Preliminary report released 28 June 2023

This preliminary report details factual information established in the investigation’s early evidence collection phase and has been prepared to provide timely information to the industry and public. Preliminary reports contain no analysis or findings, which will be detailed in the investigation’s final report. The information contained in this preliminary report is released in accordance with section 25 of the Transport Safety Investigation Act 2003.

The occurrence

At about 0600 local time on 3 April 2023, a truck driver arrived at a heavy vehicle depot located about 240 m south of the Barwon Terrace level crossing in South Geelong. They prepared the tipper truck for work in Point Lonsdale and departed the depot at about 0635. The truck proceeded in a north easterly direction from the depot along an unsealed road which ran parallel to the V/Line broad gauge railway track towards Barwon Terrace level crossing.

After travelling along the unsealed road towards Barwon Terrace, the truck proceeded onto the level crossing between the boom barriers and stop lines located on either side of the crossing (Figure 1).

Figure 1: Direction of travel of truck and train and location of level crossing

Source: Imagery © Nearmap annotated by Chief Investigator, Transport Safety (Victoria)

Earlier at about 0631, V/Line train 7727, an empty six-car set with only the driver and a conductor on board, departed Geelong Railway Station towards Waurn Ponds (Figure 2). The train was being taken to Waurn Ponds Railway Station for a passenger service to Melbourne. As the train was being relocated, it did not stop at South Geelong Railway Station.

Figure 2: Train route and location of Barwon Terrace level crossing

Source: Imagery © Nearmap annotated by Chief Investigator, Transport Safety (Victoria)

At about 0636 just prior to sunrise in overcast and dry conditions, train 7727 approached the Barwon Terrace level crossing from the north. The train driver reported that on observing the truck approaching the level crossing, they sounded the train’s horn and applied the emergency brake. Soon after, the train collided with the truck that was foul of the track. The train was travelling at about 65 km/h at the time of collision.

The force of impact caused the truck to spin around in a clockwise direction (Figure 3) and the driver was fatally injured. The truck sustained substantial damage.

The train sustained minor damage to its front, did not derail and was able to be driven to the Waurn Ponds stabling yard. The train driver and the conductor were not injured.

Figure 3: Location of truck and train after the collision

Source: Victoria Police annotated by Chief Investigator, Transport Safety (Victoria)

Context

Barwon Terrace level crossing

The Barwon Terrace level crossing was located in South Geelong, about 3.5 km from central Geelong. The rail infrastructure and the level crossing were managed by V/Line Corporation. The line in this section was a single bi-directional broad gauge track with a maximum permitted speed of 115 km/h for passenger trains.

Travelling by road in a south easterly direction (away from Geelong), Barwon Terrace intersected the rail line at an angle of about 25 degrees to the road user’s left and 155 degrees to the right. The unsealed road intersecting Barwon Terrace near the level crossing provided access to nearby light industry.

The unsealed road used to access the truck depot widened at its intersection with Barwon Terrace. There was evidence of at least two routes being used by road traffic (Figure 1). One route joined Barwon Terrace north of the protecting boom barrier. A second route (taken by the truck on this day) joined Barwon Terrace between the boom barriers. Tyre tracks on the unsealed road indicated that this second route was in regular use.  

Level crossing protection

The protection equipment at the level crossing consisted of boom barriers, flashing lights, warning bells and warning signage on each side of the crossing (Figure 4). The warning signage consisted of a Railway Crossing combination sign (R6-25), a Stop on Red Signal sign (R6-9), a Keep Tracks Clear Sign (G9-67-1A) and a Railway crossing with marker assembly sign [RX-9(L)].

The level crossing protection was observed to be working at the time of the collision.

Figure 4 - Level crossing protection equipment at the Barwon Terrace level crossing

Photograph is taken from the northern approach to the level crossing, facing south.

Source: The Office of the Chief Investigator, Transport Safety (Victoria)

The level crossing warning lights at the northern end of the crossing consisted of two sets of red flashing lights. One set of lights faced north along Barwon Terrace. A second set of flashing lights faced across Barwon Terrace towards the northern end of the intersecting unsealed road.

The truck and driver

The truck was a 1997 International tip truck and was owned by an earth moving company. The truck was empty at the time of the incident. Truck drivers used the depot daily, departing and returning to the depot regularly.

The truck driver had worked for the earth moving company for approximately one month prior to the incident. The truck driver was fatally injured in the collision.

Further investigation

To date the following investigation activities have been completed:

• inspected the location of the occurrence
• examined train operational information
• examined truck operational information
• interviewed several parties
• commenced collection of other relevant information.

The investigation is continuing and will include review and examination of:

• the operation of the level crossing
• the operation of the truck and train
• the layout of the unsealed road and access to the Barwon Terrace level crossing
• a review of the traffic management in place prior to and at the time of the incident.

Should a critical safety issue be identified during the investigation, the ATSB will immediately notify relevant parties so appropriate and timely safety action can be taken.

A final report will be released at the conclusion of the investigation.

Executive summary

What happened

On the morning of 22 April 2023, World Diana departed from berth no 3 in Bunbury under the conduct of a harbour pilot with 2 tugs assisting. The ship had to be manoeuvred into the inner harbour turning basin and turned to port to exit the harbour entrance. The turn did not go as planned and the ship’s bow grounded on a shallow bank to the east of the entrance.

The ship was then manoeuvred clear of the bank and departed the port. Subsequent inspections and surveys indicated minor hull damage and the ship was cleared to continue trading. 

What the ATSB found

The ATSB investigation found that World Diana's turn to port was started earlier than planned, which reduced the available sea room to complete the turn. During the turn, the ship’s speed was allowed to increase until there was no room to safely turn, and the ship grounded.

The ATSB also found that bridge resource management during the pilotage was ineffective. The pilot set up the portable pilot unit but did not use the unit to its full potential. The departure plan did not provide any specific information or limits for the turn to either the ship’s bridge team or the tug masters. Nevertheless, while the tug masters had previous experience with this manoeuvre and the ship’s bridge team had further resources available no concerns were raised with the pilot until it was too late to avoid the grounding.

Finally, the investigation identified that the port had not developed adequate procedures that included arrival and departure plans for larger ships required to berth starboard side alongside berth no 3.

What has been done as a result

Southern Port Authority has updated its marine pilotage standards and procedures for Bunbury with standard procedures for departing all berths, including no 3 when berthed starboard side alongside. A maximum rate of turn for turning ships in the harbour has also been specified.

Safety message

This grounding illustrates the important part that bridge resource management plays in safe pilotage. Effective use of available resources reduces the chance of single-person errors and minimises their impact.

In this instance, proper use of the portable pilot unit, effective communication and active involvement of the World Diana’s bridge team and the tug masters would have allowed the deviation from the plan to be detected in time to prevent the grounding. 

The investigation

The occurrence

On the morning of 22 April 2023, the bulk carrier World Diana was scheduled to depart the Port of Bunbury, Western Australia under the conduct of a harbour pilot. The ship was berthed starboard side alongside at berth no 3 (head-in) and needed to be manoeuvred into the inner harbour turning basin and then turned to port towards the harbour entrance (Figure 1). The ship was nearly fully laden with a cargo of grain and had a draught of 11.65 m forward and 11.69 m aft (a deep draught for the port).

Figure 1: Overview of Bunbury inner harbour with World Diana at berth no 3

Image source: Nearmaps, annotated by ATSB

From about 0542 local time, the pilot conducted a master-pilot information exchange (see the section titled Bridge resource management) on the ship’s navigation bridge (bridge), including discussing the departure plan. The 2 tugs allocated for the departure were made fast forward and aft on the port side. At 0620, the mooring gang arrived and began casting off the ship’s mooring lines as directed by the pilot.

At 0632, when all the mooring lines had been cast off, the pilot instructed both tug masters to ‘lift off’[1] using quarter power and, shortly after, asked them to increase to half power. By 0636, the ship had developed slight headway (0.3 kt)[2], with its main engine running dead slow ahead. 

Soon after, the pilot stopped the ship’s engines and commenced turning the ship to port by directing that the aft tug stop lifting off and push at half power. The forward tug was directed to continue lifting off. At 0640, the ship’s speed had increased to 1.5 kt and the engine was ordered half astern. The ship’s rate of turn was 25°/minute and the forward tug was directed to stop (no weight on the tow line) while the aft tug continued pushing on the port side aft at full power.

As World Diana turned, its headway increased (1.6 kt) and, by 0641, the ship’s bow was closing on the shallow water on the eastern side of the harbour entrance at about 2.0 kt (Figure 5). At 0642, the forward tug master advised the pilot that the yellow buoys marking the shallow water were very close. In response, the pilot asked that the tug push with full power on the port bow to arrest the turn. At 0643, the same tug master advised the pilot that the tug could not remain in its position as it would ground, and suggested pulling back on the tow line to arrest the ship’s headway. The pilot then instructed both tugs to pull back on their lines at half power.

At 0643:30, World Diana’s bow grounded on the bank and its speed rapidly reduced to zero. The pilot then manoeuvred the ship astern using its propulsion and the tugs. Once the ship was established in the centre of the turning basin, the turn was completed. At the time of the incident, a pilot transfer vessel inspected the shallow area but did not identify any evidence of a grounding therefore it was believed to have been a near miss. Consequently, there was no inspection of the ship’s hull carried out prior to departing Australia. The pilot and ship’s master continued the departure and the pilot disembarked the ship outside the outer harbour.

Two days later, the pilot reported the incident as a near miss. A subsequent review of incident data indicated a grounding, and a survey of the seabed in the incident location was arranged. The survey identified an indentation in the soft seabed where World Diana’s bow had grounded (Figure 2).

Figure 2: Post incident survey imagery of shallow water (circled)

Image source: Survey by MNGsurvey overlay on Google Earth and annotated by the ATSB

Meanwhile, the ship was en route to its discharge port in Thailand via Singapore Strait. When the ship’s managers were made aware of the grounding, an underwater hull inspection was arranged to be done in Singapore. This inspection was conducted on 1 May and identified minor contact damage of the shell plating of the fore peak tank. The ship was cleared to continue trading with the damage to be attended at its next scheduled dry docking in 2025.

Context

World Diana

At the time of the incident, World Diana was registered in the Isle of Man, managed by OSM Maritime Group, Norway, and classed with Det Norske Veritas. It had been built by Oshima Shipbuilding, Japan, in 2020.

The ship was a Panamax[3] bulk carrier with an overall length of 229 m and breadth of 32.3 m. Propulsion was provided by a MITSUI‑MAN B&W 6S60E diesel engine driving a single, fixed‑pitch right‑hand turning propeller. The ship was fitted with a single, semi-spade conventional rudder.

World Diana’s navigation bridge was equipped with navigational equipment consistent with SOLAS[4] requirements, which included a voyage data recorder (VDR). However, data for the incident was not available to this investigation. 

The ship had an appropriately qualified, multi‑national crew of 19.

The pilot

The pilot started working in the Port of Bunbury in 2007 and had completed about 4,000 pilotage movements there, including about 35 vessels of over 200 m. At the time of the incident, the pilot held a license for the movement of ships of any size permitted in the port. They were qualified to ‘assess competency as a marine check pilot’ and during the past 5 years had mostly trained new pilots.

The pilot also held an unrestricted certificate of competency as a ship’s master and had completed bridge resource management training in 2021. They had attended the Port Ash (Australia) manned model ship-handling training centre in 2022 and completed the ‘manoeuvre and handle a ship in all conditions’ training course.

In 2022, the pilot completed the Southern Port Authority manoeuvring and emergency training for the Port of Bunbury, which included a simulator exercise for ships departing berth no 3 after berthing starboard side alongside. Before the incident, the pilot had undertaken the same manoeuvre as the second pilot on one occasion and subsequently a solo pilotage of a ship of similar size to the World Diana.

The pilot had accepted the World Diana departure pilotage on the previous day and reported having had plenty of time to prepare for the pilotage and feeling well rested before the incident.

Port of Bunbury

The entrance to the inner harbour of the Port of Bunbury is about 150 m wide (Figure 3). The inner harbour has 5 berths, and a submerged rock is located within the 9 m charted depths off berth no 5 (Figure 6).

Berth no 3 is located on the western side, closest to the entrance. It is a specialised grain and woodchip loading berth, which started being used to load Panamax bulk carriers in September 2022. This larger size of ship had to be berthed starboard side alongside the berth to allow the cargo loaders to access all the ship’s cargo holds. World Diana was the 10th ship exceeding 210 m that had berthed starboard side alongside at the berth. 

Pilotage is compulsory for ships with an overall length greater than 35 m. The port does not provide a vessel traffic service but can be contacted by VHF radio at all times.

Figure 3: Bunbury harbour berth layout

Image source: Southern Port Authority, annotated by the ATSB

Bridge resource management

Bridge resource management (BRM)[5] for World Diana’s pilotage started with a master‑pilot information exchange during which the pilot presented the departure plan (Figure 4). A hand‑drawn line on the plan indicated the approximate direction of travel, including the turn to port and the locations where the tugs would be cast off. It included the calculated static under keel clearance (1.82 m), but did not include any specific information such as ship’s speed, rate of turn and clearing distances or associated limits. There was no bridge audio data available, therefore there was no record of what was discussed during the exchange. 

Figure 4: Departure plan diagram

Image source: Southern Port Authority, annotated by the ATSB

The pilot reported having asked the ship master and bridge team to voice any concerns they had about the planned manoeuvre. They also stated that as the ship master was unfamiliar with the port, it was unlikely that deviations from the plan would be recognised.

The plan included using 2 tugs, each with a bollard pull of 80 tonnes. The pilot reported briefing both tug masters while waiting for the mooring gang and that both had previously participated in the planned manoeuvre.

Portable pilot unit

Before departing the berth, the pilot set up the port-supplied portable pilot unit (PPU) – an iPad application with a GPS receiver (Safe Pilot by Trelleborg). The ATSB obtained recorded PPU data, the only data available of the incident (as noted earlier, the ship’s VDR data was not saved). The PPU provided dynamic data together with a real-time display of the ship’s position, including a prediction of its trajectory.[6]

The involved pilot advised that they preferred to conduct pilotages largely by sight, using visual cues based on local knowledge and experience, and used the PPU mostly to check ship speed and rate of turn. A review of the recorded data by the ATSB identified that the PPU was showing the ship’s trajectory throughout the manoeuvring and had predicted that it was going to ground in the minutes before it occurred (Figure 5). It also showed the ship speed was 1.9 kt just prior to grounding.

Figure 5: Portable pilot unit display at 0641

Image source: Southern Port Authority, annotated by the ATSB

The manoeuvre

The pilot portable unit data was used to recreate the ship’s path (Figure 6).

Figure 6: Actual manoeuvre path

Image source: Southern Port Authority provided PPU data overlay on harbour nautical chart and annotated by the ATSB

According to the pilot, the turn was started early to keep clear of the submerged rock near berth no 5. The pilot stated that the plan was to have the aft tug push and then pull the ship back into position, but the ship's speed unexpectedly increased. The pilot attributed this to the aft tug pushing at full power at a slight angle, increasing the ship’s headway. The pilot attempted counteracting this by running the ship’s engine half astern and reported that as the rate of turn was 22˚/minute and increasing, the propeller was ineffective in arresting the headway. The pilot then resorted to using the forward tug to push at full power, but the tug had run out of sea room. Subsequently, the pilot instructed the tugs to pull back on the tow lines in an unsuccessful attempt to prevent the grounding.

The pilot further advised that the grounding could have been due to either of the following ship manoeuvring effects: 

• Shallow water rudder effectiveness[7] – as the vessel swing was assisted by a fore and aft tug, it was determined that any degradation of rudder effectiveness due to low clearance with the harbour floor would have been overcome with the assistance of the tugs. 
• Coanda effect[8] – this was not considered a contributing factor because the ship was pulled toward the bank by the tug and there was open water on the opposite side of the ship.

Tug master report

The ATSB reviewed the incident reports for the grounding, including one submitted by the tug master of the forward tug. In it they advised that there was a trainee manoeuvring the tug at the time. The tug master advised they thought that the turn may have been started early however, they did not advise the pilot. They instructed the trainee to be prepared to go alongside the ship to pull back. When they realised that the turn was not going to plan and the tug was running out of sea room, they took over from the trainee. As the tug closed on the yellow marker, the master advised the pilot they were unable to continue pushing and suggested they could pull straight‑back, to which the pilot agreed.

The tug master provided details of a debrief with the pilot several days after the occurrence. They advised that good communication and speaking up if the crew see any issues arising, were both raised as key learnings from this incident. 

Previous manoeuvres

Pilots in Bunbury had regularly conducted ships of similar size to World Diana, with lengths up to 238 m accepted at some berths. As noted earlier, World Diana was the 10th large ship (more than 210 m) to depart berth no 3 via a turning manoeuvre to port. The first 2 departures were conducted successfully by a pilot and a safety pilot (that is, 2 pilots on the bridge). It was then decided that one pilot would conduct these pilotages. 

The ATSB compared ship track PPU data from 4 of the previous departures from berth no 3 with World Diana’s track. This showed that the ship’s turn was started earlier than the others and that it was later manoeuvred further to the east of the turning basin (Figure 7). The maximum rate of turn achieved during these departures did not indicate wide variations, with World Diana’s rate of turn similar to the incident-free departures (Table 1).

Figure 7: Ship departure tracks from berth no 3

Ships referenced in image all have an approximate length of 229 m and show a different starting position due to their movement along berth no 3 used to load different hatches. The PPU data point is taken from a single position at the bridge of the ship. Labels also used as reference for Table 1.

Image source: Southern Port Authority provided PPU data overlay on Google Earth, annotated by the ATSB

Table 1: Maximum rate of turn recorded

Pilotage procedures

The Port of Bunbury marine pilotage standards and procedures manual stated that the PPU provided to pilots was to be used for the movements of ships with draughts exceeding 11 m. The manual stated that the PPU was 'an aid to navigation and should not be relied upon solely for the passage of the vessel’. Pilots were required to follow BRM principles, and the manual included the following instructions:

SPA [Southern Port Authority] fully endorses the principles of BRM. Pilots must:

• Make it to the bridge giving ample time for the proper exchange of information between the Master and Pilot before entering the channel. 
• During the Master/Pilot exchange of information, present and discuss the intended passage plan and manoeuvre with the Master and bridge team. Information to be exchanged with the Master must include tug arrangements, prevailing weather and tidal conditions, mooring arrangements and vessel positioning. Information to be given to the Pilot should include: the vessels manoeuvring characteristics, arrival draft and the operational status of equipment and machinery. Master needs to sign the passage plan confirming the understanding of its intent. 

The procedures manual provided arrival plans for all berths, including guidance for entering the harbour. These plans indicated berthing the ship head-out (that is, bow facing harbour entrance) by turning the ship either to port or starboard as shown below for berth no 3 (Figure 8). Specific ship-handling guidance such as rate of turn or speed was not provided. The manual did not include a plan to berth a ship starboard side alongside berth no 3. No departure procedure or plan was provided for any berth. In their departure plans, pilots used a copy of the chart to hand‑draw a plan, such as in this case (Figure 4).

Figure 8: Arrival procedures for berth no 3

Image source: Southern Port Authority

Safety analysis

As World Diana was starboard side alongside berth no 3, its departure required the ship to be manoeuvred into the inner harbour turning basin and turned to port to exit the harbour entrance. During the master pilot information exchange on the morning of 22 April, the pilot provided a diagram of the departure plan, indicating the turn and the locations of the 2 assisting tugs. No specific information such as ship’s speed, rate of turn, clearing distances or associated limits was shown on the plan and no evidence was provided that these items were discussed. 

At approximately 0632, shortly after the ship had left the berth, the pilot began turning the ship to port earlier than planned using both tugs, the ship’s main engine and steering. According to the pilot, the turn was started early to keep clear of the submerged rock near berth no 5. However, the rock was located off the farthest end of berth no 5, over a ship length ahead of the ship’s bow. Significantly, starting the turn early also reduced the sea room available to turn.

By 0636, use of the ship’s main engine had resulted in developing slight headway (0.3 kt). Four minutes later, the speed had increased to 1.5 kt and the ship was turning rapidly towards the shallow waters to the east of harbour entrance. In response to the developing situation, the pilot reversed the main engine (half astern) and instructed the aft tug to push at full power on the port side to turn the ship in the limited sea room. After a couple of minutes, the pilot realised that the turn could not be made in time to avoid the shoals and attempted to arrest the turn followed by an attempt to arrest the headway by using the tugs. These measures were unsuccessful, and shortly after 0643, the ship’s bow grounded.

The pilot’s portable pilot unit (PPU) was accurately displaying the ship’s position and progress in real time and indicating useful data, such as speed and rate of turn, to safely complete the turn. At 0641, the PPU predicted that the ship would ground. However, neither the pilot nor others on the bridge were using the PPU or paying attention to its display. Additionally, the forward tug's master identified that the ship was turned early but raised no concern with the pilot until the shallow water was extremely close, a minute before the grounding.

Overall, bridge resource management (BRM) was ineffective, most likely as specific information and limits for the departure plan were only known to the pilot, which made it difficult for the bridge team to raise concerns with the pilot. Nevertheless, had the ship’s master, being a ship-handler familiar with the ship’s manoeuvring characteristics, been actively monitoring the pilotage, the early turn and ship’s increasing headway, should have become evident on the ship’s monitors as well as the PPU. The PPU was displaying information to help avoid the grounding but this was not detected. Neither the bridge team nor the forward tug master raised any concerns with the pilot about the ship-handling errors until the grounding was imminent. In addition, when the pilot became aware of the imminent grounding, they did not make full use of the ship’s main engine, which remained at half astern (not full or emergency full astern) nor were the anchors dropped.   

The investigation identified that no procedures had been developed that included arrival and departure plans for larger ships that were required to berth starboard side alongside berth no 3. This reduced the information available to pilots for these ship movements and to share with bridge teams and tug masters to ensure a common understanding of how manoeuvring would be conducted.

Findings

From the evidence available, the following findings are made with respect to the grounding of World Diana when departing berth no 3 in Bunbury, Western Australia on 22 April 2023.

Contributing factors

Other factor that increased risk

• The Port of Bunbury had not developed adequate procedures that included arrival and departure plans for larger ships that were berthed starboard side alongside berth no 3.

Safety actions

Safety action by Southern Port Authority

The Southern Port Authority has updated its Marine Pilotage Standards and Procedures Manual to include:

• standard procedures for departing all berths, including berth no 3 after berthing starboard side alongside.
• a maximum rate of turn for turning ships in the harbour of 20° per minute.

Sources and submissions

Sources of information

The sources of information during the investigation included the:

• manager of World Diana at time of incident
• pilot
• forward tug master
• Southern Port Authority
• survey completed by MCMULLEN NOLAN GROUP PTY LTD

References

Sanders, D.J. and Plumridge, M.J. (1990) The Nautical Institute on pilotage and Shiphandling. London: Nautical Institute. 

Port Ash (Version 3.7 Sept 2012) Course in General Shiphandling. Australia: Port Ash

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:

• Australian Maritime Safety Authority
• the pilot, tug masters and ship manager
• Southern Port Authority

Submissions were received from the:

• tug operator
• ship manager
• Southern Port Authority

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

Purpose of safety investigations The objective of a safety investigation is to enhance transport safety. This is done through:  identifying safety issues and facilitating safety action to address those issues providing information about occurrences and their associated safety factors to facilitate learning within the transport industry. It is not a function of the ATSB to apportion blame or provide a means for determining liability. At the same time, an investigation report must include factual material of sufficient weight to support the analysis and findings. At all times the ATSB endeavours to balance the use of material that could imply adverse comment with the need to properly explain what happened, and why, in a fair and unbiased manner. The ATSB does not investigate for the purpose of taking administrative, regulatory or criminal action. 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 2024 Ownership of intellectual property rights in this publication Unless otherwise noted, copyright (and any other intellectual property rights, if any) in this report publication is owned by the Commonwealth of Australia. Creative Commons licence With the exception of the Coat of Arms, ATSB logo, and photos and graphics in which a third party holds copyright, this publication is licensed under a Creative Commons Attribution 3.0 Australia licence. Creative Commons Attribution 3.0 Australia Licence is a standard form licence agreement that allows you to copy, distribute, transmit and adapt this publication provided that you attribute the work. The ATSB’s preference is that you attribute this publication (and any material sourced from it) using the following wording: Source: Australian Transport Safety Bureau Copyright in material obtained from other agencies, private individuals or organisations, belongs to those agencies, individuals or organisations. Where you wish to use their material, you will need to contact them directly.

The investigation

Decisions regarding the scope of an investigation are based on many factors, including the level of safety benefit likely to be obtained from an investigation and the associated resources required. For this occurrence, a limited-scope investigation was conducted in order to produce a short investigation report and allow for greater industry awareness of findings that affect safety and potential learning opportunities.

The occurrence

The owner-pilot of a Piper PA-28-181 ‘Archer’ aircraft, registered VH-FEY, planned to conduct a flight from Jandakot to arrive in Carnarvon, Western Australia (WA) on 20 April 2023 to observe an eclipse of the sun at about 1130 local time, then return to Jandakot. This was a private operation under the visual flight rules.[1]

Previous flights

On the day before the eclipse, the pilot with one passenger on board, departed Jandakot Airport at 1416 and tracked to Geraldton Airport. The pilot landed at 1617 and parked in the general aviation area. Soon after arrival, the aircraft was attended by a refueller and Avgas tanker which replenished both fuel tanks (65 L added). The pilot and passenger then left the airport for their overnight accommodation.

At 0806 the next day, the pilot and 2 passengers arrived at the aircraft. The pilot advised that during the preflight inspection, water and a number of solid particles were visible in fuel samples drained from both tanks and the fuel strainer (gascolator). A number of fuel drains were carried out until the samples were free of water. The pilot estimated that the total amount of water drained from the aircraft fuel system was in the order of 500 ml.  

Although the pilot was concerned about the amount of water that had been drained from the fuel system, they considered that the system was free of water and there should be no effect on the aircraft. The pilot conducted the usual engine run ups, did not identify any problems, and departed for Carnarvon at 0831.

The aircraft tracked direct towards Carnarvon and climbed to 6,500 ft. At about 90 NM (170 km) from Carnarvon, the pilot diverted to Shark Bay aerodrome, landing at 1020. The aircraft departed Shark Bay at 1031 and tracked to Carnarvon, landing at 1108. Engine operation during both sectors was reported as normal.              

Both fuel tanks were replenished by a refueller and Avgas tanker (81 L added). The pilot and 2 passengers experienced the eclipse and obtained lunch near the airport. When the pilot carried out a fuel drain on return to the airport, there was no water found in the samples from the tanks but there was a small amount of water drained from the fuel strainer.

At 1239, the aircraft departed Carnarvon with the pilot and 2 passengers for Jandakot via Geraldton to drop off a passenger. The aircraft track was generally direct to Geraldton and the average cruise altitude was 7,500 ft. The pilot joined the circuit at 1452 and landed at 1455. Engine operation during the flight was reported as normal.                  

The occurrence flight

After a quick stop without refuelling, the pilot and 1 passenger boarded for the flight to Jandakot. The pilot recalled that as they advanced the throttle at the start of the take-off roll, there was an unusual ‘cough’ from the engine. Given it was a long runway and the engine reached full power, the pilot continued the take-off roll while monitoring the engine. It sounded normal and the temperatures and pressures were in the green operating ranges, so the pilot continued the take‑off.

The pilot departed Geraldton at 1513 to track to Jandakot via the generally direct route aligned with the coast, similar to the reciprocal track flown the day before. To take advantage of a forecast tailwind, the pilot climbed to cruise at 5,500 ft.  

At 1559, the pilot began descent to about 4,000 ft to avoid restricted airspace near Lancelin. A further descent to 2,000 ft was initiated at 1612.

By 1632, the aircraft had reached 2,000 ft and was crossing the coast near Ledge Point (120 km north-north-west of Jandakot Airport) to track coastal over water. For the next 30 minutes the aircraft proceeded down the coast at about 2,000 ft.

The pilot advised the ATSB that they were just about to make a routine radio transmission about 10 km north of Fremantle for any traffic in the area, when engine power subsided to idle power over a couple of seconds then recovered to cruise power. (A descent, heading change, and groundspeed reduction were recorded at 1705.)   

In response, the pilot selected the mixture control to full RICH and carburettor heat to ON. The electric fuel pump was already selected ON.

Engine power then subsided and recovered several times over a period of about 2 minutes. The pilot recalled there was no roughness or indications of a mechanical failure, and it seemed like the engine was responding to the throttle being moved (without any throttle movement).  

The pilot tried different throttle settings for 20–30 seconds without any reported effect. The pilot recalled looking at the engine instruments and thinking of the need to look at the fuel quantity indicators but after the occurrence could not recall any indications.    

At this stage, the aircraft had descended to about 1,200 ft and the pilot assessed that the aircraft would not be able to reach Jandakot Airport, which was about 18 km to the south-east. The pilot also decided against trying to reach the Swan River, which was about 4 km to the south‑south‑east and on the other side of a built-up area.

Now at about 1,000 ft, the pilot observed that they were not far from Leighton Beach. Considering that the surface wind was coming from the north-east, the pilot decided to turn into wind and land on the beach (Figure 1). During the turn however, the pilot noticed there were people all over the beach and that the plan was unworkable.

Instead, they decided to ditch the aircraft in the ocean as close to shore as possible to minimise their swimming distance. The pilot recalled trying to line up with the crest of the waves in accordance with generic ditching guidance.    

At 500 ft, the pilot realised that no one had been advised of the emergency and made a MAYDAY call to Melbourne Centre. Shortly afterwards, the passenger asked if the door should be unlatched, and this was carried out.  

By the time the turn had been completed, at about 300 ft, the engine had completely lost power and the propeller stopped turning shortly afterwards. The last data point was recorded at 1709.      

Figure 1: Aircraft track from engine fluctuations to ditching

Source: Google Earth (Annotated by the ATSB)

The pilot recalled that as they were approaching the water, they tried to hold the nose up as far as possible to prevent the nosewheel contacting first and flipping the aircraft forward. When about 20–30 ft above the water the stall warning activated. To the pilot that meant the airspeed was probably about 50 kt or less but they were watching the water and did not look at the air speed indicator.

With the stall warning still going, a main wheel contacted the water and the aircraft skipped along the surface for a few seconds. Then the right wing dropped rapidly consistent with a stall and dug into the water, quickly stopping the aircraft. Water gushed up over the front of the aircraft and windscreen.

Figure 2: VH-FEY ditching touchdown

Source: Image extracted from Channel 9 News footage

The pilot and passenger were not injured and got out of the aircraft to stand on the wing. Some people swam out from shore to check if they were okay. When the aircraft began to sink after a couple of minutes, they swam to shore.

Context

Pilot information

The pilot began flight training in August 2020 and was issued with a private pilot licence (aeroplane) in November 2021 and a commercial pilot licence (aeroplane) (CPL(A)) in September 2022. To gain the flying experience required for a CPL(A), the pilot acquired VH-FEY in March 2022 and operated the aircraft on several long flights within WA. At the time of the occurrence, the pilot’s total flying experience was 360 hours.  

The pilot held a Class 1 Medical certificate that was due to expire on 2 May 2023. This specified a requirement for the pilot to wear distance vision correction.    

Meteorology

The ATSB obtained aviation meteorological information from the Bureau of Meteorology.  

From the initial graphical area forecast (GAF) for southern Western Australia on the day of the occurrence (valid 1300 to 1900 local time), visibility was forecast to be greater than 10 km, except where it was 4,000 m due to isolated smoke south of Kalbarri. In a later issue of the GAF, the area of isolated smoke had contracted to potentially affect the flight south of Ledge Point, 65 NM (120 km) north of Jandakot.

The low-level grid point wind and temperature (GPWT) forecast issued at 0837 on 20 April 2023, indicated that at 1500, the following winds were expected at 5,000 ft and 7,000 ft respectively:

• Carnarvon to Geraldton from the north-east at 12 kt and 16 kt  
• Geraldton to Jandakot from the north and north-west at 6 kt and 10 kt.

On 20 April 2023, at 1700 (5 minutes before the engine power loss), the automatic weather station at Swanbourne (5 km east of the engine power loss position) recorded the surface wind from the east at 5 to 8 kt. The recorded temperature was 23.8° and dewpoint 6.6°. When plotted on the Carburettor icing probability chart produced by CASA, the result was serious icing – descent power. 

To ascertain the risk of water contamination due to rainfall, the ATSB accessed records of daily weather observations for Jandakot and Geraldton. At Jandakot, in the 4 weeks prior to the occurrence, a total of 67.6 mm of rain was recorded over 12 days. At Geraldton, there was no rain recorded on 19 and 20 April 2023.

Aircraft and systems

The Piper Aircraft Corporation manufactured the PA-28-181 aircraft in the United States in 1975. It was first registered in Australia in 1977.

The aircraft was powered by a Lycoming O-360-A4M piston engine and fixed pitch propeller.

A metal tank in each wing contained 24 US Gals (90 L) of usable fuel. Fuel was piped from the single outlet of each tank to a 3‑position fuel selector (OFF/LEFT/RIGHT) located on the left side‑panel (forward of the pilot’s seat), then to the fuel strainer, fuel pumps, and carburettor.  

Normal operating procedures

The PA-28-181 Pilot’s Operating Handbook, issued in 1975 and last updated in 2019, advised that the fuel system should be drained daily prior to first flight and after refuelling to avoid accumulation of water or sediment. To drain the lines from the tanks, the tank selector is switched from each tank in turn, and the fuel strainer drain valve open.  

In normal operation, the electric fuel pump was to be selected ON before take-off and deselected on reaching the desired altitude. Then, for approach and landing, the electric fuel pump was to be selected ON. It was also recommended that the electric fuel pump be selected ON while changing fuel tank selection. Otherwise, the electric fuel pump should normally be OFF so that any malfunction of the engine-driven fuel pump was immediately apparent.      

The POH advised that, to keep best lateral trim for the flight, fuel should be used alternately from each tank at 1-hour intervals. It further recommended that one tank be used for 1 hour after take‑off, then the other tank used for 2 hours before returning to the first tank. At that point, the first tank will contain approximately 1.5 hrs of fuel and the second tank approximately 0.5 hr. There was a caution to not run tanks completely dry in flight.       

To reduce fuel consumption in cruise, the POH recommended that the mixture should be leaned above 5,000 ft and at pilot discretion at lower altitudes when 75% or less power was being used. Leaning was carried out by pulling the mixture control back until the engine operation became rough then advancing it until smooth running was restored.

If an exhaust gas temperature gauge was fitted, as it was to VH-FEY, the Lycoming Operator’s Manual recommended leaning to 150°F on the rich side of peak EGT for maximum power cruise or to peak EGT for best economy cruise.        

Operational practices

The pilot confirmed that their usual practice was to change fuel tank selection every hour and that this was prompted by the fuel gauge indicating 10 US Gals had been consumed. In practice, when starting with full tanks, the first and second tank changes would be when each tank indication was 20 US Gals in turn and the third and fourth at 10 US Gals.

Although the fuel gauges were calibrated a few months before the occurrence and were not reported as defective, the pilot did not rely on the gauges and considered them to only be a guide. To establish fuel on board, the pilot used a dipstick before or after flight. The pilot did not verify the accuracy of the fuel gauges by cross referencing the quantities with dipstick or refuelling figures.      

The pilot advised that the mixture was left in RICH until top of climb then leaned to a setting that was slightly rich of peak EGT and was producing smooth engine operation. For descent, the pilot’s practice was to keep the mixture leaned and adjust as required to keep the engine smooth.

When the pilot operated the aircraft at higher altitudes and leaned the mixture as much as possible, the average fuel consumption rate calculated post-flight was consistently 30 L/hr. If operating at lower altitudes without leaning, the aircraft used more fuel.

The pilot reported that, based on the advice of an experienced instructor, their practice was to select the electric fuel pump ON for the entire flight to avoid any power interruptions if the engine‑driven pump failed.

Management of the flight

The pilot advised that a few days before a flight they usually used an EFB application to calculate estimates of flight times. Prior to departure from Jandakot, a flight plan was compiled manually as per their usual practice.   

During the flight to Carnarvon via Geraldton and Shark Bay, the pilot did not consistently use the flight plan/navigation log or look at the map. The pilot advised that this was unnecessary because they were familiar with the route, having conducted the flight multiple times.   

For the return flight to Jandakot, the pilot advised that they did not compile a flight plan or maintain a fuel log. After each of the previous flights from Carnarvon, the pilot had dipped the tanks and measured about 50–60 L remaining so expected that to be the outcome unless there was a strong headwind. As the flights from Jandakot to Carnarvon had consumed a total of 146 L, and there was no extensive ground running or stopover at Shark Bay on the return journey, the pilot expected that the fuel consumed on the return would be less than that figure. In that case, the fuel remaining on arrival at Jandakot was expected to be more than 34 L.     

The pilot was monitoring progress of the flight using the EFB application.

Fuel quantity analysis

The ATSB obtained flight data that was transmitted at regular intervals from the on-board EFB application to the associated server via the mobile phone network. That data allowed for calculation of flight times[2] and in combination with refuelling records, the average[3] fuel consumption rate for the previous sectors.   

On the first sector from Jandakot to Geraldton, the approximate fuel consumption rate was calculated as 32 L/hr (based on a flight time of 123 minutes and fuel add of 65 L). This flight was preceded by extended ground running so the consumption rate based on the flight time might have been marginally lower.

On the second flight from Geraldton to Carnarvon via Shark Bay, the average fuel consumption rate was calculated as 33 L/hr (based on a combined flight time of 147 minutes and fuel add of 81 L). This fuel consumption rate was applied to the return flight from Carnarvon because it was conducted in similar conditions.     

The combined flight time from Carnarvon to Geraldton then to the engine power loss was 4 hrs and 15 minutes. At 33 L/hr, the estimated fuel burn was 140 L. Therefore, when the engine lost power, the estimated fuel on board was 40 L (Full fuel at Carnarvon: 180 L).

To establish the approximate distribution of fuel as the flight progressed from Carnarvon, the ATSB compiled a fuel log based on the pilot’s recollection of the fuel tank selections. From the flight data, the ATSB identified the time that the aircraft was at the pilot-nominated locations to identify an approximate time for each tank change. That data was inserted into the fuel log to retrospectively track the fuel burn and fuel on board as the flight progressed (Table 1).

Table 1: Retrospective fuel log for Carnarvon – Geraldton – Engine power loss

¹ Take-off at Carnarvon on right tank

² At about bottom end of Shark Bay switched to left tank

³ At about Kalbarri switched back to right tank

⁴ Landed at Geraldton on right tank

⁵ Start, taxi, and take-off at Geraldton on left tank

⁶ At about Cervantes switched to right tank

⁷ Engine power loss (right tank)

⁸ Estimated usable fuel remaining in right tank

The ATSB notes that the retrospective fuel log is based on an average fuel consumption rate and approximate timing of tank changes. As such, it is only indicative of the fuel on board in each tank at each change and at the time of the engine power loss. (If the left tank had been selected for 11 minutes more over the 2 periods of use, the left/right fuel balance would be 40/0 L.)      

The pilot believed that the right fuel gauge was showing just under 10 US Gals remaining when it was selected before the occurrence (at 1610), but was not certain of this after the occurrence. Based on the retrospective fuel log and fuel calibration figures (Table 2), the right fuel gauge would have indicated between the 5 and 10 US Gals markings.

After the occurrence, the pilot estimated that when the engine loss occurred there was about 40 L (or 10 US Gals) in the left tank and 15–20 L in the right tank.  

If the flight had continued without the engine power loss, operation for the additional flight time of approximately 15 minutes would have consumed a further 8 L (at 33 L/hr). In that case the total fuel on board after landing would have been about 32 L, which equated to an hour of flight time.  

Fuel management guidance

CASA provided guidelines for aircraft fuel requirements in Advisory Circular AC 91-15 v1.1. The following information is adapted from the AC and selected for applicability to Day VFR operation of a light aircraft, such as a Piper PA-28-181.

Pilots were advised to operate in accordance with known or estimated fuel consumption data. This could be sourced from the aircraft/engine manufacturer or taken from recent historical consumption records.

The usable fuel required at the commencement of a Day VFR flight consisted of the taxi and trip fuel expected to be consumed, and final reserve fuel (30 minutes operation at 1,500 ft above aerodrome elevation) to be protected until landing. It was expected that additional fuel would be carried for contingencies.  

According to the AC, the pilot must determine the amount of usable fuel on board before commencing a flight. Unless fuel quantity can be assured and verified (for example, full tanks), pilots should use the best available cross-check process. Those checks applicable to aircraft without ‘fuel consumed indicators’ were:

• after refuelling and having regard to any recorded post-flight fuel quantities, a check of the cockpit fuel quantity indications or visual readings against the refuelling uplift readings
• when a series of flights is undertaken by the same pilot and refuelling is not carried out at intermediate stops, checking of the cockpit fuel quantity indications against computed fuel on board.

The AC cautioned that fuel gauges, particularly on smaller aircraft, may be unreliable. Therefore, placing sole reliance on a fuel quantity gauge to assess fuel quantity and not cross-checking fuel quantity from a second source, increases the risk of being unable to determine actual fuel remaining should the fuel quantity indication system become faulty.

In-flight fuel management was described as continual validation of planning assumptions that influence fuel usage and required fuel reserves. As part of in-fight fuel management, the pilot must ensure that fuel quantity checks are carried out at regular intervals to:

• compare planned fuel consumption and actual fuel consumption
• determine the amount of usable fuel remaining
• determine whether the usable fuel remaining is sufficient
• determine the amount of usable fuel expected to be remaining when the aircraft lands at the destination aerodrome.

In-flight fuel quantity checks must include a reconciliation of the fuel remaining indicated from available aircraft fuel quantity indication systems and these should also be checked to confirm fuel balance and fuel tank quantity.

It was implied that the in-flight fuel checks would be recorded in some way such as flight plan or fuel log written entry, to allow a time-based reference to previous in-flight fuel checks for trend identification.

In all instances, it was highly recommended that the post-flight fuel quantity be determined and recorded.  

Aircraft maintenance

The last periodic maintenance inspection was carried out in October 2022. At that time the aircraft total time in service was 7,421.3 hours.

Recent maintenance certified on 10 February 2023 included calibration of the fuel quantity indication system. The results were recorded in the aircraft logbook and on a placard above the fuel gauges (Table 2). For each increment marked on the gauges as US gallons, there is a corresponding figure for usable fuel in litres. In the brackets are the figures from the previous calibration carried out on 28 December 2018.

Table 2: Fuel calibration record VH-FEY

Gauge (US Gals)	E	5	10	15	20	Full
Left (L)	0	35 (35)	60 (55)	73 (60)	83 (75)	93 (86)
Right (L)	0	26 (30)	53 (50)	69 (60)	78 (70)	89 (86)

The ATSB notes that when each fuel gauge indicated 5 US Gals during the calibration process, the right tank contained 26 L and left tank contained 35 L. At the average fuel consumption rate of 33 L/hr (utilised in the retrospective fuel log), this equated to 47 minutes and 63 minutes flying time respectively. So, for the same fuel gauge indication of 5 US Gals, the right tank would yield 16 minutes less flying time than the left.    

A review of the aircraft logbooks found 2 entries for removal and reinstallation of the right fuel tank in 1989 and 1993. These were the only records that could be associated with installation of a non‑conforming outlet fitting to the right fuel tank (see the section titled Wreckage recovery and examination).    

The engine was last overhauled and installed in 1995 when the aircraft total time in service was 5,972.9 hours. As of the last periodic inspection, the engine had been operated for 1,449 hours and 28 years since overhaul.

In 2010, the engine was removed, bulk stripped, and reinstalled. Since then, and up to the last periodic inspection, the aircraft had been operated for 426 hours and 13 years.

Since the bulk strip in 2010, the carburettor had been repaired, and various components such as the engine driven fuel pump and magnetos had been replaced or overhauled.   

The engine manufacturer issued a service instruction that specified time between overhaul (TBO) schedules. It included:

• All engine models were to be overhauled within 12 calendar years of the date they first entered service or of last overhaul.
• For the Lycoming O-360 type fitted to VH-FEY, the operating-hour TBO was 2,000 hours.

Although the engine had exceeded the calendar time TBO period, the registered operator (owner-pilot) of VH-FEY continued to operate the aircraft. This was permissible for private category operations when the engine was maintained in accordance with the Civil Aviation Safety Authority (CASA) ‘on-condition’ maintenance requirements. At the last annual inspection in October 2022, the maintenance organisation had fulfilled those requirements by completing a piston engine condition report that verified engine serviceability.

Wreckage recovery and examination

Prior to initiation of ATSB investigation

The aircraft was recovered from the ocean to the nearby beach by a salvage company. Disassembly of the aircraft for transport was supervised by a licensed aircraft maintenance engineer (LAME) with the support of the salvage company. They related the following details:   

• both fuel tanks were full of fluid
• the fuel tank drains were not leaking
• there was a distinctive smell of Avgas when the right fuel cap was removed
• the contents of both fuel tanks were drained from each standard drain point into an empty semi-transparent intermediate bulk container (IBC)
• on completion of draining tank contents into the container there was a demarcation between the upper 25–35 mm of fluid and the remainder below
• the fluid in the upper layer was consistent with Avgas and the lower level was sea water.

Based on the estimated depth of the upper layer of fluid in the IBC, the quantity of Avgas drained from the fuel tanks was in the order of 30–42 L. It was not possible to differentiate between the amount of fuel drained from the left and right tanks. The container was subsequently used for recovery of other fluids by the salvage operator so no further information about fuel tank contents was available.      

The wings and stabilator were removed and the aircraft was then transported along the beach to storage at the salvage operator’s yard.   

ATSB examination

The ATSB initiated an investigation on 2 May 2023 and carried out examinations of the engine and aircraft fuel system at the storage facility. Forward of the firewall, this included:

• basic engine condition and mechanical continuity
• fuel strainer, engine driven fuel pump and carburettor
• air filter, airbox and carburettor heat mechanism
• magneto-engine timing and spark plugs
• exhaust and muffler
• oil filter

No engine defects were identified. The fuel strainer contained primarily sea water with a small amount of Avgas. The gauze filter was about 10–15% occluded by an unidentified white paste. The carburettor bowl was drained and was all sea water.

The carburettor, engine driven fuel pump, magnetos, and oil filter were removed for further examination. This was carried out and, other than saltwater residue, there were no defects or anomalies, and the components were probably serviceable at the time of the occurrence.

Examination of the aircraft fuel system was focussed on the right fuel tank assembly and fuel line to the selector. The right tank outlet fitting did not incorporate a ‘finger’ strainer, which was a non‑conformance with the fuel system data in the PA-28 parts catalogue. This outlet fitting was a different type to the conforming left tank outlet. No foreign object or evidence of contamination was found in the right tank.

Figure 3: VH-FEY Fuel tank outlet fittings - left with finger strainer and right without finger strainer

Source: ATSB

The ATSB considered the absence of a finger strainer in the only outlet from the right tank increased the risk of foreign object obstruction to fuel flow from the tank. This scenario would require an object of about the size of the internal diameter of the outlet fitting, which was stepped from 10 mm to 7 mm. Given there were no foreign objects found in the tank and no openings in the tank that would allow migration of any objects post-ditching, this scenario was considered highly unlikely. In addition, the aircraft manufacturer advised that there were no service difficulty reports or occurrences associated with the finger strainer (72091-000).

The fuel line from the right tank through the fuel selector to the fuel strainer was unobstructed. No defects were identified in the fuel selector, which was in the right tank position consistent with the pilot account.   

The fuel sender unit was removed from the right tank and was in good condition. Given the immersion in sea water and removal of the wings it was not feasible to functionally test the fuel quantity indication system.

Although the wing flaps had been removed as part of the recovery operation, fuselage damage indicated the flaps were retracted during the ditching. This was consistent with the LAME’s recollection and the pilot’s account.     

Geraldton Airport related

In response to the pilot account of significant water drained from the aircraft fuel system at Geraldton Airport on the morning of 20 April 2023, the ATSB sought information about possible sources of contamination at the airport.

The airport refueller advised that the usual quality checks were carried out to the tanker on the morning of 19 April 2023 and this was supported by their records. There was no report of water and the refueller advised that there was no history of this occurring.

The ATSB contacted the operator of an aircraft refuelled before VH-FEY who advised that no water had been detected from the post-refuelling fuel drains and normal operation was experienced on the subsequent flight.         

Geraldton Airport is a security-controlled airport that required authorised access to airside areas. One of the CCTV cameras at the terminal was directed towards the aircraft parking area utilised by the pilot of VH-FEY.

The ATSB requested CCTV data for the period from aircraft arrival on the 19 April 2023 to departure on 20 April 2023. Due to the timing of the data recovery, data for 19 April 2023 was unavailable. The CCTV available from 0804 on 20 April 2023 showed the pilot and passengers arriving at the aircraft, some pre-flight activity, and the aircraft being taxied for take-off. Although the resolution was not high, there was evident movement that was consistent with the pilot making multiple fuel drains.                     

Emergency procedures – Engine power loss and forced landing

The pilot’s operating handbook (POH) for VH-FEY included emergency procedures for in-flight engine power loss and landing without engine power. There was no specific procedure or guidance in the POH for partial power loss or ditching. The text of the emergency procedures for engine power loss in flight is reproduced with revised formatting for readability in a report context:

ENGINE POWER LOSS IN FLIGHT

Fuel selector - switch to tank containing fuel

Electric fuel pump – ON

Mixture – RICH

Carburettor heat – ON

Engine gauges – check for indication of cause of power loss

Primer – check locked

If no fuel pressure indicated, check tank selector position to be sure it is on a tank containing fuel

If power is not restored prepare for power off landing.

Trim for 87 MPH IAS (76 KTS IAS)

When the pilot responded to the engine fluctuations, the first item was overlooked and the fuel selector remained on the right tank throughout the engine power loss sequence. The pilot explained that during initial flight training in a Cessna 172 they had memorised a ‘flow’ for practice forced landings that started at the centre of the aircraft (including fuel selector) then moved left. However, the pilot had not considered the implication of that method for the PA-28-181. So, in this case, the pilot had started in the middle but did not reach the left-mounted fuel selector because attention was diverted to preparing for the forced landing.

The text of the emergency procedures for a power off landing is reproduced below with revised formatting for readability in a report context:

POWER OFF LANDING

Locate suitable field

Establish spiral pattern 1000 ft. above field at downwind position for normal landing approach

When field can be easily reached slow to 76 MPH IAS (66 KTS IAS) for shortest landing

Touchdowns should normally be made at lowest possible airspeed with full flaps

When committed to landing:

Ignition – OFF

Master switch – OFF

Fuel selector – OFF

Mixture - idle cut-off

Seat belt and harness - tight

In the safety tips section of the POH, pilots were advised:

In an effort to avoid accidents, pilots should obtain and study the safety-related information made available in FAA publications such as regulations, advisory circulars, Aviation News, AIM, and safety aids.

The AIM reference in the POH safety tips was to the Aeronautical Information Manual published by the Federal Aviation Administration (FAA) in the United States. This addressed ditching procedures and is referenced in the next section.  

The aircraft manufacturer advised the ATSB that they were not aware of any significant risks if pilots applied the Power Off Landing procedure in the POH to a ditching. Given the wide range of forced landing scenarios in different environments, the aircraft manufacturer considered that it was not feasible to define an emergency procedure for each one. In addition, the general information about emergency procedures in the POH indicated that emergency procedures were not intended to replace pilot training or provide information that is the same for all aircraft.

Under the certification standards[4] applicable to light aircraft such as the Piper PA-28-181, there was a requirement for information concerning normal, abnormal, emergency procedures, and other pertinent information necessary for safe operation, to be provided. In the case of single‑engine aircraft, this included the procedures, speeds, and configuration for a glide following engine failure and subsequent forced landing. There was no specific requirement for a ditching procedure. 

The General Aviation Manufacturer’s Association (GAMA) issued specification No. 1 for pilot’s operating handbook released in February 1975 (the PA-28-181 POH was released in August 1975) and revised it in 1996. This document specified that procedures should be provided for forced landings under various conditions, including ‘ditching, for aircraft with extended overwater flight capability’.

Ditching guidance and training

FAA

In the emergency procedures chapter of the FAA AIM, there were various diagrams showing best heading in relation to primary swell, secondary swell, and wind. The manual specified a successful aircraft ditching was dependent on 3 primary factors in the following order of importance:

1. Sea conditions and wind

2. Type of aircraft

3. Skill and technique of the pilot   

In addition to detailed guidance about evaluation of sea conditions and selection of relative heading, the manual advised that:

Touchdown should be at the lowest speed and rate of descent which permit safe handling and optimum nose up attitude on impact. Once first impact has been made, there is often little the pilot can do to control a landplane.    

CASA

In the Australian context, CASA provided advice to operators of issues relevant to ditching an aeroplane through Advisory Circular 91-09 Ditching. This addressed preparation, selection of ditching area and direction of approach, and conduct of the actual ditching. The information provided was consistent with that in the FAA AIM.

If no type-specific guidance was available, the AC recommended that:

… the gear remain up, the flaps full, and speed at a minimum. In all cases, the desired configuration should be adopted at a safe height and the aeroplane trimmed to allow concentration on selection of the touchdown point.

For selection of touchdown point, the AC included the following points:

• if there is no manufacturer guidance, select an attitude for minimum sink rate
• wings level with the water surface on top of or on the back of a swell, not on the face of a swell
• no yaw if possible; straighten nose if crosswind exists, but avoid lowering a wing.

Other aircraft POH

For comparison, the ATSB reviewed the POHs for 2 light single-engine aircraft that included ditching procedures: Cessna 172 and Gippsland Aeronautics GA8. The POHs specified power (if available) to achieve 300 ft/min rate of descent, and approach direction relative to wind and sea state. Touchdown was at descent attitude, without flare and/or at slowest practical speed.    

Pilot training

Pilot training in Australia was carried out in accordance with the Part 61 manual of standards (MOS). The competency standards for the ‘Manage abnormal situations – single-engine aeroplanes’ unit included elements and performance criteria for ‘Perform forced landing (simulated)’ in response to a simulated complete engine failure, and simulated partial engine failure.

For both scenarios, pilots were expected to identify the engine power loss condition, perform immediate or recall actions, and optimise aircraft performance. A landing area was to be selected, taking into account that a partially failed engine might fail completely, with an appropriate flight path. Pilots were to perform emergency procedures, as time permitted, and advise air traffic services or other agencies. If engine power was not restored, the pilot was to land the aircraft ensuring the safest outcome.  

Ditching was not referenced in the elements and performance criteria, but it was listed as one of the underpinning knowledge requirements.

The pilot advised that information about ditching had been gained from flight training and reading books.    

Other occurrences – Australia

Fuel starvation and forced landing

Fuel starvation and forced landing is a common occurrence type. The following occurrence was selected for the similarity of the engine power loss symptoms to the same type of aircraft.

ATSB AO-2017-094 Fuel starvation and forced landing involving Piper PA-28-181, VH-BDB, near Bankstown, New South Wales on 19 September 2017

The pilot believed that the aircraft fuel tanks were full and intended to conduct a 30–40 minute flight on the left tank. However, the aircraft had not been refuelled since the previous flight and contained about 25 L (35 minutes flying time) in the left tank and about 55 L (78 minutes flying time) in the right tank.

After about 30 minutes flight time, engine power started to fluctuate, and became progressively worse. The pilot conducted engine failure checks but did not change the fuel tank selection. Then the engine sustained a total loss of power and the pilot conducted a forced landing. There was no fuel found in the left tank.       

Ditching

The ATSB carried out a search of its database for occurrences that were categorised as a ditching. The ATSB identified 78 occurrences in the previous 50 years, including 11 fatal accidents that resulted in 21 fatalities.[5]

Of the fatal accidents, 2 involved twin-engine aircraft (including Piper Chieftain, VH-MZK near Whyalla on 31 May 2000) and 2 involved loss of control of single-engine aircraft. The remaining 7 fatal accidents involved single-engine aircraft in controlled ditchings.     

Apart from this occurrence involving VH-FEY, there were 5 other ditchings involving the PA-28 aircraft type, including 1 fatal ditching in a river near Bankstown in 1977. There were insufficient details to establish the method of ditching, however, the aircraft overturned on landing and sank immediately.

Extended time between overhauls (TBO)

ATSB AO-2020-060 Engine failure and collision with terrain involving S.E.D.E. Morane-Saulnier MS.893A, VH-UQI, on 6 November 2020.

During cruise, the engine began running rough then failed. The pilot conducted a forced landing in an open area but the aircraft impacted trees and caught fire. The pilot was seriously injured.

The ATSB found that the engine had sustained a catastrophic mechanical failure due to separation of a piston connecting rod. The engine had not been overhauled since 1997 and the aircraft had not been operated for an extended period, which was identified as a contributing factor.  

Safety message: This investigation is a timely reminder for aircraft owners and maintainers to be cognisant of the manufacturer’s service information which ensures that the serviceability of engine and airframe systems are maintained to the highest standards. This includes strict monitoring of on-condition items, and that replacement of some parts may be warranted to ensure continued and safe operation. Consideration should also be given to preservation of the engine and its systems, should an aircraft be infrequently utilised.

Other occurrences – Outside Australia

The ATSB identified the following occurrences involving ditching of a Piper PA-28-181 aircraft:

NTSB ERA16LA109 Fuel exhaustion involving Piper PA-28-181, N29099, near Port Jefferson, New York on 20 February 2016

During a night flight with a flight instructor, student pilot, and 2 passengers on board, the engine lost power. The flight instructor diverted to land along a shoreline but, unable to see it in the darkness, decided to ditch close to where he judged the shoreline to be from house lights. The instructor held the aircraft off the water as long as possible to avoid a touchdown with excessive speed and the risk of nosing over. All of the occupants evacuated the aircraft and there were no reports of any impact-related injuries. Three of the occupants were rescued but one of the passengers did not survive.

BEA 2020-0243 Piper PA-28-181 Archer II, N5352F, off the coast of the isle of Guadeloupe on 4 July 2020

During a ferry flight the engine lost power. Although the in-flight power loss procedures was carried out, engine power could not be restored. The pilot approached without wing flaps and trimmed the aircraft slightly nose up to ditch parallel to the swell. The pilot and passenger were uninjured and were rescued by helicopter.   

Sources and submissions

Sources of information

The sources of information during the investigation included the:

• owner-pilot of the accident flight
• maintenance organisation for VH-FEY
• aircraft manufacturer
• video footage of the accident flight and other photographs and videos taken on the day of the accident
• recorded data transmitted from the EFB application on the aircraft.

References

Advisory Circular AC 91-09 v1.0 Ditching, Civil Aviation Safety Authority, November 2021. 

Advisory Circular AC 91-15 v1.1 Guidelines for aircraft fuel requirements, Civil Aviation Safety Authority, September 2021.

Pilot’s Operating Handbook Piper Cherokee Archer II PA-28-181 REPORT VB-760 Issued 15 August 1975, Revised 1 April 2019.

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:

• owner-pilot of the accident flight
• maintenance organisation for VH-FEY
• aircraft manufacturer
• Civil Aviation Safety Authority

A submission was received from the:

• owner-pilot of the accident flight

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

Purpose of safety investigations The objective of a safety investigation is to enhance transport safety. This is done through: identifying safety issues and facilitating safety action to address those issues providing information about occurrences and their associated safety factors to facilitate learning within the transport industry. It is not a function of the ATSB to apportion blame or provide a means for determining liability. At the same time, an investigation report must include factual material of sufficient weight to support the analysis and findings. At all times the ATSB endeavours to balance the use of material that could imply adverse comment with the need to properly explain what happened, and why, in a fair and unbiased manner. The ATSB does not investigate for the purpose of taking administrative, regulatory or criminal action. Terminology An explanation of terminology used in ATSB investigation reports is available here. This includes terms such as occurrence, contributing factor, other factor that increased risk, and safety issue. Publishing information  Released in accordance with section 25 of the Transport Safety Investigation Act 2003 Published by: Australian Transport Safety Bureau © Commonwealth of Australia 2023 Ownership of intellectual property rights in this publication Unless otherwise noted, copyright (and any other intellectual property rights, if any) in this report publication is owned by the Commonwealth of Australia. Creative Commons licence With the exception of the Coat of Arms, ATSB logo, and photos and graphics in which a third party holds copyright, this publication is licensed under a Creative Commons Attribution 3.0 Australia licence. Creative Commons Attribution 3.0 Australia Licence is a standard form licence agreement that allows you to copy, distribute, transmit and adapt this publication provided that you attribute the work. The ATSB’s preference is that you attribute this publication (and any material sourced from it) using the following wording: Source: Australian Transport Safety Bureau Copyright in material obtained from other agencies, private individuals or organisations, belongs to those agencies, individuals or organisations. Where you wish to use their material, you will need to contact them directly.

Executive summary

What happened

On the morning of 23 April 2023, a Saab 340A, registered VH-KDK and owned by Pel-Air Aviation, was being operated by Regional Express Airlines (Rex) for a non-revenue flight from Wagga Wagga, New South Wales, to Charleville, Queensland. While in cruise at 22,000 ft and passing to the east of Cobar, New South Wales, the flight crew received a cargo smoke indication on the central warning panel. As a precaution, the crew fitted their oxygen masks and smoke goggles. Shortly after, the cockpit filled with smoke.

The captain commenced a diversion to Cobar while the first officer made a PAN-PAN[1] call to Melbourne Centre. Thick smoke then filled the flight deck preventing the crew from effectively seeing external visual references or the aircraft’s flight instruments. While completing the emergency checklists, the crew received further warnings for avionics smoke, followed by a cabin depressurisation, and then a right engine fire detection fail indication. The crew landed at Cobar and elected to stop on the runway and evacuate the aircraft.

Shortly after landing, Fire and Rescue New South Wales personnel arrived from the Cobar station and located a heat source at the air cycle machine and in the associated wiring. After gaining access to the cabin underfloor area, the source of the heat was doused with water. An internal inspection of the aircraft found fire damage in the area around the right recirculating fan. The aircraft was substantially damaged, and the crew were not injured.

What the ATSB found

The ATSB found that a likely failure of the right recirculating fan electronic box sub-assembly resulted in an in-flight fire under the cabin floor. The fire filled the cabin with smoke, which then entered the flight deck due to a smoke barrier curtain not being fitted in place and the flight deck door being open. 

When the crew fitted their oxygen masks, it was found that the first officer’s mask microphone was not working correctly, which delayed emergency checklists being actioned. The fire also caused substantial structural damage and led to a breach of the fuselage, resulting in a depressurisation of the aircraft. 

It was also found that the Rex flight crew had not been trained or had knowledge of the differences in the cargo‑configured Saab 340 aircraft, leading to them having no familiarity with specific systems fitted. This prevented them from completing some of the required steps in the emergency checklists. 

The flight crew did not receive training on the cargo‑configured aircraft differences prior to conducting freight operations. Further, the operator’s flight crew operating manuals did not reflect the differences in the cargo‑configured aircraft interior checklists, which may have alerted the flight crew to these differences during pre-flight preparation. Additionally, the manufacturer did not have any specific pre-flight check for correct fitment of the smoke barrier curtain for cargo‑configured aircraft preparation. 

What has been done as a result

On 13 May 2023, Rex issued an Operations Notice to all pilots, highlighting the guidance on the cross-valve handle as outlined in the Saab Aircraft Operating Manual (AOM). Furthermore, this guidance has been incorporated into the Rex Flight Crew Operating Manual (FCOM). 

On 13 November 2024, Rex amended the internal inspection checklist that is contained in their Saab 340 FCOM. The amendment now requires flight crews verify the position of the cross‑valve handle during the pre-flight checks.

Rex have also updated the training information delivered in their ground school to include the cross-valve system for the cargo‑configured Saab 340 aircraft into the training syllabus.

Rex indicated they are implementing a fleetwide inspection of the recirculating fan assemblies at the next aircraft heavy maintenance cycle, with a focus on the electronic sub-assembly module.

Pel-Air have included a revision to their flight crew operating manual with a caution that the smoke barrier curtain must be installed whenever combustible material is carried in the cargo compartment. Due to contract completion, Pel-Air have ceased conducting freight operations using the Saab 340 aircraft and have since sold the aircraft. 

Saab has revised their preparatory and walk-around pre-flight checklists to include the fitting of the smoke barrier curtain when carrying cargo in the cargo‑configured aircraft. 

Safety message

It is essential for operators to ensure that flight crew are conversant with differences in aircraft configurations when required to conduct operations on aircraft they may be unfamiliar with. It is important that information is readily available and accessible and be delivered in a manner to inform flight crews on the operational requirements of the aircraft. 

Operator flight crew operating manuals need to be relevant for the aircraft configuration being utilised. Further, manufacturer checklists for pre-flight inspections are required to cover the modifications fitted, so that this is available to operators to enable them to write the appropriate documentation for their flight crews.

The occurrence

History of the flight

On the morning of 23 April 2023, a Pel-Air Aviation cargo‑configured Saab 340A, registered VH‑KDK and operated by Regional Express Airlines (Rex), was being prepared for the first stage of a non-revenue freight flight from Wagga Wagga, New South Wales, to Charleville, Queensland. The purpose of the flight was to pre‑position a Rex Saab 340 engine to Cairns, Queensland, utilising a Rex crew, consisting of a captain and first officer (FO), and operating under the Part 91 flight rules. 

The crew had flown the aircraft from Cairns the previous day, and were tasked to fly the return leg, including a refuelling stop at Charleville. The flight crew arrived at the aircraft at about 0830 local time and conducted their pre-flight checks. The captain performed the interior checks while the exterior walk around checks were conducted by the FO. The aircraft departed Wagga Wagga at about 0949, tracking for Charleville, and cruising at FL 220.[1] The captain was the pilot flying (PF), and the FO was pilot monitoring (PM).[2]

In-flight fire and diversion

At about 1052, the crew was alerted by a cargo smoke detection warning[3] on the central warning panel. They began to manage the warning by identifying and cancelling the indication. The crew then donned their oxygen masks and smoke goggles. However, once fitted, the crew had difficulty communicating due to the FO’s mask microphone not functioning correctly and being very faint. A review of the cockpit voice recorder (CVR) recording showed it took another 57 seconds for the crew to establish effective communications with each other before they could commence the emergency checks.

At 1055 the crew received a right (engine) fire detection fail caution light, followed shortly after by an air conditioner caution light. This was due to the detection of a right distribution duct over temperature which automatically closed the right engine low pressure bleed valve. The crew initially detected no smoke or fumes, however within about 60 seconds, thick black smoke began filling the cockpit.

During the process of establishing the nature of the warnings, the flight crew discussed which airport would best suit their needs for the emergency, and opted to divert to Cobar, New South Wales (Figure 1). The captain had flown to this airport on several previous occasions and was familiar with it, and from their position, they could conduct a direct approach with minimal manoeuvring.

Figure 1: VH-KDK flight overview

Source: Google Earth and Flightradar24, annotated by the ATSB

At 1056, the FO gave a PAN PAN[4] radio call and advised air traffic control (ATC) that they were diverting to Cobar. ATC arranged for emergency services to meet the aircraft upon arrival into Cobar. Due to the radio coverage in the Cobar area, ATC utilised an overflying aircraft to relay communications as the diversion progressed.

While descending through FL 160, the crew received a cabin pressure failure warning, indicating that the aircraft had lost pressurisation. This occurred 4 minutes after the initial warning of the cabin smoke. The cabin depressurisation led to the crew increasing their rate of descent to get below FL 100. 

At approximately 1058, they commenced the ‘cargo compartment smoke’ emergency checklist. The CVR indicated the crew completed the first checklist item, which called for the left bleed valve to be closed. The checklist then called for closing the cross-valve handle, however the crew was unable to locate it, with the CVR recording indicating the crew tried to find it for 61 seconds before resuming the checklist flow without actioning the cross-valve handle closure. The crew completed the cargo compartment smoke checklist as visibility on the flight deck reduced to less than 10 cm. The captain recalled sliding their seat forward to enable them to see the instrument panel through the thick smoke.

Five minutes after the PAN PAN call, the crew commenced the checklist for ‘avionic or electrical smoke or fire’.[5] The crew then conducted the ‘smoke removal’ checklist to clear the smoke from the flight deck. 

One requirement of the smoke removal checklist called for aircraft speed reduction to below 160 kt, and to open a crew hatch to aid in smoke removal. Due to the unknown severity of the on‑board fire, the crew decided to maintain their speed and not complete all the checklist items as required, enabling them to expedite their landing.

As the crew continued their approach, the volume of smoke in the flight deck began to dissipate. This allowed them to navigate using external visual cues and conduct a visual approach for the landing. Because of the unknown source of the fire, upon arrival in Cobar, the crew elected to stop the aircraft on the runway and evacuate the aircraft. 

As part of the emergency evacuation procedure, the crew activated the fire extinguisher system[6] on both engines after shutting down, and then exited the aircraft. The incident had taken 22 minutes from the first smoke warning to landing.

After evacuation, the crew noted smoke to be coming from the vicinity of the right air cycle machine at the right wing root. Shortly after landing, Fire and Rescue New South Wales personnel arrived from the Cobar station and assessed the aircraft. After gaining access to the cabin underfloor area, an electrical harness was initially found melted and smoking. Consequently, the area was doused with water. 

Further inspection of the aircraft found significant fire damage concentrated in the area around the right recirculating fan. The right recirculating fan was also significantly fire damaged. An assessment of the right engine found no evidence of a fire. The aircraft underfloor structure was substantially damaged, and the crew were not injured.

Context

Aircraft information

The Saab 340A[7] is a twin-engine turboprop aircraft designed and initially produced by Saab and Fairchild Aircraft. It is designed to seat 30‍–‍36 passengers in standard configuration and is powered by 2 General Electric CT7-5A2 turboprop engines.

VH-KDK was manufactured in Sweden in 1984 and first registered in Australia in February 1985. It was operated in passenger configuration by Regional Express Airlines (Rex), before being modified to cargo configuration in 2009. VH-KDK was then owned and operated by Pel‑Air Aviation.[8] 

At the time of the accident,[9] VH-KDK had accrued a total time in service of 48,130.6 hours and 60,046 landings and had flown 13.5 hours since the last maintenance. 

Flight crew information

Captain

The captain held an air transport pilot licence (ATPL) (Aeroplane), and a valid Class 1 aviation medical certificate. They reported a total flying time of 7,579 hours with about 5,070 of those being on the Saab 340. They had flown for the operator for about 10 years, and previously had flown for another regional airline and had operated into Cobar airport on numerous occasions. 

The captain had previously flown the Saab 340A in a passenger configuration but had not flown either the Saab 340A or B variant in a cargo configuration.

First officer

The first officer (FO) held an ATPL (Aeroplane), and a valid Class 1 aviation medical certificate with a restriction for vision correction. They had reported a total flying time of about 18,297 hours, having flown about 1,480.9 in the Saab 340B. The FO had not previously flown any Saab 340 variants in a cargo configuration.

Meteorological conditions

Graphical area forecasts provided by the Bureau of Meteorology (BoM) stated that generally good weather conditions, with little cloud, and visibility greater than 10 km existed during the flight. The terminal area forecast for Cobar indicated light winds from the east at about 10 kt with the flight crew reporting CAVOK[10] conditions existing for the time of the diversion.

Cargo configuration

VH-KDK cargo conversion

The cargo conversion modification was carried out in accordance with Saab service bulletin (SB) 340-25-280. As an overview, the SB involved removal of the passenger fit‑out and replacing it with an interior cargo liner, blanked over windows, additional cargo barrier nets, and a floor roller system (Figure 2). In conjunction with this SB, other SBs were incorporated on the cargo version, which modified the air conditioning system. This was done by removing the left recirculating fan and introducing a cross-valve handle. 

A removable smoke barrier curtain was added at the forward section of the cargo compartment. The fire extinguishing system for the passenger cargo area at the rear of the cabin (zones C1 and C2) was also removed, and additional smoke detectors were added to the cabin.

Figure 2: Cargo configuration modification

Source: Saab, annotated by the ATSB

Smoke curtain

A removable smoke barrier curtain was designed to be installed between compartment A and the front-left fuselage (Figure 2). The purpose of the curtain was to provide containment of smoke and fire within the cargo compartment in the event of an on-board fire and prevent smoke ingress to the flight deck (Figure 3). The aircraft carried a placard at the top of the entrance stairs which stated: 

Smoke barrier must be installed for all cargo operation flights.

The smoke barrier was constructed of a fibreglass impregnated vinyl which was secured in place by a Velcro perimeter and metal press studs. The aircraft owner stated that the standard procedure was that it would be left attached by the left side attachment points and secured in place by the freight handlers after loading of cargo. It was then to be checked by the FO prior to flight. 

During interview, the flight crew stated that they were not aware of the use of the smoke barrier, and that it had been located after the incident in compartment A of the cargo area, and that it was not in place on the left of the cabin. The ATSB did not determine why the engineers who loaded the engine into VH-KDK had not secured the smoke curtain.

Figure 3: Smoke barrier curtain location in exemplar aircraft

Source: Saab, annotated by the ATSB

Air conditioning system 

In passenger configuration, the Saab 340 air conditioning system is comprised of a left and right air conditioning pack (ACP) which is supplied by bleed air from its respective engine. Each ACP is mounted externally under a fairing on the lower fuselage near the rear of each wing. The system has 2 recirculating fans under the adjacent cabin floor, ducting for the cabin and flight deck conditioned air supply and return, temperature sensors and controls, and cabin and flight deck air outlets. 

The left and right ACPs supply conditioned air to the cabin, and a portion of the right ACP conditioned air is supplied to the flight deck. The left recirculating fan returns the air to the left ACP from the aircraft cabin, while the right fan extracted air from the flight deck. The avionics fan draws air for cooling the avionics from the cabin conditioned air supply. The air is then expelled under floor. 

As part of the modification from passenger to cargo configuration, the left recirculating fan and ducting were removed. This resulted in limited extraction and recirculation of any contaminated air from the cabin interior, while the right recirculating fan would extract and recirculate air solely from the flight deck. 

Cross-valve handle

In the cargo configuration, a cross-valve and handle were added to the air conditioning system ducting between the left and right ACP (Figure 4), with the manual operating handle being located at floor level, next to the FO seat. Closing of the left bleed valve and cross-valve in accordance with the emergency checklist would isolate the supply of air to the cabin in the event of cargo smoke or fire, and the right ACP would supply only to the flight deck. As part of the emergency checklist for ‘cargo compartment smoke’, the left ACP would also be isolated from supplying the cabin. 

Figure 4: Schematic of modified air conditioning system

Source: Saab, annotated by the ATSB

Recirculating fan

The right recirculating fan was a centrifugal impeller type fan and was driven by an AC motor. The fan had an in‑built inverter, supplied by 28-volt DC. The majority of the electronics for the fan unit were contained in the box sub-assembly. This included the inverter, an electromagnetic interference (EMI) filter unit and the electronic card sub-assembly. The box sub-assembly controlled the fan operation, including the thermal control. Each electric motor was equipped with:

• a thermal switch[11] located in the cooler which guarded against an abnormal temperature increase. This switch would cut off the power if the motor temperature exceeded 110°C +/− 5° (230°F +/− 41°). The fan would start again when the temperature decreased to 65°C +/− 5° (149°F +/− 41°)
• a speed sensor which guarded against an abnormal decrease of nominal speed. If the speed fell below 80% of nominal speed for more than 17 seconds, the fan would be stopped.

In 1987, Saab released a service bulletin which gave operators the option to install an upgraded recirculating fan. The original fan was a brush type motor which required regular maintenance, including brush replacement when they had worn from use. Saab had received reports of smoke and burning smells which were attributed to brushes that were incorrectly installed. The brushless fans were introduced to help eliminate this issue and also required less maintenance. 

The fan installed in VH-KDK was the new brushless fan, manufactured in 1990 and fitted in April 1996. The fan history prior to installation was unknown by the operator. The fan accrued 27,585 hours while fitted to VH-KDK. 

Recirculating fan examination

Fire damage was found in the area around the right recirculating fan and on the fan itself (Figure 5). There were no other components in the vicinity of the fan with significant fire damage. As such, it is likely the right recirculating fan was the source of the fire.

Figure 5: Damaged recirculating fan

Source: ATSB 

An examination of the recirculating fan was conducted at the ATSB’s technical facilities in Canberra. The examination found that the fire damage was most significant at the external box sub‑assembly which housed the EMI filter, the resistor support plates and electronic card sub‑assembly. The aluminium cover of the box sub-assembly had melted, the electrical wiring was damaged, and some terminals had disconnected as a result of the fire damage. There was heavy soot and melting of solder in the cooler assembly.

The electronic card sub-assembly was made up 3 circuit boards, mounted to the resistor support plate. The function of the circuit boards was for motor speed detection, timer control, and a logic card. The damage exhibited on the circuit boards showed significant burning, consistent with the other components within the aluminium cover.  

The electromagnetic interference (EMI) filter sub-assembly had considerable damage to the filter itself and to the mounting plate with signs of melting and heat tinting of the steel plate structure, indicating a significant heat source. The heat tint was indicative of temperatures of approximately 310° to 330°C. 

Of note, the fire did not appear to be associated with the motor and there was no indication of damage to the internal components of the fan and was able to rotate freely. There was carbon and soot observed on the external surface on the motor. The crew stated that there had been no circuit breakers tripped that would be associated with the failure of the electronic card sub‑assembly.

The ATSB examination of the recirculating fan could not determine the cause of the failure of the electronic components attached to the assembly. 

Pressurisation system

The Saab 340 cabin is pressurised by the 2 air conditioning packs. The pressurisation system uses bleed air drawn from each engine and was either automatically controlled by a pressurisation controller, or manually controlled by a control valve operated by the flight crew from the flight deck. 

Pressure is able to be regulated by the opening and closing of 2 outflow valves, located in the empennage. The primary outflow valve is electro-pneumatically operated by the pressurisation controller, while the secondary outflow valve is pneumatically controlled from the cockpit and used as a manual standby system.

When emergency pressure relief is required, the primary outflow valve is able to be opened with the emergency pressure dump switch. When the crew of VH-KDK experienced the smoke in the cabin and flight deck, dumping cabin pressure as stated in the ‘smoke removal’ emergency checklist was the method used to assist in rapid removal of the smoke.

Aircraft depressurisation

The severity of the fire resulted in significant damage to the surrounding underfloor furnishings, ducting and airframe structure. The damage was then sufficient to rupture the skin (Figure 6) and caused a subsequent depressurisation of the aircraft. 

Figure 6: Underfloor fire damage showing fuselage hole

Source: Operator, annotated by the ATSB 

Checklists

The pre-flight procedures for the Saab 340A aircraft, including cargo configuration aircraft, were covered by the Aircraft Operations Manual (AOM) normal procedures, produced by the aircraft manufacturer. The AOM pre-flight normal checklist contained a check of the cross-valve handle position prior to flight but did not include a specific check for correct fitment of the smoke barrier curtain. 

A flight crew operating manual (FCOM) was carried on board VH-KDK which was developed by Pel-Air, based on the aircraft manufacturer’s AOM. Unlike the aircraft manufacturer's AOM, the pre-flight checks in the operator's FCOM did not contain any reference to the cross-valve handle. Consistent with the aircraft manufacturer’s AOM, the operator’s FCOM also did not include a specific pre-flight check for correct fitment of the smoke barrier curtain. The weight and balance chapter of the FCOM did show a diagram of the smoke curtain fitted but did not include a requirement to ensure the smoke curtain was in place.

The manufacturer had an airplane flight manual supplement in place, implemented as part of the cargo configuration SB, which included fitting the smoke barrier as a limitation (Figure 7 left). There were no identified interior checks in this supplement, which included the checking of the cross-valve handle prior to flight.

The aircraft manufacturer did have emergency checklists specific to cargo‑configured aircraft. These were compiled into the quick reference handbook (QRH) which was available to flight crew in the aircraft (Figure 7 right). 

Figure 7: Flight manual supplement (left) highlighting smoke curtain use and QRH checklist (right) highlighting cargo cross-valve handle and cockpit door 

Source: Saab, annotated by the ATSB

Flight deck door

The Pel-Air FCOM stated in the Operating Limitations section that during flight, the flight deck door must be kept closed and locked at all times. It is further listed in the engine start checklist that all doors are closed before engine start. 

Evidence from the accident flight, however, shows that before the fire, the crew were operating with the cockpit door open. During interview, the flight crew indicated they closed the door, whilst performing the cargo compartment smoke checklist. This was further supported by the CVR review, where the crew were heard to state the door was to be closed as per the checklist steps, which was followed by the sound of the door shutting. 

Flight crew training

Rex conducted a ground school, including simulator training, for their new Saab 340 flight crew. Under a commercial agreement, Pel-Air flight crews were also trained by Rex. The ground school covered the 340 variants of A, B and B WT. The aim of the ground school was to provide pilots from both operators with the necessary knowledge to gain a Saab 340 type rating. The type rating covered all Saab 340 aircraft and did not distinguish between any variant or configuration of the aircraft.

Following the Rex ground school, Pel-Air then conducted further training through its line training program for its flight crews allocated to freight operations. Delivery of this training was in a practical environment, with pilots learning the systems and differences of the cargo‑configured Saab 340. This included the use of the smoke barrier and the operation of the cross-valve handle. 

The ATSB asked what the process was for Rex pilots to receive this training and knowledge. Pel‑Air advised that a pilot employed by Rex would only receive this if they were to transition to freight operations with Pel-Air in a permanent role. 

Crew familiarity of cargo aircraft

The flight crew operating VH-KDK were both Rex pilots, who were normally rostered for passenger operations. The night before the flight to Wagga Wagga, they were rostered to fly the cargo‑configured 340A. The captain recalled asking the scheduler if they needed a briefing for flying the cargo 340A, and was told that they did not, but it could be arranged if needed. 

The captain decided to speak to a Rex colleague who had flown the cargo‑configured 340A several times previously. They were told there were no differences other than the removal of the seats and a freight interior being fitted and that there were no special procedures to be aware of. 

Both Rex and Pel-Air advised that their respective operations could roster a crew to fly either operator’s aircraft if it was available. Crewing arrangements were such that there was never any mixing of crew, that is that the flight crew would consist of either 2 Rex or 2 Pel-Air flight crew on any flight.

Oxygen mask

The flight crew fitted their oxygen masks and smoke goggles shortly after receiving the cargo smoke warning and smelling the smoke. The FO conducted the functional tests after fitment and found their microphone was barely readable by the captain. The cockpit voice recorder (CVR) indicated that, although muffled, the speech from the FO was recorded and they were also able to be heard by air traffic control (ATC) throughout the emergency.  

The pre-flight checks relating to the crew oxygen system were conducted as part of the interior checklist. The FCOM detailed the checks as: 

RIGHT OXYGEN MASK .................................................................................CHECKED

Check flight crew oxygen mask and microphone in accordance with the following: 

•  …, 

•  set audio panel BOOM - MASK switch to MASK, 

•  increase INT/SPKR volume and knock on mask, 

•  speaker noise indicates proper microphone function, 

•  set BOOM - MASK switch back to the BOOM position, ….

The check on the left oxygen mask was to be performed in the same manner. Although not detected on the CVR, the captain advised the masks were both tested prior to departure. 

Aircraft damage

The damage caused by the underfloor fire was substantial. The fire had damaged underfloor air conditioning ducting and electrical wiring (Figure 8).

Figure 8: Underfloor fire damage

Source: Operator, annotated by the ATSB

Structural components in the surrounding area had been distorted by the extreme heat, including the floor panels, which had collapsed when fire crews entered the aircraft and inadvertently walked over the affected area. The seat track support structure had distorted, and the fuselage was weakened by the fire which breached the outer skin, preventing the aircraft from remaining pressurised (Figure 9).

Figure 9: Fuselage skin breach

Source: Operator, annotated by the ATSB

The fuselage in the immediate area above and below the cabin floor was buckled and delaminated. The heat from the fire most likely travelled between the interior panels and freight lining, leading to the damage observed (Figure 10). Following an engineering inspection of the fire damage, the aircraft was withdrawn from service and not repaired.

Figure 10: Right side delamination on fuselage

Source: Operator, annotated by the ATSB

Recorded data

The ATSB was supplied raw data by the operator from the flight data recorder (FDR). This data was analysed and was found to include the previous 4 flights. 

The recorded data from the occurrence flight showed that at about 59 minutes after becoming airborne at Wagga Wagga, the FDR stopped recording. The recording stopped at about the same time as the initial smoke indication. This was most likely due to fire damage to the electrical wiring which controlled the FDR. 

Flight track information was also obtained from FlightRadar24, which showed the entire flight, including the diversion and landing at Cobar (Figure 11).

Figure 11: VH-KDK flight track and diversion

 Source: Google Earth and Flightradar24, annotated by the ATSB based on CVR recordings

The CVR was removed and sent to the ATSB technical facilities in Canberra. The CVR data was downloaded, with the recovery of 4 channels of audio data of about 120 minutes duration which included the in-flight fire event. Reviewing the recorded CVR data also revealed that coincidentally, just prior to the indication of the cargo smoke caution, the flight crew had been discussing alternate airports in the area, and which one they would select if they had a need to divert. 

The recording contained information from the end of the previous flight, and from the day of incident. It included the:

• flight crew’s initial reaction to the caution warning for the smoke in the cabin
• conduct of the emergency checklists
• additional warnings as they occurred
• crew intercom and communications with Melbourne Centre
• landing at Cobar and subsequent exiting of the aircraft.

The recording also revealed that while conducting the emergency checklist for ‘cargo compartment smoke’ the crew closed the cockpit door as a loud bang was heard, indicating it was open during the flight.  

Safety analysis

Introduction

On 23 April 2023, the Regional Express (Rex) Airlines flight crew operating a Pel-Air Aviation Saab 340A, registered VH-KDK were conducting an internal revenue cargo flight from Wagga Wagga, New South Wales, to Charleville, Queensland. About 1 hour into the flight, the crew experienced an in-flight fire and diverted to Cobar, New South Wales. After experiencing thick smoke on the flight deck and then a cabin depressurisation, the crew performed a safe landing at Cobar. The aircraft was substantially damaged, and the flight crew were not injured. 

This analysis will explore:

• origin of the in-flight fire
• aircraft preparation for the flight
• oxygen mask use and technical problem of the microphone
• cabin depressurisation
• flight crew knowledge of aircraft systems
• flight crew operating with the cockpit door open
• Pel-Air and Rex flight crew operating manual information deficiencies
• training of Rex flight crews
• Saab pre-flight inspection checklists
• Rex crew familiarity of cargo aircraft. 

Origin of the in-flight fire

The source of the in-flight fire was traced to the right recirculating fan assembly. Although the fan was not damaged internally, the fire damage was most significant at the box sub-assembly, which was mounted external to the fan and housed the electrical control circuit boards. It is likely that an electrical component or components within the box sub-assembly failed, resulting in the underfloor fire. The fire damaged underfloor insulation and plastic air conditioning ducting components, which led to thick smoke filling the cabin and cockpit and aircraft structural damage. 

The avionics warning received by the crew during the diversion was most likely associated with the avionics cooling air that was being drawn from the now smoke-filled cabin. This was also stated in the ‘cargo compartment smoke’ checklist. 

The ATSB examination of the recirculating fan could not determine a cause for the failure in the electronic control cards which led to the fire. 

When the crew received the air conditioning system right duct over temperature caution light, it was most likely due to the distribution duct over temperature being affected by the fire and the melting which occurred as a result. When the over temperature was sensed, the right bleed valve closed automatically as a function of system logic for over temperature protection.    

Smoke barrier curtain

Cargo operations can have a greater fire risk than passenger operations due to the carriage of cargo that could be the source of a fire and the lack of cabin crew available to fight a fire. As such, additional protection was available to minimise flight crew exposure to cabin smoke in the form of additional smoke detectors and a smoke curtain. 

However, the smoke curtain was not installed into position by anyone involved in the flight preparation. The flight crew, who normally operated the same aircraft type but in a passenger configuration, did not notice there was a placard at the aircraft entrance stating the smoke curtain was to be fitted for all cargo flights. The flight crew remained unaware of the smoke barrier curtain and its use for cargo operations. Further, the engine being transported was positioned in the cargo area of VH-KDK, on both occasions, by Rex engineers. As the curtain was usually installed by freight handlers during normal cargo operations, it is possible the Rex engineers were also unaware of its requirement to be fitted.  

In this accident, the source of the fire was an aircraft component rather than the cargo being carried. If a similar fire occurs in a passenger‑configured Saab 340 aircraft, then the smoke curtain would not be in place. However, the smoke curtain was available and was required for use for this flight, so its non-use increased risk for this event.

The flight deck door was not closed during flight as prescribed in the operator’s FCOM operating limitations and checklists. Having the door closed would have likely prevented the smoke being able to flow into the flight deck. 

The result of not having the smoke barrier fitted and the flight deck door closed as part of the aircraft pre-flight preparation was that smoke from the fire was not contained to the cabin area and was able to move forwards toward the flight deck. 

Oxygen mask fault

The flight crew fitted their oxygen masks and smoke goggles when alerted of the presence of smoke by the central warning panel. This decision may have prevented the crew from being overcome by smoke and fumes in the cockpit in the next several minutes. However, once fitted, the crew had difficulty communicating with each other, as a result of the mask microphone being very faint and difficult for the captain to hear the first officer (FO). This appeared to be an internal fault only, as the cockpit voice recording (CVR) showed that the FO was able to be adequately heard by ATC. 

This breakdown of communication delayed the crew by 57 seconds, in which emergency checks were not initiated due to the breakdown of communication. It created confusion and distraction between the crew while trying to execute the emergency checklist. 

A review of the CVR captured prior to flight could not positively determine if the pre-flight check action in relation to the oxygen mask was performed. This is an important check of the emergency communication system whilst on oxygen and was designated as a mandatory check item for a daily inspection as required by the Rex and Pel-Air FCOM.

Cross-valve handle

While the flight crew were conducting the emergency checklist items for cargo compartment smoke, they were unable to locate the cross-valve handle. This was due to the combination of the thick smoke obscuring their vision and their lack of knowledge of the differences in the cargo‑configured aircraft. 

Had the location and function of the cross-valve handle been known by the flight crew, the time taken to identify it during completion of the emergency checklist would have been minimised, which would have limited the delay of smoke removal from the flight deck. 

In this case, the subsequent depressurisation resulted in the smoke dissipating even in the absence of the cross-valve.     

Cabin depressurisation

The weakening of the fuselage structure due to the underfloor fire resulted in a breach of the fuselage skin, which led to a subsequent depressurisation of the aircraft during the descent. Although adding to another caution alert indication for the flight crew and subsequent checklist to be conducted, it also benefited in the removal of smoke from the cabin and flight deck. 

At the time of the depressurisation, VH-KDK was at FL 160 and descending. The crew, when alerted to the depressurisation, increased the rate of descent to below 10,000 ft. The cabin depressurisation occurred 4 minutes after the initial smoke warning occurred.

Due to the size of the hole created, the smoke removal most likely occurred at a greater rate than using the aircraft pressurisation outflow valves alone. The resulting fortuitous reduction in the amount of smoke in the flight deck improved visibility and allowed the crew to carry out a safe landing into Cobar.

Crew familiarity of cargo‑configured aircraft

The flight crew had not flown or had any prior training on the cargo‑configured Saab 340 and were not familiar with the differences of the passenger configuration. The captain chose to liaise with a colleague to gain information on the cargo‑configured aircraft instead of accepting the company offer for a briefing. 

This non-formal approach to understanding the differences between the 2 aircraft types ultimately did not pass on the required operational differences and potential safety aspects of the change of aircraft configuration.

Rex and Pel-Air manuals

Both operators (Rex and Pel-Air) manuals, which were designed to provide essential information to flight crews, did not include the required information to enable the pre-flight checks to be conducted adequately. While the weight and balance chapter of the FCOM showed the smoke barrier curtain location, there was no information on its importance to cargo operations, and as the crew had not been informed of any differences, they would not have been expecting that this section contained this information. The smoke barrier curtain installation information that was contained in the Saab service bulletin and flight manual supplement was not included in the pre‑flight checklists. As a result, the flight crew did not have awareness of its use. 

The operators' manuals also did not have a check to verify the position of the cross-valve handle. As discussed above, when the checklist called for the crew to use this handle when the aircraft was already filling with smoke, the crew could not locate it.

Flight crew training

The Rex ground school provided type rating training on the Saab 340 series aircraft to both Rex and Pel-Air pilots. This training was based on the passenger‑configured aircraft. Pel-Air pilots undertook further training which gave them the knowledge and skills for the cargo‑configured aircraft. 

In scheduling their flight crews to operate the cargo‑configured Saab 340, Rex did not have a process to ensure that the additional training or knowledge sharing for their crews in the differences applicable to aircraft operated by Pel-Air was delivered.

Saab pre-flight checklists

As discussed above, both operators’ manuals had no inclusion of a pre-flight interior check for the smoke barrier curtain or the cross-valve handle. Likewise, there was no pre-flight interior check for these items in the manufacturer’s documentation. Saab confirmed that there were no checks in the pre-flight checklist for the crew to specifically verify that the smoke barrier curtain was correctly fitted.

The result of the manufacturer’s pre-flight and interior checklists not detailing information for the smoke curtain was that the operator did not detail these in their own FCOM. This information was not available for the flight crew who, even without prior knowledge of the cargo‑configured variant, would have been alerted to these changes while conducting these pre-flight checks in accordance with the FCOM. 

Findings

From the evidence available, the following findings are made with respect to the in-flight fire and cabin smoke involving a Saab 340A, VH‑KDK, 114 km east-north-east of Cobar, New South Wales, on 23 April 2023. 

Contributing factors

• It was likely that an electrical component of a control circuit board on the recirculating fan failed, resulting in an in‑flight fire under the cabin floor.
• The smoke curtain was not fitted as required for the cargo configuration, and the flight deck door was open, which allowed smoke from the in‑flight fire to enter the flight deck.
• The underfloor fire caused weakening of the fuselage structure, which led to a subsequent depressurisation of the aircraft during the descent. However, the depressurisation aided in the removal of enough smoke from the flight deck on approach to allow an unhindered visual approach at Cobar.
• Crew were not familiar with the cargo configuration and were unaware of the smoke curtain requirements and location of the cross-valve handle.
• The Pel-Air and Rex Saab 340 flight crew operating manuals did not include reference to the location and operation of the cross-valve handle or the operation and use of the smoke curtain. (Safety issue)
• Rex did not ensure its flight crews received training in the differences between passenger and freight‑configured Saab 340 aircraft, prior to being scheduled to fly freight operations. (Safety issue)
• Saab did not include the smoke curtain fitment in pre-flight documentation for the cargo‑configured Saab 340 aircraft to inform flight crew of this difference from the passenger-configured version. (Safety issue)

Other factors that increased risk

• When the flight crew donned their oxygen masks, the first officer's oxygen mask microphone did not function correctly. This led to difficulty in communication between the flight crew and a delay in responding to the emergency.
• Due to the combination of the smoke density and lack of prior knowledge, the flight crew were unable to locate the cross-valve handle during the emergency, therefore delaying the removal of smoke from the flight deck.

Safety issues and actions

Saab documentation for cargo configured aircraft

Safety issue number: AO-2023-020-SI-01

Safety issue description: Saab did not include the smoke curtain fitment in pre-flight documentation for the cargo‑configured Saab 340 aircraft to inform flight crew of this difference from the passenger‑configured version.

Operator documentation and crew familiarity

Safety issue number: AO-2023-020-SI-02

Safety issue description: The Pel-Air and Rex Saab 340 flight crew operating manuals did not include reference to the location and operation of the cross-valve handle or smoke curtain.

No formal company training

Safety issue number: AO-2023-020-SI-03

Safety issue description: Rex did not ensure its flight crews received training in the differences between passenger and freight‑configured Saab 340 aircraft, prior to being scheduled to fly freight operations.

Safety action not associated with an identified safety issue

Additional safety action by Regional Express

Rex advised that it is implementing a fleet‑wide inspection of the flight deck and passenger compartment recirculation fans at the next aircraft heavy maintenance visit. The inspection will be focused on the electronic sub-assembly module of the recirculation fan due to this component being identified to have the most significant fire damage on the fan assembly removed from VH‑KDK.

Glossary

Sources and submissions

Sources of information

The sources of information during the investigation included:

• the crew of VH-KDK
• Regional Express Airlines
• the chief pilot of Pel-Air Aviation
• the manager training and checking and head of operations for Regional Express Airlines
• Civil Aviation Safety Authority
• Bureau of Meteorology
• Fire and Rescue New South Wales
• Saab
• Airservices Australia
• the cockpit voice recorder and flight data recorder
• recorded data from Flightradar24. 

References

Australian Government 2023, Part 91 (General Operating and Flight Rules) Manual of Standards 2020, Civil Aviation Safety Authority, Canberra, ACT, viewed 30 April 2024, <Federal Register of Legislation - Part 91 (General Operating and Flight Rules) Manual of Standards 2020> 

Submissions

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

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

• Civil Aviation Safety Authority
• Airservices Australia
• Crew of VH-KDK
• Regional Express Aviation
• Pel-Air Aviation
• Swedish Accident Investigation Authority (SHK)
• Bureau of Enquiry and Analysis for Civil Aviation Safety (BEA).

Submissions were received from: 

• the captain of the crew
• Regional Express Aviation
• Pel-Air Aviation
• Swedish Accident Investigation Authority (SHK)
• Bureau of Enquiry and Analysis for Civil Aviation Safety (BEA).

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

Purpose of safety investigations The objective of a safety investigation is to enhance transport safety. This is done through:  identifying safety issues and facilitating safety action to address those issues providing information about occurrences and their associated safety factors to facilitate learning within the transport industry. It is not a function of the ATSB to apportion blame or provide a means for determining liability. At the same time, an investigation report must include factual material of sufficient weight to support the analysis and findings. At all times the ATSB endeavours to balance the use of material that could imply adverse comment with the need to properly explain what happened, and why, in a fair and unbiased manner. The ATSB does not investigate for the purpose of taking administrative, regulatory or criminal action. Terminology An explanation of terminology used in ATSB investigation reports is available here. This includes terms such as occurrence, contributing factor, other factor that increased risk, and safety issue. Publishing information Released in accordance with section 25 of the Transport Safety Investigation Act 2003 Published by: Australian Transport Safety Bureau © Commonwealth of Australia 2024   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 morning of 7 April 2023, a Fokker 70, registered VH-NUU, was being pushed back from a bay at Brisbane Airport, Queensland, to operate a passenger air transport flight to Roma. It was reported that during pushback at about 0640, a trail of fluid on the ground was observed and then found to be due to a fluid leak from the no. 2 (right) engine. Both engines were shut down and the aircraft was towed back to the bay.

When inspected, engineers determined there was a leak from a connection on the lower left side of the engine, between a rigid fuel line and the fuel flow regulator (FFR), and fuel had drained out of the engine nacelle through an access opening near the leak.

After removing the fuel line from the component, the source of the leak was determined to be a pair of elastomeric seals (O-rings), fitted to the fuel line, that had degraded to a point where they no longer could contain fuel under pressure. The seals were replaced, along with the FFR because of an unrelated defect. An engine ground run was carried out and the aircraft was returned to service.

After receiving notification of the occurrence on 12 April 2023, the ATSB commenced an investigation. The ATSB:

• obtained maintenance records
• examined maintenance information
• interviewed technical specialists
• obtained information from the engine manufacturer (Rolls-Royce).

During the investigation, and in consultation with the engine manufacturer, the ATSB noted that:

• no reason could be established for the degradation of the seals, which occurred over a period of about 6 years since they were likely changed
• maintenance records indicated that the components were installed and maintained in accordance with manufacturer requirements
• there were no instances of an engine fire resulting from fuel leaks from the FFR or other components in the same area on Fokker 70 and Fokker 100 aircraft in over 26 million flying hours
• the layout of the fuel lines on this engine type is routed to avoid ignition sources and there were no hot surfaces or sources of ignition in this zone
• fuel leaks from this location would drain away from the engine and then out and away from the nacelle through an access opening on the bottom of the lower cowl.

Therefore, the ATSB considered it extremely unlikely that a fire would develop as a result of this type of fuel leak. Further, if a fire did occur it could be detected by on-board systems (or visually by ground crews) and extinguished (along with the fuel supply being isolated from the engine nacelle).

Reasons for the discontinuation

Based on a review of the available evidence, the ATSB considered it was unlikely that further investigation would identify any systemic safety issues or important safety lessons. The ATSB did not identify any concerns with the assessment, management, and monitoring of this type of defect. Consequently, the ATSB has discontinued this investigation.

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