The occurrence

At 0912 local time on 4 November 2022, a Saab Aircraft Co 340B, registered VH-ZRC and operated by Pel-Air Aviation Pty Limited, departed Melbourne Airport, Victoria for a multi-day, multi-stop charter flight with 25 passengers and 3 crew. The crew consisted of a captain, first officer and a cabin attendant. The first officer was undergoing command training experience and was flying from the left seat, with the captain seated in the right seat. After an uneventful flight the aircraft landed at Flinders Island, Tasmania at approximately 1012 and taxied to the terminal. The passengers disembarked and, along with the cabin attendant, departed the airport for a sightseeing tour of Flinders Island. Both the captain and the first officer remained at the airport to conduct post flight duties and to prepare for the next leg of the charter to Wynyard, Tasmania, scheduled for 1430.

After the cabin attendant and the passengers returned to the aircraft and were boarded, the first officer started the aircraft’s engines and conducted the appropriate checklists. Due to the short taxi required at Flinders Island, the flight crew decided to delay commencement of the taxi until they heard the flight attendant commence the safety briefing.

The first officer released the parking brake and conducted an immediate 180° left turn out of the parking bay (Figure 1). They then proceeded to taxi the aircraft to the threshold of runway 32 via runway 23.[1] The first officer commented that there was no abnormal handling or unusual power settings required to taxi the aircraft. They decided to taxi slowly so the cabin attendant had sufficient time to prepare the cabin for take-off. The first officer also recalled slowing the aircraft with the brakes prior to entering the runways. The aircraft entered runway 32, back tracked and lined up on the runway centreline in preparation for take-off.

The first officer commenced the take-off roll, noting that a crosswind was present from the left. The first officer glanced down after setting power to check the torque gauges. When the first officer looked up again, they noted that they had drifted over to the left of the runway centreline, with the airspeed indicating 46 KIAS.[2] In response, the first officer applied right rudder and brought the aircraft back onto the centreline of the runway. The aircraft continued to accelerate to around 80 knots when the flight crew noted a reduction in the aircraft’s acceleration rate. The first officer called failure, the captain called stop and the take-off was rejected. The aircraft reached a maximum airspeed of 96 knots.

Figure 1: Flinders Island Airport

Source: Google Earth, annotated by the ATSB

When the first officer retarded the power levers the aircraft began to veer to the right of the runway centreline. They then used the nose wheel steering tiller in an attempt to keep the aircraft on the centreline. The first officer also recalled the aircraft felt like it was braking by itself, and that pressure was felt in the brake pedals under their feet.

Just prior to the aircraft coming to a complete stop the Flinders Island Airport Operations Officer (ARO) radioed the flight crew on the Flinders Island Common Traffic Advisory Frequency to advise them of smoke coming from the aircraft’s wheels. The flight crew acknowledged the radio transmission.

The first officer advised the cabin attendant and passengers to remain seated. Melbourne air traffic control was contacted and informed that VH-ZRC was disabled on runway 32 at Flinders Island. The ARO further advised the crew that the smoke had dissipated. The pilots shut down the aircraft and the passengers were disembarked.

The aircraft was inspected by the pilots after the occurrence, with the following observed:

• all 4 main landing gear wheels on both the left and right main landing gear had deflated
• the outboard wheel on the left main landing gear had a flat spot (Figure 2).

Figure 2: Left main landing gear after occurrence

Source: Supplied, annotated by the ATSB

The runway was also inspected by the pilots and the ARO, with the following observed:

• tyre marks were evident commencing 300 m from the runway threshold until the aircraft came to a stop approximately 1,150 m from the runway threshold (Figures 3 and 4)
• initial tyre marks showed a veering to the left of centreline 
• final tyre marks displayed a significant veer to the right with a change in tyre markings from a locked tyre to a deflated tyre prior to the aircraft coming to a stop (Figure 5).

Figure 3: Tyre marks on runway

Source: Supplied, annotated by the ATSB

Figure 4: Initial tyre marks from VH-ZRC on runway 32

Source: Supplied, annotated by the ATSB

Figure 5: Left main landing gear tyre marks  

Source: Supplied, annotated by the ATSB

A Rex Airlines engineering crew was flown in to inspect the aircraft. The engineers identified that the main landing gear wheels had deflated due to their fusible plugs activating. All the main landing gear wheels and brakes were replaced. Brake and parking brake testing was carried out with no faults evident, and the aircraft was returned to service.

Context

Pilot information

The captain held an Air Transport Pilot Licence (Aeroplane) and a multi-engine command instrument rating. The captain held a Class 1 aviation medical certificate. The captain had a total flying time of 4,660 flying hours with 4,461 hours on the SAAB-340.

The first officer held a Commercial Pilot Licence (Aeroplane) and a multi-engine command instrument rating. The first officer held a Class 1 aviation medical certificate. The first officer had a total flying time of 2,449.5 flying hours with 2,219 hours on the SAAB-340.

Flinders Island weather

The pilots and ARO reported that the wind during the take‑off roll was from 280° at 16 knots with broken cloud at 3,000 ft above the airport. Visibility was greater than 10 km.

Brake system

The main landing gear wheels are fitted with hydraulic disc brakes. Each landing gear has an inboard and outboard brake assembly which are powered by separate hydraulic circuits, an inboard brake circuit and an outboard brake circuit. Each circuit has its own accumulator that is pressurised, when required, by a demand electrical hydraulic pump. The brake circuits share a common hydraulic return line to the aircraft hydraulic system main reservoir. Independent wheel braking is controlled by toe pedals at the top of the rudder pedals. Each pedal is connected via a cable to its corresponding brake valves.

Figure 6: Brake system schematic

Source: Supplied, annotated by the ATSB

Parking brake

The parking brake is controlled by a handle on the left pilot’s side panel (Figure 6). The handle is attached via a push-pull cable to a parking brake valve located in the brake hydraulic circuit common return line. The parking brake is set by pulling up on the handle whilst depressing the brake pedals. This action closes an internal valve against spring pressure inside the parking brake valve, retaining hydraulic pressure in both brake circuits and maintaining brake application. The handle is then locked in the UP position by rotating the handle 30° clockwise. When the parking brake is set, the pilots reported that it is usual for there to be a firmness felt in the toe brakes on the pedals.

Figure 7: Parking brake valve internal

Source: Supplied, annotated by the ATSB

The parking brake is released by turning the handle 30° anticlockwise and pushing the handle down into the panel. This mechanically opens the return line, relieving pressure from the brake circuit, allowing the brakes to release.

The brake system requires an unrestricted hydraulic fluid flow through a single return line within the parking brake valve for normal operation (Figure 7). Any restriction of this return line will increase the time required for brake pressure to be relieved, resulting in a partially applied or dragging of the brakes. A dragging brake will generate heat within the wheel and brake assemblies. This will cause all brake components, including the hydraulic fluid, to expand, further increasing the pressure in the brake circuits. In the event of a restriction, this increase in pressure will transfer directly to an increase in brake application.

Parking brake annunciator

An amber PARK BRK ON annunciator light on the pilot’s Central Warning Panel, located in the centre of the dashboard, illuminates when parking brake hydraulic pressure exceeds 1700 psi (Figure 6). The light goes off when the parking brake handle is pushed down and/or the pressure reduces below 900 psi. The pilots recalled that there were no warnings or cautions on the Central Warning Panel prior to take-off.

Anti-skid system

The Saab 340B is fitted with an anti-skid brake system that maximises braking efficiency by monitoring wheel speed signals across all 4 main wheels. The system modulates brake pressure in the brake hydraulic circuits to prevent a wheel locking. The anti-skid valves are located within the brake circuits, upstream of the parking brake valve, and have no influence on parking brake application.

Fusible plugs

The main landing gear wheels are fitted with 3 fusible plugs each. Should a critical temperature be reached in the wheel assembly, the core of the fusible plug will melt and provide a relief mechanism allowing the tyre to deflate.

Flight data

The flight data recorder was downloaded by the operator and data from the occurrence event and the 2 previous days of flying was provided to the ATSB. ATSB examination of the recorded flight data did not identify any anomalies in relation to engine operation which could have contributed to a loss of acceleration during the event. There were no brake system parameters recorded on the flight data recorder.

Manufacturers response

The manufacturer, Saab Aircraft Co, were contacted for further information about brake system design and operation. Saab stated that due to the mechanical nature of the brake system, with cables between the pedals and the brake valves, and considering that the brake system was inspected with no faults after the occurrence, they could not identify any other system reason that could contribute to brake application other than the parking brake. They further advised that if the parking brake is released properly and the parking brake valve is serviceable, there is no possibility of both brake systems remaining on.

Saab were also asked if they were aware of any similar examples of occurrences with the Saab 340 aircraft, Saab responded that, after a search of their database, they did not find any comparable occurrences.

Post occurrence rectifications

After the occurrence, the following rectifications were carried out prior to the aircraft returning to service:

• all 4 brake assemblies were replaced
• all 4 main landing gear wheel assemblies were replaced
• all 4 main landing gear wheel axles were visually inspected with no defects identified
• the input cables to the brake control valves were visually inspected with no binding or defects evident
• a parking brake control system test was carried out with no defects identified
• a high-speed taxi and brake test was carried out with no faults.

The brake and wheel assemblies were transported to the REX engineering workshops for further examination. The examinations found:

• all 4 brake assemblies were within wear limits and the brake pistons were serviceable. All 4 brake assemblies showed signs of overheating and were removed from service
• all 4 main landing gear wheel assemblies displayed signs of overheating evident with all fusible plugs blown. The wheel assemblies were removed from service for disposal.

On 4 November 2022, a Saab Aircraft Co 340B operated by Pel-Air Aviation Pty Limited, taxied for runway 32 at Flinders Island Airport. During the take-off roll, the aircraft veered to the left and did not accelerate as expected. The crew rejected the take-off and subsequent inspection identified that one tyre was flat spotted and all the main landing gear tyres were deflated.

Subsequent post occurrence rectification and system testing was carried out. No defects or unusual wear was identified on the replaced components other than signs of overheating. The brake system and parking brake system, including handle operation, was tested with no faults identified. The aircraft was released for service with no further brake related faults reported.

Significant tyre marks, from all 4 main landing gear wheels, were observed on the runway after the occurrence. These tyre marks commenced early in the take-off roll and continued to the disabled aircraft. This evidence, as well as a review of the engine parameters from the flight data recorder and reports from the flight crew, identified that the occurrence was brake‑related and not an issue with aircraft propulsion. The brake system, consisting of 2 separate hydraulic circuits, an inboard and an outboard circuit, share a common return line. For all 4 brakes to be applied and overheat the wheel assemblies, a fault would have had to occur in both systems simultaneously or in the single hydraulic return line.

The pilot conducted an immediate 180° left turn from the hardstand as the taxi commenced. This is evidence that the parking brake was released to the extent necessary for pressure to reduce below 900 psi and the PARK BRK ON annunciator to extinguish. The pilots observed that there were no cautions present prior to the take-off roll. The pilot also noted that the aircraft was able to be taxied with no abnormal handling or any extra engine power required however the pilot also reported taxiing slower than usual, to allow cabin crew to prepare the cabin, which may have masked any brake application.

If the parking brake handle is not completely seated by the pilot, the common return line from both brake hydraulic circuits will be partially obstructed within the parking brake valve. This will restrict hydraulic fluid from flowing out of the brake system, slowing down the rate at which pressure is relieved, resulting in a partial application or dragging of the brakes. During the taxi out, the partially applied brakes created heat due to friction resulting in further brake application to the restricted system as the temperature increased.

As the aircraft commenced the take-off roll, heat from the dragging brakes increased rapidly due to the acceleration of the wheel assemblies. At 46 knots the aircraft veered to the left, likely as a result of the left tyre locking and skidding. The pilot corrected towards the runway centreline and continued with the take-off. At approximately 80 knots the pilots observed that the aircraft’s acceleration rate had reduced and the take-off was rejected.

The pilot commented that, when they reduced power, and prior to manually applying the brakes, the aircraft slowed as though the brakes were applied. This was likely a combination of an application of the brakes and the tyres deflating as identified by the change in runway tyre marks. The tyre marks had changed from a solid tyre mark for the left outboard wheel to a set of parallel lines for each individual wheel. These parallel lines are a result of the weight of the aircraft acting only on the edges of the wheel rim through the tyre to the runway, indicative of a deflated tyre. This is evidence that that the core of the fusible plugs had melted due to a build-up of heat in the wheel assemblies, resulting in the tyres deflating during the latter stage of the take-off roll. The pilot commented that when they then applied the brakes, they felt pressure in the pedals and likened it to the parking brake being set.

Consideration of all the available evidence supports a conclusion that the push-pull parking brake handle was likely not completely seated in the console resulting in the parking brake valve partially restricting the hydraulic return line. This residual pressure allowed a partial application of the brakes, or an incomplete release of the brakes, at the commencement of the taxi, resulting in the brakes dragging. This resulted in the generation of heat in the brake system, a continual increase in brake application and the rejected take-off.

From the evidence available, the following findings are made with respect to the rejected take-off involving SAAB 340B, VH-ZRC, at Flinders Island Airport, Tasmania on 4 November 2022

Contributing factors

• The parking brake handle was likely not completely reset (seated in the panel) by the pilot, resulting in residual pressure remaining in the brake system.
• Residual pressure in the brake system resulted in a partial application of the brakes during taxi. This allowed heat to generate within the brake system resulting in a gradual increase in brake application.
• The significant and increasing drag associated with the partially applied brakes resulted in a flat spotted tyre and all of the main landing gear wheel fusible plugs activating during the take‑off roll.

Safety actions

Safety action by Pel-Air

Pel-Air advised that they have taken the following safety actions:

• disseminated a Notice to Aircrew to all company pilots with detailed information on the operation of the parking brake
• reviewed the Flight Operations Training and Checking ground school information specific to the function and operation of the parking brake
• included parking brake function and operation as a focus item in the upcoming flight crew check cycle
• provided ancillary training to the occurrence flight crew.

Pel-Air also advised an intention to disseminate an occurrence briefing to all flight crew that will include engineering information related to the design and function of the parking brake system and the importance of completely seating the parking brake handle in the panel.

Sources and submissions

Sources of information

The sources of information during the investigation included:

• the flight crew of VH-ZRC
• the Flinders Island Airport Operations Officer
• Pel-Air Aviation Pty Limited
• Saab Aircraft Company
• Airservices Australia

Submissions

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

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

• the flight crew of VH-ZRC
• the Flinders Island Airport Operations Officer
• Pel-Air Aviation Pty Limited
• Saab Aircraft Company

24 October 2022

On the evening of 24 October 2022 a Virgin Australia Airlines Boeing 737-800, registered VH‑VUT, operated a passenger transport[1] flight from Brisbane to Cairns, Queensland. The captain was acting as pilot flying from the right control seat while the first officer was undertaking command training and operating as pilot monitoring in the left control seat.[2]

At 1945 local time, the aircraft was cruising in darkness at flight level (FL)[3] 380 about 215 NM to the south of Cairns. At that time, air traffic control (ATC) provided the crew with clearance to conduct the Cairns HENDO 8Y standard arrival via the BARIA waypoint[4] transition (Figure 1).

Figure 1: Jeppesen HENDO 8Y standard arrival – VH-VUT

Note: Both Virgin Australia and Qantas Airways (see 26 October occurrence) were using procedure charts provided by Jeppesen.

Source: Virgin Australia, annotated by ATSB

The flight crew entered the HENDO 8Y arrival into the flight management computer (FMC) and selected the BARIA transition. The HENDO 8Y arrival progressed into the required navigation performance (RNP) Y instrument approach for runway 33 at Cairns Airport. While clearance for the approach had not been provided at that time, the crew anticipated the clearance and loaded the approach into the FMC. The HENDO waypoint was located within the 6,500 ft minimum sector altitude (MSA)[5] segment to the south of Cairns and from HENDO, the minimum altitude for commencing the RNP Y approach was 6,800 ft above mean sea level (AMSL).

The approach procedure had 2 different initial approach fixes (IAF) (Figure 2) with associated paths to a common intermediate fix (IF) at waypoint CS540. From the BASIL IAF, the approach proceeded via CS520, CS521 and CS523, and from the HENDO IAF via CS522 and CS523. In order to load either path into the FMC, the flight crew needed to select one of the 2 approach transitions, BASIL or HENDO (see the section titled Flight management computer).

Figure 2: Jeppesen Cairns RNP Y runway 33 approach chart

Source: Virgin Australia, annotated by ATSB

The flight crew did not recognise that an approach transition selection was required and consequently did not select one. As a transition had not been selected, the FMC presented a discontinuity in the entered flight path from the HENDO waypoint (see the section titled Flight management computer). The flight crew misidentified the approach IF, CS540, as the IAF and resolved the FMC discontinuity by connecting the HENDO arrival waypoint to CS540. This selection meant that the 6,800 ft descent altitude constraint associated with HENDO in the RNP approach programming was not loaded in the FMC.

At 1954, when the aircraft was 136 NM south of HENDO, ATC cleared the flight to track direct to the HENDO waypoint and 6 minutes later the crew commenced descending the aircraft. At 2010:51, when the aircraft was about 11 NM south‑east of HENDO, ATC provided the crew with clearance to conduct the RNP Y runway 33 approach.

As the aircraft approached HENDO, it descended through about 7,300 ft with the autopilot engaged and the HENDO minimum safe altitude of 6,800 ft selected in the autopilot mode control panel. The captain then selected the approach’s minimum descent altitude of 800 ft on the autopilot mode control panel, but sensed that this selection was incorrect and therefore re‑selected an altitude of 6,800 ft. The captain then reviewed the approach briefing, confirmed that the aircraft was tracking as intended, that the vertical navigation autopilot mode[6] was active and then re-selected 800 ft.

At 2011:38, about 7 NM prior to crossing HENDO, the aircraft descended below 6,800 ft (Figure 3) and 9 seconds later descended below the 6,500 ft MSA. Six seconds later, at 2011:53, ATC observed that the aircraft had descended below 6,800 ft and contacted the crew to confirm the aircraft’s altitude. The captain then reselected 6,800 ft and manually arrested the descent. ATC then issued a low altitude alert to the crew and advised them to climb immediately. Three seconds later, at 2012:07, the aircraft stopped descending at about 6,048 ft and then commenced a climb. At 2012:28, the aircraft climbed back above 6,800 ft. No ground proximity warning system alerts were generated during the incident.

A missed approach was then commenced. During preparations for the second approach, the crew recognised that an approach transition selection was required and correctly loaded the RNP Y runway 33 approach using the BASIL transition. The crew then conducted the approach and landed without further incident.

Figure 3: Flight path of VH-VUT

Source: Virgin Australia, Airservices Australia and Google Earth, annotated by ATSB

26 October 2022

On the morning of 26 October 2022 a Qantas Airways Boeing 737-800, registered VH-VZA, operated a passenger transport flight[7] from Brisbane to Cairns. The captain was acting as pilot flying, and the first officer was acting as pilot monitoring.

At 0739, in daylight, while the aircraft was in cruise at FL 380 about 225 NM to the south of Cairns, ATC provided the crew with clearance to conduct the Cairns HENDO 8Y arrival via the BARIA waypoint transition (Figure 4).

Figure 4: Jeppesen HENDO 8Y standard arrival – VH-VZA

Source: Virgin Australia, annotated by ATSB

The flight crew entered the HENDO 8Y arrival into the FMC and selected the BARIA transition. While clearance for the RNP Y runway 33 approach had not been provided at that time, the crew anticipated the clearance and loaded the approach. The crew believed that they had only been cleared for the BARIA arrival transition and had not yet received clearance for the HENDO approach transition, and therefore did not select that transition. As the selection had not been made, the FMC did not load the instrument approach segment from the IAF to the IF and presented a discontinuity between the waypoint HENDO and the IF waypoint CS540 (see the section titled Flight management computer).

The crew noted that the waypoints CS522 and CS523 were missing from the track presented on the navigation display and contacted ATC to request confirmation of the arrival clearance. ATC then provided a clearance for the HENDO 8Y arrival with a FISHY transition. The crew reviewed the arrival chart and assessed that they could not achieve the required descent profile to proceed via FISHY and requested clarification of the arrival transition. ATC then confirmed the arrival transition was via BARIA.

The flight crew noted that the track from HENDO to CS540 passed over the locations of CS522 and CS523. As there was no cloud along the flight path and terrain was visible, the crew were not reliant on FMC programming for terrain clearance. As such, the crew decided to join the discontinuity at HENDO to CS540 and proceed with the approach. The captain also selected the HENDO minimum safe altitude of 6,800 ft in the autopilot mode control panel.

At 0808:20, when the aircraft was 18 NM east of HENDO with the autopilot engaged and descending through about FL110, ATC provided the crew with clearance to conduct the RNP Y runway 33 approach.

At 0810:42, when the aircraft was about 7 NM east of HENDO, the crew noted that the approach vertical profile presented on the primary flight display showed the aircraft to be above the programmed descent path. During the crew’s investigation into the profile deviation, the captain selected 5,500 ft in the autopilot mode control panel. Without the 6,800 ft  HENDO descent altitude programmed into the FMC, the aircraft commenced descending below 6,800 ft, and 34 seconds later below the 6,500 ft MSA.

The aircraft passed HENDO at 0811:56 at an altitude of 6,129 ft (Figure 5). The crew recognised that the aircraft had descended early and selected the altitude hold (ALT HLD) autopilot function to stop further descent. Eleven seconds after the aircraft crossed HENDO, ATC contacted the crew to verify that the aircraft had passed HENDO at the correct altitude. ATC then confirmed with the crew that the flight was operating in visual conditions and provided clearance for a visual approach.

The aircraft landed at Cairns without further incident. After landing, the flight crew discussed the incident and recognised that an approach transition selection was required. The crew then reloaded the approach using the HENDO transition and observed that all waypoints and altitude constraints were correctly programmed.

Source: Qantas, Airservices Australia and Google Earth, annotated ATSB

Context

Crew details

VH-VUT

The captain operated the flight as a training captain from the right control seat. The captain held an air transport pilot licence (aeroplane) and class 1 aviation medical certificate and had over 8,000 hours of flying experience, of which over 3,100 were on the Boeing 737.

The first officer was undergoing command upgrade training and operating the flight from the left control seat. The first officer held an air transport pilot licence (aeroplane) and class 1 aviation medical certificate and had over 8,600 hours of flying experience, of which over 5,200 were on the Boeing 737.

VH-VZA

The captain held an air transport pilot licence (aeroplane) and class 1 aviation medical certificate. The captain had over 13,800 hours of flying experience, of which over 7,400 were on the Boeing 737.

The first officer held an air transport pilot licence (aeroplane) and class 1 aviation medical certificate. The first officer had over 8,700 hours of flying experience, of which over 1,000 were on the Boeing 737.

Fatigue

The ATSB found no indicators that any of the flight crewmembers on either flight were experiencing a level of fatigue known to affect performance.

Meteorology

24 October 2022

The approach was conducted at night and terrain was not visible to the flight crew.

At 2010, 1 minute before VH-VUT descended below the HENDO altitude constraint, the Bureau of Meteorology (BoM) automatic weather station at Cairns Airport recorded the wind as 7 kt from 333° magnetic. Two cloud layers were also present: scattered[8] at 1,710 ft and broken at 2,110 ft above mean sea level (AMSL).

26 October 2022

The approach was conducted during daytime with no cloud and excellent visibility.

At 0800, 10 minutes before VH-VZA descended below the HENDO altitude constraint, the BoM automatic weather station at Cairns Airport recorded the wind as 2 kt from 213° magnetic. No cloud was recorded.

Arrival and approach procedures

Arrival naming

The HENDO 8Y standard arrival procedure included 7 individual transitions which led to a common waypoint, HENDO. The procedure was named after HENDO as the first (and only) common waypoint. The HENDO waypoint was also 1 of 2 initial approach fixes (IAF) for the Cairns RNP Y runway 33 approach. The other IAF, BASIL, was used for a different arrival procedure or following a missed approach.

The HENDO 8Y arrival led to the HENDO IAF and the arrival charts included the wording ‘from HENDO track via RNP Y RWY 33 (AR)’.

Approach transition selection

The two different IAFs of the RNP Y runway 33 approach procedure had associated paths to a common intermediate fix (IF) (CS540): from BASIL through waypoints CS520, CS521 and CS523, or from HENDO through CS522 and CS523. As there were 2 available options, the flight crew needed to select the required approach transition.

Selecting the RNP Y approach procedure in the flight management computer (FMC) provided the final approach procedure path, from CS540 through the final approach fix CS541, toward the runway and, if required, the missed approach procedure. The loaded data also included any associated altitude and speed limitations. To load the approach procedure from the IAF to the IF, the flight crew were required to select an approach transition. Selecting the HENDO transition would have loaded the track from HENDO to CS540, via CS522 and CS523, as well as any associated altitude constraints and speed limitations.

Cairns RNP Y runway 33 procedure chart

Airservices Australia and Jeppesen (an approved data service provider) published charts for the Cairns RNP Y runway 33 procedure. The charts produced by both organisations were designed and published in accordance with International Civil Aviation Organisation (ICAO) guidance.[9] Both of the aircraft involved in these occurrences used arrival and approach charts provided by Jeppesen.

The Airservices Australia chart vertical profile presentation included the full approach including the waypoints CS521, CS522 and HENDO (Figure 6).

Figure 6: Airservices Cairns RNP Y runway 33 approach chart

Source: Airservices Australia, annotated by ATSB

The Jeppesen chart (Figure 7) vertical profile did not include the waypoints CS521, CS522, CS523 and HENDO. The chart's vertical profile commenced at waypoint CS540 and approach track information on the map was emphasised with a broader line from this waypoint. The information (including altitude constraint information) relating to waypoints CS521, CS522, CS523, HENDO and their associated segments was presented on the map over shaded topographical information and with an arrow to the associated item.

Figure 7: Jeppesen Cairns RNP Y runway 33 approach chart

Source: Virgin Australia, annotated by ATSB

To provide a standardised presentation of aeronautical data for Jeppesen charts worldwide, Jeppesen chart design specifications directed that the vertical profile commence at the IF when an approach has multiple transitions. Jeppesen noted that this was the most common worldwide depiction of profile information. As the Cairns RNP Y approach had multiple transitions leading to the CS540 IF, the vertical profile commenced at that waypoint.

Flight management computer

The arrival and approach transitions were both presented on the same FMC Arrivals page (Figure 8). In the case of the HENDO 8Y arrival, the number of available selection lines on the screen was limited to only display 4 of the 7 available transitions. The remaining 3 available arrival transitions were displayed on a second arrivals page. This second page was indicated by a ‘1 / 2’ (page 1 of 2) at the top right of the screen.

The 2 approach transitions were presented on the right side of the arrivals screen. The crews of both aircraft did not recognise that the right column were approach transition selections.

Figure 8: Flight management computer transitions

Source: Virgin Australia, annotated by ATSB

If an approach transition was not selected, the segment of the approach from the IAF to the IF, and the associated altitude constraints, would not be loaded in the FMC.

As the crews did not select an approach transition, a discontinuity was created at the HENDO waypoint associated with the HENDO 8Y arrival (Figure 9). Both crews resolved this discontinuity by connecting the waypoint HENDO from the arrival procedure to the waypoint CS540 in the approach procedure. As waypoint HENDO in the FMC arrival procedure did not have the 6,800 ft descent altitude constraint (the constraint was only associated with the HENDO approach waypoint), this altitude constraint was not loaded into the FMC. Similarly, the segment minimum safe altitudes associated with waypoints CS522 (6,000 ft) and CS523 (4,900 ft) were not loaded.

Figure 9: Flight management computer (left) and navigation display (right) showing the discontinuity

Source: Virgin Australia, annotated by ATSB

Approach briefings

The objective of an approach briefing is to ensure all flight crew understand and share a common mental model for the proposed plan of action. This briefing was normally performed by the pilot flying with the pilot monitoring checking the data entered into the FMC. Both operators provided requirements across training and operation manuals for crews to ensure effective cross checking of data entered into the FMC.

VH-VUT

The Virgin Operating Policies and Procedures Manual provided the following relevant guidance for approach briefings:

The captain of VH-VUT advised that, when conducting the approach briefing, they normally prioritised the vertical profile. The captain later reported that the absent waypoints in that profile, along with the thicker map line from CS540, may have contributed to their misidentification of CS540 as the IAF.

The captain did not announce the absent waypoints during the briefing. When confirming the data entered into the FMC, the first officer did not independently review the chart and therefore similarly did not identify the missing waypoints and altitude constraints.

During the briefing and check of the entered data, the pilot monitoring (first officer) became confused as to where in the sequence of the data being read the pilot flying (captain) had progressed to. The pilot monitoring sought clarification from the pilot flying, who advised that the brief had moved to the missed approach, a number of waypoints ahead of the pilot monitoring’s anticipated location. The crew did not further investigate the misunderstanding and continued the brief from the missed approach.

VH-VZA

The Qantas Flight Administration Manual provided the following relevant guidance for approach briefings in Boeing aircraft:

During the approach briefing the flight crew identified the 2 missing waypoints between HENDO and CS540. However, the captain did not note the altitude restrictions at CS522, CS523 and HENDO and did not announce them during the briefing. Furthermore, the first officer did not independently review the chart, removing an opportunity to identify the missing altitude constraints.

Airways clearances

Both crews were provided with the same approach clearance from air traffic control:

This clearance required the crews to adhere to all approach tracking and associated altitude constraints.

The clearance phraseology was consistent with Aeronautical Information Publication[10] guidance in not including reference to the HENDO approach transition. However, for VH-VUT, because a clearance had previously been provided direct to HENDO, the approach clearance should have been prefixed with ‘when established’. As the approach clearance was provided after the FMC data error had already been made and was unlikely to highlight any error, the incorrect phraseology did not contribute to the occurrence.

The air traffic control provider, Airservices Australia, advised that both aircraft had a route clearance to Cairns Airport. This was included in the arrival instruction ‘from HENDO track via the RNP Y runway 33’. For the RNP Y runway 33 approach, the IAFs HENDO and BASIL are subject to the same concept as other RNP approaches with multiple IAFs (for example EA, EB or EC). Therefore, the IAF did not need to be specified with the approach clearance.

Similar occurrences

The HENDO 8Y arrival and RNP Y runway 33 approach were introduced in August 2017, 5 years prior to the occurrences. At the time of the release of this report, the only recorded occurrences involving a descent below minimum altitude in the vicinity of HENDO are the 2 occurrences in this report.

A previous ATSB investigation involving a similar occurrence is summarised below:

ATSB investigation AO-2017-026

On the morning of 22 February 2017, a Singapore Airlines Boeing 777-212, registered 9V-SRP, operated scheduled flight SQ291 from Singapore to Canberra, Australian Capital Territory. Prior to descent, the flight crew prepared to conduct the POLLI FOUR PAPA arrival and associated RNAV-Z approach. As the aircraft descended, ATC instructed the flight crew to conduct the POLLI FOUR BRAVO arrival. As the 2 arrivals were very similar, the flight crew elected to reprogram the POLLI FOUR BRAVO arrival into the FMC while keeping the RNAV-Z approach, creating a discontinuity in the programmed FMC flight path. The captain resolved this discontinuity by manually connecting the arrival waypoint MENZI to the approach at waypoint SCBSI. In doing so, the approach waypoint SCBSG was erased from the programmed FMC approach. The captain manually re-entered SCBSG into the FMC without detecting that an associated 7,500 ft altitude constraint was now missing.

As the aircraft continued the approach it twice descended below minimum safe altitudes before being provided with clearance to complete a visual approach.

Safety analysis

Introduction

On the evening of 24 October 2022, a Boeing 737-800 operated by Virgin Australia Airlines operated a night air transport flight from Brisbane to Cairns, Queensland. On the morning of 26 October 2022, a Boeing 737-800 operated by Qantas Airways operated the same route in daylight. During both flights, the crews did not recognise that an approach transition had to be selected when entering approach data into the flight management computer (FMC) and no selection was made.

This analysis focuses on the reasons for the crews not making the approach transition selection or identifying the data entry error prior to it resulting in both aircraft descending below the minimum safe altitude.

Transition selection

The Cairns HENDO 8Y arrival procedure had 7 arrival transitions and was named after the last waypoint in the procedure (the first common waypoint for the transitions), which was relatively uncommon. The HENDO waypoint was also one of 2 initial approach fixes (IAF) and was therefore also the name of a transition for the approach. The 2 approach transition options were presented on the right-hand side of the same FMC page as the arrival transitions, with 4 arrival transitions on the left-hand side of the same page and the remaining 3 on the next page. The crews of both aircraft did not recognise that the transitions on the right related to the approach and consequently, the requirement to select an approach transition was not immediately apparent to them.

For the crew of VH-VUT, this perception was compounded by the misidentification of the waypoint CS540 as the IAF (see the section below titled Approach chart). Separately, the crew of VH-VZA were influenced by an expectation that the wording of the approach clearance would include the nomination of a transition. However, as an airways clearance to Cairns via the HENDO 8Y arrival and RNP Y approach had been provided, no separate nomination of the approach transition was required or provided.

Ultimately, these factors resulted in both flight crews not recognising that an approach transition selection was required and consequently, none was selected. Not selecting the approach transition resulted in a discontinuity between the waypoints HENDO and CS540 in the programmed flight path.

Discontinuity resolution

Having misidentified CS540 as the IAF, the captain of VH-VUT resolved the discontinuity by manually linking HENDO from the arrival to CS540 in the approach. This presented an approach track that closely aligned with the crew’s expectations, but with the omission of the altitude constraints associated with the approach waypoints HENDO, CS522 and CS523.

On board VH-VZA, after entering the approach without selecting a transition, the crew identified that waypoints were missing from the approach. As the programmed flight path continued along the same track, the crew elected to continue the approach without the entering the waypoints into the FMC and linked the waypoint HENDO from the arrival to CS540 in the approach. This decision was possibly influenced by the fact that the aircraft was operating in visual conditions and the crew were not reliant on the FMC programming for terrain clearance. However, the crew did not identify that altitude constraints associated with the unprogrammed waypoints were omitted from the programmed flight path.

In each case, this led to the approaches continuing with the altitude constraints removed and when an altitude below the minimum safe altitude was selected, the aircraft commenced automatically descending to that altitude. This resulted in both aircraft descending below the approach altitude constraints and then the minimum sector altitude. This was contrary to air traffic control clearances and, for VH-VUT, also reduced obstacle clearance assurance as the flight was conducted in darkness.

Approach chart

The HENDO 8Y arrival and Cairns RNP Y runway 33 approach were a complex procedure pairing with similarly complex charts.

In addition, the Jeppesen approach chart used by both crews was designed and published in accordance with ICAO guidance, but did not include the waypoints HENDO, CS522 and CS523 on the vertical profile depiction. This information was included on a comparable chart produced by Airservices Australia. Had those waypoints been included on the vertical profile of the Jeppesen chart, the likelihood of the descent restrictions being identified would have been increased.

The missing waypoints on the vertical profile and thicker track line from CS540 on the approach chart likely contributed to the captain of VH-VUT misidentifying that waypoint as the IAF. These missing waypoints were also the waypoints omitted from the FMC programming if an approach transition was not selected. Therefore, their omission was not an immediate indicator of a data entry error.

Furthermore, the Jeppesen chart presented the information (including the altitude constraints) associated with the missing waypoints and segments over topographical information on the map and separated from the relevant waypoints and segments. This reduced the readability of the information and may have contributed to the crews not associating the relevant information with their respective waypoints and segments thereby further reducing the crews’ ability to identify the associated altitude constraints.

Approach Briefing

Both operators required the approach briefing to ensure that the data entered into the flight management computer included all relevant waypoints and altitude constraints from the procedure chart.

In each case, the pilot flying read from the procedure chart while the pilot monitoring reviewed the data in the FMC. This method was not fully independent and relied on the pilot flying to identify all applicable details. The missed altitude constraints (and waypoints in the case of VH-VUT) were not read out by the pilot flying and therefore, their omission was not identified by the pilot monitoring’s check. The pilot monitoring’s assessments of the correct data input was also supported by the navigation display map view tracks closely aligning with expectations.

During the approach briefing conducted by the crew of VH-VUT an opportunity was presented to pause the brief and identify the data entry error. This occurred when the pilot monitoring became confused as to the sequence of the data being read by the pilot flying. The pilot monitoring sought clarification from the pilot flying. This likely occurred as the data entered was not complete and should have acted as a trigger for reassessment of that data.

In the case of VH-VZA, the crew did identify the missing waypoints but did not fully consider the altitude constraint implication associated with these waypoints. A comprehensive brief would probably have identified these missing constraints. While the terrain was visible to the crew and they were not reliant on FMC programming for terrain protection, the airways clearance did require adherence to the limiting altitudes.

In summary, the approach briefs conducted by the crews did not ensure that the charts, and the programmed approach flight path, were fully and independently assessed. Therefore, the data entry errors leading to the removal of the altitude protections were not detected.

Air traffic control intervention

On each occasion, air traffic control quickly identified the aircraft descending below the 6,800 ft altitude constraint and immediately contacted the crews. As the VH-VUT incident was at night and not in visual conditions, the controller issued a low altitude alert to the crew and advised them to climb immediately.

The conditions were clear and during daylight for the crew of VH-VZA and therefore air traffic control was able to provide a clearance for a visual approach.

Air traffic control acts to coordinate the flow of aircraft arriving at an airport, but also plays an important role in identifying risks to aircraft. On these occasions, air traffic control intervened quickly and appropriately to resolve the risks of each descent below the minimum safe altitude.

Findings

From the evidence available, the following findings are made with respect to the flight below minimum altitude occurrences, 40 km south of Cairns Airport, Queensland on 24 and 26 October 2022.

Contributing factors

• Both flight crews did not recognise that an approach transition selection was required in the aircraft’s flight management computer. Not selecting the approach transition resulted in a programmed flight path discontinuity between the waypoints HENDO and CS540.
• The flight crews of both aircraft resolved the discontinuity by manually linking the HENDO waypoint associated with the arrival programming to waypoint CS540. This selection removed the 6,800 ft descent altitude constraint associated with the HENDO waypoint in the approach programming. With the altitude constraint removed, the programmed flightpaths led to both aircraft descending below the minimum safe altitude.
• The vertical profile depiction on the Jeppesen RNP Y runway 33 approach chart did not include the waypoints HENDO, CS522 and CS523 and the map presented the information associated with those waypoints over dense topographical information. This likely limited the ability of both crews to identify the descent restrictions associated with those waypoints.
• Both operator’s instrument approach briefing procedure included a requirement to ensure all necessary waypoints and operational constraints were included in the procedures loaded into the flight management computer. However, the briefing conducted by the flight crews did not identify that data entry errors had removed some altitude protections.

Other findings

• On each occasion, air traffic control intervened quickly and appropriately to resolve the risks of each descent below the minimum safe altitude.

Safety action not associated with an identified safety issue

Proactive safety action by Virgin Australia Airlines

Two days after the incident, Virgin Australia published a safety update for all flight crew regarding the occurrence on 24 October 2022. This update provided contextual information on the occurrence and highlighted the missing waypoints in the vertical profile depiction on the Jeppesen Cairns RNP Y runway 33 chart. The update also emphasised the requirement for an approach transition selection.

Virgin Australia also supported the safety update with a flight crew operational notice to 737 flight crew for operations into Cairns. The notice highlights the complex nature of the HENDO 8Y arrival and Cairns RNP Y runway 33 procedure pairing and provides instruction for correct FMC data entry.

Proactive safety action by Qantas Airways

The day after the incident, Qantas Airways issued an internal notice to flight crew highlighting that many arrival and approach pairings require the selection of both an arrival transition and approach transition. This notice also described the effects of a non-selection of an approach transition with the information in the notice later incorporated into the Cairns Airport Route Manual Supplement. The details of the incident were also disseminated to all flight crew in a fleet newsletter and incorporated into Qantas’ evidence based training program.

Proactive safety action by Airservices Australia

To ensure that consistent and correct phraseology is used when providing approach clearances at Cairns, Airservices Australia has issued a standardisation directive to the air traffic control unit.
 

AIP                  Aviation information publication

AMSL              Above Mean Sea Level

ATC                 Air traffic control

CASA              Civil Aviation Safety Authority

CASR              Civil Aviation Safety Regulations

FMC                Flight Management Computer

IAF                   Initial Approach Fix

IF                     Intermediate Fix

MSA                 Minimum sector altitude

RNP                 Required navigation performance
 

Sources of information

The sources of information during the investigation included:

• Airservices Australia
• Virgin Australia Airlines
• Qantas Airways
• Jeppesen
• the flight crews of both aircraft
• Civil Aviation Safety Authority
• recorded aircraft data from VH-VUT and VH-VZA.

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
• The United States National Transportation Safety Board
• Virgin Australia Airlines
• Qantas Airways
• Jeppesen
• the flight crews of both flights.

Submissions were received from:

• Airservices Australia
• Qantas Airways
• the flight crew of VH-VZA.

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

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[1]     The flight was operated under Civil Aviation Safety Regulations Part 121 (Air transport operations - larger aeroplanes).

[1]     The flight was operated under Civil Aviation Safety Regulations Part 121 (Air transport operations - larger aeroplanes).

[2]     Pilot Flying (PF) and Pilot Monitoring (PM): procedurally assigned roles with specifically assigned duties at specific stages of a flight. The PF does most of the flying, except in defined circumstances; such as planning for descent, approach and landing. The PM carries out support duties and monitors the PF’s actions and the aircraft’s flight path.

[3]     The navigation radio is the aircraft instrument that receives the radio signals from the ILS ground stations. The navigation radio interprets the signal information and then provides data to the DPUs for presentation on the EADI and the standby ILS indicator.

[4]     Instrument meteorological conditions (IMC): weather conditions that require pilots to fly primarily by reference to instruments, and therefore under Instrument Flight Rules (IFR), rather than by outside visual reference. Typically, this means flying in cloud or limited visibility.

[5]     Each dot of glideslope deviation indication equals 20% of angular deviation.