Investigation summary

What happened

On 8 November 2024, a Boeing 737-838 aircraft, registered VH-VYH and operated by Qantas Airways, commenced take-off from runway 34R at Sydney Airport, New South Wales, en route to Brisbane, Queensland. As the aircraft reached V₁ – the speed beyond which a take-off should be continued rather than aborted in the event of an emergency – the flight crew heard a loud bang and the right engine failed. Fragments of the engine landed on the grass adjacent to the runway, igniting a grass fire. The flight crew continued with the take-off, declared an emergency and began working through the relevant checklists for the engine failure, planning a return to Sydney Airport. 

The crew performed a single-engine landing on runway 34L, 30 minutes after take-off. The Aviation Rescue Fire Fighting Service (ARFFS) inspected the failed right engine for any signs of fire, after which the aircraft was cleared to return to the gate. Passengers then disembarked via standard procedures.

What the ATSB found

Although the emergency occurred at the worst possible moment, the flight crew responded quickly and decisively in continuing the take-off. All parties involved in the emergency worked together effectively, allowing a safe and uneventful return to Sydney Airport.  

An engine teardown by the manufacturer revealed that the right engine failed due to a fatigue crack in one of its high-pressure turbine (HPT) blades. The blade was liberated from the HPT disc during take-off, damaging other components in the flow path of the engine and ultimately resulting in a contained engine failure. 

The engine had been scheduled for removal on 21 November 2024 due to it nearing the manufacturer’s recommended removal threshold (RRT). Previous engines of this type had experienced failures due to the same kind of fatigue cracking, and the engine manufacturer had previously lowered the RRT to reduce the likelihood of HPT blade liberations in service. Newer HPT blade configurations had also previously been introduced, with improved failure rates.

What has been done as a result

The manufacturer performed an analysis of the engine fleet and found that although there had been several previous blade liberation events due to this kind of fatigue cracking, this engine’s HPT blade configuration (2403M91P02) still met internal reliability targets and relevant regulatory guidelines and rules. 

Safety message

This incident provides a positive example of effective training and procedures, highlighting their importance within the aviation safety framework. In this instance, faced with an emergency during a critical phase of flight, the flight crew responded decisively and appropriately in accordance with their training and procedures. 

Summary video

The investigation

The occurrence

On the afternoon of 8 November 2024, a Boeing 737-838 aircraft, registered VH-VYH and operated by Qantas Airways, was being prepared for a scheduled passenger air transport operation from Sydney, New South Wales, to Brisbane, Queensland. On board were 2 flight crew, 4 cabin crew and 175 passengers. 

At 1234:35 local time, the flight crew began the take-off roll on runway 34R. At 1235:20, at the same time as the first officer (FO) called ‘V₁’ to indicate that the aircraft had reached its decision speed (see Take-off reference speeds), a loud bang was heard in the flight deck, accompanied by a shudder through the airframe. The aircraft reached the rotation speed, V_R, 3 seconds later, and the captain pulled back on the control column to pitch the aircraft up.

The flight crew immediately identified the engine failure based on caution lights and indications. After lift-off, the captain continued along the runway heading and requested that the FO declare a PAN PAN call[1] when possible. The FO broadcast the call to air traffic control (ATC) 28 seconds after lift-off. 

The flight crew then briefly discussed the engine indications they observed, determined that the right engine had experienced severe damage, and began to action the Engine fire, severe damage or separation checklist and commenced planning a return to Sydney Airport. The flight crew then requested an inspection for runway 34R. The controller reported: 

…much FOD [foreign object debris], there’s now fire so it looks like there has been an explosion and there are bits all over the runway, so I would suggest the engine is gone.

The flight crew requested a return to Sydney Airport and ATC directed the flight accordingly. The aircraft was slightly over its maximum landing weight due to unspent fuel, and the expected landing distance was higher for a single engine landing. The flight crew therefore planned to land on runway 34L, which was longer than runway 34R (3,962 m vs. 2,438 m). In addition, ATC closed runway 34R, due to fragments from the engine, which ignited a grass fire next to the runway (Figure 1). 

Figure 1: Grass fire next to runway 34R

Source: Nine Network Australia, annotated by the ATSB

At 1251, while the aircraft was in a holding pattern at a waypoint south of Sydney Airport, the captain provided a briefing to members of the cabin crew, followed by an announcement to passengers in the cabin, informing them of the situation. Because the right engine could not be clearly seen from the flight deck, the flight crew also requested that the cabin service manager (CSM) have an off-duty pilot on board the flight photograph the right engine. Based on the photograph, the flight crew determined that the engine failure was likely contained,[2] and the FO could not see any damage to the aircraft’s right wing.

At 1301, once the relevant checklists were completed, the flight crew advised ATC that they were ready to commence the approach. ATC subsequently cleared the aircraft for landing on runway 34L, and the aircraft landed safely at 1305:50. The aircraft was cleared to roll through to the end of the runway where it could be inspected by the Aviation Rescue Fire Fighting Service (ARFFS) personnel. When ARFFS was confident that there was no risk of fire from the engine, the aircraft was clear to return to the gate, where passengers disembarked via standard procedures.

The failed right engine was inspected for damage by Qantas engineering personnel. Examination of the engine confirmed that the engine failure was contained. Borescope imagery found that 2 high-pressure turbine (HPT) blades had undergone a below‑platform separation from the HPT disc (Figure 2). 

The engine was removed from the aircraft and sent to the engine manufacturer, CFM International, for further examination. The ATSB did not attend either of these examinations.

Figure 2: Below-platform separation of 2 HPT blades

Source: Qantas Airways, annotated by the ATSB

Context

Pilot information

The captain held an Air Transport Pilot (Aeroplane) Licence, a current class 1 aviation medical certificate, and had accrued 17,554 hours of aeronautical experience. Of this, about 4,578 hours were on the Boeing 737, including 251 hours in the previous 90 days.

The FO held an Air Transport Pilot (Aeroplane) Licence, a current class 1 aviation medical certificate, and had accrued 14,809 hours of aeronautical experience. Of this, about 3,832 hours were on the Boeing 737, including 216 hours in the previous 90 days.

The captain’s most recent simulator training was in June 2024. The captain was assessed as proficient at the manoeuvre ‘Engine out between V₁ & V₂’. This manoeuvre simulated an engine failure after the decision speed was reached, but before the aircraft attained the speed required to climb on one engine. The first officer was marked proficient at the same procedure during simulator training in October 2024.

Aircraft and engine information

VH-VYH was a Boeing Company 737-838 aircraft, powered by 2 CFM56-7B24E high bypass turbofan engines. The engine is a dual-rotor, axial-flow turbofan. A cross-section of the engine is illustrated in Figure 3. 

Figure 3: CFM56-7B engine cross-section

Source: CFM International, annotated by the ATSB

One rotor consisted of a 9-stage high-pressure compressor driven by a single‑stage high‑pressure turbine (HPT), highlighted in Figure 4. The other rotor consisted of a 3‑stage low‑pressure compressor and fan, driven by a 4‑stage low‑pressure turbine. 

Figure 4: Cutaway model of a CFM56 engine

Source: ATSB

The HPT was made up of 76 turbine blades, each consisting of an aerofoil, platform and dovetail (photographs of an exemplar blade and disc are shown in Figure 5). The dovetail of each blade was secured within the HPT disc, making the platform a continuous surface around the HPT’s circumference, with the blades radiating outward. Various iterations of HPT blade were used throughout the global fleet of CFM56-7B engines due to updated blade designs. VH-VYH’s failed right engine was fitted with the 2403M91P02 configuration of HPT blades.

Figure 5: CFM56-7B HPT blade (left) and disc (right)

Source: CFM International, annotated by the ATSB

Aircraft maintenance

The most recent maintenance release for VH-VYH was issued on 7 November 2024. There were no issues listed, unresolved or otherwise, relating to operation of the right engine. 

The area around the HPT was last inspected via borescope on 25 September 2024. This inspection included the combustion chamber, HPT blades and adjacent nozzle guide vanes. There were no significant findings, although it is important to note that these borescope inspections were not capable of examining below-platform areas of the blades, which could only be inspected when they were removed from the disc. This required removal of the engine’s core and disassembly of the HPT system. For this engine, HPT disassembly would only be expected to occur when HPT blades were due for replacement. 

The right engine had completed 17,656 flight cycles, and the HPT blades were original to the engine. The engine was scheduled to be removed from the aircraft on 21 November 2024 due to a service bulletin (SB 72-1082) issued by the manufacturer in April 2023 which imposed a recommended removal threshold (RRT) of 17,900 cycles on this engine’s blade configuration (2403M91P02). 

Engine examination

An engine teardown inspection was conducted by CFM International at its technical facility in Malaysia. This was a multi-day process, with the ATSB remotely evaluating the inspection progress and observations. The examination confirmed that 2 of the 76 HPT blades had been liberated due to below-platform fractures in the dovetails. All of the remaining HPT blades had fractured at the base of the aerofoil, above the blade platform. Damage was also observed on components elsewhere in the engine, almost all found to be consequent to the HPT blade failures. The exception was evidence of birdstrike observed on the fan and low‑pressure compressor. However, there was no evidence to indicate that the bird ingestion was relevant to the HPT blade separation. 

CFM International conducted further metallurgic examination on the HPT blades and disc. Evidence of fatigue cracking was found in 28 blades, originating in the region described as the ‘min-neck’ of the blade dovetails. This was the area on the blade where the dovetail cross-section was at its thinnest point. The fatigue cracks originated on the ‘convex side’ of the blade, which is the face visible in Figure 5. 

Blade number 50 was one of the 2 blades that experienced a below-platform failure. It exhibited the most extensive fatigue cracking. Conversely, the other blade with a below‑platform failure, blade 51, exhibited no evidence of fatigue, failing purely due to tensile overstress. The manufacturer noted that there had been previous occurrences involving a below‑platform fatigue failure where the adjacent blade failed in the dovetail due to tensile overstress resulting from contact with the liberated blade. The remaining 74 blades failed due to overstress fractures at the base of each aerofoil.

The fracture morphology of blade number 50 was examined to determine how the cracking progressed. The dovetail recovered from the HPT disc is shown in Figure 6. 

Figure 6: Dovetail of blade 50 recovered from the HPT disc

The edge-of-contact (EoC) crack originated where the blade made contact with the HPT disc during normal operation. The min-neck crack originated where the dovetail’s cross‑section was at its thinnest. Source: CFM International, annotated by the ATSB

There were 2 fatigue cracks observed, propagating in a diagonally downward direction on parallel planes. These cracks initiated with small regions of low-cycle fatigue[3] (LCF) which transitioned to a larger high-cycle fatigue[4] (HCF) region. One crack originated at what the manufacturer described as the ‘edge-of-contact’ or ‘EoC’, where the blade contacted the HPT disc during normal operation. This crack propagated through approximately 70% of the dovetail cross-section. This resulted in an overstress failure of the remaining 30%, liberating the top section of the blade, including the platform and aerofoil, from the HPT disc. The edge‑of‑contact fracture as viewed from the concave side of the blade is shown in Figure 7.

Figure 7: Concave view of the edge-of-contact fracture surface

From the crack origin, LCF cracking propagated to the green dashed line. The fracture morphology then transitioned to HCF, which propagated along crystal planes within the material until it reached the red dashed lines. The remaining material then failed in overstress, resulting in the top section of the blade becoming liberated form the HPT disc. Source: CFM International, modified by the ATSB

The other crack originated in the min-neck region of the dovetail. This crack propagated through approximately 80% of the dovetail’s cross-section. The remaining cross-section was still intact when the blade separated. As part of the manufacturer’s examination, the remaining material was fractured in the laboratory, and the crack opened for inspection (Figure 8).

Figure 8: Convex view of the min-neck fracture surface

Multiple crack origins were observed, from which LCF propagated in small thumbnails. These fatigue cracks transitioned to HCF travelling along crystal planes within the material, consuming approximately 80% of the dovetail’s cross-section. Source: CFM International, annotated by the ATSB

The manufacturer’s analysis found that the min-neck cracking observed in blade 50 was the primary fracture within the blade. As the cracking propagated downward through the blade, tensile forces from disc rotation could no longer be effectively transmitted to the bottom half of the dovetail. Consequently, excessive force was placed on the top half, resulting in the propagation of the edge-of-contact crack and eventual separation of the blade.

HPT service performance

The failure mechanism in this occurrence (a min-neck fatigue crack and subsequent below platform liberation of an HPT blade) had been observed in other engine failures within the CFM56-7B fleet. At the time of writing, there were 86 events reported to the manufacturer over the course of 115 million flight hours. The majority of these engine failures occurred in 2403M91P02 and 2403M91P03 blade configurations.

CFM International’s fleet analysis found that accounting for all failures including min-neck cracks, these blade configurations remained within internal fleet reliability targets and were well within regulatory limits and guidance, including the continued operational safety guidance described by the US Federal Aviation Administration, as well as an Acceptable Means of Compliance outlined by the European Aviation Safety Agency. 

Because below-platform cracks could not be inspected without complete disassembly of the engine, the manufacturer’s primary method for reducing below-platform separations was by imposing recommended removal thresholds (RRTs) on blade configurations susceptible to min-neck cracking. The purpose of the service bulletin issued in April 2023 was to mitigate the risk of HPT blade failure by reducing the RRT from 20,000 cycles to 17,900 cycles for 2403M91P02 and 2403M91P03 blade configurations. 

In March 2025, as a result of its ongoing reliability monitoring, the engine manufacturer published a revised RRT for 2403M91P03 blade configurations, reducing it to 17,200 cycles. The 2403M91P02 fleet reliability was found to be consistent with existing reliability targets and was not adjusted. The more recent 2403M91P06 blade design included an adjusted dovetail geometry in order to reduce instances of min-neck fatigue cracking.

Take-off reference speeds

Take-off reference speeds, commonly referred to as V speeds, are provided by aircraft manufacturers to assist pilots in determining when a rejected take-off should be initiated, and when the aircraft can rotate, lift-off and climb away safely given the existing flight conditions. They are defined as follows: 

• V₁: Decision speed – the maximum speed at which a rejected take-off can be initiated. In the event of an engine failure below V₁, there is enough remaining runway distance for the aircraft to stop safely, and the take-off should be aborted. Conversely, if an engine failure occurs after V₁ is reached, the take-off should be continued. It can be said that V₁ is the ‘commit to fly’ speed. It is calculated for every take-off as it is based on aircraft available thrust, aircraft weight, flap setting, runway length and slope, wind conditions, and airport density altitude.
• V_R: Rotation speed – the speed at which the aircraft rotation is initiated by the pilot. This speed ensures that, in the event of an engine failure, lift-off is achievable and the take‑off safety speed (V₂) is reached at no higher than 35 ft above ground level.
• V₂: Take-off safety speed – the minimum speed at which the aircraft complies with the handling criteria associated with climb following an engine failure. V₂ is normally obtained by factoring the stalling speed or minimum control (airborne) speed, whichever is the greater, to provide a safe margin.

Safety analysis

Engine failure

During the take-off roll, one of the right engine’s HPT blades was liberated from the HPT disc due to pre-existing fatigue cracks in the blade’s dovetail. This region was prone to fatigue cracking in the 2403M91P02 blade configuration. The HPT blades had been scheduled to be removed from the engine 13 days later, in accordance with a service bulletin that was intended to reduce instances of such blade liberations. Due to contact with the liberated blade, the adjacent blade 51 failed through the dovetail and was also liberated from the disc. 

The 2 liberated blades were thrown into the engine shroud and likely made contact with adjacent HPT blades still fitted in the rotating disc. As a result of this contact, all of the remaining 74 blades experienced overstress failure through their aerofoils, liberating additional blade fragments from the HPT disc.

The liberated blades and other debris then travelled rearward through the low-pressure turbine and were ejected out the rear of the engine. With no torque being produced by the HPT, and debris obstructing and damaging the low-pressure turbine, the right engine failed. The flight crew observed a single loud bang and a shudder, indicating that the liberation of all HPT blades and subsequent engine failure occurred extremely rapidly. 

Given the location of the blade failure, it is likely that there was no opportunity to detect the crack during the engine’s lifespan. The removal thresholds put in place by the engine manufacturer, CFM International, did not completely prevent blade liberation events. Nevertheless, the manufacturer’s fleetwide analysis found that the CFM56-7B fleet remained within its defined reliability targets as well as airworthiness guidelines set by relevant regulators. 

Flight crew response

The decision speed, V₁, is the critical point between a take-off that should be aborted and one that should be continued. This is the worst possible time for a multi-engine aircraft to experience an engine failure during take-off, because safety margins are at a minimum whether the take-off is aborted (minimum remaining runway distance available) or continued (minimum airspeed available). When the engine failure occurred, the aircraft had reached V₁, meaning any attempt to abort the take-off would have occurred beyond the point when it was safe to do so.

Confronted with this situation, the flight crew responded quickly and decisively in continuing the take-off, declaring an emergency, identifying the problem and then working through the appropriate procedures. The flight crew, cabin crew, ATC and ARFFS all worked together effectively to enable the aircraft’s safe return to Sydney Airport.

Findings

From the evidence available, the following findings are made with respect to the engine failure involving Boeing 737, VH-VYH, at Sydney Airport, New South Wales, on 8 November 2024. 

Contributing factors

• During take-off, a high-pressure turbine blade failed due to a fatigue crack that had developed prior to the flight, and the blade was liberated from the high-pressure turbine disc. Engine damage from the liberated blade resulted in a contained engine failure.

Other findings

• The flight crew responded quickly and appropriately to an engine failure at V₁, a critical time during take-off.

Safety actions

Safety action from CFM International

Based on the number of previous engine events involving min-neck fatigue cracking of high‑pressure turbine blades, and projected events in future, CFM International reviewed its recommended removal thresholds for HPT blades on CFM56-7B engines. The review found that 2403M91P02 blade configurations were not projected to exceed reliability targets and so thresholds were not adjusted. 

Sources and submissions

Sources of information

The sources of information during the investigation included:

• flight crew
• cabin crew
• Airservices Australia
• Qantas Airways
• CFM International
• The Boeing Company
• Civil Aviation Safety Authority
• recorded data from the aircraft. 

Submissions

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

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

• flight crew
• Airservices Australia
• Qantas Airways
• CFM International
• Civil Aviation Safety Authority.

Submissions were received from:

• Qantas Airways
• CFM International.

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 2026 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 the morning of 26 October 2024, the pilot of a De Havilland Aircraft of Canada DHC‑2 Beaver aircraft, registered VH‑OHU, departed Hamilton Island aerodrome, Queensland, with 4 passengers on board, for a 10-minute scenic flight to Whitehaven Beach, Whitsunday Island. The aircraft touched down on the water with the right main gear not retracted into the float. As a result, the aircraft rapidly yawed to the right, nosed over and became submerged inverted. The pilot self-evacuated and then, when they found no one else on the water surface, promptly returned to help the passengers egress. The pilot and 4 passengers sustained minor injuries, and the aircraft was substantially damaged.

What the ATSB found

The ATSB found that, after departing Hamilton Island, the right main landing gear did not retract and had seized in the extended position, likely due to corrosion. For undetermined reasons, the pilot did not identify that the right main gear had remained extended during their pre-landing checks, either via the landing gear position indication panel, the amphibian gear advisory system (AGAS) annunciation or the wing-mounted mirror. 

In addition, the ATSB noted that the AGAS annunciation alert for an asymmetric configuration, which required immediate pilot action, was similar to a normal gear position advisory. This increased the risk that a pilot would not recognise that the gear was in an unsafe condition for a water landing.

Following the collision with water, and with the aircraft submerged and inverted, the left rear cabin door could not be opened by the pilot or passengers, which delayed their egress. However, the pilot opened the right main door and assisted all passengers to evacuate.

As required by the operator, the pilot had completed helicopter underwater escape training about one month prior to the accident and credited this as a life-saving course.  

Following several floatplane accidents in Canada, the Transportation Safety Board of Canada recommended the fitment of regular and emergency exits that allowed rapid occupant egress following a survivable collision with the water. Viking Air Limited subsequently developed push-out windows and revised more intuitive automotive-style door latches for the rear cabin door on the DHC‑2 aircraft. These modifications were not fitted to VH-OHU nor were they required by regulations. 

What has been done as a result

In response to the accident, Hamilton Island Air advised it has implemented formal initial and refresher training for pilot maintenance tasks, as well as installation of a second mirror on the right wing of its current DHC‑2 aircraft. It has developed a sign-off form to document the daily washdown and preventative maintenance procedures. In addition, it incorporated a minimum weekly systems check flight, including landing gear cycle, where the aircraft had not been recently operated. Further, it introduced annual theory training and 180-day proficiency flight checks, conducted by authorised flight training organisations.

The Civil Aviation Safety Authority has developed airworthiness bulletin AWB 32-029 Issue 1 Supplementary Type Certificated Amphibian Float Main Gear Slide Wear in Marine Environments. The bulletin recommended enhanced vigilance and maintenance actions on the landing gear components to ensure reliability of the landing gear and the actuating system.

Safety message

As shown in this accident, inadvertent water landings in amphibian aircraft with one or more gear extended can rapidly result in the aircraft becoming submerged and inverted. This investigation reinforces the effectiveness of helicopter underwater escape training, not exclusively for helicopter pilots but also for pilots who operate any type of aircraft over water such as floatplanes.

Further, this accident highlights the value of having alternate means of exiting an aircraft post-accident. This is particularly important if the pilot is unable to assist and/or the fuselage is distorted, to increase the occupants’ chance of survival in the event of an impact with water.

The ATSB SafetyWatch highlights the broad safety concerns that come out of our investigation findings and from the occurrence data reported to us by industry. One of the safety concerns is reducing the severity of injuries in accidents involving small aircraft.

The investigation

The occurrence

On the morning of 26 October 2024, a De Havilland Aircraft of Canada DHC‑2 Beaver amphibian floatplane, registered VH‑OHU and operated by Whitsunday Air Services (trading as Hamilton Island Air), was being prepared for a scenic flight from Hamilton Island to Whitehaven Beach (Whitehaven), Whitsunday Island, Queensland. The flight would typically be about 10–15 minutes, with about 75 minutes at Whitehaven, before returning to Hamilton Island.

Prior to boarding the aircraft, the 4 passengers viewed a pre-flight safety briefing video and were fitted with a pouch‑style constant wear lifejacket.[1] The pilot then conducted an additional briefing at the rear left cabin door of the aircraft. The passengers recalled this included being demonstrated how to use their seatbelts, don the lifejackets and operate the rear door handle, among other things. The passengers were seated, in pairs, in the middle and rear seat rows, with the seat to the right of the pilot not utilised.

The aircraft departed to the south-east and made a left turn to track toward Chance Bay, Whitsunday Island (Figure 1). The pilot reported that, during initial climb, they set climb power and selected the landing gear to retract (see Landing gear actuation system). The pilot noted the gear was cycling, as evidenced by the illuminated red ‘hydraulic pump’ lamps.  

At about Chance Bay, the pilot spoke with the pilot of a company helicopter that was following, via very high frequency radio transmission, to coordinate with them as they were both heading toward Tongue Point. From this location, the pilot observed the water conditions and location of boats moored along Whitehaven. They described their observation as 7 kt, from the south-east and about 3 or 4 vessels on the water at Whitehaven. They then reported observing 4 blue ‘gear up’ lights on the landing gear panel and they did not see any of the main wheels extended in the mirror mounted on the left wing (see Mirror). The pilot then conducted an orbit over Tongue Point and Hill Inlet, before making a turn and doing a second pass so all passengers could view the beaches and inlets below.

After advising the passengers they would shortly be landing, the pilot commenced the pre-landing cockpit flow checks, including isolating the passengers from the aircraft audio system. The pilot advised they confirmed 4 blue lights, ‘saw no gear visible out the left window’, completed their flow checks and commenced the descent for landing. The pilot broadcast their intent to land at the south end of Whitehaven. They then completed the ‘finals checks’ from memory, which included checking the landing gear position again, before focusing on the landing.

Figure 1: Whitehaven Beach with reference to Hamilton Island, with approximate flight path depicted in yellow

Note: Approximate flight path derived from limited passenger images and video footage. Source: Google Earth, annotated by the ATSB

Upon touching down on the water, the aircraft bounced, then yawed sharply to the right, before nosing over and becoming submerged inverted. With the aircraft quickly filling with water, the pilot released their seatbelt and went to open their door, which they reported required some force. On exiting the aircraft, their leg was caught in the seatbelt, however, they were able to free themselves and swam to the surface. At the same time, 2 of the passengers had released their seatbelts and were both trying to open the left rear cabin door, which was adjacent to where they had both been sitting. They turned the door handle one way, and tried the other way, but could not open the door.

When the pilot did not see any of the passengers on the water surface, they returned to the aircraft to help them. They swam down and attempted to open the rear left door. Despite considerable effort, with their feet positioned on the airframe either side of the door, the door would not open, so they swam over to the right rear cabin door. The right door was able to be opened, again with a degree of force required, and the pilot pulled the nearest person out and took them to the surface. After taking a breath, the pilot returned and retrieved a second person, before assisting the remaining passengers.

One of the passengers, when they realised they could not open the left rear door, and with the cabin now almost completely filled with water, swam to the right side of the aircraft. They saw their partner was still in their seatbelt, so released it and continued to search for the door handle. They then felt their partner being pulled from them and out of the aircraft. They do not recall how they exited the aircraft but found themselves on the surface. The other passenger who was initially attempting to open the left rear door reported observing their partner, but it was very difficult to see. They then recalled being pulled from the aircraft, however, their partner could not remember how they exited the aircraft.

A nearby vessel rendered assistance to the pilot and passengers and transported them to Hamilton Island for medical attention. Once aboard the vessel, the pilot looked at the aircraft and observed the right main gear wheels had not retracted into the float (Figure 2).

Figure 2: VH-OHU underside of floats, showing right main wheels not retracted

Source: Used with permission, annotated by the ATSB

The pilot and passengers sustained minor injuries, and the aircraft was substantially damaged. It was reported that the aircraft sustained further damage during the retrieval from the water, before being transported to Mackay Airport, for storage.

Context

Pilot information

The pilot held a Commercial Pilot Licence (Aeroplane), with single and multi-engine class ratings and design feature endorsements including retractable undercarriage and floatplane. The pilot also held a current class 1 medical certificate with nil restrictions.

Prior to commencement with Whitsunday Air Services (trading as Hamilton Island Air), the pilot had accrued 563 hours total aeronautical experience, with 696 water landings, in a Cessna 182 aircraft on fixed floats. On 3 September 2024, the pilot underwent a familiarisation/transition flight in a fixed float DHC‑2 aircraft with an approved flight training organisation. The pilot was then employed with Hamilton Island Air. On 10 September 2024, the pilot commenced line training through the operator’s in‑command-under-supervision (ICUS) program, operating the DHC‑2 and the GippsAero GA8 Airvan^[2] aircraft under the supervision of the operator’s ‘fixed wing specialist’ training pilot (see Operational information).

The pilot completed ICUS training with a line check on 8 October 2024. The training pilot set a 20 kt wind limitation for operations at Whitehaven for the next 25 flight hours, for the pilot to fine‑tune their skills ‘in the air and on the water’. The aircraft daily flight records indicated the pilot conducted solo flights on 15 and 25 October, consisting of circuit training at Hamilton Island. In addition, on 18 October they conducted a flight to Whitehaven, with 5 Hamilton Island Air staff as passengers, similar to the tour that was the accident flight. The accident flight was the pilot’s first flight with fare-paying passengers. 

As of the morning of 26 October, the pilot had accrued 28 hours and 84 water landings in VH‑OHU. While the pilot had accrued 84 water landings in an amphibian aircraft, typically, the landing gear was not required to be extended and then retracted during training that consisted of multiple water landings in one session. As such, their gear actuation cycle experience was likely lower.

Helicopter underwater escape training (see Helicopter underwater escape training) was a Hamilton Island Air requirement, for all its helicopter and fixed-wing flight crew, to be completed during their induction and followed by recurrent training every 2–3 years. The pilot completed their initial underwater escape training on 24 September 2024.

The pilot self-reported to being well rested and feeling ‘fully alert’ on the morning of 26 October 2024. In addition, they advised they ‘felt comfortable with the aircraft’ and they had no distractions during the preparations for landing at Whitehaven.

Aircraft information

General

VH‑OHU was an amphibian De Havilland of Canada DHC‑2 Beaver, serial number 826, a predominantly all metal high-wing aircraft manufactured in 1956 and first registered in Australia in 2015.

The DHC‑2 was originally designed and manufactured by De Havilland Aircraft of Canada, Limited. Viking Air Limited was the type certificate holder from 2006 until 2024. In August 2024, Viking Air Limited amalgamated with De Havilland Aircraft of Canada Limited, and De Havilland Aircraft of Canada Limited became the type certificate holder.

The aircraft was powered by a Pratt & Whitney ‘Wasp Junior’ R-985 9-cylinder, single row, air‑cooled radial engine, which drove a Hartzell HC B3R30-4B 3‑blade propeller. The aircraft was fitted with Wipline 6100 series amphibious floats, manufactured by Wipaire.

Cockpit and cabin configuration

There were 2 forward cockpit doors and 2 rear cabin doors. The cabin door handle was located along the aft edge of the door and required the row 1 passenger to reach behind the seat to open the door (Figure 3). The front seats were equipped with 3-point lap-sash style restraints and the 3-person cabin bench seats were equipped with 2-point lap-belt restraints.

Figure 3: Seat and door locations

Source: Pilot’s operating handbook, annotated by the ATSB

Maintenance history

The aircraft logbook statement showed the airframe, electrical, engine, instruments and radio were to be maintained in accordance with the Civil Aviation Safety Authority (CASA) Schedule 5.[3] The float system was to be maintained in accordance with Wipaire instructions for continued airworthiness.

On 6 December 2022, VH‑OHU was subject to a forced landing just after take-off from Hamilton Island. The aircraft was subsequently removed from service. The aircraft was partly disassembled and transferred to Mackay in July 2023. Between January and September 2024, the aircraft underwent scheduled maintenance conducted by a CASA‑authorised maintenance organisation. Additional maintenance included treatment of corrosion and replacement of corroded hardware and components. This included inspection of the landing gear carriage assemblies and replacement of both slide tubes and all proximity sensor switches (see Landing gear actuation system). A landing gear system retraction test was also performed at this time.

The current maintenance release was issued on 3 September 2024 and there were no recorded defects at the time of the accident. The aircraft had accrued about 18 hours on the maintenance release, with a total time of 18,342 hours. Landings were recorded on the maintenance release, however, there was no distinction between water or land, nor if the gear had been retracted during water landing training or circuits from Hamilton Island.

Landing gear system

General

The landing gear incorporated within the amphibious floats is a retractable, quadricycle type with 2 free castoring nose (or bow) wheels and 4 (2 sets of dual) main wheels (Figure 4). Steering on the water is accomplished by a water rudder located at the rear of each float, which is cabled into the existing aircraft rudder system. Steering on land is accomplished by differential braking on the main landing gear wheels.

Figure 4: VH-OHU showing the amphibious float components

Source: Maintainer, annotated by the ATSB

Landing gear actuation system

Landing gear operation is initiated by movement of the landing gear handle, with the extension and retraction accomplished by 2 electrically‑driven hydraulic pumps. When the pilot selects the gear handle to UP or DOWN, hydraulic pressure in the system will drop and pressure switches will automatically turn on the hydraulic pump motors to maintain operating pressure in the system. When the gear cycle is completed, pressure in the system will increase to the limit where the pressure switches automatically shut off the pumps. If the pressure in the system drops to a preset value, the pressure switches turn the pump motors back on and build up the pressure to the limit again. Only the main gear system operation will be detailed in this report. 

The main gear is mechanically locked in both up and down positions. When the gear is selected to UP, the main gear down hook unlatches from the rear locking pin. Hydraulic pressure exerted on the actuator piston drives the carriage assembly to move forward along the slide tube, with the wheels moving aft, until the gear up hook latches on the forward locking pin (Figure 5). With no further movement once all 4 gear are retracted into the float, hydraulic pressure will increase until the pumps automatically switch off. 

Figure 5: Main gear assembly diagrams, including VH‑OHU forward locking pin (inset)

Source: Wipaire and the maintainer (inset), annotated by the ATSB

The landing gear indication panel, to the right of the pilot’s seat (at the base of the control column), contained 10 lamps. Four blue to indicate the 2 nose and 2 main gear were up, 2 red to show hydraulic pump operation and 4 amber to indicate the gear was down. In addition to the standard equipment, VH‑OHU was also fitted with a hydraulic pressure gauge for pilot reference (Figure 6). 

Each gear actuation operates independently (no set sequence) and therefore, the main gear UP and DOWN lamps are progressively activated by proximity switches, when the respective latch hook nests over the locking pin. The red hydraulic pump lights should extinguish shortly after all 4 UP or DOWN lamps are illuminated.

The airplane flight manual supplement for the amphibian floats described ‘bulb replacement during flight’. Where a lamp is not illuminated as expected, the pilot can readily remove the lamp and a known functioning lamp can be inserted into that location. This allows the pilot to determine if the non-illumination is a defective bulb, or other system issue. 

Figure 6: Typical landing gear panel

Source: Used with permission, annotated by the ATSB

The airplane flight manual supplement for the amphibian floats included the following:

The supplement further included that, where cycling of the gear does not rectify an asymmetric condition, rather than landing on water, the preferred option is to conduct the landing on a hard surface or grass:

Landings of this sort produce little tendency to nose over when checklist procedures are used, even when conducted on hard surface runways, and will result in little or no damage to the floats.

Mirror

In addition to the landing panel gear position indication, the aircraft was also fitted with an optional mirror, installed on the left wing (Figure 7). Wipaire advised the mirror was not part of its float modification, however, it was aware it was a common addition to float planes. 

This mirror allowed the pilot in the left seat to view the position of all 4 gear. This was particularly effective to confirm if the right main gear was retracted or extended from the underside of the right float, which was not possible without the mirror. The company pilots the ATSB spoke with reported varying opinions on the effectiveness for observing the right main gear via the mirror (see Operational information). However, all reported the mirror on the aircraft was correctly aligned following the recent maintenance and was effective in determining gear position.

Figure 7: Left wing mirror location, with representation of extended gear visible view

Source: Used with permission, annotated by the ATSB

Amphibian gear advisory system

The aircraft was also fitted with a Wipaire-authorised amphibian gear advisory system (AGAS), which provided the pilot with supplementary gear position information. Following departure, once the aircraft increased through a threshold airspeed, the system was armed. Upon slowing down through the threshold airspeed, in preparation for landing, the AGAS ‘Gear Advisory’ amber lamp (Figure 8), positioned on the instrument panel in front of the pilot, would illuminate. In addition, an audio annunciation, heard through the front seat headset/s, would commence. Where all 4 gear were retracted, the annunciation would consist of ‘gear up for water landing’ (female voice). Conversely, where all 4 gear were extended, the annunciation would be ‘gear down for runway landing’ (male voice). The audio annunciation would repeat every few seconds, until silenced by the pilot pressing the gear advisory lamp. The annunciation was a prompt for the pilot to check their gear configuration was correct for the intended landing surface.

Figure 8: Example of location of gear advisory lamp in DHC‑2 instrument panel

Note: the insert is taken from the AGAS airplane flight manual supplement. Source: Used with permission, annotated by the ATSB

The AGAS also had a ‘check gear’ advisory. In this case, when the aircraft slowed through the threshold airspeed, the gear advisory amber lamp would illuminate and the annunciation of ‘check gear’ would be heard in the same female voice and similar tone as that for the ‘gear up for water landing’ advisory. There were no additional tones associated with this alert. Check gear indicated an asymmetric condition in the landing gear, where one or more proximity switches had not closed. This was designed to prompt the pilot to abort the landing and troubleshoot the discrepancy. The airplane flight manual supplement for the AGAS included the warning:

In addition, to ensure the system was functioning prior to flight, the ‘operational checklists’ detailed the ‘before take-off’ checks as:

• annunciator switch – PRESS and HOLD for 2-3 seconds
• test audio – VERIFY message is audible
• annunciator switch – VERIFY annunciator light flashes.

Wipaire advised that the ‘test’ audio check contained the gear up and gear down messages only. That is, the check gear annunciation was not included in the system test audio.

Wipaire maintenance documentation

The Wipaire instructions for continued airworthiness (ICA) described the general servicing of the floats and landing gear. The manual also included the following warnings to ensure corrosion from saltwater operations was kept to a minimum:

…

The ICA 25-hour maintenance requirements for the landing gear included washing the aircraft and floats with fresh water and inspecting surfaces and hardware for signs of corrosion, especially with saltwater use. In addition to specific nose gear maintenance actions, the main wheel bearings and main gear carriages were to be greased. This maintenance on VH‑OHU was typically conducted by the maintainer. The maintenance documentation recorded that a 25-hour float inspection was conducted by the maintainer on 5 October 2024, about 15 hours since the issue of the maintenance release.

The ICA inspection time limits and checklist section did not include a specific check for corrosion on the slide tube. Wipaire advised it was covered in the servicing section for ‘movable parts’, which detailed the inspection:

For lubrication, servicing, security of attachment, binding, excessive wear, safe-tying, proper operation, proper adjustment, correct travel, cracked fittings, security of hinges, defective bearings, cleanliness, corrosion, deformation, sealing and tension.

The 25-hour inspection was conducted with the aircraft on extended landing gear. In this configuration, the forward end of the slide tube could be inspected. However, the carriage assembly was positioned at the aft end of the slide tube, preventing inspection at this location. A gear retraction test, to check for correct operation of the gear up and down lock hooks, was to be conducted at 200-hour intervals. With the gear retracted, this then provided the opportunity to inspect the aft end of the slide tube.

Wipaire published service letter #80 AT-802 Fire Boss Slide Tube Corrosion in 2006. It described reports from operators of ‘sticking main gear actuators due to corrosion on the slide tube’. It noted that the corrosion was partially caused by gravel or debris from the main landing gear tyres eroding through the hard anodised surface of the slide tube, exposing the underlying aluminium, which was more susceptible to corrosion. Part of compliance included inspecting the slide tube for erosion and/or nicks and wiping the slide tube down with a clean rag soaked in lubricant. Wipaire advised there was no specific service letter to address corrosion for the 6000/6100 series floats.

Pilot maintenance

Due to the salt laden environment and exposure to seawater, the operator reported washing the aircraft with fresh water at the end of each operating day. In addition, greasing of the nose and main gear components, and other aircraft care activities, were periodically carried out. These additional tasks were to be carried out by an appropriately trained pilot, however, it was not recorded on the maintenance release or other formal record. It was also noted that there was no practice of washing the aircraft if it had not been operated for several days. 

The maintainer conducted the pilot maintenance training, demonstrating the additional maintenance tasks. The pilot of VH‑OHU had not yet received the formal training prior to the accident but advised that they had been shown these tasks by their training pilots.

Meteorological information

The meteorological conditions reported by the pilot at the time of accident were consistent with the Bureau of Meteorology forecast, with east-south-east winds of about 7–8 kt and good visibility. In addition, the pilot’s report and passenger footage showed the water conditions were ideal for float plane operations and sun glare was not angled into the cockpit and across the instrument panel.

Wreckage information and component examination

The ATSB did not attend the accident site or wreckage examination in Mackay, instead the ATSB liaised with the maintainer and the maintenance organisation that conducted the post-accident examination of the landing gear. The ATSB also reviewed images and video footage taken during these examinations.

Initial examination

The maintainer examined the aircraft, in the presence of the insurance representative, after it was retrieved from the ocean and provided the following observations regarding the landing gear system:

• the aircraft was significantly disrupted during the retrieval from the water, including damage to the landing gear panel, which prevented the landing gear selector position to be definitively established
• the landing gear appeared undamaged
• hydraulic fluid was drained and appeared to be of expected quantity, with no water contamination
• the 4 blue lamps were removed for testing, however, their location prior to removal was not recorded
• one of the blue lamps failed testing, however, it could not be determined if this was from seawater immersion or a pre-existing fault.

The wreckage was then transferred to Mackay for storage and further examination.

About 2 weeks after the accident, the landing gear was examined by the maintainer and an engineer from another CASA-authorised maintenance facility. They provided a report to the ATSB, with following general observations:

• hydraulic pump 1 and 2, AGAS and gear lamps circuit breakers were engaged, indicating the system was operating as expected
• it was not possible to carry out a continuity and functional check of the gear panel indication system due to corrosion and moisture from saltwater ingress
• fuses for pumps 1 and 2 ‘ON’ lamps tested serviceable
• both nose gear assemblies and the left main gear were observed to be up and locked, indicating a complete retraction
• the right main gear was extended
• some corrosion was noted on the forward face of both the left and right carriage assembly to slide tube interface.

The maintainer advised the ATSB that, when they tried to move the left main gear carriage, it initially did not move. However, ‘a small knock with a hammer freed the carriage’, which then moved freely. The carriage was likely held up by the observed minor corrosion at the slide tube interface. Further, there was ‘little to no damage’ on the slide tube, compared to the same location on the right slide tube.

Right main gear examination

Detailed examination and testing of the right main gear assembly was then conducted. The report included the following observations: 

• the down hook was found to be free of the locking pin (unlocked)
• the right main gear was approximately 1.5–2 mm from fully down
• gear position light proximity switches tested for resistance to ground with no issues
• continuity testing of the proximity sensor switches showed UP and DOWN ‘open’, which was correct for the current configuration (gear mid travel).

Hydraulic pressure was then applied to the right main gear using a hand pump and calibrated pressure gauge. With 870 psi applied in the retraction direction, the carriage did not move along the slide tube. This was despite progressively adding oil to the slide tube/carriage interface, supplying grease to the carriage, disconnecting the shock strut and applying mechanical assistance via a pry bar.

The hydraulic pressure supply was then transferred to the extend direction. The carriage and slide tube moved together and closed the 1.5–2 mm gap. With this actuation, the actuator piston moved relative to the carriage assembly and the DOWN lock engaged as per design specifications. Testing of the proximity switch showed it to be closed, correct for the configuration. The direction of hydraulic pressure was reversed to retract and the DOWN lock was observed to disengage freely, with the proximity switch again testing correctly.

The report noted that at no time did the carriage move relative to the slide tube during the testing, establishing that the carriage assembly was seized on the slide tube. When the slide tube was removed from the float, a slide hammer and block of wood was successful in separating the carriage assembly from the slide tube. A significant amount of corrosion was then noted on the slide tube.

The ATSB then requested the left and right slide tubes and carriage assemblies be provided for further examination.

Component examination

The ATSB and Wipaire conducted testing and analysis to try to determine the circumstances that allowed the corrosion to develop. Examination of the left and right slide tubes and carriage assemblies was conducted at the ATSB’s technical facilities in Canberra, Australian Capital Territory.

The right slide tube had 2 bands of corrosion that corresponded with the bushing locations in the carriage, at about the fully extended location (Figure 9). The left slide tube showed no similar damage. Both carriage assemblies exhibited grease around the UP and DOWN hooks and internally. The components were not serialised, so the history of the carriages prior to the aircraft entering Australia could not be determined.[4] 

Figure 9: Comparison of slide tubes, showing corrosion bands on the right slide tube (on the right) and location of bushings examined by the ATSB

Source: ATSB and used with permission, annotated by the ATSB

Detailed examination of the components was then conducted, with reference to the Wipaire-supplied specifications.

The slide tubes were manufactured from aluminium with an anodised coating. The slide tube dimensions were measured to be within specifications and the anodised layer was the correct thickness. The slide tube surface was non-conductive, as expected for an anodised layer.

The bushings were a tri-layer construction, with a base layer of steel, with sintered (porous) bronze and then coated in a PTFE[5] ‘sliding layer’. The bushing could be replaced and therefore, the carriage time in service did not necessarily correspond to the bushing time in service. The bushings of both carriages were examined, with observations including the internal diameters of all bushings were within drawing tolerances and the right bushings were more worn than the left (Figure 10).

Figure 10: Difference in bushing wear with the left (left) showing largely intact PTFE layer (grey) and right (right) showing significant exposure of the sintered bronze layer

Source: ATSB

The right carriage bushing located near the grease nipple was sectioned. Examination identified areas where the PTFE layer was not present, exposing the bronze layer and showing some evidence of scoring (Figure 11). The PTFE layer was non-conductive in contrast to the bronze.

Figure 11: Right carriage bushing surface showing Teflon/lead layer (grey), exposed bronze layer (copper) and some evidence of scoring (bright lines)

Source: ATSB

The slide tube corrosion patterns were consistent with galvanic corrosion between the exposed bushing bronze layer and the aluminium slide tube base metal, in the presence of salt from coastal operations. The difference in wear between the left and right carriage bushings likely influenced the degree of corrosion on the respective slide tubes. The bushings with a higher amount of retained, non-conductive PTFE layer showed significantly less corrosion on the corresponding slide tube.

The ATSB determined that there were no material or manufacturing issues identified with the slide tubes, and therefore the thin, hard anodised coating was likely damaged or worn through in this area, to allow for the dissimilar metal contact. This type of damage was also observed in discrete locations in deeper score marks on the slide tube, away from the main areas of corrosion. 

Damage to the anodise was unlikely to have been directly from the worn bushings, since the bronze is softer than the hard anodise layer, but it was possible for dirt, sand or other abrasive debris to have become entrapped between the bushings and slide tube. While there was no significant entrapped material identified during the ATSB examination, the mechanism was shown to exist, as described in Wipaire service letter #80. 

Operational information

Operator overview

Whitsunday Air Services, trading as Hamilton Island Air, conducted tourist charter flights to various locations in the Whitsundays, Great Barrier Reef and Hamilton Island areas, using a variety of fixed-wing and helicopter types. At the time of the accident, it operated a fleet of 17 helicopters and 3 fixed-wing aircraft: VH‑OHU, a GA8 Airvan and a Cessna 208.

Training pilot observations

The operator had an appointed fixed-wing specialist, who oversighted the fixed-wing operations and pilot training. The fixed-wing specialist (training pilot 1 – TP1) had advised the operator their intention to depart the organisation in September 2024. In August, they commenced correspondence with the accident pilot, in preparation for their employment and training. 

TP1 collected VH‑OHU from the maintenance organisation in Mackay. Due to the aircraft coming out of extended maintenance, and TP1 having not operated it for a period of time, TP1 reported conducting a series of test flights, including water landings near Mackay and then en route to Hamilton Island. TP1 reported that the landing gear and AGAS were operating as expected. In addition, TP1 advised the mirror was correctly oriented to view all 4 gear. TP1 then commenced training the accident pilot on VH‑OHU, between 10 and 20 September 2024, before leaving the organisation. 

Training was then conducted by the current fixed-wing specialist (training pilot 2 – TP2), from 5 October 2024. The training again included land and water landings, with TP2 advising the landing gear and AGAS systems were functioning correctly. TP2 advised the left mirror was correctly oriented, however, the right main gear could sometimes be difficult to distinguish from the background contrast (such as terrain, sky, water). TP2 reported their preference for having an additional right-side mirror, and they were in the process of procuring a second mirror at the time of the accident.

Pilot recollections

Accident day

With regard to the day of the accident, the pilot reported:

• they did not feel any operational or time pressure
• they were comfortable with operating the aircraft solo, and with passengers
• the landing area only contained a few vessels, therefore, workload was not increased
• there were no distractions from the passengers during the approach to land and landing
• while there was a checklist available, the pre-landing checks were completed from memory, which was permitted by the operator’s procedures
• they observed 4 blue lights indicating the gear was up for a water landing
• they checked the mirror
• they did not recall hearing the AGAS annunciator just prior to landing
• during the accident sequence the aircraft flipped ‘within a second and I was underwater, upside down, almost instantly submerged, no air at all’.

Following the aircraft becoming submerged inverted, the pilot advised that, due to their recent helicopter underwater escape training, they ‘came right into action’ and ‘wasted no time’. The pilot advised that they would recommend the training to pilots operating sea planes or ‘any planes over water’.

Further, the pilot reported that, had they observed the extended right wheel, they would not have conducted the water landing, and would have returned the aircraft to Hamilton Island for a runway landing.

Training and aircraft systems

The pilot reported that they were happy with their training from both training pilots. In addition, they did not perceive any difficulties with training on the DHC‑2 and GA8 Airvan concurrently. 

When discussing the mirror, the pilot described its importance in determining gear position. However, they also reported that there might be a blind spot that means the right main gear may be difficult to see.

When asked by the ATSB if the AGAS self-test was successful prior to the accident flight, the pilot reported to not being aware of this procedure. The pilot also reported to not have heard the AGAS ‘check gear’ annunciation during their training.

Seaplane operations guidance

The Seaplane Pilots Association published guidance on amphibious gear management best practices, to ‘enhance safe operations within the seaplane community’.[6] The guidance advocated the use of checklists and described triggers or cues, with each phase of flight, ‘to deter landing with the gear in the wrong position’. The ‘on water-based landing’ section included, in part:

• several gear-position validation checks, during initial flyover, pre-landing operations (1st power reduction, setting flaps et cetera) and establishing on final approach to land
• verbalise each gear position validation while visually confirming
• pay attention to the gear advisory system, if installed.

In addition, the guidance stated, ‘it is very important to crosscheck the surface intended for landing with the gear position selected and where the gear actually is positioned’ and included:

As general guidance, an amphibious aircraft should be considered more vulnerable to a catastrophic accident, which may include serious injury and death, with the gear down. While all efforts should be taken to avoid landing on either a runway or a waterway with the gear in the wrong position, landing on a runway with the gear up tends to be much more benign, with minimal damage and injuries, compared with landing on water with the gear down. Avoiding either scenario is best done by being attentive and not complacent.

Survival aspects

Helicopter underwater escape training (HUET)

HUET has been in use around the world since the 1940s and is considered best practice in the overwater helicopter operating industry. HUET is designed to improve survivability after a helicopter ditches or impacts into water. Fear, anxiety, panic and inaction are the common behavioural responses experienced by occupants during a helicopter accident. In addition to the initial impact, in-rushing water, disorientation, entanglement with debris, unfamiliarity with seatbelt release mechanisms and an inability to reach or open exits have all been cited as problems experienced when attempting to escape from a helicopter following an in-water accident (Rice and Greear, 1973).

The training involves a module (replicate of a helicopter cabin and fuselage) being lowered into a swimming pool to simulate the sinking of a helicopter. The module can rotate upside down and focuses students on bracing for impact, identifying primary and secondary exit points, egressing the wreckage and surfacing.

The ATSB has previously emphasised the importance of HUET for all over-water helicopter operators in other investigations including AO-2018-022, AO-2019-008, AO‑2020-003 and AO-2023-044. Further, HUET is included in the ATSB’s Safety Watch Reducing the severity of injuries in accidents involving small aircraft.

Safety briefing 

The ATSB viewed the safety briefing video and noted it described the operation of door handles from across the operator’s fleet, although the aircraft associated with each handle was not explicitly stated. When the ATSB discussed the briefing process with the passengers, they recalled that the video had a lot of different door handles. One passenger also noted the video seemed to be focused more on helicopters, rather than the floatplane. However, the passengers recalled the pilot briefing them at the aircraft and showing them how the door handles worked on VH‑OHU.

Emergency egress

In this accident, the passengers required assistance from the pilot to egress from the submerged aircraft. Had the pilot been unable to assist, the outcome may have been more severe.

This possibility was reported by the Transportation Safety Board of Canada (TSB) in investigation A09P0397 Loss of control and collision with water involving a DHC‑2 on 29 November 2009. Following the collision with water, the pilot and one passenger survived, however, the other 6 passengers succumbed to injuries from immersion. The report included the following safety issue:

Over the last 20 years, some 70% of fatalities in aircraft that crashed and sank in water were from drowning. Many TSB investigations found that the occupants were conscious and able to move around the cabin before they drowned. In fact, 50% of people who survive a crash cannot exit the aircraft and drown.

The TSB recommended ‘the Department of Transport require that all new and existing commercial seaplanes be fitted with regular and emergency exits that allow rapid egress following a survivable collision with water’ (A11-05).

TSB report A18A0053 Loss of control and collision with water, involving a DHC‑2 on 11 July 2018 noted the aircraft became inverted during the accident sequence. One pilot escaped through the broken front windscreen. The other pilot was unable to open their forward right door nor the cabin door, however, the first pilot was able to open the cabin door from the outside. Neither pilot had undergone emergency egress training, nor was it required. Further, the report included:

Emergency door release mechanisms, better door handles, and push-out windows have been developed for certain types of floatplanes. Some floatplane operators have installed these modifications, but many have not. 

Regulatory requirements for mandatory egress training for commercial floatplane pilots may result in some improvement in emergency egress from commercial seaplanes. However, if the regulator does not mandate or promote voluntary modifications to normal exits, seaplanes will continue to operate with exits that could become unusable following an impact, diminishing the chance occupants have to exit the aircraft following a survivable accident.

Push-out windows

Viking Air Limited (the type certificate holder at that time, now held by De Havilland Aircraft of Canada, see Aircraft information) developed ‘push-out windows’ (Figure 12) and published service bulletin V2/0003 New cabin door windows that incorporate a ‘push-out’ feature in July 2010. The service bulletin noted:

- A series of incidents involving float equipped aircraft has highlighted the need to improve emergency egress from the cabin.

- The Cabin Door Push-Out Window Kits contain a rubber-mounted right-hand and/or left‑hand passenger window which affords additional egress opportunities from the aircraft.

- Viking has designed new windows for the passenger doors that incorporate the same ‘push-out’ feature used for many years on helicopters operating overwater.

- Viking Air Limited strongly recommends that this safety improvement be incorporated on aircraft operating on floats and any wheeled aircraft operating over water, or as directed by the operator’s Regulatory Authority.

Figure 12: Example of main cabin door push-out window

Source: De Havilland Aircraft of Canada and Naomi Lacey (inset), annotated by the ATSB

De Havilland Aircraft of Canada advised it has supplied about 130 kits worldwide, with one kit to Australia. VH‑OHU was not fitted with the push-out windows, nor was it required by regulations.

Revised door latches

Viking Air Limited published service bulletin V2/0004 Installation of an automotive style cabin door latch system in November 2010. The service bulletin cited the reason as ‘the dual automotive (pull) style cabin door latch system provides better egress from the cabin in the event of an emergency’ (Figure 13). The service bulletin also noted:

- Viking Air Limited (Viking) has designed a dual automotive (pull) style cabin door latch system that is more familiar and intuitive to passengers. The existing single latch handle (rotating style) at the rear of the door has been replaced by one pull style latch handle at the same location and a second pull style latch handle in the forward portion of the door. This allows passengers in the forward and rear cabin seats to open the cabin doors in an emergency situation.

- Viking strongly recommends that this safety improvement be incorporated on all DHC‑2 aircraft or as directed by the operator’s Regulatory Authority.

De Havilland Aircraft of Canada advised it had supplied 70 door latch kits to date. VH‑OHU was not fitted with the modified door latch system, nor was it required by regulations.

Figure 13: Representation of revised door latches, with VH‑OHU door in inset

Note: the rotational-style door latch, as was in VH‑OHU, operates in one direction only. Source: De Havilland Aircraft of Canada and the operator, annotated by the ATSB

Similar occurrences

There have been a number of occurrences involving DHC‑2 where one or more wheels were extended during a water landing resulting in the aircraft nosing over and becoming inverted. This has been evidenced in several United States National Transportation Safety Board (NTSB) accident reports as summarised below.

N218RD at Oak Island, Minnesota, on 22 May 2021 (CEN21LA244)

The aircraft departed with a known hydraulic leak in the landing gear system. During the flight, the degraded hydraulic system resulted in the inadvertent extension of the left main gear. This was not identified by the pilot and the aircraft nosed over upon landing on the water and became inverted. The pilot and one passenger were not injured, and one passenger sustained serious injuries.

N9558Q at Stehekin, Washington, on 17 May 2008 (LAX08FA144)

The pilot did not raise the landing gear after take-off. The pilot also reported the flight was turbulent and bumpy, with slow airspeed due to the heavy load. This resulted in numerous AGAS annunciations, until the pilot pulled the circuit breaker to disable the ‘nuisance’ alerts. The pilot intended to reset the AGAS prior to landing but did not do so. When the aircraft landed on the water with the wheels extended, it abruptly nosed over and became inverted. The pilot and 2 passengers survived, and 2 passengers were unable to exit the aircraft and succumbed to immersion. 

N60TF at Sitka, Alaska, on 30 May 2003 (ANC03LA054)

The pilot advised they forgot to raise the landing gear following departure from land. During the water landing, with the wheels extended from the floats, the aircraft nosed down in the water. The pilot was uninjured.

N4478 at Aleknagik, Alaska, on 28 August 2002 (ANC02FA106)

The NTSB found the pilot did not raise the landing gear following departure from land. During the water landing, with the wheels extended from the floats, the aircraft nosed over and became inverted. The 2 passengers escaped with minor injuries and the pilot sustained fatal injuries attributed to immersion.

Safety analysis

Introduction

On the morning of 26 October 2024, the pilot of a De Havilland Aircraft of Canada DHC‑2, registered VH‑OHU, departed Hamilton Island aerodrome, Queensland, with 4 passengers on board for a short scenic flight to Whitehaven Beach, Whitsunday Island. Upon touching down on the water, the aircraft yawed to the right, nosed over and became submerged inverted. The pilot and 4 passengers sustained minor injuries and the aircraft was substantially damaged.

This analysis will discuss the right main gear failing to retract, the unsafe configuration not being identified by the pilot and delayed egress of the passengers. In addition, the analysis will consider why the pilot did not hear the gear annunciation. Further, the pilot’s recent underwater escape training and availability of enhanced egress aircraft modifications will also be discussed.

Right main landing gear failed to retract

Immediately following the accident, the right main gear could be seen extended from the float. Examination of the aircraft found no evidence of leakage, loss or contamination of the hydraulic fluid, and all landing gear circuit breakers were engaged. Further, the nose and left main gear had successfully retracted, indicating the anomaly was likely isolated to the right main gear.

During retraction, the main gear travels aft as it swings up into the float. Had the gear been mid-travel, such as still cycling, the impact with the water would have forced the gear to retract up into the float. Therefore, it was unlikely the right main gear moved during the impact sequence. This was consistent with the post-accident examination, which identified that the right carriage assembly had seized on the slide tube at the almost fully extended position. 

Once removed from the aircraft, forceful removal of the carriage resulted in the identification of advanced corrosion on the right slide tube. The 2 bands of corrosion were coincident with the location of the carriage bushings, near the full gear extension position. This would be expected as the aircraft was predominantly parked on land, with the gear extended.

The investigation considered scenarios conducive to the formation of this corrosion. The maintenance records prior to the aircraft entering Australia in 2015 were not available, as such, the service history of the main gear carriage assemblies, including the bushings, was unknown. While there was a significant difference in the condition of the left and right slide tubes, both tubes were installed at the same time and therefore subject to the same operational and environmental conditions.

The operator advised the aircraft was rinsed with fresh water at the end of the operating day, however, this was not formally recorded and there was no practice for rinsing when the aircraft was not operated for several days. The aircraft records showed the maintainer conducted a 25-hour float inspection on 5 October 2024 and grease was observed on the assemblies during post‑accident examination. However, as there was no requirement to retract the gear for this inspection, the position of the carriage assembly precluded visual examination of the slide tube at the location where the corrosion had developed.

Examination of the carriage bushings identified that the right bushings exhibited more wear and loss of the PTFE ‘sliding layer’, which runs along the slide tube. This had the potential for galvanic corrosion to form, however, required the degradation of the anodised layer on the slide tube to also be present. Insufficient cleaning, inadequate application of grease and/or accumulation of dust or dirt on the slide tube are known contributors to degradation of protective layers. While the extent to which they were contributory in this case was not able to be determined, it was likely that the identified corrosion resulted in the right main gear seizing.

Pilot did not identify extended right main gear

The pilot reported observing 4 blue ‘gear up’ lamps illuminated, at about Tongue Point, and during their pre-landing checks. The passenger footage showed sun glare was not angled in the direction of the landing gear panel and the pilot advised they were able to clearly identify what lamps were illuminated. However, when tested post‑accident, one blue lamp did not illuminate, although it could not be determined if this failure was due to seawater immersion or pre-existing. Further, the location of the failed lamp could not be determined as the lamps were not identified on removal from the landing gear panel. Despite this, failure of any lamp to illuminate requires troubleshooting by the pilot prior to landing. The pilot can readily determine if the lack of illumination of a lamp is due to a failed bulb or other system issue. 

The main right gear UP and DOWN proximity switches tested serviceable during the post-accident examination. The examination also noted the right main gear had unlatched from the DOWN location and moved about 1.5–2 mm in the retract direction before becoming seized. During the landing gear retraction sequence, pressure in the hydraulic system would increase until the pumps automatically switched off and the red ‘in-transit’ lamps would extinguish. In this configuration, with nil movement in the right main gear due to the seizure, it was expected that only 3 blue lamps would have been illuminated. Therefore, the investigation could not reconcile the pilot’s recollection of there being 4 blue lamps illuminated.

The mirror provided an additional method to identify the landing gear configuration. Training pilot 1 advised they could observe all wheels in the mirror following the aircraft repairs. Training pilot 2 reported sometimes experiencing difficulty in observing the right main wheels from the mirror. The accident pilot reported a blind spot, which hindered their ability to see the right main gear in the mirror. However, during the pre‑landing checks, the accident pilot reported they checked the mirror and did not observe any wheels protruding from the floats and continued with the water landing.

Another method to identify the gear position was via the amphibian gear advisory system (AGAS), which provided a visual and audio annunciation as the aircraft slowed for landing. The pilot had been communicating via the radio with the helicopter pilot, thereby showing the audio system in VH‑OHU was operational and that the AGAS annunciation was able to be heard through the headset. However, the pilot reported they could not recall hearing any annunciation prior to landing on the water. Due to disruption of the floats during the accident, the system could not be functionally tested. The pilot advised they were not aware of the pre-flight self-test of the AGAS and therefore this was not conducted prior to the accident flight. While it remained a possibility that the AGAS did not alert the pilot to an asymmetric condition prior to the landing, all 3 pilots reported the AGAS had been functioning correctly in the preceding weeks. Therefore, while it could not be conclusively determined, it was more likely the system was operational.  

The pilot’s 84 water landings in VH‑OHU did not necessarily represent the number of times they had actuated the landing gear, however, they did select the gear to retract after departing Hamilton Island. In addition, the pre-landing checks required the pilot to utilise the aircraft systems to ascertain gear position prior to each landing, regardless if the gear was cycled. Further, the pilot also reported no issues with distractions, workload or experiencing time pressures. 

Therefore, while the aircraft was fitted with multiple systems to confirm the status of the landing gear, for undetermined reasons the pilot did not identify that the configuration was unsuitable for a water landing. This resulted in the aircraft yawing to the right, nosing over and becoming submerged and inverted, a known consequence of water landings with one or more gear extended.

Landing gear annunciator 

The pilot advised the ATSB that they did not recall hearing the AGAS annunciation just prior to the landing. The ATSB’s analysis concluded the AGAS was more likely than not operational at the time of the accident. The investigation therefore considered potential reasons for the audio alert not being heard or being dismissed.

The ‘gear up for water landing’ and ‘gear down for runway landing’ are advisory only and an opportunity for the pilot to check the gear selection matches their intended landing surface. In contrast, the ‘check gear’ annunciation was alerting the pilot that the 4 gear were not all fully up or down and in an unsafe configuration for landing. However, the ‘gear up’ and ‘check gear’ both used a similar female voice and there were no additional tones to indicate the heightened importance of the ‘check gear’ alert. Further, when below the threshold airspeed, the amber ‘gear advisory’ lamp would illuminate, irrespective of the gear configuration. 

The purpose of auditory warnings is to attract attention to a problem (Salvendy & Karwowski, 2021). Ideally, advisory annunciations would sound distinctly different to other alerts to assist pilots to recognise there is problem requiring their action. Making alerts distinctive from other sounds can also inform the pilot of the priority or urgency of the problem (Yeh et al. 2016, FAA, 2016). During approach to land, with the gear in an asymmetric configuration, the AGAS would have enunciated ‘check gear’, indicating an unsafe condition. 

As the pilot would have expected to hear an annunciation with a female voice during landing, there was little to distinguish it from an alert that required action. In addition, the pilot reported they had not heard the ‘check gear’ alert during the training, reinforcing the female annunciation was to be expected and normal. This increased the risk that a pilot would not recognise that the landing gear was in an unsafe condition and removed an opportunity to consider a runway landing, the preferred option in this scenario. However, as the pilot reported not hearing any annunciation prior to landing, there was insufficient evidence to determine if the lack of distinction between the ‘gear up’ and ‘check gear’ annunciations contributed to the accident.

Passengers’ delayed egress

During the accident sequence, the aircraft rapidly filled with water, giving all on board little time to react. Despite being temporarily tangled in their seatbelt, the pilot readily exited the aircraft and swam to the surface. When no passengers appeared, the pilot swam back to the aircraft.

The 2 passengers seated next to the left rear cabin door reported they quickly released their seatbelts, and both attempted to open the door. The pilot was trying to open this door at the same time, without success. The 2 passengers recalled they attempted to locate the right rear cabin door, which was about coincident with the pilot’s decision to also try this door. The pilot managed to open the right rear door and assisted the passengers to the surface. 

The ATSB considered the circumstances that prevented the left rear door from being easily opened following the accident. It was possible that water pressure from the outside was greater than inside the cabin, until equalising as the cabin filled with water. Alternatively, distortion to the airframe during the impact sequence could have prevented door operation. While the reason could not be determined, this contributed to the delayed evacuation from the submerged aircraft.

Underwater escape training

The pilot had completed operator-required helicopter underwater escape training about one month prior to the accident. They attributed this training to their prompt escape from the inverted and submerged aircraft, and subsequent assistance to the passengers. As evidenced in previous ATSB investigations, this training has been shown to significantly increase the chances of survival in the event of a collision with water.

Enhanced egress aircraft modifications

Following multiple similar accidents where occupants initially survived but were subsequently fatally injured from immersion, the Transportation Safety Board of Canada recommended the fitment of regular and emergency exits that allowed rapid egress in the event of a collision with water. Consequently, Viking Air Limited developed push-out windows and more intuitive automotive-style door latches for the main cabin door. These modifications were not fitted to VH‑OHU nor were they required by regulations. 

In this accident, 2 of the passengers were actively searching for a means of escape, but ultimately required the pilot to open the door. However, if the pilot had been unable to assist, the accident could have resulted in dire consequences. Acknowledging that people behave differently in emergency situations, providing an alternative means of escape where one or more doors cannot be opened, increases the chance of survival. This is most relevant with submerged aircraft, yet can also expediate egress for land‑based accidents, particularly those involving a post-accident fire. 

Findings

From the evidence available, the following findings are made with respect to the landing gear malfunction and collision with water involving De Havilland Aircraft of Canada DHC‑2 Beaver, VH‑OHU, near Whitehaven Beach, Whitsunday Island, Queensland, on 26 October 2024. 

Contributing factors

• Likely due to corrosion, the right main landing gear assembly seized near the fully extended position, which prevented retraction after take-off from Hamilton Island.
• During preparations for a water landing, for undetermined reasons, the pilot did not identify the landing gear was in an unsafe condition. As a result, the aircraft landed with the right main wheels extended and then yawed to the right, nosed over and became submerged inverted.

Other factors that increased risk

• The cautionary 'check gear' annunciation was very similar to the advisory annunciation for a normal water landing, increasing the risk that a pilot would not recognise that the landing gear was in an unsafe condition.
• Following the impact, and with the aircraft submerged, the rear left door was unable to be opened by either the pilot or the passengers. As a result, the evacuation of the passengers was delayed.

Other findings

• As required by the operator, the pilot had recently completed helicopter underwater escape training, which aided with their prompt underwater egress and subsequent rescue of the passengers from the inverted and submerged aircraft.
• Push-out windows and door handles designed to expedite egress in an evacuation were available for retrofit on the DHC‑2 Beaver aircraft. VH‑OHU did not have either fitted and nor were they required to by regulation. 

Safety actions

Safety action by Hamilton Island Air

Hamilton Island Air advised the following safety action was undertaken:

• installation of a second mirror on the right wing of its current DHC‑2 aircraft
• formal initial and refresher training on the pilot maintenance tasks
• implementation of a daily washdown and preventative maintenance procedure checklist, which included a sign-off section to formally record when the activities were completed and by whom
• implementation of a minimum weekly systems check flight, including landing gear cycle, where the aircraft had not been recently operated
• implemented initial and annual theory ground school training, flight characteristics training and 180-day proficiency flight checks for all floatplane pilots, conducted by authorised flight training organisations.

Safety action by the Civil Aviation Safety Authority

Following review of the draft investigation report, the Civil Aviation Safety Authority advised it was intending to release airworthiness bulletin AWB 32-029 Issue 1 Supplementary Type Certificated Amphibian Float Main Gear Slide Wear in Marine Environments. Reflecting the information contained in the ATSB’s investigation report, the bulletin contains advice to operators and maintainers highlighting the importance of inspection and preventative maintenance aspects for retractable landing gear carriages fitted to amphibious aircraft when operated in a marine environment. The bulletin recommended that:

• during scheduled maintenance of the landing gear, particular attention should be applied during a visual inspection for evidence of corrosion or mechanical damage to the hard anodized surface of the slide tubes
• during periods of extended non-service, the landing gear slide tubes are lubricated and visually inspected for damage along their full length prior to the aircraft returning to service
• during approved pilot maintenance. the main gear slide tubes are wiped clean and lubricated and the gear carriages are completely refreshed with clean grease. 

Sources and submissions

Sources of information

The sources of information during the investigation included:

• the pilot and passengers of the accident flight
• the operator and training pilots
• the Civil Aviation Safety Authority
• De Havilland Aircraft of Canada
• Wipaire
• the maintenance organisation for VH‑OHU
• the maintenance facility that conducted the post-accident aircraft examination
• Bureau of Meteorology
• video footage from the accident flight and other photographs taken on the day of the accident.

References

Federal Aviation Administration. (2016). Human factors design standards. US Department of Transportation, United Sates Government.

Rice, E,V., & Greear, J.F. (1973). Underwater escape from helicopters. In Proceedings of the Eleventh Annual Symposium, Phoenix, AZ: Survival and Flight Equipment Association, 59-60. Cited in Brooks C. (1989) The Human Factors relating to escape and survival from helicopters ditching in water, AGRAD.

Salvendy, G., & Karwowski, W. (2021). Handbook of human factors and ergonomics (5th ed.). John Wiley & Sons, Inc, doi: 10.1002/9781119636113.

Yeh, M., Swider, C., Jin Jo, Y., & Donovan, C. (2016). Human factors considerations in the design and evaluation of flight deck displays and controls. Federal Aviation Administration, United States Government.

Submissions

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

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

• the pilot of the accident flight
• the operator and training pilots
• the maintainer of VH‑OHU
• Civil Aviation Safety Authority
• De Havilland Aircraft of Canada
• Transportation Safety Board of Canada
• Wipaire
• United States National Transportation Safety Board.

Submissions were received from:

• the operator
• De Havilland Aircraft of Canada
• Civil Aviation Safety Authority.

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.

The occurrence

Overview

On the morning of 26 October 2024, a commercial pilot licence (Aeroplane) (CPL(A)) flight test was being conducted in a Cessna 182 aircraft, registered VH-APN (APN), departing from Shellharbour Airport, New South Wales. On board APN were a pilot under examination (the CPL candidate) and a Civil Aviation Safety Authority (CASA) approved flight test examiner (the examiner).

On the same morning, a private flight was being conducted in a Jabiru UL 450 aircraft, registered 19-4079 (4079), departing from The Oaks aerodrome (The Oaks), New South Wales. On board 4079 was a pilot (the pilot of 4079), who was the sole occupant.

Around midday, APN and 4079 collided in-flight and both aircraft impacted terrain. All occupants of both aircraft were fatally injured. The following describes the events that led up to the midair collision.

VH-APN pre-flight and departure from Shellharbour Airport

Three days earlier, on 23 October 2024, a ‘CPL task’ for the flight test and other instructions were sent by email from the examiner to the CPL candidate. The CPL task was a scenario that included instructions to plan and fly from Shellharbour Airport and land at Warnervale Airport flying via Macquarie Lighthouse for some aerial photography. The task then stipulated an onward flight from Warnervale Airport to land at Cessnock Airport, with a return leg to Shellharbour via the most direct track. A map recovered from the accident site showed a red path drawn upon it, consistent with the CPL task. This map indicated that the Cessnock to Shellharbour leg was planned via an inland route passing over Prospect Reservoir and Campbelltown.

A witness account indicated that, on 26 October 2024, the flight examiner and CPL candidate had planned to meet at a local bakery at around 0730 local time, prior to starting the ground component of the CPL flight test at Shellharbour Airport, at around 0800. National Airspace Information Planning System (NAIPS)[1] records indicated that the CPL candidate submitted a flight plan at about 1005. At 1018, a radio broadcast was recorded from APN on the Shellharbour Airport common traffic advisory frequency (CTAF),[2] indicating that APN was taxiing for runway 16 for a crosswind departure.

Flight data transmitted by the CPL candidate’s electronic flight bag (EFB)[3] device (APN flight data) indicated that at 1035, APN departed Shellharbour Airport, climbing to 1,500 ft above mean sea level.[4] At 1036, a radio call recorded on the CTAF stated that APN was departing crosswind and tracking north-east toward the sea cliff bridge, with the flight proceeding in this direction (Figure 1).

VH-APN flight along the coastline and diversion to Camden Airport

APN crossed the coastline near Wollongong beach, and subsequently descended to about 500 ft, following the coast toward Sydney and passing the sea cliff bridge at about 1047. At 1054, APN flight data showed the aircraft starting to track northbound along the visual flight rules route referred to as ‘Victor 1 South’ at about 500 ft (Figure 1). As APN approached Macquarie Lighthouse, flight data indicated that the aircraft tracked slightly further away from the coastline before conducting a large ‘S’ manoeuvre, consistent with the CPL aerial photography task planned prior to the flight. The flight continued tracking as planned until abeam Long Reef at 1106, APN started to track inland, consistent with a diversion from the planned route. The track followed published visual landmarks, intercepting and tracking in a south‑westerly direction toward Prospect Reservoir along the visual ‘lane of entry’[5] route for Bankstown Airport.

APN continued tracking in a south-westerly direction toward Bringelly township, an inbound reporting point for Camden Airport (Figure 1). At 1124, APN contacted Camden Tower air traffic control (ATC), requesting clearance for a touch-and-go and to conduct some circuits. ATC gave instructions to maintain 1,800 ft, join final for runway 24 and report when APN was 3 NM (5.6 km) from the runway threshold, with the aircraft starting to track toward this position. At 1128, APN reported being 2 NM (3.7 km) from runway 24, with Camden Tower ATC clearing APN for a visual approach. Shortly after, APN called ATC again requesting to remain at 1,800 ft for a practice glide approach to runway 24, which was approved.

At 1129, the APN flight data indicated that the aircraft had joined the crosswind leg for runway 24 at 1,800 ft, with APN being cleared for a visual approach by ATC about 1 minute later. APN descended and tracked consistent with a glide approach, with a clearance for a touch-and-go issued at 1131. The pilots of APN continued in 2-way communication with Camden Tower for another circuit, followed by a request for an upwind departure from runway 24, which was approved by ATC and acknowledged by APN. At 1141, APN touched down on runway 24 for the third time and started to climb to about 1,300 ft while maintaining the runway direction. Tracking data showed that APN continued in this direction and altitude, departing the Camden Airport control zone to the west just after 1143.

19-4079 planned flight and departure from The Oaks aerodrome

On the same morning, the pilot of 4079 was conducting a private flight departing from The Oaks. The purpose of the flight was a social event to travel to Cessnock Airport and meet with other pilots who were also flying from The Oaks. The flight was arranged using a group message that invited pilots to join. The message stated that the planned departure from The Oaks was between 1000 and 1030.

During the evening prior, a message was sent by the pilot of 4079 at 1954 confirming that they intended to join the group of pilots flying to Cessnock. The group consisted of 3 pilots, each with their own aircraft that comprised 2 Jabiru aircraft, 4079 and 55-1837 (the other Jabiru), and a Sonex Legacy aircraft registered 19-2041 (the Sonex). All 3 aircraft travelling to Cessnock in the group were registered with Recreational Aviation Australia. The 2 other pilots flying to Cessnock recalled that, prior to the flight, it was decided that the pilot of the Sonex, which was a faster aircraft, would wait about 10 minutes before departing so that all aircraft would arrive at Cessnock at about the same time. 

At 1124, around the same time that APN approached an inbound point for Camden Airport, video on board 4079 showed the aircraft rolling for take-off on runway 18 right (18R)[6] from The Oaks. The other Jabiru pilot recalled hearing a ‘rolling’ radio call from the pilot of 4079 around this time. Tracking data from the other Jabiru showed that this aircraft had departed about 30 seconds prior to 4079. At 1125, automatic dependent surveillance broadcast (ADS-B)[7] flight data showed 4079 on an initial climb from runway 18R. The flight data showed that the flight path was consistent with 4079 flying a right circuit for runway 18R or 18L and departing the aerodrome on the downwind leg in a northerly direction.

Figure 1: Flight paths of VH-APN, 19-4079 and accident location

Source: Google Earth and Geoscience Australia, annotated by the ATSB

19-4079 return to The Oaks aerodrome

At interview with the ATSB, the pilot of the other Jabiru flying to Cessnock reported that they decided to turn back due to experiencing turbulence. This pilot reported broadcasting that they were turning back to The Oaks on 2 frequencies, one corresponding to The Oaks CTAF (126.70) (The Oaks radio frequency) and another frequency that was pre-arranged for en route group chatter. Neither of the other pilots flying to Cessnock recalled hearing a broadcast from the pilot of 4079 in response. At 1133, the 4079 flight data showed that the aircraft started turning back towards The Oaks in a southerly direction. Due to the other Jabiru being further north, 4079 was ahead for the return to The Oaks.

During the return, the other Jabiru pilot recalled hearing the pilot of 4079 make a 7 NM (13.0 km) inbound call on The Oaks radio frequency. While inbound, this pilot also recalled hearing another call from an aircraft that was ‘really fuzzy’ and potentially related to another aerodrome. About 6 minutes after turning back, the flight data for 4079 showed that the aircraft had started a slow right turn to the west, and then tracked directly overhead The Oaks at about 1,800 ft. The other Jabiru pilot recalled hearing the pilot of 4079 broadcast that they were joining mid-field crosswind and observed the aircraft in that position. At this time, the other Jabiru pilot estimated that they were about 3 to 4 NM (5.6 to 7.4 km) behind 4079. At 1141, the ADS-B data showed 4079 crossing directly overhead The Oaks at about 1,900 ft before turning right and starting to descend.

The Sonex pilot reported hearing the pilot of 4079 broadcast that they were ‘established downwind for runway 18’. At 1142, the 4079 flight data and onboard video showed that the aircraft descended toward runway 18 left (18L). Around this time, the pilot of the other Jabiru recalled hearing the pilot of 4079 broadcast that they were on the base leg of the circuit. The track of 4079 was in a generally south‑easterly direction toward the threshold of runway 18L, however, instead of landing, the data showed the aircraft flying along the runway at about 100 ft.

Collision between VH-APN and 19-4079

At about 1143:30, shortly after APN departed the Camden Airport control zone, the onboard video and 4079 flight data indicated that the pilot of 4079 conducted a go‑around from runway 18L at The Oaks. The onboard video showed that the pilot of 4079 was transmitting a radio communication on The Oaks radio frequency. The Sonex pilot, who was in the run-up bay for runway 36, reported that they heard the pilot of 4079 transmit they were going around and observed 4079 from their position. Around this time, APN tracking data showed that this aircraft turned slightly right onto a track of 263° (true) while continuing to maintain about 1,250–1,350 ft.

At 1144:47, the tracking data for the other Jabiru showed this aircraft had turned right base, with a spacing of about 1.1 NM (2.0 km) north of the runway 18R threshold. Neither the Sonex or other Jabiru pilot reported hearing any radio transmissions from APN that morning. At 1145:16, the 4079 flight data showed this aircraft in a right climbing turn at about 1,700 ft, and mid-way through an ovalised crosswind leg of the circuit for runway 18L or 18R. Around this time, tracking data for APN indicated that this aircraft was about 1.1 NM (2.0 km) from the runway 18R threshold, continuing to track at 263° at 1,250 ft. At 1145:34, as 4079 continued the right climbing turn, APN tracking data showed that a level left turn was conducted onto a heading of 209°. Shortly after this turn was completed, at 1145:54, APN started a straight, steady climb from 1,350 ft (Figure 2).

At 1146:00, 4079 completed the right turn onto a northerly heading. At 1146:26, the onboard video and tracking data showed 4079 leveling out at 2,200 ft, about 1.5 NM (2.8 km) from runway 18R. After this time, APN and 4079 were on relatively constant flight path trajectories for about 8 seconds, with APN captured by the onboard video of 4079 in the lower right quadrant of the windscreen. 

The onboard video and tracking data showed that the aircraft collided at 1146:34 on near reciprocal headings. Following the midair collision, the left wings of both aircraft separated, with closed-circuit television footage from a nearby residence showing both aircraft descending steeply. Both aircraft were destroyed in the subsequent collisions with terrain. All 3 pilots were fatally injured. 

Figure 2: Flight paths and vertical profiles of VH-APN and 19-4079 prior to the accident

Source: Google Earth and Geoscience Australia, annotated by the ATSB

Context

Pilot information

CPL candidate

The CPL candidate in APN held a private pilot licence (aeroplane) issued in 2021 and was issued a multi-engine class rating in May 2024. As part of the pilot’s pre‑licence test preparation, the pilot reported having a total of 237 flight hours. The pilot held a class 1 aviation medical certificate, with no restrictions, valid until 19 March 2025. 

Flight test examiner

The flight test examiner in APN held an air transport pilot licence (aeroplane) issued in 1997 and a flight examiner rating for the commercial pilot licence (aeroplane). The examiner’s CASA record showed they had conducted a total of 868 flight examinations. Most of the examinations were multi‑engine instrument proficiency checks, with the first of these performed in June 2009. Notably, there were 14 examinations, for the issue of either commercial, private, or recreational flight crew licences. The examiner started conducting these tests in June 2018. Additionally, the examiner held a low-level rating (aeroplane) and low-level (aeroplane) training was included in their flight instructor rating.

On 16 May 2024, as part of their aviation medical examination, the pilot reported having a total of 25,214 flight hours. The pilot held a class 1 aviation medical certificate, with a requirement for reading correction to be available, valid until 16 November 2024. 

Pilot of 19-4079

The pilot of 19-4079 held a Recreational Aviation Australia (RAAus) pilot certificate,[8] with a cross‑country endorsement issued in June 2023, which also satisfied the requirements of a biennial flight review. On 4 April 2024, the pilot reported to RAAus having a total of 168 flight hours. The pilot had submitted a medical declaration to RAAus on 19 June 2022.[9]

Aircraft information

VH-APN

VH-APN (Figure 3) was a Cessna Aircraft Company 182P 4-seat, high‑wing (strut‑braced), single-engine aircraft equipped with a fixed tricycle landing gear. It had a Teledyne Continental Motors O-470 engine and was fitted with a McCauley 2-blade, constant‑speed propeller. APN was manufactured in the United States in 1976. It was placed on the Australian aircraft register that same year with a registration of VH‑RKC. The registration was changed to VH-APN in August 1996 and transferred to the current owner in 2021. 

APN was painted in a yellow (wings) and grey (fuselage) livery. The aircraft was fitted with a mode A/C transponder and 2 very high frequency transceiver radios. It was not fitted with ADS-B, nor was this required.

Figure 3: VH-APN

Source: Supplied

19-4079

19-4079 (Figure 4) was a Jabiru UL 450 amateur-built high-wing (strut-braced) light aircraft with a fixed tricycle landing gear. It had a Jabiru 2200J, 4-cylinder engine. Construction of 4079 was completed in 2004 and it was placed on the RAAus aircraft register on 23 February 2004. The registration was transferred to the current owner in 2022. 4079 was painted white. The aircraft was fitted with one very high frequency radio and a SkyEcho II portable ADS-B transceiver.[10] It was not fitted with a transponder, nor was this required. 

Figure 4: 19-4079

Source: Supplied

Meteorological information

The nearest available Bureau of Meteorology weather forecasts and observations to The Oaks was at Camden Airport.

At 1130, a routine report[11] of weather observations was issued for Camden Airport that reported light winds from a south-westerly direction (218° (magnetic) at 6 kt), with no cloud detected, visibility greater than 10 km, and the temperature was 18°C.

At 1154, following the accident, a special meteorological report[12] was published that showed light winds from the north-west (308° (magnetic) at 5 kt), visibility had reduced to 5 km in haze, no cloud was detected, and the temperature was 19°C.

The reported weather observations, which showed no cloud was detected, were consistent with the onboard video on 4079 (Figure 5). Additionally, at the time of the accident, the video did not show any notable reduction in visibility from any meteorological phenomena such as haze. Further, the Bureau of Meteorology weather observations at 1-minute intervals for Camden Airport showed that the visibility was greater than 10 km until shortly after the accident (at 1147) when it began slowly reducing.

The onboard video from 4079 also showed that, during the go-around on runway 18R at about 1143, the northern airport windsock was facing east indicating that there was minimal wind (Figure 5).

Figure 5: The Oaks windsock at 1143:28

Source: Airservices Australia and ATSB

Aerodrome and airspace information

The Oaks aerodrome

The Oaks aerodrome was a non-controlled aeroplane landing area,[13] located 7 NM (13 km) west‑south-west of Camden Airport. It had an elevation of 880 ft above mean sea level and 2 parallel grass runways aligned in a north-south direction. Runway 18R/36L was 900 m long, while runway 18L/36R was 800 m. All circuits were conducted to the west of the aerodrome to avoid overflying the township of The Oaks. The Oaks utilised the shared CTAF designated radio frequency of 126.7. 

An icon and label for The Oaks aerodrome was published on all visual aeronautical charts. Additionally, a caution label, surrounded by a red box adjacent to The Oaks on the visual terminal chart stated: 

CAUTION YOAS CCT ALTITUDE A019 RECOMMEND OVERFLY NOT BELOW A025

The caution label indicated to pilots that the potential circuit altitude for aircraft flying at The Oaks was up to 1,900 ft above mean sea level and recommended that they overfly the aerodrome above 2,500 ft.

Figure 6 is an extract of the visual terminal chart for Sydney showing the relative locations of The Oaks aerodrome and Camden Airport, and the caution placard.

Camden Airport

Camden Airport was a certified aerodrome with an elevation of 230 ft above mean sea level. The main runway, 24/06, was paved. Camden Tower had a part time control tower providing an air traffic control service in the surrounding class D airspace during operating hours. During the accident flight, the tower was active, with communications on the radio frequency 120.1. The class D airspace extended in a 2 NM (3.7 km) radius around the airport, represented by the blue dashed circle on Figure 6.

Figure 6: Extract of Sydney visual terminal chart dated 13 June 2024 showing The Oaks aerodrome and Camden Airport

Source: Airservices Australia, annotated by the ATSB

Airspace information

The accident flights were mostly conducted outside controlled airspace, designated as class G airspace. APN also operated in class D airspace while the aircraft was within 2 NM (3.7 km) of Camden Airport.

Airservices Australia’s Aeronautical Information Publication (AIP) ENR 1.6 – 7.1.4 required civil aircraft flying in class D airspace to set their transponder code to 3000. When operating in class G airspace, the AIP required pilots to set their transponder code to 1200.

The area extending beyond 2 NM (3.7 km) from Camden in the direction of The Oaks aerodrome was class G airspace below 4,500 ft above mean sea level.[14]

After leaving controlled airspace, such as when APN departed Camden class D airspace, pilots need to decide what radio frequencies will be required for future transmissions and what frequencies they should maintain a listening watch on. One of the frequencies in the area between Camden and The Oaks was the Sydney Centre area very high frequency, 124.55. This frequency was used by Airservices Australia to provide air traffic services. Additionally, pilots may broadcast their intentions on this frequency to assist with maintaining traffic separation.

Recorded information

Data sources

Neither aircraft was equipped with a flight data recorder or cockpit voice recorder, nor were they required to be. Broadcasts made on The Oaks CTAF were not recorded. The following data sources have been used for this investigation:

• ADS-B data from 4079
• ATC audio data for APN
• CTAF audio data from Shellharbour Airport for APN
• closed-circuit television footage from a nearby residence showing post‑collision dynamics
• data transmitted/recorded from devices running electronic flight bag applications for APN, 4079 and 55-1837
• transponder data for APN.

Transponder data

Transponder data for APN showed that the code was changed from 1200 to 3000 when the aircraft was approaching the Camden class D control zone. The transponder code continued to transmit on code 3000 until the collision.

19-4079 onboard video camera

4079 was fitted with an onboard video camera that was attached to a roof panel inside the cabin. The ATSB recovered the camera at the accident site, which was downloaded at the ATSB’s technical facility in Canberra. Initial observations from the video included:

• the aircraft had no evident technical problems during the flight
• the radio was selected to the frequency 126.7 at the time of the accident
• lights on the radio, along with the push-to-talk button on the control yoke, indicated the pilot was transmitting and receiving radio calls during the flight
• 4079 and APN were both on relatively constant trajectories, with 4079 being straight and level and APN climbing at the time of the collision, with no avoiding action evident by either pilot
• the aircraft were travelling on a generally reciprocal heading, impacting on the left side of each aircraft, with the fuselage of 4079 passing underneath the left wing of APN. 

Wreckage and impact information

Wreckage location

The accident site was located about 2.7 km west of The Oaks aerodrome in heavily treed terrain. The 2 primary wreckage locations were approximately 520 m apart, with 4079 north of APN (018^º true) (Figure 7). A debris field was located about halfway between the 2 main wreckage locations. Most wreckage items found in the central area were from the left wing of 4079, with a small number of components from APN. Most of the central wreckage was found within a radius of about 50 m.

Figure 7: Accident site location in relation to The Oaks

Source: Google Earth, annotated by the ATSB

Orientation of 19-4079 and VH-APN during the collision

Yellow paint was found on portions of the left wing and left-wing strut of 4079, consistent with being transferred from APN. These areas of the left wing of 4079 also showed signs of leading‑edge penetration to about halfway through the wing chord, at about the mid‑span position.

The left-wing strut of APN was found near the main wreckage of APN, consistent with being attached to this aircraft at the time of the collision with terrain. White paint was found in 2 places of this strut, with leading edge damage observed in these areas, consistent with being transferred from the left wing and left-wing strut of 4079.

A relatively small dent with light‑coloured paint transfer was located on the leading edge of APN’s left wing, with a longitudinal light-coloured paint transfer on the underside of the wing around this location. The relative orientation of the frontal left wing and left-wing strut damage on 4079 and left-wing strut damage on APN, was consistent with 4079 being upright during the collision. Based on the geometry of 4079, the coloured paint transfer on the underside of the left wing of APN was likely from the upper vertical fin section of 4079. The fin likely separated from the aircraft after being struck by the left wing of APN in the location of the light-coloured paint. The upper vertical fin section of 4079 was not located.

In summary, the paint transfer marks, and damage observed on site was consistent with APN and 4079 colliding on the left sides of each other on near reciprocal headings. The left wing and left-wing strut of 4079 primarily impacted the left strut of APN, and the upper fin of 4079 subsequently striking the left-wing leading edge of APN.

19-4079 wreckage

Examination of the main wreckage site and surrounding broken tree branches for 4079 indicated that the aircraft had impacted the ground at a steep angle, with little forward movement, resulting in a localised wreckage field. The ATSB inspection found no evidence of pre-accident flight control damage. 

All of the aircraft was accounted for, excluding a section of the outboard left wing, and the upper vertical fin. An aileron fitting for 4079 was co-located with the left wing of APN.

VH-APN wreckage

Witness marks in surrounding trees showed that APN impacted terrain in a steep nose down attitude. There was a significant post-impact fire at the primary wreckage site, which limited the ATSB’s ability to examine the wreckage. The inspection of the available evidence did not identify any pre-accident flight control damage. The left wing of APN was located about 50 m from the main wreckage, consistent with this wing separating in‑flight during the accident sequence.

Operations around non-controlled aerodromes

See-and-avoid principles

The Oaks was a non-controlled aerodrome, where separation was maintained by ‘alerted see‑and-avoid’ principles guided by CASA advisory circulars AC 91‑10 Operations in the vicinity of non-controlled aerodromes and AC 91-14 Pilots’ responsibility for collision avoidance. These stated that pilots should broadcast position and intention information so that nearby traffic would have an awareness of the aircraft and be able to plan accordingly.

AC 91-14 also highlighted the ineffectiveness of pilots relying solely on visually detecting other aircraft that are on a conflicting flight path, referred to as ‘unalerted see-and-avoid’. It noted increased traffic density as one of the factors increasing the risk of collision, necessitating a pilot using ‘alerted see-and-avoid’ principles. Airspace in the vicinity of non-controlled aerodromes has a higher traffic density. The primary tool of alerted see‑and-avoid is radio communications that enhance pilot situational awareness.

Operations in the vicinity of non-controlled aerodromes

The AIP provided guidance for pilots flying in the vicinity of non-controlled aerodromes. The vicinity of non-controlled aerodromes was defined as a distance of 10 NM (19 km) horizontally and within a height above the aerodrome that could potentially result in conflict. It recommended that aircraft transiting in the vicinity should avoid flying over the aerodrome at an altitude that could result in conflict with operations, including the circuit area and the arrival and departure tracks.

Additionally, the CASA Civil Aviation Advisory Publication (CAAP) 166(3) outlined hazardous zones for operations near non-controlled aerodromes, including:

- The most hazardous area for collisions is within a space bounded by a cylinder of airspace 5 NM [9 km] in diameter and up to 3,000 ft above aerodrome elevation.

- Most collisions occur on downwind or on final approach. There are many distractions during this time, including configuring the aircraft, completing checklists, setting equipment and communicating...

When APN departed Camden controlled airspace, it was approximately 5 NM (9 km) from The Oaks aerodrome, already within the vicinity of the aerodrome and within the recommended 10 NM (19 km) inbound broadcast location.

Circuit pattern

A circuit is an established procedure for arriving and departing aerodromes. They assist pilots with configuring and positioning the aircraft to make a stabilised approach to the runway in use. A circuit when flown in its entirety includes upwind, crosswind, downwind, base, and final legs. When arriving and departing a non-controlled aerodrome, CASA recommended pilots join the circuit area via the methods highlighted in blue in Figure 8.

The key recommended methods to join the circuit depicted (Figure 8):

• Overflying the aerodrome more than 500 ft above the circuit height before descending on the side not being used and joining the circuit over the middle of the runway (midfield crosswind).
• Joining the circuit at circuit height on the downwind leg (including joining at 45° in the middle of the downwind leg).

CASA did not recommend joining the circuit on base or a 3 NM (5.6 km) straight in approach.

Figure 8: Circuit join methods with recommended circuit joins highlighted in blue

Source: Civil Aviation Safety Authority 

Circuit procedures are well established, and pilots learn the circuit terminology during their early training. This allows them to know where to look when they hear a broadcast, which includes a certain leg of the circuit. Pilots should broadcast their position and intentions on the local radio frequency to assist other pilots with alerted searching.[15] Additionally, pilots can use the ‘look, talk, and turn’ strategy, which involves the pilot checking for traffic, making the broadcast and then carrying out the turn (AC 91-10). Other pilots in the area will hear the broadcast, know where to look, and will have an increased chance of visually acquiring the aircraft while it has the most surface area visible during a turn.

The CASA CAAP 166-2 Pilots’ responsibility for collision avoidance in the vicinity of non‑controlled aerodromes noted that variations in the recommended circuit join may increase the risk of collision. Additionally, climbing and descending in the circuit area was not recommended as visual acquisition of traffic could be difficult: 

An aircraft (a small one in particular) will often be rendered difficult to see by the patterns in the surface of the earth when viewed from above, and particularly when over urban areas. Conversely, an aircraft when viewed from below can potentially be much more easily seen against a uniformly overcast cloud background or blue sky. All pilots would be aware of the difficulty seeing aircraft that have the sun directly behind them.

Circuit area

The size of a circuit area was not explicitly defined in Australian legislative instruments, procedures or guidance. However, various technical publications refer to distances from and heights above runways in certain operational circumstances. The Airservices Australia AIP stated that aircraft would normally be outside the circuit area when at least 3 NM (5.6 km) from the departure end of the runway, while the United States Federal Aviation Administration’s Airplane Flying Handbook defined the downwind leg of the circuit as a track approximately 1 NM (1.9 km) parallel to the intended landing runway. 

Designated airspace in aeronautical charts showed airports with air traffic control towers had airspace reserved (control zones), to be used only by aircraft operating within the circuit. For Camden Airport, the control zone extended 2 NM (3.7 km) from the aerodrome reference point,[16] and is shown by the dashed-blue circle in Figure 6. In many other cases, control zones extended up to 3 NM (5.6 km) from the reference point.

The FAA’s Airplane Flying Handbook stated that, for a typical piston aircraft, a standard final approach would result in a 3° approach angle. Additionally, CASA required aircraft to be established on the final leg, no lower than 500 ft above ground level. To achieve a 3° approach angle, the aircraft would need to be positioned at 500 ft at approximately 1.5 NM (2.8 km) from the runway threshold. However, the AIP stated:

9.2.5 Pilots may vary the size of the circuit depending on:

(a) the performance of the aircraft;

(b) safety reasons; or

(c) in accordance with the Aircraft Flight Manual, Pilot’s Operating Handbook, or company Standard Operating Procedures.

The height at which the circuit legs are flown is dependent on aircraft performance. The AIP section 9.6.1 stated for medium performance aircraft, like APN and 4079, the standard circuit height was 1,000 ft above the aerodrome elevation. At The Oaks, this equated to 1,900 ft above mean sea level. As noted in the section ‘Circuit pattern’ above, aircraft may be joining the circuit at a height at least 500 ft above the circuit height. In this case, at The Oaks up to 2,400 ft above mean sea level. This is also highlighted in the caution label on the visual terminal chart for The Oaks (Figure 6), with a recommended minimum overfly height of 2,500 ft above mean sea level.

Based on this, the area where medium performance aircraft could be expected in The Oaks circuit ranged from overhead to a distance up to 3 NM (5.7 km) from the runway, and up to at least 1,500 ft above the aerodrome or 2,400 ft above mean sea level.

Circuit direction

A circuit is typically conducted to the left side of the runway in use and involves the aircraft making left turns (Figure 8), which assists the pilot who is normally sitting in the left seat to keep the runway in sight. However, some aerodromes such as The Oaks runway 18L and 18R had local procedures that required pilots to fly circuits to the right side of the runway in use and make right turns. Aerodromes where right circuits were required are listed in the En Route Supplement Australia.[17]

At non-controlled aerodromes, the runway in use was determined by pilots using the aerodrome. The runway selected should be the runway that was most closely aligned into wind and was serviceable. Pilots wishing to use a different runway for operational reasons were required to do so without conflicting with other aircraft using the most into wind runway.

At the time of the accident, the windsock at The Oaks was facing east and indicating minimal wind, so the wind direction did not favour any particular runway. Runways 18L and 18R were being used by 4079 and the other Jabiru.

Radio communications

Aircraft operating in the vicinity of a non-controlled aerodrome were required to make broadcasts on the aerodrome frequency whenever reasonably necessary to do so to avoid a collision (AIP 9.1.4). On receiving a broadcast of a potential conflict, a pilot was required to respond by transmitting their own callsign and, as appropriate, aircraft type, position, actual level and intentions. Additionally, when making a standard broadcast pilots should also address the station (location) being called.

While CASA did not require any additional broadcasts, the AIP did recommend pilots make broadcasts as detailed in Table 1.

Table 1: Recommended broadcasts at non-controlled aerodromes

Proximity between APN and the other Jabiru

APN tracked from Camden in a westerly direction towards The Oaks and entered the circuit area of The Oaks at low level. At the time there were 2 aircraft conducting circuits to land, 4079 and the other Jabiru (55-1837). 

At 1143:07, the other Jabiru passed overhead runway 18L, entering the circuit area at about 1,900 ft. At 1145:00, the other Jabiru had completed a right turn onto the base leg for runway 18R and was descending through about 1,800 ft to land, heading in an easterly direction. At the same time, tracking data showed APN at about 1,350 ft and tracking in a westerly direction, on a near-reciprocal heading to the other Jabiru. At 1145:17, tracking data indicated the other Jabiru passed 375 m in front of and about 400 ft above APN. The position of each aircraft at that time is shown in Figure 9.

The pilot of the other Jabiru stated they did not see APN nor were they aware APN was in the area until after the collision with 4079.

Figure 9: Flight tracks of VH-APN and the other Jabiru (55-1837)

Source: Google Earth and ATSB

Radio communications

Radio communications from several sources were evaluated and combined to produce a detailed timeline. These included witness statements, the onboard video recording from 19-4079, flight tracking data, and available CTAF and ATC recordings. This section reviews the recorded data and interview recollections relating to radio communications by the pilots of APN, 4079, the other Jabiru and the Sonex during the accident flights.

The purpose of this section is to provide context about the effectiveness of radio communications between each aircraft involved.

Overview of radio communications during flight of 19-4079

The ATSB evaluated the recollections of the other Jabiru and Sonex pilots who were operating in the vicinity of The Oaks during the flight of 4079. The accounts were largely consistent, although there were some differences in recollection of radio call sequences. For some parts of the flight, each pilot remembered different aspects, which is considered normal. Where there were discrepancies, these were considered in relation to each other and the recorded data to determine the likely order and content of transmissions.

The onboard video showed transmissions being made and received by 4079 throughout the flight on The Oaks radio frequency (CTAF) and the pre-arranged group chatter frequency. Both pilot witnesses reported hearing radio calls from the pilot of 4079 throughout the flight. The method to identify the type, frequency, time and duration of these transmissions is documented in Appendix – Radio transmissions captured by 19‑4079.

The flight track of 4079 was synchronised with the radio transmission data from the onboard video, and this is shown in (Figure 10). The red coloured parts of the track show the position of 4079 when the pilot was transmitting and the green shows the locations of 4079 when receiving radio calls. The grey parts of the track show the locations when no radio transmissions were made or received by 4079. For context, Figure 10 also contains labels for key parts of the flight for 4079 that are cross-referenced in figures for orientation and discussed in the text below.

Figure 10: Flight track showing the position of 19-4079 when no transmission was detected (grey lines), and when radio calls were transmitted (red lines) and received (green lines) by 19-4079 during the accident flight

Source: Google Earth and ATSB

19-4079 departure and return to The Oaks aerodrome

Turn back call

When the decision was made to return to The Oaks, the other Jabiru pilot reported broadcasting this intention on both the CTAF and group chatter frequency. However, neither the other Jabiru or Sonex pilots heard a response, or a similar call from the pilot of 4079. As such, the ATSB evaluated the most plausible reason why both pilot witnesses did not hear the pilot of 4079 respond to the other Jabiru pilot’s decision to turn back. 

The evaluation of the video evidence showed the pilot of 4079 receiving a call on the CTAF frequency, which was likely the turn back discussion. After this, the pilot of 4079 broadcast a transmission on the group chatter frequency, which may not have been monitored by the other pilots at that time. The timing of this transmission also aligned with the turn back of 4079, as shown by the recorded data.

Inbound call

The onboard video and tracking data showed that the pilot of 4079 made a transmission when 7 NM (13 km) from The Oaks on the CTAF. This was consistent with the recollection of the other Jabiru pilot who recalled hearing 4079 make an inbound call on The Oaks frequency.

Unintelligible call

When they were about 3–4 NM (5.6–7.4 km) from The Oaks, the other Jabiru pilot reported hearing a ‘really fuzzy’ radio call on CTAF. This transmission was correlated on the video recording with a 10.6 second radio transmission that was received by 4079 on the CTAF. At the same time as this transmission, flight data indicated APN was on the base leg of a touch-and-go at Camden Airport. As APN would have been on the Camden Airport frequency, the fuzzy call on the CTAF was not likely to be APN.

Communications on The Oaks frequency prior to the collision

While the likely content of each transmission was evaluated for the entire flight of 4079, a particular focus was during the period from 4079 joining the circuit for runway 18L or runway 18R on a mid-field crosswind leg until the collision with APN. The results of this evaluation are detailed in Table 2, Figure 11, Figure 12 and Figure 13. 

Table 2 details the time and duration of all radio transmissions received by 4079 based on the examination of the video, with the reference numbers correlating with reference numbers in Table A2 of the Appendix. The likely information communicated by each pilot on The Oaks frequency were estimated based on the combined analysis of the onboard video, tracking data and accounts from the 2 witness pilots. The results of this evaluation, including the relevant aircraft location are shown in the 2 right-most columns of Table 2.

The tracks of each aircraft in the circuit area of The Oaks with radio transmissions overlaid are shown in Figure 11 for 4079, Figure 12 for the other Jabiru and Figure 13 shows APN in proximity to the other Jabiru. These figures show the same type of information as Table 2, with colours of the tracks corresponding to transmissions by the pilot of 4079 in red, transmissions received in green, and no transmissions on frequency in grey. Transmissions are numbered sequentially in the direction of flight and correspond to rows in Table 2 and Table A2 of Appendix A. All transmissions during this phase of flight were on The Oaks frequency.

Table 2: Timing and duration of radio transmissions longer than 0.1 seconds, sent and received by the radio fitted to 19-4079 from when 19-4079 tracked west for a mid-field crosswind circuit join, combined with the likely content of transmissions

Figure 11: Flight track showing the position of 19-4079 with no transmission was detected (grey lines), and when radio calls were transmitted (red lines) and received (green lines) by 19-4079 after returning to The Oaks to the collision

Source: Google Earth and ATSB

Figure 12: Flight track of the other Jabiru, showing positions with no transmissions detected (grey lines), and when signals were transmitted (red lines) and received (green lines) by 19-4079 after returning to The Oaks to the collision

Source: Google Earth and ATSB

Figure 13: Flight tracks of VH-APN and the other Jabiru, showing where no transmissions were detected (grey lines), and when signals were transmitted (red lines) and received (green lines) by 19-4079 after returning to The Oaks to the collision

Source: Google Earth and ATSB

Evaluation of radio calls after go-around of 4079

As 4079 was on the upwind and crosswind legs, 3 groups of transmissions occurred, with references 56–59, 60–64 and 65 in Table 2 and Table A2, and aircraft positions circled in Figure 11, Figure 12 and Figure 13. Around this time, the 2 pilot witnesses both recalled 3 communications exchanges, specifically:

• an exchange between the pilot of 4079 and the Sonex pilot about changing the runway direction
• a base turn call by the pilot of the other Jabiru
• an exchange between the Sonex pilot and the other Jabiru pilot about the separation between 4079 and the other Jabiru.

As these communications occurred shortly prior to the collision, each of the 3 recalled communications exchanges, and radio calls until the final transmission by the other Jabiru pilot are discussed below.

Broadcasts about changing the runway

At 1144:04, the 4079 flight data indicated that the aircraft had passed the end of the runway and was climbing following the go-around. Five seconds later, a short 2.3 second radio call was broadcast by the pilot of 4079, followed by a 13.3 second broadcast received and another 1.8 second transmission by the pilot of 4079, with about 2‑second gaps in between transmissions (Figure 11 and Table 2 references 56-58). This was consistent with the Sonex pilot reporting that, as 4079 turned onto the crosswind leg of the circuit for runway 18R, the pilot of 4079 called them on the radio asking if it would be okay to land on runway 36. The Sonex pilot recalled broadcasting that the very light wind would allow runway 36 to be used, but that others (specifically the other Jabiru pilot) were using runway 18. The Sonex pilot noted that this was their last interaction with the pilot of 4079.

Broadcast as the other Jabiru turned onto base

At 1144:33, flight tracking data showed that the other Jabiru had just started to turn onto the base leg for runway 18R. The Sonex pilot recalled that, immediately after the previous radio exchange with the pilot of 4079, the other Jabiru pilot broadcast that they were on base for a full stop landing on runway 18R. This account aligned with the onboard video, which showed a 4.4 second radio call made at this time (Table 2, Table A2 and Figure 12 reference 59),[19] which was about one second after the broadcast by the pilot of 4079, likely regarding a potential runway change (Table 2 reference 58) . 

The pilot of the other Jabiru recalled that their call on base was prior to the discussion about changing runway, but noted that they were not ‘really paying attention’ due to them being confident that no conflict existed between them and 4079. However, flight tracking data showed that the other Jabiru was still on the downwind circuit leg during the first 3 calls in this group (references 56–58 in Figure 12). Additionally, the pilot of 4079 made the first transmission in this group (reference 56 in Table 2), very likely about the runway change. Therefore, based on the factors discussed, it was considered more likely that the base call by the other Jabiru pilot occurred after both transmissions from the pilot of 4079.

Broadcasts about separation between 19-4079 and the other Jabiru

At 1144:44, about 5 seconds after a previous transmission, another 5 radio calls were received on The Oaks frequency over the next 30 seconds, with 2 radio calls being about 8 seconds long and 3 under 2.5 seconds (Table 2 references 60-64). During this time, flight tracking data showed that 4079 was on an ovalised crosswind leg (Figure 11 references 60-64), and the other Jabiru was on the base leg (Figure 12 references 60‑64), both for runway 18L or runway 18R. 

The flight tracking and radio transmission data was consistent with the account of the Sonex pilot who reported that, after the base call by the other Jabiru pilot, they responded over the radio saying that they still had 4079 in sight and that the other Jabiru pilot would be safe to land. The Sonex pilot recalled the last time they saw 4079 was climbing to the west as 4079 was on the crosswind leg.

The other Jabiru pilot also recalled the Sonex pilot broadcasting that they could see both the other Jabiru and 4079 and that they were well separated. In contrast, the other Jabiru pilot recalled this communication occurring when they were on short final. Based on the available evidence, it was considered more likely that the exchange over the radio between the Sonex pilot and the other Jabiru were communications with reference 60–64 as listed in Table 2. This was as the other Jabiru was on the base leg (Figure 12) and 4079 was still in sight of the Sonex pilot on the crosswind leg (Figure 11).

The other Jabiru turns onto final approach

Although not mentioned explicitly during interview, the other Jabiru pilot stated that at The Oaks, they mainly only make base and final calls, indicating that these calls were normally performed. This was consistent with a transmission received by 4079 as the other Jabiru started to turn onto final (Figure 12 and Table 2 reference 65).

Communication between 4079 and the other Jabiru on short final

The onboard video showed the pilot of 4079 looking outside forward and to the right while transmitting over the flight radio on The Oaks frequency (Table 2 reference 66). The pilot of the other Jabiru recalled that the pilot of 4079 broadcast that they had lost sight of the other Jabiru. Tracking data showed that the other Jabiru was close to the threshold of runway 18 and 4079 was in the mid-downwind position at this time, with the pilot recalling that they responded via radio to say that they were on short final (for runway 18) (Table 2 reference 67). The relative positions of 4079 and the other Jabiru during these radio calls (references 66 and 67) are shown in Figure 10 and Figure 11. Following this exchange, the pilot of 4079 tapped the broadcast button twice (less than 0.1 seconds), consistent with acknowledging the transmission by the other Jabiru pilot. This was the last radio communication captured by the onboard video.

Breaks in transmissions

Broadcasts on The Oaks frequency after APN departed from Camden were arranged in groups of calls when there was less than 3 seconds between transmissions. The purpose was to characterise notable periods without transmissions where there may have been an opportunity for radio calls to be made by other aircraft if they were on the CTAF. The results of this grouping are shown in Table 3.

There were 2 notable periods of more than 40 seconds where there were no recorded transmissions:

• Between the transmission coinciding with the go-around of 4079 and the subsequent transmission, starting at 1143:25.1 and shown by the grey track between references 55 and 56 in Figure 11, Figure 12 and Figure 13.
• Following a transmission coinciding with the other Jabiru turning onto final approach until the final transmission by 4079 when on mid-downwind (between references 65 and 66 in Figure 11, Figure 12 and Figure 13).

Table 3: Broadcast and non-broadcast periods captured by the onboard video on 4079 radio on The Oaks frequency between APN departing Camden airspace until the collision

Radio communication information for VH-APN

This section examines recorded radio calls broadcast by APN from the initial contact with Camden Tower through to the collision. A total of 14 calls were recorded on the radio frequency for Camden Tower (120.10). No calls by APN were recorded after the aircraft departed Camden airspace on the Sydney area frequency (124.55), noting that transmissions were not recorded on The Oaks CTAF.

The last recorded transmission for APN occurred at 1138.36 with APN reading back the clearance for a touch-and-go on runway 24 for an upwind departure from Camden Airport.

The ATSB performed a qualitative assessment of the radio transmissions recorded for APN during the accident flight. The assessment was based on the ‘Plain-Language Radio Check Procedure Words’ (prowords) described in ACP 125(G).[20] An ATSB evaluation of the recorded radio transmissions made by APN indicated the signal strength was between good and loud and the signal readability was between readable and clear. This equated to a minimum score of 4 out of 5 on the assessment scales, with every recorded message able to be determined.

The ATSB also assessed the approximate range of APN from ground-based recording stations. The largest distance between APN and a ground-based station was at 1124:42, as APN approached Camden Airport. In the following 30 seconds, APN was transmitting and receiving radio calls to and from Camden Tower. The distance between APN and Camden Tower during this time was between 6 NM (11.1 km) and 7 NM (13.0 km). For these radio calls, the time between APN receiving a message from Camden Tower and responding was less than 1 second, with the readback of all instructions being accurate and correct. Therefore, from the available evidence, the radio fitted to APN was likely to be operational leading up to the accident.

Terrain shielding considerations

The ATSB examined the potential for high terrain to prevent radio signals being transmitted between 4079 and APN. A key time identified was during the go-around, when 4079 was about 100 ft above runway 18L, at a similar height to elevated terrain to the east and toward APN. At that time, there was very likely a direct line of sight between 4079 and APN. At all other times, 4079 was higher, meaning that there was clear line of sight between 4079 and APN until the collision.

The maximum distance between APN and 4079 after APN departed Camden airspace was about 4.5 NM (8.3 km) as APN departed Camden Airspace. This distance remained between 3 NM (5.6 km) and 4 NM (7.4 km) as APN approached The Oaks and 4079 was on the crosswind legs, before reducing to the collision. Therefore, based on the evidence available, it was considered likely that any transmission by APN on The Oaks frequency would have been detected by 4079 and have been visible in the onboard video.

During the same time, the other Jabiru and APN were also within line of sight. The other Jabiru was above the height of the surrounding terrain until on final approach, when APN had started to climb after remaining at about 1,250 ft above mean sea level since departing Camden. The distance between APN and the other Jabiru after transmission 56 by the pilot of 4079 and until the collision was less than 3.5 NM (6.5 km).

The ATSB identified that terrain shielding was possible between the Sonex and APN after APN departed Camden airspace. A notable period for potential shielding was around the time that APN turned left and started to climb, after radio call with reference 65 (Figure 13 and Table 2). The line of sight between the Sonex and APN has not been fully assessed. However, at the time of the radio calls with reference 60–64 (Figure 13 and Table 2), APN was likely in line of sight of the Sonex.

In conclusion, 4079 and the other Jabiru were likely within line of sight and range of APN for the entire period after APN departed Camden.

Safety action

Safety action by the owner of VH-APN

The owner of VH-APN reported that they have equipped one of their aircraft with an ADS-B transceiver. They also have plans to install 2 further ADS-B out units on 2 of their 3 other aircraft.

Further investigation

To date, the ATSB has:

• examined the wreckage
• examined aircraft components and other items recovered from the accident site
• collected surveillance data from Airservices Australia
• collected OzRunways data for relevant aircraft
• collected pilot and aircraft records
• conducted interviews with relevant parties
• conducted detailed analysis of video recordings and radio transmissions
• reviewed aircraft, pilot, aerodrome and operator documentation
• conducted detailed analysis of the aircraft flight paths
• reviewed procedures at non-controlled aerodromes
• liaised with the NSW Police Force.

The investigation is continuing and will include, further:

• analysis of video recordings
• review of similar occurrences
• review of previous flight tests conducted by the flight test examiner
• review of procedures and practices relating to the conduct of flight tests
• review of communication, electronic conspicuity and surveillance equipment, and interviews with relevant parties.

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.

Appendix – Radio transmissions captured by 19‑4079

Overview

The ATSB performed measurements of the timing of radio transmissions sent and received by 19‑4079 during the accident flight. The measurements were performed using the onboard video fitted to 19-4079 that showed the 3 different states, based on a light fitted to the radio, where:

• a red light indicated transmissions were being sent by the pilot of 4079
• a green light indicated transmissions were being received by 4079
• no light indicated that no transmission was being received on the selected frequency.

An example of screen captures from the onboard video for these 3 states is shown in Figure A1.

Figure A1: Screen captures of the radio fitted to 19-4079 during send (red light), receive (green light) and no transmissions (no light)

Source: ATSB

The ATSB also recorded the frequency that was selected against each transmission and the timing of any frequency changes that occurred during the flight. The radio instrument fitted to 4079 is shown in Figure A2, with an exemplar image showing the active (upper) and standby (lower) frequency that can be toggled by the user.

Figure A2: Radio instrument model fitted to 19-4079

Source: ATSB (left) and Microair Avionics Pty Ltd (right)

Methods

Frame measurements

The ‘Syntheyes’ computer program[21] was used to identify the exact frame the light turned on and turned off, which was tabulated. The identified frames were converted to an elapsed time for the associated video using the video frame rate (29.97).

Frequency changes

The times when frequency changes were selected by the pilot were identified. This was achieved through the frequency change dial on the instrument or the frequency flip button on the control yolk. The frequencies identified are shown under the ‘Frequency’ columns of Table A1 and Table A2. Legible frames in these intervals were identified.

Synchronisation of onboard video with UTC[22] time

The onboard video on 4079 also showed a tablet fitted to the left side of the aircraft dashboard. An application being used by the pilot (OzRunways) showed the UTC time to the nearest minute (hh:mm) in the top information panel. Time was corrected to the nearest second using the frames in the video when the minute changes occurred.

The tablet was intermittently visible in the video due to the pilot covering it in frame. However, there were 2 instances where a change in minute occurred on the tablet that was captured between video frames on the onboard video. The elapsed time between these 2 instances was less than 0.2 seconds, indicating that the elapsed time in the onboard video and the tablet were in close agreement. The time recorded by the tablet was synchronised with the flight data at the time of collision. The video creation time was also examined, however, it was not in agreement with the flight data or the time shown on the tablet and was not used for further analysis.

Radio transmissions to and from 19-4079

Results from the measurements of the time and duration of radio calls sent and received by 19-4079 are shown for the accident flight between take-off up to the point where 4079 returned to The Oaks (Table A1), and from the return to the accident (Table A2). Measurements shorter than one-tenth of a second (0.1 seconds) were excluded. The reference number included was used in the main body of this report, with the frequency and transmission type (receive or transmit) recorded for each. The reported time was at the start of each transmission.

Table A1: Timing and duration of radio transmissions longer than 0.1 seconds, sent and received by the radio fitted to 19-4079 during the accident flight, from start of the flight to the return to The Oaks 

Table A2: Timing and duration of radio transmissions longer than 0.1 seconds, sent and received by the radio fitted to 19-4079 during the accident flight, after the return to The Oaks to the accident

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