook for the minimum rate of descent procedure with a power failure, but there was no reference to this airspeed in the low rotor RPM recovery procedure. However, there was reference to 55 kt as a target airspeed to recover from overpitching events in on-line educational videos. This suggested that it was a known and recognised target airspeed within the industry.

The ATSB selected another light helicopter and reviewed the emergency procedure checklists for evidence of advisory airspeed information. It was noted that there were numerous instances throughout the various checklists of advisory airspeeds to assist a pilot in their recovery actions. These included immediate actions and subsequent considerations.

The ATSB noted that the low airspeed-low RPM accidents were often associated with operations at low heights where lowering the collective lever may not be an option. These circumstances may require a variation to the published procedure, such as an overshoot (known as an escape manoeuvre) with full throttle to increase airspeed so that the collective lever can then be lowered to reduce the power required. If a pilot has not been exposed to this in a risk managed training environment, and their response to this scenario is instead based upon rote learning the procedure, they may not have the knowledge and handling skills to apply to the situation.

Therefore, the ATSB considered that the inclusion of the minimum power airspeed as a subsequent consideration to the immediate actions for low rotor RPM recovery could improve the safety-critical information available to pilots. In addition to making less experienced pilots aware of this airspeed, the inclusion of it in the procedure may lead to the promotion of broader discussion and understanding of the power curve, the risks associated with low airspeed-low rotor RPM conditions, and how to adapt the emergency procedure actions to the various scenarios in which it might be encountered.

On-board recordings

In this investigation, it was fortunate that the operator and passengers volunteered video recordings of the accident flight. This enabled the ATSB to focus on the relevant technical and human factors, without expending resources on unnecessary inspections and tests in an attempt to rule-in or rule-out out potential contributing factors. However, several key pieces of evidence from the accident flight, such as the pilot’s grip on the throttle twist grip and attempts to recover rotor RPM, were not recorded. The development of the low rotor RPM condition on take-off was captured by chance alone.

The availability of the helipad and passenger video recordings assisted the investigation in the identification of operational factors that were not all apparent from the various interviews and statements obtained. This enabled the ATSB to focus the safety lessons on the actions needed to reduce the risk of future similar accidents.

Findings

From the evidence available, the following findings are made with respect to the rotor RPM decay and hard landing involving a Robinson R44 helicopter, registered VH-HGX, 5 km south of Ayers Rock Airport, Northern Territory, on 17 January 2018.

Contributing factors

• During take-off, the helicopter's rotor RPM steadily decayed due to a likely limited opening of the engine throttle, which resulted in the engine power produced being less than the power required. The reason for the limited opening of the throttle could not be determined.
• Following activation of the low rotor RPM warning, the pilot initially did not apply full throttle and lower the collective lever to avoid a climb, which resulted in the rotor RPM decaying further to a level from which the pilot could not recover.
• While attempting a forced landing, the rotor RPM decayed to an extent that the pilot was unable to arrest the rate of descent sufficiently to prevent a hard landing, resulting in serious injuries to the occupants.

Other factors that increased risk

• The pilot had inadvertently adopted a practice of running the engine up manually with the governor off during passenger transfers, which increased the risk of an inoperative governor not being detected prior to take-off.
• Professional Helicopter Services did not have a calibration schedule for their passenger scales, which were under-reading. This increased the risk of their helicopters not achieving their expected take-off performance. [Safety Issue]
• The Robinson R44 pilot’s operating handbook low rotor RPM recovery procedure did not include reference to the minimum power airspeed for the helicopter as a consideration, which may assist a pilot to recover from a low rotor RPM condition. [Safety Issue]

Other findings

• The passenger and helipad video recordings of the flight provided essential data to understand how the accident developed. However, this investigation would have benefited from flight data recorder or image recorder data to maximise the safety lessons for industry.

Context

Pilot information

The pilot held a Commercial Pilot (Helicopter) Licence with about 300 hour’s total flying experience and a Class 1 Aviation Medical Certificate with no restrictions. The pilot’s training was conducted on the Robinson R22 and R44 helicopters with the operator. The pilot was offered a job at the operator’s Uluru Base on completion of training. After passing a company check flight in the R44 on 12 July 2017, the pilot moved to the Uluru Base and started work the same month.

The pilot was initially employed in-command-under-supervision. On 21 September 2017, the pilot was cleared by the operator as pilot in command for passenger flights after successfully completing the operator’s line training for the local airport procedures, helipad procedures, scenic flight patterns, radio procedures and no-fly zones. The pilot had accumulated about 180 hours on the R44 from July 2017 until the accident flight.

72-hour history

The pilot had a couple of rest days prior to starting work at 0930 on 17 January and had been on duty for about 8 hours and 52 minutes at the time of the accident. The pilot had completed six scenic flights, which was about 1 hour and 30 minutes of flight time, plus a return flight to the airport for refuelling (about 5 minutes each direction). When asked about fatigue management, the pilot reported that it was a good work-rest schedule and that it was a comfortable work arrangement. Business was normally performed with a morning and afternoon crew. The morning crew would start at sunrise, if required, and end at 1400 when the afternoon crew would take over. The pilot reported being well rested and fit for duty on the day of the accident.

Helicopter information

General details

The Robinson Helicopter Company (RHC) R44 Raven 1 is a four-seat piston-engine helicopter, powered by a Lycoming O-540-F series six-cylinder carburetted engine. VH-HGX was manufactured in 2000 and registered in Australia in May of the same year. The last 100‑hourly maintenance inspection was completed on 15 January 2018, at which time it had accumulated 3,489.5 airframe hours. That inspection included an engine governor system functional check and cylinder compression check. They were all assessed serviceable.^[9] In addition, the engine air filter was ‘replaced for company convenience’.

Engine power and drive

The engine take-off power (TOP) is rated at 260 horsepower (hp) at 2,800 revolutions per minute (RPM), which can be maintained up to a pressure altitude of 800 ft. Maximum continuous power (MCP) of 235 hp can be maintained up to a pressure altitude of 4,000 ft.^[10] Robinson provide pilots with the de-rated figures of 225 hp and 205 hp for TOP and MCP respectively at 2,718 RPM. This allows the helicopter to maintain engine performance on a climb from sea level to several thousand feet before the power available will start to decay below their published TOP.

The rotors are driven by the engine with a V-belt drive system and gearboxes. The drive system reduces the engine RPM of 2,718 to the main rotor RPM of 408. The engine and rotor RPM are both presented to the pilot as a percentage on the cockpit tachometer gauges, so that they are matched under normal operating conditions. An engine governor system is installed to provide automatic control of engine RPM, which will control the rotor RPM via the associated drive-train.

Engine throttle control and governor system

RHC reported that there are three ways the engine throttle can be manipulated, via the same mechanical input at the carburettor, as follows:

The correlator: a linkage between the collective lever^[11] and the throttle. As the collective is raised, the throttle is opened and as the collective is lowered, the throttle is closed. This performs the majority of the throttle control in-flight. Provided the throttle is already partially open to achieve 102 per cent RPM on the ground, full throttle can be achieved by the correlator.

The governor: an electronic throttle control using a controller unit and motor to fine tune the engine RPM through a friction clutch, which applies a twisting force to the pilot’s throttle grip. The further away from the target speed (102 per cent), the faster the controller will move the throttle to return to the target, but for the most part, it is very small, slow movements.

The pilot: in normal flight the pilot is not required to manipulate the throttle, but more aggressive manoeuvres or demanding environments may require the pilot to make manual adjustments. The governor can be overridden by the pilot gripping the throttle (twist grip located on the end of the collective lever) and turning as needed.

The MAP sensor measures air pressure downstream of the throttle, which is less than atmospheric pressure when the engine is running. The MAP will increase if the throttle is opened, or if the engine RPM decays, or combination of the two.

The engine throttle control is depicted in Figure 5. The engine right magneto (RM) senses engine RPM, which is sent to the governor controller. The governor controller provides the correction signal to the engine throttle via the governor motor, friction clutch and pilot’s twist grip on the collective lever. This provides a closed-loop system to maintain RPM. Figure 5 shows the components in green that were tested during the investigation, the components in yellow are the cockpit gauges and those in blue represent the air intake path.

Figure 5: R44 engine throttle control

Source: ATSB

In Figure 5, the governor switch is represented in the off position, which will illuminate the ‘governor off’ light. The governor switch is located at the end of the collective lever and was not visible in any videos. When the switch is closed (on position) by the pilot, the ‘governor off’ light will extinguish to indicate the controller is receiving electrical power - the light does not provide a fault indication.

If there is a fault with the right magneto points, a faulty signal will be sent to the controller, which will respond accordingly. The engine tachometer in the cockpit receives a signal from the same source as the controller (RM). Therefore, irregular engine RPM indications (erratic movement) will be present if the points are producing a faulty signal. This was not observed on the passenger video or reported by the accident pilot.

The governor controller is active from 79–111 per cent engine RPM. Within the active range there is a 1 per cent wide dead-band from 101.5–102.5 per cent where it will not take action provided the RPM is steady. At 101.5 per cent there is a step change in the controller output voltage, followed by a ramp increase to maximum voltage output at about 97 per cent, which is maintained to the cut-off at 79 per cent. The controller dead-time^[12] was not published, but the advice received from RHC was as follows:

From the pilot’s perspective, the output response is typically immediate, but the result may not be. For example, if the throttle is half open and the collective is aggressively raised, causing the RPM to drop, the governor will immediately open the throttle aggressively, but if the load on the engine is greater than power available (at that lower RPM), the RPM will be slow to increase.

Overtravel spring

During the ATSB’s examination of the wreckage (refer to section titled Post-accident tests and inspections), the overtravel spring assembly was found bent (Figure 6), most likely as a result of the ground impact. Robinson reported that, from the overtravel spring to the engine throttle valve, the system can be considered to be a purely mechanical link and extension or compression of the overtravel spring does not occur during normal flight regimes, only at the extremes of throttle travel.

With reference to Figure 6, the arm connected to the collective lever assembly and overtravel spring assembly can move vertically or in rotation. When the collective lever is raised or lowered, it will move vertically to increase or decrease engine throttle. When the pilot rotates the twist grip, or driven by the governor motor, it will rotate to increase or decrease engine throttle.

Figure 6: VH-HGX collective lever assembly and overtravel spring assembly

Source: ATSB

Post-accident tests and inspections

The ATSB did not conduct an on-site visit to inspect the wreckage and impact. However, from the various video recordings, the ATSB and RHC noted the engine operation ‘sounded good’ until the sound of the engine RPM being retarded by the decaying rotor RPM became noticeable.

The pilot who flew the accident helicopter earlier on the day reported that it was achieving the pilot’s operating handbook (POH) published TOP range of 24.2–25.8 in Hg MAP and that the movement of the twist grip could be felt as the governor adjusted the throttle to maintain RPM. In addition, the accident pilot reported that the helicopter was ‘operating correctly’ at take-off. As a result of this information, the ATSB was primarily interested in the helicopter information related to the engine power and RPM control.

Right magneto, light bulb and switch

Following the accident, at the request of the ATSB, the right magneto was removed from the helicopter by the insurance surveyor. An inspection and test of the right magneto and associated wiring was conducted. No fault was found with the right magneto tachometer points used for the engine tachometer and the governor controller, and the magneto tested serviceable. No fault was found with the associated wiring. The ‘governor off’ light bulb and governor switch were later tested and also found to be serviceable, but with the limitation that each item was tested in isolation as the instrument panel was already removed from the airframe.

Governor controller test

Following the inspection of the magneto and wiring, the governor controller was removed and sent to RHC to perform an inspection and functional test of the unit under the supervision of the United States National Transportation Safety Board. There were no indications of tampering or thermal damage, and the unit’s electrical connector was clean and pins straight. A functional test was performed in accordance with the RHC process. The test results were observed to be within specifications and no fault was found.

ATSB post-onsite wreckage examination

Following the serviceability assessment of the governor controller, the ATSB examined the stored wreckage to inspect and test the governor motor, friction clutch and pilot’s throttle twist grip, in accordance with RHC’s procedures. After removal of the damaged surrounding structure, and disconnection of the deformed overtravel spring, the components were found to be in a satisfactory condition to be tested in situ.

Each test was repeated with no fault found and assessed to be serviceable. The ATSB noted the governor motor was capable of rotating the pilot’s twist grip from full closed to full open in about 8 seconds. The friction clutch operated as designed when hand pressure was increased on the twist grip, which provided override of the governor motor and full manual control of the arm in both vertical and rotational movement.

The governor switch was in the off position when the ATSB attended the wreckage. The operator reported a witness at the accident site noted the switch was in the off position, but this was only observed after the occupants had been removed from the wreckage. Therefore, it was possible that the switch was disturbed after impact.

The governor circuit breaker and low RPM light and horn circuit breakers were in. The warning lights’ circuit breaker (includes ‘governor off’ light) was out. However, several other circuit breakers for systems that were observed to be working during the flight were also out, which indicated that some circuit breakers tripped during the accident.

Robinson helicopters have been subject to isolated cases of obstruction to the air induction systems from a deterioration of components, such as air filters. This has resulted in several service defect reports in Australia, including reports of loss of power, and several RHC service bulletins on the subject of air filter deterioration.

The R44 maintenance manual low power troubleshooting checklist included inspecting the air induction system for obstructions. Therefore, the ATSB reviewed post-accident images of the condition of the air filter fitted to VH-HGX. The air filter was found to have been pushed up through the carburettor by the ground impact while the engine was running, resulting in considerable damage to the air filter and the carburettor ingesting sand and debris. As such, the ATSB was unable to determine the condition of the air filter prior to impact.

Engine performance study

According to the R44 POH, the MCP limit was 24.2 in Hg MAP at 2,000 ft pressure altitude and 40 °C (205 hp). An additional 1.6 in Hg can be added to MCP for a 5‑minute TOP rating of 25.8 in Hg MAP (225 hp). Passenger footage of the previous flight revealed the helicopter climbed to about 3,500 ft pressure altitude at 22–23 in Hg MAP, which indicated the engine was producing 187–197 hp at an elevation about 1,700 ft above the helipad. This was consistent with the performance of the engine as reported by the pilot who operated the helicopter earlier on the day of the accident.

The right rear seat passenger’s video provided an uninterrupted view of the cockpit instruments during the first 8 seconds of the departure, which was sufficient time for the MAP to indicate a response from either governor or pilot throttle input. Therefore, the video recording period of t=0 to t=8 was chosen for the engine performance review. The video indicated the low rotor RPM warning started about 3 seconds after take-off (t=3).

Cockpit instrument indications

The cockpit instrument indications for vertical speed (VSI – ft/min), airspeed (ASI - kt), MAP (in Hg) and engine RPM (%) were plotted (Figure 7). The measurements were based on passenger video footage of instrument readings using 1 second time intervals. Therefore, the accuracy of any individual data point should be treated with caution. As the engine and rotor RPM decayed together (within the tolerance of 1 per cent of each other), the rotor RPM trend can be inferred from the engine RPM trend.

The top left graph of Figure 7 shows that the vertical speed reduced after the low rotor RPM warning activated but remained positive (climbing). A number of factors could have accounted for this change, such as a loss of ground effect, increase in forward cyclic or reduced collective setting. The top right graph shows the airspeed steadily increased after it started to provide a reliable indication. The bottom left graph shows the MAP steadily increased and the bottom right graph shows the RPM steadily decreased.

Figure 7: Data plot of instrument indications

Note: The data plots of instrument indications include a red vertical line for the low rotor RPM warning at t=3 seconds. The dashed line at the start of the airspeed indicates unreliable indications.

Source: ATSB

Engine power

Using the RPM, MAP, environmental conditions and the Lycoming O-540-F series performance chart, the ATSB plotted the engine horsepower from t=0 to t=8 seconds (Table 1). The lowest RPM on the chart was 2,500 (93.8 per cent RPM), therefore, the results for t>=6 were based on extrapolated data but considered to provide a reliable trend based on the helicopter’s increasing airspeed and positive rate of climb. As the RPM continued to decay, data points beyond t=8 did not appear to change the trend but resulted in the need for greater extrapolation of the charts, which increased uncertainty in the results obtained. Therefore, these have not been included.

Although engine power is proportional to RPM, it is also proportional to mechanical and volumetric efficiency, which may improve as the RPM decays. This can result in a relationship between power and RPM that is not strictly linear. The engine manufacturer was unable to provide a power (or torque) curve for the engine, so it could not be determined at what RPM the engine power would start to decay, but the ATSB accept that the power available would have reduced at some stage during the departure as the RPM decayed.

The Table 1 figures indicate that MAP and engine power were increasing during take-off, but at a decreasing rate. The engine manufacturer’s fuel consumption charts indicate that the same throttle setting will produce a higher MAP at a lower RPM. Therefore, a MAP equivalent to the MCP throttle setting did not appear to have been achieved in this period. Figure 8 depicts the trend in engine power as a percentage of 205 hp (MCP) and the trend in RPM decay.

Table 1: Engine power

Figure 8: Trend in engine power and RPM

Note: The trend in engine power and RPM includes a red vertical line for the low rotor RPM warning at t=3 seconds.

Source: ATSB

Airflow restriction

The low MAP and power during take-off indicated the engine was producing good suction power but receiving inadequate airflow. Therefore, the limited power output from the engine during take‑off was considered by the ATSB to potentially be the result of a partial obstruction of the intake airflow or restriction of the throttle butterfly valve (stuck throttle), upstream from the MAP sensor. This would produce a low MAP and decay in RPM when the collective lever was raised. However, engine power increased during take-off at the same time that the RPM was decaying, which indicated that the throttle was opening and intake airflow was able to increase. Passenger footage of the helipads revealed they were clean and free of debris, and that the passengers were escorted to and from the helicopters on the pad. This suggested the RPM decay was unlikely to be the result of a foreign object obstruction or stuck throttle.

Overpitching

Overpitching is a phenomena that happens when the collective pitch is increased to a point where the main rotor blade angle of attack creates so much drag that all available engine power cannot maintain or restore normal operation rotor RPM.^[13]

There are two commonly understood mishandling techniques, which can result in a pilot overpitching the helicopter during take-off. If a pilot raises the collective lever to a point beyond the full throttle position (where full throttle was required to maintain RPM), then there will be more power required by the rotors than power available from the engine, resulting in a rotor RPM decay. However, during the accident flight, the rotor RPM started to decay when the MAP was below the published MCP rating. There was also an indication that power increased after the decay started. Therefore, a rotor RPM decay as a result of the pilot raising the collective lever beyond the full throttle position was considered very unlikely.

A second mishandling technique involves a pilot raising the collective lever at a rate that is faster than the rate at which the correlator and governor open the throttle, and the pilot does not compensate by adding more throttle. In this case, the rotor RPM may rapidly decay to a level that is too low for the engine power available to recover. According to RHC, the further away from the target RPM, the faster the governor will move the throttle, and for the R44, the engine power response to a throttle input is almost instantaneous. Therefore, as the engine RPM decays the throttle setting should increase and provide a corresponding increase in the MAP as the governor attempts to recover the engine RPM.

The rotor RPM decayed at a relatively steady rate of 11 per cent over 8 seconds. During this period, the MAP did not increase to a value representative of full throttle. Therefore, the decay in RPM as a result of the pilot raising the collective lever at a rate faster than the governor could immediately respond to, was considered unlikely.

Summary

The instrument indications, and subsequent plots of power and throttle, were consistent with the pilot raising the collective lever during the initial climb and acceleration phase of the take-off. This indicated there was mechanical continuity between the collective lever and the engine throttle. In addition, the engine run-up from idle prior to lift-off indicated there was mechanical continuity from the pilot’s twist grip to the engine throttle.

As the helicopter was operating at near maximum all-up-weight and a high density altitude environment, a high collective lever setting, requiring a high engine power, would have been expected for this phase of flight. Therefore, it was concluded that, as the power required by the rotors increased during take-off, the engine throttle position did not increase by a corresponding amount to produce sufficient power to maintain RPM. In addition, there was no MAP indication of a corrective input to the throttle, equivalent to MCP–TOP, in response to the RPM decay in the initial 8 seconds of the video.

Operational information

Yulara Town helipad

The Yulara Town helipad was part of the operator’s Uluru Base, which included scenic flight operations from Kings Canyon and a maintenance facility at Ayer’s Rock Airport. The Uluru operations were managed by an area manager and deputy area manager. The Yulara Town helipad comprised two concrete pads and a building located on the west side of the Yulara Resort facility. In support of the operation, the operator published local ‘PHS Town Helipad Procedures’. The local procedures included housekeeping, general safety and operational rules, flight procedures and record keeping.

Oversight

The operator’s senior management reported that their oversight of the Uluru Base included regular phone calls with the area manager and deputy area manager, and site visits. The site visits included conducting company check and training flights, and holding staff meetings.

In the 2017 calendar year, the chief pilot visited the base for pilot training, supervision and staff meetings in April, May, August and September. The general manager operations visited the base in April, May, July and August. In addition to the visits made by senior management, the operator reported there were multiple visits by their instructors throughout the year for training and check flights to ensure standardisation against company procedures.

Charter group weights

On the day of the accident, the area manager was involved in the flying activities for the afternoon charter group and the deputy area manager was responsible for managing the ground operations. Prior to the activity day, the operator sent the charter group organiser a blank manifest for them to fill in the names and weights of the passengers. This was returned to them with names only and no weights recorded. Therefore, when the passengers arrived at the helipad on the day, they were individually weighed using the operator’s scales.

After weighing, the passengers were divided into groups and allocated to helicopters on the manifest in a manner to ensure the maximum weight limits were not exceeded. The operator used one Aerospatiale AS350 helicopter and three R44 helicopters for the operation. The practice of weighing individual passengers for a flight was in accordance with best practice for aircraft with small seating capacities, rather than using standard weights.^[14] However, at the time of the accident, the operator’s passenger scales were not subject to a calibration schedule.^[15]

The passengers on board the accident helicopter and on other flights reported that the scales under-recorded their weights. Personal reports of weights indicated an error of 6–9 per cent, and hospital records indicated an error of 11.8–12.2 per cent for the pilot and one passenger. The overall error for the occupants on the accident flight was an under-estimation of 9.6 per cent.

Running turn-around procedure

The passenger boarding and disembarkation from the helicopters was conducted as a running turn-around (RTR) procedure. There is no RTR procedure in the normal procedures section of the POH, therefore the operator developed their own procedure. According to the operator, the RTR procedure was for the pilot to run the engine down to idle and turn off the governor prior to passenger disembarkation. After passenger boarding, the pilot should turn on the governor and run the engine and rotors up to 102 per cent RPM. There was no requirement during the RTR to check the low rotor RPM warning.

Turning the governor on before running the engine up from idle during the RTR was consistent with the RHC R44 ‘starting engine and run-up’ checklist. The operation of the governor can be checked by allowing it to accelerate the engine from 79 to 102 per cent. Robinson reported that ‘the pilot should ensure the governor is operating properly when rolling the throttle open during the start-up checks’.

During the RTR, the accident pilot would run the engine down to idle and turn off the governor for the passenger disembarkation. However, after passenger boarding the pilot would run the engine up manually, with the governor off, check the operation of the low rotor RPM warning from 90 to 98 per cent RPM, then turn the governor on, make a radio call, and check indications were in the ‘green’^[16] in the hover after lift-off.

Passenger phone footage of the pilot’s previous flight RTR revealed the low rotor RPM warning check was being conducted with the governor off, consistent with the pilot’s reported practice. The pilot submitted that they were trained to check the governor was on and working before take-off, and that they were confident this was done after the low rotor RPM horn check. The passenger footage of the accident flight departure indicated the ‘governor off’ light was extinguished, which would have provided a visual indication to the pilot that the governor was selected on.

The Civil Aviation Safety Authority (CASA) reported that this practice was not in accordance with the POH procedures, which indicated that the governor should be on prior to engine start and remain on until shut-down. Robinson safety notice 36, issued in 2000, required ensuring the governor was selected on before increasing RPM above 80 per cent. The Civil Aviation Safety Authority also reported that if the ‘governor off’ light globe had extinguished without the governor being selected on, the pilot may not have been alerted to the possibility that the governor was off.

Take-off procedures

The operator had published normal (in-ground-effect^[17] - IGE) and confined area (out-of-ground-effect - OGE) take-off procedures in their operations manual. In addition, they had published a local departure procedure for the Yulara Town helipad, which required their pilots to avoid overflying the Yulara Resort on departure and approach. The operator’s take-off procedures were as follows:

Normal take-off profile:

Adopt a 3 foot hover at take-off RPM and note the power being used. For passenger carrying charter operations the power margin^[18] MUST BE sufficient to ensure there is no height loss during the initial take-off phase. Conduct the pre take off checks. Lower the nose slightly and wait for the helicopter to move. As the speed builds up, keep gradually lowering the nose until you get an accelerating attitude that is NOT excessive. This ensures that you are in the best possible configuration to handle an engine failure during this phase of take-off.

As you pass effective translational lift^[19] (ETL) speed maintain the selected attitude and raise the collective slightly to commence climbing. Don’t use excessive power prior to reaching the BROC [best rate of climb] speed, as this is the most critical part of the take-off. This ensures that you remain outside the height/velocity curve [avoid area].^[20]

Confined area / Steep (when obstacles preclude the use of a normal take-off profile):

Before lifting off, check for obstructions around the helicopter and plan to make maximum use of the available space for take-off. Before commencing the take-off, check for overhanging trees ABOVE THE HELICOPTER and ALONG THE TAKE-OFF PATH. For passenger carrying charter operations, there MUST BE sufficient power to maintain an OGE hover before commencing the take-off.

Commence a vertical climb and check the RPM and power before moving forward. If these parameters are not acceptable, descend vertically back to the pre take-off position and re-assess the situation. Aim to clear the obstacles by a minimum of 15 ft. Do not climb higher than necessary to achieve this.

The normal take-off profile allowed the helicopter to accelerate forward at a height of typically less than one rotor diameter until it reached its best rate of climb speed before initiating a positive rate of climb. The confined area take-off required the helicopter to climb vertically and initiate the take‑off from a height greater than one rotor diameter, and therefore the helicopter required OGE performance. The operator reported that their confined area take-off procedure was designed to ensure there is sufficient power available to clear obstacles by 15 ft, while minimising exposure to the avoid area of the height-velocity diagram.

Accident flight take-off

Helipad camera video footage captured the accident helicopter arrive at the far pad (pad 2), and change passenger loads for what would be the accident flight.^[21] The footage showed the helicopter lift-off and continue to climb vertically to a height of about half a rotor diameter (16.5 ft)^[22] before transitioning into forward flight 5 seconds after lift-off, while continuing to climb. The take-off direction selected by the pilot required the helicopter to clear smaller trees closer to the pad and then larger trees beyond the smaller trees (Figure 9).

Figure 9: Departure path from pad 2

Source: Passenger footage from previous flight

At the start of the passenger video, the helicopter had started to transition forward. The altimeter then indicated a climb of about 20 ft in the 3 seconds from the start of the recording to the activation of the low rotor RPM warning. The airspeed increased from no positive indication to about 25 kt in this period, which was consistent with a take-off into wind. Consequently, it was likely the helicopter had reached a height of about 37 ft, and accelerated through translational lift, when the low rotor RPM activated (Figure 10). The proximity of the trees at the time of the low rotor RPM warning did not permit a safe abort.

Figure 10: Approximate position of the low rotor RPM warning

Source: Operator, annotated by the ATSB

The operator noted that the MAP at the start of the passenger video indicated the helicopter had sufficient power margin for the take-off profile, and that the observed profile complied with their procedural requirement to ‘not climb higher than necessary’.

Helicopter performance

Meteorological information

Ayers Rock Airport is at 1,626 ft in elevation. On the day of the accident at 1830, the recorded airport weather was temperature of 38 °C, QNH^[23] 1007 hPa and wind of 9 kt from 080° (the pilot reported the helipad windsock indicated about 5–10 kt).^[24][25] This resulted in a pressure altitude of 1,788 ft and density altitude of 4,936 ft. Based on the Ayers Rock Airport weather and helicopter tracking data provided by the operator, the ATSB estimated the pilot’s take-off direction included about a 6 kt headwind component and 7 kt cross wind component from the right. However, the increase in airspeed on take-off suggested the local wind above tree height might have been stronger.

Take-off weights, profiles and power

The helicopter’s published maximum weight was 1,089 kg. The planned weight for the flight (group 9) was 1,046 kg.^[26] Using the actual weights provided by the passengers following the accident and hospital records for the pilot and right rear seat passenger, the ATSB calculated the take-off weight was about 1,080 kg.^[27] The two previous flights for VH-HGX were at the planned weights of 1,038 kg (80 L fuel – group 8) and 1,073 kg (90 L fuel – group 7) respectively. Applying the error from the accident flight to the occupants of the two previous flights produced estimated weights of 1,067 kg and 1,105 kg, 22 kg below and 16 kg above the maximum weight of the helicopter.

The accident flight take-off weight was within the helicopter’s published weight for an IGE take-off, but it exceeded the weight for an OGE take-off, which was about 1,025 kg. The deputy area manager reported that the traffic pattern for the flights permitted either an IGE or OGE take-off option, noting the OGE was more into wind. He also commented that the accident flight departure looked similar to the pilot’s previous departures, and that none of the pilots had provided a reduced operating weight for OGE performance.

It was initially unclear to the ATSB why the pilot reported following the procedure for the confined area take-off, but had not provided a reduced OGE operating weight. The operator explained that the OGE chart is used for a flight planned to a confined area to ensure there will be an adequate power margin for the arrival and departure. The Yulara Town helipad was not a confined area and there was no requirement to use the OGE chart. In addition, the operator had recommended that a confined area take-off could be conducted/continued if the IGE MAP during the hover power check was 2 in Hg below TOP, which the passenger video indicated the accident flight had.

Although the pilot reported following the confined area procedure, the helipad and passenger video indicated the take-off started from IGE and translational lift was likely achieved at, or close to, a height equivalent to OGE. The operator described this as a steep profile, rather than a confined area profile. The Civil Aviation Safety Authority (CASA) reported that there is no strict definition for a confined area and that the avoid area of the height-velocity diagram (used for a steep or OGE take-off) for this category of operation is a recommendation and not mandatory.

The Civil Aviation Safety Amendment (Part 133 – Australian air transport operations – rotorcraft) Regulations 2018 are scheduled to commence in December 2021. They will see the introduction of performance class operations, which CASA reported will provide greater regulatory effect to the avoid area in the height-velocity diagram and take-off weight performance criteria, similar to the current standards for this type of operation in the United States^[28] and Europe.^[29]

Low rotor RPM recovery procedure

Immediate actions

According to the R44 POH, the recommended procedure to recover from a low rotor RPM warning condition (warning horn and caution light) was as follows:

To restore RPM, immediately roll throttle on, lower collective and, in forward flight, apply aft cyclic.

Lowering the collective lever will reduce the power required by the rotors to aid the recovery of rotor RPM. However, in the R44 helicopter the correlator will decrease the throttle when the collective is lowered and reduce engine power unless the pilot rotates the twist grip to roll throttle on. This is a standard response, irrespective of the operational state of the governor system, because the pilot can apply throttle faster than the governor.

The operator reported that if the collective lever is lowered in an attempt to recover RPM in the R44 Raven 1 with the throttle already fully open, then the pilot must hold the twist grip open against overtravel spring pressure to keep the engine throttle fully open and prevent a loss of engine power during the recovery.

Robinson reported that if the throttle is fully open and the collective is lowered, the correlator linkage will decrease the throttle accordingly. If the pilot rolls on throttle while lowering the collective, as per the procedure, the throttle will remain open and may, or may not, compress the overtravel spring. Pilots should not be concerned if the spring is compressed or not, they should continue to roll the throttle on and lower the collective until the RPM is recovered.

A pilot may not necessarily know if the throttle is fully open or not, when the low RPM warning is activated. If the throttle is not fully open and the collective is lowered, followed by the pilot instantly rolling on throttle enough to compress the overtravel spring, an overspeed is probable.

The ATSB and Robinson noted that lowering the collective lever from level flight may result in a descent, and therefore this action may be inappropriate when the helicopter is close to obstacles. However, in the accident flight, the helicopter continued to climb on departure and Robinson indicated that, ‘if the pilot performed the recovery procedure, reducing collective just enough to stop the ascent [climb] and acceleration, the RPM would most likely have recovered and increased immediately’.

Minimum power airspeed (Vy)

The minimum power airspeed (Vy) for the R44 is 55 kt. This will provide the greatest power margin in‑flight (lowest collective lever position to maintain airspeed and altitude), and correspondingly the best rate of climb (maximum excess power). However, there was no reference to this airspeed in the POH low rotor RPM recovery procedure. Robinson reported the reason for this as follows:

The recovery procedure is designed for immediate correction of low RPM, it would be the pilot’s responsibility to determine the best course of action to prevent a recurrence depending on the circumstances. The power margin would be a consideration.

With respect to airspeed and the immediate actions for low rotor RPM recovery, CASA reported the following:

Aft cyclic should only be applied with substantial forward speed. When at slower speeds, which is when low rotor RPM is dangerous, forward cyclic should be applied very gently to gain airspeed.

The ATSB discussed low rotor RPM recovery with one of the operator’s Robinson helicopter flight instructors who had viewed the passenger video footage. The instructor noted from the footage that the MAP appeared to be low for the departure and that, after initially increasing airspeed, the helicopter pitched up in the turn and the airspeed decayed. Consequently, the helicopter remained on the ‘back-end of the power curve’.

The instructor suggested that the recovery technique, while departing over obstacles where there is no suitable landing, should be to ‘apply full throttle, get speed on and reduce the collective to reduce pitch as speed increases… [to attain the] bottom of the power curve’. This will increase the power margin to facilitate RPM recovery. The instructor reported that the techniques for RPM recovery are taught and assessed in the ‘governor malfunctions’ element of the operator’s pilot training syllabus.

The pilot who flew the accident helicopter earlier in the day reported that they were taught to increase throttle and lower the collective lever to regain rotor RPM. Following the accident the pilot ‘learned…some [pilots] would increase airspeed to gain lift to overcome RPM droop [decay]’. The ATSB reviewed various online training videos for R44 low rotor RPM recovery and noted there were references to 55 kt as a target speed during the recovery, but that recovery would occur as soon as there was a sufficient power margin available.

Robinson have produced a series of instructional videos to support the training of R22 and R44 pilots in several subject areas, which are associated with high risk flight conditions. They include the following:

• energy management
• mast bumping
• low rotor RPM (blade stall)^[30]
• low-G hazards
• rotor RPM decay.

These videos are publicly available from their company website.^[31] In their training video: Energy Management, RHC reported that the three forms of energy available to a pilot are rotor RPM, airspeed and height. The minimum power airspeed is highlighted as providing the greatest power margin. The ‘back side’ of the power curve is described as the situation where the helicopter will require more power to fly slower, which makes it an unstable region for power and airspeed. They reported that one of the most common causes of helicopter accidents is the situation where the pilot allows the rotor RPM and airspeed to decay.

Figure 11 depicts a generic power curve for a helicopter in stable level flight. As airspeed increases, the power required to produce lift reduces, and the power to overcome fuselage drag increases, producing a bucket-like curve. A reduction in engine power and/or increase in weight will reduce the power margin available. At low airspeeds, a combination of high weight, high density altitude and low RPM could result in the power required becoming greater than the power available. To recover rotor RPM, a positive power margin is required. That is, the power produced (normally limited by the power available) must exceed the power required.

Figure 11: Generic power curve for stable level flight

Source: ATSB

To accelerate the helicopter in level flight, the pilot applies forward cyclic control, which tilts the main rotor disc forward. This increases the power required, which is why CASA advise to apply forward cyclic ‘very gently’ if at slower airspeeds. Hence, any loss of airspeed below Vy will result not only in an increase in the power required for level flight, but also a further increase in the power required if an attempt is made to accelerate to regain Vy.

The flight envelope power requirements for many light helicopters, such as the R44, are not published. However, RHC reported that the Vy power requirement would be approximately 60 per cent of the zero airspeed (OGE hover) power. The ATSB applied a correction for half a rotor diameter height to the accident flight helicopter’s power, taking 164 hp as the hover power prior to the pilot initiating take-off. The correction for ground effect provided an approximate zero airspeed power of 188 hp.^[32],^[33] This resulted in a Vy power of approximately 113 hp. Therefore, the power produced on departure would have provided a margin of about 76 hp to the power required at Vy.

The R44 POH emergency procedures section includes references to recommended airspeeds for pilots to fly in various emergency situations. They include the autorotation airspeeds for the minimum rate of descent and for the maximum range. The ATSB selected another light helicopter, the Aerospatiale AS350, certified to similar standards as the R44, and reviewed the emergency procedure checklists for evidence of recommended airspeed information. It was noted that there were numerous references to recommended airspeeds to assist a pilot in either their immediate or subsequent emergency procedure recovery actions.

Pilot’s training

The pilot was trained by the operator on a commercial pilot licence (helicopter) course from the period June 2016 to June 2017. In consideration of the pilot’s performance during training, the operator offered the pilot a job at their Uluru Base.

The pilot’s training records indicated that handling governor failures in the R22 was covered in July 2016, for which the instructor recorded ‘good RPM recovery and monitoring’. The ATSB discussed the pilot’s throttle handling with two of the pilot’s instructors. They reported that the technique of a pilot over-riding the governor input with a tight grip on the collective lever twist grip was well known throughout the industry (known as ‘strangling the throttle’). This was a focus point for students at the beginning of their training and was not identified as an ongoing problem for the accident pilot. There was no report of this problem in the pilot’s training records to indicate otherwise.

During the pilot’s company check flight on 12 July 2017 the governor failure sequence and limited power were assessed. The check pilot reported that the pilot’s ‘general flying was excellent’, limited power was ‘very good’ and confined area operations were ‘all ok’, but included a focus point for the pilot to ‘check PWR/RPM [power margin, engine and rotor RPM] before rolling out of a confined [confined area]’.

Calculating IGE and OGE performance was captured in the pilot’s training, which included confined area flying training. However, according to one of the pilot’s line training instructors,^[34] it was not specifically assessed during the line training at the Uluru Base, where the pilot was cleared to fly the line on 21 September 2017. The line training sign-off flights for the helipads were conducted without passengers, but with an emphasis on the safest departures and approaches. The pilot’s training report included out-landings, confined area, weight and balance, and flight planning.

A minimum of three take-offs and landings were flown to each pad during the line training. The instructor did not note any problems, which would have prevented a recommendation for the pilot’s release to line, and there was no indication the pilot was ‘strangling the throttle’. The pilot’s grip on the collective lever was not visible in the passenger video of the accident flight take-off, but it was noted that the pilot appeared to hold the cyclic with a light grip in the video of the accident flight and an earlier flight.

Survival factors

The helicopter came to rest inverted with significant damage to the landing gear, airframe and seating. The rear left seat and front left seat passengers were able to exit from the wreckage, but the pilot and rear right seat passenger required assistance to exit from the wreckage. A company AS350 helicopter tracking behind VH-HGX provided first response with the operator’s personnel. On arrival at the accident site, they assisted the remaining occupants to egress from the wreckage.

After the occupants of VH-HGX were removed from the wreckage, the AS350 was used to ferry emergency response personnel and equipment to the accident site. The Yulara Clinic Manager triaged the occupants based on the assessment of the nature of their injuries and administered medical assistance to stabilise them before their evacuation. They were subsequently evacuated to the local medical clinic by helicopter and emergency services vehicles when last light precluded further flights to the accident site.^[35]

The iBrace Survivor Questionnaire^[36] was completed for the pilot and passengers with the following results:

• The pilot, seated in the front right seat, was wearing a 3-point harness and was unable to exit unassisted from the wreckage. The pilot suffered a broken back, spinal cord injury and a wound to the right arm.
• The front left seat passenger was wearing a 3-point harness and was able to exit unassisted from the wreckage. The passenger suffered multiple fractures, which included back, ribs, chest, pelvis and heel, and a laceration to the elbow. The passenger did not recall being shown a brace position, and reported that the pilot did not make a ‘brace’ call prior to impact, but did announce ‘we are going down’.
• The rear right seat passenger was wearing a 3-point harness, which reportedly broke during the accident. The passenger reported that they were not provided with a ‘brace’ warning prior to impact and that they were unable to exit unassisted from the wreckage. The passenger suffered an eye injury, broken back, spinal cord injury, and fractures to the chest, abdomen and pelvis area, and a deep cut to the ankle.
• The rear left seat passenger was wearing a 3-point harness and was able to exit unassisted from the wreckage. The passenger suffered cuts and bruises to the head and face, and bruising and soft tissue injuries to the torso. The last announcement the passenger heard from the pilot was that they were ‘going down’. The passenger braced for impact, but was not shown a brace position and reported that the pilot did not make a ‘brace’ call prior to impact.

The helicopter’s certification standard for emergency landing conditions was based upon providing the occupants with a reasonable chance of escaping serious injury in a minor crash. This was based on the helicopter absorbing the landing loads with an ultimate descent velocity of five feet per second.^[37] The damage to the underside of the helicopter (refer Figure 3), suggested that the landing was outside of the certification standard to prevent serious injuries.

Previous occurrences

Governor malfunctions

A review of the CASA service defect reporting system revealed three prior reported incidents of R44 governor malfunctions, dated 26 May 2017, 23 October 2014 and 7 September 2012. No part number information was provided for the report dated 7 September 2012, but the other two reports indicated the governor controllers had the same part number as the accident helicopter, D278-1.

The report dated 23 October 2014 stated: ‘Pilot reported the governor was not functioning correctly. Governor was replaced with serviceable item. AC [aircraft] tested serviceable.’

The report dated 26 May 2017 stated: ‘While in cruise, pilot noticed the main rotor RPM decayed and low rotor horn activated. Pilot maintained RPM by manually opening the throttle and established that the governor controller was u/s [unserviceable]. The helicopter was flown manually on the throttle per the approved flight manual. The Governor controller was replaced with an overhauled item per RHC MM [maintenance manual].’

Low airspeed-low rotor RPM accidents

A review of previous ATSB investigations, which involved low airspeed-low rotor RPM conditions in the R44, was conducted. The review found two fatal accidents involving low experience commercial pilots, operating their helicopters in a high-density altitude environment with a full load of passengers on board.

• 200600979: A commercial pilot and three passengers were fatally injured while conducting aerial work – survey. The helicopter had insufficient performance to hover or operate at slow speed OGE and collided with terrain following an over-pitching event. The pilot had 327.8 hours total helicopter flight time, which included 143.9 hours in the R44.
• AO-2008-062: A commercial pilot and three passengers were fatally injured during a scenic charter flight. The investigation found the helicopter was operated OGE in the hover or at slow speed with marginal performance for the purpose of photography. The pilot had recorded about 477 hours flight time, which included 346 hours in the R44.

Previous related safety issue

In response to the AO-2008-062 accident sequence of events, the ATSB raised, and closed, safety issue AO‑2008-062-SI-01: Robinson-specific training, on 7 July 2010.

Safety issue

There was no Australian requirement for endorsement and recurrent training conducted on Robinson Helicopter Company R22/R44 helicopters to specifically address the preconditions for, recognition of, or recovery from, low main rotor RPM.

Proactive action by the Civil Aviation Safety Authority

The Civil Aviation Safety Authority (CASA) has advised that it will review the requirements for initial pilot training and endorsement and recurrent training on all helicopters. This will include a review of the Helicopter Flight Instructors Manual.

Civil Aviation Safety Authority update to safety issue

The Civil Aviation Safety Authority reported that as a result of the review into helicopter pilot training, they undertook to conduct all flight tests for the initial issue of helicopter instructor ratings and their renewals in an effort to raise the standard of flight training activities. The CASA Helicopter Flight Instructors Manual was amended in 2012 to include a new section 25: Hazards.

A project to develop a Civil Aviation Advisory Publication (CAAP) 5.14-3(0): Helicopter Flight Instructor Training, was started, but not completed due to work commitments to the Civil Aviation Safety Regulations 1998 Part 61: Flight crew licensing - Manual of Standards. The Part 61 Manual of Standards incorporated aeronautical knowledge and practical flight standards to address the risks identified in AO-2008-062-SI-01. The current training standards for the Commercial Pilot Licence (Helicopter) were transferred from the previous licensing scheme to Part 61, including the competency standards from the previous day visual flight rules syllabus to the Part 61 Manual of Standards.

The introduction of Part 61 required pilots of R22 and R44 helicopters to complete initial flight training and a flight review on each type. In addition, it is a condition for pilots operating the R22 or R44 to complete a flight review on either type within the preceding 24 months.

Cockpit image recording equipment

The absence of recording equipment can result in limiting fatal accident investigations to the basic mechanics of the accident, without insight into the operational and human factors. In the event of a non-fatal accident with serious injuries, the physical and psychological trauma may adversely affect the memories of the occupants, resulting in a limited and, or erroneous recollection of events. This severely limits the ability of the investigation to communicate safety lessons to the industry and provide policy makers with informed safety recommendations.

The Robinson family of helicopters, including the R44, do not currently have the option for flight data, cockpit voice or image recorders. However, RHC reported they are in the final phases of getting United States Federal Aviation Administration approval for a cockpit video system and expect to begin deliveries in 2020. There are versions available for all their helicopter models. The system will start recording on helicopter start-up and record video and audio for the entire flight and will capture the final seconds before power is lost.

Robinson are also certifying a new governor for their piston-powered helicopters. The governor has recording capabilities, which include multiple parameters (including rotor RPM) that will be available for maintenance and accident investigation purposes. The new governors will be standard on all R22s and R44s ordered since late January 2020. In addition, RHC is finalising a control position recorder, which will record limited information on cyclic and collective position, rotor and engine RPM, and global positioning system location. Robinson are installing prototype units on their eight company-owned helicopters, which are flown regularly, to collect reliability data before the units are provided to owners. The product is intended to become standard on all models of RHC helicopters.

The Civil Aviation Safety Regulations 1998 Part 133 will introduce the regulatory requirement for flight data and cockpit voice recorders into rotorcraft air transport operations in Australia. However, the requirement will not include light helicopters, and it is this sector of the industry that comprise the vast majority of the ATSB’s fatal helicopter accident investigations. The need to introduce cockpit image recorders has been recognised and advocated by several investigation bodies. These include:

• United Kingdom Air Accidents Investigation Branch: Report on the accident to AS332 L2 Super Puma helicopter, G-WNSB on approach to Sumburgh Airport on 23 August 2013. Safety Recommendations 2016-014 and 2016-015 issued to the European Aviation Safety Agency.
• New Zealand Transport Accident Investigation Commission: Aviation inquiry AO-2015-002 Mast bump and in-flight break-up, Robinson R44, ZK-IPY, Lochy River, near Queenstown, 19 February 2015. Safety Issue 014/16 issued to the Secretary of Transport.
• US National Transportation Safety Board: Loss of control at take-off, Air Methods Corporation Airbus Helicopters AS350 B3e, N390LG, Frisco, Colorado, July 3, 2015. Safety Recommendations A-13-12 and A-13-13 issued to the Federal Aviation Administration.^[38]

__________

9. The cylinder compression test results were: 79, 77, 74, 77, 78 and 76 pounds per square inch. According to the engine manufacturer, the test is conducted with an air supply pressure of 80 pounds per square inch. The engine is assessed satisfactory if the readings for all cylinders are equal (within 5 pounds per square inch) and above 70.
10. As no temperature compensation is provided, it has been assumed that the pressure altitude figures are for standard atmospheric conditions and therefore equate to the same density altitude figures.
11. Collective: a primary helicopter flight control that simultaneously affects the pitch of all blades of a lifting rotor. Collective input is the main control for vertical speed.
12. Controller dead-time is the time required for a change in input to produce a change in output.
13. International Civil Aviation Organization (ICAO) Manual of Aircraft Accident and Incident Investigation. Chapter 15: Helicopter investigation.
14. Civil Aviation Advisory Publication 235-1(1): Standard passenger and baggage weights, advised that the use of standard passenger weights results in a high probability of overloading.
15. Calibration of measuring equipment is performed to ensure the product operates to within a defined acceptable error or accuracy limit. A calibration interval is set to ensure continued conformance with those accuracy limits.
16. The green operating range for the engine tachometer was 101–102 per cent RPM.
17. Ground effect is usually defined as within one rotor diameter of the ground (33 ft for the R44; note that the rotor mast is 10.75 ft when the helicopter is on the ground). At less than one rotor diameter the ground resists the rotor downwash and less power is required to hover. As the helicopter climbs vertically from ground level, the downwash dissipates into the surrounding air and more power is required to hover and take-off.
18. Power margin: difference between the power required and the power available. In this report it is also used to refer to the difference between the power required and the power produced during RPM decay in flight.
19. Translational lift normally occurs at about 12–15 kt airspeed and provides a reduction in the power required for flight.
20. The avoid area in the height-velocity diagram is a combination of height and airspeed, within which, it may not be possible to safely land the helicopter after an engine failure.
21. The local time displayed on the helipad camera was estimated to be about 8 minutes behind the actual time.
22. The R44 rotor diameter is 33 ft. The rotor radius/diameter was the dimension used to estimate the height of events on the helipad camera footage.
23. QNH: the altimeter barometric pressure subscale setting used to indicate the height above mean sea level. Standard atmospheric pressure is 1013.2 hPa.
24. The wind speed is a mean speed over a 10-minute period.
25. The helipad was fitted with a windsock to provide local wind conditions for arrivals and departures.
26. This was based on the helicopter basic empty weight 675 kg, plus 320 kg for the occupants and 51 kg (70 L) for fuel.
27. This was based on the helicopter basic empty weight 675 kg, plus 354 kg for the occupants and 51 kg (70 L) for fuel.
28. United States Code of Federal Regulation Part 136 – Commercial air tours and national parks air tour management. Subpart A – National air tour safety standards. Part 136.13: Helicopter performance plan and operations.
29. European Aviation Safety Agency CAT.POL.H.405: Take-off.
30. According to the R44 POH, a main rotor blade stall will either ‘cut off the tailcone’ or the helicopter will ‘just stop flying and fall at an extreme rate’.
31. The training videos can be found through Robinson Helicopter Company/Training/SFAR 73 Training: www.gyronimosystems.com/SFAR/
32. Hayden JS 1976, The effect of the ground on helicopter hover power required, in 32nd AHS Annual Forum, Washington DC, cited in Filippone A 2006, Flight performance of fixed and rotary wing aircraft, American Institute of Aeronautics and Astronautics Inc., USA.
33. The formula did not include a variable for the surface condition, which may influence the actual result obtained.
34. There were two instructors involved in the pilot’s three line training flights.
35. The evacuation priority of the injured occupants to medical facilities was based on the assessment by emergency response personnel in attendance at the site.
36. Davies JM, Wallace WA, Colton CL & Yoo KI (in press). Two aviation accident investigation questionnaires for passenger & crew survival factors & injuries. Aviation Medicine and Human Performance.
37. United States Code of Federal Regulations Part 27.561, issued 2 October 1965.
38. These followed earlier recommendations for crash resistant flight data recorders to be fitted to new and existing aircraft that were not already required to have them fitted.

Additional details

Pilot details

Aircraft details

Sources and submissions

Sources of information

The sources of information during the investigation included the:

• Civil Aviation Safety Authority
• Insurance Senior Surveyor
• Northern Territory Police
• Professional Helicopter Services
• witnesses
• Robinson Helicopter Company.

References

Australian Transport Safety Bureau 2017. AO-2016-172: Forced landing involving Robinson R44, VH-SJK, 16 km S of Sydney Airport, NSW, on 17 December 2016. Canberra.

Australian Transport Safety Bureau 2010. AO-2008-062: Collision with terrain – 6 km NE Purnululu ALA, Western Australia – 14 September 2008, VH-RIO, Robinson Helicopter Company R44. Canberra.

Australian Transport Safety Bureau 2007. 200600979: Collision with terrain – 10 km west of Gunpowder Mine, Qld – 21 February 2006, VH-HBS, Robinson Helicopter Company R44. Canberra.

Civil Aviation Safety Authority 2018. Civil Aviation Safety Amendment (Part 133) Regulations 2018. Canberra.

Civil Aviation Safety Authority 2018. Civil Aviation (Part 133) Manual of Standards 2018 (Draft). Canberra.

Civil Aviation Safety Authority 2015. Advisory Circular 21-35(1.1): Calibration of inspection and test equipment. Canberra.

Civil Aviation Safety Authority 2014. Civil Aviation Advisory Publication 92-2(2): Guidelines for the establishment and operation of onshore Helicopter Landing Sites. Canberra.

Civil Aviation Safety Authority 1990. Civil Aviation Advisory Publication No. 235-1(1): Standard passenger and baggage weights. Civil Aviation Publications Centre. Carlton, Victoria.

Davies JM, Wallace WA, Colton CL & Yoo KI (in press). Two aviation accident investigation questionnaires for passenger & crew survival factors & injuries. Aviation Medicine and Human Performance.

Hayden JS 1976, The effect of the ground on helicopter hover power required, in 32nd AHS Annual Forum, Washington DC, cited in Filippone A 2006, Flight performance of fixed and rotary wing aircraft, American Institute of Aeronautics and Astronautics Inc., USA.

International Civil Aviation Organization 2011, Manual of Aircraft Accident and Incident

Investigation Part III: Investigation, Doc 9756, ICAO, Montréal.

Kroes MJ, Watkins WA, Delp F & Sterkenburg R 2013, Aircraft maintenance and repair, 7th edn, McGraw-Hill, USA.

Submissions

Under Part 4, Division 2 (Investigation Reports), Section 26 of the Transport Safety Investigation Act 2003 (the Act), the Australian Transport Safety Bureau (ATSB) may provide a draft report, on a confidential basis, to any person whom the ATSB considers appropriate. Section 26 (1) (a) of the Act 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 operator, pilot, passengers, Civil Aviation Safety Authority, Insurance Senior Surveyor, Northern Territory Police, Robinson Helicopter Company and United States National Transportation Safety Board.

The submissions from those parties were reviewed and were considered appropriate, the text of the draft report was amended accordingly.

Purpose of safety investigations & publishing information