Avionics/flight instruments

Investigation summary

What happened

At around 1830 on 10 February 2025, a Sharp Airlines Fairchild SA227, registered VH‑UZN, was being prepared for a freight operations flight from Townsville Airport to Brisbane Airport, Queensland, with 2 crew on board.

The captain conducted an undocumented abbreviated external inspection of the aircraft. Around the same time, the first officer removed engine bungs and static port covers, however, could not reach the pitot tube covers located on the nose of the aircraft. This was communicated to the captain, who advised they would remove them, however, the captain subsequently forgot. 

During the take-off run, both crew members recognised that the airspeed indicators were rising slower than anticipated, however, by this time, the captain was uncertain if there was sufficient runway remaining to safely stop the aircraft and elected to continue the take-off. During the climb, the first officer identified that the pitot tube covers have been left installed on the pitot tubes, which they announced to the captain. The crew then returned the aircraft to Townsville for an uneventful landing. 

What the ATSB found

The ATSB found that due to a combination of a memory lapse and incorrect assumption the pitot tube covers were not removed prior to departure. It was also identified that the operator’s expectation as to what external aircraft inspection was required prior to this flight was not clearly stated in the procedures. In addition, the operator’s expectation that crews would fit pitot tube covers when the aircraft was unattended on the ground for 60 minutes or longer was inconsistent with its written procedures.

Further, the external security check, required to be completed prior to every flight, did not include ensuring the pitot tube covers had been removed. 

Finally, the flight crew did not recognise that slow rising airspeed indications was symptomatic of blocked pitot tubes and, as a result, did not reject the take-off. 

What has been done as a result

Sharp Airlines advised that it was reviewing the company standard operating procedures to ensure clarity of process for pre-flight inspections. 

Safety message

This occurrence highlights the importance of conducting an airspeed check early in the take-off run and recognising that if this is not as expected that the take-off should be rejected. Flight crews should be aware of the typical symptoms associated with a blocked pitot tube, and that the airspeed may slowly increase.

The occurrence also illustrates the importance of procedures clearly stating what inspections are required and when. Flight crew pre-flight inspections are an important risk control. If inspections are not done correctly, it increases the risk of defects not being identified and/or the aircraft not being correctly configured for flight.

The occurrence

Background

This incident occurred on 10 February 2025, however, due to a reported administrative error, the ATSB was not advised until 18 July 2025. The ATSB subsequently commenced an investigation on that day. As the interviews with the flight crew were conducted 5 months after the occurrence, their recollection of the occurrence was degraded.

Pre-flight 

At around 1830 local time on 10 February 2025, a Sharp Airlines Fairchild SA227-DC Metro 23, registered VH-UZN, was being prepared for a freight flight from Townsville Airport to Brisbane Airport, Queensland with 2 crew on board. 

The operator’s freight flights were usually conducted as a single-pilot operation, however, due to the aircraft’s autopilot being unserviceable, 2 flight crew were required to operate the aircraft. As such, the captain and first officer (FO), who normally conducted regular public transport operations, were relocated to Queensland for one week, to conduct freight operations. 

Both crew members signed on for duty that morning at 0100 in Brisbane and signed off at 0818 in Townsville, where they spent the day resting in a hotel room. They re‑commenced the shift shortly after 1800 to operate the Townville to Brisbane sector. All of the flight planning had been completed during the first duty, so the crew reassessed the conditions to ensure nothing had changed. The preparation for the flight, including the inspection of the aircraft, was conducted just prior to last light with no visibility restriction.

It was the captain’s responsibility to conduct or allocate the pre-flight external inspection (see the section titled External inspections). They advised that, as they had flown the aircraft earlier that day, a daily inspection had already been completed, and a crew change inspection (see the section titled Crew change inspection) was not required.

Instead, the captain advised they conducted an abbreviated inspection, which they did not discuss with the FO. The FO advised that they had flown with the captain on a few occasions previously and the captain had always conducted the pre-flight inspection, and they expected this to occur on this day. 

Regardless, to assist the captain, as they had done on previous days, the FO commenced some of the pre-flight tasks by removing the engine bungs and static port covers and preparing the aircraft for the aircraft loaders to arrive. They were unable to reach the pitot tube covers on the top of the nose cowl of the aircraft (Figure 1). The FO reported that they normally used a portable step, that was available in the passenger transport aircraft, to remove the pitot tube covers. However, the step was not available in the freight configuration aircraft.

In addition, they could not reach a ladder that was stowed in the rear locker as it had moved to the far side of the locker during flight. They placed the engine bungs and static port covers into a bag that they then placed on the ground beside the forward cargo hold, to remain until the pitot tube covers were removed and also placed in the bag.

Figure 1: Pitot tubes on Fairchild SA227

Source: EastWest Aviation, annotated by the ATSB

The captain was inside the aircraft completing pre-flight paperwork when the FO entered the aircraft and advised them that they could not reach the pitot tube covers. The captain acknowledged this and advised they would remove them. 

There were delays of around 30 minutes while the crew waited for the aircraft loading to be completed. During this time, it had started raining heavily and became dark. The FO noticed that the bag containing the bungs and static covers was filling with water from the rain. In response, they retrieved the bag and placed it into the forward locker, observing ‘remove before flight’ tags in the bag.

Only aircraft operating at the Brisbane base had static port covers that also had ‘remove before flight’ tags attached, which the FO advised were identical to the tags attached to the pitot tube covers. As such, the FO, seeing the ‘remove before flight’ tags, presumed the captain had removed the pitot tube covers and placed them in the bag.

There were then further delays as the aircraft required reloading, and the captain was required to recalculate the manual trim configuration for the aircraft. The captain later stated feeling frustrated by the loading delays and that they likely felt some self-induced time pressure to depart, to avoid the worst of the incoming weather. They also later advised the operator that due to the heat and humidity, they did not wear the rain jacket provided, which may have influenced them not wanting to be outside the aircraft longer than necessary. 

Once loading was complete and the aircraft was ready for departure, in accordance with company procedure, the FO commenced the final external security check (see the section titled External security check) which included a ‘4,3,2,1 check’ (see the section titled 4321 check). This check did not require that they inspect the pitot tubes to ensure the covers had been removed. 

As the FO returned to the entry door, the captain stepped outside the aircraft. The FO incorrectly presumed that the captain was going to inspect the aircraft. However, neither crew discussed the external inspection, nor the final 4,3,2,1 check, prior to closing the aircraft’s main door.

Flight

The crew reported that as the aircraft commenced taxiing the heavy rain continued and it was very difficult to see out the front of the aircraft, and they did not detect the pitot tube covers. The crew reported that they completed all the required procedures prior to lining up on the runway including, as part of the ice protection and ignition step, selecting the pitot heat to ON. 

During the initial stage of the take-off run, the captain set take_­­-off power and then the FO took control of the aircraft (see the section titled Flight crew responsibilities during take‑off). At this time, the FO checked the airspeed, expecting to see it around 80 kt, but noted that it was fluctuating around 60–70 kt. The FO referenced the left side airspeed indicator, which also appeared to be fluctuating below 80 kts, quickly assessed how much runway was remaining, and called words to the effect of ‘Airspeed. Reject’. 

Around the same time, the captain had also observed that their airspeed was indicating lower than they expected, and when the FO made the ‘reject’ call, they looked at the GPS unit which was indicating around 100–110 kt groundspeed. Noting there was minimal wind, the captain believed the GPS unit to be reasonably accurate and felt that the aircraft was ready to rotate.

Taking into consideration the wet runaway and not being sure how much runway was left due to the limited visibility, the captain made the decision to continue the take-off as they considered it was safer rather than risk running off the end of the runway. The captain called words to the effect of, ‘too fast, we’re going’. 

During the initial climb, the FO heard a flapping noise coming from the front of the aircraft and identified that the pitot tube covers had been left installed on the pitot tubes, which they announced to the captain. 

The FO referenced the GPS for speed to continue the climb and, shortly after, the FO’s airspeed indicator appeared to return to normal operation as it was indicating consistent with the GPS speed.  

The crew discussed the situation and decided to return to Townsville Airport. The FO remained pilot flying due to having an operable airspeed indicator, while the captain contacted air traffic control (ATC) requesting a return to Townsville due to a technical problem. ATC provided radar vectors for the return, and the FO landed the aircraft uneventfully at 1958. 

Following the post-flight inspection, the operator reported that the captain’s side pitot cover was mostly intact, and heat fused to the pitot tube. The FO’s side pitot cover had disintegrated, and the remnants of the cover had slid down to the rear of the pitot tube such that it did not obstruct normal operation. 

Context

Flight crew details

The captain held a Commercial Pilot License (Aeroplane) and a class 1 aviation medical certificate. They had accumulated 3,642 flight hours, including 3,424 on the SA227‑DC.

The first officer (FO) held a Commercial Pilot License (Aeroplane) and a class 1 aviation medical certificate. They had accumulated around 5,000 flight hours, including 854 hours on the SA227-DC.

Analysis was undertaken to determine if fatigue was a factor which contributed to the captain forgetting to remove the pitot covers prior to departure. The time of day, crew work and rest patterns, and indicators of alertness were considered. The analysis concluded that the captain was unlikely to be experiencing fatigue at the time of the occurrence.

Due to the time that had passed between the incident and the crew being interviewed, the FO was unable to accurately recall their rest patterns in the days leading up to the occurrence. However, they advised that they felt rested and fit for duty.  

Aircraft information

The Fairchild Swearingen SA227-DC is a low-wing, pressurised, twin-turboprop aircraft, manufactured in the United States in 1996 and issued serial number DC881B. It was registered in Australia as VH-UZN in 2005. The aircraft was fitted with 2 Garrett turbine TPE3311 engines. 

The aircraft was fitted with a flight data recorder; however, the data was not downloaded by the operator at the time and had been overwritten when the ATSB was notified of the occurrence. 

External inspections

The operator’s Flight crew operating manual (FCOM) stated there were 3 types of external inspections:

• daily inspection (first flight of the day)
• crew change inspection
• post-flight inspection. 

In addition, prior to closing the aircraft’s main door, both crew members were required to conduct a final security check, and the FO was required to do a ‘4321 check’. 

Daily inspection 

The operator’s Operations manual stated that:

A daily inspection is to be carried out as per the instructions in the Flight Crew Operating Manual for the aircraft type by the Pilot-in-Command or if he / she so delegates to, a person with the appropriate authority … on the first flight of the day for that aircraft.

The FCOM stated that the inspection consisted of an internal and external inspection. Further it stipulated (Figure 2) the path that flight crew should take when conducting the daily walk-around inspection. The numbers represent pause points to inspect a particular section of the aircraft, and each were associated with certain check items. One of the items to be checked was the condition of the pitot probes.

Figure 2: Schematic showing pre-flight walk-around path required prior to the first flight of the day

Source: Sharp Airlines flight crew operating manual

Crew change inspection

The crew change inspection was to be conducted whenever crew accepted an aircraft for duty and the aircraft had already flown that day. 

The FCOM stated that: 

It is not to be confused with a daily inspection. If an aircraft already operated by the crew has been taken offline for maintenance this inspection will be repeated. It consists of a Crew Change External Inspection and a Crew Change Internal Inspection. These inspections are similar to the Daily Inspection but omitting [first flight of the day] FFD items (unless that system had maintenance performed on it) and complete only hash (#) items on the internal component. Certification for the completion of this inspection was not required.

Among other items, the removal of bungs, pitot covers and wing tip flags was required as part of the crew change inspection. 

External security check

In addition to the daily inspection (required for the first flight of the day), the FCOM required both crew members to conduct an external security check every flight, immediately prior to the cabin door being closed. This check comprised of the following:

• Check cargo and baggage is secure

• Tail stand (if fitted) is removed, stowed and pin retained

• All hatches, cowls and fuel caps closed

• Rotate the propellors to check for thermal distortion

• Check all ground equipment and the manoeuvring area is clear

4321 check

Prior to the cabin door being closed, the FO was also required to do an extra check, which the operator called a ‘4321 check’, and included: 

Whilst standing at the front of the aircraft confirm with the “4,3,2,1 check” the following: 

• 4 x doors latched and secure (excluding the main door at this stage) 

• 3 x wheel chocks removed 

• 2 x engine intakes and area underneath are clear, and 2 x fuel caps secure 

• 1 x pogo stick (if fitted) removed.

Whilst this check is the RP [right pilot] responsibility, LP [left pilot] are not absolved from taking due care and diligence in this matter.

Post-flight inspection

The FCOM also set out the requirements for post-flight inspection. This was required to be conducted after each sector, and at the end of a duty period. The FCOM stated that after each sector the flight crew was required to, among other items:

• Ensure engine bungs, pitot covers and tail stand (if applicable) are in place. 

An overview of the aircraft was to be conducted, checking the general condition and presence of any fluid (leaks or drips) on the aircraft or the adjacent ground.

Securing the aircraft

In addition to the post-flight inspection, the FCOM stated that on the last flight of the day, or if the aircraft was to be left unattended for greater than 60 minutes, the crew were required to secure the aircraft and conduct a terminating checklist (Figure 3). Securing the aircraft required the crew to:

• Ensure the A/C is parked correctly and in a safe secure area 

• Ensure controls are locked (seat belt on last flight only) 

• Chock all 3 landing gears. 

• Tail stand in place (if fitted).

• Fit Engine Intake and Pitot covers (last flight only). 

• Check cargo compartment lights (nose locker and rear) are off. 

• Check for any fluid leaks under the A/C. 

• Check tyres for wear and condition. 

• Check all Beacons/Exterior Lights are serviceable. 

• Complete and secure all Company Documentation (as appropriate).

• Complete a review of spare [Aircraft maintenance logs] AML, [Deferred defect list] DDL, [Flight deck log] FDL & ensure a spare book is available. 

• Consult the TERMINATING Checklist when carrying out the above actions (Figure 3) 

Despite the above list including the item ‘Fit engine intake and pitot covers (last flight only)’, Sharp Airlines later clarified that engine intake and pitot tube covers were expected to be fitted if the aircraft was left unattended for 60 minutes or more. 

Figure 3: Sharp Airlines terminating checklist

Source: Sharp Airlines flight crew operating manual 

Sharp Airlines further advised that, although the first part of the duty was conducted on the same day, it expected that the flight crew should have conducted a full external (preflight) inspection, as a termination check had been completed at the end of the previous flight. However, the procedures did not state what checklist was required in this situation.

Flight crew responsibilities during take‑off 

The captain (left pilot (LP)) was responsible for the take-off brief which included stating:

If prior to V1 you see anything that could adversely affect the safety of the flight clearly call “FAILURE” or clearly state “[the condition]”. I will decide whether to continue or reject the take-off by clearly stating either “CONTINUE” or “REJECT”

For a right pilot (FO) take-off the FCOM stated that:

• The LP advances the power levers to approx. 25–40% [torque] TQ whilst holding the aircraft on the brakes (paved surfaces only) and checks the BETA lights are off and calls [continuous alcohol water injection] “CAWI ON” (if CAWI required).

• The LP (Captain) observes the increase in TQ and the AWI pump lights are on (if CAWI required). Sets the power levers at 3% below required TQ calls “HANDING OVER” at approx. 60kts (ensure [nose wheel steering] NWS is released) and then calls “POWER SET” and leaves their hand on top of the power levers until V1.[1]

• RP responds, “TAKING OVER” and his/her hands remain clear of the power levers.

• LP Constantly scans the instruments for an impending failure or abnormality and calls “80kts”.

Sharp Airlines’ policy was that between 80 kt and V1 the take-off would only be rejected if there was an engine failure, a fire or the aircraft was otherwise unsafe or unable to fly.

Pitot static system 

Pitot tubes

Pitot tubes are components of the aircraft’s pitot-static system. The Fairchild SA227-DC has 2 pitot tubes, which are attached to the upper cowl of the aircraft’s nose (Figure 1). The pitot tubes point directly into the airflow, measuring the total air pressure. This information and the static pressure, delivered by static ports on the fuselage, are used to compute the aircraft’s indicated airspeed. If the pitot tube is partially or completely blocked, airspeed indications will be inaccurate. 

The pitot tubes have a heating system to prevent ice build-up. This is required to be selected ON prior to entering known icing conditions. The weather information from the Bureau of Meteorology for the time of the flight indicated that icing conditions were forecast above 10,000 ft. This required that the pitot heat was selected ON prior to take‑off. 

Pitot tube covers

Pitot tube covers provide protection from foreign object obstruction when the aircraft is on the ground. They typically incorporate a ‘remove before flight’ warning tag/streamer (also known as a flag or ribbon) intended to alert relevant personnel of their presence. 

Flight data 

Take-off and landing data was not retained by the crew or the operator post-incident, however, the operator provided a recreated take-off and landing data (TOLD) card, with V1 calculated to be 114 kts. 

The ADS-B flight data available to the ATSB had limited data points and parameters. During the take-off run, the recorded data periodicity was approximately 20 seconds, and this restricted an accurate estimation of the take-off location and groundspeed of the aircraft. 

This data was compared to historical recorded flight data of 19 take-offs of another SA227-DC aircraft from Townsville Airport runway 01. Comparing the pitch attitude and indicated airspeed parameters in the historical data against the available ADS-B parameters for the flight, the ATSB was able to identify an approximate rotation location on runway 01 during the incident flight (Figure 4).

Figure 4: Estimated rotation location VH-UZN from historical flight analysis

Source: Google Earth using ADS-B exchange data, annotated by the ATSB 

The ATSB estimated that the rotation speed (VR)[2] of VH-UZN, based on historical flights, was likely in the lower range of values between 112–130 kt. 

Related occurrences

The ATSB has investigated several occurrences where ground use equipment has been left on aircraft due to inadequate flight crew inspections and/or inadequate operator guidance. 

Airspeed indication failure on take-off involving Airbus A330 (AO-2018-053)

On 18 July 2018, a Malaysia Airlines Airbus A330, took off on a regular public transport flight from Brisbane, Queensland, to Kuala Lumpur, Malaysia. As the covers had been left on the aircraft’s 3 pitot probes, the instruments showed a red speed flag in place of the airspeed indication from early in the take-off, and unrealistically low airspeeds afterwards. The flight crew did not respond to the speed flags until the aircraft’s speed was too high for a safe rejection of the take-off, and the take-off was continued.

Aircraft preparation event involving Link Airways Saab 340 (AO-2022-055)

A propeller strap became embedded in a Link Airways Saab 340B regional airliner’s cabin on take-off from Canberra in November 2022. The ATSB’s investigation found that several factors contributed to the propeller strap not being noticed or removed by the first officer, captain, or dispatcher, prior to departure, including that the guidance provided by Link Airways for training of Swissport dispatchers did not explain the appearance, function and importance of the propeller strap.

Aircraft preparation event involving Saab 340B (AO-2022-058) 

On 16 November 2022, a Regional Express (Rex) Saab 340B, was prepared for a scheduled air transport flight from Cairns Airport to Bamaga, Queensland. As the crew taxied the aircraft to the runway, an engineer on a nearby parking bay noticed something hanging from the aircraft and contacted the tower. The crew returned the aircraft to the bay. Aircraft parked overnight at Cairns were required to be fitted with an operator designed bung installed in the horizontal stabiliser trim actuator cove to prevent bird nesting. The inspection revealed the horizontal stabiliser bungs had not been removed and were still installed in the left trim actuator cove.

Aircraft preparation event involving a Hawker Beechcraft Corporation B200 (AB-2024-025)

On 8 May 2024, a Hawker Beechcraft B200 was being prepared for an air transport flight at Darwin Airport. Prior to departure, the pilot completed the preflight inspection, confirmed that both red flags were in their possession, and secured these items along with the propeller covers inside the aircraft. However, the pilot did not detect that the flag for the right-side cover had detached from the cover, nor that the cover was still attached to the pitot tube.

During the take-off, the pilot detected a speed discrepancy on their cockpit instrumentation. They continued the climb to 3,000 ft before returning via a visual approach to Darwin Airport. 

During the post-flight inspection, the pilot identified that the right-side pitot cover was still in place, covering the pitot tube.

Aircraft preparation event involving Saab 340B (AO-2024-059)

On 19 November 2024, the aircraft was prepared for departure from Melbourne Airport. After the pilots started the engines, a passenger told the flight attendant they had seen a strap restraining the left propeller before it began to spin. The propeller strap was then found attached to the propeller, with the pins that connect it to the engine cowling broken on start‑up.

The report noted the final external walkaround check of the aircraft required the first officer to remove the propeller strap from the propeller, before rotating the propeller to a required position. However, the first officer inadvertently left the propeller strap attached, instead only disconnecting and removing the strap extension, which connected the propeller strap to the aircraft stairs to prevent them from being retracted while the strap is in place.

Once the first officer was in the flight deck, the ground handler assigned to the dispatch, who was a trainee, did not detect the propeller strap from their position at the nose of the aircraft, and provided the crew with a signal to start the engine.

Meanwhile, the pilots conducted the engine start checklist, which included a requirement for the captain to check that the left engine was clear. The captain also did not detect the propeller strap and proceeded to start the engine.

Safety analysis

A Sharp Airlines Fairchild SA227 departed Townsville Airport with pitot tube covers fitted. This analysis will discuss the pre-flight actions of the flight crew regarding the pitot tube covers and consider the operator’s procedures for pre-flight inspections. It will further examine the crew’s decision to take-off with unreliable airspeed. 

Pre-flight inspection 

The captain considered that the daily inspection had already been completed in the early hours of the morning on the previous sector, and therefore, it was not required to be completed prior to this flight. They also did not consider that a crew change external inspection was required. Consequently, they reportedly conducted an abbreviated walk‑around inspection prior to the incident flight but did not reference any aircraft or operator checklist. 

The first officer (FO) assisted the captain by removing the engine bungs and static port covers. However, they were unable to reach the pitot covers on the nose of the aircraft and asked the captain to remove them. The captain advised that they would do so, but subsequently forgot. Additionally, the FO did not confirm with the captain that the pitot covers had been removed, likely due to seeing ‘remove before flight’ tags in the bag and incorrectly assuming those were attached to the pitot covers.  

There was no further discussion between the captain and the FO regarding the external aircraft inspection, and the pitot covers were not removed prior to departure.

Operator’s guidance

The operator’s Flight crew operating manual (FCOM) required flight crews to secure the aircraft and conduct a terminating check if the aircraft was to be unattended for more than 60 minutes. While it was the operator’s expectation that a full daily inspection of the aircraft was required once a termination check had been completed; the procedures did not clearly state this, and it did not occur on this occasion. 

The operator did have an abbreviated checklist, the crew change checklist, and it is possible some flight crew were conducting this checklist on returning to the aircraft after completing the terminating check, however, the procedures also did not specify that this was required. 

In addition, the operator also expected that engine bungs and pitot covers would be fitted when the aircraft was on the ground for periods over 60 minutes; however, the procedure (securing the aircraft) specifically stated that they should be fitted only after the last flight. This created the potential for confusion among flight crew as to when they should be fitted.

Further, while the final ‘4321’ visual check was designed for quick turnarounds, it required that the engine intakes were checked, and although engine bungs were only required to be installed when the pitot tube covers were installed, it did not require that the pitot tube covers were checked. 

Poor visibility

It is likely that due to the night‑time conditions and heavy rain, neither flight crew detected the pitot covers in place, as they would have during the day, while taxiing the aircraft.

Similarly, there was no opportunity for air traffic control, other pilots or ground staff to visually observe the pitot tube covers in place. As such, the pitot tube covers remained in place undetected.

Airspeed indications during take-off

The captain's decision to take off once the crew recognised that the airspeed was unreliable was understandable in the circumstances, and probably at, or close to V1. However, there was opportunity for the crew to have recognised earlier in the take-off run that the airspeed indicators were not functioning correctly, as the speeds were slowly increasing. Continuation of the take-off was likely due in part to neither crew realising that airspeed could still increase with pitot covers on. 

Findings

From the evidence available, the following findings are made with respect to the unreliable airspeed indications on 10 February 2025:

Contributing factors

• Due to the combination of a memory lapse and incorrect assumption, the aircraft’s pitot covers were not removed prior to departure.
• Sharp Airlines’ Flight crew operating manual required that:

- a terminating check be completed if the aircraft was unattended for more than 60 minutes, but did not specify what checks were to be completed on return to the aircraft

- pitot covers should be installed after the last flight of the day only, where the operator required that they be installed if the aircraft was unattended for longer than 60 minutes.

In addition, the final visual check, completed by the first officer prior to closing the doors, did not include checking that pitot covers had been removed. (Safety issue)

• Likely due to poor visibility, the flight crew did not detect the pitot tube covers were still in place prior to commencing the take-off.
• During the take-off run, the crew did not detect that the airspeed indicators were not indicating correctly, likely due to observing that they were slowly increasing, resulting in the crew not rejecting the take-off. 

Safety issues and actions

Final pre-flight external inspection 

Safety issue number: AO-2025-041-SI-01

Safety issue description: Sharp Airlines’ Flight crew operating manual required that:

• a terminating check be completed if the aircraft was unattended for more than 60 minutes, but did not specify what checks were to be completed on return to the aircraft
• pitot covers should be installed after the last flight of the day only, where the operator required that they be installed if the aircraft was unattended for longer than 60 minutes. 

In addition, the final visual check, completed by the first officer prior to closing the doors, did not include checking that pitot covers had been removed.

Glossary

Sources and submissions

Sources of information

The sources of information during the investigation included the:

• flight crew of the incident flight and another pilot who conducted flights for the operator
• Sharp Airlines
• ADS-B data. 

References

• Sharp Airlines, Metro 3/23 Flight Crew Operating Manual, Issue 09, Revision 2, 24 June 2024
• Sharp Airlines, Operations Manual, Section A6 – Flight Conduct, Revision 22, 24 June 2024. 

Submissions

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

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

• flight crew of incident flight
• Sharp Airlines
• Civil Aviation Safety Authority.

No submissions were received.

Purpose of safety investigations The objective of a safety investigation is to enhance transport safety. This is done through:  identifying safety issues and facilitating safety action to address those issues providing information about occurrences and their associated safety factors to facilitate learning within the transport industry. It is not a function of the ATSB to apportion blame or provide a means for determining liability. At the same time, an investigation report must include factual material of sufficient weight to support the analysis and findings. At all times the ATSB endeavours to balance the use of material that could imply adverse comment with the need to properly explain what happened, and why, in a fair and unbiased manner. The ATSB does not investigate for the purpose of taking administrative, regulatory or criminal action. 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 1 July 2024, a Cessna 310R, registered VH-ZMB, was returning to Alice Springs from Willowra aircraft landing area, Northern Territory (NT), with only the pilot on board. 

During an instrument approach in instrument meteorological conditions, the pilot reported receiving false indications from the attitude indicator and directional gyroscope. The aircraft deviated from the published approach path and tracked perpendicular to the approach track, below minimum sector altitude (MSA). 

The pilot notified air traffic control at Alice Springs tower of the situation, before obtaining a clearance to track from their present position back to the initial instrument landing system approach point, for a subsequent attempt at landing.

A second approach was then flown, followed by a successful landing at Alice Springs Airport.

What the ATSB found

The ATSB found that the pilot, whilst established on the ILS approach to Alice Springs, likely experienced spatial disorientation that led to an undesired flight path, below the MSA.

In their state of distress, the pilot did not broadcast a PAN PAN call notifying air traffic control of their situation. Further, air traffic control did not issue a safety alert, which would have alerted the pilot that they were in unsafe proximity to terrain and needed to climb immediately. This was also influenced by the pilot not broadcasting a PAN PAN, but could have been made independently.

Once the pilot was outside of the required tolerances for the instrument approach and below the MSA, the pilot did not conduct a missed approach, remaining below minimum sector altitude for an extended period.  

Other factors that increased the risks identified in this investigation include post‑occurrence fault finding that found the artificial horizon exhibited deviations outside the manufacturer’s required tolerances. Additionally, the pilot’s choice to not make use of the autopilot for the approach may have increased their workload and the subsequent risk of spatial disorientation during the instrument approach procedure.

What has been done as a result

The operator has since introduced an automation policy for the use of autopilot in instrument meteorological conditions and in high workload single-pilot operations. 

Safety message

Pilots should not hesitate to report an urgent condition when encountering situations that may not be immediately perilous but significantly increase risk. Broadcasting a PAN PAN call when there is uncertainty about the safety status of the aircraft will alert ATC to the need for immediate assistance.

Air traffic control has a duty of care to provide safety alerts to pilots on becoming aware that an unsafe situation such as proximity to terrain has, or may, occur. 

Once an aircraft is no longer on an established approach path and doubt exists as to its lateral position and location, a missed approach should be conducted, including an immediate climb to achieve a safe altitude, clear of terrain.

The investigation

The occurrence

On the morning of 1 July 2024, a Cessna 310R, registered VH-ZMB, conducted a passenger transport flight[1] to Willowra aircraft landing area, NT, and was repositioning[2] to Alice Springs, NT, with only the pilot onboard. 

At approximately 1020 local time, the pilot commenced an instrument landing system (ILS) approach[3] for runway 12 at Alice Springs Airport. This approach was manually flown (not utilising the autopilot system), in instrument meteorological conditions.[4] 

At 1022:05, the aircraft was established at 4,250 ft above mean sea level (AMSL) on the approach into Alice Springs Airport on the published ILS approach profile. About 25 seconds later, the pilot recalled receiving erroneous instrument indications from the artificial horizon (AH). At 1022:30, flight data showed the aircraft departing the ILS to the left, and tracking at a perpindicular direction from the approach path with unusual aircraft bank angles (AOB) (Figure 1). 

Figure 1: VH-ZMB flight path

Source: ATC recordings and recorded flight data, overlaid on Google Earth and annotated by the ATSB

At 1022:47, the pilot contacted air traffic control (ATC), using their callsign twice. The pilot reported an issue with the instruments and requested clearance to commence a second approach. The ATC controller observed, and ATC recordings indicate, a level of stress in the voice of the pilot at this time. 

ATC subsequetly cleared the pilot to climb to 5,500 ft and to track directly to the initial approach fix for the ILS (position LISZT).

At 1023:36, nearly a minute after obtaining a clearance from air traffic control and over a minute from leaving the ILS profile, the pilot commenced a sustained climb. 

Recorded flight data indicated that during this time, the aircraft was below the minimum sector altitude of 4,300 ft and tracking towards rising terrain. The aircraft came within its closest proximity to terrain as it passed the ridgeline at about 810 ft above ground level.

At 1024:30 the pilot acheived an altitude of 4,300 ft enroute to position for a second approach.

A subsequent ILS approach was then flown into Alice Springs, followed by a successful landing.

Table 1: Sequence of events

Source: ATC recordings and recorded positional data tabulated by the ATSB 

Context

Pilot qualifications and experience

The pilot held a commercial pilot licence (aeroplane) and a valid class 1 aviation medical certificate. The pilot reported a total flying time of 386 hours with about 66 of those being on the Cessna 310. The pilot obtained a multi-engine aeroplane instrument rating in February 2024. The pilot reported accruing 27.3 total hours of instrument flight time with 5.7 hours being accrued in the last 90 days. The pilot had been employed with the operator since April 2024 and had completed their Operator Proficiency Check – IFR [5], on 17 May 2024. 

Aircraft

The Cessna 310R is a twin-engine, low-wing, 6-seat, unpressurised aircraft equipped with retractable landing gear. The aircraft was manufactured in 1976 and had greater than 16,600 hours recorded on the maintenance release. VH-ZMB was fitted with Garmin 430W avionics, coupled with a traditional avionics suite (Figure 2). 

Figure 2: Photo of cockpit instruments from perspective of left (pilot) seat

Source: Operator annotated by the ATSB

The pilot reported that placement of the standby artificial horizon on the far right‑hand side of the instrument panel (Figure 2) precludes the pilot from observing angles of bank (especially to the left). However, the pilot also reported utilising the standby AH as the primary means of spatial orientation, both during the occurrence and post‑occurrence to fly the second approach and identified that recovery to a safe altitude was ultimately slowed by the significant workload of stabilising the aircraft on a limited instrument panel.

Weather conditions

Weather conditions in the Alice Springs terminal area at the time of the occurrence were identified as a moderate south-easterly wind of 10 kt, with greater than 10 km of visibility. The cloud was reported as scattered (between 3–4 oktas[6]) at 900 ft, broken (between 5–7 oktas) at 1,300 ft and overcast (8 oktas) at 2,400 ft above ground level. The pilot reported the approach was conducted in instrument meteorological conditions and recalled being in stratiform cloud [7] from 7,000 ft to 2,500 ft AMSL.

Instrument landing system approach

The Alice Springs ILS runway 12 initial approach fix is a waypoint designated as LISZT which is about 15 NM (27.8 km) from the end of runway 12. The approach descent commences at 11.5 NM (21.2 km) from the runway 12 threshold, on a standard 3° descent profile. The missed approach procedure is to track 116° magnetic and climb to 5,500 ft AMSL. 

Minimum sector altitude 

Minimum sector altitude (MSA) is the lowest altitude which will provide a minimum clearance of 1,000 ft above all objects located within a specified area. This specified area is contained within a circle, or a sector of a circle of 25 NM (46.3 km) or 10 NM (18.5 km) radius centred on a significant point.

In the case for Alice Springs, the significant point being used as the datum reference point is the Alice Springs VHF Omni Directional Range (VOR) station[8]. 

The 10 NM MSA in the area around Alice Springs Airport is 4,300 ft AMSL.

Missed approach procedures

The missed approach procedure plays a pivotal role in instrument approach safety. It provides a standardised procedure for managing an aborted approach and landing attempt, ensuring appropriate terrain clearance to safely conduct flight operations in diverse environmental conditions. 

Section 15.11 of the Part 91[9] Manual of Standards contains specific circumstances where a missed approach must be conducted. 

A summary of these circumstances is as follows:

• during the final segment of an instrument approach, where the aircraft is not maintained within the applicable navigation tolerance for the aid in use
• when the required visual reference is not established at or before reaching the missed approach point from which the missed approach procedure commences
• when a landing cannot be made from a runway approach, unless a circling approach can be conducted in weather conditions equal to or better than those specified for circling
• when visual reference is lost while circling to land from an instrument approach.

Procedures outlined in the Aeronautical Information Publication (AIP) state that a missed approach must be conducted under certain conditions if the aircraft is below MSA. These conditions include, but are not limited to: 

• issues arising with the radio aid,

• visual reference not being established, and

• a landing cannot be effected from the runway approach. 

Operational procedures require that during a missed approach manoeuvre, an immediate climb is carried out to achieve an altitude that will remove the aircraft’s exposure to the risks of collision with terrain. 

Instrument approach procedures

An instrument approach or instrument approach procedure (IAP) is a series of predetermined manoeuvres for the orderly transfer of an aircraft operating under instrument flight rules from the beginning of the initial approach fix to a landing, or to a point from which a landing may be made visually.

An IAP enables a descent below the MSA, positioning the aircraft to safely approach and land.

Operations below MSA increase the risk of collision with terrain or obstacles which are an immediate threat. Maintaining the published instrument approach path assures the pilot of obstacle clearance below the MSA. Outside of these areas, while below the MSA and in instrument meteorological conditions (IMC), separation from terrain and obstacles cannot be guaranteed and the pilot must conduct a missed approach procedure. 

Recorded data

Automatic dependant surveillance broadcast (ADS-B) Exchange and Flightradar24 data was collected by the ATSB and was supplemented with OzRunways data provided by the pilot.

ATSB analysis combined the ADS-B flight data and the OzRunways aircraft track data to ascertain the track position and orientation of the aircraft during the occurrence.

At 1022:30 the aircraft deviated significantly to the left of the approach path resulting in the aircraft no longer being established on the ILS approach. The aircraft was below the MSA at 3,900 ft and continued to descend to the lowest point of 3,320 ft.

About 35 seconds later the aircraft crossed a ridgeline, further reducing the vertical separation with terrain to 810 ft above ground level.­­­­

Recorded data indicated (Figure 3) that 30–40 seconds after speaking to ATC and approximately 70 seconds after leaving the ILS approach profile, the pilot commenced a sustained climb and began tracking to the initial approach fix of LISZT. During this time the aircraft was operated below the MSA. 

Figure 3: Aircraft vertical profile

Source: ADS-B Exchange, Flightradar24 and OzRunways data analysed and annotated by the ATSB

Recorded data identified a significant left turn, greater than 60° AOB, with a subsequent bank to the right of greater than 40° AOB and a further left correction (Figure 4). These occurred while the aircraft was still descending. The descent was arrested, at an altitude of about 3,320 ft. With minimal climb observed for about 30 seconds before approaching rising terrain, the aircraft then passed over the ridgeline at a height of approximately 810 ft (Figure 3). (Note: Graphical figures contain smoothed data profiles that may not precisely reflect the exact data point at an exact period).

Figure 4: VH-ZMB bank angles

Source: ADS-B Exchange, Flight Radar 24 and OzRunways data analysed and annotated by ATSB

Vacuum‑powered gyroscopic instrumentation (artificial horizon)

The Cessna 310R is fitted with gyroscopic instruments[10] including an artificial horizon (AH), heading indicators and turn coordinators (turn and bank).

The vacuum system instruments on the Cessna 310R consist of 2 directional gyros, 2 AH gyros and the suction gauge. 

The artificial horizon is the main instrument pilots use to fly through IMC. This instrument is considered a master instrument because it presents pitch and bank attitude information directly against an artificial horizon. It is a critical instrument to allow pilots to fly through non-visual and low-visibility conditions. It indicates the aircraft's orientation relative to the earth, expressed in pitch, roll, and yaw.[11]

Figure 5: Generic example of an artificial horizon

Source: Wikipedia

The gyroscopic instruments are powered by the vacuum system, consisting of a vacuum pump on each engine, pressure relief valve for each pump, a common vacuum manifold, vacuum air filter and suction gauge. Air pressure is used to rotate vanes to spin the instrument gyroscopes thus utilising gyroscopic forces as a mechanism that keeps the instrument level with respect to the direction of gravity. The AH gyro is mounted in a double gimbal, which allows the aircraft to pitch and roll as the gyro stays vertically upright.

The pilot reported that during the approach they noticed that the suction gauge was indicating ‘low pressure’. A partial blockage or issue in the pilot suction line, immediately after the air filter, could affect the pilot (left-side) AH and the suction gauge, with nil effect on the copilot (right-side) gauges.

However, post‑occurrence maintenance inspections and ground runs could not identify any abnormalities in the vacuum system.

Figure 6: Example of the suction gauge

Source: ATSB

Post occurrence maintenance testing of the artificial horizon identified a gradual drift in pitch, up to 7°, and up to 4° drift in the roll axis over a period of 20 minutes. The AH deviations were gradual, inconsistent and outside the manufacturer’s required tolerances. 

Flight automation and operator policy

Flight automation, such as an approved autopilot, utilises different control systems and technologies that reduce the requirements of human interaction.

An autopilot system can reduce the pilot’s workload. This is achieved by the automation taking over routine tasks such as maintaining altitude, heading, and airspeed. Subsequently allowing the pilot mental capacity to focus on other critical aspects of the flight, such as monitoring systems, flight path, weather conditions and communicating with air traffic control. This is particularly useful in times of a high workload environment. 

The operator’s policy did not detail requirements on when it was appropriate or required to use the autopilot.

PAN PAN call

A ‘PAN PAN’ transmission is used to describe an urgent situation, but one that does not require immediate assistance. Examples of such situations include instrument malfunctions, deviation from route or entering controlled airspace without a clearance. 

When an air traffic controller receives a PAN PAN call from an aircraft, the controller will declare an alert phase.[12] The Safety bulletin What happens when I declare an emergency, released by Airservices Australia, stated that ATC may provide a range of support services including: 

• passing information appropriate to the situation, but not overloading the pilot

• allocating a priority status

• allocating a discrete frequency (where available) to reduce distractions

• notifying the Joint Rescue Coordination Centre (JRCC), appropriate aerodrome or other agency

• asking other aircraft in the vicinity to provide assistance.

An aircraft is in an urgency condition the moment that the pilot becomes doubtful about position, fuel endurance, weather, or any other condition that could adversely affect flight safety. The time for a pilot to request assistance is when an urgent situation may or has just occurred.

No ‘PAN PAN call was made by the pilot during the occurrence.

Air traffic control safety alert

A safety alert issued by air traffic control is instructions prefixed by the phrase 'SAFETY ALERT'. The AIP outlines a safety alert as:

ATC will issue a Safety Alert to aircraft, in all classes of airspace, when they become aware that an aircraft is in a situation that is considered to place it in an unsafe proximity to:

1. terrain;

2. obstruction;

3. active restricted areas; or

4. other aircraft. 

A safety alert should trigger an appropriate response from the pilot to address and resolve the undesirable state.

When the pilot made contact with ATC, the controller reported observing a level of stress in the pilot’s voice and noticed the pilot tracking perpendicular to the approach path for the runway 12 ILS, below the MSA, towards rising terrain. 

No safety alert was made by air traffic control during the occurrence.

Spatial disorientation 

Spatial disorientation (SD) occurs when a pilot has a false perception of the motion or orientation of the aircraft with respect to the Earth (Ledegang & Groen, 2018), subsequently incorrectly interpreting the aircraft attitude, altitude or airspeed.

The ATSB publication Accidents involving Visual Flight Rules pilots in Instrument Meteorological Conditions (AR-2011-050) explains the basis of SD.

In order to correctly sense the orientation of the body relative to its environment, a pilot relies on a number of sensory systems in order to establish or maintain orientation: 
» the visual system 
» the vestibular system, which obtains its information from the balance organs in the inner ear 
» the somatic sensory system which uses the nerves in the skin and proprioceptive senses in our muscles and joints to sense gravity and other pressures on the body. 

The visual system is by far the most important of the three systems, providing some 80 per cent of the raw orientation information. In conditions where visual cues are poor or absent, such as in poor weather, up to 80 per cent of the normal orientation information is missing. Humans are then forced to rely on the remaining 20 per cent, which is split equally between the vestibular system and the somatic system. Both of these senses are prone to powerful illusions and misinterpretation in the absence of visual references, which can quickly become overpowering. 

Pilots can rapidly become spatially disoriented when they cannot see the horizon. The brain receives conflicting or ambiguous information from the sensory systems, resulting in a state of confusion that can rapidly lead to incorrect control inputs and resultant loss of aircraft control.

The ATSB research report, An overview of spatial disorientation as a factor in aviation accidents and incidents (B2007/0063)identified that spatial disorientation is a very common problem and estimates that the chance of a pilot experiencing SD during their career is in the order of 90 to 100%. This report also detailed several international studies showing that SD accounts for some 6 to 32% of major accidents, and some 15 to 26% of fatal accidents. The report also identified that the true prevalence of SD events is almost certainly underestimated. 

The FAA Advisory Circular, Pilot’s spatial disorientation (FAA AC60-4A) discussed the challenges associated with recovering from spatial disorientation. The results of a test conducted with qualified instrument pilots found that it took as much as 35 seconds to establish full control by instruments after a loss of an applicable visual reference.

Safety analysis

This analysis will explore the factors that involved aircraft directional changes, resulting in the aircraft deviating from the published ILS approach. The deviations occurred whilst the pilot was manually flying, in instrument meteorological conditions. The consequence of this deviation led to extended flight below the minimum sector altitude with increased pilot workload prior to recovering to a safe altitude. 

The pilot reported being concerned with the aircraft’s location in relation to terrain, however, believed the aircraft was under control, attributing the unusual attitudes indicated on the artificial horizon to an instrument error rather than the aircrafts attitude.

The pilot reported that, at the time, false indications by the vacuum instruments were incorrectly indicating a turn to the right, which the pilot believed to be a consequence of erroneous instrument indications. The pilot recalled that their initial response to correct this was a turn to the left and believed that the vacuum instruments were still incorrectly indicating a level of bank even though the aircraft was level. 

ATSB analysis of the recorded data reviewed the aircraft pitch and bank angles, descent and climb profiles, and aircraft tracks and timings confirmed that the instrument indications (at this time) correlated with high levels of bank and the aircrafts track. 

Furthermore, although the pilot remembered observing a low vacuum pressure indication, a post‑incident system inspection indicated no identified problems with vacuum pumps or the check valves.

As such, it is almost certain that there was no instrument malfunction to the extent believed by the pilot. Rather, with no visual cues due to the IMC, the pilot likely became spatially disorientated and interpreted the real instrument indications as false as they mismatched the pilot’s sensed orientation.

As is common in spatial disorientation, the pilot likely followed their sense of direction rather than the (perceived faulty) instruments, leading to directional changes of up to 90° from the approach track as well as left and right angles of bank up to 65°, whilst continuing to descend. 

However, post‑occurrence maintenance fault‑finding of the artificial horizon did identify a gradual drift in pitch, (up to 7°) and roll, (up to 4°) over a period of 20 minutes. While this may have indicated a degree of unserviceability of the instrument, this was not consistent with the reported sudden and absolute failure reported by the pilot. 

Prior to the deviations on approach in IMC, the pilot descended below the minimum sector altitude. However, after deviating from the approach and no longer meeting approach tolerances, the pilot did not conduct a missed approach as quickly as practicable to achieve an altitude that would remove the aircraft’s exposure to the risks of collision with terrain. 

Subsequently, the pilot was below MSA and no longer offered the protection of being on the approach. This situation was further exacerbated by the aircraft being in unusual attitudes and tracking perpendicular to the approach path, without intent. If this high-risk situation had been identified either by ATC issuing a safety alert or the pilot issuing a PAN PAN call, (a PAN PAN call should have triggered a safety alert to climb), a climb could have been expedited and the risk of proximity to terrain removed sooner than was the case. 

Pilots should not hesitate to report an urgent condition when encountering situations that may not be immediately perilous but significantly increase risk. 

ATC recordings indicated that the pilot notified ATC that they had incorrect artificial horizon information and had lost glidepath guidance. The pilot used their callsign twice, (which can often precede a distress call), and other verbal cues were also identified by the controller to indicate the pilot was under a level of stress. Being below the MSA and off the ILS, with indications of stress, was an opportunity for the controller to issue a safety alert to the pilot to climb immediately.

In an urgent situation such as this where the safety of the aircraft was uncertain, the broadcast of a PAN PAN call would have been appropriate. Had a PAN PAN call been broadcast, ATC would have almost certainly issued a safety alert. This would have required the pilot to conduct an immediate climb, removing their subsequent risk exposure to collision with terrain.

Flight data and recordings indicated that the aircraft was below MSA, from leaving the approach profile to commencing a sustained climb to a safe altitude, for greater than one minute. Additionally, the time elapsed from notifying ATC (below MSA), to commencing a sustained climb to a safe altitude, was greater than 30 seconds. During this time, in IMC, the aircraft came within 810 ft of terrain.

Instrument flight can be considered one of the more challenging operational environments to which a pilot can be exposed. Single-pilot operations have the potential to increase pilot workload (ALPA 2019). 

Manually flying a single pilot approach in IMC increases the workload of any pilot. In this occurrence, the suspected loss of a primary instrument during an instrument flight rules approach, departing the ILS approach, experiencing unusual aircraft attitudes in IMC, and subsequently conducting a second approach all increased the workload of the pilot. Use of the autopilot system has the potential to significantly reduce the workload on pilots during this approach. This is achieved by the autopilot taking over routine tasks such as maintaining altitude, heading and airspeed. Thus, allowing the pilot to focus on other critical aspects of the flight. Whilst compliant with operator procedures at the time, use of the autopilot may have reduced the risk of spatial disorientation of the pilot on approach. The pilot reported that the autopilot could not be engaged post the occurrence, when positioning for the second approach.

Use of automation can afford the pilot spare mental capacity to recognise and address navigational deviations and tolerances. Thus, aiding the pilot to respond to the operational demands of the flight in a correct and timely manner.

Findings

From the evidence available, the following findings are made with respect to the flight below minimum sector altitude involving Cessna 310R, VH-ZMB, 14 km west-north-west of Alice Springs Airport, Northern Territory, on 1 July 2024.

Contributing factors

• At about 8 NM from Alice Springs whilst established on the ILS approach in instrument meteorological conditions, the pilot likely experienced spatial disorientation that led to directional changes of up to 90° from the approach track as well as left and right angles of bank up to 65°, whilst continuing to descend.
• The pilot did not maintain track or glidepath and deviated from instrument landing system below the minimum sector altitude. Once outside of the required tolerances, the pilot did not conduct a missed approach, which increased the risk of collision with terrain.
• Air traffic control did not issue a safety alert. This would have alerted the pilot that they were in unsafe proximity to terrain and needed to climb immediately.
• The pilot did not broadcast a PAN PAN call notifying air traffic control and other traffic of their situation, leading to the pilot remaining below minimum sector altitude for an extended period without air traffic control instruction to climb.

Other factors that increased risk

• Post occurrence fault‑finding of the artificial horizon, identified gradual and inconsistent deviations outside the manufacturer’s required tolerances.
• The pilot did not utilise the autopilot for the approach even though they were in a high workload environment. The appropriate use of autopilot can reduce workload and subsequent risk of spatial disorientation such as during an instrument approach.

Safety actions

Safety action by Avcharter

The operator has since introduced an automation policy for the use of autopilot in conditions applicable to instrument meteorological conditions (IMC) and in high workload single-pilot environments. 

Sources and submissions

Sources of information

The sources of information during the investigation included:

• the pilot of the flight
• the head of flight operations for the operator
• Civil Aviation Safety Authority
• the aircraft manufacturer
• the maintenance organisation for VH-ZMB
• independent avionics specialists
• Airservices Australia
• recorded data from the GPS unit on the aircraft.

References

Airservices Australia. (2024) Aeronautical Information Publication Australia. 

Airline Pilots Association International (ALPA) (2019) The dangers of single pilot operations Retrieved from 

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

Bailey, R. E., Kramer, L. J., Kennedy, K. D., Stephens, C. L., & Etherington, T. J. (2017, September). An assessment of reduced crew and single pilot operations in commercial transport aircraft operations. InN2017 IEEE/AIAA 36th Digital Avionics Systems Conference (DASC) (pp. 1‑15). IEEE.

Barnum, F., & Bonner, R. (1971). Epidemiology of USAF spatial disorientation aircraft accidents, 1 Jan 1958-31 Dec 1968. Aerospace Med, 42, 896-898.

Braithwaite, M., Durnford, S., & Crowley, J. (1998b). Spatial disorientation in US Army rotary-wing operations. Aviation Space Environ Med, 69, 1031-1037.

Cessna 1976, Pilot’s Operating Handbook, Cessna 310 Skyhawk, model C310R 

Cheung, B., Money, K., Wright, H., & Bateman, W. (1995). Spatial disorientation implicated accidents in the Canadian forces, 1982-92. Aviation Space Environ Med, 66, 579-585.

Civil Aviation Safety Authority. (2020) Part 91 (General Operating and Flight Rules) Manual of Standards.

Federal Aviation Authority. (1983). Advisory Circular AC60-4A: Pilot’s spatial disorientation

Gillingham, K., & Previc, F. (1996). Spatial orientation in flight. In R. DeHart (Ed.), Fundamentals of aerospace medicine (2nd ed., pp. 309-397.). Baltimore: Williams & Wilkins

Hixson, W., Niven, J., & Spezia, E. (1972). Major orientation error accidents in regular Army UH-1 aircraft during FY 1969. Accident factors report namrl1169. Pensacola, FL: Naval Aerospace Medical Research Laboratory.

Knapp, C., & Johnson, R. (1996). F-16 class a mishaps in the U.S. Air Force, 1975- 93. Aviat Space Environ Med, 67, 777-783

Ledegang, W. D., & Groen, E. L. (2018). Spatial disorientation influences on pilots’ visual scanning and flight performance. Aerospace medicine and human performance, 89(10), 873-882.

Lyons, T., Ercoline, W., O’Toole, K., & Grayson, K. (2006). Aircraft and related factors in crashes involving spatial disorientation: 15 years of U.S. Air Force data. Aviat Space Environ Med, 77, 720-723.

Moser, R., Jr. (1969). Spatial disorientation as a factor in accidents in an operational command. Aerospace Med, 40, 174-176.

Singh, B., & Navathe, P. (1994). Indian Air Force and world spatial disorientation accidents: A comparison. Aviation Space Environ Med, 65, 254-256.

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 peon 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 flight
• The operator
• Air traffic controller
• Airservices Australia
• Civil Aviation Safety Authority

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.

On the evening of 24 October 2022 a Link Airways SAAB 340, registered VH-VEQ operated an air transport flight from Canberra, Australian Capital Territory to Sydney, New South Wales.[1] The captain was acting as pilot flying, and the first officer as pilot monitoring.[2]

At 1944 local time, as the aircraft approached Sydney, air traffic control cleared the aircraft for the instrument landing system (ILS) approach to runway 34 left via the waypoint SOSIJ. This was the first ILS approach conducted in the aircraft on that day, with the captain acting as pilot flying.

Unknown to the crew, and prior to commencing the approach, a fault within the left (captain’s) display processor unit[3] resulted in the captain’s electronic attitude director indicator (EADI) erroneously presenting a constant ‘on glideslope’[4] indication regardless of the aircraft’s altitude relative to the glideslope and without an EADI glideslope failure indication. Audio from the cockpit voice recorder and flight crew interviews indicated that the first officer’s EADI also probably presented similar erroneous information intermittently and without a failure indication.[5] The EADI localiser[6] course deviation and standby attitude direction indications were not affected.

As the aircraft approached SOSIJ in cloud, at night and with the autopilot engaged, the crew commenced a 90° left turn to intercept the localiser (Figure 1). The aircraft subsequently intercepted the localiser at an altitude and distance from the runway that positioned it close to being on the glideslope for the runway 34 ILS approach. The crew continued the approach using the autopilot and observed that the aircraft did not commence descending as expected to maintain the glidepath. In response, the captain disconnected the autopilot and manually increased the descent rate to that expected for the approach.

Figure 1: Flight path of approach

Source: Recorded flight data and Google Earth, annotated by ATSB

When the aircraft was about 5 nm from the runway, the crew conducted an altitude and distance check which showed that the aircraft was close to the glideslope. As the aircraft descended below 1,373 ft above mean sea level (AMSL) at 1,920 feet per minute, and with the erroneous ‘on‑glideslope’ indication still present, the captain re‑engaged the autopilot. The autopilot maintained this descent rate, resulting in the aircraft deviating significantly below the glideslope.

As the aircraft descended below 1,000 ft AMSL, the crew recognised that the approach was unstable due to the flaps not being in the required position. At about the same time, the ground proximity warning system activated to alert the crew to the glideslope deviation and, in response, the crew commenced a missed approach.

Following the missed approach, the crew carried out a required navigation performance approach to the runway and landed without further incident.

Executive Summary

What happened

On 10 June 2022, the flight crew of a Boeing 737-476SF freight aircraft, registered ZK-TLJ, noted a 340 ft discrepancy between the captain’s and first officer’s altitude when operating in reduced vertical separation minimum airspace after departing Perth Airport, Western Australia. They had also observed an airspeed and Mach number difference, but this was within the manufacturer’s stipulated limits. The aircraft was descended, and the flight crew completed the Quick Reference Handbook - Airspeed Unreliable procedure. It was determined that the first officer’s instruments were reliable for a return to Perth. After landing, ground crews found foreign residue adhered to the lower surfaces of all 4 pitot-static probes.

What the ATSB found

The ATSB established that, during an engine ground run 2 days prior to the incident, the pitot‑static probe covers were not removed, and the automatic pitot heat was not isolated as required by the ground run procedures checklist. As a result, the covers melted onto the probes. Although cleaned, residue remained on the probe surfaces, which had the potential to compromise the accuracy of the pitot-static instruments in-flight. It was also established that pitot‑static probe covers made from polyvinyl chloride material were used, which increased the risk of the covers melting onto the probes if left on during engine operation.

Air traffic control were not advised of the altitude discrepancy of 340 ft, which exceeded the maximum allowed altimetry system error for reduced vertical separation minimum airspace of 200 ft. Therefore, adequate vertical separation with other aircraft could not be assured by air traffic control.

What has been done as a result

The maintenance organisation has undertaken several procedural initiatives to reduce the likelihood of melted pitot-static probe covers in the future. The most notable being the use of high temperature resistant Kevlar™ covers replacing the extant polyvinyl chloride covers. They have also ensured that checklists are readily available, and the safety briefing conducted at the start of each day discusses threat and error management, and local hazards.

Safety message

Aircraft barometric air data sensing instrumentation components are extremely sensitive to damage and disruption. This incident highlights the importance of maintaining a high level of attention to damage and contamination when working on, and inspecting these components, particularly on aircraft certified to operate in reduced vertical separation minimum airspace. Where there is doubt, the probes should be removed and tested by an approved facility. Further, it demonstrates the need to appropriately action and complete checklists, and for flight crew to advise air traffic control of altimetry system errors.

The investigation

The occurrence

On 10 June 2022, an Airwork Boeing Company 737 aircraft, registered ZK-TLJ, was being operated as a freight service from Perth via Port Hedland, Western Australia to Christmas Island. On board were the captain as pilot monitoring, first officer (FO) as pilot flying,[1] an avionics licenced aircraft maintenance engineer (LAME), and load master.

At about 0951 Western Standard Time,[2] the aircraft departed Perth on climb to the designated cruising altitude of flight level (FL)[3] 330, operating in reduced vertical separation minimum (RVSM)[4] airspace. As the FO’s altimeter passed FL 320, the FO called ‘one to go’ in reference to the approaching designated cruise altitude. The captain noted that the call was made early according to their altimeter reading.

The aircraft levelled off at FL 330 (33,000 ft) using the FO’s altimeter coupled to autopilot B.[5] At that time, the flight crew noted the captain’s altimeter displayed 32,660 ft. They also noted differences between the captain’s and FO’s indicated airspeed and Mach number of 265 kt and 269 kt, and 0.745 M, and 0.762 M, respectively.

The flight crew, in discussion with the LAME and Airwork maintenance watch, decided to return to Perth for maintenance. At this stage, they assessed that the aircraft was overweight for a direct return and landing at Perth, so they decided to continue on the current heading and carry out troubleshooting to determine the accuracy of the altimeters. The Quick Reference Handbook (QRH) Airspeed Unreliable procedure was consulted to determine the validity of the displayed airspeed and altitude. The procedure makes use of a table, which required the aircraft to descend to FL 300, the flight crew to set the aircraft pitch attitude and Mach indications against the aircraft weight and adjust the engine N₁[6] speed to achieve level flight. By comparing the values displayed against the known configuration, the accuracy of the instruments could be assessed.  

An air traffic control (ATC) clearance was requested and provided for a descent to FL 300 and the flight crew completed the QRH procedure. They determined that the FO’s instruments were reliable, and the remainder of the flight was conducted using those instruments.

The flight crew notified ATC that they required a return to Perth for ‘operational reasons’, and a clearance was provided. On descent into Perth, the flight crew noted that the altitude discrepancy on their altimeters began to decrease until about 10,000 ft, from which point they provided consistent indications. The aircraft landed at Perth without further incident.

Post-flight inspection

After landing at Perth, engineering staff inspected the 4 combined pitot-static probes and found residue on all 4 probe surfaces (Figure 1). All of the probes were subsequently removed, and the pitot‑static lines were flushed with nitrogen. This was carried out in accordance with the manufacturer’s maintenance procedures, which did not require a sample of any debris to be collected and analysed. Therefore, the presence of debris in the pitot-static system was not determined.

The probes were replaced with serviceable items, the system was tested, assessed serviceable, and the aircraft returned to service. The pitot-static probe covers onboard the aircraft were also inspected and found to have had a temporary repair applied to them (Figure 1).

Figure 1: Pitot-static probe and covers

Source: Airwork, annotated by the ATSB

Pitot-static system

The pitot-static system is a set of air pressure-sensitive instruments used to measure an aircraft’s airspeed and altitude. Erroneous altimetry indications can be induced by a partial or full blockage of the static air pressure sensing system, or by turbulent air over the static pressure sensing ports.[7] Static pressure sensing instruments are carefully designed to minimise the risk of turbulent air over the sensing ports, however a small amount of contamination or damage to the ports, or area surrounding the ports, can result in turbulent air and a reduction in instrumentation accuracy.

The 737-476SF has 4 combined pitot-static probes fitted to the nose of the aircraft, 2 alternate flush static ports for the standby altimeter, and connecting tubing. The pitot-static lines are self‑draining, and where this is impractical, drain traps are provided. The pitot-static probes are independently connected to the 2 independent air data computers (ADC1 and ADC2), which convert the barometric pitot-static pressures into a digital signal to be displayed on the captain and FO altitude, airspeed, and Mach instruments. The pitot-static probes are electrically heated to prevent the formation of ice on the probes which can disrupt or block the normal flow of air.

In April 2021, the aircraft was made compliant with United States Federal Aviation Administration airworthiness directive[8] 2019-09-10. This required completion of Boeing alert service bulletin SB737-30A-1064, which modified the pitot heat system to energise automatically on engine start to avoid inadvertent flight into icing conditions with pitot-static heat off. The system senses the engine running using the low oil pressure switch on either engine.

Pitot-static probe covers

Pitot-static probe covers are used to provide protection from contamination when on the ground. Covers were not routinely fitted to the aircraft during turn around inspections, except in locations where an increased risk of contamination existed. The covers generally travelled with the aircraft and were fitted and removed by ground crew as required. The covers were to be fitted during extended periods on the ground.

The aircraft maintenance organisation had substituted the Boeing recommended Kevlar™[9] pitot‑static probe covers with locally manufactured items, made from a commercially available polyvinyl chloride material. The Kevlar™ covers were specifically designed to withstand high temperature associated with the inadvertent application of pitot-static heat, without causing damage to the pitot-static probes.

Ground maintenance

On 8 June 2022, a scheduled engine wash was conducted on the right engine by Airwork maintenance personnel, assisted by contract maintenance personnel, at Brisbane Airport. The maintenance personnel comprised of a certifying LAME, a participating LAME, and an AME under supervision. The contract maintenance personnel operated the ground support equipment.

The engine wash procedure required several dry motors[10] of the engine for the introduction of the detergent solution and rinse, followed by operation of the engine at idle for 10 minutes.

The operator’s internal investigation established that the task was completed in stages, alternating between the certifying LAME and the participating LAME. Further, there was limited communications between the LAMEs, and they performed the task from memory without reference to the Airwork 737-300/400 ground run procedures checklist. This checklist required the pitot‑static covers to be removed, and the pitot-static heat circuit breakers to be opened to disable the heat system, prior to motoring or starting the engine.

Following completion of the wash, the participating LAME noticed that all 4 pitot-static probe covers had remained fitted during the dry motor and engine run operations, which resulted in the covers melting onto the probes. The covers were subsequently removed, and the tubes were cleaned using a plastic scraper, a scouring pad and solvent. A detailed visual inspection was carried out on the probes, and they were assessed serviceable. The aircraft was returned to service on 9 June 2022 and completed about 11.5 hours of flying over 7 sectors with no reported incidents, prior to the flight on 10 June 2022.

The damaged covers were hung on a board with a note describing the incident and that replacement covers had been ordered. Later that day, another engineer saw the covers, and put flame proof tape on them so that they could be reused until the replacements arrived.

ATSB examination

The 4 probes were sent to the ATSB’s technical facilities in Canberra for detailed examination. That examination identified varying amounts of foreign residue adhered to the lower surface of all 4 pitot-static probes. The right upper and lower probes presented with foreign object debris in the pitot drain ports. The source of this debris could not be determined.

The depth of the residue varied between almost none on the right upper probe, to a maximum of about 0.4mm in an uneven, rippled profile on the right lower probe (Figure 2). An internal examination was not conducted.

Figure 2: Pitot-static probe residue

Source: ATSB

Recorded information

Quick Access Recorder (QAR) data from the incident and previous flights was analysed by Boeing and the ATSB. By design, the QAR only recorded data from ADC1, which precluded the direct reading of the FO’s altitude indications. However, the QAR also recorded altitude data from the traffic alert and collision avoidance system,[11] which was acquired from the selected transponder. On the incident flight the transponder was set to acquire data from ADC2. From this the FO’s altitude indications were able to be indirectly determined.

The analysed data for the 7 flights between Brisbane and Perth showed minor discrepancies between the captain’s and FO’s altimeter during climb and descent, but no notable discrepancy in cruise flight was recorded. It could not be determined from this data if the transponder/ traffic alert and collision avoidance system was selected to acquire data from ADC1 or ADC2 during these flights. The recorded magnitude of the climb and descent altimetry error was small and unlikely to be noticed by flight crews. The source of these errors could not be determined from the recorded data and could have resulted for various reasons not linked to the ground maintenance incident on 8 June 2022.

The incident flight analysis showed that the FO’s altimeter indicated a higher reading than the captain’s, varying between 300 ft and 390 ft, throughout the cruise portion of the flight.  Information regarding the reported airspeed and Mach number discrepancy could not be obtained from the recorded data due to the ADC limitation described above. Using the values provided by the flight crew, the discrepancy was within the 20 kt or 0.030 M requirement specified in the QRH, for the airspeed indicators to be considered reliable.

Reduced vertical separation minimum airspace

The aircraft’s transponder was manually selected to use data from either ADC1 or ADC2. The altitude information passed from the selected ADC to the transponder was also used by ATC and the aircraft’s traffic alert and collision avoidance system to monitor aircraft altitude and maintain safe vertical separation between other aircraft.

During the incident flight, the aircraft was operating in reduced vertical separation minimum airspace (RVSM), which was between FL 290 and FL 410. In RVSM airspace, vertical separation is reduced from 2,000 ft to 1,000 ft. Aircraft are required to meet specified minimum accuracy requirements for airspeed and altitude, as well as a specific RVSM minimum equipment list, prior to being approved to fly in RVSM airspace. Flight crews are also required to closely monitor the altimeters for agreement prior to entering and throughout flight in RVSM airspace.[12] If there is a disagreement of greater than 200 ft and the flight crew believe that one of the primary altimeters is functioning normally, they must couple the autopilot to that altimeter and notify ATC ‘For information, operating on one primary altimeter only’.[13]

According to the International Civil Aviation Organization,[14] altimetry system errors may occur for various reasons including from damage to the pitot-static system. These faults can send incorrect data to ATC and the traffic alert and collision avoidance system, as well as the aircraft’s altimeters. In turn, this could result in a breakdown of vertical separation and increase the risk of collision, as depicted in Figure 3, if the error is not detected by the flight crew and reported to ATC.

Figure 3: Altimetry system error risk

Source: International Civil Aviation Organization

Altitude discrepancy

The FO’s call of 1,000 ft remaining until the assigned cruising altitude of FL330 differed from what was observed at that time by the captain on their respective altimeter. Likewise, after reaching that altitude, a 340 ft discrepancy was also identified between the FO’s and captain’s altimeters. This was consistent with the recorded flight data, which showed about the same discrepancy at the top of climb. The discrepancy varied during cruise flight between about 300–390 ft and always maintained a FO’s altimeter high indication. At the time, the flight was operating with a reduced vertical separation of 1,000 ft between other aircraft.

While the flight crew also identified slight differences between the indicated airspeeds and Mach numbers, these were within the manufacturer’s stipulated error limits for flight as stated in the Quick Reference Handbook.

Plastic pitot covers

The aircraft manufacturer recommended the use of Kevlar™ pitot-static probe covers as this material could withstand the high temperatures associated with the automatic operation of the pitot heat system at engine start if the covers were inadvertently left fitted. However, the operator had sourced locally made polyvinyl chloride covers, which were less resistant to heat. This increased the risk of the covers melting onto the probes if left on during engine operation.

Covers not removed prior to maintenance

The Airwork 737-300/400 ground run checklist required the removal of the pitot‑static probe covers and isolation of the pilot heat system. However, the operator reported that the checklist was not used when performing the scheduled engine wash 2 days prior to the incident flight. Rather, maintenance personnel completed the task by memory. This resulted in the pitot-static probe covers not being removed and the pitot-static heat circuit breakers not being opened prior to engine motoring and start. The risk of performing a maintenance error was potentially exacerbated by the maintenance personnel carrying out the task in alternating stages, with limited communication between them, as reported by the operator. As a result, the covers melted, and residue was deposited onto all 4 pitot-static probes.

Pitot-static probe residue

After identifying that the pitot-static probe covers had melted, the probes were cleaned and a visual inspection performed, before being returned to service. However, a post-incident inspection of the probes and the ATSB’s examination found residue from the covers remained on the probe surfaces.

Despite this, the analysis of the QAR data showed a stable altimetry system error extending back to the 7 flights after the engine wash. Further, the 7 flights had been completed between the wash and the incident flight with no reported altitude discrepancies from flight crews. Although the decision to not replace the pitot-static probes increased the risk of error resulting from turbulent air over the static pressure sensing ports, the QAR data did not demonstrate a link between the remaining residue and the incident flight.

Altimetry error in RVSM airspace

Consistent with the recorded data, the flight crew noted a 340 ft altitude discrepancy when at FL 330. If the primary altimeters diverged by greater than 200 ft when operating in RVSM airspace, ATC were to be notified. While the captain notified ATC that they required a descent and a subsequent return to Perth for operational reasons, they did not advise them of the discrepancy. This was based on the flight crew’s understanding that they had established the FO’s altimeter was accurate.

Altimetry system errors not only result in erroneous indications to the flight crew, but the protection systems afforded by ATC and the aircraft’s traffic alert and collision avoidance system can also be degraded. Therefore, it is important that flight crews advise ATC of any errors so ATC can assure adequate vertical separation exists with other aircraft.

From the evidence available, the following findings are made with respect to the unreliable altitude indications involving Boeing 737-476SF, ZK-TLJ, about 167 km west of Meekatharra Airport, Western Australia on 10 June 2022.

Contributing factors

Other factors that increased risk

Safety action by Airwork

Airwork advised that they have taken the following safety actions:

• Changed all pitot-static probe covers to Boeing ‑approved recommended covers that are made of heat resistant material (Kevlar™).
• They will release a safety statement after every potential safety occurrence as an interim measure prior to the completion of a formal internal investigation.
• This occurrence will be included in the Airwork engineering human factors training course.
• Airwork engineers conduct safety briefing at the start of the day to identify hazards/risks and control measures to prevent harm. The form used for the briefing was reviewed and additional information was included, providing guided cues for discussions regarding threat and error management, and local hazards.
• Ensured that checklists are readily available to use before the commencement of engine ground runs.
• Reviewed the change and risk management processes when there is an airworthiness directive.
• Published a safety alert around the importance of submitting a safety report as soon as practicable after an event has occurred.
• Published a safety alert to engineers and all staff about the importance of using checklists.

Sources and submissions

Sources of information

The sources of information during the investigation included the:

• captain
• Airwork safety and engineering personnel
• Boeing Aircraft Company
• recorded flight data
• Bureau of Meteorology
• Airservices Australia.

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
• Airwork
• United States National Transportation Safety Board 
• New Zealand Transport Accident Investigation Commission
• Boeing Aircraft Company
• Civil Aviation Safety Authority.

Submissions were received from:

• Airwork
• Boeing Aircraft Company
• the flight crew.

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