Incorrect configuration

Investigation summary

What happened

At 1851 local time on 24 July 2025, the crew of an Alliance Airlines Embraer ERJ 190, registered VH‑A2T, departed Cairns, Queensland, for a passenger transport flight to Brisbane. For the departure, the crew took off from runway 15 with a clearance to follow the AKROM 1 standard instrument departure (SID). 

As the aircraft became airborne in darkness, the captain, acting as pilot monitoring, announced ‘pitch rate’ to alert the first officer, who was pilot flying, that the aircraft’s rotation had slowed. Both crewmembers then focused on the aircraft flight path, and the retraction of the landing gear was inadvertently omitted.

As the aircraft continued climbing and turning left to follow the SID, the flight crew received 2 radio altimeter annunciations and observed the flight director unexpectedly command a right turn. After completing the left turn to follow the SID, the first officer engaged the autopilot, and the aircraft started a right turn toward terrain. The captain identified the turn and instructed the first officer to turn left back to the required track.

As the aircraft then continued along the SID, the captain recognised that the landing gear was still extended and quickly retracted it. The landing gear completed retracting when the aircraft had reached a speed of 252 kt, 17 kt above the maximum landing gear retraction speed.

The flight continued and the aircraft landed at Brisbane without further incident at 2044. Following the flight, the aircraft was inspected and found to be undamaged.

What the ATSB found

The ATSB found that the 'pitch rate' announcement was made at a time when a ‘positive rate’ announcement would normally be expected. This resulted in both flight crewmembers focusing on the pitch angle and the first officer was not prompted to call for landing gear retraction.

As the aircraft turned left to follow the SID, the crew were presented with radio altimeter alerts and unexpected flight director indications. These distractions increased the flight crew's workload and delayed their identification of the extended landing gear. Upon recognising the still extended landing gear, the captain reflexively retracted it without first checking the aircraft speed.

What has been done as a result

Alliance Airlines accelerated its program to upgrade E190 aircraft from load 25 avionics to load 27 and at the time of the release of this report, all E190s in the Alliance Airlines fleet have been upgraded. This should prevent recurrence of the unexpected flight management system indications presented to the crew during this incident.

In addition, the load 27 avionics upgrade incorporated electronic checklists that require associated actions to be undertaken before the electronic checklist is completed. 

Safety message

This incident highlights the impact a combination of omitted actions and distractions can have on aircraft operations, during what is often a high workload period. Such situations can create challenges in responding to the unexpected with potential for a reduction in safety when pilots act rapidly and reflexively. In these situations, pilots may not be able to effectively process information or consider all relevant factors, which reduces the ability to make good decisions. 

Crews of Embraer ERJ 190 aircraft equipped with load 25 avionics should also be aware that, on occasion, these systems may provide unexpected indications. This has been observed on multiple occasions on the Cairns AKROM 1 SID. When faced with unexpected indications, crews should use primary instruments to ensure that flight path requirements are adhered to.

The investigation

The occurrence

On the evening of 24 July 2025, the crew of an Alliance Airlines Embraer ERJ 190, registered VH‑A2T, prepared to operate a passenger transport flight from Cairns to Brisbane, Queensland. For the flight, the captain acted as pilot monitoring (PM), and the first officer as pilot flying (PF).[1] For the departure, the crew were provided with clearance to follow the AKROM 1 standard instrument departure (SID) (see the section titled Cairns runway 15 AKROM 1 standard instrument departure). While preparing for the flight, the captain advised the first officer that on previous flights, the first officer’s rotation[2] rate was slower than required and, as adherence to the SID climb requirements was essential for terrain avoidance, the rotation rate would be a point of focus for the departure.

In darkness at 1851 local time, the aircraft commenced a take-off from runway 15 with the lateral navigation flight guidance mode selected. After passing the rotation speed of 143 kt, the first officer commenced the rotation to the target pitch attitude of about 15° nose up. The aircraft became airborne, and the captain assessed that as the aircraft passed 10° pitch angle, the rotation rate slowed. To alert the first officer, the captain announced, ‘pitch rate’.

This announcement came at about the same time that the PM would normally announce ‘positive rate’ after checking that a positive rate of climb was indicated on the aircraft instrumentation. This ‘positive rate’ announcement would then trigger the PF to request the retraction of landing gear. On this occasion, the lateral navigation mode activated and, after the captain announced ‘pitch rate’, both crewmembers then focused on the aircraft flight path and the retraction of the landing gear was inadvertently omitted.

The aircraft continued climbing and turning left to follow the SID. As the aircraft climbed through about 840 ft above mean sea level (AMSL), the primary flight displays presented 2 radio altimeter alerts in quick succession and the engine indicating and crew alerting system (EICAS) presented ‘RADALT MISCOMPARE’ and ‘APPR 2 NOT AVAIL’ messages (see the section titled Radio altimeter). The crew noted these indications and determined that they were not relevant to that phase of flight and therefore took no action.

As the first officer manually turned the aircraft left to follow the SID, the aircraft followed a turn radius smaller than the flight management system’s (FMS) precalculated turn (see the section titled Flight instrumentation) and turned onto the SID 030° track[3] to the left of the FMS calculated track position (Figure 1). As the turn continued, the FMS targeted the wider track and the crew observed the flight director indications on the primary flight display unexpectedly command a right turn. The first officer briefly followed the right turn command by reducing the angle of bank from 24° left to 10° left before then increasing the angle back to 20° left to complete the turn.

Once the first officer established the aircraft on a 030° track, the autopilot was engaged while the flight director continued to indicate a right turn. The autopilot then started a right turn to intercept the FMS calculated 030° track position. At about the same time, air traffic control instructed the crew to change radio frequency. As the aircraft commenced the right turn, the captain identified the turn away from the SID track toward the high terrain and instructed the first officer to turn left to follow the 030° track. The first officer then engaged the autopilot heading mode and selected 030° and the aircraft turned left to a heading of 030° and continued climbing.

Figure 1: Departure flight path (initial)

Source: Recorded data from VH-A2T and Google Earth, annotated by the ATSB 

The aircraft then continued along the SID and after climbing above 4,000 ft AMSL, turned right toward the waypoint AKROM. As the aircraft continued climbing toward AKROM, the captain, whose headset was not noise-cancelling, noted that the ambient noise was louder than expected and recognised that the landing gear was still extended. At about the same time, the first officer noted the landing gear extended indication on the EICAS. In response, while the aircraft was accelerating through 243 kt – 8 kt above the maximum landing gear retraction speed of 235 kt – the captain retracted the landing gear without first checking the indicated airspeed. The landing gear completed retracting when the aircraft had reached a speed of 252 kt, 17 kt above the maximum retraction speed (Figure 2).

Figure 2: Departure flight path

Source: Recorded data from VH-A2T and Google Earth, annotated by the ATSB

The flight continued and, at 2044, the aircraft landed at Brisbane without further incident. Following the flight, the aircraft was inspected and found to be undamaged.

Context

Flight crew details

The captain held an Air Transport Pilot Licence (Aeroplane) and a class 1 aviation medical certificate. The captain had 15,192 hours of flying experience, of which 1,680 hours were on the Embraer 190 aircraft type, with 137 hours accrued in the previous 90 days. 

The first officer held an Air Transport Pilot Licence (Aeroplane) and a class 1 aviation medical certificate. The first officer had 6,131 hours of flying experience, of which about 1,353 hours were on the Embraer 190 aircraft type, with 213 hours accrued in the previous 90 days.

The ATSB found no indicators that the flight crew were experiencing a level of fatigue known to adversely affect performance.

Operational information

Cairns Airport runway 15 AKROM 1 standard instrument departure 

High terrain partly encircles Cairns Airport from the north-west through south-west and to the south-east. To avoid the high terrain, the AKROM 1 standard instrument departure (SID) required aircraft departing runway 15 to make a left turn at the earlier of either reaching 400 ft AMSL or passing the departure end of the runway (DER) (Figure 3). During the turn, flight crew needed to maintain a bank angle of at least 25° and a speed of no more than 190 kt until the aircraft was established on a track of 030°. The location of the 030° track was dependent upon both the position that the left turn was commenced and the radius of the turn. The departure required maintenance of the 030° track until intercepting the 080° radial of the Cairns very high frequency omni range navigation aid (VOR) and then followed that track until the aircraft climbed above 4,000 ft AMSL. The departure then turned to the waypoint AKROM.

Figure 3: Runway 15 AKROM 1 standard instrument departure

Source: Airservices Australia, annotated by the ATSB 

Take-off standard operating procedures

The operator’s standard operating procedures manual (SOPM) required the pilot monitoring (PM) to verify a positive rate of climb immediately after take-off and then announce ‘positive rate’. After that announcement, the pilot flying (PF) confirmed the positive rate of climb and called for the landing gear to be retracted, and the PM then selected the landing gear ‘up’. 

The SOPM also specified a normal rotation rate of 3° of pitch angle per second.

Aircraft information

The aircraft was an Embraer ERJ 190‑100 IGW, manufactured in Brazil in 2008 and issued serial number 19000179. It was registered in Australia as VH-A2T on 19 July 2024. The aircraft was fitted with 2 General Electric Company CF34-10E5 turbofan engines. 

The maximum indicated airspeed at which the landing gear could be retracted or extended was 235 kt and the maximum airspeed with the landing gear in the extended position was 265 kt.

Flight instrumentation

The ERJ 190 was equipped with an integrated avionics system. VH-A2T was equipped with a ‘load 25’ version of the avionics. At the time of the incident, Alliance Airlines operated ERJ 190 aircraft equipped with both ‘load 25’ and upgraded ‘load 27’ avionics.

The flight management system (FMS) in ‘load 25’ equipped aircraft was designed to dynamically calculate the location of down path tracks, but only when these paths were inactive. Once the path became active, their location was fixed. The system should have predicted the 030° track leg of the AKROM 1 SID relative to where the system sequenced the 400 ft altitude crossing or departure end of the runway point. The avionics manufacturer, Honeywell, advised that in this case, the FMS sequenced the termination of the 400 ft altitude leg early and appeared to fix the location of the 030° track leg before it could be updated based on the position of the commencement of the left turn. 

Subsequently, and as intended by design, the FMS did not recalculate the location of the 030° track during the turn. As a result, when the crew turned to the 030° track to the left of the FMS precalculated track, the FMS, still targeting the wider track, commanded a right turn to intercept that track (Figure 4).

Figure 4: Representation of primary flight and navigation displays during the left turn

Note: The figure is based on an animation of the incident. The flight director representation is different to actual aircraft, and indications are included that are not presented in the actual aircraft. Negative roll values indicated a left turn, positive a right turn. Source: Embraer, annotated by the ATSB 

Recorded automatic dependent surveillance broadcast (ADS-B) data from previous AKROM 1 departures flown by VH-A2T identified 2 additional flights where the FMS had precalculated the 030° track at a wider location. On those occasions, the ADS-B data indicated that the flight crews followed the flight director commands and intercepted the wider track (Figure 5).

Figure 5: Departures of VH-A2T equipped with ‘load 25’ avionics

Source: Recorded data from VH-A2T and Google Earth, annotated by the ATSB

For ‘load 27’ equipped aircraft, the flight path was continuously updated as FMS track legs were flown and while in transition between them. This resulted in more accurate tracking of departure paths (Figure 6). 

Figure 6: Departure paths of an E190 equipped with ‘load 27’ avionics

Source: Recorded data from VH-UYY and Google Earth, annotated by the ATSB

Radio altimeter

The Embraer ERJ 190 was fitted with 2 radio altimeters. These provided each crewmember with an indication of the height of the aircraft above underlying terrain measured using radio waves. When a difference in the height measured by the 2 radio altimeters exceeded a dynamic threshold, an ‘RA’ alert was presented on the primary flight display (Figure 7) and the RADALT MISCOMPARE alert was presented on the EICAS. Whenever this condition was detected, the associated EICAS message APPR 2 NOT AVAIL was also displayed.

Figure 7: Radio altimeter alert

Note: The figure is based on an animation of the incident and indications (such as the radio altimeter readings) are included that are not presented in the actual aircraft. Source: Embraer, annotated by the ATSB 

United States Federal Aviation Administration Advisory Circular AC 25-7D Flight Test Guide for Certification of Transport Category Airplanes stated the following guidance and measurement conditions for radio altimeter certification:

32.1.5.5 Radio Altimeter System. 

32.1.5.5.1 The radio altimeter system should display to the flightcrew, clearly and positively, the altitude information that indicates the airplane main landing gear wheel height above terrain.

32.1.5.5.2 Verify that the altimeters display altitude without loss of signal indications or excessive fluctuations, under the following measurement conditions: 

• Pitch angle ±5° about the mean approach attitude. 

• Roll angle zero to ±20°. 

On departure from Cairns, the alerts were generated while the aircraft was operating over relatively flat terrain and when the aircraft’s pitch angle was about 14° nose up and the roll angle about 23° left. While the investigation did not determine the reason for the different radio altimeter readings that led to the radio altimeter alerts, the aircraft’s pitch and roll values at the time exceeded the guidance and measurement conditions specified in the FAA circular.

Light and meteorology

The departure was conducted in night visual meteorological conditions. The sun had set at 1802, 49 minutes before the departure, and the moon was below the horizon.

At the time of the departure, the Bureau of Meteorology automatic weather station at Cairns Airport recorded the temperature as 23°C and the wind as 9 kt from 161° magnetic. There was no recorded cloud, and visibility was recorded as 58 km.

Recorded data

Analysis of flight data from the flight data recorder fitted to VH‑A2T showed that the rotation rate during the take‑off was 1.49 degrees per second until the aircraft was pitched 9.7° nose up and then 1.73 degrees per second until 14.9° nose up. The pitch attitude stabilised at about 16° nose up during the turn.

As the aircraft turned left through a heading of 080°, the flight director began commanding a right turn (Figure 8). At 1853:08, the autopilot was engaged in the lateral navigation mode and while the flight director continued to command a right turn. The aircraft then rolled right, following that command. At 1853:20, while flying a heading of 058° the autopilot mode changed from lateral navigation mode to heading mode with 030° selected. The aircraft then began rolling left to turn to that heading.

At 1856:35, the landing gear was selected up at a speed of 243 kt. The landing gear completed the retraction sequence at 1856:47 as the aircraft accelerated to 252 kt.

Cockpit voice recorder data capturing the incident was not available as it had been overwritten.

Figure 8: Recorded flight data

Source: ATSB 

Safety analysis

Non-retraction of landing gear

During the take-off, the first officer rotated the aircraft slower than required, prompting the captain to call for an increase in pitch rate. The captain’s attention then remained focused on monitoring the pitch attitude of the aircraft throughout the rotation manoeuvre to ensure the required pitch attitude targets were being achieved. Because of this, the captain likely did not have sufficient opportunity to move onto the next task, verifying the aircraft’s positive rate of climb, before it passed through 400 ft – the point at which the terrain avoidance turn was to be initiated. Consequently, the task step of verifying and announcing positive climb performance was not fully completed and the captain did not make the ‘positive rate’ announcement. 

In the absence of the captain’s announcement, the first officer was not prompted to request landing gear retraction, and the landing gear remained extended. The captain’s announcement of ‘pitch rate’ at about the same time that the acoustically and semantically similar ‘positive rate’ announcement would normally be made, potentially caused interference in working memory (Lentoor 2023) and possibly gave both flight crew a false sense that the latter action had been successfully performed.

Delayed identification and overspeed

During the initial climb, which was a high workload phase of the flight, abnormal radio altimeter alerts and unexpected flight director indications further increased the flight crew’s workload. In particular, when the autopilot was engaged, it commenced a right turn toward high terrain in response to an unexpected flight director indication. This prompted the captain’s intervention and the crew’s attention then narrowed to focus on parameters which would enable them to verify the aircraft’s lateral tracking performance. Wickens (2009, 2021) notes that attentional tunnelling occurs under conditions of elevated stress and deliberate task focus and can cause other task-relevant stimuli to be ignored.

Consequently, increasing flight deck wind noise and abnormal engine indicating and crew alerting system (EICAS) indications, both of which provided an indication of the landing gear’s extended state, were not initially detected. Furthermore, the turn and speed restrictions of the departure also likely masked the performance degradation due to the extended landing gear, further reducing the likelihood of identifying that it was still extended.

As the flight crew’s workload decreased in the latter portion of the departure, the effects of attentional tunnelling reduced, and the noise from the landing gear increased as the aircraft accelerated. The captain (whose headset was not noise-cancelling) then detected the increased cockpit wind noise and was alerted to the misconfiguration of the landing gear. At about the same time, the first officer identified the landing gear extended indication on the EICAS.

As the aircraft had travelled well beyond the normal gear retraction point and was accelerating, the captain likely perceived some urgency to act upon noticing that the landing gear was still extended and experienced associated increased stress. Under such conditions research has shown that people often do not make optimal decisions and may act more reflexively (Dismukes and others, 2007). 

Under time pressure and stress, experts may revert to a recognition primed decision mode (Klein, 2014), making rapid and intuitive interpretations of a situation and selecting actions based on their most familiar experiences.

The landing gear was normally retracted well below the retraction limiting speed, and this speed was not normally checked by the other crew member. Therefore, the captain reverted to their most familiar experience and initiated gear retraction without first confirming the action with the first officer and did not check the gear retraction limiting speed. Consequently, the landing gear retraction was initiated 8 kt above the 235 kt retraction limit speed and the retraction completed 17 kt above that speed.

Findings

From the evidence available, the following findings are made with respect to the landing gear overspeed involving Embraer E190, VH-A2T on 24 July 2025.

Contributing factors

• After take-off, the pilot monitoring made a 'pitch rate' announcement at a time when a 'positive rate' announcement would normally be expected. This resulted in both flight crewmembers focusing on the pitch angle and the pilot flying was not prompted to call for gear retraction. Subsequently the crew's attention was focused on following the departure flight path and the landing gear was not retracted.
• As the aircraft turned left to follow the standard instrument departure, abnormal radio altimeter indications were presented, and the flight management system unexpectedly commanded a right turn. When the autopilot was engaged, the aircraft briefly followed the commanded turn before the captain intervened. These distractions increased the flight crew's workload and delayed their identification of the extended landing gear.
• After recognising that the landing gear was still extended, the captain reflexively retracted the landing gear at a speed above the maximum landing gear retraction speed.

Safety actions

Safety action by Alliance Airlines

Alliance Airlines has accelerated its program to upgrade E190 aircraft from load 25 avionics to load 27 and at the time of the release of this report, all E190s in the Alliance Airlines fleet have been upgraded. This should prevent recurrence of the unexpected flight management system indications presented to the crew during this incident.

In addition, the load 27 avionics upgrade incorporated electronic checklists that require associated actions to be undertaken before the electronic checklist is completed.  

Sources and submissions

Sources of information

The sources of information during the investigation included:

• the flight crew
• Alliance Airlines
• the aircraft and avionics manufacturers
• Bureau of Meteorology
• recorded data from VH-A2T.

References

Dismukes, R., Goldsmith, T. E., & Kochan, J. A. (2015). Effects of acute stress on aircrew performance: literature review and analysis of operational aspects. National Aeronautics and Space Administration Technical Memorandum, NASA/TM-2015-218930.

Klein, G. (2014). The recognition-primed decision (RPD) model: Looking back, looking forward. In Naturalistic decision making (pp. 285-292). Psychology Press.

Lentoor, A. G. (2023). Cognitive and neural mechanisms underlying false memories: misinformation, distortion or erroneous configuration? AIMS neuroscience, 10(3), 255.

Wickens, C. D., & Alexander, A. L. (2009). Attentional tunnelling and task management in synthetic vision displays. The international journal of aviation psychology, 19(2), 182-199. 

Wickens, C. D., & Carswell, C. M. (2021). Information processing. In Handbook of human factors and ergonomics (pp. 114-158). John Wiley & Sons.

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 flight crew
• Alliance Airlines
• the aircraft manufacturer
• the avionics manufacturer
• Civil Aviation Safety Authority
• the United States National Transportation Safety Board.

Submissions were received from:

• the flight crew
• Alliance Airlines
• the aircraft manufacturer
• Civil Aviation Safety Authority.

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 evening of 2 July 2025, a Virgin Australia Airlines Boeing 737‑800 aircraft, registered VH-YFZ, operated a scheduled passenger flight from Sydney, New South Wales, to Melbourne, Victoria.

During the arrival into Melbourne, the aircraft exceeded 2 speed limitations on the standard terminal arrival route, and air traffic control issued 2 speed reduction instructions, likely to maintain separation from traffic.

Perceiving the ATC instructions to be urgent, the crew hastened the conduct of the approach actions and missed arming the speedbrake and performing the landing checks. As the aircraft descended below 1,000 ft above airfield elevation the crew assessed the approach to be stable and continued, resulting in the aircraft landing with the speedbrake not armed, which resulted in it not automatically deploying. Noticing this, the captain moved their hand to the lever to raise it manually. However, the speedbrake simultaneously automatically deployed as the first officer selected reverse thrust. Thereafter the aircraft’s deceleration was sufficient, and the flight concluded without further incident.   

What the ATSB found

The ATSB found that the flight crew allowed the aircraft to exceed speed limitations on the arrival, resulting in air traffic control requiring them to reduce speed. The crew were slow to take positive steps to reduce speed requiring ATC to instruct them to slow further. The crew’s attention became focused on achieving the requested speed reductions, which likely resulted in them omitting to arm the speedbrake and conduct the landing checks. 

As the aircraft passed 1,000 ft above airfield elevation, neither flight crew recognised that the speedbrake was not armed and the landing checklist had not been completed, resulting in the approach continuing despite the stabilised approach criteria not being met.

Safety message

Threat and error management (TEM) principles state that flight crews' proactive management of workload throughout the flight is a key defence against capacity and attention-related errors. 

Checklists are a vital defence against human error and are integral to maintaining flight safety. This occurrence highlights the importance of adhering to standard operating procedures and ensuring checklists are conducted at the appropriate times. 

Many of the speed limitations built into approach procedures are designed to facilitate predictable traffic flows and manage both controller and flight crew workloads. Exceeding the published approach speeds without clearance compromises this risk control and introduces the threat of additional workload and demands on attentional resources.

Many transport jets, such as the 737-800, have a limited capacity to simultaneously descend and decelerate when in a clean configuration. In some modes and flight conditions the aircraft’s autopilot system will be unable to meet altitude and airspeed constraints contained in arrival and approach procedures. The flight crew must therefore be vigilant in monitoring and managing the aircraft’s descent profile and energy condition and be ready to intervene as necessary. 

Correct management of the aircraft’s profile and energy during the descent is an effective countermeasure against approach and landing accidents. The Flight Safety Foundation (2000) provides guidance to flight crew on this matter (FSF ALAR Briefing Note 4.1 – Descent-and-approach Profile Management) as part of its broader approach and landing accident reduction (ALAR) toolkit.

The investigation

The occurrence

On 2 July 2025, a Virgin Australia Airlines Boeing 737-800 aircraft, registered VH-YFZ, was operating a scheduled passenger flight,[1] VA882, from Sydney, New South Wales, to Melbourne, Victoria. On board were the captain as pilot monitoring (PM),[2] first officer as pilot flying (PF), 4 cabin crew and 170 passengers. 

At 2040 local time the aircraft commenced an initial descent from its cruising altitude with a clearance from the Melbourne centre air traffic controller (ATC) to track via the BOOIN ONE ALPHA standard terminal arrival route (STAR) (Figure 1). ATC did not remove any of the speed restrictions associated with the arrival.

Seven minutes later, descending through flight level 140,[3] the aircraft was transferred to the Melbourne approach ATC, who cleared the flight for further descent via the STAR, initially to 5,000 ft, and soon after to 3,000 ft. ATC also issued a clearance for the ground based augmentation system (GBAS) landing system (GLS)[4] approach to runway 16, but again did not remove any speed restrictions. 

With the autopilot engaged in VNAV PTH pitch mode (see the section titled Automatic flight modes), the aircraft’s descent was momentarily arrested at 10,000 ft, to decelerate to less than the maximum speed constraint of 250 kt below that altitude. However, as the airspeed decreased to about 260 kt, the autopilot recommenced the descent, and the aircraft’s deceleration ceased. Subsequently, the aircraft crossed the ENSEG waypoint,[5] located approximately 21 track miles from the runway threshold at 263 kt, 33 kt above the speed required at that waypoint by the arrival procedure. 

When the aircraft was approximately 15 track miles from the runway threshold, around 4 NM from initial approach fix BELTA and descending through 5,250 ft above mean sea level (AMSL), ATC instructed the flight crew to reduce their speed to 180 kt. At this stage, the aircraft was in a clean configuration[6] and slowly decelerating through 240 kt. Shortly thereafter the flight crew began to extend the initial stages of flap and deployed the speedbrake. 

Figure 1: BOOIN ONE ALFA standard instrument arrival procedure chart 

The chart shows graphical section of the STAR with the applicable speed restrictions highlighted in red by the ATSB. Source: Airservices Australia

Just over one minute later, as the aircraft was abeam BELTA and midway through the turn to the final approach course, ATC requested a further reduction in speed to 160 kt, likely for traffic separation. The crew perceived the ATC request to be urgent and began selecting flaps earlier than normal to arrest the aircraft’s speed. The aircraft passed abeam BELTA, with the speedbrakes still deployed, decelerating through 206 kt and descending through an altitude of 4,000 ft AMSL. 

Shortly after passing BELTA at 199 kt, flap 10 was selected, and then the speedbrake was stowed. Twenty seconds later, at approximately 9.5 NM from the runway threshold and descending through 3,650 ft AMSL, flap 15 was selected and the landing gear was extended. While the operator’s standard procedures call for the speedbrake lever to be placed into the armed position after the selection of flap 15, it remained in the stowed position for the remainder of the approach. 

The flight crew selected the landing flap configuration of 30, approximately 8.5 NM from the runway threshold at 3,330 ft AMSL, but did not action the landing checks, as called for in the operator’s standard procedures. 

Figure 2: Aircraft flight path and key events during the transition from the arrival to the approach procedure

Source: Google Earth and Flightradar24, annotated by the ATSB

The aircraft descended through the 1,000 ft above airfield elevation stabilised approach gate (see the section titled Stabilised approach requirements) on the GLS course and glideslope, with the airspeed stable at 150 kt, but with the speedbrake lever still in the stowed position and the landing checks incomplete. The crew advised the ATSB that the stabilised approach criteria were assessed, but neither crewmember recognised that they had not been met. As a result, they continued the approach. 

Upon touchdown, the captain sighted the speedbrake lever and noted that it had not automatically moved to the deployed position. As they moved their hand to the lever with the intention of manually extending the speedbrakes, the lever began to automatically deploy, coincident with the first officer selecting reverse thrust.

The aircraft decelerated normally and exited the runway. As the flight crew began their post‑landing actions, the captain noted that the line pointers on both yoke‑mounted checklists had not been moved below the bottom of the approach checks, signalling that the landing checks had not been completed. After manoeuvring the aircraft onto the stand and shutting down the engines, the flight crew discussed what they thought had probably happened. The first officer was unaware that the speedbrake had not been armed prior to landing, nor that the landing checks had not been performed. 

Context

Flight crew background

The captain and first officer both held an air transport pilot licence (aeroplane) and a class 1 aviation medical certificate. The captain had around 13,600 total flight hours (5,500 on the 737), and the first officer had just over a total of 3,000 hours at the time of the incident. The flight was the captain’s first in almost a month, having been away from work on annual leave. They advised that although they were comfortable with the flight, they felt slightly below their normal performance capability.

Aircraft information

VH-YFZ was a Boeing 737-800, serial number 41005, manufactured in the United States in 2017. The 176-seat aircraft was fitted with 2 CFM International CFM56-7B24E turbofan engines. 

Speedbrake system

The Boeing 737-800 speedbrake system is comprised of 6 hydraulically-actuated spoiler panels on the upper surface of each wing, 4 flight spoilers and 2 ground spoilers. In flight, only the flight spoilers may be extended, and are used symmetrically across the wings to increase drag. On the ground, both flight and ground spoilers may be extended to assist with deceleration. 

The 737 NG Flight crew training manual stated that: 

The use of speedbrakes with flaps extended should be avoided, if possible. With flaps 15 or greater, the speedbrakes should be retracted. If circumstances dictate the use of speedbrakes with flaps extended, high sink rates during the approach should be avoided. Speedbrakes should be retracted before reaching 1,000 feet AGL [above ground level].

Operation of the speedbrakes is achieved via the speedbrake lever. This lever can also be set in the ARMED position. In flight this will not result in speedbrake extension, however after landing, when the conditions are met, all spoiler panels will automatically raise to their maximum extent.

Normally, for the speedbrake system to operate automatically during landing, the following set of conditions must be met:

• speedbrake lever in the armed position and the light illuminated
• radio altitude less than 10 ft
• landing gear strut compressed
• both thrust levers retarded to idle
• main landing gear wheels spun up (more than 60 kt).

However, if the speedbrake lever is not in the armed position during landing, the speedbrake system will also automatically operate when the following conditions are met:

• main landing gear wheels spun up (more than 60 kt)
• both thrust levers retarded to idle
• reverse thrust levers positioned for reverse thrust.

Automatic flight modes

The aircraft’s automatic flight system consisted of the autopilot flight director system (AFDS) and autothrottle (A/T). They could be used together in a number of distinct modes to achieve lateral and vertical navigation, and speed management. For descents, a vertical navigation mode could be selected via the VNAV switch on the mode control panel (MCP). The aircraft’s flight management computer (FMC) would command the AFDS pitch and A/T to fly a pre‑programmed vertical profile, attempting to accommodate waypoint altitude and airspeed constraints. 

In most scenarios, selecting VNAV engaged the VNAV PTH mode, where maintenance of vertical flightpath was prioritised over airspeed. In certain situations, such as steep descent profiles in clean configuration, the aircraft may be unable to decelerate or maintain airspeed limits, even with idle thrust. In these situations, VNAV PTH mode would seek to achieve the programmed descent path, including altitude constraints, and may allow the airspeed to increase within broad limits, before reverting to a speed prioritised mode (VNAV SPD). 

Standard operating procedures

Approach configuration sequence

The operator’s 737 NG Flight Crew Operations Manual (FCOM) specified a normal sequence of flight crew actions for a GLS approach, as well as the areas of the flight deck for which each flight crew member was responsible. 

When the first officer was operating as the pilot flying, it was their responsibility to move the speedbrake lever to the ARM position and verify the status of the corresponding annunciator, prior to landing. At around 2,000 ft above airfield elevation, the normal procedure specified that the speedbrake arming action should occur, immediately after the pilot flying called for ‘Gear Down’ and ‘Flaps 15’.   

The normal procedure also specified that it was the pilot flying’s responsibility to call for the landing checklist to be completed at around 1,500 ft above airfield elevation. This should normally occur as part of a second block of configuration actions, immediately after the pilot flying called for the landing flap to be set and the threshold target speed to be bugged.

The Quick Reference Handbook (QRH) section of the FCOM specified the normal landing checklist, and contained the following items, all to be confirmed by the pilot flying: 

Engine start switches………………………..CONT 

Speedbrake………………………………......ARMED

Landing gear………………………………….Down

Flaps……………………………………..……Green light

A checklist and movable position marker were mounted to each of the aircraft’s control yokes. The occurrence happened at night in a darkened cockpit and the checklists did not have backlighting. 

Stabilised approach requirements

The operator’s normal procedures for a GLS approach called for the flight crew to assess the approach against stabilisation criteria at 1,000 ft above airfield elevation and initiate a missed approach if the conditions were not met. The criteria were specified under the operator’s stabilised approach policy, contained within their general operating policies and procedures manual. They were as follows:

• briefings and normal checklists completed
• aircraft in the correct landing configuration
• aircraft on the correct lateral and vertical flight path
• sink rate, no greater than 1,000 fpm
• thrust setting appropriate for the aircraft configuration and trajectory
• speed within -5 kt to +10 kt of the speed target.

Instrument arrival procedure speed restrictions

The STAR contained several speed limitations (Figure 1). Airservices Australia’s Aeronautical Information Publication (AIP) Enroute 1.5 - 47 included the following requirements:

10.2.1      Unless explicitly cancelled or amended by ATC, the pilot must follow the vertical and lateral profile of the STAR and comply with any published speed restrictions.

On this occasion ATC did not cancel the speed restrictions when clearing the flight to conduct the STAR.

Safety analysis

The flight crew used the autopilot’s vertical navigation path (VNAV PTH) mode and auto throttle to manage the aircraft’s descent profile and airspeed for the arrival.

On this occasion, and as per expected system performance, in a clean configuration, the autopilot was unable to sufficiently reduce speed such that it could simultaneously meet the descent profile and airspeed requirements of the arrival procedure. With no additional drag added by the flight crew, the aircraft continued to maintain an airspeed around 30 kt higher than the speed restrictions in the STAR, until the air traffic controller issued a speed reduction instruction and the flight crew modified the aircraft’s configuration.

The crew perceived the ATC instruction to be urgent and advised that this increased their workload. It is likely the crew focused their attention on monitoring the airspeed and ensuring the flaps were extended promptly, but within their operational limits. Wickens (2021) describes attentional narrowing as a focus on a limited set of information at the expense of other sources. This focus can cause steps in the linear sequence of a procedure to be skipped. 

As the aircraft was decelerated to final approach speed and configured for landing earlier than normal, it is probable that the crew omitted to arm the speedbrake and call for the landing checks because their attention was focused on achieving the ATC‑requested airspeed reduction. Compounding this, the captain perceived that their monitoring performance was modestly degraded due to a lack of recent flying experience. 

During the final segment of the approach, while the aircraft was on the approach path and the speed had reduced to the required approach speed, the aircraft did not meet all the stabilised approach criteria since the landing checklist had not been completed, and the speedbrake was not in the armed position. 

Findings

From the evidence available, the following findings are made with respect to the incorrect landing configuration involving Boeing 737, VH-YFZ, near Melbourne Airport, Victoria, on 2 July 2025.

Contributing factors

• The aircraft exceeded speed restrictions during the arrival and the crew did not take appropriate action to slow the aircraft in a timely manner. This resulted in the air traffic controller issuing instructions to reduce speed further and the crew subsequently not arming the speedbrake and performing the landing checks.
• As the aircraft passed 1,000 ft above airfield elevation, neither flight crew recognised that the speedbrake was not armed and the landing checklist had not been completed, resulting in the approach continuing despite the stabilised approach criteria not being met.

Sources and submissions

Sources of information

The sources of information during the investigation included:

• the pilots of the incident flight
• operational documentation from Virgin Australia Airlines
• Airservices Australia
• ADS-B data from Flightradar24
• recorded data from the aircraft Quick Access Recorder. 

References

• Flight Safety Foundation. (2000). ALAR briefing note 4.1: Descent-and-approach profile management. In Approach and landing accident reduction (ALAR) toolkit. Flight Safety Foundation. https://flightsafety.org/wp-content/uploads/2016/09/alar_bn4-1-profilemgmt.pdf
• Wickens, C. (2021). Attention: Theory, principles, models and applications. International Journal of Human–Computer Interaction, 37(5), 403-417. 

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 pilots of the incident flight
• Virgin Australia Airlines
• Civil Aviation Safety Authority.

Submissions were received from:

• the pilots of the incident flight
• Virgin Australia Airlines. 

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

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

Investigation summary

What happened

On 12 February 2025, Alliance Airlines Embraer E190, VH-UYO, was operating Qantas flight QF1888 from Cairns, Queensland to Darwin, Northern Territory. At 1634 local time, passing the initial approach fix for the instrument landing system (ILS) approach to Darwin Airport’s runway 29, the auto‑flight system approach mode unexpectedly disarmed and reverted to basic flight director modes. The aircraft then deviated right and then left of the ILS course, before intercepting the lateral course at about the final approach fix. 

Passing 1,000 ft above aerodrome elevation, the aircraft was above the glideslope, at a high rate of descent and high airspeed. The flight crew elected to continue the approach, as the aircraft was then in visual meteorological conditions. Passing 500 ft, the flight crew assessed that the aircraft was stabilised, although still too fast. The pilot monitoring subsequently identified that the flaps were not in the landing configuration and selected the correct position. The flight crew continued the approach and conducted an uneventful landing. 

What the ATSB found

The ATSB found that on crossing the initial approach fix for the ILS approach, due either to a system synchronisation issue or the pilot flying inadvertently disarming the approach mode, the aircraft’s auto‑flight system reverted to roll and flight path angle modes. 

Following the unexpected mode change, the pilot flying did not reengage approach mode or disconnect the autopilot. This likely contributed to the aircraft deviating outside the required lateral tolerance of the approach below the minimum safe altitude while in instrument meteorological conditions. 

Additionally, the ATSB found that the flight crew did not discontinue the approach when the aircraft was unstable at the 1,000 ft stabilisation height as they incorrectly assessed that they could continue to 500 ft in visual meteorological conditions with multiple stabilised approach criteria unmet.

In the limited time available to stabilise the aircraft by 500 ft, the flight crew incorrectly assessed that the aircraft was stable and continued the approach, unaware that the pilot monitoring had inadvertently selected an incorrect flap configuration. 

Finally, the ATSB found that Alliance Airlines' standard operating procedures were unclear about the criteria for continuing an unstable instrument approach to 500 ft when aircraft entered visual conditions.

What has been done as a result

Following this incident, Alliance Airlines issued an operations notice ‘to improve clarity and compliance’ with the stabilised approach criteria. The notice detailed the stabilised approach policy. It also amended the stabilisation height such that for 3‑dimensional and 2‑dimensional instrument approaches, and straight‑in visual approaches, the stabilised criteria were to be met by 1,000 ft above aerodrome elevation. The 500 ft stabilisation height applied only to a visual circuit or circling manoeuvre approaches. The notice reminded flight crew of Alliance’s ‘non punitive go‑around policy’ and required all unstable approaches to be reported. Finally, Alliance Airlines conducted a flight data review of unstable approaches over the previous 6 months operations to identify similar occurrences.

Safety message

The Flight Safety Foundation’s (FSF) Reducing the risk of runway excursions report found that, in the 16 years to 2009, the most common accident was a runway excursion, accounting for 33% of all aircraft accidents. The highest risk factor for runway excursions was identified as an unstable approach. Further, an FSF survey (Normalization of Deviance) identified that only 3–4% of approaches were unstable but that in over 97% of those, the flight crews did not conduct a go-around. It stated: 

Noncompliance with standard operating procedures (SOPs) — especially tolerance of unstabilized approaches — is a serious impediment to further reduction of accident risk. 

Guidance from the International Air Transport Association for preventing unstable approaches stated that pilots must be trained to understand the risks of an unstable approach, because an unstable approach can be completed successfully, which may reinforce bad practice.

Additionally, this incident highlights how important continuous attention to automatic flight system modes displayed on the primary flight display is to the maintenance of situation awareness. 

This incident also illustrates the need for effective flight crew monitoring. The Flight Safety Foundation identified that monitoring can be improved by standard operating procedures, increased emphasis and practice, and stated:

One of the most important aspects of a safe flight operation is the requirement for crewmembers to carefully monitor the aircraft’s flight path and systems, as well as actively cross-check each other’s actions.

The investigation

The occurrence

On the afternoon of 12 February 2025, Alliance Airlines (Alliance) Embraer ERJ 190‑100 IGW (E190), registered VH‑UYO, was operating Qantas flight QF1888 from Cairns, Queensland to Darwin, Northern Territory. On board were 2 flight crew, 2 cabin crew and 49 passengers. The captain was the pilot flying (PF), and the first officer was the pilot monitoring (PM).[1] 

After departing Cairns, the aircraft climbed to cruise at flight level (FL) 340.[2] En route the flight crew obtained air traffic control (ATC) clearances, first to deviate up to 30 NM (56 km) left, and later up to 50 NM (93 km) right of the planned route to avoid hazardous weather. At 1614 Darwin local time the flight crew received clearance to descend to FL 120. Just over 2 minutes later they requested a further clearance to deviate up to 60 NM (111 km) right to avoid weather. 

At 1619 the flight crew requested, and received, a clearance to deviate up to 70 NM (130 km) right of route and to track direct to waypoint LAPAR, once clear of the weather. About 2 minutes later, descending through FL 190, the aircraft turned left from a position about 30 NM (56 km) right of the planned route, to track 60 NM (111 km) direct to LAPAR (Figure 1).

Figure 1: VH-UYO recorded flight data showing weather diversion and tracking to LAPAR

Source: Google Earth overlaid with FlightRadar24 data, annotated by the ATSB

At 1622 the PM contacted Darwin Approach ATC, advised they were descending to FL 120, had received automatic terminal information service (ATIS) X‑ray (X), and were tracking direct to LAPAR. ATIS X included advice of:

• the expectation of an instrument approach
• wet runways
• wind from 340° at 15 kt, with a maximum 15 kt crosswind on runway 29
• visibility of 2,000 m
• showers of rain
• scattered[3] cloud 1,200 ft above aerodrome elevation. 

The PM advised the approach controller when the aircraft was approaching FL 120, and received further clearance to descend to 9,000 ft and, 2 minutes later, to 7,000 ft. At 1629, as the aircraft descended through about 8,000 ft, the controller requested a reduction to ‘minimum clean speed’, as by radar VH‑UYO was showing a groundspeed of 270 kt, which exceeded the 250 kt maximum indicated airspeed below 10,000 ft. Although the aircraft’s airspeed at that time was 250 kt, the flight crew actioned the request to reduce speed, advised that they were approaching 7,000 ft, and were then cleared to descend to 5,000 ft.

At 1631, the approach controller cleared the flight crew to descend to 3,000 ft and conduct the instrument landing system (ILS)[4] -Z approach to runway 29. LAPAR was the initial approach fix[5] for the ILS and was aligned with the runway centreline (Figure 2).

Figure 2: VH-UYO flight path (green/blue) and ILS‑Z localiser path (black) showing key events (blue arrows)

Source: FlightRadar24 data overlaid on Google Earth, annotated by the ATSB

The PM selected flap 1 as the aircraft descended through about 4,600 ft. About 30 seconds later, the approach controller instructed the PM to contact the tower controller when leaving 3,000 ft. In preparation for the ILS, the PF then pressed the approach (APP) pushbutton on the aircraft’s guidance panel, arming the approach mode. This also armed flight director (FD) localiser (LOC) lateral and glideslope (GS) vertical modes. With approach mode armed, when the aircraft intercepted the localiser (at LAPAR), LOC should become the active lateral mode and when it subsequently intercepted the glideslope, GS should become the active vertical mode.

As LAPAR was a ‘fly-by’ (rather than a ‘flyover’) waypoint, the aircraft’s flight guidance and control system (FGCS) pre‑empted the turn and passed by LAPAR at 1634:51, at 183 kt airspeed and at the selected altitude of 3,000 ft. The selected altitude was then wound down to 2,200 ft and 2 seconds later, the FGCS captured the localiser and the recorded flight data showed LOC and flight path angle (FPA) modes became active. One second later, the lateral mode reverted to the basic FD ROLL mode (Figure 2 No 1 and Figure 3).

Figure 3: Flight mode annunciation display showing localiser (LOC) capture followed by reversion to basic modes (ROLL/FPA)

Recorded flight data showed LOC mode became active and then disarmed within 1 second. The active mode was recorded every second, but the armed mode was recorded every 2 seconds. Hence at 1634:56, the recorded data showed LOC as both the armed and active mode. Source: Embraer animation of recorded flight data, annotated by the ATSB

The FO recalled being very surprised seeing the ROLL/FPA modes. In those modes, the aircraft captured and maintained the roll angle and flight path angle it was in at the time of activation. At that time, the aircraft was:

• aligned with the localiser
• at a flight path angle of approximately 0°
• half a dot above the glideslope
• banked 20° right.

After intercepting the localiser, the ILS frequency became the active navigation source for the aircraft’s primary flight display (PFD), for the remainder of the flight. As such, lateral deviation from the localiser and vertical deviation from the 3° glideslope would be depicted on the PFD with 2 dots in each direction (left‑right/up‑down), with 2.5 dots representing full‑scale (or greater) deviation. Localiser deviation was also depicted by a course deviation indicator (CDI) and dots either side of the course on the compass instrument on the lower part of the PFD (Figure 4).

Figure 4: Compass instrument course deviation indicator aligned with the localiser at 1634:56

Source: Embraer animation of recorded flight data, annotated by the ATSB

Following activation of the ROLL/FPA modes, the aircraft deviated right of the localiser, maintaining approximately 20° roll for about 20 seconds, as it descended. After 14 seconds, the PM selected the landing gear down and the PF moved the heading bug and selected heading (HDG) mode to command the aircraft to turn left towards the localiser. 

The CDI exceeded half scale deflection (1.5 deviation dots) at 1635:16. The aircraft was then outside the lateral flight tolerance for the ILS and below the 10 NM minimum safe altitude of 3,000 ft.   

At 1635:30, the PM contacted the Darwin aerodrome (tower) controller and advised that they were ‘just slightly right of the localiser and re‑intercepting’ (Figure 2 No 2). The controller responded with the instruction to ‘maintain 2,000 [ft] until glidepath interception’. The PM read back ‘maintain 2,000’, but not ‘until glidepath interception’. The controller then stated: ‘once you’ve intercepted the glidepath, cleared the ILS’. The PM did not respond. 

The controller later advised the ATSB that 2,000 ft was the highest minimum vector altitude around Darwin Airport, which assured terrain separation, and there was no conflicting traffic. The controller reported that although the PM did not complete the readback, they had read back the safe altitude. The controller assessed that the flight crew were ‘working really hard’ to get back onto the ILS and would let ATC know when they wanted further descent or commenced a missed approach. The captain reported that they wanted to get re‑established on the localiser so they could conduct the published missed approach under automation if required. On reaching the maximum deviation to the right of the localiser, the aircraft was (Figure 5):

• banked 27° left
• at full scale localiser deflection
• one dot above the glideslope
• at 2,470 ft above mean sea level (AMSL)
• descending at 1,254 ft/minute (fpm). 

Figure 5: Primary flight display at 1635:30 showing full‑scale localiser deviation (localiser left of the aircraft)

Source: Embraer animation of recorded flight data, annotated by the ATSB

Flap 2 was selected at 1635:55, at about 2,200 ft AMSL. The active lateral mode automatically changed from HDG to LOC mode one second later, but because the APP mode was not armed, GS mode did not become active although the aircraft was within one dot of the glideslope. The aircraft then passed through the localiser 52° off the runway heading, before entering a right turn, as the FGCS commanded re‑interception of the localiser course. 

At 1636:22, 177 kt airspeed and 2,000 ft, the PF advised the controller that ‘Qantas 1888 is established’ (Figure 2 No 3). Established was defined as being within half full‑scale deviation of the specified track.[6] The aircraft was then (Figure 6):

• at full-scale localiser deviation
• banked 33° right
• nearly 2 dots above the glideslope. 

Figure 6: Primary flight display at 1636:22 showing full‑scale localiser deviation (localiser right of the aircraft) and nearly 2 dots glideslope deviation (glideslope below the aircraft) 

Source: Embraer animation of recorded flight data, annotated by the ATSB

The PM then requested further descent, to which the controller replied, ‘cleared ILS runway 29’, and just below 2,000 ft, the PM selected flap 3. 

At 1636:51, the aircraft passed the final approach fix (FAF) TOROT (Figure 2). At the FAF, the PM was required to call out ‘FAF, height checked, missed approach altitude set’. At that time:

• the FAF procedure height was 1,330 ft and the aircraft was at 1,695 ft (AMSL)
• the aircraft was at full‑scale deviation above the glideslope and descending at 1,331 fpm
• the set altitude was 800 ft, and the missed approach altitude was 3,000 ft.

After the FAF, Alliance’s standard operating procedures required the aircraft to be within one dot of the localiser and glideslope. The procedures also stated that the aircraft should regain the 3° profile no later than 1,500 ft above aerodrome elevation. However, passing 1,500 ft, the aircraft was full‑scale deviation above the glideslope and descending at over 1,500 fpm. 

Passing about 1,100 ft AMSL, the PM intended to select flap 5, but inadvertently selected flap 4. Flap 4 had the same flap and slat extension as flap 5, but flap 4 was a take‑off configuration not a landing configuration (see the section titled Flap configuration).

At 1637:16, the aircraft passed 1,000 ft radio altitude,[7] which coincided with Alliance’s stabilisation height of 1,000 ft above aerodrome level (AAL) for conducting an instrument approach. Contrary to the stabilised approach criteria, the:

• airspeed was 162 kt, 29 kt above approach speed (V_AP) – faster than the permitted V_AP + 10
• flap setting was 4 instead of flap 5 – not in the landing configuration
• before landing checks had not been completed
• aircraft was 1.4 dots above the glideslope – not within the allowable 1 dot of the glideslope
• descent rate was 1,582 fpm – higher than the allowable rate of descent than 1,000 fpm.

Providing all other stabilisation criteria were met, Alliance permitted the airspeed to be higher than V_AP + 10 until 500 ft in visual meteorological conditions (VMC)[8] by day. 

The captain recalled that the aircraft entered VMC at about 2,500 ft. However, the FO reported that just prior to 1,000 ft, they were ready to call out ‘unstable’ approach, when the captain stated that they were now ‘visual’ and could therefore continue the approach and be stabilised by 500 ft. The captain later reported that the lower stabilisation height of 500 ft in VMC was the approved procedure at their previous company. The FO reported being uncertain about Alliance’s policy and deferred to the captain. 

Alliance procedures stated that below 1,000 ft AAL, the descent rate ‘shall not normally’ exceed 1,000 fpm. The descent rate exceeded 1,000 fpm until 1637:29, when passing 723 ft radio altitude, with the PF arming the APP mode 3 seconds later and LOC/GS becoming the active modes. The selected altitude was then set to the missed approach altitude of 3,000 ft. 

At 1637:42 and 500 ft radio altitude, contrary to the stabilisation criteria in VMC, the:

• airspeed was 17 kt above V_AP, with a maximum of V_AP + 10 permitted
• aircraft was not in the landing configuration (flap 4 was a take‑off setting). 

The PM observed that although slightly fast, the speed was trending down, and the flight crew reported thinking the aircraft met the stabilised approach criteria at 500 ft. The PM reported having completed the before landing checklist (gear and flaps) at about 800 ft, but at 411 ft radio altitude, identified that the flap lever was in the flap 4 detent and quickly moved it to the flap 5 position. The flap transitioned to the flap 5 position at 345 ft radio altitude.

The aircraft decelerated to the target approach speed V_AP (133 kt) at 264 ft radio altitude. The captain disconnected the autopilot at 212 ft radio altitude and manually flew the aircraft to an uneventful landing at 1638:32.

Context

Flight crew information 

The captain and first officer each held an air transport pilot licence (aeroplane), Embraer E190 type rating and a class 1 aviation medical certificate. 

The captain had a total flying time of 7,100 hours, 4,000 of which were on Embraer E190 aircraft, and 150 of those were accrued in the last 90 days. The captain had previously flown Embraer E120 aircraft for about 6 years and E190 aircraft for another 4–5 years with a different operator. As a direct entry captain to Alliance, the captain conducted 6 sectors and then a line check before operating for about 2 years with Alliance on the E190 aircraft. The captain was a training captain at their base and had conducted some of the first officer’s training. 

The first officer had a total flying time of 16,325 hours, 274 of which were on the Embraer E190, and 130 of those were accrued in the last 90 days. The FO commenced ground training for the Embraer E190 type rating with Alliance in May 2024 and started operating for Alliance in late September 2024. 

The captain reported having slept 7 hours the previous night, 6 hours the night before that, and assessed their fatigue as ‘Okay, somewhat fresh’. The FO reporting having slept 8.5 hours on each of the previous 2 nights and assessed their fatigue as ‘Very lively, responsive, but not at peak’.[9] There was no evidence that fatigue was a factor in this occurrence. 

The captain assessed their workload during the approach as 8/10. Their workload was increased by diverting around weather and a thunderstorm building in the vicinity of the airport, flying the descent in manual speed mode and the approach in manual modes. The FO assessed their workload during the approach as 10/10, in attempting to achieve the stabilised approach criteria. 

Approach mode disarming

VH-UYO had Load 27 Honeywell flight management system (FMS) software, which used flight director (FD) modes and non‑FMS navigation for the ILS approach. Provided the ILS approach was part of the flight plan and NAV 1 and 2 were in AUTO FMS mode, the system would transition from FMS navigation to ILS approach through the preview mode at 150 NM. The recorded flight data showed that both NAV 1 and 2 frequencies were selected to the Darwin runway 29 ILS‑Z, and the PM reported that preview mode selected as expected.

The transition from FMS to FD navigation could also be done manually by pressing the VOR/LOC (V/L) button on the guidance panel. The V/L button selects VOR or LOC as the primary navigation source for the on‑side PFD and toggles between VOR/LOC1 and VOR/LOC2. The recorded data showed that the primary navigation source was FMS1 until it changed to VOR/LOC1 at 1634:57, less than one second after LOC became active before dropping out, and remained VOR/LOC1 until after landing. 

Embraer analysed the recorded flight data and identified that when the auto‑flight control system (AFCS) captured LOC mode, the display systems had not transitioned to the LOC navigation source. In that situation, the localiser capture is invalidated, and the autopilot reverts to ROLL/FPA. Although the navigation source only recorded every 4 seconds, Embraer advised that this was the most likely reason for the mode reversion. Honeywell advised that as the recorded data rate was less than the system update rate, there was insufficient information to assess whether a synchronisation issue existed. However, Honeywell will assess whether aircraft operators have reported any similar events.  

Pressing the approach (APP) pushbutton arms approach mode if it is not armed or active, and disengages or disarms approach mode if it is armed or active. In interview several weeks after the incident, the captain reported that they pushed the APP button once to arm the approach mode after receiving ATC clearance for the ILS, and probably inadvertently pushed it again, disarming the mode, on receiving a second clearance for the ILS.

However, ATC recordings showed that the second ILS clearance was received about 50 seconds after the mode reversion and a third clearance 40 seconds later. The captain also reported having re‑armed approach mode as soon as they selected heading mode after the reversion (at about 2,700 ft), but a review of flight data identified that the approach mode was not re‑armed until 620 ft AAL. 

The approach mode armed status was recorded every 2 seconds in the flight data and was armed 1 second before LOC captured and not armed (just less than) 1 second after LOC capture. Therefore, the possible second press of the APP button would have to have occurred within 1 second of the LOC capture. 

Mode reversion

The E190 Aircraft Operations Manual described roll hold (ROLL) mode as the basic lateral mode. Depending on the bank angle at the moment of ROLL activation, the autopilot (AP) will maintain the following bank angles until another lateral mode is selected: 

• bank angle at 6° or below: AP levels the wings
• bank angle above 6° and below 35°: AP holds the present bank angle
• bank angle at or above 35°: AP maintains a bank angle of 35°

Relevant to this occurrence, roll mode is activated:

• when there is no lateral mode active and a vertical mode is selected
• by deselecting an active lateral mode. 

Roll mode is deactivated when another lateral mode is activated.

Flight path angle (FPA) is the basic vertical mode, except during take‑off. The FPA can be used for vertical navigation by selecting a higher or lower altitude and then pressing the FPA button. 

Alliance’s procedures required changes in lateral and vertical engaged modes to be announced by the pilots:

• the pilot who changes the flight mode checks on the flight mode annunciator (FMA) and verbally confirms the selected mode
• the other pilot verbally confirms the new flight mode. 

The procedures also stated that:

When the aircraft does not perform as expected, the autopilot must be disconnected and manual flight promptly established. 

Flap configuration

The E190 has slats on the leading edge of the wing and flaps on the trailing edge. There are 7 slat/flap control lever positions: up, 1–5 and full. Flap 4 is a take‑off configuration, and normal landing configurations are flap 5 or full. In flap 4 and flap 5 positions, the flaps extend to 20° and slats to 25°. Although the physical positioning of the flaps and slats is identical, the flight system logic triggers different warnings based on the selected position as follows: 

• Retard mode reduces the thrust levers to idle during flare on landing. This only occurs when the slat/flap lever position is at 5 or full and landing gear is down.
• Enhanced ground proximity warning system (EGPWS) mode 2 – excessive terrain closure rate operates mode 2A when flaps are not in the landing position and 2B with flaps down and in the landing position. Violations of the alert envelopes produce aural ‘TERRAIN TERRAIN’ and ‘PULL UP’ alerts. Mode 2B has a desensitized alert envelope with a reduced upper height limit and a higher closure rate when:
  • flaps are in the landing position
  • on an ILS, the aircraft is within +/- 2 dots of the localiser and glideslope
  • within 5 NM and 3,500 ft of the runway (and terrain awareness is functioning)
  • during the first 60 seconds after take‑off.
• EGPWS mode 3 alerts if a decrease in altitude occurs immediately after take‑off or during a go‑around when the flaps are not in a landing configuration (‘DON’T SINK’ aural and GND PROX PFD alerts).
• EGPWS mode 4 unsafe terrain clearance depends on radio altitude, airspeed, landing gear and flap position. In mode 4B, with landing gear down and flaps not in the landing configuration, pilots hear a ‘TOO LOW, FLAPS’ alert and see a GND PROX alert on the PFD, when below 159 kt airspeed and 245 ft radio altitude. Mode 4C operates when the landing gear or flaps are not in the landing configuration and will trigger a ‘TOO LOW, TERRAIN’ aural alert. 

On this occasion, had the flight crew continued towards landing with flap 4 configured, they would likely have received any or all of ‘TERRAIN TERRAIN’, ‘PULL UP’, ‘TOO LOW FLAPS’, and ‘TOO LOW TERRAIN’ aural alerts. 

Threshold and approach speeds      

The aircraft’s reference speed (V_REF) is 1.3 times the stalling speed (V_S) and is the minimum recommended speed at 50 ft over the threshold. It is used for landing distance calculation and is the speed to which the airspeed reference bugs are set before an approach. The approach speed (V_AP) exceeds the reference speed to account for gusts or windshear. Alliance’s E190 standard procedures defined V_AP = V_REF = + 1/2 steady headwind component + gust increment, limited to a minimum of V_REF + 5 kt and maximum V_REF + 20 kt. 

Meteorological conditions 

Forecast 

The Bureau of Meteorology (BoM) graphical area forecast encompassing the Darwin area, issued at 1359 and valid between 1430–2030 local time, stated:

• visibility greater than 10 km, scattered cumulus/stratocumulus clouds with bases 4,000 ft above mean sea level and tops above 10,000 ft, and bases from 2,000 ft over sea to 30 NM (56 km) inland
• 1,000 m visibility in scattered heavy showers of rain, occasional towering cumulus clouds with bases at 2,000 ft and tops above 10,000 ft
• 500 m visibility in occasional heavy thunderstorms with rain, occasional cumulonimbus clouds with bases from 2,000 ft and tops above 10,000 ft, broken stratus between 500 and 1,500 ft
• moderate turbulence below 400 ft in smoke and thermals over land until 1830. 

There was a tropical cyclone off the northern coast of Western Australia but no SIGMET[10] for the Northern Territory. 

The Darwin Airport forecast (TAF)[11] issued at 0851 was valid for 30 hours from 0930 on 12 February until 1530 on 13 February. Two subsequent TAF amendments were issued before the occurrence, one at 1148 and another at 1452. All TAF cloud heights are above aerodrome elevation. All had the same forecast for:

• wind from 340° (True) at 12 kt
• visibility greater than 10 km
• light showers of rain
• scattered cloud at 2,000 ft. 

For the period of the aircraft’s approach, 1614–1638, the forecast and amendments included (intermittent) periods of up to 30 minutes of:

• visibility reducing to 1,000 m in heavy showers of rain
• broken cloud at 500 ft
• scattered towering cumulus with bases at 2,000 ft.

Forecast to occur from 2330 on 11 April to 1330 on 12 April, there was a 30% probability of thunderstorms for periods up to 1 hour with:

• variable direction winds of 15 kt winds gusting to 30 kt
• visibility reducing to 500 m in thunderstorms and heavy rain
• broken cloud at 400 ft
• scattered cumulonimbus clouds with bases at 2,000 ft. 

A third TAF amendment was issued at 1642 (4 minutes after the aircraft landed), which included an additional intermittent period lasting up to 30 minutes of: 

• visibility reducing to 500 m in thunderstorms and heavy rain
• broken cloud at 400 ft
• scattered cumulonimbus clouds with bases at 2,000 ft. 

Observations 

The following weather observations at Darwin Airport occurred during the time of the aircraft’s approach.

At 1617, a special report of meteorological conditions (SPECI)[12] was issued, which included: 

• 3,000 m visibility
• thunderstorms in the vicinity (lightning detected outside the 8 km radius of the airport)
• few cloud at 1,500 ft
• broken cloud at 2,600 ft
• few cumulonimbus clouds at 2,000 ft.

At 1630, a SPECI was issued that included: 

• 4,000 m visibility
• heavy showers of rain
• few cloud at 1,500 ft
• scattered cloud at 1,900 ft
• broken cloud at 4,000 ft
• detail that 2 mm of rain had fallen in the previous 10 minutes.

At 1637, one minute prior to landing, a SPECI was issued that included:

• 8,000 m visibility
• thunderstorms and rain
• scattered cloud at 1,300 ft
• broken cloud at 3,600 ft
• few cumulonimbus clouds with bases at 2,000 ft
• advice that 0.6 mm of rain had fallen in the previous 10 minutes.

Radar imagery

The BoM Darwin/Berrimah radar was located 7 km south‑east of Darwin Airport. 

Radar images showed moderate rain in the Darwin Airport area at 1614, that reduced to light to no rain around the time of the approach. The associated cloud/cell was stationary, and according to the BoM, it was not unusual to have a stationary rain/storm sitting over the airport in the wet season. The BoM information about that radar included: 

Heavy rain over the radar site will cause attenuation of all signals. Path attenuation also occurs when the radar beam passes through an intense thunderstorm cell; the returned signal from cells further along that path will be reduced...it may 'undershoot' high level storms and rain echoes may appear less intense than actual rainfall rate.

The BoM advised that due to attenuation, the light rainfall indicating on the radar image at 1634, may have been less intense than the actual rainfall rate. 

Webcam

The BoM provided webcam images for each minute from 1634–1638 facing north and east. 

At 1638, the aircraft would have been due east of the webcam on final approach, at about 300 ft, probably the light visible in the east view at 1638 (Figure 7).

Figure 7: BoM webcam image facing east at 1638 and probable aircraft light 

Source: Bureau of Meteorology, annotated by the ATSB

The cell with heavier rain to the north was evident in the north view at 1638 (Figure 8).

Figure 8: BoM webcam image facing north at 1638 

Source: Bureau of Meteorology

Figure 9 shows satellite imagery of cloud cover at Darwin Airport at 1640, and lightning strikes that occurred in the 10 minutes prior (red) and during the period 10–30 minutes prior (orange).

Figure 9: Cloud cover at 1640 and recorded lightning strikes 

Source: Satellite image originally processed by the Bureau of Meteorology from the geostationary meteorological satellite Himawari-9 operated by the Japan Meteorological Agency. Lightning data sourced from Weather Zone Lightning Network

Automatic terminal information service 

The Royal Australian Air Force’s Darwin Airport automatic terminal information service (ATIS)[13] X‑ray (X) was issued at 1610 and included advice to expect an instrument approach and that runways 29 and 36 were active for arrivals, with runway 29 in use for departures. The runways were wet, with surface condition code 555. ATIS X‑ray also detailed the following weather conditions:

• wind from 340° at 15 kt, maximum 15 kt crosswind on runway 29
• visibility 2 km
• showers of rain
• cloud scattered at 1,200 ft
• temperature 30°C
• QNH 1007.[14]

ATIS Yankee (Y) came into effect at 1624, with the only change being a temperature reduction to 27°C. 

Based on the forecast and observed weather conditions at the time of the approach, the flight crew could not have anticipated VMC or expected to remain clear of cloud until below about 1,200 ft.

Recorded data

Flight data from the aircraft’s quick access recorder (QAR) for the incident flight was analysed by the ATSB and Embraer. 

Key parameters in the vertical flight path, depicted in Figure 10, identified that between LAPAR and about 600 ft AAL, there were:

• 7 vertical mode changes (purple)
• 11 selected altitude changes (cyan)
• significant variations in flight path angle (orange)
• significant variations in vertical speed (pink) and rates of descent exceeding 1,600 fpm including below 1,000 ft AAL.

Figure 10: QAR data including key vertical flight path parameters 

Source: Alliance Airlines QAR data, analysed by the ATSB

Although cockpit localiser and glideslope indications showed full‑scale deviation of 2.5 dots on the primary flight display and compass instrument, the recorded QAR data captured up to 5 dots deviation. Key parameters depicted in Figure 11 showed: 

• airspeed (red) remained above the target approach speed of 133 kt (V_AP) (purple) until 1638 (deviation in kt – green)
• 5 dot left and right deviations from the localiser course between LAPAR and TOROT
• 3 dot deviation above the glideslope approaching TOROT.

Figure 11: QAR data depicting speeds and key lateral flight path parameters 

Source: Alliance Airlines QAR data, analysed by the ATSB

Approach briefing

Alliance procedures required flight crew to conduct a briefing before commencing an approach. It detailed the requirements for an instrument approach briefing and a visual approach briefing. There was no policy on re‑briefing during an instrument approach if a transition to a visual approach occurred. Alliance advised that the expectation was for flight crew to continue an instrument approach even if visual reference was established. 

Descent below lowest/minimum safe altitude 

Alliance’s Operations Policy and Procedures Manual (OPPM) required all flights to be planned and conducted under instrument flight rules (IFR).[15] Company policy allowed the use of visual approaches and departures, but pilots were not permitted to downgrade to visual flight rules.

The OPPM section 7.4.11.1 stated that operation below the lowest/minimum safe altitude (LSALT/MSA) was permissible only when:

• under radar control;

• in accordance with a published [distance measuring equipment] DME arrival instrument approach or holding procedure;

• when necessary during climbing after departure from an airport, or

• when flying in VMC by day. 

CASR Part 91 Plain English Guide stated that in accordance with sub‑regulation 91.305 Minimum heights – IFR flights, aircraft must not be flown below the lowest/minimum safe altitude except when taking off or landing in VMC by day, or in accordance with: 

• a published visual or instrument approach or departure procedure
• an air traffic control clearance. 

Instrument landing system approach 

Darwin Airport runway 29 ILS-Z approach is depicted in Figure 12.

Figure 12: Darwin ILS-Z approach 

Source: Jeppesen

The Aeronautical Information Publication (AIP)[16] stated that:

Unless authorised to make a visual approach, an IFR flight must conform to the published instrument approach procedure nominated by ATC.

During an instrument approach, flight crew were required to maintain the aircraft’s flight path within certain flight tolerances. For an ILS approach the AIP stated:

Pilots must conform to the following flight tolerances:

a) To ensure obstacle clearance, both [localiser/Ground based augmentation system (GBAS) landing system] LOC/GLS final approach course and glideslope should be maintained within half scale deflection (or equivalent on expanded scale).

b) If, at any time during the approach after the [final approach point] FAP, the LOC/GLS final approach or glideslope indicates full scale deflection, a missed approach should be commenced.

Although the AIP wording combined the terms ‘must’ and ‘should’, Airservices Australia confirmed that aircraft were required to comply with the vertical guidance of the glideslope when conducting an ILS approach, and that descent outside this vertical guidance could be safety critical. 

Alliance’s Standard Operating Procedures Manual (SOPM) detailed the procedure for conducting an ILS approach. This included:

The standard profile assumes the aircraft will approach 3,000 ft AFE [above field elevation] with Flap 1 selected and will be configured with landing flap with checklists complete prior to stabilization altitude. 

Standard calls were documented in the Alliance SOPM, which stated: 

Deviation calls are to be made if the listed deviation limit is exceeded and no corrective action has been observed. Upon acknowledgement of a deviation, corrective action must be taken.

Table 1 is an extract of the standard calls relevant to this approach. 

Table 1: Selected standard calls 

Source: Alliance Airlines 

Alliance’s OPPM section Instrument approaches included:

Any time the PNF [pilot not flying]/PM calls deviations from 'on slope' the PF should make corrections to avoid flight path excursions towards full scale. 

The PNF/PM should continue slope deviation calls until the glideslope indicator stops moving toward full scale and whenever the indicator is at full scale.

…

When continuing the approach, continually cross-check visual profile indications against glideslope profile indications down to 100 ft AGL…Duties of the PNF/PM apply on all instrument approaches through to 100 ft above threshold height, even if visual flight conditions are encountered before reaching the minimum.

The same section stated:

During a visual approach using the ILS, the glideslope calls do not need to be given.

Visual approaches

The term ‘visual’ was used by: 

• ATC to instruct a pilot
• a pilot to accept responsibility

to see and avoid obstacles while operating below the minimum vector altitude or minimum/lowest safe altitude. 

Alliance permitted flight crew to conduct visual approaches by day and night in accordance with AIP requirements. The AIP required an IFR flight to conform to the published instrument approach procedure unless they were authorised by ATC to make a visual approach. By day, ATC could authorise an IFR aeroplane to conduct a visual approach when:

• the aircraft is within 30 NM of the aerodrome
• the pilot has established and can continue flight to the aerodrome with continuous visual reference to the ground or water
• visibility along the flight path is not less than 5,000 m or the aerodrome is in sight. 

If these conditions existed, the AIP stated:

the pilot need not commence or may discontinue the approved instrument approach procedure to that aerodrome…

In controlled airspace, an ATC clearance was required to conduct a visual approach. The pilot was required to report ‘visual’ to signify to ATC that the visual approach requirements could be met and maintained as part of any request for a visual approach. The pilot was then required to maintain the track or heading authorised by ATC until (by day) within 5 NM (9 km) of the aerodrome. 

The Alliance OPPM stated that in VMC on a visual approach, the aircraft must join the circuit on the upwind, crosswind or downwind leg, or make a straight-in approach after establishing on final approach by 5 NM. During this occurrence, when 5 NM from the airport, the aircraft was about 1 km left of the extended runway centreline.

The required visual approach callouts at 500 ft stabilisation height were:

• if stabilised criteria satisfied: PM verifies or calls out ‘500 STABLE’
• otherwise: PM verifies or calls out ‘500 NOT STABLE’ and the PF initiates a go‑around. 

The flight crew had not briefed for a visual approach, advised ATC they were visual or received clearance to conduct a visual approach. 

Go-around and discontinued approach 

The Alliance OPPM included Non punitive go around policies, and listed conditions which, if encountered, the PF should consider carrying out a go‑around. The conditions included those that could lead to stabilised approach requirements not being adhered to. The Alliance SOPM distinguished between a discontinued approach and a go‑around in which take‑off/go‑around (TOGA) thrust was applied.

SOPM 5.20.4 Discontinued approach included: 

During the initial phase of the approach, there may be a situation where the approach needs to be discontinued. If the aircraft is at or near the missed approach altitude, far from the missed approach point and not fully configured for landing, a go around procedure may not be appropriate. The go around can lead to an excess thrust that may result in overshooting the missed approach altitude. For this situation, a discontinued approach is recommended.

NOTE

❖ A Go-around should be conducted:

o In Day VMC below 500FT AFE,

o In [instrument meteorological conditions] IMC[17] or at night below 1000ft AFE.

SOPM 5.20.3 Go-around included: 

No approach should be initiated unless the prevailing conditions have been understood and the crew found that landing is acceptable without undue risk. Philosophically all approaches should be treated as approaches followed by missed approaches, and landing should be treated as the alternate procedure. This mindset depends on a good approach briefing, on the knowledge of the missed approach procedure and on proper programming of the FMS.

Alliance advised that in this incident, a discontinued approach at 3,000 ft (when the approach mode disarmed) would have been appropriate. 

Stabilised approach criteria

A stabilised approach is one where an aircraft maintains a constant angle descent to the runway while other key flight parameters such as airspeed and aircraft configuration are controlled within specific ranges. An approach is stable when all the stabilisation criteria specified by the operator are met.

According to an International Air Transport Association report Unstable approaches: risk mitigation policies, procedures and best practices (IATA, 2017), historical commercial aviation accident data indicated that many accidents occurred during the approach and landing phases of flight. Frequent contributing factors were an unstable approach and subsequent failure to initiate a go‑around. Failure to maintain a stable approach could result in landing too fast or too far down the runway, a hard landing, runway excursion, loss of control, or collision with terrain. The report also highlighted the importance of callouts in enhancing situational awareness and encouraging rapid error correction. 

The report described an operator’s minimum stabilisation height as a ‘gate’ at which if the aircraft was not stable on the approach path in the landing configuration, a go‑around must be executed. Additionally, although many operators have one gate for IMC and a lower gate for VMC, variations in stabilisation heights between operators, approach types and meteorological conditions (VMC/IMC) could cause confusion. As a result, many airlines implemented a single set of criteria and one gate for a particular approach type, such as 1,000 ft for an instrument approach, and 500 ft for visual circuit or circling approaches. Having a single gate also makes it easier for an operator to track compliance using flight data monitoring programs.

The Flight Safety Foundation’s Approach and landing accident reduction briefing note 7.1 – Stabilized Approach described the benefits of a stabilised approach as:

• increasing the flight crew’s situational awareness of the:
  • horizontal
  • vertical
  • airspeed
  • energy state
• more time and attention for monitoring communications, weather and aircraft systems
• more time for monitoring by the PM
• defined criteria to support land or go‑around decision‑making
• consistent landing performance. 

Alliance’s standard operating procedures required all flights conducting instrument approaches to be stabilised by 1,000 ft above aerodrome level, and an immediate go‑around was required for any approach that did not meet the following stabilised approach criteria: 

a) the correct flight path;

b) only small changes in heading/pitch are required to maintain the correct flight path;

c) the aircraft speed is not more than V_APP + 10 knots indicated airspeed and not less than V_REF;

d) the aircraft is in the correct landing configuration;

e) sink rate is no greater than 1,000 feet per minute

f) thrust or power setting is appropriate for the aircraft configuration;

g) all briefings and checklists have been completed;

h) specific types of approaches are stabilized if they also fulfil the following

i. instrument landing system (ILS) approaches must be flown within one dot of the glideslope and localizer

ii. a Category II or Category III ILS approach must be flown within the expanded localizer band

i) unique approach procedures or abnormal conditions requiring a deviation from the above elements of a stabilized approach require a special briefing to have been completed prior to beginning the approach.

• Note 1: A momentary excursion is permitted for points (c) & (e). A momentary excursion is defined as a deviation lasting only a few seconds and where every indication is that it will return to the stabilised criteria as listed in points (c) & (e).

• Note 2: Where the nominal descent path for a particular approach requires a descent rate greater than 1000 fpm. This is only permitted when expected rates of descent have been briefed prior to the approach being commenced. 

Stabilized Heights 

All flights shall meet all of the above stabilized approach criteria by 1,000 feet above aerodrome level except under the following circumstances: 

Visual approach: 

Speed may be higher than VAPP + 10, provided it is within limits and expected to reduce to Vapp+10 or below by no later than 500ft AAL.

Note 3: Visual conditions as defined by Jeppesen AUS or AIP - the pilot has established and can continue flight to the airport with continuous visual reference to the ground or water; and visibility along the flight path is not less than 5000m.

…[followed by Visual circuit, Circling approach and RNP-AR approach]

An approach that does not meet, or subsequently exhibits sustained deviations outside of these criteria requires an immediate go-around.

Alliance advised that the Note 3 under the Visual approach heading was supposed to clarify that the term ‘visual approach’ and the associated policy was not only for the situation where flight crew were cleared for a visual approach, but included when they encountered visual conditions during an instrument approach. 

Alliance SOPM section Intercepting glideslope from above, included:

Several different situations, such as ATC restriction, may lead to a glideslope interception from above. If that happens, the pilots must take the appropriate actions to guarantee a stabilized approach. If the stabilized approach criteria are not met, the PF must initiate a Go Around. The approach must be stable before reaching 1000 ft AGL (IMC), 500 ft (VMC), or other altitude in accordance with company policies. 

Alliance’s SOPM (5.16.7) Stabilised approach stated that the aircraft must meet the stabilised approach criteria in the OPPM, and included: 

For a 3D instrument approach or a visual approach (except for a visual circuit or circling approach) the aircraft should be established on profile by 3000ft AFE. If, due to operational circumstances the aircraft is not on a 3° profile, an acceptable flight path should be maintained to regain profile no later than 1500ft AFE. Descent rate limits are outlined in the OPPM.

The OPPM specified ‘Descent rate limits’: 

The following values for the rate of descent below the transition altitude shall not normally be exceeded:

• 3000 fpm down to an altitude of 3000 ft above aerodrome level (AAL).

• 2000 fpm down to an altitude of 2000 ft AAL transitioning to 1000 ft AAL

• 1000 fpm below 1000 feet AAL

The SOPM (5.16.7) Stabilised approach also stated: 

On the normal profile, the aircraft should approach 3,000 ft AFE with Flap 1 selected. Flap 2 should be selected leaving 3000ft. The landing gear should be selected down and flap 3 selected no later than 2000ft AFE. Final landing flap should be selected such that all stable approach criteria can be satisfied.

Alliance advised that in the previous 4 years, almost all their approach incidents occurred following selection of flap 2 below the prescribed 3,000 ft. They reported that delayed selection of flap 2 ‘then compresses everything’.

Guidance material for Part 121.200 from CASR Part 121 Acceptable means of compliance/guidance material - Australian air transport operations—larger aeroplanes included discontinuing an approach to continue in VMC as one situation that reduced the likelihood of a stabilised approach and should be avoided where not operationally necessary.

Crew coordination 

The captain reported being aware when the aircraft was outside half scale deflection of the localiser and more than half scale deflection above the glideslope, which was why they advised ATC and were cleared to maintain the minimum vector altitude. The captain could not recall whether they had advised ATC they were visual but assessed that they could continue the unstable approach below 1,000 ft as they were in visual conditions. The captain reported that there were no callouts from the PM and if they were not stable at 500 ft, the captain would have expected an ‘unstable’ callout from the PM and would have conducted a go‑around. 

The FO (PM) reported that normally they would aim to be fully configured and stable by 1,500 ft and the ‘absolute latest’ by 1,000 ft for an instrument approach. In this case they were not, which is why the captain called ‘visual’ and said they would use the visual approach ‘gate’ of 500 ft. The FO reported that in that split second (passing 1,000 ft), they agreed with the captain to continue because they were visual, although the aircraft was above the glideslope and ‘slightly’ fast, the speed was trending down, and the FO thought that the aircraft was fully configured for landing. The FO assessed that the aircraft was stable at 500 ft, unaware that the flaps were incorrectly configured, and had they called ‘unstable’ at 500 ft, the captain would have been obliged to conduct a go‑around.  

The FO also reported that the en route diversions and storms near the airport may have resulted in perceived time pressure to continue the landing. They had sufficient fuel to discontinue the approach and make a second attempt. 

The cockpit voice recording was not retained for the investigation. The flight crew could not recall whether the PF called out mode changes after the mode reversion. The PM reported calling distance and heights for the profile, but did not make speed, slope or track deviation calls because the PF was taking corrective action. 

The Alliance OPPM detailed task sharing and the responsibilities of the PF and PM and noted that this was particularly important in high workload phases of flight, including approach and landing. It also stated that the PM should:

query the PF actions that are not understood or considered inappropriate. He/she should also demonstrate assertiveness and express advocacy to share any concern on the flight progress. 

Alliance OPPM defined authority gradient as ‘the relative authority of air crew in the chain of command … if the gradient is too steep, air crew may be unwilling or unable to express their beliefs to those in higher authority’. 

Similar occurrences 

Unstable approach involving Embraer 190, VH‑UZI, about 4 km north‑east of Brisbane Airport, Queensland, on 9 May 2024 (AO‑2024‑030)

During approach to Brisbane Airport, the aircraft automated ILS flight mode unexpectedly disengaged. The flight crew focused on troubleshooting the unexpected change and recapturing the ILS flight director mode, rather than conducting a go‑around. During that time, the flight crew did not effectively monitor the aircraft's flight path, and the aircraft exceeded the stabilised approach criterion of one dot glideslope deviation. 

After recognising that the aircraft was low, the captain increased the aircraft pitch, resulting in an enhanced ground proximity warning system (EGPWS) glideslope warning. The flight crew did not perform the required terrain avoidance manoeuvre, instead continued the approach. The captain arrested the aircraft’s descent and re‑established the aircraft on the glidepath, before continuing the approach and landing.

Alliance took safety action in response to that occurrence including issuing an operational notice to remind flight crew of the stabilised approach criteria and go‑around requirements. 

Descent below glideslope involving Fairchild SA227, VH‑VEU, about 17 km north‑east of Brisbane Airport, Queensland, on 2 July 2024 (AO‑2024-040)

During the ILS approach, the aircraft descended below the 3° glideslope, triggering an air traffic control ATC minimum safe altitude warning about 8 NM (14 km) from the runway. ATC advised the crew that they were observed below the glideslope, however the aircraft continued descent below the glideslope until 3 NM (6 km) when the descent rate was reduced. The aircraft then passed above the glideslope before the rate of descent increased again and subsequently the glideslope was re‑intercepted from above 1 NM (2 km) from the runway at 500 ft. The aircraft then followed a stabilised flight path to landing.

The investigation found that the pilot monitoring was not monitoring the glideslope and did not challenge the pilot flying to correct the deviation and reduce the aircraft’s descent rate. Additionally, the operator's standard operating procedures contained areas of inconsistency when an aircraft entered visual conditions during an instrument approach, and that the AIP was unclear as to whether pilots were required to comply with precision approach flight tolerances.

The aircraft operator subsequently amended its standard operating procedures as follows:

• the instrument approach procedure has been updated:
  • the approach brief now requires discussion of expectations if visual conditions arise
  • the statement that ‘during a visual approach using the ILS, the glideslope calls do not need to be given’ has been removed
  • a requirement to make callouts using reference to visual slope indications has been added.
• a note has been added to the visual approach procedures stating that crew require a clearance to discontinue an instrument approach in controlled airspace
• increased focus on pilot monitoring skills during:
  • proficiency checks, which will now include standard instrument departure and standard arrival routes
  • line training for new flight crew
• addition of a pilot monitoring sector to the annual line check.

Safety analysis

Mode reversion

Nearing the initial approach fix (LAPAR) for the Darwin Airport runway 29 instrument landing system (ILS)‑Z approach, the aircraft’s approach, localiser and glideslope modes were armed, with the correct ILS frequency set as the armed navigation source. As the aircraft flew by LAPAR, the localiser mode engaged for one second before the auto‑flight system reverted to lateral roll and vertical flight path angle modes. 

It is possible that this occurred due to the captain inadvertently pressing the approach pushbutton at the same time the localiser captured. The captain recalled that this occurred because they received a second ATC clearance for the ILS, however, at that time, they had only been cleared for the ILS once. They received a second clearance about 50 seconds later and a third clearance 40 seconds after that. The pushbutton was not recorded in the data but pressing it when approach mode was armed would disarm approach mode consistent with the mode reversion. 

Embraer's analysis of the recorded data found that the ILS navigation display source had not engaged at the time localiser mode became active. Therefore, it was most likely that this non‑synchronisation led the flight control and guidance system to invalidate the capture and revert to basic modes. The avionics manufacturer, Honeywell, advised that as the recorded data did not update as frequently as the system status, it was not possible to determine whether a synchronisation issue existed.  

The mode reversion resulted in the aircraft maintaining the 20° right bank and approximately level flight path angle that were present at the time of the mode reversion. 

Automation and approach continuation

Alliance’s procedures stated that if the auto‑flight system was not doing what the pilot expected, they were to disconnect the autopilot and manually fly the aircraft. However, following the unexpected mode change, the captain, who was the pilot flying (PF), did not re‑engage approach mode or disconnect the autopilot until about 200 ft above the aerodrome elevation, in accordance with normal landing procedures. This resulted in the aircraft deviating beyond the permitted tolerance from the localiser course and above the glideslope.

It took less than 3 minutes from the mode reversion at 3,000 ft, to the aircraft being established on the ILS and in the landing configuration, about 400 ft above aerodrome elevation. During that time, there were several changes to the lateral and vertical modes, selected heading and altitude, and significant variations in vertical speed, as the PF manipulated the auto‑flight system to recapture the localiser and glideslope. 

There were also several triggers for the flight crew to discontinue the approach. The flight crew reported that their en route weather deviations and thunderstorms in the vicinity of the airport may have led to perceived pressure to continue the approach, but that there was adequate fuel on board to discontinue and conduct a second approach. 

Once outside the lateral tolerance of the approach, the aircraft was operating contrary to the air traffic control (ATC) clearance and descended below the minimum safe altitude, likely while in instrument meteorological conditions (IMC). The pilot monitoring (PM) reported that they did not call out the course deviations, as the PF was actively working to correct them. Instead, after descending about 500 ft, the PM advised ATC they were re‑intercepting the localiser and was assigned the minimum vector altitude to ensure terrain separation. As a result, the aircraft then maintained altitude, while the glideslope diverged beneath the flight path. 

The PM did not read back the ATC clearance to descend once they had intercepted the glideslope, consistent with being focused on monitoring tasks and their self‑assessed 10/10 workload during the approach. The PM selected flap 2 as the aircraft captured the localiser, about 800 ft below the normal (but not mandatory) 3,000 ft flap 2 selection height. Alliance reported that this late selection had a similar effect to other recent approach incidents, where the associated delayed speed reduction reduced the time available to stabilise the approach. 

As the aircraft passed the final approach fix (FAF) and then descended through 1,500 ft, it was established on the localiser but 3 dots above the ILS glideslope. Alliance’s procedures required the ILS to be flown within 1 dot of the glideslope, and stated that aircraft ‘should be’ on the 3° glideslope no later than 1,500 ft. 

The PF reported stating to the PM that they were visual at about 2,500 ft, but the PM reported this occurred just as the aircraft approached 1,000 ft. Without a cockpit voice recording, it could not be determined when visual flight conditions were established. 

At 1,000 ft, which was the stabilisation height for an instrument approach, the PF incorrectly assessed that although several stabilised criteria were not met, as they were then in visual conditions, they could continue (unstable) to 500 ft. Although this had been the procedure at the PF’s former company, Alliance required all stabilised approach criteria, other than airspeed, to be met at 1,000 ft. The PM was sufficiently unsure of Alliance’s policy to defer to the captain’s experience, as the senior base training captain who had conducted some of the PM’s training. 

At 500 ft, the PM assessed that the stabilised approach criteria were met as, although the airspeed was still slightly fast, it was trending down, and they continued the approach. Although the flight crew reported having completed the before landing checks prior to 500 ft, shortly afterwards, the PM identified that they had inadvertently selected a take‑off flap setting (passing about 1,100 ft) instead of a landing setting, which they had not detected earlier. The PM rectified the flap setting and an uneventful landing followed. 

Although the landing was uneventful, had the incorrect flap setting not been rectified, thrust retard mode would not have engaged during the landing flare, and EGPWS warnings would have been triggered by the use of different tolerances than with the aircraft configured for landing. The use of selected heading and selected altitude to drive the aircraft’s trajectory meant that these may not have been set correctly had a go‑around been initiated either by the flight crew or ATC. 

A coupled ILS approach should require minimal flight crew intervention other than monitoring. Continuing an approach using inappropriate modes increased the likelihood of an unstable approach. International research showed that unstable approaches and failure to initiate a go-around could result in landing too fast or too far down the runway, a hard landing, runway excursion, loss of control, or collision with terrain. Although visual conditions reduce the risk of collision with terrain, they do not mitigate against landing incidents resulting from poor energy management. 

Alliance stabilisation heights

Alliance provided stabilised approach criteria consistent with international and Civil Aviation Safety Authority guidance, including airspeed, flight path and energy management parameters, to reduce the risk of landing accidents. However, Alliance’s minimum stabilisation heights at which these criteria were required to be met, varied between approach types and meteorological conditions, and were not clearly documented. 

Alliance specified a stabilisation height of 1,000 ft for instrument approaches, but under the heading Visual approach, permitted a 500 ft stabilisation height for an instrument approach in VMC, provided only the airspeed exceeded the stable speed criterion, and all other stabilised approach criteria were met. Additionally, elsewhere in the procedures for intercepting a glideslope, it stated that an approach must be stable before reaching 1,000 ft in IMC, 500 ft in VMC ‘or other altitude in accordance with company policies’. Alliance did not have a policy for transitioning from an instrument approach to a visual approach and advised that its expectation was for flight crew to continue an instrument approach even when entering VMC.

In this incident, the lack of clarity regarding which of the stabilised approach criteria were not required before continuing to 500 ft, resulted in the flight crew incorrectly assessing that they could continue to 500 ft in VMC while the criteria were not met for:

• speed
• rate of descent
• glideslope
• landing configuration
• before landing checks complete.  

International Air Transport Association guidance stated that using a single stabilisation height for one type of approach, regardless of weather conditions, can reduce confusion and make it easier for operators to track stabilised approach compliance using flight data monitoring. Clear stabilisation heights also support flight crew decision-making to initiate a go‑around. 

Findings

From the evidence available, the following findings are made with respect to the unstable approaching involving Embraer E190, VH-UYO, near Darwin Airport, Northern Territory, on 15 February 2025.

Contributing factors

• On crossing the initial approach fix for the instrument landing system (ILS) approach, due either to a system synchronisation issue or the pilot flying inadvertently disarming the approach mode, the aircraft’s auto‑flight system reverted to roll and flight path angle modes.
• Following the unexpected mode change, the pilot flying did not re‑engage approach mode or disconnect the autopilot. This likely contributed to the aircraft deviating outside the required lateral tolerance of the approach below the minimum safe altitude while in instrument meteorological conditions.
• The flight crew did not discontinue the approach when the aircraft was unstable at the 1,000 ft stabilisation height as they incorrectly assessed that they could continue to 500 ft in visual meteorological conditions, with multiple stabilised approach criteria unmet.
• In the limited time available to stabilise the aircraft by 500 ft, the flight crew incorrectly assessed that the aircraft was stable and continued the approach, unaware that the pilot monitoring had inadvertently selected an incorrect flap configuration.
• Alliance Airlines' standard operating procedures were unclear about the criteria for continuing an unstable instrument approach to 500 ft when aircraft entered visual conditions.

Safety actions

Safety action by Alliance Airlines 

Alliance Airlines issued an operations notice ‘to improve clarity and compliance’ with the stabilised approach criteria. It detailed the stabilised approach policy. It also amended the stabilisation height such that for 3‑dimensional and 2‑dimensional instrument approaches, and straight‑in visual approaches, the stabilised criteria were to be met by 1,000 ft above aerodrome elevation.

The 500 ft stabilisation height applied only to visual circuit or circling manoeuvre approaches. The notice reminded flight crew of Alliance’s ‘non punitive go around policy’ and required all unstable approaches to be reported.

Alliance Airlines also conducted a flight data review of unstable approaches over the previous 6 months to identify similar occurrences.

Sources and submissions

Sources of information

The sources of information during the investigation included:

• the flight crew and air traffic controllers
• Alliance Airlines
• Airservices Australia
• Bureau of Meteorology
• Embraer
• Honeywell
• recorded flight data.  

References

Civil Aviation Safety Authority (2023, December 20). CASR Part 121 Acceptable means of compliance/guidance material - Australian air transport operations—larger aeroplanes. Retrieved May 15, 2025, from Part 121 of CASR Australian air transport operations - larger aeroplanes | Civil Aviation Safety Authority

Civil Aviation Safety Authority (2025, January). CASR Part 91 Plain English Guide version 4.2. Retrieved May 15, 2025, from Part 91 plain English guide version 4.2 

Flight Safety Foundation (2000). Approach and landing accident reduction Briefing Note 7.1: Stabilized Approach. Retrieved May 15, 2025, from FSF ALAR Briefing Note 7.1: Stabilized Approach 

Flight Safety Foundation (2015, June 8). Normalization of Deviance. Retrieved May 15, 2025, from Normalization of Deviance - Flight Safety Foundation

International Air Transport Association (2017). Unstable approaches: risk mitigation policies, procedures and best practices. Retrieved May 15, 2025, from Unstable approaches: risk mitigation policies, procedures and best practices 

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 flight crew and air traffic controllers
• Alliance Airlines
• Airservices Australia
• Civil Aviation Safety Authority
• Bureau of Meteorology
• Embraer
• Honeywell
• United States National Transportation Safety Board
• Brazil Aviation Accident Investigation and Prevention Center.

Submissions were received from:

• Airservices Australia
• Alliance Airlines
• the first officer
• Embraer.

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. Terminology An explanation of terminology used in ATSB investigation reports is available here. This includes terms such as occurrence, contributing factor, other factor that increased risk, and safety issue. Publishing information Released in accordance with section 25 of the Transport Safety Investigation Act 2003 Published by: Australian Transport Safety Bureau © Commonwealth of Australia 2025 Ownership of intellectual property rights in this publication Unless otherwise noted, copyright (and any other intellectual property rights, if any) in this report publication is owned by the Commonwealth of Australia. Creative Commons licence With the exception of the Commonwealth Coat of Arms, ATSB logo, and photos and graphics in which a third party holds copyright, this report is licensed under a Creative Commons Attribution 4.0 International licence. The CC BY 4.0 licence enables you to distribute, remix, adapt, and build upon our material in any medium or format, so long as attribution is given to the Australian Transport Safety Bureau.  Copyright in material obtained from other agencies, private individuals or organisations, belongs to those agencies, individuals or organisations. Where you wish to use their material, you will need to contact them directly.

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.

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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.