Context

Horizontal stabiliser bungs

Use of horizontal stabiliser bungs

The procedure for the use of horizontal stabiliser bungs (bungs) was implemented by the operator in March 2017 at both Cairns and Townsville Airports. This followed an increase in the number of occurrences where birds had nested in the tail section of aircraft parked overnight during the warmer, humid months. The operator’s engineering department devised a solution with the design and fabrication of bungs to be installed in the elevator trim actuator coves on the upper surface of the horizontal stabilisers (Figure 1).

Figure 1: Horizontal stabiliser bungs

Source: Regional Express Pty Ltd annotated by the ATSB

The horizontal stabiliser bungs (Figure 2) were listed as site-specific equipment for use at both Townsville and Cairns. They consisted of a foam pad, which fitted into the actuator cove, attached to a board for both the right and left elevator. They were connected by a tether rope which had a conspicuity flag marked ‘remove before flight’.

Figure 2: Horizontal stabiliser bungs

Source: Regional Express Pty Ltd

Training

The operator advised that all staff were trained and assessed in the use of the bungs prior to the bungs’ introduction. A training package was developed for contracting agents that included a presentation to familiarise ground staff with the new bungs. The training was delivered by a member of the operator’s airport services ground training department and involved the ground handler operating under supervision to obtain on-the-job training. Once assessed as competent, the ground handler would be approved for unsupervised operations. No additional training was provided by the ground handling agent because the procedure was governed by the airline.

The operator advised that the use of bungs was also covered as part of the induction training for pilots new to type.

Ground handling procedures

The contractor provided ground handling services for the operator at both ports where the bungs were used. They advised that the operator’s procedures for the use of bungs were defined in the operator’s airport services manual (ASM). There was no checklist for these tasks, but ground staff followed the operator’s ASM procedures.

A presentation used by the operator’s ground training department for these pre‑ and post‑flight duties, advised ground agents that:

This procedure typically saw the bungs installed after the flight crew had left the aircraft and removed prior to the flight crew arriving at the aircraft the following morning.

Storage of bungs

The ground handling pre-flight duties section in the ASM provided the following guidance:

During interview, the flight crew advised that this procedure did not apply to site‑specific equipment such as the horizontal stabiliser bungs. It referred to the general instructions for the storage of items such as the pitot tube covers and engine inlet bungs, where specific storage locations were defined on the aircraft. Ground handling staff confirmed that the operator’s ASM procedures did not specify where the bungs were to be stored and that the agent stored these bungs in a container next to the parking bay. These containers were used to store several sets of bungs and were not allocated to a specific parking bay or airframe. Once the bungs were placed in the container, there was no way of knowing which bungs had been removed from what aircraft.

The training presentation, used to familiarise ground handling staff with the bungs, included the use of engine exhaust bungs (exhaust bungs) at Cairns. These exhaust bungs were also retained by the ground handling agent, however, the presentation included guidance for where these bungs should be stored (Figure 3). Similar to the horizontal stabiliser bird bungs, multiple sets were stored together in the designated storage bins.

Figure 3: Exhaust bung storage bins

Source: Regional Express Pty Ltd annotated by the ATSB

Flight crew awareness

The first officer (FO) completed their induction and commenced line training in March 2022. While familiar with the bungs at the time of the occurrence, the FO did not recall being briefed on their use during their induction. They also advised that their first exposure to the bungs was after seeing them installed on other aircraft at Cairns. Additionally, they reported having never handled the bungs before the day of the occurrence.

The airline’s primary means of communicating the use of bungs to flight crew was through the route manual where the following delegation of responsibilities appeared:

Additionally, the bungs appeared in the FCOM where they were listed as a check item in the external inspection of the tail area.

Both flight crew were aware of the information relating to the bung in the route manual but also believed that a company notice to air crew (NOTAC) would be provided to crew when the bungs were in use during summer months.[4] In the absence of a NOTAC on this flight, the crew believed that the bungs were not being used, although they had noticed the sporadic presence of the bungs fitted to aircraft at Cairns prior to the occurrence. The operator confirmed that while the route manual referred to the increased risk of bird nesting during the summer months, the manual also stated that the ground agent would install the bungs upon termination of service indicating that they would be used throughout the year. During interview, the ground handler confirmed that the bungs were installed every night.

The information available to the flight crew did not require them to handle the bungs but stressed that they must ensure the bung was removed before the pre-flight inspection. However, there were no instructions provided on how the crew should ensure the bungs had been removed. The flight crew advised the bungs could not be seen from the ground as the horizontal stabiliser fairings (Figure 1) obscured the bung when they conducted an external inspection, unless they moved further from the tail than would otherwise be required when completing the external inspection. In addition, the bungs could not be removed from the ground and required the crew to notify a ground handler if they were found installed during the external inspection.

Pre-flight preparations

Ground crew

The tasks required to dispatch a Rex Saab 340 aircraft were defined in the ground handling section of the company’s ASM. Access to operational information was provided to all ground handling agents to ensure the latest information was utilised with control of the documents remaining with the operator’s training department.

ZLJ terminated at Cairns the evening prior to the occurrence. The ground handling agent confirmed that while the post-flight duties were completed in accordance with the ASM, the operator’s procedures did not require a record of the installation of the bungs, and no additional details were available. As such, it could not be determined if the bung was installed correctly, or by whom, on the evening of 15 November 2022.

Video footage of ZLJ parked on the bay on the day of the occurrence, revealed that ground handling staff passed the rear of the aircraft multiple times while completing the pre-flight duties. During interview, the ground handler in charge advised that neither the bungs nor the tether rope were visible at any time. Further, they advised that they were easily detected when installed correctly and could not be missed with the conspicuity tag normally hanging below the tail and next to the rear cargo door (Figure 1).

Flight crew

Flight crew pre-flight procedures are documented in the company FCOM. The horizontal stabiliser bungs were identified in the external inspection, which formed part of the daily inspection. As this was the first flight of the day for ZLJ, the daily inspection of the tail area included visual checks of the following:

• static dischargers
• tail lights
• ELT antenna
• confirmation that the horizontal stabiliser bung had been removed.

Both crew members conducted external checks of the aircraft. The captain initially walked around the aircraft and noted that the bungs and associated tether rope were not visible. The FO then conducted the required external inspection in accordance with the FCOM and advised that they did not see the bungs, despite passing the tail area of the aircraft on several occasions.

Additional checks that may have identified the bungs

The Saab 340 is fitted with a gust lock system. When the handle in the cockpit is engaged, it mechanically locks the elevator, ailerons, and rudder to prevent damage in windy conditions. The gust lock is released while a stall test is conducted. The stall check is completed by the captain prior to the aircraft’s first flight of the day. During this check, the captain would release the gust lock, apply back pressure to the control column and test the stall recognition and recovery protection systems. This is achieved by applying and maintaining aft control column pressure then holding the test button to check that the stickshaker, aural alert and stick pusher activate. Once the test is complete, the gust lock is re-engaged.

The captain was unable to recall if this was the first flight of the day for the aircraft and could not confirm if this check was completed.

An additional flight control check was part of the line-up checklist and would normally have been completed prior to runway entry. It involved a co-ordinated response from the crew to release the gust lock and then check the flight controls. The captain would check the rudder and the FO would manipulate the control column to ensure full and free movement of the aileron and elevator controls. The crew confirmed that the tower controller notified them of the hanging bung before this check had been completed.

During analysis of the airport CCTV footage (Figure 4), the bung was not visible while the aircraft was being prepared, nor was it visible as the aircraft taxied away from the bay. However, the aircraft was not clearly visible in the footage. Later, when the bung was observed hanging from the aircraft, the left bung was still inserted into the trim actuator cove and the tether rope and right bung was hanging from the left horizontal stabiliser.

Figure 4: Airport CCTV footage

Source: Cairns Airport Pty Ltd

Design and considerations

The operator’s engineering department designed and had the bungs manufactured. They determined that because the design did not require alteration of the airframe, a CASA approved‑ engineering order was not required.

The ATSB contacted the aircraft manufacturer to ascertain if the elevator trim actuator cove had been identified as a known area for similar nesting occurrences. Saab advised that they had only received one other report of bird nesting, and a handful of reports involving spider or insect nesting, from Australian operators. Additionally, Saab did not manufacture protection for this particular area of the aircraft, and they had not been involved in the design and manufacture of such a device. Significantly, the manufacturer provided a list of considerations that they felt would be appropriate for such a device. These included:

• checklist and visual indicators to aid in identification
• consequences if the cover was forgotten with regards to jamming or fouling of flight controls.

The operator confirmed that while a risk assessment had not been completed specifically for the bird bungs themselves, the decision to implement the bird bung procedure was to address the bird nesting safety concern and reduce the potential risk to passengers, crew, and the aircraft itself. There were no reports, prior to this occurrence, of aircraft dispatched with bungs installed in the trim actuator coves. However, it was reported that bungs had previously fallen out of the trim actuator cove in wind and were later found in nearby parking bays.
 

Safety analysis

Installation of the horizontal stabiliser bung

On the morning of the occurrence, there were significant distractions for the ground handling agent. Despite this, there were no significant time pressures during the early part of the day when the aircraft preparations began, and the ground handler removed the pitot and other aircraft covers. During this time, and later in the aircraft preparation, they were working around the rear of the aircraft on a number of occasions and the horizontal stabiliser bungs (bungs) were not detected.

In addition, while the flight crew were not expecting that the bungs would be installed, they both conducted external inspections of the aircraft, with the first officer (FO) stating they paid particular attention to the rear of the aircraft. The FO also removed the tail stand from under the tail of the aircraft where the bung conspicuity flag would have been hanging prior to entering the aircraft after the external inspection was completed. Neither pilot detected the bungs.

The ATSB analysis of the CCTV footage also did not detect the bungs while the aircraft was parked at the bay, nor as the aircraft taxied to the runway. Together, this would indicate that the bung was not installed correctly or possibly the tether rope with the ‘remove before flight’ conspicuity flag was not hanging from the horizontal stabiliser, as designed.

Procedures to ensure the removal of the bungs

The training package provided to the ground handling agent indicated that the horizontal stabiliser bird bungs were to be retained by the agent, but did not specify how or where the bungs were to be stored. As the containers utilised by the agent stored multiple sets of bungs together, it could not be determined what equipment had been removed from what aircraft. This prevented any positive assurance check by ground handlers or flight crew that the bungs had been removed. This was also the case for the engine exhaust bungs.

Existing airline checklist procedures ensured that flight crew account for other covers and bungs that had been removed from the aircraft during pre-flight inspections. However, there was no pre‑flight procedure on how to check the aircraft for the installation of the horizontal stabiliser bird bungs. In the absence of a prescribed method of assurance, the flight crew walkaround inspection procedures relied on visual confirmation that the bungs had been removed by ensuring that the conspicuity flag was not visible. In this instance, when the conspicuity flag was not detected by both ground crew and flight crew, both parties would most likely have continued preparations with the belief that the bungs were not installed.

This occurrence revealed the potential for the horizontal stabiliser bungs to go undetected if incorrectly installed or not displaying as designed and identified a gap in the assurance procedures for the operator.

Risk assessment

While a risk assessment of the bird nesting hazard led to the implementation of the procedure to install the horizontal stabiliser bungs, the operator did not conduct a separate risk analysis of the potential hazard a control surface bung could induce. Although the design incorporated features to aid in the recognition of the bungs when they were installed correctly, the evidence indicated that the design allowed for an incorrectly installed bung or one not displaying as designed to go undetected.

Existing procedural checks designed to detect fouled or jammed controls did not identify the incorrectly installed bung and there was no documented consideration given to assuring that a bung would be ejected prior to take-off, after which time it could have had the potential to adversely affect the safety of a flight.
 

Findings

From the evidence available, the following findings are made with respect to the aircraft preparation event involving Saab 340B, registration VH-ZLJ, at Cairns Airport, Queensland on 16 November 2022.

Contributing factors

No procedure for storage and accountability

Safety issue number: AO-2022-058-SI-01

Safety issue description: There were no formal procedures for the storage and accountability of horizontal stabiliser bungs after they were removed from the aircraft.

Safety recommendation description: The Australian Transport Safety Bureau recommends that Regional Express Pty Ltd continues reviewing the use of horizontal stabiliser bungs and takes action to address the limitations associated with the current procedures around the storage and accountability of equipment removed from an aircraft.

Horizontal stabiliser bung design considerations

Safety issue number: AO-2022-058-SI-02

Safety issue description: The design of the horizontal stabiliser bungs did not consider aspects that would ensure the identification of an installed bung, or the safe operation of the aircraft if the bungs were not removed prior to flight.

Safety recommendation description: The Australian Transport Safety Bureau recommends that Regional Express Pty Ltd further reviews the horizontal stabiliser bungs design and pre-flight procedures to ensure that installed bungs are readily identifiable and will not adversely affect the continued safe operation of the aircraft if not removed prior to flight.
 

ASM                 Airport Services Manual

CASA               Civil Aviation Safety Authority

CCTV               Closed-circuit television

FCOM              Flight crew operations manual

FO                   First officer

NOTAC            Notice to air crew

Sources and submissions

Sources of information

The sources of information during the investigation included:

• the flight crew of VH-ZLJ
• Regional Express Pty Ltd
• Aus Flight Handling
• Cairns Airport Pty Ltd
• Saab Aircraft Co.

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-ZLJ
• Regional Express Pty Ltd
• Aus Flight Handling
• Saab Aircraft Co
• Swedish Accident Investigation Authority
• Civil Aviation Safety Authority.

A submission was received from:

• Regional Express Pty Ltd

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

The occurrence

On 14 November 2022, a Robinson Helicopter Company R22 Beta, registered VH-LOS, was being operated in the Arafura Swamp, about 30 km south of Ramingining Aerodrome, Northern Territory (Figure 1). The helicopter was being used as part of an animal mustering operation, which also included multiple land vehicles.

Figure 1: Map of the Northern Territory showing the location of the accident site and nearby locations

Source: Google Earth, locations labelled by ATSB

At about 1800 local time, the mustering operation concluded for the day. The pilot of VH-LOS instructed a member of the mustering group to drive a grader vehicle to the southern edge of the swamp. The pilot planned to collect the grader driver and fly them back to the mustering camp, located about 20 km to the west.

Other members of the mustering operation departed the swamp in land vehicles, heading towards the camp. A witness recalled that VH-LOS was on the ground when the group departed, and they expected the pilot would depart soon after they left.

Flight tracking information showed VH-LOS took off from the swamp at 1803, flew around the swamp before tracking to the south, landing at the edge of the swamp at 1818. The helicopter was then started at 1837, and tracked to the mustering camp, landing and shutting down at 1854. The track of these flights is shown in Figure 2. The flight tracking information showed the helicopter was started again at 1921, before the flight tracking record ended about 1 minute later while the helicopter was still at the camp. The flight tracking device deactivated at 1925 after the helicopter had remained idle at the camp location and the device had lost external power (see Recorded information).

Figure 2: Map of Arafura Swamp and key locations, and track of VH-LOS

The yellow track shows the flight departing from Arafura Swamp at 1803 and shutting down south of the swamp at 1818. The red track shows the flight from the edge of the swamp to the mustering camp departing at 1837 and landing at 1854.

Source: Google Earth, with aircraft tracking plots overlayed by ATSB based on records obtained from recorder onboard VH-LOS

The grader driver travelled from the swamp towards the planned meeting point, which took about 30 minutes. They waited for about 10 minutes before deciding to return to camp on the grader when the helicopter did not arrive. The grader did not have a radio capable of communicating with the helicopter.

The other members of the mustering operation arrived back at the camp and noticed that neither the helicopter pilot nor the grader driver were there. One witness recalled it took about an hour to return to camp, and that the group arrived when it was close to dark, but not ‘pitch black’. Another group member recalled that they arrived after dark, at about 1945 to 2000.

The grader driver arrived at the camp at about 2100. Members of the mustering operation became increasingly concerned about the wellbeing of the helicopter pilot and commenced a search using land vehicles from about 2100 until 0100 on 15 November.

Early on 15 November, members of the mustering operation phoned an acquaintance who had access to the aircraft flight tracking information. The internet-based display showed VH-LOS at the mustering camp, having not moved since the previous evening.

The mustering group members then contacted some acquaintances who attended the area in helicopters and commenced an aerial search from about 1100. The helicopter wreckage was located at about 1300, about 6 km from the mustering camp. The pilot was deceased, and was found outside and resting against the helicopter. The helicopter was destroyed.
 

Pilot information

Licence and experience

The pilot held a Commercial Pilot Licence (Helicopter) and a valid Class 1 aviation medical certificate. The pilot also held a single engine helicopter rating, and a low level rating with aerial mustering (helicopter) and sling endorsements. The pilot did not hold an instrument rating or a night visual flight rules (VFR) rating.

The pilot’s logbook recorded over 6,200 hours total aviation experience, however no records had been made of flights conducted after March 2022.

Events prior to the accident

The pilot flew VH-LOS to Ramingining on 10 November 2022 and operated around the Arafura Swamp in the days prior to the accident. Aircraft tracking records showed that the helicopter was operated until 1859 on 11 November and until 1931 on 12 November. It is likely that these flights were conducted near or after the end of civil twilight (see Celestial illumination information).

Post-mortem examination and medical information

A post-mortem examination of the pilot was conducted by a qualified pathologist, on behalf of the Northern Territory Coroner. The pathologist’s report indicated that their examination was impeded due to the elapsed time between the accident and the recovery of the pilot’s body to a suitable mortuary facility. Only limited toxicology analysis could be performed, and although a high concentration of alcohol was detected the analysis could not determine if some or all of the measured alcohol (0.18%) was the result of post-mortem changes.

The pathologist’s report identified that the pilot sustained multiple injuries, including a fracture to the left femur, however the injuries were likely survivable. The report found that death was most likely the result of environmental exposure following the collision, with the left femur fracture contributing to reduced mobility.

The pathologist also observed no obvious evidence of injury consistent with being caused by a harness or seatbelt.

Witnesses recalled that the pilot was fit and healthy prior to the accident, and there were no indications that the pilot was experiencing any unusual stress. No witnesses recalled the pilot consuming alcohol or other drugs in the days before the accident.

Aircraft information

VH-LOS was a Robinson Helicopter Company R22 Beta helicopter, serial number 1715, powered by a Textron Lycoming, O-320-B2C, 4-cylinder piston engine. It was manufactured in the United States in 1991, and first registered in Australia in January 1995, and was equipped and maintained to a day VFR standard. The R22 has 2 seats, with the pilot flying from the right seat, and each seat was fitted with a seat belt and inertia reel shoulder strap, similar to those used in motor vehicles. VH-LOS did not have doors fitted at the time of the accident.

Recorded information

VH-LOS was not fitted with a flight data recorder or cockpit voice recorder, nor was it required to be.

The operator of VH-LOS tracked the aircraft using a system configured for the TracPlus tracking service. The system consisted of a RockAir device located in the helicopter, which was capable of transmitting the aircraft location using satellite and cellular networks. Registered users could log into the TracPlus website to view the aircraft track and position.

At the accident site, the ATSB found the RockAir unit outside the helicopter. A data card recovered from inside the unit included records showing the recorded tracks of VH-LOS on the afternoon of 14 November, as well as log files for the RockAir system. The files showed the final recorded position of VH-LOS was at the mustering camp location at 1925.  

The manufacturer of the RockAir reviewed the log file from the day of the accident and noted the following:

• The pilot of VH-LOS did not manually deactivate the aircraft tracker.
• The RockAir was performing normally on the day of the accident.
• The device was in a mode where it would deactivate if external power was removed, unless it detected the aircraft was moving above a speed threshold.
• The RockAir automatically deactivated at 1925 when the device lost power.
• There were 36 other instances on the day of the accident where the device lost power for 2-5 seconds, however the unit reverted to battery power because the aircraft was moving.
• It was not possible to determine the reason for the power supply interruptions, with mechanical movement of the power supply being a possibility.

Weather and environment

Weather

Members of the mustering operation recalled that conditions were fine while they were operating around the Arafura Swamp on the afternoon of 14 November, with no storms overhead. The grader driver recalled conditions as being cloudy, and that it was dark that night.

An analysis prepared by the Bureau of Meteorology (BOM) identified a thunderstorm to the east of the accident site at about 1730, which moved west during the evening. The analysis stated that outflow from the thunderstorm could have produced variable direction winds with gusts up to 35 kt. Near the thunderstorm, heavy rainfall with reduced visibility and broken low cloud were possible.

BOM also supplied observations for the evening of 14 November and the morning and afternoon of 15 November, at Milingimbi (about 60 km north of the accident site) and Bulman (about 130 km south-west of the accident site). BOM advised that these observations should be used as an estimate only for conditions at the accident site. These observations showed it was a hot and humid night in north-east Arnhem land, with temperatures from 27 to 33°C and humidity of 35 to 90% recorded.

Conditions became hotter and less humid during the day on 15 November. At 1300, when the helicopter wreckage and pilot were found, Milingimbi and Bulman recorded 33°C and 55-60% humidity. Witnesses recalled that conditions that day were hot.

Celestial illumination information

Sunset at the location of the mustering camp on 14 November 2022 was 1835 and the end of civil twilight (last light)[1] was 1858. Nautical twilight[2] was 1924 and astronomical twilight[3] was 1951.

The moon was a waning gibbous, rising at 2337 on 14 November with about 71.3% of the visible disk illuminated. There was no environmental lighting in the vicinity of the accident site.

Accident site and wreckage information

The accident site was located 6 km east of the mustering camp, in a flat clearing scatted with small trees and anthills. There were no sources of terrestrial light. None of the trees had damage consistent with a helicopter rotor strike, and there was no evidence of a bird strike or indications of a post-impact fire.

The helicopter was found on its left side, with significant compression of the nose and underside of the forward left section of the fuselage (Figure 3). The compression damage indicated that the helicopter collided with terrain at about 45° nose-down, and 30° left side low. There was a short wreckage trail extending about 13 m, with all helicopter parts present at the accident site and no evidence of an in-flight break-up.

Figure 3: VH-LOS wreckage

Source: ATSB

Indentations on the terrain nearby indicated a main impact point about 6 m aft and 4 m right of where the helicopter was found. Anthills forward of the main impact point showed damage consistent with having been struck by the rotor blades, and both rotor blades presented with evidence of ground strikes. One main rotor blade was liberated as the result of a ground strike, and was found about 30 m to the right of the wreckage trail. The cockpit windscreen had shattered and remnants were scattered around the accident site along with the contents of the aircraft.

The tail cone and tail rotor assembly remained connected to the fuselage, however presented as deflected down and curled under the helicopter. Site examination showed that both of the bladder-type fuel tanks remained intact and contained fuel. Examination of the helicopter’s flight control system and drive train did not indicate any pre-existing defects that could have affected the control or function of the helicopter. Damage signatures to engine rotating components indicated that the engine was operating at the time of the collision with terrain.

The pilot was found in a reclined position on the north-western side of the aircraft (next to the right helicopter seat), with their head rested against the helicopter. There was a large water bottle on the ground nearby. The screw-cap lid had been removed and the drinking spout exposed, suggesting it was likely the pilot was capable of opening and drinking from the water bottle after the accident.

Helicopter restraints

Both helicopter seatbelts were found to be buckled. The lap belt was in its normal secured position at the base of the seat, while the shoulder belt (which connected from the top right to the lower left), was pulled behind the seat base.

The seatbelt assembly had three anchor points, with the two lower anchor points connected to the pilot’s seat frame. The pilot’s seatbelt was found to be secured to its anchor points. The pilot’s seat had been significantly disrupted, pulled in the direction of impact away from the helicopter structure. The separation of the seat structure was very likely a result of the forces generated by the pilot restrained by the seat belt and being propelled in the direction of impact.

Regulatory information and guidance

Visual flight rules

Flight under the VFR must be conducted in conditions that enable the pilot to determine the aircraft’s position by visual features in the external environment. VFR flights are only permitted at night if:

• the pilot in command is authorised to conduct a flight under the instrument flight rules or at night under the VFR, and
• the aircraft is appropriately equipped for flight at night.

The CASA VFR guide stated that ‘night is that period between the end of evening civil twilight and the beginning of morning civil twilight... last light (is) the end of civil twilight’. The guide further stated that cloud cover or poor visibility may cause daylight to end at a time earlier than the forecast time, and allowance should be made for these factors when planning a flight near last light.

Civil Aviation Order 20.18 described the requirements for helicopters operating under the instrument flight rules (IFR) or at night under the VFR. Among other requirements, for a helicopter operating at night where attitude cannot be maintained using visual external surface cues, the helicopter must also either equipped for IFR flight with an autopilot or automatic stabilisation system, or be operated by a qualified 2 pilot crew. VH-LOS was not equipped for night flight under the VFR.

A member of the mustering operation who had flown with the pilot did not recall the pilot using procedures or routines for determining a ‘last flight’ time to avoid flying in the dark. They recalled that the pilot had emphasised the importance of having a visible horizon while flying in near dark conditions, to provide a reference for the position of the terrain.

Additional guidance for night VFR flight in dark night conditions

Dark night conditions exist when there is little or no celestial illumination, in locations where no significant ground lighting is available.

The CASA advisory circular Night VFR rating provided guidance to pilots conducting operations under the night VFR (NVFR). This guidance highlighted that while suitably endorsed pilots may safely fly visually in night conditions where there is adequate celestial illumination or other sources of light, visual flight is significantly more hazardous in dark night conditions.

There may be times when there is bright moonlight or extensive ground lighting available, making a night operation only a little more difficult than flying in daylight. However, there may be dark night conditions (i.e. without moonlight or significant ground lighting) that can make it very difficult to discern the natural horizon and maintain control of the aircraft by reference to external visual references.

The absence of a visible horizon during dark night conditions is a particular hazard. As highlighted by Gibb and others (2010), seeing a horizon is ‘crucial for orientation of the pilot’s sense of pitch and bank of the aircraft’. The Night VFR rating advisory circular identified this risk, noting:

CASA strongly recommends that NVFR operations take place only in conditions that allow the pilot to discern a natural visual horizon or where the external environment has sufficient cues for the pilot to continually determine the pitch and roll attitude of the aircraft.

The ATSB’s Avoidable Accidents publication Visual flight at night accidents identified that of 26 accidents during night visual meteorological conditions (VMC), [4] almost all occurred on dark nights. Visual flight at night accidents highlighted that:

When flying over land or oceans without light sources, on dark nights with no visible moon, visual flight at night is essentially the same as instrument flight.

Requirements for emergency locator transmitters

An emergency locator transmitter (ELT) is designed to send a distress signal to a network of satellites in an emergency. The Civil Aviation Safety Regulations Part 91 (General Operating and Flight Rules) Manual of Standards (MOS) required aircraft to be fitted with an ELT. For flights such as that conducted by VH-LOS, aircraft may be equipped with an automatic ELT, which is fixed to the aircraft and designed to automatically activate in the event of a severe impact (g) forces.  Alternatively, the ELT can be a manually activated and removable survival ELT, also referred to as personal locator beacons (PLB). The MOS required that if an ELT is a PLB, the pilot in command must ensure it is carried either on their person, in or adjacent to a life raft, or adjacent to an emergency exit.

VH-LOS was equipped with an ACR ResQLink 400 PLB. To activate the ResQLink, the user needed to first lift the antenna and expose the on/off button, then press the on/off button for 2 seconds.

The ATSB observed that the PLB remained inside the helicopter post-accident, and was attached to the helicopter's centre console. There was no apparent damage to the unit, and the battery was in-date. The antenna was in the folded-down position with the on/off button covered. There was not evidence that the pilot had attempted to operate the PLB after the accident.       

Figure 4: ResQLink activation instructions (left) and condition in-situ at VH-LOS accident site (right). The image on the right shows the antenna and power button guard remained in the down position

Requirements for search and rescue notification

The Part 91 MOS required that for VFR flights conducted in a designated remote area, the pilot must submit a flight plan, nominate a SARTIME (search and rescue time) for arrival, or leave a flight note with a responsible person. The Airservices Australia publication En Route Supplement Australia showed designated remote areas within Australia. The Arafura Swamp, the accident site, and all other areas the helicopter was operating in in the days prior to the accident were within a designated remote area.

The Part 91 MOS described the requirements of the holder of a flight note, including that they must immediately contact the Joint Response Coordination Centre (JRCC) if the flight becomes overdue.

The pilot of VH-LOS did not leave a formal flight note, however, it was understood the pilot would meet the grader driver at a particular location. When the helicopter did not meet the grader driver or return to the camp on the evening of 14 November, it was understood by the members of the mustering operation that the pilot was overdue. However, they did not contact any authority that night. The first call to emergency services (a 000 call) was made after the helicopter wreckage had been found on the afternoon of 15 November.

One member of the mustering operation recalled that it was not uncommon for the pilot of VH-LOS to arrive later than expected, as the pilot sometimes conducted additional unplanned flights. They also recalled that there had been occasions that the pilot had landed in an out-location and not returned until the following day.

When the helicopter did not return as expected on 14 November, members of the mustering group considered the possibility that the pilot had landed and were hopeful of the pilot returning the following day. They also considered the possibility that the pilot encountered problems and landed, and would be waiting to be found by road vehicles. In this context, members of the mustering group reported that they did not become highly concerned about the pilot until the morning of 15 November.

Related occurrences

Since the 2013 publication of Visual flight at night accidents, the ATSB has investigated multiple fatal accidents involving light helicopter pilots operating on dark nights in areas that did not contain any local ground lighting. Examples include:

• AO-2014-144: The ATSB found that the pilot, who did not hold a night VFR rating or instrument rating, continued flying towards the destination after last light (end of civil twilight), then in dark night conditions without local ground lighting, inadvertently allowed the helicopter to descend into terrain.
• AO-2016-031: The ATSB found that the pilot, who was only qualified to operate in day-VFR conditions, departed on a night flight and continued towards the destination in deteriorating visibility until inadvertently allowing the helicopter to descend into water.
• AO-2021-006: The ATSB found that the pilot, who did not hold a night VFR rating or instrument rating, continued flying towards their destination after last light, through the period of civil twilight and into astronomical twilight. In dark night conditions without local ground lighting the pilot inadvertently allowed the helicopter to descend into terrain.

Safety analysis

Flight after last light

The helicopter collided with terrain sometime after 1925 on 14 November 2022. There was no indication of any mechanical problem contributing to the collision with terrain, the helicopter had sufficient fuel on board, and there was no evidence of collision with a bird or another objects. A post-mortem examination indicated the pilot probably survived the accident, and there was no evidence of medical factors that would have resulted in the pilot becoming suddenly incapacitated.

Although the timing of the accident could not be precisely determined, aircraft tracking records indicate that the accident flight took place after nautical twilight. The pilot did not have a rating to fly at night under the VFR. VH-LOS was not equipped for flight by reference to the aircraft instruments, and the pilot did not have a rating for flight under the instrument flight rules.

The accident occurred in an extremely remote location with no nearby terrestrial lighting. On the evening of the accident, the moon rose late and provided no illumination for the accident flight.  Depending on how long the aircraft flew prior to the collision with terrain, conditions would have become darker later in the evening, and cloudy conditions associated with a westerly-moving storm system may have further reduced visibility. Considering the last recorded position of the aircraft and the accident location, it is likely that the accident flight was in an easterly direction, meaning sunset was behind the direction of travel. As such, the ATSB concluded that the accident flight was conducted in dark night conditions due to the absence of both celestial and terrestrial lighting.

Spatial disorientation describes the phenomenon of a pilot becoming unable to correctly perceive the position, movement and orientation of their aircraft. When flying under the VFR, pilots rely on external visual cues to maintain spatial awareness, including the orientation of the aircraft (which way is up), and the proximity to terrain. In dark night conditions, when there is no celestial illumination and no nearby terrestrial lighting, there are no external visual cues available to pilots. In such circumstances, spatial disorientation is highly likely unless pilots have access to and utilise aircraft instrumentation. This risk was highlighted in Visual flight at night accidents:

In very dark environments, VMC  is essentially the same as IMC[5] in terms of available external visual information. The only real difference is that lights on the ground may be seen in VMC. In remote areas where there are no lights or ambient illumination, there is essentially no difference. Pilots cannot see the ground and have no external visual cues available to assist with their orientation.

The decision by the day VFR qualified pilot to operate a helicopter which was not equipped for night flight after last light was inherently unsafe and increased the risk of unintentional collision with terrain. The dark night conditions on the night of the accident meant that regardless of the pilot’s ability to fly using external visual cues at night, there were none. In these conditions, the pilot likely became spatially disoriented, and unintentionally allowed the helicopter to descend into the terrain.

The significant nose-down and left-side down attitude of the aircraft wreckage, and the short wreckage trail, were consistent with the pilot flying at slow speed and developing an unusual aircraft attitude in the moments prior to collision. The wreckage, being only 6 km from the last known position of the helicopter, indicates that the disorientation and collision occurred soon after the commencement of the flight in dark night conditions.

Survivability

The post-mortem examination identified that the pilot was probably not fatally injured by the collision with terrain. The damage to the helicopter seat indicated that the pilot was at least partially restrained by the seatbelt during the collision. However, considering to the absence of observed bruising associated with a seatbelt, it is possible that the pilot was either only partially restrained (by the lap belt only), or slipped out of the seatbelt in the collision. The direction of impact (lower left) and shoulder belt orientation (top right to lower left), are consistent with the latter explanation. After the collision, it is likely the pilot manoeuvred out of the buckled restraint, outside of the damaged helicopter which was laying on its side. With injuries reducing the pilot’s mobility, the pilot likely planned to wait for rescue.

The post-mortem report further identified it was likely that the pilot succumbed to environmental exposure. There were up to 17.5 hours from when the helicopter collided with terrain and when the pilot was found deceased the following day. Although the pilot likely had a water bottle available and was shaded by the helicopter on the morning of 15 November, conditions were hot and humid. Therefore, this analysis examined the safety systems that could have led to the earlier recovery of the pilot.

Personal locator beacon

The mandatory carriage of emergency locating equipment is a risk control used to facilitate the prompt identification of aircraft accidents, and the timely and accurate response by emergency services. VH-LOS was equipped with a manually-activated PLB, however the pilot did not activate this beacon following the accident. Had the pilot activated the PLB, it is almost certain that a search and rescue response would have located the aircraft, increasing the likelihood the pilot would have survived the accident.

To ensure the PLB is accessible after a collision, regulations require the PLB is carried on the person of the flight crew or adjacent to an emergency exit. The PLB carried in VH-LOS was secured to the centre console, which, in a small helicopter such as a Robinson R22, is nearby the aircraft exits and the pilot’s seated position.

When the helicopter collided with terrain, conditions were dark and the pilot may not have been able to locate the PLB. Once outside the helicopter, in poor visibility and with limited mobility (due to the significant leg injury), the location of the PLB inside the helicopter was effectively inaccessible to the pilot. This highlights the advantage of carrying a PLB on the person of pilots, particularly in one-person operations.

VH-LOS was not equipped with an automatically activated ELT. As in this accident, manually activated PLBs may not be effective in situations where a pilot survives an accident but is incapacitated or is otherwise unable to access the PLB. An automatic ELT will provide another opportunity to alert search and rescue authorities in these situations.

Notification to emergency services

Regulations within the aviation industry require pilots to notify responsible persons of the details of flights, including a planned departure and landing time. The requirements then follow that the Joint Response Coordination Centre (JRCC) should be notified of a potentially missing aircraft, so that a search and rescue response should be initiated.

In this instance, members of the mustering operation at Ramingining became increasingly concerned about the wellbeing of the pilot during the night of 14 November. They conducted a land-based search on the night of 14 November, hoping that the pilot had landed and could be seen from the road. Becoming significantly concerned on 15 November, they requested some acquaintances to conduct an aerial search, which led to the identification of the deceased pilot. Throughout this time, no calls were made to appropriate authorities.

When the pilot was first identified as missing, the level of concern and the perceived urgency of the situation was influenced by previous experiences where the pilot had returned much later than expected. The mustering operations, being conducted in an extremely remote environment, involved a necessity to frequently resolve problems without the assistance of formal authorities. Furthermore, the members of the mustering operation (other than the pilot) had limited engagement with aviation systems and regulation.

While noting the circumstances which contributed to emergency services not been immediately notified in this instance, a prompt formal notification of a missing aircraft is the most effective action personnel on the ground can take. Emergency calls will result in the JRCC being notified, and the JRCC are capable of deploying very capable assets for finding a missing aircraft with minimal delay or at first light the next day.
 

Findings

From the evidence available, the following findings are made with respect to the collision with terrain involving Robinson R22 Beta, VH-LOS, near Ramingining, NT on 14 November 2022.

Contributing factors

• The pilot operated the helicopter after nautical twilight. However, the pilot did not have an appropriate qualification, and the helicopter was not suitably equipped, for night flight.
• The flight was conducted in dark night conditions due to the absence of both celestial and terrestrial lighting. As a result, the pilot likely became spatially disorientated which led to a collision with terrain.
• The pilot did not activate the personal locator beacon, which was probably inaccessible to the pilot once they left the helicopter after the accident. In addition, authorities were not notified when the aircraft was missing. In combination, this resulted in a delay to the pilot being located before succumbing to environmental exposure after sustaining survivable injuries in the accident.

Sources and submissions

Sources of information

The sources of information during the investigation included the:

• persons involved in the mustering operation at Arafura swamp
• crew of the helicopters who searched for the helicopter after the accident
• Civil Aviation Safety Authority
• Northern Territory Police Force
• aircraft manufacturer
• recorded data from the flight tracking device on the aircraft.

References

Australian Transport Safety Bureau, 2013, Avoidable Accidents No. 7 – Visual flight at night accidents: What you can’t see can still hurt you. Australian Government, Canberra

Gibb, R., Gray, R. and Scharff, L., 2010. Aviation visual perception: Research, misperception and mishaps. Routledge.

Civil Aviation Safety Authority, 2022, Advisory Circular AC 65-05 v1.1 - Night VFR rating. Australian Government, Canberra.

Civil Aviation Safety Authority, 2023, Visual Flight Rules Guide. Australian Government, Canberra.

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 aircraft owner and operator
• the aircraft manufacturer
• the aircraft tracking device manufacturer
• the aircraft tracking service provider

No submissions were received.

Purpose of safety investigations The objective of a safety investigation is to enhance transport safety. This is done through: identifying safety issues and facilitating safety action to address those issues providing information about occurrences and their associated safety factors to facilitate learning within the transport industry. It is not a function of the ATSB to apportion blame or provide a means for determining liability. At the same time, an investigation report must include factual material of sufficient weight to support the analysis and findings. At all times the ATSB endeavours to balance the use of material that could imply adverse comment with the need to properly explain what happened, and why, in a fair and unbiased manner. The ATSB does not investigate for the purpose of taking administrative, regulatory or criminal action. 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.

[1]     This inspection was a ‘Line Check 1’ (or LC1) daily inspection.

[2]     Also referred to as a prop (propeller) strap extension.

[3]     Airstairs are a passenger and crew stairway that form an integral part of the aircraft and, after use, are hinged up and stowed on board.

[4]     A ground handling person who coordinates and performs various activities during dispatch. In this case, the role did not have any direct regulatory or airworthiness responsibilities.

[5]     The core engine speed can differ from the propeller speed, as the two are not mechanically linked. When the engine is running, the exhaust flow exerts a rotational force on the propeller via a turbine.

[6]     Sterile cockpit procedures are part of the Civil Aviation Safety Regulations and require pilots to only perform duties essential to the aircraft’s safety during certain critical phases of flight, including take-off.

[7]     Stringers are structural components that run the length of an aircraft fuselage.

[8]     After the prop straps are removed, the propeller is to be moved to the ‘X’ position with the blades at a 45° angle. See Use and stowage.

[9]     The tail strut, or ‘pogo stick’ supports the tail of the aircraft during loading/unloading and refuelling. It is stowed in the cargo bay of Saab 340B aircraft.

The occurrence

On 19 October 2022, at 0148 Coordinated Universal Time (UTC), a Boeing 737-8FE aircraft, registered VH-YFT and operated by Virgin Australia as flight number VA942, departed Brisbane Airport, Queensland, on a domestic scheduled passenger flight to Sydney, New South Wales (Figure 1).

At about 0220, the flight crew contacted air traffic control and advised they were maintaining FL 340.[1] The enroute controller issued the flight crew a BOREE 3 ALPHA standard instrument arrival (STAR)[2] for runway 34L.[3] The flight crew read this clearance back to the controller, including runway 34L.

The enroute controller later advised the flight crew that the Sydney Airport automatic terminal information service (ATIS)[4] had been amended. However, both the original and amended ATIS indicated that runways 16L and 16R were in operation for arrivals and departures.

During the descent, the crew contacted Sydney Approach, informing them they were on descent to 10,000 ft and acknowledged receipt of the current ATIS. At this point, the aircraft was at about 17,275 ft and 6 NM from waypoint[5] BOREE. The approach controller replied, confirming runway 16L and to expect an independent visual approach[6] via the STAR to 6,000 ft.

Immediately, the crew questioned the runway assignment informing the approach controller they had been assigned 34L, rather than 16L. The approach controller confirmed that runways 16L and 16R were in operation, and that 16L had been assigned. The flight crew accepted runway 16L, and the approach controller advised the crew that ‘…if you do need some extra track miles to get down to let me know [to] give you some vectors.’ The aircraft continued as cleared and joined the approach as normal.

At about 0245, the approach controller contacted the enroute controller and notified them that VA942 had been incorrectly issued runway 34L. The enroute controller then checked their recorded radio transmissions. They then verified with another aircraft, also recently issued the BOREE 3A Arrival, that they had been assigned 16L, as intended.

Figure 1: Flight path of VA942 with respect to when the runway was assigned.

Source: FlightAware and Google Earth, annotated by ATSB.

Context

Enroute controller

The enroute controller had about 24 years’ experience and was rated, endorsed, and fulfilled all recency requirements. They were responsible for 2 adjacent sectors during their shift.

Work schedule

The enroute controller reported fit for duty for their planned 8-hour shift at 0530 local time, with a scheduled shift end time of 1330. In the previous 3 weeks, the enroute controller had accepted some additional overtime shifts and extended shifts. They reported obtaining good quality 6‑7 hours sleep the night before, and their usual sleep in the previous 72 hours.

The error occurred approximately 10 minutes prior to their scheduled shift end time, and the controller reported feeling ‘fully alert’ at the time. After the occurrence, the work scheduling software indicated that the shift had a predicted fatigue level of high.[7] However, fatigue was not considered to be a contributing factor.

Workload

It was reported that the sector was fully staffed that day, with provision for in-shift relief breaks. The controller advised they were ‘relatively busy’ and were communicating with 10 other aircraft around the time of the occurrence. They estimated that they were operating at a capacity of about ‘six out of ten’. Overall, the workload across the 2 sectors was manageable at the time of the occurrence, and not considered to be a contributing factor.

Issuing of clearance

The enroute controller for this sector provided initial sequencing, STAR clearances, and initial descent instructions for aircraft bound for Sydney Airport from the MAESTRO system. MAESTRO is a tactical traffic sequencing software used for aircraft arrivals at Sydney Airport, and other domestic airports across Australia. It uses actual position and speed information of aircraft to determine the landing order and displays this information to air traffic controllers. This information can then be used to inform decisions about aircraft speed control, vectoring or holding to maintain an orderly traffic flow.

When the enroute controller issues a clearance to aircraft, they check the runway allocation in MAESTRO, then select the aircraft designator on the air situation display (ASD), which opens a drop-down list of runways. The controller then selects the issued runway on the ASD and during the hear-back process, checks that all the information is correct. The aircraft designator also displays other information, including the aircraft's flight level.

At the time of the occurrence, the ASD and MAESTRO displayed flight VA942 assigned for runway 16L and maintaining FL 340. The enroute controller issued the clearance using the standard phraseology, and reported they were looking at the flight level in the aircraft designator when they did this.

Standard Terminal Arrival Route (STAR) clearance

The BOREE 3A arrival positioned aircraft to receive radar vectors to final for all Sydney Airport runways, including 16L and 34L. Waypoint BOREE is the initial approach fix, and the track then later branches for the different runways at waypoint OVILS (Figure 2). The crew reached waypoint BOREE about one minute after the correct runway was confirmed, which required that the approach be re-briefed by the crew. In this case, the change to the approach required that the aircraft fly the procedure as briefed to OVILS where radar vectors would then be provided by ATC.

Figure 2: BOREE 3A Arrival STAR Chart

Source Airservices Australia, annotated by ATSB.

Virgin Australia procedures

Virgin Australia’s flight procedures for the verification of weather and terminal information included a requirement for flight crew to independently review information from the ATIS during arrival preparations.

Virgin Australia did not specifically mandate flight crews to conduct a cross check between the clearance and ATIS. They reported that this would be difficult to implement due to several factors:

• STARs can be issued at various distances depending on the destination
• STARs can be received before the ATIS information is received
• ATIS can’t be specified at set distances, due to the operational mix of aircraft communication addressing and reporting system (ACARS)[8] and non-ACARS aircraft
• dynamic runway changes can occur without notice, or without it highlighted in the ATIS information (e.g., ’from time XXX expect RWY xx’)

During the enroute phase of the flight, the enroute controller notified the crew of the ATIS update from ‘X‑ray’ to ‘Yankee’. Both transmissions listed ‘RWY: 16L AND R FOR ARRS AND DEPS’.  

The enroute controller later advised they were ‘surprised’ that the crew did not question the runway assignment during the read-back process, because the assigned runway was different to that stated in the ATIS.

Safety analysis

The enroute controller reported that when the crew of VA942 initially made contact and the STAR was provided, runway 16L was selected from the available runways as intended. However, they were looking at the flight level (FL 340) on the ASD, when they issued the clearance for 34L. This skill-based error most likely occurred because of the interference of information between FL 340 and 34L. Verbal slips of this nature are more likely to occur when there is a high degree of similarity between the presentation of simultaneous, related information, while performing a familiar and repetitive action.

The read-back and hear-back procedure was the opportunity for both parties to detect the error before it propagated further. However, on this occasion the error went undetected. The radio recordings confirmed that the standard phraseology was used during the communication, and the flight crew correctly read-back the assigned runway 34L, and this was acknowledged by the enroute controller.

There was information available to the crew in the ATIS indicating that runway 34L was not in operation. This provided an opportunity to identify and question the conflicting clearance and ATIS information between themselves, but the evidence obtained by ATSB showed that they did not enquire further with ATC until they were in contact with the approach controller, who correctly assigned 16L.

Findings

From the evidence available, the following findings are made with respect to the air traffic control error involving Boeing 737, VH-YFT, near Sydney Airport, New South Wales on 19 October 2022.

Contributing factors

• The enroute controller verbally issued the clearance to the flight crew to land on runway 34L instead of 16L, which was not identified during readback. This slip was likely due to the similarity between the flight level (FL 340) and runway 34L.

Other findings

• The flight crew did not enquire further with ATC about the runway assignment of 34L until the approach controller provided runway 16L.

Sources and submissions

Sources of information

The sources of information during the investigation included:

• the involved air traffic controllers
• FlightAware
• Airservices Australia
• Virgin Australia Airlines Pty Ltd
• VATPAC ATC Standard Operating Procedures Hub

References

Safety behaviours: human factors for pilots 2nd edition. Resource booklet 4 Communication. Civil Aviation Safety Authority

Air Traffic Flow Management: Harmony for ANSPs. Briefing Paper for Pilots. Version 5. Air Services Australia 2016.

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 involved air traffic controllers
• Airservices Australia
• Virgin Australia Airlines Pty Ltd

No submissions were received.

Purpose of safety investigations The objective of a safety investigation is to enhance transport safety. This is done through: identifying safety issues and facilitating safety action to address those issues providing information about occurrences and their associated safety factors to facilitate learning within the transport industry. It is not a function of the ATSB to apportion blame or provide a means for determining liability. At the same time, an investigation report must include factual material of sufficient weight to support the analysis and findings. At all times the ATSB endeavours to balance the use of material that could imply adverse comment with the need to properly explain what happened, and why, in a fair and unbiased manner. The ATSB does not investigate for the purpose of taking administrative, regulatory or criminal action. 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.

[1]     Flight level: At altitudes above 10,000 ft in Australia, an aircraft’s height above mean sea level is referred to as a flight level (FL). FL 340 equates to 34,000 ft.