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.

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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.

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