Overview of the investigation

The occurrence

On 24 December 2021, the ATSB commenced a transport safety investigation into a fatal accident involving an amateur-built Jodel D11 aircraft, registered VH-WBL, at Ball Bay about 34 km north‑north-west of Mackay Airport, Queensland, on the same day.

At about 0740 Eastern Standard Time,^[1] the pilot reported starting the aircraft at the Ball Bay airstrip and conducting engine run-ups before the passenger boarded for a private pleasure flight. After the passenger boarded, the pilot taxied the aircraft to the northern end of the runway and conducted a second engine run-up and magneto check, with no anomalies detected. The aircraft was then lined up for a take-off towards the south-east. The ground run and take‑off were uneventful until the aircraft reached a height of about 60 ft, when the engine started to intermittently cut-out. The pilot ‘pumped’ the throttle lever. However, the engine failed and power could not be restored. As there was insufficient runway remaining to land ahead, the pilot turned the aircraft left towards the beach for a forced landing.

Impact marks in the sand indicated that, during the landing, the left main wheel struck the ground first followed by the aircraft nose. One propeller blade (wooden) broke off, and the aircraft rotated and rolled onto its right side before coming to rest partially inverted about 22 m from the initial impact mark. The passenger was fatally injured, and the aircraft was destroyed. The pilot was taken to Mackay Hospital and self-discharged on the same day.

The wreckage was removed from the accident site by the Queensland Police Service Mackay Forensic Crash Unit and transported to a secure facility for examination.

Pilot and aircraft history

The ATSB visited Mackay from 12 to 16 January 2022 and the investigation found that:

• The pilot did not hold a Civil Aviation Safety Authority aeroplane pilot licence, aircraft maintenance engineer licence or authorisation to perform or certify for maintenance on the accident aircraft.
• The aircraft was issued with a standard certificate of airworthiness in 1978.
• The pilot purchased the aircraft from the owner-builder in 2011.
• The aircraft logbook statement specified that it was to be maintained in accordance with the Civil Aviation Authority^[2] Schedule 5. All components were lifed ‘on condition’, except those within the scope of relevant airworthiness directive requirements and the engine. The time‑in‑service between maintenance release issue was at 100‑hours or 12‑month intervals, whichever was earlier. The operational category was ‘private’.
• The most recent maintenance release was issued in 2015 by the pilot, who was not authorised to do so. The expiration date was recorded as ‘27/1/16’, the system of maintenance was recorded as in accordance with ‘Schedule 5’ and the operating category as ‘experimental private’. It contained the pilot’s daily inspection certifications for 2015 and further entries in 2021, after the maintenance release had expired (none recorded for the period 2016–2020).
• The aircraft logbook entries for periodic inspections in accordance with Schedule 5 ended with the last entry in March 2011. There was no entry for the maintenance release issued in 2015.
• The engine logbook entries ended in January 2014, with the last entry certified by the pilot.
• The last entry in the pilot’s logbook for VH-WBL was in 2015.

Wreckage examination

The ATSB conducted a preliminary examination of the wreckage, but did not identify anything obvious that would lead to the engine completely failing. Relevant observations are noted below:

• The tachometer indicated a time of about 6 minutes between engine start and the accident.
• The remaining propeller blade did not exhibit any damage, which was consistent with a loss of power.
• The core of the engine was intact with the crankcase free from impact damage and the cylinders securely attached. The engine rotated freely and the valve train was observed to respond to crankshaft rotation.
• A differential pressure (leak) check was performed on the engine cylinders with the engine at ambient temperature. One cylinder recorded a low result for a compression check of 16/80. The others recorded 55/80, 74/80 and 76/80.
• There was sufficient engine oil and the oil filter was relatively clean with no significant debris.
• An internal examination of the exhaust system showed that the muffler inner matrix had collapsed with loss of matrix material to both mufflers. However, the condition of the matrix should not have prevented the operation of the engine.
• The gascolator was dislodged in the accident and no fuel was found in the carburettor float bowl.
• The main fuel tank dip stick was bent during the accident and indicated there was sufficient fuel for flight at impact. This was the tank selected for the flight and was gravity-fed to the engine. The tank had split open, resulting in the loss of all the contents, and therefore no examination of this fuel was possible. The right-wing fuel tank contained blue aviation gasoline (100LL) and the left-wing fuel tank contained green fuel, which was likely a blend of aviation gasoline with yellow unleaded motor gasoline. Both wing tanks passed a water test.
• Although not used on the accident flight, the electric fuel pump for the wing tanks contained fuel that failed a water test. The pump filter was found to be clean and unobstructed.
• A functional check of the engine ignition switch did not reveal any defect with the magneto switching.
• The flight controls were connected and free to move in the correct sense. However, the aileron control cables were significantly corroded at their outboard thimble and sleeve.
• The passenger’s seat belt had completely failed at 2 locations. Both the pilot and passenger’s seat belts were manufactured in May 1973 and were required to be removed from service prior to 1 January 1990 in accordance with Civil Aviation Safety Authority airworthiness directive AD/RES/24: Aeronautique Seat Belts and Harnesses. At the time the airworthiness directive was issued in 1990, the aircraft was being maintained by an approved maintenance organisation.

Safety message

This accident highlights the importance of following standards for the maintenance and operation of aircraft. The Civil Aviation Safety Authority airworthiness directive AD/RES/24 regarding seat belt replacement was cancelled in 2009 with the explanation that ‘As all affected aircraft would have been modified long ago, this AD is no longer required’. However, compliance with this airworthiness directive was missed on this aircraft for about 30 years, despite both seat belts displaying the affected manufacturer’s label and their inspection was a requirement under Schedule 5.

Reasons for the discontinuation

The Civil Aviation Safety Authority have put in place regulations designed to ensure aircraft are airworthy and pilots are properly trained and qualified. When owners operate outside of the rules, they remove the built-in safety defences and undetected problems are more likely to emerge. Given that the aircraft and engine had not been maintained in accordance with the regulations for about 10 years, a more detailed investigation to find the source of the engine failure would have unlikely led to the identification of broader systemic safety issues. On that basis, the ATSB determined that there was limited safety benefit in continuing to direct resources at this investigation when compared with other priorities and elected to discontinue this investigation.

__________

1.  Eastern Standard Time (EST): Coordinated Universal Time (UTC) + 10 hours.
2.  Predecessor to the Civil Aviation Safety Authority.

Executive summary

What happened

On 28 January 2022, shortly before noon, the bulk carrier Goliath collided with the moored tugs York Cove and Campbell Cove in Devonport, Tasmania. The tugs, which were unmanned at the time, sustained significant damage and subsequently sank. Authorities ashore initiated pollution control and oil spill recovery measures and the ensuing loss of fuel and other oils from the tugs were largely contained. Goliath sustained minor damage to its bow while the tugs were both subsequently declared a constructive total loss.

What the ATSB found

The ATSB found that, in the process of a transfer of manoeuvring controls from Goliath’s bridge to the bridge wing, the correct steering mode was not selected. Consequently, control of the ship’s rudders remained at the wheel, inside the ship’s wheelhouse, while the master attempted to manoeuvre the ship in the swing basin using the bridge wing VecTwin joystick panel. The master’s manoeuvring orders, issued in the belief that the ship was in joystick steering mode, had the effect of increasing the ship’s speed as it closed on the tugs before colliding with them.

The investigation found that neither the master nor the second mate had undertaken the required bridge resource management (BRM) training and that BRM on board was ineffective. The design of the ship’s joystick system was also identified as having increased the risk as it was misleading and did not provide a positive visual confirmation that the correct steering mode had been selected.

Finally, the ATSB observed that, while the TasPorts risk assessment for Devonport had considered the potential for collisions between ships manoeuvring in the swing basin and smaller vessels in the vicinity, the risk of injury to personnel on board those smaller vessels was not specifically considered. On this occasion, it was largely fortuitous that there were no personnel on board the tugs at the time of the collision.

What has been done as a result

CSL Australia arranged for all deck officers serving on board Goliath, to attend bridge resource management (BRM) training ashore. Additionally, the ship’s health safety environment and quality (HSEQ) manager and HSEQ superintendent also undertook the training, and a new dynamic navigation audit was instituted to allow for regular audits focused on implementation of BRM on board. The safety management system requirement for BRM training was also incorporated into crew training schedules across the CSL Australia fleet.

Goliath’s VecTwin joystick panels were modified to incorporate a positive visual indication that joystick steering mode was selected, and the transfer of control checklist modified accordingly. The company’s standing orders, bridge checklists and the ship’s procedures on navigation, watchkeeping and passage planning were amended to specify the conditions under which the relief of watchkeeping officers could take place during pilotages or during extended manoeuvres.

TasPorts’ investigation into the accident resulted in several recommendations for proposed safety action, including recommendations to prohibit Goliath using the swing basin to berth port side alongside if vessels are berthed at berth number Three West, to introduce changes to the Devonport pilot exemption conditions, training, assessment, and renewal processes and to clarify the applicability of tidal restrictions relevant to Goliath’s port calls.

Safety message

The various concepts, techniques, and attitudes that together comprise bridge resource management remain among the most effective measures available to identify and eliminate, or rectify, human error. Training in the various elements that comprise effective BRM provides a foundation upon which competency may be built through experience and practice. In addition, the design of bridge systems can also play a part in mitigating the risks of human error by incorporating intuitive and conspicuous indications of correct operation and conversely, of errors or incorrect settings.

Summary video

The occurrence

Overview

On 28 January 2022, the 143 m Australian-registered, bulk cement carrier Goliath (Figure 1) collided with the moored tugs York Cove and Campbell Cove in Devonport, Tasmania. The tugs, which were not manned at the time, sustained significant damage and sank shortly after. Authorities ashore initiated pollution control and oil spill recovery measures with the ensuing loss of fuel and other oils from the tugs largely contained. Goliath sustained minor damage to its bow while the tugs were both subsequently declared a constructive total loss.[1]

Pre-arrival activity

On the morning of 28 January 2022, Goliath was on passage from Melbourne, Victoria to Devonport, Tasmania. The ship had departed Melbourne the previous evening and was bound for the bulk cement facility at Devonport’s berth number One West, where it usually berthed port side alongside.

Figure 1: Goliath, alongside at berth number One West, Devonport

Source: TasPorts

Shortly after 1000 Eastern Daylight-saving Time,[2] the officer of the watch (third mate) began to complete the ship’s bridge arrival checklist in preparation for arrival at Devonport. This included checks of the bridge equipment and other machinery. By about 1020, most of the checks in the bridge arrival checklist had been completed, including checks of the ship’s steering gear,[3] whistle, and very high frequency (VHF) radios. By 1050, the deck crew reported that the ship’s anchors had been unsecured and made ready for use. Shortly after, the third mate began reducing the ship’s sea speed using the main engine slow down program. At about the same time, the master came to the bridge and, shortly after, took over the conduct of the ship. At about 1055, the master moved the main engine telegraph from ‘navigation ahead’ to manoeuvring ‘full ahead’.

At about 1106, as the ship approached Devonport port limits (Figure 2), the third mate tested the ship’s bow thruster and had the main engine put on stand-by for manoeuvring. Shortly after, the watchkeeping integrated rating (IR)[4] came to the bridge for helmsman duties. At about 1108, the master called Devonport vessel traffic service (VTS) on the port’s VHF radio working channel (VHF channel 14). The master reported the ship’s maximum draught of 6.6 m and pilotage exemption details to the VTS and requested permission to enter port limits and proceed inwards. The VTS granted permission and advised that there was no other traffic expected in the port.

The weather at the time was overcast with slight seas and a light north-easterly breeze. The tide was ebbing with low water at Devonport predicted at 1422 with a height of tide of 0.50 m.[5]

Figure 2: Section of chart Aus 164 showing Goliath’s track

Source: Australian Hydrographic Office, annotated by the ATSB using electronically recorded data

At about 1110, the ship’s steering mode was switched from autopilot to manual steering using the steering mode selector switch located on the starboard side of the steering console (see the section titled Steering system), and the IR began steering. The master continued reducing the ship’s speed, moving the telegraph to ‘half ahead’ and by 1128, to ‘slow ahead’. Shortly before 1130, the chief mate came to the bridge and, after a brief hand over, relieved the third mate who proceeded to the aft mooring stations.

Navigation within port limits

At 1130, Goliath passed the breakwater inbound. At the time, the ship’s bridge team comprised the master, chief mate, helmsman, and the deck cadet.

At about 1140, the second mate came to the bridge with the intention of relieving the chief mate. The second mate and chief mate, situated to starboard of the steering console, began discussing the state of various ship’s machinery, personnel, and bridge equipment. The helmsman was steering, and the master was stationed to port of the steering console where the main engine telegraph, bow thruster controls and VecTwin steering control joystick were located (see the section titled Goliath’s manoeuvring system and Figure 3). By this time, the master had placed the telegraph on ‘dead slow ahead’ and shortly after, to ‘stop’.

Figure 3: Goliath's bridge layout showing the location of various controls and equipment

Source: CSL Australia, modified and annotated by the ATSB

At about 1142, crew on board the mooring lines boat Rubicon called Devonport VTS on VHF channel 14 advising that it was underway in preparation to assist with Goliath’s berthing. The call was acknowledged by VTS. Following this, at about 1143, Rubicon called Goliath on VHF channel 14, requesting a radio check. On board Goliath, the master asked the second mate to deal with the radio call as he was busy conducting the ship in the approach to the swing basin.

After a brief discussion with the master and chief mate about which radio to use, the second mate moved to the left of the master to use one of the 2 VHF radios located on the bridge-front console (Figure 4). One of those radios was generally used to maintain a listening watch on VHF channel 16[6] and the other to monitor working frequencies such as the port’s working channel (in this case, channel 14). A portable VHF radio was normally reserved for berthing communications (channel 6).[7] The second mate acknowledged Rubicon’s call on channel 14 and advised that the ship was standing by on channel 6.

Figure 4: Goliath's bridge showing location of various controls and equipment

Source: CSL Australia, modified and annotated by the ATSB

By this time, the engine had been placed on ‘dead slow astern’ and the master used the main engine and bow thruster to commence slowly turning the ship to starboard in preparation to swing it to a northerly heading for approaching the berth. Shortly after, the engine telegraph was placed on ‘slow astern’ and, a few seconds later, the helmsman advised the master that the ship was no longer steering (that is, it was no longer responding to the rudder due to the ship’s decreasing speed). The master advised the helmsman that he was finished with the wheel and the helmsman promptly left the bridge for the aft mooring stations.

At about 1144, Rubicon’s crew again called the ship, requesting a radio check, this time on VHF channel 6. Recorded audio from Goliath’s voyage data recorder (VDR)[8] indicates that the call from Rubicon was almost certainly received on one of the 2 VHF radios on Goliath’s bridge-front console, indicating that one of the radios was set on channel 6. Following a brief period of confusion over which radio to use to respond, the second mate responded to the call using one of the bridge-front console radios. The second mate then remained beside those radios, to the left of the master, while the chief mate went to locate the portable VHF mooring radio. At about this time, a further brief VHF radio transmission between VTS and another vessel also resulted in the officers on the bridge voicing some confusion.

The collision

At about 1145, as the ship continued turning slowly to starboard, the master stopped the engine in readiness to transfer controls to the port bridge wing conning station.

As was normal practice on board, the master then called out to the chief mate that he was ready to ‘change over’ (that is, for controls of the ship’s steering and propulsion to be transferred to the port bridge wing conning station for the master to move outside, complete the swing and berth the ship). The second mate (who was closer to the port bridge wing door) verbally acknowledged the master’s order and recalled going out on to the bridge wing and taking control of the main engine, bow thruster and VecTwin steering system (joystick) on their respective panels on the port bridge wing console.

Once the second mate confirmed that the wing console was ready, the master walked out and took the con at the port bridge wing conning station (Figure 5). The chief mate, who had walked to the bridge wing door and observed the second mate taking control of the propulsion and steering at the wing console, then left the bridge and went down to the mess room.

Figure 5: Goliath's port bridge wing conning station (looking forward)

Source: ATSB

By this time, Goliath was turning slowly to starboard in the swing basin and its speed was about 1.2 knots. The third mate reported clearances to the shore from the ship’s port quarter while the bosun stationed on the foc’sle reported clearances ahead of the ship. At 1145:52, the master announced to the second mate that he was placing the bridge wing engine telegraph on ‘slow ahead’ (Figure 6). As was standard practice on board, the second mate went back inside the bridge and confirmed that the wheelhouse telegraph was appropriately replicating the master’s engine telegraph orders. The master set the VecTwin joystick to the ‘astern to port’ setting[9] and continued to use the bow thruster to swing to starboard. The second mate positioned himself just outside the wheelhouse door to monitor the ship’s swing and assist the master as required.

Figure 6: Section of chart Aus 164 showing Goliath's track and sequence of collision

Source: Australian Hydrographic Office, annotated by the ATSB using electronically recorded data

As the manoeuvre progressed, the master felt that the ship was not swinging as expected and was closing with 2 tugs, which were moored at berth number Three West ahead. In an effort to arrest the ship’s headway, the master set the VecTwin joystick to the ‘astern’ setting[10] and, at 1147:22, placed the main engine at ‘half ahead’. A few seconds later, at 1147:29, the master used ‘full ahead’, but the ship’s headway continued to increase, with the speed now about 2.9 knots. Meanwhile, the bosun had begun reporting rapidly decreasing clearances to the tugs ahead. The bridge engine telegraph data logger shows that at 1147:41, the telegraph was placed at ‘half ahead’ before quickly being returned to ‘full ahead’. At 1148:04, the master placed the telegraph at ‘navigation ahead’ (that is, the maximum ahead engine telegraph setting).  The ship’s speed had increased to 4 knots.

With the ship’s speed still increasing, the master checked the rudder angle indicator located in front of the port wing console and then observed that both rudders were still amidships and not at the angles corresponding to the VecTwin joystick setting as expected. The master called out to the second mate that the steering was not in VecTwin steering mode and immediately brought the engine telegraph to ‘slow ahead’ and then to ‘stop’.

At about the same time (1148:22), Goliath collided with the two tugs ahead. (Figure 7). The ship’s speed was 4.7 knots as it struck the port midships area of the tug York Cove, which was moored outboard, and alongside, of the tug Campbell Cove.[11] Both the tugs were severely damaged and began taking on water almost immediately. The tug Wilga and the fishing vessel Del Richey II, berthed to the north and south of the two damaged tugs respectively, were not impacted.

Figure 7: Goliath, immediately before the collision with the tugs

Source: TasPorts

On board Goliath, the second mate had run into the wheelhouse, checked the steering mode selector switch on the steering console and realised that it was still in manual steering mode. The second mate immediately switched it over to VecTwin (joystick) steering mode while the master placed the engine at ‘half astern’ followed by ‘full astern’ and, by 1148:31, at ‘emergency astern’.

At about 1149, crew on board the lines boat Rubicon called Devonport VTS on VHF channel 14 and reported that Goliath had collided with York Cove. Meanwhile, the fishing vessel Del Richey II, which was manned, began preparing to get underway and render assistance.

Shortly after, at about 1150, the second mate called Devonport VTS on VHF channel 14 and reported the collision. By this time, Goliath had started moving astern and the master decided to focus on getting clear of the tugs and berthing the ship. The chief mate, who had been resting in the mess room had felt the impact of the collision and come up to the bridge.

Subsequently, as the master manoeuvred the ship towards its berth, crew on deck began sounding the forepeak tank to check for possible hull damage. Meanwhile, the chief mate and second mate monitored the tank levels on the bridge’s ballast control screen.

Emergency response

At about 1154, two other vessels in the port (Searoad Mersey II and Torquay Ferry) called VTS on VHF channel 14 and advised that they were standing by to render assistance if required. Meanwhile, VTS notified key Tasmanian Ports Corporation (TasPorts)[12] personnel of the incident including the harbour master and deputy harbour master.[13]

On receiving advice of the collision, the TasPorts state operations centre[14] activated the port’s crisis management and incident management teams while port personnel began to organise oil spill response equipment and oil containment booms.

On board Goliath, its berthing now proceeded normally with the master using the engine, bow thruster and VecTwin steering joystick to bring the ship alongside. By 1159, the first mooring line had been passed ashore. At 1204, the master called VTS on the telephone about the collision and was informed that no one had been on board the damaged tugs. The master subsequently reported the collision to the ship’s manager (CSL Australia) and to the Australian Maritime Safety Authority (AMSA). There were no reported injuries on board Goliath and, by 1218, the ship was all fast, port side alongside, at berth number One West.

By about 1220, both damaged tugs had developed a list to starboard as they took on more water and oil began to escape (Figure 8). By this time, the fishing vessel Del Richey II had cast off from its berth and taken up station nearby to assist. The tug Wilga remained alongside the berth.  

Figure 8: York Cove and Campbell Cove about 20 minutes after the collision

Source: TasPorts

At about 1300, the TasPorts crisis management team met and appointed an incident controller to lead the incident management team and manage the incident response. Shortly after, AMSA placed a detention order on Goliath.[15] Meanwhile, Devonport’s mooring lines boats Rubicon and Dasher were engaged in setting up available oil containment booms around the damaged tugs. By about 1331, the booms were secured in place around the two foundering tugs and the undamaged tug Wilga.

TasPorts also notified the Environment Protection Authority (EPA) Tasmania[16] and Marine and Safety Tasmania (MAST)[17] of the incident and engaged a salvage company to undertake oil recovery operations from the sunken tugs. At 1436, MAST issued a navigation warning advising mariners of the incident and to avoid navigating in the area. By 1500, an EPA incident management team had been put in place by the State Marine Pollution Controller with the initial goal of protecting sensitive areas and collecting spilled oil as quickly as possible.[18]

By about 1700, both tugs had sunk in about 7 m of water off their berth (Figure 9). It was estimated that there had been 54,000 litres of diesel and other oil on board Campbell Cove and 15,000 litres on board York Cove, of which an unknown quantity had escaped the booms into the wider Mersey River estuary. By 1800, specialised oil containment booms and an EPA oil skimmer had been deployed.

On 29 January, while skimming and other spill response operations continued, aerial surveillance operations confirmed the escape of oils from the containment area.

Figure 9: The submerged York Cove and Campbell Cove

Source: ATSB

On 30 January, the EPA declared a ‘level 2 marine pollution incident’[19] in accordance with the Tasmanian Marine Oil and Chemical Spill Contingency Plan (TasPlan) and its agreement with TasPorts and MAST. The EPA assumed responsibility for oversight of the response and for the control and management of environmental aspects related to the incident. TasPorts was tasked with control of containment and oil recovery operations within the containment area. In addition, personnel from the Department of Natural Resources and Environment Tasmania, supported by EPA staff, monitored shorelines over the following days for signs of pollution and affected wildlife.

On 31 January, the tug Wilga was extracted from within the containment area, a larger skimmer from the AMSA’s National Plan stockpile was deployed and MAST declared a prohibited area due to the ongoing oil spill response activity. The next day, the EPA detained[20] Goliath and EPA inspections of the shoreline and surrounding areas identified small quantities of oil and several bird mortalities.

On 3 February, following temporary repairs, AMSA issued consent for Goliath to undertake a single voyage to Melbourne for further repairs. On 4 February, the EPA released Goliath from its detention, and the ship sailed.

By 11 February, salvage teams had recovered more than 18,000 litres of diesel, lubricating oil, and hydraulic oil from the sunken tugs. An estimated 10,000 litres of fuel and oil remained unaccounted for and probably had not escaped from the tugs’ hulls.

On 15 February, the EPA State Marine Pollution Controller formally advised TasPorts that the level 2 marine pollution incident response had been completed, and responsibility for ongoing aspects of the response were transferred to TasPorts.

Damage and recovery

The collision resulted in the destruction of the wharf’s fendering system, which was subsequently repaired.  Further assessment of the damage to the concrete wharf face was required to be undertaken.

Damage sustained by Goliath was limited to deformation of its bulbous bow shell plating and internal structural members and, a non‑penetrating crack in the starboard bow’s shell plating. Following the repairs in Melbourne and after meeting other regulatory requirements, AMSA released Goliath from detention on 10 February and the ship returned to service.

Both York Cove and Campbell Cove were declared constructive total losses. On 11 March 2022, United Salvage were awarded the tender for removal of the wrecks of the sunken tugs. In July 2022, the heavy-lift ship AAL Melbourne was engaged to lift and remove the tugs’ wrecks. The ship arrived in Devonport on 7 August and recovered York Cove’s wreck (Figure 10). Campbell Cove’s wreck was also recovered by 12 August. During the recovery operation, an unknown quantity of oil escaped the containment area although EPA surveys of the shoreline and water did not detect any affected wildlife. AAL Melbourne departed Devonport on 16 August for Brisbane, Queensland where the tugs were to be scrapped (recycled).

Figure 10: York Cove being recovered

Source: TasPorts (Courtesy of Rob Burnett Images)

Context

Goliath

Ship details and history

Goliath is an Australian‑registered, self-unloading, bulk cement carrier built in 1993 by Hanjin Heavy Industries in Ulsan, Republic of Korea. At the time of the collision, the ship was classed with Lloyd’s Register and owned by CSL Australia. It was managed and operated by CSL Australia and engaged almost exclusively in the carriage of cement from Devonport, Tasmania to Melbourne, Victoria.

The ship was originally owned by Cement Australia until it was purchased by CSL Australia in 2007. Following the change of ownership, the ship was managed by Inco Ships until 2015 when management was taken over by CSL Australia.

Goliath was equipped with the necessary navigational, and other equipment, machinery and systems required by SOLAS[21] for a ship of its size. This included radar, automatic identification system (AIS), gyrocompass and electronic chart display and information system (ECDIS), which was the ship’s primary, and back-up means of navigation. Goliath was also equipped with a Japan Radio Company JCY 1850 voyage data recorder (VDR) from which data and information useful to the investigation was recovered, including audio recordings from the bridge.

Goliath’s main propulsion was provided by a Sulzer 5RTA 52 engine developing 6,080 kW driving a single, fixed pitch, right-handed propeller. The ship was also equipped with an Ulstein 883 kW bow thruster.

Ship’s crew

Goliath had a predominantly Australian crew of 17, including the master, 3 deck watchkeeping officers, chief engineer and 3 engineers, 2 cadets, 6 integrated ratings (IRs), including a trainee, and a cook. The ship was operated on a 6-week crew roster with many of the crew regularly assigned to the ship over several years.

The master had about 46 years of seagoing experience, with over 20 years in the rank of master with CSL Australia and, previously, another company. The master held a United Kingdom master’s certificate of competency, the equivalent Australian certificate of recognition and pilotage exemption certificates for Melbourne and Devonport. The master began working on board Goliath in 2002 as a third mate and was promoted to master after CSL Australia became its owners in 2008 and had continued in that rank since. The master had re-joined the ship about a week before the accident.

The chief mate had about 28 years of seagoing experience and had been a chief mate for about 8 months. The chief mate held an Australian chief mate’s certificate of competency and had worked on board Goliath since 2008. The chief mate had re-joined the ship 2 days before the accident.

The second mate had about 15 years of seagoing experience and had been second mate for about 8 months. The second mate held an Australian second mate’s certificate of competency and had also worked on board Goliath since 2008. The second mate had re-joined the ship about 3 weeks before the accident.

Hours of work and rest

Goliath’s deck officers maintained a traditional 4-on 8-off watchkeeping schedule at sea. Hence, the three watchkeeping officers kept a 4-hour navigation watch followed by 8 hours of rest opportunity or time to carry out non-watchkeeping duties. The master did not stand a navigational watch at sea.

The ship had departed Melbourne for Devonport at 1612 on 27 January (the day before the accident) and the night was spent underway at sea in good weather. This provided all the deck officers an opportunity for a full 8 hours of uninterrupted rest or sleep.

The master reported going to bed by about 2200 on 27 February and sleeping well until waking at 0600 on the morning of the accident. The master recalled being well rested and alert in the time leading up to the accident.

The chief mate had joined the ship during the port call at Melbourne after spending 2 nights in a hotel due to a delay with the ship’s berthing. The chief mate recalled sleeping reasonably well the night before the accident although still adjusting to the sleep environment on board and being at sea. The chief mate kept the usual navigational watch between 0400 and 0800, followed by breakfast and some paperwork, until about 1130, before relieving the third mate on the bridge. The chief mate reported being reasonably well rested and alert in the time leading up to the accident (although it was nearing the usual time for the rest period).

The second mate kept the 0001-0400 watch and then went to bed by about 0500 before waking at about 1100. The second mate then had lunch before going up to the bridge to relieve the chief mate. The second mate reported being well rested and alert in the time leading up to the accident.

Analysis of the master, chief mate and second mate’s recorded hours of work and rest found that they were compliant with the minimum hours of rest as required by the relevant international conventions[22] and the Australian Maritime Safety Authority’s (AMSA) Marine Order.[23]

Goliath’s manoeuvring system

Steering system

Goliath was fitted with a Hamworthy Industramar VecTwin steering system comprising 2 highlift, Schilling rudders installed symmetrically behind the propeller. Each rudder was independently driven by a Frydenbø-Mjølner HS 120 rotary vane steering gear unit, each fitted with 2 steering motors.

The steering gear could be remotely operated from the bridge in 4 main control modes:

• autopilot steering
• manual steering (wheel control)
• non-follow-up (NFU) steering
• VecTwin steering (joystick control).

Additionally, and similar to other ships, the steering could be operated locally from the steering gear room in case of an emergency involving the failure of the remote operating systems.

When steering in autopilot or manual steering modes, the 2 rudders operate in unison based on rudder angle commands respectively from the autopilot or the manual steering wheel. In non‑follow-up (NFU) mode, the rudders could be operated either independently with separate levers (tillers) or by a single lever.[24] In VecTwin steering mode, a joystick was used to control the rudders.

The steering could be operated in any mode when conning from inside the wheelhouse. When conning the ship exclusively from the bridge wing conning stations, joystick steering was the only available means of rudder control.

The mode of steering operation was selected by means of a manually operated selector switch on the bridge steering console (Figure 11). The selected steering mode was indicated by the illumination of the respective symbol on the steering selector switch panel, and on the autopilot panel on top of the steering console.

Rudder angle indicators were fitted in the wheelhouse, on each bridge wing (port and starboard), and in the steering gear room.

Figure 11: Goliath's wheelhouse, steering console, and steering mode selector switch

Source: ATSB

VecTwin steering mode

In VecTwin (joystick) steering mode, a joystick was used to select various pre-set combinations of rudder angles which, with ahead inputs on the ship’s main engine, allowed for the generation of thrust in different directions and for enhanced manoeuvrability, particularly at slow speeds. The system coordinated the 2 rudders independently with rudder angle settings ranging from 105° outboard to 25° inboard depending on the joystick setting selected (Figure 12). On board Goliath, VecTwin steering mode was generally only used at speeds under 2 knots, which generally limited its use to low-speed manoeuvring in port. 

When using the VecTwin steering mode, ahead inputs on the main engine could be used to generate astern thrust, transverse thrust or even to ‘hover’, all with the propeller kept rotating in the ahead direction. For example, with the ‘astern’ joystick setting selected, each rudder was set to 105° outboard, with ahead inputs on the main engine generating astern thrust to slow/stop the ship or move the ship in the astern direction. This meant that the ship could be slowed, stopped, or moved astern without the need to stop the engine and engage astern propulsion, as usually required for conventional ship manoeuvring.

Figure 12: VecTwin steering joystick showing settings and corresponding rudder angles

Note that the direction of ship motion shown for various VecTwin joystick rudder angle settings is the direction of the resultant ship motion when ahead main engine movements are used in combination with the respective joystick setting.

Source: ATSB

Joystick design

There were 3 VecTwin joystick control panels, one in the wheelhouse and one on each bridge wing conning station.[25] Control could be taken at any one of the joystick panels by pushing the ‘joystick call up’ push button and the joystick selected for command was indicated by the illumination of a ‘joystick on’ indicator light on the respective panel.

During the ATSB’s on site investigation, investigators’ testing of the system determined that the illumination of the ‘joystick on’ light was independent of, and unrelated to, the steering mode selected. The illumination of the ‘joystick on’ light only indicated which joystick panel was selected and that control was possible from that panel.

This meant that the ‘joystick on’ light remained illuminated at whichever joystick panel had been selected (or last selected) even when the chosen steering mode was a mode other than ‘joystick control’ (such as ‘autopilot’ or ‘manual’ steering modes).

This was contrary to the understanding of the master and other deck officers who believed that the illumination of the ‘joystick on’ light was also indicative of the steering being in the correct VecTwin joystick steering mode. That is, the officers believed that the illumination of the ‘joystick on’ light was only possible if the steering mode selector switch had been turned to the right setting to select joystick steering mode.

Interview accounts also indicate that, in practice, there was no consistency among the involved officers regarding the use of the ‘joystick on’ light as an indicator of a successful transfer of control. At interview, the master stated that they often checked for the illumination of the ‘joystick on’ light to assure themselves that transfer had been successfully executed and that steering was in joystick mode. However, the chief mate and second mate both reported that they largely ignored the light and did not assign any significance to it either as an indicator of transfer or otherwise. It was also reported that the bridge joystick panel ‘joystick on’ light was usually left obscured by covering it with an opaque plastic bottle cap.

Following the accident, CSL Australia arranged for modification of the joystick control panels to provide affirmative visual confirmation that the correct steering mode had been selected and that the panel was selected for command (Figure 13). The modification was completed in April 2022.

Figure 13: Joystick panel at the time of the accident (left) and after modifications (right)

Source: CSL Australia, modified and annotated by the ATSB

Previous VecTwin steering incidents

As part of this investigation, the ATSB sought records of past incidents involving Goliath and its VecTwin joystick steering system. TasPorts records showed 2 relevant incidents involving Goliath (described below). At the time of those incidents, Goliath was owned by CSL Australia and managed by Inco Ships. As such, there was no record of those incidents or of the implementation of the resulting proposed corrective action within the CSL Australia incident management database. Neither of the 2 earlier incidents involved officers on board at the time of this accident

Devonport, 2007

On 10 December 2007, while manoeuvring Goliath in the Devonport swing basin, the master selected the ‘astern’ joystick setting on the port bridge wing joystick panel and ordered ahead inputs on the main engine telegraph to slow the ship for the final approach to the berth. However, the master observed that instead of slowing down, the speed was increasing. The master checked the rudder angle indicators and realised the rudders were amidships. Despite the master then ordering ‘full astern’, the bow made contact with the shore, resulting in some minor paint damage to the bulbous bow. There was no damage to shore infrastructure or pollution.

Following the incident, the steering mode selector switch was reset to manual steering before joystick mode was selected again. The joystick steering system then operated as normal and the ship berthed without further incident. The shipboard investigation found that joystick steering mode had been correctly selected, and control correctly transferred to the port bridge wing conning station. Subsequently, it was found that there were several loose connections and wiring with poor terminations in the steering mode selector switch mechanism, which resulted in the steering mode remaining in manual steering.

The incident resulted in a proposal to amend the ship’s procedures to include a requirement for a functional test of the steering following a change in the selected steering mode.

Devonport, 2009

On 15 May 2009, while manoeuvring Goliath in the swing basin, the master selected the ‘astern to starboard’ joystick setting on the port bridge wing joystick panel and ordered ‘slow ahead’ on the main engine telegraph. However, the master found that the ship was not swinging as expected, so ordered ‘half ahead’. At about that time, the master realised that the rudders were still amidships and that joystick control had not been accepted on the port bridge wing joystick panel. The master immediately pushed the ‘joystick call up’ push button, selected the ‘astern’ joystick setting and ordered ‘full ahead’ to slow down the ship. The master subsequently ordered ‘full astern’ and used the bow thruster to avoid colliding with the wharf ahead. Goliath narrowly avoided colliding with Campbell Cove, which was moored at berth 3W, but it did collide with an aluminium walkway for the small craft mooring pontoon north of the berth. There was only minor paint damage to the ship’s bow but substantial damage to the walkway and mooring pontoon. The moorings of 2 pilot launches at the pontoon also parted.

The shipboard investigation found that the master did not take control of the VecTwin joystick on the wing joystick panel and there was no verbal confirmation between the master and chief mate to confirm the transfer of control had been successfully completed. The investigation also identified that although there was a general practice for the transfer of controls, this was not documented and was not followed on the day. Importantly, the investigation identified that the design of the joystick panel did not incorporate an unambiguous indicator that control had been successfully transferred.

The incident resulted in a proposal to identify and document the indications of a successful transfer of controls and to identify locations where the transfer could occur safely in advance of committing to a critical manoeuvre. The corrective action also recommended that the improved process be captured in the ship’s passage plan and the ship’s officers be familiarised with the procedure and provided refresher training on aspects of good ‘bridge resource management’.

Safety management system

The International Safety Management (ISM) Code[26] has as its objective the prevention of human injury or loss of life and the avoidance of damage to the environment and to property. Among other things, it requires companies to provide for safe practices in ship operations, to assess all identified risks to ships, personnel and the environment and, to establish appropriate safeguards against these risks. The Code aims to achieve this by requiring companies to develop, implement and maintain a safety management system (SMS), with instructions and procedures to ensure the safe operation of ships, to prepare for and respond to emergencies and to conduct regular audits and reviews of the system.

Goliath’s SMS consisted of general procedures and instructions broadly grouped under sections such as fleet operations, company operations and safety and environmental procedures. The section on fleet operations covered navigation including procedures for passage planning, watchkeeping, and bridge resource management while the safety and environmental procedures covered risk assessment and risk management. These generic procedures applied to ships across the fleet and were augmented by the company’s standing orders. Additionally, each ship was required to develop master’s standing orders and ship-specific checklists taking into account the particular ship’s operations, circumstances, and equipment.

Passage planning

CSL Australia’s procedures for passage planning were largely aligned with the requirements of the relevant international conventions and best practice. Goliath’s passages were planned from berth‑to‑berth and generally required little change between voyages. The passage plan included guidance notes relevant to specific waypoints. For example, for the waypoint in the swing basin, the plan advised the master to monitor transit points during the swing and to take care not to develop unwanted headway towards the berth. The plan did not include any guidance on safe locations for the transfer of controls.

An ‘exempt master pilotage briefing’ card, completed as part of the ship’s pre‑arrival and pre‑departure checks, was used to capture information such as the weather, state of the tide, traffic, draught, and other variables relevant to port entry or departure.

The exempt master briefing card for Devonport documented information such as tidal restrictions applicable to berthing, relevant port rules including courses and speeds within port limits and the dimensions of the swing basin. The briefing card included a short checklist with reminders to monitor the ship’s course and speed, helm orders and that the ship was proceeding according to the agreed passage plan. The card also included a check titled ‘Bridge Control transfer procedure confirmed’ but did not include guidance or information on safe locations where the transfer of controls could or should take place before the ship was committed to a manoeuvre.  The briefing card for Goliath’s arrival in Devonport on the day of the accident was initialled by the master and all 3 deck officers and the bridge control transfer procedure check was marked completed.   

Watchkeeping

Goliath’s SMS procedures relating to navigational watchkeeping were largely aligned with the requirements of the STCW Code[27] and other internationally recognised publications reflecting best practice on the subject, such as the Bridge Procedures Guide.[28]

The ship’s schedule of working arrangements described a traditional watchkeeping roster with one officer of the watch (OOW) on duty at any given time. In addition, the ship’s procedures called for a deck officer to assist with mooring and unmooring during port calls. While the role of the additional deck officer was usually allocated based on whether the mooring/unmooring operation occurred in the first or second half of the 4-hour watch, the roles of the additional officer and OOW were often allocated by agreement among the officers, or by their own initiative.

More importantly, the company’s standing orders also specified that the OOW was not to be changed over during a navigational manoeuvre. However, the definition of what constituted a ‘navigational manoeuvre’ was not specified.

Critical operations checklist

Goliath’s SMS defined critical tasks and operations as those with an initial risk rating of significant, high, or very high and that were performed more than 3 times a year. Every critical operation or task was to be supported by a checklist and other tools such as work permits, if required.

The risk assessment for the transfer of bridge controls between the wheelhouse and wing assessed the risk of an incorrect transfer of joystick steering to be ‘very low’. The risk of a similar incorrect transfer for the main engine was also assessed as ‘very low’ while the risk of an incorrect transfer of the bow thruster controls was assessed as ‘medium’. Nevertheless, a critical operations checklist was developed to provide a documented procedure for the transfer of bridge controls from the wheelhouse to the bridge wing conning station and vice versa. 

Goliath’s documented procedure for the transfer of bridge controls to the wing described a sequential series of 5 steps and checks to ensure a safe and successful transfer of steering control, summarised as follows:

• Bridge wing and wheelhouse joysticks to be set to the ‘ahead’ position.
• Change the steering mode selector switch from ‘manual steering’ to ‘joystick steering’.
• Confirm that the indicator light on the steering console indicates ‘Joystick control’.
• To take joystick control at the bridge or bridge wing joystick panels, press the green button.
• Test VecTwin joystick function to confirm rudder movement.

A laminated copy of the transfer procedure was kept in a folder on the bridge along with other critical operations checklists (Appendix A).

On the day of the accident, 4 out of the 5 steps and checks in the transfer of control were either not carried out or were overlooked. The joysticks were not set to the ahead position and the steering mode selector switch was not switched over to joystick steering. The 2 checks that may have been able to identify that the steering was not in the correct mode: the check of steering console ‘joystick control’ light and the test of the joystick to move the rudders, were not carried out by either the master or the second mate.

Bridge resource management

Bridge resource management (BRM) can be defined as the effective management and utilisation of all resources, human and technical, available to the bridge team to ensure the safe completion of the vessel’s voyage.[29] BRM provides a method of organising the best use of these resources to reduce the level of operational risk. Its key safety aspect is to put in place defences against ‘single-person errors’, with the aim of avoiding serious incidents.

Published AMSA guidance stated that BRM techniques were integral to responsible navigation practices and that well executed BRM techniques enhanced safety and reduced the risk of single person errors.[30] An AMSA marine notice[31] on the subject also noted that effective BRM should include the following considerations, among others:

• Navigational and operational tasks and responsibilities should be clearly defined and delegated.
• Navigational, operational, and general safety priorities should be set and consistently reviewed in the context of the prevailing circumstances and conditions.
• Masters and officers in charge of a navigational watch, who regularly undertake the same voyage/route, should be mindful of the risks associated with human performance limitations (such as the effects of fatigue and workload on vigilance and monitoring tasks) and familiarity, to retain resilience.

Goliath’s SMS highlighted the need for effective BRM. The SMS stated that the primary goal of BRM was the elimination of single-person errors and the procedures expanded on several elements of good BRM.

Bridge resource management is a broad topic covering many inter-related subjects. Key principles of effective BRM include situational awareness and shared mental models, closed loop communications, briefing and debriefing, challenge and response, delegation, and short-term strategies. The implementation of these principles on any ship’s bridge is the responsibility of all bridge team members.

Situation awareness and distraction

The concept of situation awareness is closely associated with the concept of a shared mental model. Situation awareness can be defined as ‘using cognitive processes to develop and maintain a mental model upon which decisions are made’ or more simply as knowing what is going on around you. In relation to a ship’s passage, situation awareness is dependent on working memory and is, therefore, affected by distraction, interruption, and stimulus overload.

Distractions during the completion of a task increase the likelihood of error. Distractions can be related to the task or from some external, unrelated source or event. An individual, or team, can also become completely occupied (fixated) with one event or task and therefore distracted from the overall objective. Minimising possible distractions is important for effective BRM.

Goliath’s SMS emphasised the need for officers to avoid distractions particularly during navigation in port or in restricted waters. In particular, the SMS advised that bridge team members should avoid getting engrossed in unimportant VHF radio communications.

At interview, Goliath’s master, chief mate and second mate, all reported being distracted by the VHF radio calls from the mooring lines boat. The evidence indicates that the relatively unimportant activity associated with responding to the radio calls and locating the mooring radio clearly occupied the officers’ attention and distracted them during the ship’s approach to the swing basin.

The process of transferring manoeuvring controls to the bridge wing was a highly regimented, often repeated activity for the second mate. The routine practice was to stand by the steering console and await the master’s order to transfer controls. Whenever the order was given, the second mate’s usual practice was to immediately reach out and use the steering mode selector switch to select joystick mode before proceeding to the wing to complete the transfer process.

The handover and distraction from the radio calls before the incident resulted in the second mate moving away from the usual station near the steering mode selector switch, disrupting the routine process for transferring controls. The second mate also recalled the master’s order on the day was unexpected (usually the second mate was ready and waiting for the order).  

Roles and responsibilities

A key element of effective BRM requires that all bridge team members involved are aware of their roles and responsibilities. Duties should be clearly and unambiguously assigned to specific individuals, who should confirm that they understand their responsibilities and tasks should be performed according to a clear order of priority. A mutual understanding of individual roles and responsibilities in executing the agreed plan makes it more likely that single-person errors are detected early.

On the morning of the accident, the chief mate took over as OOW from the third mate at about 1130. About 10 minutes later, the second mate came up to the bridge intending to relieve the chief mate. This occurred at what was a high workload phase of the passage. The ship was passing the narrowest section of the passage into port (known as ‘the cut’) and approaching an area where large ships, such as the Searoad Mersey II, were moored. This section of the passage also included the approach to the swing basin where several critical steps had to be taken, such as the initiation of the swing and the transfer of controls to the wing. During this time, radio calls from the mooring lines boat distracted Goliath’s officers. When the master ordered the transfer of controls, it was directed at the chief mate, but it was the second mate who acknowledged the order and moved to carry it out.

The second mate could not recall whether the watch was formally handed over, but in responding to the master’s order to transfer control, assumed that it had and that the chief mate was no longer required on the bridge. The chief mate also shared the same understanding of the handover.

The master and second mate also had a different understanding about who was responsible for testing the operation of the bridge wing joystick following the transfer of controls. The master believed that the checklist required the OOW transferring the controls to test the function of the joystick. However, the second mate was of the understanding that function tests of the propulsion and steering were to be left to the master. The master stated that the joystick was usually tested and its operation confirmed using the rudder angle indicators but, on the day of the collision, it was not.

Error management

The detection and management of errors is key to avoiding serious incidents. Error management seeks to detect errors and control their effects to minimise negative outcomes. It generally comprises measures designed to limit the occurrence of errors and their adverse consequences.

Goliath’s master and second mate both knew that the manoeuvre in the Devonport swing basin allowed little room for error due to factors such as the dimensions of the basin and environmental conditions. While the tide and weather at the time of the accident were relatively benign, once committed to the manoeuvre, it required the master’s sustained attention, and unrestricted use of all the ship’s manoeuvring aids and equipment.

The procedure for the transfer of controls provided a sequential series of steps and checks which, if carried out, offered the safest method for the transfer. For example, the procedure required that the autopilot panel be checked to ensure the ‘joystick control’ sign was illuminated, and that the joystick function was tested (by checking that the rudder angle indicators moved to match the joystick setting selected). These checks provided opportunities to identify errors and, if any were identified, for these to be quickly rectified as part of the transfer process.

Past incidents on board Goliath (see the section titled Previous VecTwin steering incidents) had demonstrated the value of having pre-planned locations where the steps and checks associated with the transfer of controls could be safely carried out and identified issues rectified before committing the ship to a manoeuvre. At the time of the incident, no such planned locations were identified or documented in the ship’s passage plans.

Complacency

Goliath’s master had worked on board the ship since 2002 and had been its regular master since 2008. In that time, the master estimated having successfully conducted over 1,000 port arrivals and departures using the VecTwin joystick system, in various states of weather, tide and light. A significant proportion of these manoeuvres were at Devonport. Similarly, the chief mate and second mate had also worked on board the ship for over a decade. In the second mate’s case, the entirety of their career as a deck officer had been spent on board Goliath, largely operating between the ports of Melbourne and Devonport.

Schager (2008)[32] states:

… it may be wise to avoid exaggerated emphasis on time only. Parallel with length of time or quantity of experience, we should also emphasise the content or quality of experience.

We seldom refer to the actual content of experience. It is possible that a person, even with long experience, hasn’t met many situations from which he/she could benefit professionally, nor faced many critical or hazardous situations. Most work on board a ship involves routine and repetitiveness in such a way that another year in the same position does not necessarily add much to anybody’s competence.

Some repetitive experience can also be detrimental as it induces a sense of routine, safety, and normality in an otherwise risky environment. Over time, an officer’s respect for what he or she is doing might decrease while the skills and quantity of experience increase.

This sense of extended experience in the task or role can build up and, over time, result in a false sense of security or an illusionary feeling sometimes called complacency.

According to Schager (2008), complacency may be defined as:

being a state of mind. It is an unconcerned attitude, e.g. in connection with the presence of danger and risk, where individuals behave and think in a routine-like mode, anticipating an uneventful and ordinary development of the present situation.

Schager also stated that:

Complacency is a passive state, not an active one, and no one chooses to be complacent. It creeps into one’s mind imperceptibly. Individuals are therefore unaware of being complacent and would, if asked, reassuringly deny it. Instead, individuals would probably justify their state of mind as rational, realistic, reasonable and in line with situational requirements, as well as a sign of experience.

Complacency can lead to such things as disbelief when something unexpected happens. It can lead to a false sense of security as well as a false sense that the situation is under control when it isn’t. It can furthermore lead to deficient risk assessment or to repress risks and not paying proper attention to what one is engaged in.

Table 1 below sets out the times and sequence of manoeuvring orders and other associated events in the lead up to the collision (based on engine telegraph and VDR data).

Table 1: Sequence of manoeuvring orders and events

Following the initial order of slow ahead and joystick setting of ‘astern to port’, the master found that the ship was not swinging as expected. In response to the ship’s increasing speed, the master set the joystick to ‘astern’ and increased engine rpm to ‘half ahead’, then ‘full ahead’ and ‘navigation ahead’, which further increased the speed.

In that time, it would have become increasingly obvious that there was something abnormal and a collision was becoming unavoidable. However, the master did not check the rudder angle indicators until 2.5 minutes after the first order of ‘slow ahead’ likely indicating that they were not unduly concerned with the progress of the manoeuvre.  

The risk of complacency in Goliath’s bridge team due to the frequent, repetitive nature of the team members was highlighted by a placard on the bridge that paraphrased Schager’s findings on the detrimental nature of repetitive tasks.

Emergency response

Goliath’s SMS included emergency contingency plans for collision. While the drills schedule did not specifically include a requirement to conduct drills for responding to a collision, there was evidence of several past oil spill drills which incorporated a collision in the drill scenario.

As the collision became imminent, no attempt was made to warn the tugs ahead or personnel in the vicinity (either by sounding the ship’s whistle or using the VHF radio). Following the collision, the master manoeuvred the ship away from the tugs, notified VTS and berthed the ship.

Post-collision activity on board was timely and appropriate and included the sounding of tanks, damage assessments and reporting. The general emergency alarm was not sounded however all the ship’s personnel were awake and alerted to the collision by other means.

Bridge resource management training

The importance of BRM and usefulness of BRM training is recognised internationally. The STCW Code (1995, as amended) required companies to develop and issue watchkeeping guidance to masters and officers based on bridge resource management principles.[33]

In 2010, the Manila amendments to the STCW Convention and Code introduced mandatory requirements for masters and deck officers to demonstrate knowledge of bridge resource management as part of their respective competency requirements.[34] While the Code allowed for competence to be demonstrated in various ways including through training or experience, companies were responsible for providing training in areas where seafarers did not have appropriate training or required refresher training.

Goliath’s SMS reflected this need for BRM training and required that all deck officers undertake formal BRM training (including simulator training) organised by the company or at a recognised shore establishment. The SMS also required that BRM refresher training be carried out at intervals not exceeding 3 years.

At the time of the collision, the master and second mate had not completed any formal BRM training. The chief mate had last undertaken BRM training about 13 years prior, in 2009.

Audits

On 18 November 2021, an annual internal audit was conducted on board Goliath to verify the ship’s compliance with the requirements of the ISM Code and Maritime Labour Convention,[35] among others. While there were no non-conformities identified, the audit resulted in one observation recommending that the ship’s master and chief mate attend BRM training as required in the ship’s SMS.[36] The observation also recommended that the company review the relevant sections of the SMS and include the requirement for regular BRM refresher training in the company’s training matrix.

TasPorts

Port of Devonport

The port of Devonport, located on Tasmania’s north coast, is a key entry point into Tasmania for passengers and cargo. The port accommodates berths for ro-ro vessels, tankers, ferries, and bulk carriers and serves as the Tasmanian port of call for the TT Line ferries between Melbourne, Victoria and Devonport, Tasmania. Each year between 3 and 4 million tonnes of cargo transit through the port. This includes the export of wheat, grain and cement and the import of fertilisers, fuel, and consumables.

The port of Devonport was managed and operated by the Tasmanian Ports Corporation (TasPorts); a Tasmanian State-owned company responsible for 11 Tasmanian ports including Devonport, and the Devonport airport. Among other things, TasPorts was responsible for the provision and maintenance of port infrastructure and navigational aids and the delivery of pilotage, towage, and vessel traffic services (see the section titled TasPorts).

Berth activity

Berth number Three West (berth 3W) was a general use berth used by Devonport’s tugs, other small commercial craft, and fishing vessels. These small vessels were often manned when alongside the berth.

On the day of the accident, there had been up to 4 persons scheduled to carry out maintenance and other routines on board the 2 tugs berthed together (Campbell Cove and York Cove). Shortly before the collision, coincidentally, all of them left the tugs for lunch or work elsewhere. Incidentally, at the time there were 3 persons on board Del Richey II, berthed immediately south of the tugs. Wilga, berthed just north of the 2 tugs, however, was not manned at the time.

Swing basin

A swing basin or turning basin is a designated body of water generally located in a port or shipping channel to allow ships to turn or reverse their direction of travel. Swing basins are a common feature of ports across Australia and the world. Devonport’s swing basin was used by all large ships that called at the port. The ships that used it most often were those that called regularly at Devonport including Goliath, the TT Line ferries and Searoad ships. As these ships called at the port regularly, they were generally also exempt from taking a pilot or tugs. Almost all ships turning in the swing basin, including Goliath, turned to the west (towards berth 3W).

TasPorts’ vessels

TasPorts owned, managed, and operated several vessels for the provision of harbour towage, pilotage, and mooring operations. At the time of the collision, Devonport was serviced by the tugs Wilga, Campbell Cove and York Cove, the mooring lines boats Dasher and Rubicon and the pilot launch Tamar.

York Cove (Figure 14) was an Australian-registered tug built in 1990 by Ryochu Kairiku Unyu, Japan. The tug operated under other names in Japan and the Republic of Korea until it arrived in Australia in 1998 and was re-named York Cove.

Figure 14: York Cove

Source: TasPorts

Campbell Cove (Figure 15) was an Australian-registered tug built in 1976 by Carrington Slipways in Newcastle, New South Wales. The tug initially operated at the port of Newcastle until about 1998 when it relocated to Devonport.

At the time of the collision, both tugs were classed with Lloyd’s Register.

Figure 15: Campbell Cove

Source: TasPorts

Port procedures manual

Tasmanian Ports Corporation (TasPorts) was engaged by Marine and Safety Tasmania (MAST) and the Environment Protection Authority Tasmania (EPA) to undertake specified marine safety functions. This was achieved through a deed of agreement between the 3 organisations and supported by delegations and authorisations under the relevant legislation to TasPorts and its employees. Under the deed, TasPorts was engaged to perform and deliver the following functions, among others:

• provision of port communication services
• maintenance of navigation aids
• provision of pilotage services
• preparation of a pilotage code
• training of pilots
• administration of pilotage exemption certificate requirements
• regulation enforcement in pilotage areas
• provision of emergency response services including oil spill response functions.

In carrying out the above functions, TasPorts developed relevant manuals and plans, including a ports procedures manual, marine pilotage code, crisis management manual, incident management plan and oil spill contingency plan.

The TasPorts port procedures manual provided information on pilotage, operating parameters in applicable ports, incident reporting, vessel traffic services (VTS) and emergency response. The manual and its procedures applied to the 5 Tasmanian primary ports (including Devonport) and 6 secondary ports.[37]

Vessel traffic service

TasPorts operated an authorised vessel traffic service (VTS), providing advisory information to vessels. The VTS also served as the primary communications centre for contact with vessels and was tasked with monitoring pilot exempt master requirements. TasPorts procedures required any vessel intending to enter, depart or move within the port to report to VTS. While there was no documented requirement in the port’s procedures for a radio check between the lines boat and ships, such checks are generally consistent with good practice.

On the day of the accident, Goliath reported to VTS as required before entering port limits. Shortly after, the mooring lines boat Rubicon reported to VTS when departing the wharf in preparation for Goliath’s berthing. Following this, Rubicon conducted a radio check with Goliath, first on VHF channel 14 and then on channel 6. Goliath’s deck officers reported that these radio calls were highly unusual. The master, chief mate and second mate also stated that they were unexpected and contributed to them being distracted during the approach to the swing basin.

Radio communications during previous port calls

The ATSB analysed recorded VTS radio traffic from 3 of Goliath’s previous arrivals at Devonport in January 2022 to determine whether a radio check between the ship and assigned mooring lines boat was standard practice.

During a port call on 22 January, there was no radio check conducted between Goliath and the assigned mooring lines boat Dasher. Similarly, on 18 January, there was no evidence of a radio check being conducted between the ship and Dasher.

During a port call on 9 January, there was a radio check conducted between Goliath and Dasher although, on this occasion, the radio check was initiated by Goliath’s master.[38] This radio check was probably prompted by a planned lifeboat drill on board the ship, which would require the assistance of the mooring lines boat.

In summary, there is some evidence to support Goliath’s officers’ accounts that the radio check from the mooring lines boat Rubicon was unusual and out of the ordinary. However, in submission, TasPorts stated that such radios checks were not an unusual occurrence.  

Incident reporting

TasPorts procedures required that all maritime incidents in pilotage areas be reported to MAST and VTS. If required, incidents would be investigated, and recommendations made to reduce the likelihood of a similar occurrence. Incident reports were also entered into the TasPorts incident management system and reviewed during 3-yearly risk assessments where they were used to inform improvements to the port procedures and pilotage manual. TasPorts was also required to retain accident and incident reports and records of other risk events for review by MAST during the annual port audit process.

During this investigation, TasPorts located, retrieved, and provided the ATSB with information on two previous incidents involving Goliath in Devonport (see the section titled Previous VecTwin steering incidents).

Risk assessment

As part of this investigation, the ATSB sought to assess whether the 2007 and 2009 Goliath incidents had any influence on the subsequent risk management in Devonport. In both the earlier incidents, Goliath narrowly avoided colliding with berth 3W and, in the 2009 incident, with Campbell Cove, which was moored alongside at berth 3W.

The ATSB sought the most recent TasPorts risk assessment as well as the last five 3-yearly risk assessments. The ATSB was provided with a pilotage and port risk assessment from 2019 and a safety review of Devonport pilotage services from 2008. There were no port or pilotage risk assessments completed between 2008 and 2019 and, there was no record available of risk assessments conducted prior to 2008.

2008 safety review

The 2008 safety review of pilotage services at Devonport and the associated workshop considered hazards associated with the provision of pilotage services to various berths and at various points of the pilotage. The review noted that berth number One West (Goliath’s berth) was the most exposed to the effects of tide and that there was potential for an incident if the ship’s exempt master were unfamiliar with the manoeuvring system. Control measures included the port’s pilotage exemption requirements and pilotage training.

The review identified that the physical constraints of the port made a number of berthing manoeuvres difficult. It recommended that smaller commercial vessels be relocated from berth number 3W to ease access to berth number Four West (used by larger bulk carriers) thereby improving safety and operability for the port. The review also suggested implementing a ‘large vessel approaching’ alert to warn small vessels operating near the mouth of the Mersey River of bow waves from passing large vessels.

2019 pilotage and port risk assessment

The 2019 risk assessment was aimed at reviewing the core hazard in several Tasmanian ports with the aim of ensuring that all reasonable precautions were in place. The core hazard for Devonport was assessed to be a grounding in the channel or swing basin. The assessment considered the potential threats that could lead to such a scenario as well as the control measures in place noting that these were different for piloted vessels and pilot exempt vessels.

The assessment concluded with a recommendation that all piloted vessels over 95 m in length use a tug for arrival and departure. There were no recommendations made regarding pilot exempt vessels and no consideration of any other scenarios.

VTS risk assessment

In addition to the 2008 and 2019 risk assessments, TasPorts also provided the ATSB with a risk assessment conducted in 2020 as part of TasPorts’ VTS accreditation process. As such, the assessment was focused on risks and risk controls related to aids to navigation rather than more general risks. The assessment included a consideration of past incidents and near misses however there was no evidence that Goliath’s 2007 and 2009 incidents were among those considered.

The assessment identified a scenario involving an ‘allision’[39] between a vessel manoeuvring in the swing basin and a wharf. The potential consequences identified included damage to the ship, infrastructure and environment, closure of the port and, notably, also collision with other vessels. Loss of life of personnel on board the vessels, however, was not among the consequences considered. Existing risk control measures included port and vessel procedures, VTS monitoring, navaids, pilot training and experience, and vessel audits. Nevertheless, the residual risk associated with this scenario was assessed as being ‘High’.[40]

The risk assessment also proposed further control measures which, if implemented, had the potential to further reduce the risk. These proposed further measures included the development of new procedures between VTS, pilots and pilot exempt masters, upgrades of VTS technology, continuous BRM training and VTS training. While TasPorts was subsequently authorised as a VTS provider, it is not known if any of the other additional proposed control measures were implemented or if the identified risk was re-assessed and found to have reduced.   

Pilotage in Devonport

The TasPorts port procedures manual laid out the operating parameters for ships calling at Devonport including pilotage and towage requirements, tidal restrictions, and exemptions.

Pilotage exemption

Generally, TasPorts rules required all vessels over 35 m in length to engage a pilot unless the vessel’s master held a valid pilotage exemption certificate (PEC). The TasPorts marine pilotage code set out the required standards for obtaining and renewing pilot licences and pilotage exemption certificates while MAST was the responsible authority for the issue of the licences and exemptions. TasPorts’ marine pilotage code acknowledged the importance of BRM and human factors in pilotage operations. The code required pilots to undertake BRM training prior to the issue of a pilot’s licence, but this requirement did not extend to the issue of pilot exemption certificates.

Goliath’s master held a valid pilotage exemption certificate for Devonport that was first obtained in 2008 and been regularly renewed. The initial application for the pilotage exemption required the master to complete 15 trips[41] with a pilot on board and to pass a local knowledge test for the port in addition to other requirements such as medical fitness and holding an approved seagoing qualification. PECs were valid for a period of 12 months and could be renewed for a further 12 months by completing at least one voyage in the pilotage area. Additionally, vessels over 75 m in length were required to undertake an audit of the ship’s port and pilotage related bridge documentation.

In June 2021, the harbour master instituted an additional requirement for masters seeking to renew a PEC. Exempt masters at several ports in Tasmania, including Devonport, were now required to undertake a check pilotage in addition to the bridge documentation audit. On 21 July 2021, Goliath’s master undertook a check pilotage for Devonport with a licenced check pilot. The check pilotage occurred during arrival at the port and included a bridge documentation audit.

The check pilot’s report noted that the ship’s passage plan and waypoints were consistent with the TasPorts approved plan, that closed loop communications and challenge and response mechanisms were used to effect on the bridge and that communications with VTS were as required. Overall, the report concluded that the master’s conduct of the pilotage was good and conducted in compliance with all relevant port regulations. Goliath’s master’s PEC was subsequently renewed for a further year based on having satisfactorily completed the check pilotage and bridge documentation audit.

Towage and tidal restrictions

TasPorts procedures required ships of Goliath’s size to engage at least 2 tugs for all arrivals and departures at Devonport although this requirement could be reduced if the ship had a bow thruster and/or a stern thruster. The procedures included a specific exemption for Goliath which could arrive or depart without towage (as it was equipped with a bow thruster and VecTwin steering) provided the ship’s under keel clearance was adequate. Nevertheless, Goliath’s master advised that the tug exemption did not prevent them from engaging tug assistance when conditions warranted it and that they had done so several times in the past without issue.

The procedures also stated that, when Goliath was under pilotage, the ‘middle 2 hours of the ebb tide’[42] were to be avoided and that the ship was not to berth ‘in the 'middle of the ebb tide’.[43] TasPorts advised that the tidal restriction on berthing was originally introduced in 2011. The restriction was only strictly applicable when the ship had a pilot on board and not when being piloted by an exempt master for whom it was only recommended guidance. Similarly, while Goliath’s passage plan and exempt master pilotage briefing card also documented the tidal restriction, the master indicated that it was only recommended guidance.

TasPorts advised that the origin and underpinning reasoning for these tidal restrictions could not be conclusively established, although it was probably associated with managing any difficulties encountered in berthing Goliath at berth number One West during an ebb tide.

Similar occurrences

Over the years, flag administrations and safety investigation agencies in Australia and overseas have investigated several incidents involving ships colliding with infrastructure and/or other vessels while manoeuvring in port. Common themes identified in these investigations include the effectiveness of BRM and the management of risk in ports.

Wahei Maru

On 7 November 2018, the Japanese-registered bulk carrier Wahei Maru collided with the wharf in the port of Kobe, Japan. The ship was equipped with a VecTwin steering system similar to Goliath’s. The incident resulted in damage to the ship’s bow and to the wharf.

The Japan Transport Safety Board’s (JTSB) investigation found that, on the approach to the wharf, the ship’s master had not changed the steering selector switch over to the VecTwin steering mode. As the ship closed on the wharf, the master used the joystick to select the ‘astern’ setting on the VecTwin rudders and gave increasing engine movements ahead in effort to slow the ship.

The master did not notice that the rudder indicators showed that both rudders were still in the ‘hover’ (neutral) position. The ship subsequently collided with the wharf at a speed of about 4.3 knots. The JTSB report noted that corrective action taken by the ship’s owner included the creation of a procedure for the changeover which was posted on the steering console and the installation of an audible alert which sounded briefly when the steering selector switch was set to VecTwin steering.  

Grand Rodosi

On 8 October 2010, the Liberian-registered bulk carrier Grand Rodosi, collided with the Australian fishing vessel Apollo S in Port Lincoln, South Australia. As a result of the collision, Apollo S, which was not manned at the time, was crushed against the wharf and sank shortly afterwards. Grand Rodosi sustained several relatively small holes in its bow shell plating.

The ATSB transport safety investigation report MO-2010-008 found that the collision occurred during the final turn to approach the berth because the ship’s main engine continued to run ahead despite astern engine telegraph orders by the pilot on the bridge. The main engine, which was being operated from the engine control room, was not allowed sufficient time for starting air to stop the ahead running engine. Consequently, when fuel was introduced into the engine, it continued to run ahead, despite the astern telegraph orders. The investigation also found that the incorrect operation of the engine was not identified by anyone on the ship’s bridge or in the engine room control room until after the collision and that BRM principles could have been better applied during the passage to the berth. Finally, the investigation found that while the port operator had identified several hazards and risk relevant to pilotage in Port Lincoln, the risk of a ship colliding with a wharf or another ship on an adjacent berth, while the berthing manoeuvre was being attempted, had not been identified.

Amarantos

On 10 April 2000, the Maltese-registered bulk carrier Amarantos collided with the wharf in Wallaroo, South Australia. The collision resulted in substantial damage to the wharf, piles, and the grain loader and its supporting superstructure on the wharf. The ship sustained minor non‑structural damage.

The ATSB transport safety investigation report 

found that the ship’s speed of approach was misjudged by the ship’s pilot on the final approach to the berth. The investigation found that the tugs assisting the ship lacked the power and manoeuvrability to arrest the ship’s momentum and that the angle of approach to the wharf left little room for error. The investigation also found that there was a lack of proper BRM on board and that there was no formal risk assessment completed for the berthing and unberthing of ships of Amarantos’ size in the port of Wallaroo.

Safety analysis

Introduction

On 28 January 2022, shortly before noon, the bulk carrier Goliath collided with the moored tugs York Cove and Campbell Cove in Devonport, Tasmania. The tugs, which were not manned at the time, sustained substantial damage, and subsequently sank. Authorities ashore initiated pollution control and oil spill recovery measures and the ensuing loss of fuel and other oils from the tugs were largely contained. Goliath sustained minor damage to its bow while the tugs were both subsequently declared a constructive total loss.

There were no technical failures or other mechanical issues which could have affected the operation of Goliath’s propulsion and steering systems. It was also considered unlikely that the ship’s officers were experiencing a level of fatigue known to affect performance. Therefore, the following analysis examines the events, actions and conditions leading up to the collision, including the management of bridge resources on board Goliath and the factors that influenced the behaviour of the personnel involved. The analysis also considers the management of risks associated with ships manoeuvring in swing basins in the context of operations at Devonport.  

Goliath

The collision

Goliath’s approach to its berth in Devonport involved turning the ship to starboard in the swing basin before it was brought alongside and moored. The practice on board was for the master to manoeuvre the ship through the swing and the subsequent berthing from the conning station on the port bridge wing. This required the transfer of propulsion and steering controls to the port bridge wing. As joystick control was the only available means of rudder control on the bridge wing, joystick steering mode needed to be selected before transferring steering control to the bridge wing.

However, on the day on the accident, when controls were transferred to the bridge wing, the steering mode selector switch was not switched over from manual steering to joystick steering. Consequently, the ship’s steering remained in manual steering mode, controlled by the wheel on the steering console inside the wheelhouse. The master though believed that the transfer of manoeuvring controls to the bridge wing had been successful, and therefore began to manoeuvre the ship using the bridge wing controls.

However, the master’s manoeuvring input did not have the desired effect because control of the rudders remained inside the wheelhouse. When the master realised that the turn was not progressing as expected and that the ship was moving ahead towards the berth, the master selected the ‘astern’ joystick setting and increased the engine setting to ‘half ahead’ in an attempt to slow the ship. This decision was consistent with the master’s belief that the ship was in joystick steering mode, although a glance at the rudder angle indicators would have made it apparent that the rudders were still amidships.

As Goliath advanced on the berth and the moored tugs at an increasing speed, the master continued to issue increasing engine telegraph orders ahead. The engine’s rpm was increased from ‘half ahead’ to ‘full ahead’ and finally to ‘navigation ahead’ to slow the ship. However, the ship’s speed kept increasing. Seconds before the collision, the master checked the rudder angle indicators and realised that they were still amidships. By this time, the collision was unavoidable.

Critical operations checklist

Goliath’s safety management system (SMS) required that a checklist be developed for operations which were conducted frequently, and which were considered to present a significant risk. The transfer of manoeuvring controls from the wheelhouse to the wing was one such operation for which a checklist had been developed.

The procedure for the transfer of steering controls involved a sequence of 5 actions and checks which, if carried out, would have ensured that control had been safely and effectively transferred to the wing. However, a critical step in the sequence—the switching of the steering selector switch to joystick steering mode—was not carried out. Two further checks, which could have alerted the officers to this oversight—a check of the autopilot panel and a function test of the VecTwin joystick, were also not carried out.

Bridge resource management training

The importance of effective bridge resource management (BRM) to the safe navigation of ships is a universally accepted tenet. Regulations not only require that guidance on watchkeeping and navigation be based on BRM principles but that knowledge of, and training in, BRM be part of competence requirements for masters and deck officers. The aim of these formal requirements is to ensure effective BRM by providing navigators, in addition to necessary behaviours, techniques and tools, a proper appreciation of the vital importance of BRM in preventing accidents. Goliath’s SMS recognised this importance and placed expectations on the ship’s officers to conduct the ship in accordance with best practice BRM principles. In support of this, the SMS also included requirements for deck officers to be provided with BRM training.

However, at the time of the accident, Goliath’s master and second mate had never undertaken BRM training. Although the chief mate had completed this training, it had been about 13 years prior. BRM training would have provided the officers with the techniques and tools to support effective BRM. That in turn would probably have resulted in the single person‑errors that contributed to this accident being detected and the collision prevented. 

Events and conditions on Goliath’s bridge

In the 20 minutes leading up to the collision, there were 2 changes of the officer of the watch (OOW). During the handover from the chief mate to the second mate, radio calls from the mooring lines boat distracted both officers and the master from what was otherwise a well-practiced manoeuvre that had been safely executed many times before. Less than a minute had passed after the last radio call before the master ordered the transfer of controls to the bridge wing.

The second mate was taken by surprise when the order was given, probably due to a loss of situation awareness with regard to the ship’s progress on the approach to the swing basin. The second mate immediately moved to respond to the master’s order but in doing so, overlooked the selection of the correct steering mode. This error probably occurred because, when they heard the order, they were not standing where they otherwise would have been (next to the steering console) had they not been distracted by their need to deal with the radio traffic.

The need to change the OOW during a pilotage is a foreseeable risk. The change involves potential disruption to the bridge team and distraction of personnel. There is also the risk of loss of information during the handover, a loss of the shared mental model and loss of situation awareness. The company’s standing order that changes to the OOW were not to occur during a manoeuvre primarily sought to mitigate that risk. However, the definition of what constituted a manoeuvre was open to interpretation, and consequently this order was not effectively implemented on board. 

Following the (incomplete) transfer of manoeuvring controls, the master began manoeuvring the ship in the belief that all controls had been transferred successfully. The master and second mate had conflicting understandings of who was responsible for the function test of the joystick that was required by the transfer of bridge controls checklist. Consequently, checks in the wheelhouse and on the bridge wing that could have identified the error were not carried out by either officer.

Good practice dictated that the master visually check any rudder angle order issued against the rudder angle indicator. However, this did not occur until collision was imminent, despite the mounting evidence that their manoeuvring inputs were not having the desired effect. A check of the rudder indicators at any time after the transfer of controls would have immediately alerted the officers to the situation. This would have allowed time to either select the correct steering mode, operate the main engine astern conventionally or take other action to minimise damage and to alert other port users to the situation.

It is also possible that the master’s long association with the ship, calls at the same ports, experience in the role, and repetitive use of the VecTwin joystick system without incident, influenced their perception of the risk involved with the manoeuvre. The master’s use of increasing engine orders ahead to slow the ship, the failure to check the rudder angle indicators, to use conventional astern propulsion or to sound the ship’s whistle indicate that they probably believed that the situation was under control almost until the collision. This points to a confidence in the conduct of the manoeuvre and a false sense of security in the unerring operation of the VecTwin system that was at odds with the actual risks involved. 

Past incidents

Goliath had previously been involved in 2 incidents involving the VecTwin joystick steering system and its use. On both occasions, there were several circumstances that were similar to this accident. Both earlier incidents occurred during arrival at Devonport, while the ship was manoeuvring in the swing basin, and involved an ineffective transfer of steering control to the bridge wing joystick. Both incidents resulted in the ship making contact with the shore or the wharf in the vicinity of berth number Three West, with the ship narrowly avoided colliding with Campbell Cove in one instance.

While acknowledging that Goliath’s current managers were not the ship’s managers at the time, these earlier incidents, and the potential lessons learned, offered valuable opportunities to prevent future incidents due to similar contributing factors. They also offered opportunities to identify other factors and improvements that could contribute to the safety of future operations and a reduction of risk.

Safety action that resulted from these earlier incidents included the drafting of a procedure for the transfer of controls and for function testing of the bridge wing joystick. However, other proposed safety action such as amending passage plans to identify and document safe locations for the transfer of controls or for providing refresher bridge resource management training were not implemented. The incidents also offered an opportunity to assess the design of the joystick and its indicator lights from a human centric point of view.    

Joystick design

Goliath’s master and other deck officers had an incorrect understanding of the significance of the joystick panel indicator lights. The master believed that the illumination of the green ‘joystick on’ light signified that the joystick could be used to operate the ship’s rudders. They also understood that this must have meant that the ship was in joystick steering mode, that is, the illumination of the ‘joystick on’ light was confirmation that joystick steering mode had been selected on the steering console.

However, the design of the system was such that the illumination of the ‘joystick on’ light bore no relation to the steering mode selected and therefore provided no positive indication that the correct steering mode had been selected.

TasPorts

An analysis of risk assessments from TasPorts show that elements of the risks associated with vessels in the swing basin were identified, albeit in the context of risks to the provision of port services. However, specific risks to personnel on board vessels alongside at berth 3W did not appear to have been considered. The potential for incidents involving vessels manoeuvring in the swing basin and the risks they posed to vessels alongside at berth number 3W was not unforeseeable. Records show at least 2 previous incidents involving Goliath, where the ship narrowly avoided colliding with berth 3W (including one instance with Campbell Cove alongside).

In Devonport, pilot- and tug-exempt ships such as Goliath, the TT Line ferries and Searoad ships regularly utilise the swing basin to manoeuvre in the port. The risk control measures in place at Devonport to manage the risks associated with ships manoeuvring in the port generally relied on pilotage services, the port’s pilotage exemption requirements (in the case of pilot exempt masters), VTS monitoring, effective BRM and port procedures. However, the fact that the collision between Goliath and the tugs did not result in injury to personnel who may have been on board the tugs or adjacent vessels is largely attributable to good fortune rather than effective risk management.

The existence and use of swing basins as well as the associated risks to vessels in the vicinity and to personnel on board are not unique to Devonport. However, the defined scope of this investigation precluded a more comprehensive analysis of incidents, risks, and risk controls associated with vessels manoeuvring in swing basins in Devonport and more widely in ports across Australia.

Nevertheless, consideration of port risks relating to personnel and small vessels in the vicinity of swing basins and other areas where larger vessels manoeuvre would likely improve the safety of operations.

Findings

From the evidence available, the following findings are made with respect to the collision involving the bulk carrier Goliath and tugs York Cove and Campbell Cove, in Devonport, Tasmania on 28 January 2022.

Contributing factors

• During the transfer of steering and propulsion controls from Goliath’s wheelhouse to the port bridge wing conning station, the steering mode selector switch was not changed from manual steering to joystick steering mode. Consequently, control of the rudders remained at the wheel inside the wheelhouse.
• On transferring to the bridge wing, Goliath's master manoeuvred the ship in the belief that the ship’s steering was in joystick steering mode (which allowed for the use of ahead inputs on the main engine to generate astern thrust). Consequently, as the ship closed on the tugs and wharf, the master’s efforts to slow the ship and avoid collision by using ahead inputs on the main engine had the opposite effect of increasing the ship’s speed, resulting in the collision with the tugs.
• Actions and checks for the effective transfer of steering controls from one conning station to another, documented in the safety management system’s critical operations checklist for transfer of bridge controls, were not fully complied with. Had the actions and checks described in the checklist been carried out, it is likely that the failure to select the correct steering mode would not have occurred or been identified in time to be rectified.
• Bridge resource management was ineffective because:
  • The chief mate and second mate were engaged in watch hand over activity in the lead up to a critical phase of the passage
  • all the officers on the bridge were distracted by the unexpected and relatively unimportant radio traffic with the mooring line boat
  • at the time the master issued the order to transfer controls to the bridge wing, there was no consistent understanding of whether the watch hand over had been completed and which of the mates was assisting the master
  • neither the master nor the second mate identified that the correct steering mode had not been selected, that steering control remained at the wheel or that the master’s joystick rudder angle and main engine telegraph orders were not having the desired effect until it was too late to avoid the collision
  • the master’s perception of the risk involved with the manoeuvre and the transfer of controls had probably diminished over time due to complacency resulting from extended service on board.
• Neither the master nor the second mate had undertaken required bridge resource management training. This probably contributed to the ineffective implementation of bridge resource management on board, which resulted in the single person errors that contributed to this accident not being detected. (Safety issue)

Other factors that increased risk

• Corrective action, proposed as a result of a previous incident involving factors related to the use of the joystick steering system in 2009 (and while under the ship’s previous management), were not reflected in Goliath's safety management system and had not been fully implemented on board. This lost opportunity to learn and implement corrective action increased the risk of future similar incidents.
• The illumination of the joystick steering panel’s ‘joystick on’ light indicated which panel was selected (or last selected) for use and bore no relation to the steering mode selected. This increased risk as it was misleading and contrary to the understanding of the ship’s officers who believed that the illumination of the light was only possible when the joystick steering mode was selected. (Safety issue)
• TasPorts’ risk assessments for Devonport included consideration of a potential collision between ships manoeuvring in the swing basin and vessels moored in the vicinity, however, the risks to personnel on board those moored vessels and possible risk control measures were not considered.

Safety issues and actions

Bridge resource management training

Safety issue number: MO-2022-002-SI-01

Safety issue description: Neither the master nor the second mate had undertaken required bridge resource management training. This probably contributed to the ineffective implementation of bridge resource management on board, which resulted in the single person errors that contributed to this accident not being detected.

Design of joystick indicator light

Safety issue number: MO-2022-002-SI-02

Safety issue description: The illumination of the joystick steering panel’s ‘joystick on’ light indicated which panel was selected (or last selected) for use and bore no relation to the steering mode selected. This increased risk as it was misleading and contrary to the understanding of the ship’s officers who believed that the illumination of the light was only possible when the joystick steering mode was selected.

Safety action not associated with an identified safety issue

Additional safety action by CSL Australia

On 3 June 2022, CSL Australia advised the ATSB of amendments made to Goliath’s safety management system procedures for navigation, passage planning, watchkeeping, master/pilot exchange and the bridge arrival and departure checklists. The amendments included a requirement for watch handovers during pilotage to be planned and agreed upon by the master in advance and for safe areas to be identified for such handovers to take place.

Additional safety action by TasPorts

On 12 December 2022, TasPorts advised the ATSB that the port’s investigation into the accident resulted in several recommendations for proposed safety action. These included recommendations to:

• amend the port procedures manual to require that Goliath engage a tug and to prohibit the use of the ship’s VecTwin steering system when berthing in Devonport
• amend the port procedures manual and other port rules to prohibit Goliath from swinging on arrival if vessels are alongside at berth number Three West
• review the risk assessment for the port of Devonport with a view to identifying additional mitigation measures
• review Pilotage code to include emergency training for pilotage exemptions
• review and update the port procedures manual to clarify the requirements for Goliath’s entry, pilotage, manoeuvring and berthing in the port including clarifying the applicability of any tidal restrictions.

Glossary

AIS                   Automatic Identification System

AMSA               Australian Maritime Safety Authority

BRM                 Bridge resource management

CSL                  Canada Steamship Lines

ECDIS              Electronic chart display and information system

EPA                 Environment Protection Authority

HSEQ               Health safety environment and quality

IR                     Integrated Rating. Integrated ratings are qualified to perform the duties of both an able seaman and an engine rating.

ISM                  International Management Code for the Safe Operation of Ships and for Pollution Prevention, 1995, as amended

MAST               Marine and Safety Tasmania

NFU                  Non-follow-up steering

PEC                 Pilotage exemption certificate

RPM                 Revolutions per minute

SMS                 Safety management system

SOLAS             The International Convention for the Safety of Life at Sea, 1974, as amended

STCW               Standards of Training, Certification and Watchkeeping for Seafarers, 1995, as amended

TasPlan            Tasmanian Marine Oil and Chemical Spill Contingency Plan

TasPorts           Tasmanian Ports Corporation

VDR                 Voyage data recorder

VHF                  Very high frequency (radio)

VTS                  Vessel Traffic Service

Sources and submissions

Sources of information

The sources of information during the investigation included the:

• Australian Maritime Safety Authority
• Bureau of Meteorology
• CSL Australia
• directly involved officers and crew of Goliath
• Environment Protection Authority Tasmania
• investigation reports from the Japan Transport Safety Board
• Marine and Safety Tasmania
• recorded information from Goliath’s voyage data recorder (VDR)
• records, documents, manuals, and logbooks from Goliath
• Tasmanian Ports Corporation
• the master of the fishing vessel Del Richey II.

References

Australian Maritime Safety Authority, 2020, Pilot advisory note, Bridge resource management and the reduction of single person errors—advisory note, Canberra, Australia.

Australian Maritime Safety Authority, 2021, Marine Notice 07/2021 Responsible navigational practices, Canberra, Australia.

Australian Transport Safety Bureau, Report No. 157, Contact between the Maltese flag bulk cargo vessel Amarantos, Wallaroo, SA, 10 April 2000, ATSB, 2000.

Australian Transport Safety Bureau, Report No. MO-2010-008, Collision between the Liberian registered bulk carrier Grand Rodosi and the Australian registered fishing vessel Apollo S in Port Lincoln, SA, 8 October 2010, ATSB, 2012.

Cannon-Bowers, JA, Salas, E, Converse, S A (1993). Shared mental models in expert team decision making. In Mathieu, J, Heffner, T, Goodwin, G, Salas, E, Cannon-Bowers, J. The influence of Shared Mental Models on Team Process and Performance. Journal of Applied Psychology 2000, Vol 85, No. 2, pp. 273-283. American Psychological Association Inc, 2000.

Focus on Bridge Resource Management. Washington State Department of Ecology, 2007.

International Chamber of Shipping 2016, Bridge Procedures Guide, Marisec Publications, London.

International Maritime Organisation (IMO), Standards of Training, Certification and Watchkeeping for Seafarers (STCW) Code, 1995, as amended, IMO, London.

International Maritime Organization (IMO) 1995, International Management Code for the Safe Operation of Ships and for Pollution Prevention (ISM Code) as amended, IMO, London.

International Maritime Organization (IMO) 2014, The International Convention for the Safety of Life at Sea (SOLAS) 1974 as amended, IMO, London.

International Transport Workers’ Federation, STCW A guide for seafarers, ITF, London.

Schager, B. Human Error in the Maritime Industry – How to understand, detect and cope. Marine Profile, Sweden, 2008.

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:

• directly involved officers and crew of Goliath
• CSL Australia
• Australian Maritime Safety Authority
• Environment Protection Authority Tasmania
• Tasmanian Ports Corporation
• Marine and Safety Tasmania.

Submissions were received from:

• Goliath’s master and second mate
• CSL Australia
• Australian Maritime Safety Authority
• Environment Protection Authority Tasmania
• Tasmanian Ports Corporation
• Marine and Safety Tasmania.

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

Appendices

Appendix A

Critical operations checklist – Bridge controls changeover procedure

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]     A constructive total loss, in the case of damage to a ship, occurs when the cost of repairing the damage under its insurance terms would exceed the value of the ship when repaired.

[2]     Eastern Daylight-saving Time (EDT): Coordinated Universal Time (UTC) + 11 hours.

[3]     The testing of the steering gear was done with the steering in manual mode and with all four steering motors running. The test involved the officer of the watch (third mate) on the bridge applying up to 20° of helm to either side, on both rudders, and the deck cadet physically verifying the rudder movements in the steering gear room.

[4]     Integrated ratings are qualified to perform the duties of both an able seaman and an engine rating.

[5]     Predicted high water was at 0741 with a height of tide of 3.42 m above chart datum.

[6]     VHF channel 16 (156.800 MHz) is the international distress, safety and calling frequency. All VHF-equipped vessels are required to maintain a continuous listening watch on this frequency at sea.

[7]     VHF channel 6 was the Devonport VHF working channel used for pilotage, towage, and berthing communications.

[8]     A voyage data recorder is designed to collect and store data from various shipboard systems in compliance with SOLAS requirements.

[9]     In VecTwin steering (joystick) mode, the ‘astern to port’ joystick setting sets the port rudder to a rudder angle of 105° to port and the starboard rudder to a rudder angle of 75° to starboard. In this setting, ahead movements of the ship’s main engine could be used to generate astern thrust and swing its stern to port.

[10]    In VecTwin steering (joystick) mode, the ‘astern’ joystick setting sets the port rudder to a rudder angle of 105° to port and the starboard rudder to a rudder angle of 105° to starboard. In this setting, ahead movements of the ship’s main engine could be used to generate astern thrust

[11]    Campbell Cove was moored with its head to the north while York Cove was moored outboard of Campbell Cove with its head to the south.

[12]    The Tasmanian Ports Corporation (TasPorts) is Tasmania’s State-owned company responsible for the operation and management of eleven Tasmanian ports (including Devonport).

[13]    The harbour master and deputy harbour master are responsible for overseeing navigational safety and ensuring compliance with regulatory and statutory requirements for the 11 Tasmanian ports operated by TasPorts.

[14]    The TasPorts state operations centre (TSOC) was the main control hub for all port security functions including monitoring of CCTV, alarms, and other functions.

[15]    A detention is an intervention action taken by the port State to ensure that the ship will not sail until it can proceed to sea without presenting a danger to the ship or persons on board, or without presenting an unreasonable threat of harm to the marine environment, regardless of whether such action affects the scheduled departure of the ship.

[16]    The Environment Protection Authority (EPA) is Tasmania's independent statutory environmental regulator.

[17]    Marine and Safety Tasmania (MAST) is a statutory authority established to ensure the safe operation of vessels, provide, and manage marine facilities, and manage environmental issues relating to vessels in Tasmania.

[18]    The person with the overall responsibility for ensuring that a response to a tier 2/3 incident is managed and coordinated appropriately and with the authority to direct response and clean-up arrangements at a management level.

[19]    According to the Tasmanian Marine Oil and Chemical Spill Contingency Plan (TasPlan) and the National Plan for Maritime Environmental Emergencies (National Plan), level 2 Incidents are more complex in size, duration, resource management and risk and may require deployment of jurisdiction resources beyond the initial response.

[20]    Pursuant to section 51(1) of Tasmania’s Marine-related Incidents (MARPOL Implementation) Act 2020.

[21]    International Maritime Organization, 2014, The International Convention for the Safety of Life at Sea (SOLAS) 1974 as amended, IMO, London.

[22]    International Maritime Organisation, The International Convention on Standards of Training, Certification and Watchkeeping for Seafarers 1978, as amended, IMO, London.

[23]    Marine Orders, also described as regulatory instruments or legislative regulations, are legal instruments made by AMSA pursuant to powers under Commonwealth legislation.

[24]    In non-follow-up (NFU) mode, the movement of rudder to port or starboard is controlled using a lever. The lever is released when the rudder reaches the required angle.

[25]    At the time of the collision, the starboard bridge wing joystick control station was not in commission.

[26]    International Maritime Organization, 2018, International Management Code for the Safe Operation of ships and for Pollution Prevention (ISM Code) as amended, IMO, London.

[27]    International Maritime Organisation, Standards of Training, Certification and Watchkeeping for Seafarers (STCW) Code, 1995, as amended, IMO, London.

[28]    International Chamber of Shipping 2016, Bridge Procedures Guide, Marisec Publications, London.

[29]    Focus on Bridge Resource Management. Washington State Department of Ecology, 2007.

[30]    Australian Maritime Safety Authority, 2020, Pilot advisory note, Bridge resource management and the reduction of single person errors—advisory note, Canberra, Australia.

[31]    Australian Maritime Safety Authority, 2021, Marine Notice 07/2021 Responsible navigational practices, Canberra, Australia.

[32]    Schager, B. Human Error in the Maritime Industry – How to understand, detect and cope. Marine Profile, Sweden, 2008.

[33]    STCW Code (1995, as amended), Section B, Chapter VIII/2, Part 3-1 – Guidance on keeping a navigational watch, Bridge resource management.

[34]    The STCW Convention prescribes minimum standards relating to training, certification and watchkeeping for seafarers which countries are obliged to meet or exceed. The STCW Code supports, explains, and expands on the basic requirements contained in the Convention’s regulations. Part A of the Code is mandatory while Part B of the Code contains recommended guidance intended to help implement the Convention.

[35]    The Maritime Labour Convention was established in 2006 under the International Labour Organization to consolidate all up-to-date standards of existing international maritime labour conventions and recommendations and introduced modern standards for the working and living conditions of seafarers. The convention came into force in 2013.

[36]    With respect to the ISM Code, a ‘non-conformity’ means an observed situation where objective evidence indicates the non-fulfillment of a specified requirement and an ‘observation’ means a statement of fact made during a safety management audit and substantiated by objective evidence.

[37]    The applicable ports were defined in the Marine and Safety (Pilotage and Navigation) Regulations 2017 (TAS).

[38]    The master at the time was a different officer and not the person who was master on the day of the accident.

[39]    An ‘allision’ is a term used to describe a collision between a vessel and a fixed object or structure or with another stationary vessel.

[40]    High risk was defined as a level of risk for which substantial and urgent efforts must be made to reduce it to ‘ALARP’ [As low as reasonably practicable] levels within a defined time period. Significant funding was likely to be required and services may need to be suspended or restricted until risk control options had been actioned.

[41]    A ‘trip’ meant a single voyage into or out of a port or marine pilotage area.

[42]    For example, on the day of the accident, when high water was at 0741 and low water was at 1422, TasPorts identified the middle 2 hours of the ebb tide as being between 1001 and 1201.

[43]    The procedures defined the middle of the ebb tide to be the period beginning 1.5 hours after high water and ending 2.5 hours before low water. For example, on the day of the accident, Goliath arrived on an ebb tide with the ‘middle of the tide’ lasting from 0911 to 1152.   

Safety summary

What was done

As part of the investigation into the mid-air collision involving Piper PA-44-180 Seminole, VH-JQF, and Beech D95A Travel Air, VH-AEM, near Mangalore Airport, Victoria, on 19 February 2020 (AO-2020-012) the ATSB identified concerns around the pilots' ability to visually identify the other aircraft in time to take avoiding action.

In response to this, the ATSB initiated an aircraft performance and cockpit visibility study to determine at what times the aircraft may have been visible to the crew of the opposing aircraft.

This assessment involved the review of available literature covering the see and avoid concept, the techniques used to assess visibility and analysis of the recorded automatic dependent surveillance broadcast (ADS-B) data from each aircraft. Exemplar aircraft were modelled, and this information was used to calculate the positions of aircraft structure relative to the pilots’ eye positions. This, combined with the analysed ADS-B data, was used to perform an assessment of the size and location of the other aircraft in the pilots’ field of view. Following this an assessment of the benefits of ADS-B IN systems for the purposes of enhancing a pilot’s mental model was undertaken. Finally, using this information an animation was developed that represented the flights from the perspective of each of the pilots involved. The animation also includes a cockpit display of traffic information to demonstrate the benefits ADS-B IN information could have provided for the early detection of the conflicting traffic.

What the ATSB found

The study found that the pilots of both aircraft were unlikely to have acquired the other aircraft visually due to meteorological factors, aircraft closing speed and shielding of the opposing aircraft by cockpit structure with 2 of the 4 pilots likely having the opposing aircraft shielded from their view at key moments. The ATSB analysis indicated that even in clear conditions, more favourable to visual acquisition, the closing speed and shielding by the aircraft structure would have limited opportunities to acquire the other aircraft.

Neither accident aircraft was equipped with ADS-B IN systems. The study shows that had the aircraft been equipped with this technology the pilots would have been alerted to the position of the other aircraft much earlier than by visual acquisition. Both a cockpit display of traffic information with an ADS-B traffic alerting system or an electronic conspicuity device connected to an electronic flight bag application could have provided this. While effective radio communication remains the primary means of self-separation in non-controlled airspace, the targeted and accurate information provided by ADS-B IN can provide the pilot significant assistance.

Safety message

To ensure that a pilot’s mental models of conflicting traffic is accurate, they should use all available information, including the rules of the air, radio, air traffic control (ATC) services and visual scanning to locate and separate from other traffic. Where a visual scan is being used, pilots should always remember to move the whole head to avoid approaching traffic being shielded behind structure within their field of view.

The proliferation of relatively low-cost ADS-B IN and ADS-B OUT equipment, whether inbuilt or in conjunction with electronic flight bag applications on personal electronic devices can provide a significant improvement in this capability. With ADS-B IN and ADS-B OUT installed, aircraft can be more certain of the location of traffic, particularly outside ATC radar and ADS-B ground station coverage areas.

Acknowledgements

The ATSB acknowledges the assistance of the United States National Transportation Safety Board Office of Research and Engineering, the RTCA (formerly Radio Technical Commission for Aeronautics), Moorabbin Air Services and Yarra Valley Aviation in the development and preparation of this study.

Introduction

Background

On 19 February 2020 Piper PA-44-180 Seminole, VH-JQF (JQF), and Beech D95A Travel Air, VH-AEM (AEM) collided in mid‑air 8 km south of Mangalore Airport, Victoria. At the time of the collision AEM was inbound to Mangalore Airport on an instrument rating training flight, with an instrument rating student and an instructor on board. JQF had recently departed Mangalore Airport for an instrument rating examination flight with a pilot under examination and an examiner on board.

This was the first mid-air collision between 2 civil‑registered aircraft operating under the instrument flight rules (IFR) in Australia. As the collision was outside of controlled airspace, air traffic control (ATC) was required to provide traffic information on other IFR aircraft, but not ensure separation. This meant that the pilots were self-separating using radio communications and, where possible, the ’see and avoid’ principle. A key part of the investigation was to determine the likelihood that the pilots of each aircraft could detect the other in sufficient time to take avoiding action. Multiple papers and studies conducted by agencies and organisations around the world, including the ATSB, have identified significant limitations with the ’see and avoid’ principle.

The ATSB sought to establish what influence the position and performance of the aircraft, the cockpit structure and human performance limitations had on the pilots’ ability to detect traffic. Further, the ATSB sought to determine what effect an automatic dependent surveillance broadcast (ADS-B) IN system would have had on the pilots’ ability to detect traffic as they converged.

In Australia IFR aircraft are required to be equipped with ADS-B OUT, primarily to increase ATC surveillance service coverage. ADS-B OUT data can also be received and processed for traffic information by aircraft fitted with ADS-B IN systems. Neither aircraft involved in this accident were fitted with ADS-B IN equipment.

The ATSB consulted the United States National Transportation Safety Board (NTSB) Office of Research and Engineering following their study of a mid-air collision that occurred near Ketchikan, Alaska. That study included an animation that replicated the flight paths and view from each aircrafts’ cockpit and simulated the aircrafts’ ADS-B IN traffic displays.

That NTSB study was one of many they performed looking at the effects of cockpit visibility and aircraft performance in mid-air collisions. The ATSB sought the guidance of performance specialists at the NTSB as to the process used to carry out their study. Based on that advice the ATSB gathered location, aircraft and performance data from operators, manufacturers, Airservices Australia (Airservices), and the Civil Aviation Safety Authority (CASA), to conduct this study.

Aim

The aircraft performance and cockpit visibility study sought to understand the performance characteristics of AEM and JQF in the lead up to the mid-air collision to produce a virtual recreation of the flights. Human performance and aircraft structural obscuration were then considered to determine the pilots’ ability to detect the other aircraft. The study also considered the role an ADS-B IN system could have played in increasing the opportunity for timely detection of traffic.

Scope

This study was conducted as part of the analysis for investigation AO-2020-012 Mid-air collision involving Piper PA-44-180 Seminole, VH-JQF and Beech D95A Travel Air, VH-AEM, 8 km south of Mangalore Airport, Victoria on 19 February 2020. The flight data used for the study was primarily the raw ADS-B data broadcast from each of the aircraft.

The investigation found that the collision likely occurred in or close to cloud, limiting the ability of the pilots in each aircraft seeing the other aircraft. However, this study also considered the likelihood for visual acquisition had better weather conditions existed.

Methodology

The methodology for this study is based on similar studies performed by the NTSB Office of Research and Engineering. The completion of the study consisted of the following steps:

1. A literature review looking at available information related to human visibility and perception characteristics, aircraft tracking and collision avoidance technologies and aircraft specifications.
2. Calculation of the aircrafts’ position and performance characteristics using applicable aircraft information and available recorded data, in this case ADS-B data.
3. Development of scale 3-dimensional models of the internal and external structures of representative aircraft using laser scanning technologies and determination of the pilot’s approximate eye position within each model.
4. Development of 2-dimensional representations of each pilot’s view of the aircraft structure. The relative position of the other aircraft was located on this representation to determine when it would have been shielded from the pilot’s view.
5. Based on the literature review and consultation with ATSB human factors specialists, human performance was considered to determine where and when the pilots may have been able to detect the other aircraft.
6. Additional technologies were explored to establish what role these could have played in increasing the pilot’s ability to detect the other aircraft prior to the collision.
7. Finally, an animation was developed using position and performance data showing the cockpit view for both pilots in each aircraft overlaid with exemplar cockpit traffic displays and alerts (not fitted to the accident aircraft). This was supplemented by recorded air traffic control data.

Notes

• Throughout this report standard aviation units are used unless specifically stated. These units are nautical miles for distance, feet for altitude and knots (nautical miles per hour) for speed.
• All times in this report are referenced to Eastern Daylight‑saving Time (EDT - Universal Co‑ordinated Time (UTC) + 11 hours), which was the accident location time zone.
• This report is intended to support the AO-2020-012 investigation report and should be read in conjunction with, and in the context of, that report. It relies and expands on factual content presented in that report.
• Unless specifically stated otherwise, any reference to the ’investigation report’ should be taken as referring to the ATSB AO-2020-012 investigation report. 

Background

Aircraft Information

AEM

As described in the aircraft information section of the investigation report:

The Beech D95A Travel Air is a 4 to 6 seat, low wing, retractable-tricycle-undercarriage aircraft fitted with 2 180 horsepower Textron Lycoming IO-360-B1B reciprocating engines driving constant speed, two-bladed propellers.

AEM [Figure 2] was manufactured in the United States in 1966 with serial number TD 682. It was first registered in Australia in 1967, and prior to the departure from Tyabb, the aircraft had accumulated 7,400.3 hours in service.

The aircraft was certified for IFR and charter operations and was equipped with dual controls for the student and instructor. The aircraft was also equipped with a Garmin GNS530 radio communication and GNSS navigation system, together with a second communication radio. The aircraft was also fitted with a Garmin GTX335 ADS-B OUT transponder. AEM did not have any ADS-B receiving equipment.

To determine where and when JQF would have been in the view of AEM’s pilots, the positions of both aircraft, AEM’s Euler angles ^[1] (pitch, roll and yaw) and the location of AEM’s cockpit structure, relative to the pilots’ eye positions, were required.

The positions of JQF and AEM were calculated from available ADS-B data (see the section titled Position estimation) and the location of each aircraft’s cockpit structure was developed from laser scans of exemplar aircraft (see the section titled Aircraft modelling). No recorded data was available for the Euler angles of either aircraft. These were calculated from the aircraft’s position and a range of aerodynamic and physical properties of the aircraft (see the section titled Calculation of Euler angles). These properties included aircraft weight, wing area and the lift co-efficient as a function of the angle of attack (lift-curve). Figure 1 shows the 3‑view diagram of the Travel Air from the aircraft’s maintenance manual.

Figure 1: Travel Air 3‑view diagram

Source: Aircraft manufacturer

Figure 2: Travel Air VH-AEM

Source: Aircraft operator, annotated by the ATSB.

Lighting

The initial airworthiness requirements for the Travel Air outlined the type, intensity, colour, and visibility arcs, in both the horizontal and vertical planes, of the various position lights around the aircraft. The ATSB confirmed that the lighting installed on AEM was in accordance with these requirements.

Position lights, also referred to as navigation lights, are primarily designed for identifying location and orientation at night and their usefulness during the day, is relatively low due to their low intensity. Therefore, they were not expected to be operational at the time of the collision.

In addition to position lights AEM was equipped with upper and lower beacons (flashing red lights). These beacons were required by regulation 196 of the Australian Civil Aviation Regulations (CAR) to be used when an aircraft is in flight or operating on the manoeuvring area of an aerodrome at night or in low visibility. However, the performance standards or intensity of this lighting was not defined. As a result, its effectiveness in aiding visual acquisition was not able to be determined.

The aircraft was not fitted with strobe lights. No further information was available as to the lighting that was installed on the aircraft or its intensity at the time of the accident.

Speed slope windscreen

The factory design of the Travel Air included a two-piece windscreen with a defined centre spline separating left and right panels. Since the introduction of the aircraft, the United States Federal Aviation Administration (FAA) has issued multiple supplemental type certificates (STC) relating to the replacement of the windscreen with a single piece, as was standard for later models of this type of aircraft.

Sometime prior to 1976 AEM was modified with an updated single piece ’speed slope’ windscreen. Due to the age of the modification, the actual date that it was carried out and what STC it was carried out under could not be confirmed. This modification made 2 changes that affected the pilot’s visibility. In addition to removing the centre spline of the windscreen it increased the slope of the screen moving its intersection point with the front of the fuselage further forward and increasing the size of the glareshield required to fill the space between the instrument panel and the windscreen.

JQF

As described in the aircraft information section of the investigation report:

The Piper PA-44 Seminole is a four-seat, low-wing, twin-engine light aircraft. It is powered by 2 180 horsepower Textron Lycoming O-360-E1A6D reciprocating piston engines. JQF [Figure 3] was fitted with three-blade, constant speed and full-feathering aluminium propellers.

The Seminole is equipped with hydraulically operated, retractable, tricycle landing gear. JQF was manufactured in the United States in 1979 with serial number 44-7995291. It was first registered in Australia in 1990. The aircraft was owned by the operator. Prior to the accident flight, the aircraft had accumulated a total flight time of 11,190.6 hours.

The aircraft was certified for IFR and charter operations. It was equipped with dual controls for the student and instructor. The aircraft was also equipped with a Garmin GNS430 radio communication and GNSS navigation system and a second communication radio. The aircraft was fitted with an Appaero Stratus Mode-S transponder unit, which had ADS-B OUT transmit capability only.

To determine where and when AEM would have been in the view of JQF’s pilots, the process applied to AEM for calculation of Euler angles and location of the cockpit structure and pilots eye position was also applied to recorded position data for JQF.

Figure 4 shows the 3‑view diagram of the Seminole from the aircraft’s maintenance manual.

Figure 3: Seminole JQF

Lighting

The initial airworthiness requirements for the Piper PA-44-180 defined the requirements and specifications for lighting fitted to the aircraft. The aircraft was certified under Part 23 of the Federal Aviation Regulations in 1978. Under this certification the aircraft was required to be fitted with an anti-collision lighting system if being used for night operations. This system was required in addition to the aircraft’s position lights. Colourisation must be in either aviation red or aviation white and the required intensity is described formulaically depending on flash intensity. Minimum required intensity above or below the vertical plane is stated as 400 candela between 0‑5°, 240 candela between 5‑10°, 80 candela between 10‑20° and 40 candela between 20‑30°.

The ATSB determined that JQF was fitted with wingtip strobes that were integrated with the position lights. As per procedure, navigation lights would not have been switched on during the day. However, the anti-collision lights were switched separately in the cockpit and examination of the wreckage indicated that these lights were likely to have been on at the time of the collision. The wingtip lights (Figure 3) were Whelen A650PGD1 and A650PRD1 with the ‘R’ and ‘G’ indicating the colour of the position light.

In addition to these lights the aircraft was also fitted with a Whelen Prometheus Plus PAR36 landing light (Figure 3) rated for an intensity of 60,000 candela. To avoid this light interfering with the flight crews’ vision it was set back in the front nose cowl of the aircraft. This reduced its ability to be seen at certain angles away from directly in front of the aircraft. The operator reviewed the light determining that the beam extended 20° either side of straight ahead. The light was visible at 40°, but it was difficult to determine if the light was on. Beyond 70° the light was not visible.

Under procedures outlined in the En-Route Supplement Australia (ERSA) for operating in the vicinity of Mangalore Airport, the landing light should have been switched on within 10 NM of the airport or in the training area. Wreckage examination indicated that the landing light was likely on at the time of collision.

Figure 4: PA-44-180 3 view diagram

Source: Aircraft operator

Recorded Data

As part of the investigation the ATSB reviewed ADS-B data, radar data and ATC recordings provided by Airservices. Data was also collected from an electronic flight bag (EFB) application that was in use by the student pilot of AEM. The EFB data did not provide any additional information so was not considered for further analysis in this study. Neither aircraft was equipped with a flight data recorder or a cockpit voice recorder, nor were they required to be, due to their size and type of operation. No data was recoverable from any of the instruments on board either aircraft.

Recorded ADS-B data

The ATSB obtained 2 data sets from Airservices: filtered data (combined ADS-B and radar) and raw ADS-B data. The filtered data is used for ATC display and alerting functionality and is filtered to approximately 5 second intervals.

Raw ADS-B data records every signal received by ground stations from ADS-B equipped aircraft. These transmissions from each aircraft are at approximately 0.5 second intervals but are not uniform to avoid simultaneous transmission with other aircraft and subsequent data loss.

Further discussion of the operation of ADS-B can be found in the ADS-B and Position estimation sections.

Figure 5 shows the comparison between the raw ADS-B data and filtered data. Due to scaling requirements only the last 20 seconds of AEM’s flight path is shown. All data recorded from JQF’s take-off until the collision is shown. For display, data has been converted to rectangular cartesian co-ordinates with the threshold of runway 05 at Mangalore Airport used as the reference point for the data (an explanation of this process can be found in the Position estimation section). For each point of the filtered data the time and the altitude recorded are shown.

The ATSB analysis of the data also calculated the collision altitude. This analysis determined that the aircraft were at approximately 4,125 ft above means sea level at the point of collision (see the section titled Position information for further detail).

It was noted that in the filtered data there were points beyond the end of the raw data and the estimated collision location. This was due to a projection capability within the Airservices system that accounts for short term loss of signal by estimating the position of the aircraft based on previous track and speed information.

Air traffic control recordings

The ATSB obtained and reviewed air traffic control recordings of communications between Melbourne Centre air traffic controllers and aircraft in the area. The Mangalore Airport common traffic advisory frequency (CTAF) was not recorded. Table 1 shows the communications between air traffic control and both AEM and JQF on the Melbourne centre frequency during the flight. Figure 5 shows the location of JQF at the time the departure call to the controller was initiated.

Figure 5: Raw ADS-B and filtered data comparison ^[2].

Source: ATSB

Table 1: Key traffic information on Melbourne Centre frequency

Source: Airservices, annotated by the ATSB

Meteorological Information

The study considered the effect cloud, background luminosity, wind and sun position may have had on the pilots’ ability to detect the approaching aircraft.

Cloud information

The ATSB reviewed both the forecast and actual cloud conditions for Mangalore Airport at the time of the collision. The Mangalore Airport automatic weather service (AWS) recorded 2 layers of cloud, one scattered at approximately 3,500 ft above ground level (AGL) and a second layer, broken at approximately 4,200ft AGL. To verify this information imagery from Bureau of Meteorology (BoM) weather cameras at Kilmore Gap and Wahring Field were reviewed. Further imagery was provided from a Victoria Police Air Wing helicopter taken 1 hour and 16 minutes after the accident. It indicated that the cloud layer was between approximately 4,050 ft and 4,900 ft above mean sea level with some patchy cloud below this. Figure 6 and Figure 7 show the Kilmore Gap and Wahring Field weather cameras. Figure 8 and Figure 9 show the Victoria Police Air Wing images and Figure 10 shows the approximate locations of these photos relative to the estimated collision point.

Figure 6: Weather camera image from Kilmore Gap

Source: BoM

Figure 7: Weather camera at Wahring Field

Source: BoM

Figure 8: View of base of cloud from the Victoria Police Air Wing helicopter taken approximately one hour after the accident (altitude approx. 4,000 ft)

Source: Victoria Police

Figure 9: View of top of cloud from the Victoria Police Air Wing helicopter taken approximately one hour after the accident (altitude approx. 4,900ft)

Source: Victoria Police

Figure 10: Weather imagery locations relative to Mangalore Airport and the collision point

Source: Google Earth, BOM and Victoria Police annotated by the ATSB

Extent of cloud

The BoM also provided the ATSB with satellite imagery showing the extent of cloud at the approximate time of the accident. Figure 11, taken 4 minutes before the collision, shows extensive cloud around Mangalore Airport with more broken areas towards the north and west and increasing cloud to the south and east.

Figure 11: Satellite image showing cloud coverage of central Victoria 11:20 EDT 19/02/2020

Source: BOM annotated by the ATSB

Background luminosity

Background luminosity is the calculation of the effective brightness of the background against which an object is being perceived. During the day, the background luminosity depends on the time of year and atmospheric conditions including cloud. The actual background luminance on the day of the incident was unable to be determined. Table 2 reproduced in Hobbs, 1991 from the Illuminating Engineering Society’s Lighting Handbook provided approximate values for luminance in common conditions. Due to the cloud cover on the day and the time of year, the ATSB used the overcast value of 300 cd/m² for further assessment.

Table 2: Luminance of common backgrounds

Source: IES Handbook in ATSB – Hobbs 1991

Wind information

Wind plays a key role in the calculation of aircraft performance and Euler angles. Unfortunately, none of the available meteorological or other recorded data captured the wind at altitude at the time of the collision. As a result, the ATSB estimated the wind at altitude using data from the BoM’s grid point wind and temperature forecast (GPWT), issued at 0644 on 19 February 2020 and valid from 1100 that day. The chart indicated that at approximately 5,000 ft the wind was from 200° true and the wind speed was between 30 and 35 kt.

Sun position

Where the sun is visible, or close to the edge of the field of view, the sun’s glare can reduce a pilot’s ability to locate nearby traffic. Due to the sun’s consistent movement across the sky its position relative to a point on the earth’s surface can be calculated with a reasonable degree of accuracy. The ATSB obtained data on the sun’s position relative to the collision position (location and altitude) from the United States National Oceanic and Atmospheric Administration.^[4] For the final 270 seconds leading up to the impact, the Azimuth ^[5] and Elevation ^[6] angles of the sun relative to the collision point varied from 58.26 to 56.98° and 50.8 to 51.56° respectively.

Human performance information

Object perception

It is not possible to state how large an object needs to be in a person’s field of view before they are able to distinguish it. This is due to a wide variety of factors both internal and external to the viewer and include the background that an object is seen against, where in the field of view it appears, relative motion of the object, vibration and physiological factors such as fatigue, age and hypoxic effects.

Multiple studies and reports give varying values as to what the minimum perceptible size of an object may be. One such example is an NTSB report from a mid-air collision in 1987 (NTSB, 1988), where 12 minutes of arc (0.2°) was suggested. Other examples suggest between 24 - 36 minutes of arc (0.4-0.6°) is more realistic, especially if conditions are sub optimal (Morris, 2005). The 2 main factors that will affect the size of the aircraft in the pilot’s eye are the dimensions of the aircraft and distance from the viewer. Figure 12 shows the change in visual angle and the time to collision at various constant closure speeds for an aircraft with a 40 ft wingspan. ^[7]

Figure 12: Visual angle and Time to Impact for various closure rates

Source: (Morris, Midair Collisions: Limitiations of the See-and-Avoid Concept in Civil Aviation, 2005)

For perspective, a piece of paper measuring 4 by 20 mm positioned lengthwise subtends an angle of 0.2° horizontally in the field of view when viewed from 5.73 m away.

Physiological blind spot

When considering at what point an object can be perceived, it is also necessary to consider the blind spot associated with the structure of the human eye (where the optic nerve exits the eye). This covers approximately 5° of azimuth and 7.5° of elevation. In most cases this is overcome by binocular vision where each eye can see what is in the blind spot of the other. However, where an object obscures perception from one eye, then in combination with the blindspot of the other eye, can potentially prevent an object being seen entirely. (Hobbs, 2004)

Relative movement

An object will be more easily perceived, regardless of where it is in the field of view, if there is relative movement between the object and viewer. (Hobbs, 2004) This is due to the human brain’s evolutionary adaptation to perceive movement as an indicator of threat. In many cases aircraft on collision courses will not have relative movement and so the eye will take longer to detect the aircraft. The perception and location of relative movement in the field of view is assisted where there is a stationary object, such as a structure, past which the object is moving. In this case the viewer will more easily locate the target if it is moving or transiting past the cockpit structure which will remain constant in the pilot’s field of view. Under ideal conditions where there is a stationary reference point proximal to the target movements of 0.017 - 0.034° of arc per second may be detected. When no such references are available it will require a 10-fold increase in movement for detection. (ATSB, 2002)

Strobe or other aircraft lighting may be used to create apparent movement or a focal point that attracts the viewer to the object.

There have been a range of studies assessing the effectiveness of various lights on people’s ability to see or perceive an object. Where an object is in a known position, a light even of relatively low power can be detected. Where a light is required to attract the attention of a viewer, particularly where it is in that person’s peripheral vision, it is required to be 5-10 times brighter than a light where a person is already alerted to the location and is simply looking for confirmation (Bullough, 2011).

Reaction time

Once an object is perceived by the viewer it takes time for the person to identify it, realise it is a threat, determine the appropriate course of action and implement that course of action. (ATSB, 2002) In the case of aircraft approaching one another, the implementation of that course of action will not only require an input to the controls from the pilot but also a reaction from the aircraft.

Based on a range of research, the FAA published an advisory circular that defined standard reaction time for a pilot from perception to the aircraft reacting. This table showed that from seeing an object to aircraft reaction was 12.5 seconds. Of this the 2 most significant portions are the determination that the other aircraft is on a collision course and determining the appropriate course of action. These 2 elements make up 9 of those 12.5 seconds. Table 3 is taken from the relevant FAA Advisory circular (AC 90-48D CHG 1.

Table 3: Aircraft Identification and Reaction Times Chart

Source: Federal Aviation Administration

Theoretically, this means that, with no alert or guidance, if an object on a collision course is perceived less than 12.5 seconds prior to impact then the impact will occur regardless of a pilot’s attempted evasive actions. The time available for pilots to react can be increased through the introduction of an external or internal stimulus that alerts the pilot to traffic that poses a collision threat, provides an estimate of the location or if the aircraft is on a collision course a manoeuvring recommendation to resolve the conflict (a ’resolution advisory’).

Avoidance alerting

Mental model

A pilot’s mental model of the airspace around them is a key tool in good airmanship and conflict avoidance, regardless of the type of airspace operated in. The model requires an understanding of:

• the rules and regulations governing the airspace
• what traffic is in the airspace
• what traffic is relevant
• how relevant traffic is moving
• the intentions of the traffic’s pilot
• traffic’s performance.

This is then compared to the pilot’s intentions and the characteristics of their aircraft to determine the likelihood of conflict with the traffic.

A pilot’s mental model is affected by a range external and internal inputs. Internally pilots rely on:

• experience
• understanding of the airspace system
• understanding of their aircraft and its performance
• instrumentation
• on-board systems such as ADS-B or a Traffic Collision Avoidance System (TCAS)
• their view of the surrounding airspace.

Externally, the model is supplemented by radio communications, whether from ATC or directly or indirectly by other pilots on relevant frequencies and data relating to weather or procedural information that may be available digitally through a range of electronic devices. Increased accuracy and frequency of information available to a pilot can increase the accuracy of their mental model, and therefore reduce the risk of conflict with other traffic.

Alerting

As discussed above, for a pilot to detect a threat and effectively manoeuvre to avoid a collision the aircraft must be large enough for the pilot to detect it by eye and then react with sufficient time to manoeuvre and avoid the conflict. With an effective mental model based on radio or other detection technologies pilots can be aware of aircraft and conflict potential well beyond the limits of the human eye and at distances that allow ample time to arrange separation.

The alerts that assist in the development of the mental model can be either internal or external. External alerts could be direct communications or area broadcasts from either ATC or other aircraft. These alerts do not necessarily apply directly to the pilot and will often not require any action. They assist the pilot’s mental model development and conflict avoidance in 3 ways:

Internal traffic alerts are provided by aircraft systems. These alerts have a range of advantages over externally provided alerts, including:

In discussing the relative effectiveness of internal and external alerting, Hobbs (1991) made the following statement.

Traffic alerts [presumably those provided by an aircraft collision avoidance system (ACAS)] were found to increase search effectiveness by a factor of eight. A traffic alert from ATS or from a radio listening watch is likely to be similarly effective

This paper was written prior to the introduction of the ADS-B system and the development of ADS‑B IN based traffic alerting systems. The similarities between the types of alerts that older ACAS and ADS-B IN systems can provide to the pilot would suggest that a similar increase in detection potential would be possible.

Not only do these alerts make it more likely that a threat aircraft will be detected or detected earlier, they also reduce the time required to take avoiding action. In the Reaction time section above, the time required from detection to implementation of avoiding action is cited as 12.5 seconds. Of this, 7.3 seconds is required for the pilot to detect the conflicting aircraft and recognise it as a threat. An internal alert can provide the pilot with the position and threat status of an aircraft limiting the delay from location and threat determination. Consequently, with ACAS, including ADS-B IN it is less likely that aircraft will converge without pilots realising and taking action to ensure separation.

Finally, it is important to note that outside of controlled airspace aircraft may not be required to have ADS-B or TCAS functionality and may not carry a radio or make broadcasts. Therefore, an effective lookout that covers as much of the sky as possible remains a critical component of conflict avoidance.

Case Study: Collision on runway between Extra EA-300 aeroplane, VH-EXR and Guimbal Cabri G2 helicopter, VH-LTO, Caloundra Airport, Queensland, on 18 September 2020 ATSB Investigation: AO-2020-051 On 18 September 2020, a high-performance single engine aeroplane VH-EXR (EXR), collided on the runway with a training helicopter VH-LTO (LTO) at Caloundra Airport, Queensland. EXR was conducting check circuits while LTO was conducting a stop and go landing during a navigation exercise. As part of the investigation, the ATSB identified that several radio transmissions from 3 different aircraft (including the accident aircraft) were either misheard, not heard or misinterpreted. The pilots of EXR did not hear or accurately assimilate the radio calls from LTO. The inaccurate assimilation was based on their understanding of the aircraft type and the operational requirements/ procedures at Caloundra. The student pilot of LTO made 6 broadcasts on their approach to, and within, the circuit area. They identified EXR and believed it had identified them due to a radio transmission indicating that EXR was landing ’number 2’, However, a third aircraft had just conducted a touch and go and this was likely the aircraft that the pilot’s in EXR believed they were following, not LTO. Of the 2 pilots in EXR, the rear seat pilot recalled hearing a transmission from the helicopter but they understood that the aircraft would be on a 500 ft circuit approaching the helipad and not in the same circuit as the aircraft and so did not warrant their attention. The front seat pilot of the aeroplane, who was the pilot in command and pilot flying at the time of the incident did not recall hearing any calls from the helicopter and further commented that while helicopters used the airport regularly, they were not usually in the circuit. Consequently, the pilot of LTO believed that the occupants of EXR were aware of their presence, while neither pilot of EXR expected the helicopter to be on the runway. With visibility restricted by the aircraft’s structure, flight profile and the near‑stationary helicopter, no pilot was able to detect the other aircraft until they collided. Both aircraft sustained substantial damage but there were no injuries. Propeller strike mark and skid damage to VH-LTO                                  Source: Aeropower, annotated by the ATSB In this accident, both the limitations of visual acquisition and a limited or incorrect mental model of the surrounding traffic were present. While the pilots were providing the relevant communications for alerting, as they were not being correctly received or interpreted, they were unable to enhance the visual acquisition opportunity. While internal alerting functionality was not available in this case, it would have provided all 3 pilots with a better understanding of the location of the other aircraft, their movements and assisted them in visual acquisition and collision avoidance.

Pilot eye position

Each pilot’s eye position relative to the aircraft structure is the combination of several factors. The study considered the pilot’s height, seat position, and head movement. The pilots’ heights were obtained from their CASA medical records. The ATSB utilised a human analogue during this study to replicate the seated heights of the pilot’s in the opposing seat and the shielding from their head and torso.

The seat position for each pilot prior to the impact were not able to be determined from the wreckage examination. When ATSB investigators attended exemplar aircraft to gather data in support of this study, persons of the same approximate height as the pilots sat in the control seats and positioned the seats to an appropriate and comfortable position for operating the aircraft. These seat positions were recorded along with the scan data for further analysis.

In some cases, aircraft are developed with a ’design eye position’ the location from which operators are intended to view the cockpit. Neither of the manufacturers of the accident aircraft were able to locate or provide the ATSB a design eye position for their aircraft.

Movement of the pilot’s head, both translational and rotational, creates variability in both the eye position and field of view. The study considered a range of position and rotation of the eyes. Two matrices were developed simulating eye translation and rotation and the view of the cockpit and location of the target aircraft from these positions was determined. Further description of this process, and results, can be found in the Sensitivity analysis and Field of view sensitivity sections.

Workload

The human brain has limited processing capacity. When multiple sources of information need to be perceived and processed at the same time this can limit the ability of the pilot to attend to each of them effectively. For pilots, tasks including operating or listening to the radio, talking or conducting mental calculations can reduce a pilot’s eye movement, and effective field of view. (Hobbs, 2004)

Research has shown that stimuli, particularly those in the peripheral vision are more difficult to detect when attention is focused on a priority task. Data from NASA indicated that undertaking concurrent tasks while performing a visual scan can reduce pilot eye movement by up to 60%. (Hobbs, 2004)

Onboard AEM both pilots would be expected to have a slightly elevated workload as, in addition to regular flying duties, the instructional flight included the first VOR approach in this aircraft for the student. In JQF, not only was the flight an examination, meaning that both the examiner and the candidate would likely have been experiencing a higher workload, but they were also in the take‑off and climb phases of flight which also have relatively higher workload requirement.

Field of view

A pilot’s field of view or visual field, measured in azimuth and elevation angles from the eye, determines how far from the centre point an object can be effectively located. This field will vary from person to person and can change based on a range of factors including age, and existing visual conditions/diseases. A binocular field of view typically traverses through 190° of azimuth and 135° of elevation with a slight bias towards downwards perception (+60° elevation, -75° elevation). (Gibb, Gray, & Scharff, 2010) Within this are multiple layers of vision covering the rest of the visual field with decreasing acuity as they move further away from the centre.

For simplicity in this study the visual field has been broken into 3 areas

Figure 13 shows an exemplar silhouette of an equirectangular ^[8] 360° view of a Vans RV-8 aircraft cockpit showing the 3 visual areas field of views.

Throughout this report these coordinates will be used to describe the pilot’s visual field. It is worth noting that while all objects in the field of view might be visible to the pilot it is unlikely that all objects, particularly ones on the extremities or in areas where there is a large amount of visual clutter or activity will be detected (Gibb, Gray, & Scharff, 2010).

Figure 13: Fields of view example

Source: ATSB

Empty field myopia

When there is nothing in the field of view that the viewer is specifically focussed on the eye returns to a ’default’ position and focusses on a point 0.5‑1 m in front of it. This can lead to a viewer being unaware of potential threats proximal to them. This is referred to as empty field myopia. (Hobbs, 2004)

Pilot scanning

To improve the effectiveness of ’see and avoid’ and to overcome issues with ’empty field myopia’ and the ’blind spot’ pilots are trained to visually scan the airspace around them for potential threats. This is usually combined with an internal scan of the aircraft’s instruments.

General guidance is to ensure that the entire visual field is scanned by moving and rotating the head to reveal objects otherwise lost behind aircraft structure or in visual traps. ^[9] The FAA recommends a series of regularly spaced eye movements that cover approximately 10° of the visual field and where that area is focused on for one second to allow the eye to adjust and focus in this area to enable detection.

It is further recommended that external viewing occupies 66‑75% of the scan time, with the remainder spent scanning instruments and looking inside the aircraft. (FAA, 2017) Research indicates that the recommended amount is reversed with instrument rated pilots spending up to 66% of their time looking in the cockpit. When they were aware of the presence of traffic this decreased to 49%. This research also indicated that pilots are likely to scan the centre of windscreen thoroughly but neglect scanning of the edges of a windscreen. (Colvin, Dodhia, & Dismukes, 2005)

IFR pilots are taught to focus more of their scanning inside the aircraft and less externally. This is due to an increased focus on instruments in this type of flight and a heavier reliance on procedural separation techniques.  

Glasses

The use of glasses can affect multiple characteristics around a person’s vision. Usually this will improve perception of objects allowing the viewer to perceive objects more clearly at certain ranges and in certain parts of the visual field. However, they add another layer of material through which a person can look and create distortion. They also add further areas of shielding where frames intersect with the wearers sight lines.

Lighting

The ability of a person to perceive an object depends on the contrast ratio between the background and the object itself. This ratio can be increased using anti-collision lighting which will not only provide additional contrast against the background but in the case of strobe or rotating beacons provide movement that can attract the viewers’ attention alerting them to the presence of a threat.

Regulatory background

Regulation 196 of the Civil Aviation Regulations (CARs) require that aircraft conducting IFR operations in Australia be fitted with green, red and white navigation lights dependent on position on the aircraft. In addition, they must be fitted with at least one red anti-collision beacon or aviation white strobe lighting. The operational requirements for these lights are defined within the Civil Aviation Orders.

These documents specify operational requirements and so do not specify the technical requirements for either of these types of lights. The type and performance specifications for lights are defined within the airworthiness and certifications standards for the aircraft. The requirements and fitted lighting for both AEM and JQF are outlined in the Aircraft lighting sub-sections within each Aircraft information section.

Visibility

There has been a wide body of research into the effectiveness of aircraft lighting in improving visual detection of aircraft. A range of agencies around the world have encouraged aircraft owners and operators to fit anti-collision lights. The luminance of traditional aircraft lights meant the presence of these lights was of minimal advantage particularly in bright background lighting conditions such as those experienced in daylight (Hobbs, 2004).

Much of the available research into the effectiveness of aircraft lighting was carried out prior to the introduction of light emitting diode (LED) lighting when standard lighting intensities were in the order of a maximum of 300‑400 candela. As Figure 14, reproduced in (Hobbs, 2004), shows that for these lights to be effective at 3 nautical miles, background luminance cannot be more than approximately 30 candela (equivalent to a very dark day). On a full sunlit or even an overcast day lights of this power this would not be sufficient for an operator to see let alone draw attention.

Figure 14: Required effective intensity of lights

Source: Harris 1987 in ATSB – Hobbs 1991

Currently available lighting

Over the past 15‑20 years LED technology has become more commonly used in almost all lighting applications including aviation lighting systems. Due to lower power consumption, higher brightness and longer lifetimes, LEDs provide a significant advantage over the traditional incandescent or halogen bulbs (US DOE, 2022).

The provision of these improvements has led the FAA to encourage the use of landing lights when an aircraft is operating within 10 NM of an airfield or below 10,000 ft (FAA, 2020). The low power consumption and increased brightness of modern LED landing lights provide for visibility at significant distances even in bright daylight. For example, the sunspot series of LED landing lights produced by AeroLEDs in the United States have candela ratings between 150,000 and 420,000 (AeroLEDS, 2021) which is more than sufficient for a light to be seen at distances of 3 NM even outside of the foveal region of highest visual acuity (Figure 14). It is important to note that many landing lights do not have strobe functionality and so must use brightness and contrast alone to attract the viewers’ attention to the target.

A recommendation to use the taxi and landing light within 10 nautical miles, including within the circuit area, was also part of the standard flight procedures for Mangalore Airport as outlined in the ERSA and made up part of the standard operating procedures for JQF. 

Aircraft modelling

Discounting meteorological and human performance factors, which are considered separately, this study assumed that the aircraft would be visible from one another unless an opaque part of the aircraft’s structure was directly in line between, or shielding, the pilot’s eye position from the ’target’ aircraft.

To accurately determine the location of the aircraft’s structure from both pilots’ eye positions the ATSB modelled exemplar aircraft of those involved in the accident. Two full scale digital models were developed representing the aircrafts’ external and internal structures.

Point clouds were developed from data gathered using a FARO Focus series laser scanner. Each point is representative of the position of the material that reflects a laser beam put out by the scanner. As the scanner sweeps through 360° of azimuth and 150° of elevation it creates points representing the three-dimensional location of the aircraft’s structure. Noting that the laser will only capture data when a reflection is received, transparent objects such as windows may not be identified or identified accurately. However, their position can be deduced from the surrounding structure.

As the scanner can only ’see’ in a direct line of sight, a single scan cannot capture the whole aircraft as some areas will be in the scanner or aircraft’s shadow. To overcome this, a series of known points or ’targets’ are set up around the aircraft and then the scanner placed in multiple locations where both the aircraft’s surfaces and the targets can be seen. The ATSB utilised 2 different types of targets - spheres and checkerboards placed throughout the space at locations likely to be overlapped by multiple scans.

The utilisation of spheres provided a target that maintains its shape when viewed from any angle so can be referenced in any scan where it is visible. Checkerboards are used as they are easy to transport and position in larger numbers, however flat surfaces mean that they are only usable when the scanner can capture the whole checkerboard. The patterns created by the targets allows multiple scans to be combined or ’merged’ by the scanner software. ^[10] The number of targets and their distribution simplifies the processing as it creates more identifiable patterns in the targets that the software can identify.

Once merged the scans generate a point cloud and are processed into a triangulated mesh. Both the cloud and the mesh are dimensionally accurate representations of the whole aircraft.

For this study, the scans were performed at multiple locations around each aircraft, and inside the aircraft. This resulted in 4 models being produced for each aircraft:

The point cloud that was generated by the scanner contained all the points that the scanner had been able to see. This included not only the aircraft but the surrounding environment. Additionally, depending on the nature and material that that the laser was reflecting off there was some ’noise’ or unwanted points in the scan. To overcome this the scan data was automatically and then manually cleansed and these points were removed from the point cloud.

Both aircraft were modelled with propellor blades in a single static location. The wreckage analysis (see investigation report) determined that the engines and propellors of both aircraft were operational up to the collision. While the propellors are a solid structure, the speed with which they would have been rotating meant that the pilot’s visibility through the propeller disc would not have been significantly impeded by them. The propellor blades were removed during the modelling stage.

Aircraft were modelled on the ground with the landing gear extended. Due to the position of the landing gear, it is not visible to the pilot during flight and therefore does not impede detection of a target aircraft. As such, the gear was retained within the models of both aircraft. The attitude of the aircraft when sitting on the landing gear is different to that while in flight. This was accounted for by levelling the aircraft model when converting each aircraft from the scanner axis system to the body axis system, see point cloud conversion section for further details.

AEM

For the study, AEM was substituted with VH-IJM (IJM) a Beechcraft E95. While AEM was a D95A, the fitment of the ’Speed Slope’ windscreen modification (see the section titled Aircraft information) meant that it was more accurately represented for structural purposes by the E95. While scanning IJM, ATSB personnel also viewed VH-FLM, a D95A that had retained the original windscreen layout, and took photographs for comparison with both AEM and IJM.

The model developed of IJM comprised 22 external scans and 9 internal scans taken over the course of a day while the aircraft was hangered. At the time of scanning IJM was not fitted with dual cockpit controls as AEM was at the time of the accident. The ATSB reviewed photos of AEM configured with dual controls and determined that the control yoke for the right seat pilot would not have affected the pilot’s visibility and so it was not considered as necessary for accurate model development.

Figure 15 shows IJM during preparation for scanning, surrounding it are a range of targets, both checkerboards and spheres. Figure 16 shows a panoramic image taken by the laser scanner when situated over the right pilot’s seat. Panoramic images like this were taken at each scanner head location and are used by the scanner software to ’colourise’ the point cloud. Figure 17 shows the 3-dimensional point cloud model of IJM.

Figure 15: IJM prepared for scanning.

Source: ATSB

Figure 16: Panoramic image taken by laser scanner when scanning from right pilot’s seat

Source: ATSB

Figure 17:  3-dimensional point cloud model of IJM

Source: ATSB

JQF

For the study, JQF was substituted with VH-NLO (NLO) a PA-44-180 Seminole manufactured approximately a year prior to JQF. NLO was scanned by ATSB personnel over the course of 2 days while hangered. When scanned, NLO was equipped with 2 bladed propellors compared to JQF’s 3 bladed propellors. However as discussed previously, due to their limited impact on visibility, the propellor blades were removed from the models. The ATSB reviewed imagery of NLO and JQF with 2 and 3 bladed propellors, it was determined that, while not dimensionally identical, the spinner domes from the 2 and 3 bladed propellors were similar enough to not require further assessment or modification of the aircraft model.

The model of NLO consisted of 23 external scans and 8 internal scans. To facilitate scanner positioning within the aircraft, seats were removed prior to interior scanning and were replaced as necessary for locating a human analogue to replicate the second pilot’s eye positioning. Figure 18 shows NLO in the hangar at Mangalore Airport during preparation for scanning with checkerboard and spherical targets visible. Figure 19 is a panoramic image taken by the laser scanner when positioned approximately at the left pilot’s eye position. Figure 20 shows the 3-dimensional point cloud model of NLO.

Figure 18: NLO prepared for scanning

Source: ATSB

Figure 19: Interior panoramic view of NLO from left seat pilot’s position – note sun visors in the lowered position

Source: ATSB

Figure 20: 3-dimensional point cloud model of NLO

Source: ATSB

Point cloud conversion

All points in the 3-dimensional models were recorded relative to an origin point, in the case of the aircraft scans, this was relative to the location of the scanner head when the first scan was taken. These co-ordinates are referred to as being in the Scanner Axis System. To accurately calculate the position of the target aircraft relative to the viewer aircraft the target’s position must be expressed relative to the viewer aircraft and in its co-ordinate system, this system is referred to as the viewer aircraft’s Body Axis System. To convert from the Scanner Axis System to the Body Axis System each point must be translated and rotated using a series of matrix transformations. ^[11]

Calculating the rotation and translation matrices relied on the identification of a series of 3‑dimensional points in the Scanner Axis System with known co-ordinates in the Body Axis System. For this study the ATSB used the left and right wing tips, the nose and rear of the aircraft and the highest point on the tail as identified on the aircraft 3 view diagrams (Figure 1 and Figure 4). These points were identified in both the Scanner Axis System and in the aircraft’s Body Axis System. From this the ATSB calculated the transformation matrices and applied the rotation and translation to the point clouds for each model.

Pilot eye positions were defined in the Scanner Axis System and the same transformations were applied to compute their coordinates in the aircraft’s Body Axis System.

With the aircraft fuselage and pilot’s eye position in the aircraft’s Body Axis System the azimuth and elevation angles of the aircraft structure relating to the pilots’ eyes were calculated. These positions were then represented on a 2D plot with the target aircraft locations to establish the windows where the target aircraft (see the section titled Locating the target aircraft) was shielded from view.

Refining the pilots’ eye positions

The location of the pilots’ eyes was based on the locations of the eyes of the human analogue used in the study. Due to potential differences between the position of the human analogue’s eyes and the pilots’ eyes a matrix of possible eye positions (see the section titled Sensitivity analysis) was developed and the pilot’s view of the cockpit structure from each position in the matrix was examined. Using pilot and aircraft characteristics and images of both the accident and exemplar aircraft cockpits, investigators selected optimised eye positions within the matrix of eye positions. Throughout the remainder of this study these optimised eye positions were used as the primary eye positions for assessment and calculations. The original position taken from the human analogues were used in the sensitivity analysis section to identify the difference that small movements of the eye position could make to visibility and referred to as the ’displaced eye position’.

Locating the target aircraft

The location of the target aircraft in the field of view of the pilot of the viewer aircraft can be defined in terms of the azimuth and elevation angles from the viewer to the target, as depicted in Figure 21. To compute these angles, the target aircraft’s coordinates are first transformed from an Earth-based coordinate system into the viewer aircraft’s body-axis coordinate system.

The area of the pilot’s field of view taken up by the viewer aircraft’s structure can similarly be expressed in terms of the azimuth and elevation angles (from the pilot’s optimised eye position) defining the boundaries of the structure. At points where the azimuth and elevation coordinates of the target aircraft overlap those of the viewer aircraft’s structure, the target can be considered to be ’shielded’ from the pilot of the viewer aircraft. Similar considerations can be used to determine the location and shielding of the sun in a pilot’s field of view.

Figure 21: Azimuth and elevation angles from viewer aircraft to target aircraft

Source: NTSB

Automatic Dependent Surveillance – Broadcast

ADS‑B OUT

ADS-B collates and transmits a range of gathered and calculated aircraft parameters based on Global Navigation Satellite System ^[12] (GNSS) data. Parameters include:

• aircraft position - latitude, longitude and geometric altitude
• position accuracy
• time the position was recorded
• unique aircraft identifier ^[13]
• flight id (in this case the aircraft registration mark)
• performance information including
  • ground speed,
  • track angle and
  • rate of climb or descent.

In addition, ADS-B can be connected to other aircraft systems to provide more accurate display data including heading, barometric altitude and vertical rate.

ADS-B transponders can also transmit emergency indicators using dedicated transmission settings. The system is defined as automatic as it does not require an external interrogation before transmitting its data and dependent as it relies on a GNSS source for position information.

Data is transmitted line of sight on an open 1090 MHz frequency and can be collected by a range of receivers. In Australia, Airservices operates and maintains the ADS-B network for air traffic control. There are multiple other networks and individual receivers that provide a range of coverage patterns within Australia and globally. Individuals may even build their own receivers to obtain traffic information about aircraft operating nearby.

Additionally, recent improvements in technology have allowed for ADS-B receivers to be fitted to satellites which can provide significantly greater coverage than ground‑based receiving stations. Further details relating to reception networks for ADS-B data can be found in the Receiver network coverage section below.

Except for certain exempted aircraft, as of 2 February 2017 under Civil Aviation Orders 20.18, it is required that all aircraft operating IFR be ADS-B OUT equipped. These exemptions expired for Australian aircraft on 1 January 2020. This requirement assists ATC in locating IFR aircraft and providing separation inside controlled airspace, and a traffic information service in non-controlled airspace, where ADS-B coverage is available.

ADS-B vs Mode C and Mode S transponders

Traditionally aircraft identification has relied on interrogation of a Mode C or Mode S transponder fitted to the aircraft. These 2 systems provide a series of aircraft parameters, 3 for mode C and 7 for standard mode S which are then supplemented by data from secondary surveillance radar (SSR) information. This allows ATC to establish course, speed, climb or descent, the aircraft’s position and other performance parameters for ATC traffic management purposes. The data provided by a Mode C or Mode S transponder when interrogated, is referred to as a ’squawk’. (Device Technologies Inc., 2019)

Conversely, ADS-B transmissions do not require interrogation. The ADS-B system automatically transmits relevant data at an average rate of 2 per second, this is referred to as a ’squit’.

ADS-B transmissions contain up to 49 parameters referred to as ’extended squitter’. This volume of data gives it a significant advantage over the older mode S and mode C transponders. (Garmin Aviation, 2021) The additional benefit is that any appropriate receiver can accept the signal and can unpack it for relevant information about an aircraft without the need for interrogation.

Receiver network coverage

Airservices Australia

Airservices maintains a network of 50 ADS-B receivers based around mainland Australia, supported by 7 wide area multilateral receivers based in Tasmania (TASWAM) which provides both radar and ADS-B coverage. (CASA, 2019) The coverage provided by each of these stations depends on the surrounding terrain and consequent shielding of signals. (Airservices Australia, 2020) Figure 22, Figure 23 and Figure 24 show the network coverage, as of May 2020, at altitudes of 5,000, 10,000 and 20,000 ft respectively. Mangalore Airport is within the Airservices ADS-B networks coverage area with coverage down to ground level.

In Class G airspace ^[14], outside of these coverage areas and without ADS-B IN technology, pilots of aircraft not fitted with Traffic Collision Avoidance Systems (TCAS), whether flying under IFR or visual flight rules (VFR) must rely on procedural separation and accurate radio communications for their mental model of the airspace and traffic around them.

Figure 22: Airservices ADS-B receiver coverage 5,000 ft ^[15]

Source: Airservices Australia

Figure 23: Airservices ADS-B receiver coverage 10,000 ft

Source: Airservices Australia

Figure 24: Airservices ADS-B receiver coverage 20,000 ft

Source: Airservices Australia

Third party networks

Other third-party organisations or individuals may use a separate network of receivers with differing coverage patterns to that provided by Airservices. This can provide better coverage in certain areas where these organisations may have a specific focus. One such example of this is the utilisation of third-party receivers by the AvPlan EFB to supply its subscribers with ADS-B data.

This application was available on an iPad device carried by the student pilot of AEM, but it was not able to be determined whether a traffic information display was selected at the time of the collision. Furthermore, investigation by the ATSB determined that prior to or at the collision altitude, this network would not have located JQF and so would not have provided traffic information prior to the collision.

Satellite ADS-B reception

Mounting ADS-B receivers to a satellite network provides continuous global coverage of ADS-B equipped aircraft. This information can then be provided to relevant air navigation service provider (ANSP) or third-party subscribers improving coverage at low altitudes and away from airports and population centres (Aerion, 2021). Satellite coverage does not guarantee reception as it depends on the signal strength of an aircraft’s transmitter, requiring a minimum of a 125 watt transmitter if only fitted with a top mount ADS-B antenna (Aerion, 2021).

In Australia it is a requirement for aircraft manufactured on or after 9 February 2012, with a maximum take-off weight of more than 5,700 kg or a max cruising speed of greater than 250 kt, to be fitted with ’diverse’ antennas (meaning top and bottom mounted) (CASA, 2020). Diverse antennas provide the best coverage for both ground based and satellite ADS-B receivers. In most cases, larger aircraft are fitted with this antenna layout even if older than the requirement as it forms a part of the TCAS system. Diverse antennas are particularly important when the aircraft structure may shield an antenna. (Aerion, 2021) This is most common when the aircraft are on or close to the ground, or when manoeuvring in flight.

Supplementary technologies

Some EFB applications allow users to share device GNSS data to provide traffic information to other subscribers using a data connection. While this does provide an improvement to the situational awareness there are 3 primary drawbacks:

1. The display of data can lag significantly due to the transmission time required between devices via a data connection.
2. A data connection is required to be able to transmit or receive the information for display. It is important to note that the lack of an internet connection will not impact the ability for a device to receive a GNSS signal and so the viewing device’s position will still be able to be displayed but not traffic.
3. Position information is only available for other users of that specific application who have the traffic transmission functionality operational. This may give the pilot a false sense of the traffic picture around them. ^[16]

ADS-B IN

ADS-B IN refers to an aircraft that is equipped with a device that can receive other aircrafts’ transmitted ADS-B information. ADS-B IN data can provide location and proximity information on local traffic shown on a cockpit display or personal electronic devices with appropriate software.

In Australia, the fitment of ADS-B IN provides improved awareness of all IFR traffic and ADS-B OUT equipped VFR traffic. This can assist pilots in locating aircraft when traffic information is provided by ATC. It can also provide pilots outside of ATC coverage with accurate information of proximal traffic at ranges far greater than that detectable by the human eye.

Due to the signal characteristics and technology that is in use, ADS-B receivers are small and lightweight. This enables them to be fitted into aircraft avionics packages or attached, either wired or wirelessly to personal electronic devices in the cockpit. Installing these receivers improves significantly on data from EFB applications as it displays all nearby ADS-B equipped traffic in near real time.

Cockpit display of traffic information

Cockpit display of traffic information (CDTI) is a system used to display ADS-B IN information to the pilot to enhance spatial and situational awareness and assist in visual acquisition of traffic. The CDTI screen shows in a planar or overhead view the location of proximal traffic to the aircraft, over either a moving map or against a plain background with range rings depicting distances from the aircraft. These systems have a range of settings that can be adjusted to display or remove certain aircraft or distractions as per flight crew requirements.

ADS-B traffic alerting system

ATAS is an add on to ADS-B IN functionality that can provide alerts about the location, speed and direction of proximal traffic to a pilot with the aim of reducing the risk of mid-air collision. When aircraft are projected to breach certain defined proximity thresholds the ATAS system audibly alerts the pilot to the intrusion with a standard phraseology that states ’Traffic, direction [by clock co-ordinate], ^[17] altitude [high, same level, low], distance, current activity [ascending, level, descending]’.

Unlike most other ADS-B IN functionality, the ATAS system has an audible only implementation that can provide an alert to the pilot. However, in many cases it is combined with display functionality on the CDTI screen whereby the traffic triggering the alert is highlighted on the screen.

An example of a CDTI screen with integrated ATAS is shown in the Cockpit display of traffic information study section of the safety analysis.

Traffic Collision Avoidance System

Traffic collision avoidance system (TCAS) is a separate traffic avoidance system that utilises transponder interrogation of mode C and mode S units. The system interrogates the other aircraft’s transponder and calculates the relative position of other aircraft. It then, analyses the track of the host aircraft and approaching aircraft to determine if there is a collision risk. The system provides 3 levels of alerting for nearby traffic that is within a defined area around the host aircraft: (FAA, 2011)

If fitted to both aircraft the TCAS systems will work together providing opposing resolution advisories that reduce the risk of collision. With the development of ADS-B technologies and more accurate aircraft positioning using GNSS data, TCAS systems have been able to be augmented with ADS-B and ATAS functionality.

The FAA provides guidance in Advisory Circular (AC) 20-172B as to how the systems can be integrated effectively so that duplicated alerts are not received based on the ADS‑B and radar returns. In addition to the increased accuracy of ADS-B data, another advantage is that it provides information on more distant targets.

Complementary technologies

In the United States ADS-B IN is supported by 2 other technologies to improve a pilot’s situational awareness of traffic proximal to them - Automatic Dependent Surveillance – Rebroadcast (ADS‑R) and Traffic Information Service – Broadcast (TIS-B). These systems are an advancement on ADS-B and radar technology and combine ADS-B information, gathered via an onboard ADS-B IN system with traffic information from ATC to provide pilots of ADS-B IN equipped aircraft with a better picture of the traffic around them.

The ADS-B network in the United States differs from that in Australia in that it uses a second ADS-B frequency. This reduces congestion and provides infrastructure for additional ADS‑B functions such as graphical weather information. The second frequency, 978 MHz Universal Access Transceiver (UAT) is used primarily by general aviation aircraft, operating at lower levels (below 18,000 ft).

While many ADS-B IN devices support both reception and display of both frequencies, some ADS‑B devices cannot. In these cases, the ADS-R network provides a rebroadcast of the alternate frequency to those aircraft that require it. Within the contents of the extended squitter parameters is an indicator of whether an aircraft is dual frequency enabled and, if not, what frequency it is broadcasting on. This allows the ADS-R network to rebroadcast relevant transmissions on the relevant frequencies without causing duplicate or over transmissions.

Due to the additional delay required for the ground stations to receive, decode and retransmit the data, there is an increased lag in reception and analysis of ADS-R data. Additionally, ADS-R systems will only work in areas where the aircraft is in range of a relevant ADS-B ground station. (FAA, 2017)  

TIS-B provides ADS-B IN equipped aircraft with approximate location and speed of aircraft detected by ATC primary and secondary surveillance radar, which is then transmitted to aircraft on the relevant ADS-B frequencies for display and utilisation in traffic alerting. This means that aircraft equipped with only a mode C or mode S transponder can be more easily located by ADS‑B IN equipped aircraft, enhancing the opportunity for visual acquisition by aircraft crew.

The system also uses position and altitude information to filter the volume of traffic data broadcast to an ADS-B IN client aircraft. TIS-B will only transmit data associated with transponder-only (non‑ADS-B OUT) aircraft detected within 15 NM horizontally and +/- 1,750 ft vertically of the ADS-B IN client aircraft. (FAA, 2017).

The implementation of these technologies, ADS-R and TIS-B, carries with them a significant expense and at this stage they have not been introduced in Australia. As more aircraft, particularly in general aviation, become ADS-B equipped and depending on the technologies and frequencies used there may be an increased appetite to introduce these systems. (Airservices Australia, 2016)

Regulator guidance

In support of the mandating of ADS-B OUT for IFR aircraft in Australia, both CASA and Airservices have produced a range of guidance material to assist pilot’s in the implementation and operation of ADS-B. Specifically, in July 2020 CASA released an advisory circular (AC 91-23 v1.0) titled ADS-B for enhancing situational awareness. The documentation covers the requirements and benefits of ADS-B OUT. However, pilots do not have real time access to ADS-B data without a device that can receive and process this data (ADS-B IN.)

Section 9.1.1 of the AC states:

Being able to receive ADS-B transmissions from other aircraft and to display that information to the pilot is an essential component of ADS-B technology to enhance a pilot's situational awareness. The capability to receive ADS-B transmissions is generally referred to as 'ADS-B IN'.

This is followed by a statement in section 9.2.1 of the AC that ADS-B IN technology is not required in any Australian aircraft.

Without the accompanying ADS-B IN functionality, ADS-B OUT only provides increased situational awareness to ATC.

Electronic conspicuity devices

Electronic Conspicuity (EC) devices are designed to assist in the identification of aircraft operating under the VFR and are not required to meet the same ADS-B OUT standards as equipment fitted to aircraft operating under the IFR. In September 2020, CASA approved these relatively cheap portable devices so aircraft could be more easily identified by both ATC and aircraft fitted with ADS-B IN systems.

The most recent iteration of these devices includes ADS-B IN functionality allowing them to display ADS-B OUT equipped traffic on a moving map relative to the receiving aircraft through portable electronic devices. The GNSS receivers that these devices use do not necessarily meet an aviation technical standard. Subsequently while Airservices can receive the transmissions and information from these devices the information is not currently displayed to ATC for airspace management and separation.

EC devices have significantly lower transmit power than full IFR ADS-B installations. This means that the distance the signal can travel and still be received and decoded is lower. This does not affect the ability for traffic to be detected by other aircraft in the area at ranges significantly greater than visual acquisition. However, it would limit their ability to be detected by satellite or ground based ADS-B receivers. This could hamper, search and rescue operations or accident investigations.

For example, the Sky Echo 2 produced by uAvionics and an approved EC device by CASA has a nominal transmit power of 20 watts (uAvionics, 2022) allowing it to be detected at ranges of up to 40 NM (OzRunways, 2022). As discussed in the satellite ADS-B reception section a minimum transmit power of 125 watts is required for satellite reception.

While not specifically designed for fitment to IFR aircraft, the use of these devices with ADS-B IN functionality connected to an EFB application can provide a cost-effective alternative to fitment of a certified ADS-B IN system. Additionally, their portability allows for a single unit to be used across multiple aircraft that already have ADS-B OUT provided the unit’s ADS-B OUT functionality is disabled. This ensures that duplicate traffic information is not transmitted.

The SkyEcho 2, can be connected to the AvPlan or OzRunways EFBs. This device can be used for ADS-B IN and OUT or it has ability for the transmit function to be disabled and only used as an ADS-B IN device. Where ADS-B OUT functionality is not required, such as in an IFR aircraft with certified ADS-B OUT, the uAvionix ’Ping’ provides an ADS-B IN functionality at a lower price point without a transmit capability.

ADS-B fitment

Currently it is a requirement for aircraft operating under the IFR to be ADS-B OUT equipped. To better understand the current environment relating to ADS-B fitment in those aircraft operating under the VFR, CASA conducted a voluntary survey of VFR pilots and aircraft related to equipment including ADS-B that was currently carried on the aircraft. The survey, conducted between March and May 2021, received unique applicable responses from 1,936 pilots relating to the 2,245 aircraft, which was deemed by CASA to be broadly representative of the VFR community in Australia. For the purposes of the survey, CASA further broke down the VFR group into general and sport aviation. General aviation is VH-registered aircraft, except gliders, paragliders, gyroplanes, and Sport aviation aircraft are those registered with sports and recreational organisations. (Civil Aviation Safety Authority, 2021)

The survey found that approximately 40% of general aviation aircraft are fitted with some form of ADS-B OUT, with 15‑18% also fitted with some ADS-B IN capability. For sport aviation aircraft this is considerably lower with less than 20% of aircraft fitted with some form of ADS-B and approximately 6‑8% fitted with or using an ADS-B IN device.

Of those general aviation aircraft that were equipped with ADS-B about 47‑50% indicated that they also had diverse antennas (top and bottom mounted). For sport aviation aircraft this was only about 14‑21% indicating that they had diverse antennas. As discussed in the Receiver network coverage section, diverse antennas provide an increased likelihood of detection by reducing shielding due to aircraft structure.

As part of the survey, CASA also looked at where these aircraft are typically operated. They found that up to 38% of General aviation aircraft and 11% of Sport aviation aircraft with ADS-B are operating in an area without ATC coverage. In these areas, the fitment of both ADS-B OUT and ADS-B IN devices is more important as there is no third-party alerting capability, such as ATC, to provide traffic information.

CASA also asked pilots about their use of EFB applications, with approximately 80% of VFR pilots utilising an EFB application, including almost 90% of general aviation pilots. Of the responses received 70% reported using either AvPlan or OzRunways as their EFB application of choice, both of which have the capability to be linked with an ADS-B device.

However, only 15‑20% of pilots reported that they had linked the EFB application with an available ADS-B device. The survey results stated:

Interestingly, pilots of general aviation aircraft have a higher level of EFB use, but a higher proportion of sports aviation pilots have their EFB linked to ADS-B. Examining aircraft that have some form of ADS-B shows that for pilots who fly general aviation aircraft, only between 28.5% and 36.0% link ADS-B to their EFB. Whereas for pilots who fly sports aviation aircraft equipped with ADS-B, between 64.1% and 80.4% link ADS-B to their EFB. (Civil Aviation Safety Authority, 2021)

Finally, the survey asked about awareness and intentions around low cost ADS-B units (EC devices). Up to 70% of VFR pilots were aware of the availability of these devices and of those, up to 50% indicated their interest in purchasing a unit. However, 37% of the survey’s respondents indicated that it would be at least 6 and more likely 12 months before they would purchase an ADS-B device.

Limitations of ADS-B IN systems

ADS-B IN systems have a significant number of advantages for pilots flying under either VFR or IFR. However, it is important to also note the limitations of the system and remind pilots that these systems are designed to assist them in their responsibilities to maintain an effective lookout for traffic and communicate in the event of a potential conflict.

ADS-B IN systems can only detect ADS-B OUT equipped traffic that is within the line of sight of the aircraft. This means IFR aircraft and ADS-B equipped VFR aircraft (including those equipped with EC devices) can be detected. Additionally, as ADS-B OUT is not mandated for all aircraft, there will remain traffic that cannot be detected and pilots must maintain a lookout and listening watch on the relevant radio frequency to ensure they are aware of all traffic in the area.

Finally, ADS-B IN functionality and traffic information should not be used to second guess or override an ATC instruction in controlled airspace.

Methodology and results

Introduction

This section outlines how human factors, aircraft performance, aircraft structure and technological considerations either affected, or could have affected, this accident. It also details the processes that the ATSB used to calculate aircraft position and performance characteristics from ADS-B data.

The factors affecting the views from each pilot’s seat and where the opposing or target aircraft would have appeared in the visual field and how reaction time, visual field and perception size affected the ability to detect the aircraft are also analysed. Finally, it illustrates how available technology could have provided additional alerting capabilities for the pilots, improving their mental model, and increasing their ability to detect and avoid the other aircraft.  

Aircraft performance study

Position estimation

As discussed in the Recorded Data section, the ATSB received all available raw ADS-B data from the Airservices receiver network for both aircraft. To be able to effectively use this data for both position estimation, calculation of Euler angles and further analysis of visibility, it needed to be processed. Specifically, position data for the 2 aircraft was interpolated to common sampling points in a common co-ordinate system and smoothed to eliminate unrealistic jumps that could introduce spurious noise in parameters calculated from the data.

The following sections outline this process and how it was undertaken.

Filtering and refinement of raw ADS-B data

For AEM the raw ADS-B data set contained 6,565 points covering 24 minutes from 10:59:59 till 11:24:20. For JQF the data set contained 539 data points covering approximately 4.5 minutes from 11:19:55 to 11:24:20. On review, it was determined that both data sets contained a volume of data that would need to be filtered out before further analysis could be completed. This primarily focused on the removal of repeated data points or data points that had the same position for 2 different times.

Figure 25 and Figure 26 show the difference in time recorded between data receptions for the 2 aircraft. The maximum time between received data points for AEM data was 6.5 seconds and for JQF it was 2.4 seconds. As noted in the Recorded data section, to avoid over transmission and data loss, ADS-B transmissions are not at constant time intervals. Variation is semi-random between 0.4 and 0.6 seconds (Francis, et al., 2011). The reception of signals depends not only on the transmission but also on any shielding, from either terrain or aircraft structure, between the transmitter and receiver.

The ATSB’s review of the data identified 3,788 points in the AEM data set that were reporting the same position as another point in the data set. Of these 2,059 were identified as repeat data points (reporting same time and position) with the remaining 1,729 within one second of one of the adjacent points. For JQF the ATSB review identified 117 points that were reporting the same position, of these 49 were identified as repeat points and the remaining 68 were within one second of an adjacent point. A filter was applied to the data to remove repeated points. Where multiple points of the same position were identified, the first data point was retained.

After the repeated points were removed, variation between data points for JQF was between 0.390 and 2.406 seconds, with an average interval of 0.628 seconds. For AEM the variation was from 0.258 – 6.508 seconds with an average interval of 0.526 seconds.

Figure 25: JQF time between signal receptions

Source: ATSB

Figure 26: AEM time between signal receptions

* Note: Maximum recorded separation between signal receptions was 6.5 seconds, due to the scaling of the graph this has been truncated to 3 seconds. All calculations and data analysis used 6.5 seconds’ difference for the relevant data point.

Source: ATSB

Conversion to rectangular cartesian co-ordinates

ADS-B data contains aircraft latitude and longitude position in decimal degrees to 9 decimal places. The data was simplified by converting from latitude and longitude to rectangular cartesian co-ordinates. In this case, eastings and northings in meters relative to a reference point within a certain area on the earth’s surface. While not as accurate globally as latitude and longitude, these cartesian co-ordinates allow for simpler calculations of relative positions and proximities when locations are nearby. For this study the ATSB utilised a batch processing application of Geoscience Australia’s Geodetic Calculator ^[18] to convert the data from latitude and longitude to eastings and northings.

To simplify the data processing, the co-ordinates were identified relative to a reference point within the global co-ordinate system. In this case, while JQF departed runway 23 the threshold of runway 05 at Mangalore Airport was utilised, as the aircraft passed over this point while airborne. ^[19] Figure 27 and Figure 28 show JQF and AEM’s flight paths in cartesian co-ordinates in meters relative to this reference point. Although altitude was recorded in feet, no conversion of the data was required at this stage.

Data smoothing

While GPS data is highly sampled and relatively accurate, positional and altitude discrepancies do occur, which can cause jumps or steps in the data. Additionally, ADS-B altitude is recorded in 25 ft steps. Further calculations, particularly calculation of the Euler angles, using raw data would lead to unrealistic variation in multiple parameters. This, in turn, would affect the positioning of the aircraft and structure in later visibility calculations. To account for this, the ATSB smoothed both position and altitude data using a series of methods including integrations and running averages. The result of this smoothing was best fit lines through the data points that more accurately represented the flight profiles than the raw data set.

The following figures show the smoothed tracks for both position and altitude compared to the data recorded in the raw ADS-B Data. Figure 29, 30 and 32 show the location and altitude of AEM in comparison to the smoothed data. Figure 31 and Figure 33 show the same information  for JQF. The figures show that the smoothed data accurately represented the position for both aircraft, and it removes the ’stepped’ nature of the altitude.

Resample data

To simplify the calculations and enable the aircraft positions over time to be compared, the position of each aircraft needed to be known at a constant time interval with a common time base. As the time intervals between raw ADS-B data points is not constant the data needed to be resampled to a constant time interval. The smoothed data developed through the process described above can be represented as a curve of the aircraft position through time. The position of each aircraft along these curves at a constant time interval, in this case 0.5 seconds, from a defined base point were obtained. The time 11:20:00 was selected as the base point for the analysis as it was close to the take-off time of JQF and simplified calculations being on a 10-minute divisor.

Figure 27: JQF flight track in relative cartesian co-ordinates

Source: ATSB

Figure 28: AEM flight track in relative cartesian co-ordinates

Source: ATSB

Figure 29: AEM calculated position vs ADS-B position

Source: ATSB

Note: Due to scaling constraints and resolution of the image the line representing the AEM calculated positions is not visible beneath the AEM ADS-B location data. To confirm the correspondence the ADS-B data was removed from this graph and a check carried out. To overcome scaling constraints the final 30 seconds of AEM’s data was reproduced in Figure 30 and shows the similarity between the ADS-B and calculated positions.

Figure 30: AEM calculated position vs ADS-B position (last 30 seconds)

Source: ATSB

Figure 31: JQF calculated position vs ADS-B position

Source: ATSB

Figure 32: AEM calculated altitude vs ADS-B altitude over time

Source: ATSB

Figure 33: JQF calculated altitude vs ADS-B altitude over time

Source: ATSB

Calculation of Euler angles

If the position of an aircraft as a function of time is known, then it is possible to estimate the Euler angles provided the following are known (O’Callaghan, 2020):

      1.    The motion and density of the air mass relative to the earth (wind)
      2.    The lift co-efficient as a function of the angle of attack
      3.    The gross weight of the aeroplane
      4.    The sideslip and lateral acceleration of the aircraft are negligible (aircraft is in co-ordinated flight).

Where actual values were available or could be calculated from known information for these parameters, they were used. Where values were not available, they were estimated based on known parameters about the aircraft, conditions and the type of operation.

In their aircraft performance and cockpit visibility study, the NTSB described how the Euler angles could be calculated (O’Callaghan, 2020):

The position of an airplane as a function of time defines its velocity and acceleration vectors. In coordinated flight [assumed], these vectors lie almost entirely in the plane defined by the airplane’s longitudinal and vertical axes. Furthermore, any change in the direction of the velocity vector is produced by a change in the lift vector, either by increasing the magnitude of the lift (as in a pull-up), or by changing the direction of the lift (as in a banked turn). The lift vector also acts entirely in the aircraft’s longitudinal-vertical plane, and is a function of the angle between the aircraft longitudinal axis and the velocity vector (the angle of attack, 𝛼). These facts allow the equations of motion to be simplified to the point that a solution for the airplane orientation can be found given the additional information about wind and the airplane lift curve (i.e., 𝐶_𝐿 vs. 𝛼).

Euler angles, based on the ATSB’s smoothed position data, are shown below. Figure 34 - 36 show the pitch, roll (bank angle), heading (magnetic and true) of both AEM and JQF as a function of time leading up to the collision. Figure 37 shows the computed air and ground speeds of both aircraft.

The data showed that AEM had some minor deviations in pitch, less than 5°, throughout the final 260 seconds of the flight. Over the last 80 seconds of the flight the aircraft’s pitch trended downwards until the final 10 seconds when it trended up by approximately 2°. Variation in roll was minimal, apart from several spikes in the bank angle, none more than 5°. Heading and track angle remained near constant throughout final 260 seconds with the aircraft travelling north.

Data for JQF showed it making turns as per the flight path with changes in roll and heading corresponding to these manoeuvres. Throughout the flight, pitch remained in an upward trajectory with some reduction in areas where the aircraft levelled or decreased its rate of climb. Figure 38 shows the rate of climb in feet per minute based on the smoothed altitudes.

Figure 34: Aircraft pitch angles over time

Source: ATSB

Figure 35: Aircraft roll (bank angle) over time

Source: ATSB

Figure 36: Aircraft heading and track angles

Source: ATSB

Figure 37: Aircraft speeds over time

Source: ATSB

Figure 38: Aircraft rate of climb

Source: ATSB

Collision geometry

Based on the estimated positions and calculated performance characteristics, the ATSB sought to estimate the collision geometry between the 2 aircraft. The aim of this was to determine whether the collision geometry based on the performance analysis agreed, within limitations of the data, with that determined using the on-site wreckage assessment. This provided a cross check to both the performance analysis and the on-site wreckage assessment.

Aircraft proximity

The ATSB first analysed the position data, within the resampled smoothed data set, over time looking at the distances and altitudes between the 2 aircraft. This established the collision location, geometry and aircraft closure rate (see the section titled Aircraft closure rate).

The following parameters were calculated for this assessment, aircraft metres east and north of the Mangalore Airport runway 05 threshold over time and lateral, vertical and total proximity over time. To calculate the total proximity over time, altitudes were converted to meters. Figure 39 to Figure 43 show the results for each of these parameters.

Figure 39: Aircraft metres east of runway 05 threshold

Source: ATSB

Figure 40: Aircraft meters north of runway 05 threshold

Source: ATSB

Figure 41: Lateral proximity

Source: ATSB

Figure 42: Vertical proximity

Source: ATSB

Figure 43: Total proximity

Source: ATSB

Geometry projection and estimation

The ATSB extrapolated 3 additional data points beyond the end of the previously assessed data set. Based on previous analysis, it was understood that this would take the aircraft through and beyond the estimated point of collision. These calculations resulted in Figure 44 with the projected position of the aircraft at 11:24:20.05. This was calculated to be the first time that either aircraft would have passed through the centreline of the other and represented the time of the collision. The linear representations of the aircraft accurately depict scale but does not accurately depict the structure’s shape.

The data showed a similar collision geometry to that estimated from the wreckage examination (Figure 45 and Figure 46). The ATSB estimated and plotted the difference. It was determined that there was approximately a 5-10 metre difference between the projected and estimated collision geometries. Based on the resolution of the data available, and the range of inherent errors both in the positions and the assumptions that had to be made to complete the analysis, it was concluded that the 2 data sources supported one another. It was further noted that, due to disturbance of both aircraft wreckages, the collision geometry calculated based on the wreckage examination also relied on a level of estimation of the aircraft position and orientation.

The ATSB’s analysis indicated that approximately 0.55 seconds before the collision AEM was on a true heading of 352° and JQF on a true heading of 132°, giving a relative angle of 140°. At this time JQF and AEM were estimated to be at approximately the same level (JQF 4,124 ft and AEM 4,127 ft) with JQF maintaining its altitude and AEM descending towards Mangalore Airport at a reducing rate. Based on this the estimated collision altitude was 4,125 ft. The ground speeds of the aircraft were 92 kt and 192 kt, for JQF and AEM respectively and the closing speed was approximately 244 kt (see the section titled Aircraft closure rate for further detail).

Figure 44: ATSB aircraft ADS-B position projection

Source: ATSB

Figure 45: ATSB collision geometry estimation

Source: ATSB

Figure 46: Estimated collision geometry from wreckage analysis – investigation report.

Source: ATSB

Aircraft closure rate

Based on the position assessment, the closure rate between the 2 aircraft was calculated. For the final 260 seconds prior to impact, the rate varied between 197‑271 kt, with an average closure rate of 244 kt. Figure 47 shows the change in closure rate in the period leading up to the impact, with the rate increasing to just above the average in the final moments before the collision.

Figure 47: Aircraft closure rate (kt)

Source: ATSB

Research presented in the Object perception section and shown in Figure 12, indicated that for these aircraft with a closure speed of 245 kt, it would be expected that the angular size of the target aircraft would have been approximately 0.4-0.5° about 10-12 seconds before the collision.

Cockpit visibility study

As detailed previously, at the time of the collision one or both aircraft were likely in or had just emerged from cloud. Additionally, research presented in the Reaction time section indicated that at least 12.5 seconds is required for aircraft pilots to effectively see and avoid a converging aircraft.

The cockpit visibility assessment will consider the likelihood that the pilots could have detected each other within this timeframe, even if the environmental conditions had been more conducive to visual acquisition. It will consider a scenario where a cloud layer was present, but at a higher altitude, resulting in greater visibility while having little impact on the presence of the sun, the background luminance or contrast values for the aircraft.

Aircraft observed size

Based on the positional and performance analysis outlined in the previous section, the ATSB determined the approximate angular size of the target aircraft in the eyes of the pilots of the viewer aircraft. For this assessment, the azimuth and elevation angles to the following 5 different points on the aircraft were considered:

• intersection point of wings and centreline of the fuselage
• nose
• tail
• forward tips of both wings.

The difference between the maximum and minimum azimuth angles represents the maximum angular size of the aircraft in the pilot’s eye. As Figure 48 - Figure 51 show there was little change in the aircrafts’ relative size until the last 10-12 seconds before the collision.

AEM

In the case of AEM, the target aircraft’s angular size (if visible and without obstruction) would have been approximately 0.39° 12.5 seconds prior to the collision. This increased to 1°approximately 5 seconds before the collision and 7.5° in the last second before impact. Based on the research presented earlier, it is highly unlikely, even with clear conditions that the target aircraft would have been a perceptible size to the pilots of AEM 12.5 seconds before the impact, limiting opportunities for avoiding action.

JQF

In the case of JQF, the target aircraft’s angular size would have been (if visible and without obstruction) approximately 0.43° from either pilot’s field of view 12.5 seconds prior to the collision. This increased to 1° approximately 6 seconds before the collision and 8.6° in the last second before the collision. As above, it is highly unlikely that AEM would have been a perceptible size to the pilots of JQF 12.5 seconds before the impact to have permitted avoiding action.

Figure 48: Angular size of JQF from AEM for the last 260 seconds.

Source: ATSB

Figure 49: Angular size of JQF from AEM for the last 15 seconds

Source: ATSB

Figure 50: Angular size of AEM from JQF for the last 260 seconds.

Source: ATSB

Figure 51: Angular size of AEM from JQF for the last 15 seconds

Source: ATSB

Sun consideration

Sun location

With the azimuth and elevation from a particular location known, it is possible to calculate the azimuth and elevation angles from the aircraft to sun as both the aircraft and the sun move over time. As discussed in the Meteorological Information section, the ATSB obtained the sun azimuth and elevation relative to the collision point for the 270 seconds leading up to the accident. These values were obtained at 30 second increments and a linear interpolation was used to calculate positions at half second intervals equivalent to the resampled position data. From this the azimuth and elevation from each aircraft to the sun were calculated.

Figure 52 and Figure 53 show the azimuth and elevation angles from AEM and JQF to the sun over time. Figure 54 and Figure 55 show the location of the sun in relation to the cockpit structure from the position of both left and right seat pilot’s for AEM. Figure 56 and Figure 57 show azimuth and elevation for JQF.

Sun visors

Both AEM and JQF were fitted with visors to limit sun glare. Due to the disruption of the wreckage on both accident sites it was not possible to determine if the visors were being used at the time of the collision.

AEM’s flight path altitudes indicated that it was above the cloud during its flight and so the sun visors may have been utilised during some portions for the flight. However, the presence of cloud at and above the approximate collision altitude and the ATSB analysis of the aircraft trajectories and sun positions indicated that the sun was in such a position that the visors are unlikely to have been necessary. Consequently, they were considered to have been in the stowed position.

The location and flight path of JQF was entirely beneath the could layer at approximately 4,200 ft and within its estimated extents. The ATSB analysis of the aircraft trajectory and sun position also indicated that the sun was in a position whereby the visors would not have been necessary and have subsequently been considered in the stowed position.

Differently to AEM, the visors of JQF were see through (see Figure 19). Instead of a solid barrier they had a tinted piece of Perspex that could be brought down into the pilot’s field of view to limit sun glare. While this does not have as significant an impact on visibility as the solid visor, the tinting of the Perspex can disguise objects in the visual field or make them harder to see by either changing the contrast between the object and the background or dimming lights intended to indicate position.

Sunglasses

Sunglasses worn by pilots can have a similar effect, particularly those with polarised lenses. However as discussed in the above paragraphs, the lighting conditions and sun positions would tend to indicate that it is unlikely that glasses were being worn in the lead-up to the collision.

One of the 4 pilots involved in the accident required vision correction for exercising the privileges of their license, while this does not preclude the use of standard sunglasses in conjunction with contact lenses there are also several other options available for glare reduction. These include over-glasses, prescription sunglasses the use of transitions lenses, which adjust filtering based on brightness. Given the conditions it is unlikely that these options were in use at the time or that transitions would have provided significant filtering given the background luminance of an overcast day.

Figure 52: Azimuth and elevation angles from AEM to sun

Source: ATSB

Figure 53: Azimuth and elevation angles from JQF to sun

Source: ATSB

Figure 54: AEM left seat pilot azimuth and elevation angles to sun

Source: ATSB

Figure 55: AEM right seat pilot - azimuth and elevation angles to sun

Source: ATSB

Figure 56: JQF left seat pilot - azimuth and elevation angles to sun

Source: ATSB

Figure 57: JQF right seat pilot - azimuth and elevation angles to sun

Source: ATSB

Aircraft contrast

Calculation of visual contrast for the target aircraft depends on the luminance of the aircraft and the luminance of the background that it is seen against. The ratio of these 2 factors give the aircraft’s contrast. The higher the contrast, the easier it is for an object to be detected against its background.

Background luminosity

The background luminosity depends on the:

• light source
• background that the aircraft is seen against.

The light source in this case was the sun diffused through a layer of cloud. However, the background was subject to change from the perspective of each viewer aircraft depending on whether the target aircraft was above or below the horizon line.

The background depends on both the flight path profile and the topography. To simplify the process of determining the background characteristics, the ATSB utilised the animation produced for the investigation (see the section titled Animation development). The simulation software used to produce this animation contains a reasonable approximation of the area’s topography allowing determination of whether the aircraft could be seen against the sky or the topography.

This review indicated that of the last 260 seconds of the flight, if meteorological conditions allowed, the pilots of AEM, would not have seen JQF against the background of the sky until the last 5 seconds where it would have transitioned over the horizon line. For the pilots of JQF, AEM, if visible through cloud, would have been silhouetted against the sky until the last second where it would have been crossing the horizon line.

While the difference between the sky and topography has an impact on the contrast, it was not possible to quantify due to the presence of the cloud reducing the difference between the background luminance levels of the sky and the topography. Due to this, and as discussed in the Background luminosity section, the ATSB was not able to determine a reliable value for the background luminosity on the day of the incident.

Aircraft luminosity

Calculation of the luminance value for an aircraft depends on the.

• location and brightness of the light source that is illuminating the target aircraft
• surface area of the target aircraft that is visible to the viewer
• reflectance value of the target aircraft
• proximity of the target aircraft and the viewer aircraft.

Light source

As detailed above. the source of illumination for the aircraft was the sun. However, due to the presence of the cloud the aircraft would have been viewed under diffuse light through the cloud. Estimations for luminance values from the sun on overcast days vary depending on the source of the data. Due to the amount of cloud and the time of year and day it was estimated that the light intensity from the sun through cloud would sit at the upper end of these values, being approximately 3000 lux.

Surface area

Surface area of the target aircraft that is visible at any time is a function of the aircraft’s relative heading. pitch and bank angles. Visible surface area varies from its minimum when the target aircraft is level on a reciprocal track to its maximum when it is banked on a near‑perpendicular track. Additionally, on a reciprocal track, the greater the pitch angle, whether positive or negative, the more of the surface area will be visible.

Reflectance value

Reflectance value is a measure of how much light a surface will reflect and how much it will absorb. The reflectance values for AEM and JQF were estimated based on the aircraft layouts and colour schemes at the time of the accident. The predominantly white paint schemes at the time of the incident would have likely increased their reflectance value.

Unlike AEM, JQF had a 2-tone paint scheme with the lower half of the aircraft fuselage and the outer portions of the wings painted a darker blue. This paint scheme, with this colour choice, meant a reduction in the aircraft’s overall reflectance value when compared to AEM.

Aircraft proximity

As detailed previously (Figure 43), the distance between the 2 aircraft was calculated.

Evaluation

The ATSB reviewed all the information available for calculating the contrast for the 2 aircraft. While it was determined that such a calculation could be made, the uncertainty resulting from limited information available for estimation of background luminosity, light source, and the reflectance values rendered any calculation of contrast values unusable. Further review undertaken in the Aircraft observed size, Closure rate, Target shielding sections and development as part of the Animation development section indicated that there were a range of other parameters that were likely to have had as great, if not greater, impact on the aircraft’s visibility from one another.

Aircraft lighting

As discussed in the Lighting section of Human performance information, aircraft lighting assists a pilot in locating a target aircraft that may be beyond their visual range. The ATSB reviewed the available information about the lighting that was fitted to both aircraft to look at whether it could have improved the opportunity for detection.

AEM

The review of information about AEM was not able to locate specific information about the lighting that was fitted to the aircraft. It was assumed that the aircraft was fitted with a lighting package that complied with the requirements of its certification and the relevant civil aviation regulations as discussed in the Aircraft information section. Due to the availability of newer more powerful lighting packages, this was considered a worst-case scenario.

For this review, position lights were considered at 40 candela maximum for the wingtips and 20 candela for the rear. Reviewing this information against the chart presented in Figure 14, these lights, if they had been switched on, would have provided little opportunity for detection at a distance that was useful for collision avoidance. No further information was available as to the presence or power of other lighting such as landing or taxi lights.

JQF

For JQF, the addition of strobe lights would have provided additional contrast if they had been activated. However, the best opportunity for attracting the attention of AEM’s pilots was likely to have been the aircraft’s landing light, which had a luminosity of 60,000 candela. Based on information from the operator, the procedures outlined in ERSA and the wreckage examination, it is highly likely that the light was on in the lead up to the collision. Reviewing against Figure 14, at 3 nautical miles and against the background luminance of 300 cd/m², a light with this intensity would have been visible in both the foveal and out to almost all the inner visual field. The aircraft were approximately 3 NM apart at 11:23:35, 45 seconds prior to the estimated collision time. At this time the target aircraft’s angular size would have been only 0.062° of the pilots’ view, meaning that on size alone it was unlikely to be detected.

These calculations assume an unobstructed line of sight between the viewer and the light. In the case of JQF’s landing light there were 2 additional considerations: the positioning of the light and the environmental conditions.

The landing light was located on the nose of the aircraft, set back into the nose cowl by approximately 30 mm to avoid direct line of sight to the pilots. This meant that the arc through which it was visible in front of the aircraft was reduced. The operator reviewed the lights fitted to a similar aircraft and determined that the beam arc was 20° either side of straight ahead the aircraft and 4° above to 8° below the horizontal axis. The full light was visible to 40° either side of straight ahead, however it had a significantly reduced luminance to the point where it was not possible to determine if it was switched on. Part of the light was visible to approximately 70° either side of straight ahead. The most powerful illumination and the best chance of visual acquisition was within the central beam. Therefore, only the central beam and its visibility were considered for further study.

The assessment of visibility of the light was based on the azimuth and elevation angles from JQF to AEM. Azimuth angles between -20 and 20° and elevation angles between -8 and 4° from JQF were the time that the light would have been directed at the target aircraft (AEM). The azimuth and elevation angles from AEM to JQF’s nose, calculated in the Aircraft observed size section, were then used to determine where JQF’s landing light would have appeared to the pilots of AEM when directed at AEM, and what areas of the pilot’s visual field the light would have appeared in.

The analysis identified 4 windows of time where AEM would have been within the arc of JQF’s landing light. These totalled 74 seconds and varied in length from 5.5 seconds to 50 seconds and when the aircraft were separated by distances of between 12.5 and 1.7 NM. Of these 74 seconds, for the first 32.5 of them JQF’s nose would have been within the foveal region of AEM’s pilots. Assuming the pilots continued looking straight ahead, the aircraft remained within 3° of left side of the pilot’s foveal region for the remaining 41.5 seconds.

The 2 best opportunities for visual acquisition of the light were 10 seconds between 11:23:04 and 11:23:14, between 76 and 66 seconds before the collision and 5.5 seconds between 11:23:47.5 and 11:23:52.5 between 32 and 27 seconds before the collision. During the first opportunity aircraft proximity was between 5.01 and 4.37 NM, when the aircrafts angular size was between 0.069‑0.076° in the pilot’s field of view. The second opportunity the proximity was between 2.09 and 1.75 NM, when the aircraft’s angular size was between 0.160‑0.188° (Figure 58). These results were also compared against the cockpit structure of AEM (see the section titled Target shielding).

It was determined that for the optimised pilot eye position the target aircraft (JQF) was not shielded from either pilot in AEM by the cockpit structure during any of the times when the landing light would have been visible.

Figure 58: Visibility windows for JQF landing light from AEM

Source: ATSB

Considering the intensity of the landing light, it is highly likely that, if environmental conditions allowed, the pilots of AEM would have been able to perceive and locate JQF based on its use of the landing light, at least 27 seconds prior to the collision and possibly between 76 and 66 seconds. At these times the ability to detect based on aircraft size alone was unlikely, and other than movement, there was no other specific characteristic that would have diverted attention of either pilot towards JQF.

With the presence of cloud, the effectiveness of the landing light to aid visual acquisition was reduced. The significance of the reduction was dependant on the extent of the cloud, with even a powerful landing light unable to penetrate significant distance through thick cloud. As it was not possible to ascertain the specific extent of the cloud in the vicinity of the accident, the actual detection opportunity offered by the light could not be determined.

Aircraft position assessment

As discussed in the Locating the target aircraft section, the position of each aircraft relative to the other can be used, along with consideration of the viewer aircraft’s structure to determine when the aircraft was visible from a particular pilot’s viewpoint. The azimuth and elevation angles between the 2 aircraft were calculated considering each was the ’viewer’ and the ’target’. These values, based on the smoothed data (see the section titled Position information) are plotted in Figure 59 and Figure 60.

Due to the location of the GPS antennas on the aircraft being close to the pilot’s eye position (within 500 mm) the position of the aircraft and the pilot’s eye position (optimised eye position – see the section titled Refining the pilots’ eye positions) for the purposes of locating the target aircraft have been considered the same. Figure 61 and Figure 62 show the view and target aircraft locations from the optimised pilots’ eye position in AEM and Figure 63 and Figure 64 show the view and target aircraft locations from JQF pilots’ optimised eye positions.

The target aircraft positions have been coloured to indicate that aircraft’s movement over time with the colour transiting from blue through green to red showing times getting closer to the collision. As discussed in the Sun consideration section, the azimuth and elevation angles to the sun were also plotted, indicating the sun’s movement in the field of view over time. As discussed previously, it shows the sun well above and away from the pilot’s viewpoint and entirely obscured by structure.

Figure 59: Azimuth and elevation angles from JQF to AEM

Source: ATSB

Figure 60: Azimuth and elevation angles from AEM to JQF

Source: ATSB

Figure 61: AEM left seat pilot’s view (optimised eye position) with target aircraft and sun positions.

Source: ATSB

Figure 62: AEM right seat pilot’s view (optimised eye position) with target aircraft and sun positions.

Source: ATSB

Figure 63: JQF left seat pilot’s view (optimised eye position) with target aircraft and sun positions

Source: ATSB

Figure 64: JQF right seat pilot’s view (optimised eye position) with target aircraft and sun positions

Source: ATSB

Target shielding

The ATSB’s optimised eye position (see the section titled Refining the pilots eye position) and views as presented in the Aircraft position assessment section, were used for further assessment of the times that the target aircraft would have been shielded from the view of the pilots by the aircraft’s structure. The ATSB reviewed azimuth and elevation angles of the aircraft structure and of the target aircraft, determining when the target aircraft would have been shielded from each pilot.

A series of 8 charts were developed, 2 for each pilot. The first showed the windows during which the target aircraft would, or would not, have been shielded from the approximate time that JQF became airborne until the approximate time of the collision, 260 seconds later (11:20:00‑11:24:20). The second shows the final 15 seconds before the collision, which as discussed in the earlier Aircraft observed size section, is the time when the target aircraft likely became visible to the pilot (assuming no cloud obscuration).

Pilots of AEM

Based on the ATSB’s optimised eye position, the target aircraft sat centrally, but relatively low in the windshield view. The cockpit structure did not shield the target aircraft from either of the pilots. As a result, charts showing target shielding times were excluded from this section of the report.

It is important to note that, while the target aircraft was not shielded from either pilot’s optimised eye positions, it would only have taken a relatively small movement of the head to shield the target for a considerable portion and at key times. The Sensitivity analysis section considers this further.

Pilots of JQF

The manoeuvring flightpath of JQF meant that the target aircraft, while approaching on a relatively stable heading, moved significantly through both pilots’ fields of view (traversing more than 180° of azimuth). For the right seat pilot, the target aircraft was shielded from their view for 95 of the last 260 seconds across 7 different shielding windows by different parts of the cockpit structure.

After 11:23:54 (26 seconds before the collision), when the target aircraft traversed 0.2° of the pilot’s field of view, the target aircraft was shielded for 21 seconds (81% of this time). The aircraft would have emerged from behind the instrument panel briefly approximately 19.5 seconds before the collision for about 4 seconds, but this was only to traverse between the instrument panel and the right pillar.

For the final 15 seconds the aircraft was completely shielded from the right seat pilot by the cockpit’s right pillar. The right pillar traversed approximately 20° of the pilot’s field of vision and immediately before impact the aircraft occupied no more than 9° of azimuth, shielding it completely/near completely from the pilot’s view.

Figure 65 and Figure 66 show the angular size of the aircraft and the time windows when it would have been visible to the right seat pilot for the final 260 seconds and in the final 15 seconds.

Figure 65: JQF right seat pilot’s visibility

Source: ATSB

Figure 66: JQF right seat pilot’s visibility last 15 seconds

Source: ATSB

AEM was shielded from JQF’s left seat pilot’s view by JQF’s structure for approximately 80 of the final 260 seconds split across 6 windows. These windows varied in length from 4.5 seconds to 20 seconds.

Approximately 52.5 seconds or 66% of the time that the target aircraft was shielded was before 11:23:30 when the aircraft would have traversed only 0.1° of the pilot’s visual field. However, different to the right seat pilot, the target aircraft would have become visible approximately 14.5 seconds prior to the estimated collision time. The target aircraft would likely have emerged from behind the instrument panel near the windscreen mounted compass and with an angular size of slightly less than 0.4°.

Figure 67 and Figure 68 show the angular size of the aircraft and the time windows when it would have been visible to the left seat pilot for the final 260 seconds and in the final 16 seconds.

Evaluation

Based on the ATSB optimised eye position there was very limited opportunity for the pilots of JQF to visually detect AEM with sufficient time for the aircraft to be manoeuvred to avoid the collision.

For the right seat pilot, the aircraft was likely entirely obscured during critical phase where it may have been possible to visually acquire the target aircraft and initiate an avoiding manoeuvre. While the left seat pilot probably had a window whereby the aircraft could have been visually acquired and an avoiding manoeuvre initiated, based on the aircraft’s size and the time available, the pilot would have been required to:

• identify an object on the opposite side of the windscreen centre spline of angular size less than 0.5°
• determine it was a threat and initiate a manoeuvre within 15 seconds.

Research suggests that this was possible, however it required that each of these steps was carried out efficiently and there is no delay in the detection of the target or determination of the threat status of the aircraft.

Figure 67: JQF left seat pilot's visibility windows

Source: ATSB

Figure 68: JQF left seat pilot visibility windows - last 15 seconds

Source: ATSB

Relative movement

Relative movement increases the opportunity for visual acquisition of a target. With the position of the target aircraft tracked across the viewer pilots’ field of view at constant, half second, intervals the speed of angular motion can be determined. For the purposes of the study the angular speed of movement was considered as a combination of the change in azimuth angle and elevation angle every 0.5 seconds (Figure 69), which was converted to a value in degrees per second.

Figure 69: Calculation of speed of angular motion

Source: ATSB

As discussed in the Object perception section, relative movement of 0.017-0.034°/ second (1-2 arcminutes/second) can be detected under optimal conditions where the movement is proximal to a stationary reference. A ’stationary reference’ was considered to exist when the target was within 5° of azimuth or elevation of the cockpit structure.

Where such a reference was not available, 0.17-0.34°/seconds (10-20 arcminutes/ second) was required to be detected. For an aircraft, the location of the aircraft structure in the pilot’s visual field will remain constant and so will act as the stationary reference point. As the Aircraft position assessment and target shielding sections discussed, the aircraft’s position in the visual field at defined intervals was known so its angular speed through the visual field could be calculated.

AEM

JQF’s movement across the visual fields of the pilots of AEM was significantly less than AEM’s movement across JQF.

This corresponded to lower angular speeds, with a range of between 0.012 and 10.64° per second, and an average angular speed of less than one third of that of JQF at 0.290° per second. For 12.5 seconds, of the 260 seconds leading up to the collision, the aircraft had an angular movement of less than 0.034° per second (2 arcminutes per second) and was unlikely to have been detectable.

For 65 seconds the target aircraft would have had an angular velocity of greater than 0.34° per second and therefore likely detectable with no stationary reference point. For the remaining time the target aircraft was more likely to be detected if it was proximal to a stationary reference point. Figure 70 and Figure 71 show the angular speed of the target aircraft and the times it was proximal (within 5° of azimuth or elevation) to stationary aircraft structure for the left and right seat pilots.

For AEM’s right seat pilot, as discussed in the Target shielding section, the target aircraft was close to but not obscured by the cockpit structure. For 219.5 of the final 260 seconds, the aircraft was proximal to the cockpit structure. Of the remaining 40.5 seconds, 37 were before 11:21:17.0 which was 182 seconds before the collision when the distance between the aircraft was approximately 12.5 NM and the target aircraft traversed only 0.02° in the pilot’s visual field.

The target aircraft then did not exit the proximal region again until 4 seconds before the collision, however by that time it would have been larger than 1° in the pilots’ visual field and there would have been insufficient time to react to prevent the collision.

For AEM’s left seat pilot the target aircraft was initially close to the centre of the windscreen and moved throughout the final 260 seconds towards the left cockpit pillar. This location limited the opportunity for enhanced visual acquisition due to proximity to cockpit structure with the target aircraft proximal to the cockpit structure for only 47.5 of the final 260 seconds. However, of these 47.5 seconds, 35 occurred over the last 75 seconds before the collision, including all but the last 1.5 seconds of the final 24.5 seconds leading into the collision. As discussed in Aircraft observed size the target aircraft at this point was getting larger and the combination of the movement in proximity to stationary structure increased the visual acquisition opportunity.

Figure 70: Target aircraft structure proximity and angular velocity - AEM right seat pilot

Source: ATSB

Figure 71: Target aircraft structure proximity and angular velocity - AEM left seat pilot

Source: ATSB

JQF

The angular velocity of AEM through JQF’s visual field varied from 0.03 to 10.33° per second with an average of 0.96° per second. Of the final 260 seconds AEM’s angular speed was sufficient to be detectable by the pilots of JQF without a stationary reference point for 184 seconds, or about 71% of the time.

For the remaining 76 seconds the aircraft’s movement through the field could be located if it was proximal to a stationary reference point. Due to the change in the pilot’s eye position from the left to right seat pilot as presented in the Target shielding section, the times when this occurred were different for the left and right seat pilots. Figure 72 and Figure 73 show the times for the individual pilots when the target aircraft was proximal to the aircraft structure and had a lower threshold for detection of relative movement. Both charts show that the closer to the time of collision the more time that the target aircraft spent proximal to, or obscured by, the structure.

For JQF’s right seat pilot the target aircraft was proximal of aircraft’s structure, but unshielded, for 139.5 of the final 260 seconds before the collision. The final time that the aircraft was not proximal to the structure and unshielded was between 34 and 30 seconds before the collision. At this time the aircraft was just over 2 NM away and the size of the target aircraft was approaching 0.2° in the pilot’s field of view, making the presence of the stationary reference of the cockpit structure less necessary for visual acquisition.

For JQF’s left seat pilot, the target aircraft was at the boundary of the aircraft’s structure but unshielded for 127 of the final 260 seconds before the collision. Approximately 15 seconds before the collision the target aircraft emerged from behind the aircraft instrument panel and moved towards the centre of the right windscreen. At this point the target aircraft would have had an angular velocity approximately 4° per second and an angle of 0.4° in the pilots’ visual field.

Evaluation

The movement of both AEM and JQF across the viewer pilot’s visual fields provided relative motion that increased visual acquisition potential. For the pilots of JQF, the target aircraft moved through a larger part of the visual field, and at a greater rate, increasing opportunity based on movement. With a significant portion of this movement proximal to stationary cockpit structure a reference was available for movement to be detected against.

As discussed in the Target shielding section this also meant that the target aircraft spent a significant portion of time obscured from view. This was particularly significant when the aircraft was at the limits of visual acquisition capability, 15-20 seconds prior to the collision. For AEM the target aircraft has less than one-third the average speed of motion in the lead up to the collision. For the right seat pilot, the movement of the target aircraft low on the windshield meant that the instrument panel and the centrally mounted compass provided stationary reference for the target’s movement.

For the left seat pilot, the target aircraft’s position higher in the windscreen meant that there was no stationary reference available for the initial time, however the movement towards the aircraft’s left cockpit pillar meant that at the critical time in the lead up to the collision the aircraft was not only unshielded but also in a position where its relative movement could have attracted the pilots attention.

The utilisation of the 5° proximal window is an important consideration. If the head or eyes were moved or rotated slightly, the stationary reference of the cockpit structure would change and may have obscured the target aircraft. This aspect will be discussed in the following Sensitivity analysis (Movement of the pilot’s eye position) and Field of view sensitivity (Rotation of the pilot’s eyes) sections.

Figure 72: Target aircraft structure proximity and angular velocity - JQF right seat pilot

Source: ATSB

Figure 73: Target aircraft structure proximity and angular velocity - JQF left seat pilot

Source: ATSB

Sensitivity analysis

As introduced in the Refining the pilots’ eye position section, optimised eye positions for each pilot were selected from a matrix of possible positions. The matrix moved the head and associated eye position 0.01, 0.03, 0.05 and 0.10 m along each axis generating 729 different eye positions and views for each of the 4 pilots. The original eye position prior to optimisation has been referred to as the ‘displaced’ eye position.

The following section presents the results of a target shielding analysis done on the displaced eye positions the equivalent of that which was done in the Target shielding section. For the purposes of this assessment the optimised and displaced eye positions are not the eye positions that show the least shielding time or the greatest visibility opportunity for the target aircraft. The purpose of the comparison between the optimised and displaced positions is to demonstrate the difference that small positional changes can make to visibility opportunity.

Through the process of selecting the optimised eye position, investigators reviewed imagery that represented the eye positions at the extremities ^[20] of the matrix. They examined the difference these made to the detectability of the target aircraft and its likely shielding behind cockpit structure. For example, as would be expected, the lower that a pilot sits in the structure the more shielding is provided by the instrument panel and the less likely an aircraft approaching from below the elevational origin will be detected. This movement in the vertical plane also effects the shielding of other parts of the aircraft structure outside the cockpit such as the wings and engine cowling.

AEM pilots

For AEM’s right seat pilot, displacement was 1 cm back, 3 cm right and 1 cm up (Figure 74). As with the optimised eye position, the target aircraft was not shielded during the final 260 seconds leading up to the impact. However, the displacement placed the target aircraft’s track closer to the central compass and the instrument panel meaning further small movements, particularly vertically, could lead to significant shielding of the target.

For AEM’s left seat pilot, displacement was 1 cm back, 5 cm left, with no vertical position shift. (Figure 75) This equated to a 70 second increase in the time that the target aircraft was shielded from view (Figure 76). Critically, this increase fell entirely within the last 90 seconds prior to the collision. The last practical visual acquisition opportunity before the target aircraft moved behind the left pillar was 27.5 seconds before the collision, when the aircraft made up 0.18° in the pilot’s field of view. The aircraft re-emerged from behind the cockpit pillar 1.5 seconds before the collision (Figure 77), however this did not provide sufficient opportunity for a reaction, let alone an evasive manoeuvre.

Figure 74: AEM right seat pilot ATSB displaced eye position

Source: ATSB
 

Figure 75: AEM left seat pilot ATSB displaced eye position

Source: ATSB

Figure 76: AEM left seat pilot’s visibility windows – displaced eye position

Source: ATSB

Figure 77: AEM left seat pilot’s visibility windows final 15 seconds – displaced eye position

Source: ATSB

JQF pilots

The shift between optimised and displaced eye position for JQF’s right seat pilot was 1 cm forward, 5 cm left and 3 cm down (Figure 78). This change in positioning equated to an increase in target shielding time of 54.5 seconds with an additional 5 shielded windows over the final 260 seconds, for a total of 149.5 seconds across 12 shielding windows. Critically, the aircraft remained shielded from the right seat pilot for the final 15 seconds prior to the estimated impact.

The last opportunity for the pilot to locate the aircraft would have been approximately 19 seconds before the impact time and the aircraft would have appeared for approximately 3 seconds while transitioning between the instrument panel and the right cockpit pillar. At this time the aircraft would have an angular size of approximately 0.3° in the pilot’s field of view. Figure 79 and Figure 80 show the target viewing windows over the final 260 and 15 seconds respectively.

For the left seat pilot of JQF the shift between optimised and displaced eye position was 5 cm back, 3 cm left and 5 cm up (see Figure 81). This resulted in a decrease in target shielding by 4.5 seconds with one more shielding window, totalling 74.5 seconds over 7 shielding windows. The aircraft would have appeared in the pilot’s view approximately 15 seconds before the impact, at a size of approximately 0.36° in the pilot’s field of view. Prior to this, the aircraft would have been shielded by the instrument panel and the central pillar of the windscreen for approximately 23 seconds. Figure 82 and Figure 83 show the times the aircraft was shielded by the cockpit structure.

Figure 78: JQF right seat pilot ATSB displaced eye position

Source: ATSB

Figure 79: JQF right seat pilot’s visibility windows - displaced eye position

Source: ATSB

Figure 80: JQF right seat pilot’s visibility windows final 15 seconds - displaced eye position

Source: ATSB

Figure 81: JQF left seat pilot ATSB displaced eye position

Source: ATSB

Figure 82: JQF left seat pilot’s visibility windows – displaced eye position

Source: ATSB

Figure 83: JQF left seat pilot’s visibility windows final 15 seconds – displaced eye position

Source: ATSB

Evaluation

The sensitivity analysis identified that even small movements in the pilot’s eye position could have a very significant impact on the target shielding. The left seat position of AEM demonstrated the most significant change to the pilot’s eye position, with an increase in the shielding time of 68.5 seconds. This included almost all the last 20 seconds of flight where the pilot has the best chance of visual acquisition.

By contrast, analysis of the left seat position of JQF shows that similarly small movements in the eye position could reduce the shielding time, with the displaced eye position giving 4.5 additional seconds where the aircraft was visible to the pilot. While this time was not at a critical phase (the aircraft still emerged approximately 15 seconds before the collision), it demonstrated the difference that these small movements could make.

For the right seat pilots a similar contrast was present. For JQF, the movement increased the shielding time by almost a minute (54.5 seconds) throughout the final 260 seconds with much of this increase occurring later in the timeline where it limited visual acquisition opportunity. The right seat pilot of AEM remained entirely unshielded for all the final 260 seconds. Interestingly, this showed the difference that the speed slope windscreen made, one of the reasons that JQF’s shielding time was much higher was that the target aircraft was obstructed by the central pillar of the cockpit as it crossed the windscreen.

Further detail on other eye positions tested are outlined in attachment A to this report.

In summary, this analysis demonstrates the importance of moving the head when scanning and searching. Moving the head changes the location of the shielding obstructions, potentially overcoming the lack of relative movement associated with intercepting courses at constant speed.

Field of view

The aircraft positioning and target shielding considerations to this point have included the entire spherical field around the eye position. However, as discussed in the Field of View section, a person can only see and perceive a certain portion of this area at any point in time. It is therefore important to consider where the aircraft was within the field of view throughout the flight.

As previously discussed, the ATSB has defined 3 areas of the human vision where objects are likely to be located without specifically looking for them and where something on the target will be required to attract attention (such as a strobe light). The area for the full field of view were defined as 190° of azimuth by 135° of elevation. For the inner field a literature review was unable to provide a definitive value for the size of this area, however for this study the size of the inner field was estimated as 60° of both azimuth and elevation evenly distributed around the centre of the field of view. Making up the inner 10° of both azimuth and elevation, the foveal region or the area of highest, daylight, visual acuity was also represented. The following sections show these 3 areas as they relate to the position of the aircraft and the opportunity for visual detection.

The following section and the Field of view sensitivity section that follows present an examination of where the target aircraft likely appeared in the field of view of each pilot, assuming that they were looking out of the windscreen. Given the stage of each flight, with AEM preparing to conduct an instrument approach, and JQF conducting an instrument departure, it must be considered that each of the left seat pilots were likely spending more time conducting instrument scans than visual scans outside the window. While this limits how effective this assessment was for the accident case, it also demonstrates the importance of scanning through the whole visual field to best aid visual traffic acquisition.

AEM

Figure 84 and Figure 85 show the pilot views from AEM with the outer, inner and foveal regions of the field of view identified. The target aircraft fell within the inner field for the entire 260 seconds. Therefore, the pilot should have been able to perceive it when it was of a sufficient size to be located. The foveal region is the area of maximum visual acuity and where objects are most likely to be detected.

For both the left and right seat pilots of AEM, JQF spent most of its time on or within the boundaries of this area. For AEM’s pilots the target aircraft was within the foveal region for 154.5 of the final 260 seconds. This included the first 147.5 seconds, 6 seconds between 11:23:40 and 11:23:46, and the last second before the collision. Upon exiting the foveal region at this time, the target aircraft proceeded to a maximum of 16° to the left of the centre of field of view before coming back towards the centre of the field.

Figure 84: AEM left seat pilot - fields of view – optimised eye position

Source: ATSB

Figure 85: AEM right seat pilot - fields of view - optimised eye position

Source: ATSB

JQF

Through the final 260 seconds, AEM transitioned through 101° of azimuth from -64.1° to 36.4° and 22° of elevation from 7° to ‑15°. As the target’s elevation remained entirely within the inner field of view, the further analysis will only consider its positioning for azimuth.

The target started in the outer field of view, initially moving to the left and a minimum azimuth value of -64° before increasing elevation and transiting back towards the inner field of view. The aircraft entered the inner field of view on the left of the pilot’s view (-30° azimuth) at approximately 11:21:16, looping further into the region and back out again, exiting into the outer field of view at 11:21:50. After 7 seconds the target re-entered the inner visual field and passed through the foveal region from 11:22:19 to 11:23:09 and continued across the inner field of view, exiting at 11:24:05, and continued in the outer field of view until the collision.

As the inner visual field is the area that a pilot is likely to be able to detect an object without having attention specifically drawn to it, the timings and size of the target aircraft within this area are critical. At 11:21:16 when the target aircraft entered the visual inner visual field it made up only 0.02° of the pilot’s visual field - a size that is very unlikely to be detectable. 41 seconds later, when the aircraft re-entered the inner visual field it had almost doubled in size to 0.035° in the pilot’s visual field. The size continued to increase as the target crossed the inner and foveal fields.

By the time the target exited the inner field of view at 11:24:05, it was 0.35° in the pilot’s field of view and at a size that was likely detectable. This has not considered shielding of the target aircraft by the cockpit structure, which will vary between the 2 pilots. For the left seat pilot of JQF, of the 162.5 seconds that the aircraft traversed through the inner and foveal regions it was shielded by cockpit structure for approximately 40% of this time by the left windscreen pillar, instrument panel and the centre windscreen pillar and compass.

For the right seat pilot of JQF, of the 162.5 seconds that the aircraft is traversed through the inner and foveal regions, it was shielded by cockpit structure for over 35% of this time, by the centre windscreen pillar and compass, the top of the instrument panel and the right windscreen pillar.

Figure 86 and Figure 87 Show the field of view from the left and right seat pilots of JQF and the time window through which the target aircraft was traversing the inner field of view.

Figure 86: JQF left seat pilot - fields of view – optimised eye position

Source: ATSB

Figure 87: JQF right seat pilot - fields of view – optimised eye position

Source: ATSB

Field of view sensitivity

The earlier Sensitivity analysis section considered the movement of the pilot’s eyes while facing forward. Rotation of the head and eyes will have different effects on the field of view. Due to the distance of the eyes from the axis of rotation (centre of the neck) rotating the head will affect both the field of view and the location of the eyes, affecting the position of the ‘target’ aircraft and the location of the ‘viewer’ aircraft structure. The field of view can also be affected by rotation of the eyes themselves, however this only affects the field of view and not the position of the ‘target’ aircraft or structure.

As the head is rotated about its horizonal axis the eyes, being forward of the axis, will move in the x-y plane relative to their original position. Figure 88 shows a highly stylised example of the effect that a 30° rotation can have on X and Y positions of the eye relative to the heads point of rotation. An equivalent movement of the eyes will occur in the Y-Z plane when the head is rotated about its vertical axis. Discounting binocular vision considerations, which for the purposes of this section are considered negligible, these movements of the eye position will have the same effect as the movements of the eye position discussed in the Sensitivity analysis section. The rotation of the field of view that occurs with the rotation of the head will also occur when the eyes are rotated independently of the head.

Figure 88: Example of eye position displacement due to head rotation (top down view).

Source: ATSB

If the eyes are rotated about their own axis this movement will not induce a movement affecting the eyes position only the field of view, subsequently position of the target aircraft and the cockpit structure do not change. However, the position within the field of view will change. As discussed in earlier sections, the appearance of objects in different areas of the visual field can make them more or less likely to be detected by the pilot.

Figure 89 shows a highly stylised image of the effect that a rotation of the eyes horizontally has on the field of view. A 30° rotation has been used to show the effect of the rotation more clearly on the field of view, the following analysis will consider rotations up to 9°. Rotation of the eyes about their horizontal axis will affect the field of view in the azimuth plane while rotation about the eyes vertical axis affect the elevation angle. Note the constant eye positions as the head has remained stationary against the rotated field of view.

Figure 89: Field of view change with eye rotations (top down view.)

Source: ATSB

The ATSB considered a matrix of eye rotations that moved the field of view 3, 6 and 9° in both the positive and negative directions of azimuth and elevations and analysed the resultant effect. This produced 49 different fields of view, but as per the previous analysis these rotations have only been applied to the ATSB’s optimised eye position for each pilot.

The analysis below considers the extremities of rotations, separately considering the changes to detectability of the aircraft based on its position in the differing fields of view. While this provides an insight into the detectability and location, it only considers a snapshot in time at the maximum value examined. In a real-world scenario, the pilot’s head and eyes will constantly move and rotate through the scanning process, combining the effects of the Sensitivity analysis, the discussion of head rotation presented above and the eye rotations that will be explored below. Throughout a flight pilots will also look at various instruments or systems in the cockpit, other flight crew members or passengers constantly changing the field of view and the focus location.

AEM

The comparatively small movement of the target aircraft through the field of view of AEM’s pilots meant that the rotations made relatively little difference to what area of the pilot’s field of view the target aircraft appeared. The negative azimuth rotations brought the later locations of the aircraft more into the foveal field than the original viewpoint. A negative azimuth rotation of 9°, as shown in Figure 90 and Figure 91, increased the amount of time that the aircraft spent in the foveal region from 154.5 seconds to 244.5 of the final 260 seconds.

The 15.5 seconds that the aircraft did not spend in the foveal region was the first 15.5 seconds of data recorded and would have been at a time when the aircraft would not have been detectable due its angular size in the pilot’s view. At this rotation the target aircraft moved into the foveal region at approximately 11:20:15.5 when the aircraft were separated by approximately 16 NM. It remained in the foveal region until the estimated time of collision. For the left seat pilot, this eye rotation also brought the left cockpit pillar into the foveal region. While it did not impact target aircraft visibility, the appearance of the stationary structure in the key part of the visual field may have had 2 effects:

• provided a better capacity for the detection of relative movement by making the stationary object more obvious.
• increased the likelihood of a focal trap with a stationary object being so prominent, which would reduce opportunity for detection.

For the right seat pilot, this brought the centrally‑mounted compass into the field of view, which would have a similar impact as a static point in the field of view.

Figure 90: AEM left seat pilot FOV azimuth (Az) -9° elevation (El) 0°

Source: ATSB

Figure 91: AEM right seat pilot FOV Az -9° El 0°

Source: ATSB

Rotating the eyes positive 9° of azimuth, as shown in Figure 92 and Figure 93, located the target aircraft within the foveal region for the first 52.5 of the final 260 seconds. While the target exited the foveal window, it remained within the inner field of view where the likelihood of detection remained good.

For both the left and right pilots, this brought elements of the cockpit structure into the foveal view. For the left pilot, part of the compass was within the foveal region and for the right pilot, part of the right pillar and instrument panel were then in the foveal view. While these were then visible within this region, they were also away from the position of the target aircraft so their effectiveness in assisting detecting relative movement would have been minimal.

Figure 92: AEM left seat pilot FOV Az 9° El 0°

Source: ATSB

Figure 93: AEM right seat pilot FOV Az 9° El 0°

Source: ATSB

As with azimuthal rotation, elevational rotation only significantly affected how much time the target aircraft spent in the foveal region. As above, rotation of the pilot’s eyes was considered 9° above and below the elevational origin.

Rotating the pilot’s eyes 9° above the origin is equivalent to the pilot scanning towards a distant location or the horizon, as shown in Figure 94 and Figure 95. For this rotation the target aircraft was within the foveal region for 34.5 of the last 260 seconds. Of these 34.5 seconds, 33.5 of them were within the first 2 minutes following JQF’s take-off when the aircraft was outside of visual range. The final second within the foveal region was at 11:21:17, 3 minutes and 3 seconds before the estimated collision time. At this time, the target aircraft would have an angular size of only 0.02° in the field of view and so was likely undetectable.

A rotation of 9° below the origin, as shown in Figure 96 and Figure 97, is the equivalent of a pilot looking at instruments in the top part of the instrument panel. At this rotation the target aircraft was within the foveal region of 150 of the final 260 seconds. The target aircraft was in the foveal region across 3 windows. The first 2 of these windows totalled 144 seconds and were completed before 11:22:27 when the aircraft was 0.04° in the pilot’s field of view. The remaining 6 seconds were between 11:23:40 and 11:23:46, where the aircraft ranged between 0.12 and 0.16° in the pilot’s field of view

For both pilot’s this field also brought a portion of the instrument panel into the foveal region, providing a stationary structure in the field of view. The advantage of this would have been greater for the right seat pilot, with the movement of the aircraft closer to the stationary structure than for the left pilot.

Figure 94: AEM left seat pilot FOV Az 0° El 9°

Source: ATSB

Figure 95: AEM right seat pilot FOV Az 0° El 9°

Source: ATSB

Figure 96: AEM left seat pilot FOV Az 0° El -9°

Source: ATSB

Figure 97: AEM right seat pilot FOV Az 0° El -9°

Source: ATSB

JQF

The effect of the eye rotations was greater for the pilots of JQF, with the target aircraft moving not only though the foveal region but also from outer region to inner region and back out again. As discussed in the Target shielding section, for the optimised eye position, the target aircraft was shielded during multiple windows to both pilots of JQF. While the rotation of the eyes did not affect the relative position of the target or the structure, the timings when the aircraft was more likely to be detected were dependent on what part of the visual field it was in.

If the aircraft was shielded while it was in the foveal or inner regions it was less likely to be detected. As with the AEM examples, the following sections consider the effect of positive and negative 9° rotations in both azimuth and elevation angles. These will show the extremities of the movement examined in a real-world scenario as a pilot rotated their eyes to scan or look out the cockpit and subsequently the visual field will move through these rotations and viewpoints.

A positive azimuth rotation of 9° retained the aircraft within the full visual field for its entire trajectory. The target aircraft entered the inner field of view at 11:21:20, 179.5 seconds before the collision and exited the inner field at 11:21:35. During this time it remained unshielded to the left seat pilot but was shielded for the entire time from the right seat pilot by the centre spline of the windscreen and the centrally mounted compass. The target then re-entered the inner visual field at 11:22:06, 134 seconds before the collision and remained in the inner field until the collision. While during this time it was shielded from the right seat pilot for 53 seconds and from the left seat pilot for 48 seconds.

Within this final 134 seconds the target aircraft moved in and out of the foveal region twice totalling 21 seconds within the foveal region. Of these 21 seconds, for the right seat pilot 8 of them were calculated as shielded by cockpit structure. For the left seat pilot, the target aircraft was shielded for 19.5 seconds. The target aircraft exited the foveal region at 11:23:54, 26 seconds prior to the collision. From this time until the collision, the target aircraft was shielded from the left seat pilot for 11 seconds and from the right seat pilot for 21 seconds. Figure 98 and Figure 99 show the left and right seat pilot’s views with a positive 9° azimuthal rotation.

Negative azimuth rotation of 9° retained the target aircraft within the full field of view for its whole trajectory. With this shift, the target aircraft exited the inner field before the time of the collision. The target aircraft remained in the inner or foveal visual field for 134 seconds split over 2 windows. The first, 122.5 seconds, starting at 11:21:12 and exiting at 11:23:14.5, approximately 66 seconds before the collision. Of this time the target aircraft was obscured by cockpit structure for 46.5 and 38.5 seconds to the left and right seat pilot’s respectively.

The second entry to the inner field was for 13.5 seconds. The target aircraft entered at 11:23:46 and exited at 11:23:59.5, approximately 21 seconds before the collision. Of this time the target was shielded by structure for 11.5 and 4.5 seconds to the left and right seat pilot’s respectively.

The aircraft was in the foveal region of the visual field for 62.5 seconds split over 2 windows. The target entered the foveal region for 9 seconds, entering at 11:21:22.5 and exiting at 11:21:31.5, 168.5 seconds before the collision. Of these 9 seconds the target was shielded by cockpit structure for the whole time to the right seat pilot and remained unshielded to the left seat pilot.

The second entry to the foveal region lasted 53 seconds, entering at 11:22:08 and exiting at 11:23:00.5, approximately 79.5 seconds prior to the collision. The target aircraft was shielded by cockpit structure for 5.5 and 12 seconds from the view of the left and right seat pilot’s respectively. Figure 100 and Figure 101 show the left and right seat pilot’s views with a -9° degree azimuthal rotation.

Figure 98: JQF left seat pilot FOV Az 9° El 0°

Source: ATSB

Figure 99: JQF right seat pilot FOV Az 9° El 0°

Source: ATSB

Figure 100: JQF left seat pilot FOV Az -9° El 0°

Source: ATSB

Figure 101: JQF right seat pilot FOV Az -9° El 0°

Source: ATSB

The maximum and minimum elevation values of the target aircraft were 7 and -15° respectively. Therefore, rotations in this direction were less likely to affect the pilot’s visibility windows than movements in azimuth. A rotation of 9° below the elevational origin indicated 3 windows in which the target aircraft was in the pilot’s inner visual field and one where it was in the pilot’s foveal region.

The first window, between 11:21:16.5 and 11:21:50.5 (34 seconds), finishing approximately 210 seconds before the collision. Within this period, the target aircraft was shielded by structure for 11 and 17 seconds for the left and right pilot’s respectively. Through this window the maximum angular size of the aircraft was 0.033°, well below the detectable threshold.

The second window was 128 seconds, between 11:21:57 and 11:24:05, ending approximately 15 seconds before the collision. Throughout this window the target aircraft was shielded by structure for 52.5 and 39.5 seconds to the left and right seat pilot’s respectively. At the time the aircraft exited the inner field it had an angular size of approximately 0.35°.

The final entry into the inner field was 0.5 seconds at 11:24:18 approximately 2 seconds before the collision. The target would have been visible to the right seat pilot and shielded from the left seat pilot. The angular size of the aircraft would have been approximately 4.5°, making it easily detectable. However, by this time it would not have been possible to execute a successful evasive manoeuvre.

During the second movement of the target aircraft through the inner visual field it also traversed the foveal region between 11:22:19.5 and 11:23:10. Within these 51.5 seconds the aircraft was shielded by cockpit structure for 14.5 and 11.5 seconds for the left and right seat pilots respectively. Figure 102 and Figure 103 show the left and right seat pilot’s views with a -9° elevational rotation.

The final rotation that has been considered in the sensitivity analysis is positive elevation rotation of 9°. This rotation was considered important to review as the location the target aircraft was just below the elevational origin leading up to the final part of the track. The data indicated that with this rotation the aircraft entered and exited the inner field at the same times as the previous rotation. This was to be expected due to the relatively small changes in elevation over time compared to azimuth and the size of the inner visual field.

Due to the position of the target aircraft in the visual field for this eye position the target aircraft did not enter the foveal region at any during time during the final 260 seconds leading up to the collision. As shown in Figure 102 and Figure 103, the rotation at certain points would only have to be slightly less in this direction and it would have fallen into the pilot’s foveal field.

Figure 102: JQF left seat pilot FOV Az 0° El -9°

Source: ATSB

Figure 103: JQF right seat pilot FOV Az 0° El -9°

Source: ATSB

Figure 104: JQF left seat pilot FOV Az 0° El 9°

Source: ATSB

Figure 105: JQF right seat pilot FOV Az 0° El 9°

Source: ATSB

Evaluation

Accurately tracking the movement of the pilots’ head and eyes, was not possible with the available information. Based on the previous positional analysis of the pilots’ eyes, an optimised eye location was chosen and subsequently a series of rotations of the eyes were considered to assess what effect they might have had on the target aircrafts visibility. The presentation of the extremities of these rotations indicates what the maximum effect was likely to be. However, as previously stated, the actual rotation would probably have been constantly changing as the pilot scanned both inside and outside the aircraft.

For the occupants of AEM these rotations were only likely to have altered when the target aircraft was within the region of highest visual perception (foveal region). Additionally, they also had the potential to alter where in the field of view parts of the aircraft structure sat and subsequently affected the possibility of detection of the aircraft through either the identification of relative movement or the creation of a possible focal trap near the position of the aircraft.

For JQF’s pilots, due to the amount of the field of view that the target aircraft traversed, the impact of these rotations on the time that the aircraft was in the inner field of view was more significant. The negative azimuthal rotations brought the target aircraft into the inner field sooner. For the left seat pilot this was negated by the presence of aircraft structure but for the right seat pilot it was unshielded.

However, the target aircraft also departed the inner visual field sooner when its relatively smaller size made it less detectable. Conversely, the earlier detection opportunity by the right seat pilot had minimal impact on them due to shielding of the aircraft structure, for the final part of the flight path. The left seat pilot had less obstructions once the target aircraft moved out of the inner visual field, but the position of the target aircraft, first behind the centre windscreen spline and then behind the instrument panel further limited opportunity for detection.

The movement of the foveal fields of view with the elevational change was most pronounced with the increase in elevation. The movement of the eyes upward took the target aircraft entirely out of the foveal region. While this would not have prevented the aircraft from being detected, as it could still be in the inner field, at distance and during daylight the foveal area offers the best opportunity for detection.

Cockpit display of traffic information study

Alerting

The concept of internal and external alerting was previously discussed in the Avoidance Alerting section. This section will focus on internal alerting systems but as detailed previously, these work in conjunction with external alerts to assist in the development of the mental model. In the lead up to this accident the occupants of both JQF and AEM were provided with radio advice (external alerts) via air traffic control identifying the presence and approximate location of the other aircraft.

In addition to these alerts, in the 4 minutes leading up the collision the controller also received 2 short term conflict alerts (STCA) on the 2 aircraft. ^[21] These were not passed through to the pilots, nor were they required to be (refer to investigation report for further details). Subsequently, they were not considered further as a potential source of external alerting.

The radio communications provided by the controller were one potential source of external alerting. Communications on a common frequency (CTAF), whether directed to the receiver or simply overheard, also assists pilots to develop an accurate mental model of the surrounding traffic. The pilots of JQF and AEM were managing 2 or 3 different frequencies respectively. Both aircraft communicated with the Melbourne Centre controller, and procedurally were required to broadcast on the Mangalore Airport CTAF.

Additionally, as they were inbound to Mangalore Airport, the pilots’ of AEM, would probably have accessed broadcast weather information, which was on a separate frequency. Even with dual radios, the need to engage with different frequencies limited the pilots’ opportunity to establish communications with one another or hear information from another aircraft (or ATC) that may have assisted in the development of their mental model.

As the ATSB concluded that the pilots did not establish communications with each other on the CTAF or other frequencies, it was assumed for the purposes of this study that the only external alerts received were the individual communications with the controller on the Melbourne Centre frequency. Considering this scenario, the pilots’ mental model of the location of the other aircraft was developed with limited information. Further, in the key moments just before the collision, when the aircraft were of a detectable size, the only provided traffic information was 2‑5 minutes old, limiting its effectiveness to assist visual acquisition.

Internal alerting

The ATSB considered 2 options for internal alerting systems that were available, but not fitted or in use at the time of the accident. The first was an EFB application and attached ADS-B IN device providing information to the pilot. However, due to the lack of alerting functions on commonly utilised EFBs at the time of the accident, and the number of different available options, replication of one EFB application would not necessarily have been representative. It was therefore decided to replicate an approved and RTCA DO-317B‑compliant system ^[22] (see the following section) to demonstrate a best practise example of how ADS-B IN traffic alerting can significantly enhance situational awareness.

The presented imagery illustrates the system as it would have appeared to the pilots and how it would have reacted to the presence of the other ADS-B OUT equipped aircraft. It will also detail what alerts and associated information would have been displayed in accordance with the standard. The appearance and displayed information for individual systems, or implementations, may be different to that presented.

CDTI and ATAS in built – RO-317B compliant

Using the ADS-B position and altitude data calculated in the Aircraft performance study, the ATSB developed input data for a simulation program based on material provided by the RTCA (formerly Radio Technical Commission for Aeronautics) and NTSB for demonstration purposes. To improve the realism of the simulation, the ATSB also added in ADS-B returns for other aircraft in the area that were detected by the Airservices network.

The presented display (Figure 106) depicts 3 range rings at 15, 6 and 2 NM around the viewer aircraft. These range rings are normally adjustable using the zoom level of the display however, for the purposes of this demonstration the zoom functionality has been disabled. The simulated CDTI display shows the position and orientation of each aircraft (target) relative to the viewer aircraft. Beside the traffic icon (blue unfilled arrowhead), there is information about the aircraft. This can display a range of parameters, but in this case has been limited to only show vertical proximity and tendency. The number beside the aircraft shows the vertical proximity in 100 ft increments either above (+) or below (-) and the arrow shows vertical tendency - up arrow, indicating climbing, and down arrow, indicating descending, at more than 500 feet per minute.

The display has 3 levels of alert or display change to assist the pilot. The first is a transition from traffic to proximal traffic. This identifies that another aircraft has moved to within 6 NM and 1,200 ft of the viewer aircraft. This does not trigger an aural alert but changes the display of the target aircraft from a blue outlined arrowhead to a blue filled arrowhead. Within this zone the ATAS system calculates 2 separate radii around each of the target aircraft called the protected airspace zone (PAZ) based on target closing speed and distance and the collision airspace zone (CAZ) defined as a 500 ft radius around the target and 200 ft vertically. These zones are continuously redefined based on updated ADS‑B information received about each target aircraft.

Once the aircraft is projected to breach either the PAZ or CAZ around a target aircraft within the next 15 seconds an audible alert is triggered in the ATAS system. If the system is linked to a CDTI, the CDTI will also show a change in the target aircraft symbol. If the breach is projected to occur in more than 15 seconds the ATAS will hold the alert until a second predicted breach is received at which point the system will alert. This is designed to limit nuisance alerts.

This alert tells the pilot the relative bearing (in clock co-ordinates), distance to, relative vertical position, and current activity (climbing, descending or level) of the target aircraft. The identifier on the CDTI screen also changes from a blue filled arrow to a yellow arrowhead in a circle.

Based on these requirements and the calculated aircraft positions for both aircraft the ATSB has developed CDTI and ATAS simulations of the final 260 seconds of the accident flight.

The following figures show the exemplar CDTI displays at key moments throughout the sequence. Specifically, when the aircraft would have become visible on each other’s CDTI displays and when PAZ and CAZ breach alerts, provided audibly to the pilot as well as displayed on the CDTI, would have been triggered.

Figure 106 shows the CDTI displays of both AEM and JQF at 11:20:01, (259 seconds before the collision), the approximate take‑off time of JQF. At that time, no ADS-B equipped targets would have been displayed.

Figure 106: CDTI displays at 11:20:01

Source: ATSB

Figure 107 shows the CDTI displays at 11:20:43 (3 minutes and 37 seconds before the collision) when the target aircraft first became visible on the display at 15 NM from the viewer aircraft with about 4,600 ft vertical proximity.

Figure 107: CDTI displays at 11:20:43

Source: ATSB

Figure 108 shows the CDTI displays when the aircraft transitioned to proximal traffic, with the target aircraft showing as a blue filled arrowhead while other ADS-B traffic on the screen remained unfilled. Note: at that time the target aircraft was inside the 6 NM range ring and had a vertical proximity indication of +/- 12 (indicating traffic is 1 200 ft above or below). The one second time difference between the change to proximal traffic on the displays (11:23:38 – JQF and 11:23:39 - AEM) was due to the resampling during the data processing for the animation making the transition appear one second later on the AEM display.

Figure 108: CDTI displays at change to proximal traffic

Source: ATSB

Figure 109 shows CDTI displays and associated alert at the time the aircraft were projected to breach the PAZ the around the target aircraft as defined by the closing speed of approximately 245 kt. Note the change in display of the target aircraft to the more prominent yellow, clearly identifying it from other ADS-B traffic. The text shown on the display would have been enunciated through the pilot’s headset or the internal communications system and is not displayed on screen.

There is also a slight variation in the times that this alert occurs for the 2 aircraft (2 seconds, 11:23:48 – JQF and 11:23:50 – AEM). This is most likely due to differences in estimation of future track points for each aircraft and associated projected PAZ breaches.

Figure 109: CDTI displays at the time of the PAZ breach alert

Source: ATSB

Figure 110 show CDTI displays and associated alert at the time that the viewer aircraft projected a breach of the CAZ around the target aircraft. Note the aircraft remained in the highly visible yellow colouring. Again, there is a slight variation in the times that this alert occurs for the 2 aircraft (2 seconds, 11:23:54 – JQF and 11:23:56 – AEM). This is most likely due to differences in estimation of future track points for each aircraft and associated projected CAZ breaches.

Figure 110: CDTI displays at the time of the CAZ breach alert

Source: ATSB

Animation Development

To assist in the visualisation and understanding of the accident sequence and to give a more realistic visualisation of what pilots may have seen, the ATSB developed an animation of the final 260 seconds leading up to the accident. This animation was developed using Microsoft Flight Simulator X (FSX) software using the optimised eye position of each of the 4 pilots involved. The animation development consisted of 4 parts:

• flight path development and integration
• cockpit visualisation and modelling
• environmental condition modelling and visualisation
• recording and integration with animated CDTI display.

The following sections briefly outline how each of these were carried out and what information was used in their development.

Flight path development and integration

Through the Aircraft performance study, the ATSB developed a smoothed flight path based on ADS-B data for both aircraft. FSX does not have a native ability for flight paths to be imported and have aircraft fly them. To enable this, the ATSB utilised a third party add‑on application called FS Recorder ^[23] to import and record the flight paths with cockpit views from each pilot’s position.

Cockpit visualisation and modelling

Aircraft selection

The animation relied on the viewer seeing a representative target aircraft. Neither a D95A Travel Air or a PA-44 Seminole were native to FSX and so representative models had to be sourced. Due to functionality built into FSX users could develop or modify aircraft to suit their needs. A Piper PA-44 Seminole model was able to be located and freely available for download. ^[1] This model was utilised for external modelling purposes, with the cockpit panels replaced with ATSB developed cockpit masks (see the section below titled Cockpit masks).

An FSX‑compatible model of a D95A Travel air was not able to be located. Consequently, a Beechcraft Baron, which was provided native with FSX, was used for this animation. The Baron fuselage is approximately 600 mm longer than the Travel Air, but both have the same twin engine, low wing configuration. The ATSB assessed that the differences between the 2 aircraft would have little impact on the animation. Internal cockpit views were removed and replaced with the ATSB cockpit mask of the Travel Air.

Aircraft lighting

As discussed previously in the Aircraft lighting section, lights provide enhanced opportunity for visual acquisition of the target aircraft. FSX has functionality to allow aircraft lighting to be simulated and activated, this included landing, position, and anti-collision strobe lights. As it was determined that JQF’s landing light may have provided AEM’s pilots an improved opportunity for visual acquisition, consideration was given to utilising lighting on the model of JQF. However, testing identified that the simulated lights were lower power than those on the aircraft and unlikely to be representative of that fitted to JQF. Consequently, the final animation was created with all lighting switched off.

The model used to simulate AEM also had lighting available however this lighting was not representative of that which was fitted to the accident aircraft. Due to this and the previous determination that lighting installed on AEM was unlikely to have provided any detection advantage for the JQF pilots it was also switched off for the development of the animation.

Camera positions

The camera position of FSX was used to replicate the pilots eye positions. The standard FSX camera position provided visualisation of a maximum of 90° horizontally and approximately 54° vertically. ^[25] The process of calculating these angles was developed by the NTSB and is described in Appendix B of O’Callaghan, 2020 supported by Hestnes 2011. Horizontally, the 90° was split either side of the zero-point, giving a view of azimuth values from -45 to 45°. Where objects lay outside this, they were not visible to the viewer unless the camera was rotated, or the field of view was expanded.

Rotating the field of view allows the viewer to see objects within that new area, however it removes the portion of the screen that the camera has been rotated away from. To best recreate the visual field a second camera, and in this case a third, co-located with the first but rotated through a set angle was used. The second camera was rotated 90° positive giving a view of 45 through 135° of azimuth. The third camera was rotated through 90° negative giving a view of -45 through -135° of azimuth. The view of the second and third cameras were located on separate displays of the same resolution placed to the appropriate side of the main displays. This provided a view of 270° of azimuth with 54° of elevation, further cameras and screens can be used to show more of the visual field however in this case it was not considered necessary. The simulated views on each screen were recorded concurrently.  

It is important to note that the rotation of the cameras leads to discontinuities in the visualised image, most notably the apparent rotation and position of the horizon line as viewed from the cockpit. This apparent rotation is due to the projection of the horizon line onto a flat surface as they are recorded. If the 2 screens to either side of the main view are located physically at 90° to one another, the effect is less pronounced. Figure 111 and Figure 112 show the 270° from both AEM and JQF at the start of the animation.

Figure 111: 270° view from AEM depicting terrain and meteorological conditions

Source: ATSB

Figure 112: 270° view from JQF depicting terrain and meteorological conditions

Source: ATSB

Cockpit masks

With cameras positioned, cockpit masks were developed and placed over the cameras view to represent the physical obstruction to the pilots’ sight lines from the cockpit structure. FSX and the various aircraft came with native cockpit layouts or panels that aimed to provide the user with a realistic experience. However, the dimensional accuracy of these cockpit layouts was not known so they could not be relied upon for visualisation. These cockpit views are stored within the aircraft file structure as image files that are loaded for the aircraft when the flight is created.

Using the cockpit imagery, the 3-dimensional models developed from the laser scan data and optimised pilot’s eye position, the ATSB created dimensionally accurate cockpit masks as the pilots would have experienced them. The masks were then scaled to the correct size for the visual field displayed by each camera view and placed in the aircraft’s file structure in place of the existing panels.

The cockpit mask was created as a single bitmap image. FSX defines a specific colour (black) as transparent, giving an unobstructed view in these areas. Any other colours in the mask will show as solid colour with their transparency able to be adjusted from solid to fully transparent. To allow the viewer to get a better understanding of when the target aircraft is shielded by the structure and where it is located behind the structure, for the purposes of the animation, the transparency of the cockpit mask was set to 30%.

Figure 113 shows a single panel cockpit mask as developed for the left seat pilot of AEM. Note the black areas that FSX recognises as fully transparent. This mask was overlaid on the central screen depicting azimuth angles of -45° through 45°. Figure 114 shows the complete mask that is sectioned for the 3 screens and depicts as 270° of azimuth -135° through 135°. Figure 115 and Figure 116 show the cockpit mask panels with a transparency of 30% overlaid on the simulated views from AEM and JQF at the start of the animation.

Screen resolution

When projected onto a display the target aircraft can only become visible to the viewer when it reaches the size of one pixel. With a full high definition screen (resolution of 1920 x 1080 pixels) and a FOV of 90° per screen, each pixel makes up approximately 0.047° (approximately 3 arc minutes) of azimuth. This is well below even the ideal size of human perception of 0.2° (12 arc minutes), as discussed in the Object perception section. Due to this, the utilisation of a higher resolution screen was not considered necessary. Based on the ATSB analysis, JQF occupied one pixel in the AEM animation at approximately 11:22:29.50 (129.5 seconds into the animation), and AEM reached the size of a pixel in the JQF animation at 11:22:31.50 (131.5 seconds into the animation).

Figure 113: Scaled central cockpit mask left seat pilot (LSP) of AEM (depicting azimuth -45 through 45°)

Source: ATSB

Figure 114: Scaled cockpit mask of LSP of AEM (depicting azimuth -135 through 135°)

Source: ATSB

Figure 115: Cockpit mask overlaid on 270° view from AEM (260 Seconds before collision)

Source: ATSB

Figure 116: Cockpit mask overlaid on 270° view from JQF (260 Seconds before collision)

Source: ATSB

Condition modelling and visualisation

FSX has the capability to model terrain, sun position, based on date and time, and meteorological conditions. While this is designed to improve the user’s simulation experience it also allows for more accurate recreation of real-world conditions. To accurately represent the desired conditions wind, cloud, rain, and certain other parameters can be modified based on the user’s preference. Using this functionality, the ATSB developed 3 scenarios.

The first was in accordance with the conditions recorded by the Mangalore Airport weather station at the time of the accident. The conditions were inputted into the FSX weather simulation process using base altitudes, cloud types and ceilings estimates based on available imagery and an assessment of whether the cloud layers continued to the base of the next layer.

The second considered the scenario outlined at the start of the Cockpit visibility assessment section, with a cloud layer being present but at a sufficient altitude that the aircraft’s line of sight was not be obscured. An overcast cloud level was set at 5,000 ft and the animation was repeated with these conditions. Finally, to give an indication of the effect of the cloud compared to a clear day, all weather was switched off and the simulation was repeated with sky clear conditions. Figure 117, Figure 118 and Figure 119 show the conditions from AEM at the start of the 3 simulations and Figure 120, Figure 121 and Figure 122 show the conditions from JQF at the start of the simulations. These figures use the left seat pilot’s viewpoint.

Figure 117: View from AEM with simulated conditions – 260 seconds before collision

Source: ATSB

Figure 118: View from AEM with 5,000 ft cloud level – 260 seconds before collision

Source: ATSB

Figure 119: View from AEM with clear conditions – 260 seconds before collision

Source: ATSB

Figure 120: View from JQF with simulated conditions – 260 seconds before collision

Source: ATSB

Figure 121: View from JQF with 5,000 ft cloud level – 260 seconds before collision

Source: ATSB

Figure 122: View from JQF with clear conditions – 260 seconds before collision

Integration of CDTI displays

As outlined in the CDTI section, the ATSB developed cockpit displays and alerting functionality for both aircraft for the final 260 seconds of the flight. The timestamps between the CDTI data and the cockpit animations were aligned, and the 2 animations were overlayed to show the alerts in real time.

Results

The animation, combined with the CDTI displays, were played back in real time and recorded by investigators. The following show the views from both AEM and JQF at critical times in the lead up to the collision. The figures below show the outlook from AEM and JQF, as per the accident conditions simulation, (centre panel of the animation) at:

• the times that the target aircraft transitioned to proximal traffic on the CDTI
• the times that the PAZ and CAZ breaches were projected and the accompanying ATAS alerts received
• 13 (chosen as based on the research it is the last opportunity to detect and have sufficient time to avoid), 10, 5 and 1 second before the collision.

The target aircraft’s location has been identified with a red circle. Figure 123 to Figure 136 ^[26] show views from AEM at these key times and Figure 137 to Figure 150 ^[27] show the view from JQF. Examples showing the same set of imagery, but for clear skies, can be found in an attachment to this report.

While the animation resolution is not as great as the human eye, it clearly shows the limitations of visual acquisition of target aircraft, regardless of the external conditions. The alerting capability of the CDTI and ATAS not only gives the pilot significantly greater warning about the presence of an aircraft but also provides them with a location and altitude to assist in visual acquisition and avoidance of the target.

Video animation 1: The collision as viewed from VH-AEM right seat.

Source: ATSB

Video animation 2: The collision as viewed from VH-AEM left seat.

Source: ATSB

Video animation 3: The collision as viewed from VH-JQF right seat.

Source: ATSB

Video animation 4: The collision as viewed from VH-JQF left seat.

Source: ATSB

Conclusion

The collision between AEM and JQF was the first mid-air collision of 2 IFR aircraft in Australia. In supporting the investigation, the ATSB sought to better understand the potential for visual acquisition of each aircraft considering the:

• information that was available to the pilots
• structure, performance and systems of each aircraft
• human performance limitations
• environmental conditions at the time.

The ATSB also reviewed other technologies that, if available, may have provided additional information to the pilots and enhanced their mental model of the surrounding airspace and traffic.

To do this the ATSB:

• undertook a literature review of human factors and the involved technological elements
• reviewed and conducted significant analysis on ADS-B data from the Airservices Australia receiver network
• reviewed aircraft structural, equipage and wreckage information, air traffic control recordings and personnel information.

The ATSB then developed exemplar cockpit displays using RTCA DO-317B‑compliant CDTI displays and analysed their likely effectiveness in alerting the pilots to the impending collision had they been fitted.

Key conclusions

• Analysis of the ADS-B data and on-site wreckage examination identified that the aircraft collided approximately 2,645 meters east and 6,820 meters south of the runway 05 threshold at Mangalore Airport with a relative angle of approximately 140° and at an altitude of approximately 4,125 ft, with JQF colliding with the top of AEM.
• Meteorological information indicated that cloud likely obscured the aircraft up until the collision, or until immediately before the collision, meaning that the pilots had insufficient time to visually acquire the opposing aircraft before the collision.
• Based on analysis of the flight paths, regardless of cloud conditions and aircraft structural considerations, the size, closing speed and contrast meant it was unlikely that the pilots would have been able to visually locate the target aircraft, determine it was a threat and initiate a manoeuvre in sufficient time to avoid the collision.
• Based on the ATSB’s optimised pilot eye positions, the pilots of JQF would likely have had the aircraft structure obscuring the target aircraft at critical times as AEM approached. This would have limited visual acquisition opportunity to either earlier times when the aircraft was smaller in the visual field or later when there was insufficient time to initiate and complete an avoiding manoeuvre.
• Based on the optimised eye positions, the viewpoints of the pilots in AEM were not obstructed by cockpit structure in the 260 seconds leading up to the collision.
• Sensitivity analysis of pilot eye position indicated that relatively small movements had a significant effect on aircraft structural obscuration of the target aircraft and where in the visual field the aircraft appeared.
• The 60,000 candle power landing light fitted to JQF provided the best opportunity for visual acquisition of the aircraft. Despite its position set back in the nose cowl limiting its effective arc there were multiple windows during which it could have been visible to the pilots of AEM and at its rated power it could draw the pilot’s attention even without a strobe functionality.
• Neither aircraft was fitted with an internal alerting capability. While one of the pilots of AEM had an electronic flight bag application available, it was not paired with an ADS-B IN device. This limited the traffic information that was available to the pilot and the version of the application which was used did not have an alerting function for nearby traffic.
• The pilots of both aircraft were reliant on external alerting, such as radio communications, to provide traffic information on aircraft that could not be visually acquired to develop their mental model of the operating environment.
• Utilising ADS-B IN enables pilots to accurately locate other aircraft without the need for an external alert and at significantly greater distances than are possible with the human eye. In this case, the presence of ADS-B IN equipment, combined with a suitable cockpit display would have provided accurate speed and position information on the aircraft well before it was detectable visually, while also aiding the sighting of an approaching aircraft.
• The animation developed by the ATSB using Flight Simulator X and FS Recorder clearly illustrates the limitations of visual acquisition and the significant additional alerting time provided by ADS-B IN displays.

References

Aerion. (2021). It’s Just ADS-B. Retrieved from Aerion: https://aireon.com/resources/overview-materials/its-just-ads-b/

Aerion. (2021). Technical Specifications. Retrieved from Aerion

AeroLEDS. (2021). SUNSPOT 36-4000 TECHNICAL SPECIFICATIONS. Retrieved from AeroLEDS: https://aeroleds.com/products/sunspot-36-4000-landing-light/

AeroLEDS. (2021). The LED Advantage. Retrieved from AeroLEDS: https://aeroleds.com/the-led-advantage/

Airservices Australia. (2016, December). ADS-B - Questions and Answers for Owners of General Aviation Aircraft. Retrieved from Airservices Australia: https://www.airservicesaustralia.com/wp-content/uploads/FAQ_ADS-B_DEC16…

Airservices Australia. (2020, May). ADS-B coverage. Retrieved from Airservices Australia: https://www.airservicesaustralia.com/about-us/projects/ads-b/ads-b-coverage/

ATSB. (2002). AVIATION SAFETY INVESTIGATION REPORT 200201846 - Piper PA-28-161, VH-IBK, Socata TB-9, VH-JTV, Bankstown Airport, NSW, 5 May 2002. Canberra: ATSB.

Bullough, J. D. (2011). Aviation Signal Lighting: Impacts of Lighting Charactaristics on Visibility. Advances in Applied Science Research, 16-26.

CASA. (2019). Airspace Review of Hobart - December 2019. Canberra: CASA.

CASA. (2020). Civil Aviation Order 20.18 (Aircraft equipment — basic operational requirements) . Canberra: CASA.

Civil Aviation Safety Authority. (2021, July). VFR Equipment Survey Results. Retrieved from Civil Aviation Safety Authority: https://consultation.casa.gov.au/stakeholder-engagement-group/vfr-equip…

Colvin, K., Dodhia, R., & Dismukes, R. K. (2005). Is Pilots Scanning Adequate to Avoid Mid-Air Collisions? International Symposium on Aviation Psychology, (pp. 141-146). Dayton.

Device Technologies Inc. (2019, May 3). Extending Your Squitter – A Key Part of ADS-B. Retrieved from Device Technologies, Inc.: https://www.devicetech.com/aerospace/extending-your-adsb-squitter/

FAA. (2011). Introduction to TCAS II Version 7.1. Washington D.C.: U.S. Department of Transportation - Federal Aviation Administration.

FAA. (2017). Scanning for Other Aircraft. In FAA, Aeronautical Information Manual (pp. 8-1-7). Washington DC: Department of Transportation.

FAA. (2017). Section 5. Surveillance Systems. In FAA, Aeronautical Information Manual (pp. 4-5-1 - 4-5-21). Washington DC: FAA. Retrieved from FAA.

FAA. (2020). Night Operations - Aircraft Lighting and Equipment. In FAA, FAA Airplane Flying Handbook (pp. 10-5). Washington DC: US Department of Tranportation.

Federal Aviation Administration. (2016). Pilots' Role in Collision Avoidance. Advisory Circular 90-48D.

Francis, R., Vincent, R., Noel, J.-M., Tremblay, P., Desjardins, D., Cushley, A., & Wallace, M. (2011). The Flying Laboratory for the Observation of ADS-B Signals. International Journal of Navigation and Observation, 1-5.

Garmin Aviation. (2021). Garmin Aviation - ADS-B academy. Retrieved from Garmin: https://www.garmin.com/en-AU/aviation/adsb-FAQ/

Gibb, R., Gray, R., & Scharff, L. (2010). Aviation Visual Perception. Surrey: Ashgate Publishing Limited.

Hestnes, I. (2011, March). Visual system tutorial - Flightdeck737. Retrieved from ivarhestnes.com: https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&cad=rja&…

Hobbs, A. (2004). Limitiations of the See-and-Avoid Principle. Canberra: Australian Transport Safety Bureau.

Morris, C. (2005). Midair collisions: Limitations of the see-and-avoid concept in civil aviation. Aviation Space and Environmental Medicine, 357-365.

NTSB. (1988). AIRCRAFT ACCIDENT REPORT - Midair Collision of Skywest airlines Swearingen Metro II, N163SW, and Mooney M20, N6485U, Kearns, Utah, January 15, 1987. Washington DC: NTSB.

O’Callaghan, J. (2020). Aircraft Performance & Cockpit Visibility Study. Washington DC: NTSB.

OzRunways. (2022, 4 25). SkyEcho Portable VFR ADS-B IN and OUT. Retrieved from OzRunways

uAvionics. (2022, 4 25). SkyEcho Electronic Conspicuity - Tech Specs. Retrieved from uAvionics: https://uavionix.com/products/skyecho/#specs

US DOE. (2022, March 25). LED Lighting. Retrieved from United States Department of Energy - Energy Saver: https://www.energy.gov/energysaver/led-lighting

Sources and submissions

Sources of Information

The sources of information during the investigation included:

• ATSB investigation AO-2020-012
• ATSB investigation report AO-2020-051
• ATSB investigation report 200201846
• United States National Transportation Safety Board
• Civil Aviation Safety Authority
• Airservices Australia
• United States Federal Aviation Administration
• United States Department of Energy
• operators of VH-AEM and VH-JQF
• manufacturers of VH-AEM and VH-JQF
• aircraft and maintenance documentation from VH-AEM and VH-JQF
• operators of VH-NLO and VH-IJM
• RTCA (formerly Radio Technical Commission for Aeronautics)
• Recorded Raw and filtered ADS-B data as provided by Airservices Australia
• Bureau of Meteorology
• National Oceanic and Atmospheric Administration of the United States
• Microsoft Flight Simulator X and supporting documentation
• FS Recorder and supporting documentation

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 parties:

• Airservices Australia
• Civil Aviation Safety Authority
• United States National Transportation Safety Board

Submissions were received from

• Airservices Australia
• Civil Aviation Safety Authority
• United States National Transportation Safety Board

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

Attachment A

Attachment A - Extremities of pilot’s eye position

This attachment contains imagery showing the cockpit views for the extremities of each pilot’s eye position as developed for the Refining the pilot’s eye position section. The images show the right, left, upper, lower, forward, and rearward extremities considered when refining the eye position

      -    Figures 1 to 6 show the extremities for AEM’s left seat pilot
      -    Figures 7 to 12 show the extremities for AEM’s right seat pilot
      -    Figures 13 to 18 show the extremities for JQF’s left seat pilot
      -    Figures 19 to 24 show the extremities for JQF’s right seat pilot

All images developed by the ATSB.

Figure 1 AEM left seat pilot - right extremity

Figure 2 AEM left seat pilot - left extremity

Figure 3 AEM left seat pilot - upper extremity

Figure 4 AEM left seat pilot - lower extremity

Figure 5 AEM left seat pilot - forward extremity

Figure 6 AEM left seat pilot - rearward extremity

Figure 7 AEM right seat pilot - right extremity

Figure 8 AEM right seat pilot - left extremity

Figure 9 AEM right seat pilot - upper extremity

Figure 10 AEM right seat pilot - lower extremity

Figure 11 AEM right seat pilot - forward extremity

Figure 12 AEM right seat pilot - rearward extremity

Figure 13 JQF left seat pilot - right extremity

Figure 14 JQF left seat pilot - left extremity

Figure 15 JQF left seat pilot - upper extremity

Figure 16 JQF left seat pilot - lower extremity

Figure 17 JQF left seat pilot - forward extremity

Figure 18 JQF left seat pilot - rearward extremity

Figure 19 JQF right seat pilot - right extremity

Figure 20 JQF right seat pilot - left extremity

Figure 21 JQF right seat pilot – upper extremity

Figure 22 JQF right seat pilot - lower extremity

Figure 23 JQF right seat pilot - forward extremity

Figure 24 JQF right seat pilot - rearward extremity

Attachment B

This attachment contains imagery that is the equivalent of figures 121 – 148 of the report with the simulated weather conditions altered to show a ‘sky clear’ day. As per the images in the report they show the main view from each pilot’s eye position at key moments in the sequence, including the CDTI displays and cockpit masks of the areas that would have been shielded.

• Images A through N show the view from AEM 42, 30, 24, 13, 10, 5 and 1 second before the collision.
• Images O through AB show the view from JQF 42, 32, 26, 13, 10, 5 and 1 second before the collision.

These images were used for a comparison with those in the report considering the visibility of the target aircraft but also as confirmation of the location of the aircraft against topography or the sky for aircraft contrast considerations.

Image A: View from AEM left seat pilot (LSP) when JQF transitions to proximal traffic on CDTI display

Source: ATSB

Image B: View from AEM right seat pilot (RSP) when JQF transitions to Proximal Traffic on CDTI display

Source: ATSB

Image C: View from AEM LSP when JQF triggered PAZ breach and ATAS alert

Source: ATSB

Image D: View from AEM RSP when JQF triggered PAZ breach and ATAS alert

Source: ATSB

Image E: View from AEM LSP when JQF triggered CAZ breach and ATAS alert

Source: ATSB

Image F: View from AEM RSP when JQF triggered CAZ breach and ATAS alert

Source: ATSB

Image G: View from AEM LSP 13 seconds before the collision

Source: ATSB

Image H: View from AEM RSP 13 seconds before the collision

Source: ATSB

Image I: View from AEM LSP 10 seconds before the collision

Source: ATSB

Image J: View from AEM RSP 10 seconds before the collision

Source: ATSB

Image K: View from AEM LSP 5 seconds before the collision

Source: ATSB

Image L: View from AEM RSP 5 seconds before the collision

Source: ATSB

Image M: View from AEM LSP 1 second before the collision

Source: ATSB

Image N: View from AEM RSP 1 second before the collision

Source: ATSB

Image O: View from JQF LSP when AEM transitions to Proximal Traffic on CDTI display

Source: ATSB

Image P: View from JQF RSP when AEM transitions to Proximal Traffic on CDTI display

Source: ATSB

Image P: View from JQF RSP when AEM transitions to Proximal Traffic on CDTI display

Source: ATSB

Image Q: View from JQF LSP when AEM triggers PAZ breach and ATAS alert

Source: ATSB

Image R: View from JQF RSP when AEM triggers PAZ breach and ATAS alert

Source: ATSB

Image S: View from JQF LSP when AEM triggers CAZ breach and ATAS alert

Source: ATSB

Image T: View from JQF RSP when AEM triggers CAZ breach and ATAS alert

Source: ATSB

Image U: View from JQF LSP 13 seconds before the collision

Source: ATSB

Image V: View from JQF RSP 13 seconds before the collision

Source: ATSB

Image W: View from JQF LSP 10 seconds before the collision

Source: ATSB

Image X: View from JQF RSP 10 seconds before the collision

Source: ATSB

Image Y: View from JQF LSP 5 seconds before the collision

Source: ATSB

Image Z: View from JQF RSP 5 seconds before the collision

Source: ATSB

Image AA: View from JQF LSP 1 second before the collision

Source: ATSB

Image AB: View from JQF RSP 1 second before the collision

Source: ATSB

Glossary

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 2022 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. Euler angle: Angles describing the rotation of a body in three-dimensional space
2. Times depicted are in EDT and altitudes in feet above mean sea level (AMSL)
3. STCA: Short Term Conflict Alert - a system intended to assist the air traffic controller in preventing a collision between aircraft by generating, in a timely manner, an alert of a potential or actual infringement of separation minima.
4. The National Oceanic and Atmospheric Administration Solar position calculator is available online at - ESRL Global Monitoring Laboratory - Global Radiation and Aerosols (noaa.gov)
5. Azimuth angle – Angular measurement horizontally from position directly ahead of the viewer through a full revolution (-180° through 180°). Angles to the right are positive and angles to the left are negative.
6. Elevation angle – Angular measurement vertically from a point directly in front of the viewer to a point directly above or below them (-90° through 90°). Angles above the horizontal are positive and angles below are negative.
7. Wingspans of accident aircraft - AEM 37.82 ft and JQF 38.5 ft
8. An equirectangular image is where a 360-degree image is projected onto a flat 2D surface with equal azimuth and elevation angle.
9. Visual Trap – When the viewers gaze becomes focussed on a particular object in the foreground of the field of view neglecting objects in the distance. For example, a pilot becoming focussed on a blemish on the windscreen rather than scanning the whole visual field for traffic.
10. ARO Scene 2019 version was used for the merging the scan data and processing the models.
11. A mathematical process that translates and rotates in 3 dimensions for conversion between co-ordinate systems.
12. Global Navigation Satellite System (GNSS) is a constellation of satellites used for locating a receiver on the earth. The Global Positioning System (GPS) is one example.
13. ICAO 24-bit address is a unique airframe code that is issued to an aircraft when it is registered.
14. Airspace in Australia is separated into different classes that may be either controlled (Class A, Class C, Class D, Class E) or non-controlled (Class G). Different services are offered to aircraft that operate in these airspace classes, based on the flight rules the aircraft is operating under (see the section titled Airspace in the investigation report).
15. The images showing ADS-B network coverage do not include the coverage patterns for the 7 TASWAM stations.
16. While there have been attempts to harmonise the traffic functionality between application providers to assist pilots in traffic awareness they have, as of the time of publication, been unsuccessful.
17. Clock co-ordinate: A method of communicating relative position using the numbers of an analogue clock face to identify relative position usually with the pilot’s aircraft at the central axis of the face.
18. Geoscience Australia’s Geodetic calculators can be found at Geodetic Calculators (ga.gov.au).
19. The threshold of runway 05 at Mangalore Airport is located at 36.893415o S, 145.173053o E which converts to 337211 m E, 5915392 m S (Zone 55) in rectangular cartesian co-ordinates.
20. Extremities were considered as the furthest point on the grid in a specific direction where the eye position was still within the structure of the cockpit. In some cases, the movements of the eye position shifted the visual position outside the cockpit structure either into or through a door or the roof. In these cases, the next position closer to the initial estimate was considered as the extremity.
21. A third STCA was received by the controller on JQF and VFR traffic in the circuit. This was determined to be a nuisance alert and not relevant..
22. RTCA DO-317B was the standard that outlined the operational performance requirements of aircraft surveillance applications, including performance standards for ADS-B IN systems (including CDTI and ATAS).
23. FS Recorder is a Freeware add-on to FSX developed by Matthias Neusinger for recording and replay of flights in FSX. It was previously available at http://www.fs-recorder.net/, however the website is no longer available.
24. Piper Seminole Model was downloaded from Fly Away Simulation Piper PA-44-180 Seminole for FSX (flyawaysimulation.com)
25. These values are for an FSX window with an aspect ratio of 1.78 (monitor resolution of 1920 x 1080 pixels), at a ’zoom’ setting of 0.3.
26. for the online version of the report figures 123-136 have been replaced with video animation’s 1 and 2 showing the view from the right and left seats, respectively, of AEM in the final 260 seconds in the lead up to the collision. The time of the PAZ and CAZ breaches are annunciated in the video and the location of JQF 12 seconds before the collision is shown with a light blue circle. The still frame images as described above are in the PDF version of the report or by pausing the video.
27. for the online version of the report figures 137-150 have been replaced with animation video’s 3 and 4 showing the view from the right and left seats, respectively, of JQF in the final 260 seconds in the lead up to the collision. The time of the PAZ and CAZ breaches are annunciated in the video and the location of AEM 12 seconds before the collision is shown with a light blue circle. The still frame images as described above are in the PDF version of the report or by pausing the video.

Overview of the investigation

At approximately 0323 on 15 January 2022, the driver of 6MB4 reported losing air on the Up Main at 452.000 km, at Bethungra, NSW. Shortly after, the driver reported that three wagons (RRAY07213S, RRQY08515T and QQCY01120F), in the centre of the consist of 33 wagons, had derailed. The wagons sustained substantial damage with major damage to the track infrastructure. The train crew were uninjured.

Australian Rail Track Corporation was the rail infrastructure manager for the line.

ATSB’s preliminary evidence collection identified that:

• the derailment of train 6MB4 resulted from a screwed journal. The cause of the bearing failure could not be determined due to the large amount of consequential damage sustained, preventing a complete teardown and analysis of the failed bearing
• wheelset 7E3S080144 was fitted to wagon wheelset position 5 of QQCY01120F within bogie QRYE2079. New bearings were installed at the rolling stock maintainer’s facility and released to service on 2 September 2020. Records from the maintainer documented that the bearings fitted were an ‘Class E’ (6” x 11”) packaged bearing manufactured by Timken on 01/2020 and 12/2019. The bearings were fitted new and had not received a reconditioning maintenance event. These bearings covered 370,907 km to the point of failure
• there were no issues identified with the train management of train 6MB4
• there were no identified track defects in the region of or approaching the derailment site
• the condition monitoring equipment available on the operational route did not provide indications of a bearing showing signs of distress.

Reasons for the discontinuation

The ATSB considered the contributing factors to the derailment were a result of a failed bearing. The reasons for that failure were unable to be conclusively determined.

In response to the incident, Pacific National have proposed the following safety actions be initiated:

• work collaboratively with ARTC to implement further Hot Bearing Detector wayside equipment across the Melbourne to Brisbane corridor, to assist with identifying bearing failure modes that do not produce acoustic signals
• undertake a review of the practices and processes at their rolling stock maintenance provider, with particular focus on techniques and tooling used to measure journal diameter.

Based on this information, the ATSB considered it was very unlikely that further investigation would identify any systemic safety issues or identify opportunity for the enhancement of transport safety. Consequently, the ATSB has discontinued this investigation.

Executive summary

What happened

On 31 December 2021, a Kavanagh B-350 hot-air balloon, registered VH BSW and operated as a scenic charter flight by Picture This Ballooning (PTB), was being prepared near Glenburn, north of the Yarra Valley, Victoria, with one pilot and 16 passengers. The pilot conducted a pre-flight safety briefing and departed shortly after, intending to land near Yarra Glen.

About 42 minutes into the planned 1‑hour flight, the pilot received a report that the surface wind near the landing area was increasing. The pilot assessed multiple landing options over the next 17 minutes while the wind was increasing. The pilot then made an approach to a landing field and the balloon landed hard with 2 passengers seriously injured.

What the ATSB found

The ATSB found that the pilot rejected several suitable landing fields to avoid possible post‑landing logistical and operational difficulties. This progressively reduced the safe landing sites available to the pilot.

The field in which the pilot decided to land contained fences not previously known to the pilot, powerlines downwind, and no known landing sites further along the balloon's track. This landing site presented high risks in the prevailing windy conditions.

The landing was complicated by the balloon descending faster than intended, bouncing off the ground back into the air, and then manoeuvres to clear fences. These factors, in combination with the prevailing winds and nearby power lines, led to the pilot descending the balloon rapidly from an excessive height resulting in the hard landing.

The investigation also found that all required actions of the pre-flight passenger safety briefing were not completed, probably due to time pressure and the pilot’s assumption that all passengers would understand an abbreviated briefing. The incomplete briefing probably resulted in 2 passengers adopting a deep squat position during the hard landing, causing their injuries.

The ATSB further identified that the maximum number of passengers that the balloon operator allowed to be carried on the balloon meant that there was insufficient room in the basket for them to adopt the landing position specified in the operator's procedures to reduce the risk of injury.

What has been done as a result

The balloon operator has reduced the maximum number of passengers that the balloon can carry to ensure that all passengers can achieve the required backwards facing landing position. The operator is also reviewing maximum passenger capacities on all of its balloons.

Safety message

This accident demonstrates the importance of passengers adopting the correct body position during landing to reduce the likelihood and severity of injury. The pre-flight briefing is critical in ensuring passenger preparation, particularly as opportunities to reinforce the information during flight may be limited. Pilots should use all available resources (such as, passenger demonstrations and safety briefing cards) to ensure that each passenger understands the landing position and its importance. Further, commercial balloon operators are reminded to ensure that all passengers can physically achieve the required landing positions to reduce the risk of injury.

When faced with deteriorating wind conditions, pilots should prioritise occupant safety in the selection of a landing field. This reduces the risk of a hard landing or accident. Post flight logistical or operational considerations are of secondary importance.

The occurrence

Early on the morning of 31 December 2021, a Kavanagh B-350 hot-air balloon, registered VH‑BSW and operated as a scenic charter flight by Picture This Ballooning (PTB), was being prepared for departure near Glenburn, north of the Yarra Valley, Victoria, with one pilot and 16 passengers. Another balloon of the same operator, and four other balloons from different operators, were also being prepared for take-off at the same location.

At about 0420 Eastern Daylight-saving Time,^[1] the pilot of VH-BSW obtained relevant weather information from both the Bureau of Meteorology and another balloon pilot and assessed the conditions as suitable to depart. The pilot intended landing south-east of Yarra Glen (Figure 1).

Figure 1: Balloon flight track

Source: Google Earth, annotated by ATSB

After the passengers had climbed into the basket, the pilot conducted a pre-flight safety briefing and, at 0547, the balloon departed for an anticipated 1-hour flight. Shortly after, the balloon’s ground crew member travelled in a car towards the intended landing area to assist with balloon and passenger retrieval.

The pilot climbed the balloon to a cruise altitude of between 2,500 and 2,700 ft above mean sea level (AMSL), before allowing the balloon to descend into the Yarra Valley to reduce the balloon’s speed. The balloon levelled off at about 200 ft above ground level (AGL) at 0620 and a speed of 15 kt.

At about 0629, the pilot heard the radio broadcast of a ground crew member from another balloon operator that the surface winds were increasing to about 10 kt near the intended landing area. At this time, the pilot started looking for landing sites.

At about 0632, the pilot instructed the passengers to take up landing positions and made an approach to the intended landing area. As the balloon descended, the wind turned the balloon west, away from the site, preventing the landing from being completed. The pilot continued to assess landing options over the next 14 minutes (see the section titled Potential landing sites). During this time, the balloon’s groundspeed varied between 9 and15 kt.

At about 0646, the balloon’s flight continued over a small hill before the pilot instructed the passengers to again get into the landing positions. The pilot intended to float above a seeded field, and land in an adjacent field further along the balloon’s track (Figure 2). Shortly before reaching the seeded field, the pilot pulled the parachute vent line for about 10 seconds to descend for landing (see the section titled Balloon information).

Shortly after, the balloon started descending faster than the pilot anticipated. The pilot operated the burners but was unable to arrest the balloon’s descent and the bottom of the basket contacted the ground. The balloon then started rising so the pilot pulled on its rip line, opening the vent to deflate the balloon (see the section titled Balloon information), intending to touchdown over a nearby fence.

Figure 2: Balloon approach and landing

Only relevant fences have been marked. Source: Google Earth, annotated by ATSB

After the balloon climbed into the air, the pilot noticed another fence running diagonally across the intended landing area along the flight path. The pilot held the rip line to maintain the size of the vent opening, and the balloon continued over this fence, reaching a height of about 40 ft. The pilot then resumed pulling the rip line, opening the vent further and the balloon descended rapidly, landing hard in the field at about 0648. After the basket touched down, it tipped over and was dragged for 30-40 metres along the ground before coming to rest.

The balloon and basket were not damaged during the hard landing, but two passengers sustained serious leg injuries. There was another occurrence reported to the ATSB involving one of the other balloons that had departed Glenburn that morning, but the circumstances of that event were unrelated to the development of this accident.

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1. Eastern Daylight-saving Time (EDT): Coordinated Universal Time (UTC) + 11 hours

Context

Balloon information

VH-BSW was a Kavanagh B-350 balloon which included an envelope, double T‑partitioned basket with 32 rope handles (Figure 3) and 4 passenger compartments, a three burner system and 3 propane fuel tanks.

Figure 3: Double-T partitioned basket (example)

The depicted basket has a four-burner system. Source: Kavanagh Balloons

The balloon was equipped with a Lite Vent deflation system. In-flight venting was achieved by pulling on the parachute vent line which in turn pulled the vent panel at the top of the balloon for a controlled release of air. Releasing the vent line allowed the vent panel to close. The parachute vent was used to descend the balloon, such as when approaching to land. For final landing, when the balloon was close to the ground, the rip line was pulled so that the centre of the vent panel was pulled down into the balloon for rapid deflation. The more the rip line is pulled, the larger the vent opening, and the more air allowed to escape through the vent. Releasing the rip line does not close the vent panel.

The balloon’s flight manual included the following information about the rip line:

The centre pull rip line must not be activated if the basket floor is more than 2 metres (six feet) above ground level unless during an emergency landing.

WARNING: Operation of the Lite Vent or Smart Vent centre pull rip line will cause the balloon to empty very quickly and could cause damage and/or injuries if this limitation is ignored.

The balloon was also fitted with rotation vents on the side of the envelope which the pilot could operate to orientate the balloon during flight. These vents were used to ensure that the long side of the basket was perpendicular to the direction of travel during landing.

Pilot information

The pilot held a commercial pilot licence (balloon), with significant balloon piloting experience which included 3,000 hours of flying, of which 300 hours were on the Kavanagh B-350. In the previous 90 days, the pilot had flown 26 hours, including 18 on the B-350.

Meteorological information

Weather considerations

A temperature inversion is a layer of air in which the temperature increases with height, rather than decreasing as is normal. A low-level or surface inversion occurs when the ground cools overnight by radiating heat, also cooling the layer of air closest to the ground. These low-level inversions form a stable layer of air, typically extending a few hundred feet and prevent the higher altitude wind from mixing with the lower level winds near the ground.

An inversion layer can dissipate when the ground is heated by the sun, which allows the higher altitude winds, with relatively higher speed, to mix down towards the earth’s surface. It is for this reason that balloon pilots aim to conduct flights before an inversion layer breaks down and wind conditions deteriorate.

The Civil Aviation Safety Authority (CASA) advisory circular AC 131-02v2.0 Manned free balloons - Operations provided the following guidance on the stability of the atmosphere:

Paragraph 3.2.18. Thermals and atmospheric instability can seriously affect the safety of flight in lighter‑than‑air aircraft. In conditions of higher ambient temperatures, such as can exist in the summer months, pilots should be aware of the possibility that flying conditions may change very quickly as the temperature rises.

Paragraph 3.2.19. Pilots preparing to conduct a flight in higher ambient temperatures, when atmospheric instability may exist during the planned flight or on landing, should access as many local weather information sources and meteorological forecasts as practicable. Pilots should pay attention to any forecast temperature and humidity increases in the forecast period and be prepared to amend the flight plan.

Pre-flight

The pilot recorded the information provided by the Bureau of Meteorology (BoM) telephone briefing on the morning of the flight. These included:

• Coldstream temperature observation 12.9 °C (at 0420)
• Surface wind from north-northeast at 5 kt for the expected flying time (0600-0700)
• 2,000 ft wind from north-northwest at 20-25 kt

The pilot also received information from another balloon pilot^[2] that the inversion layer would be starting to break down earlier than usual but still after the expected landing time.

The pilot completed a pre-flight load chart, recording a surface temperature of 16 °C and with sufficient lifting capacity available to conduct the flight. The ATSB review of the balloon’s load chart indicated that the lifting capacity for the balloon was sufficient to conduct flights up to 4,000 ft with a surface temperature of up to 23 °C.

Forecast

The Yarra Valley Meteogram^[3] showed 100 ft wind from north-northeast at 5 kt for the expected flying time. The F160 model forecast indicated a temperature inversion at about 800 ft AMSL, with wind speeds above the inversion increasing with height (10-30 kt). The inversion was forecast to break down between 0900 and 1100.

Data and observations

The balloon’s GPS unit recorded the balloon’s velocity (and thus wind speed and direction) during the flight. In the final 10 minutes of the flight between 0 and 150 ft AGL, the balloon’s speed varied between 9 and 17 kt.

The pilot described the wind conditions during the latter portion of the flight as ‘gusty’ and that the reason for the unintended touchdown with the ground just before the final landing might have been due to turbulent wind on the leeward side of the small hill the balloon floated over.

Passenger safety briefings

The operator’s Operation’s Manual (OM) and Emergency Procedure’s Manual (EPM) contained the following information on passenger safety briefings:

Passengers are to be briefed on the ballooning experience in general and safety aspects of ballooning (for example, the fan, landing positions, exiting the basket). Pilots should make use of the PTB checklists and briefing cards found on board all PTB balloon baskets.

Brief passengers inside the basket on landing positions before take-off (passengers must practise and demonstrate the landing position)

Assume you will always have a difficult landing so be confident that all passengers can take their landing positions without a further briefing.

Before landing, brief the passengers on the landing procedure.

During emergency landings, advise passengers to expect a hard landing and instruct them into the brace position with knees bent.

Safety briefing cards

Civil Aviation Order 20.11^[4] (Emergency and lifesaving equipment and passenger control in emergencies) required that passenger safety information cards be available to passengers on any charter flight with a seating capacity greater than 6. It stated that the cards must be carried in a convenient location and detail the passenger brace position for an emergency landing.

The operator’s OM and EPM manuals outlined that each balloon was to carry a passenger briefing card which was to be mounted inside the basket and available at the meeting point.

The briefing cards provided information on balloon safety, including landing instructions, and a pictorial representation of the body position to adopt during landing (Figure 4).

Figure 4: Operator safety briefing card

Source: Picture This Ballooning, annotated by ATSB

Pre-flight briefing

Advisory circular AC 131-02v2.0 provided guidance on pre-flight briefings:

Paragraph 4.1.6.2…The safety briefing will usually be conducted by the PIC and should include the following:

an instruction and demonstration of the landing position, appropriate to the balloon design, that a passenger must adopt for landing.

…an instruction to flex the knees on touch down to minimise the effect of any impact during landing.

The pilot reported that a verbal pre-flight briefing about the landing positions was provided to the passengers while they were in the basket and included instructions to hold onto the rope handles, bend the knees, that there might be multiple bounces during the landing, and that the basket might tip over and drag.

The balloon was fitted with a video camera that captured images before and during the flight at 5 second intervals. The images during the pre-flight briefing did not appear to show the passengers demonstrating the landing position, and not all passengers reported being asked to provide the pilot with a physical demonstration. The pilot advised that the passengers were possibly not asked to demonstrate the landing positions as there was some time pressure during take-off due to the forecast weather. The pilot also assumed that verbal instructions for the passengers on‑board (all reported to be English speaking) would be sufficient to understand the landing positions. The two passengers injured during the hard landing reported that the briefing felt rushed without a lot of emphasis on the landing position.

The passengers were not asked to review the safety briefing cards before or during the flight. The pilot reported not using the cards during recent pre-flight briefings because the passengers on these flights had primarily been English speaking and the pilot believed that the briefing cards were only effective with non-English speaking passengers.

Pre-landing briefing

Advisory circular AC 131-02v2.0 provided guidance on pre-landing briefings:

Paragraph 4.1.6.5. On final approach to landing the PIC should ensure all passengers are comfortable in the landing position and be prepared to correct any anomalies before touch-down.

During the pre-landing briefing, the pilot:

• instructed passengers to adopt the landing positions during the approach
• visually checked that the passengers were in the landing positions
• re-iterated at appropriate times to stay in the landing positions
• warned that there was going to be a hard landing.

Most passengers recalled being verbally instructed to adopt the landing positions and after the initial bounce, being told to brace for a hard landing. Both passengers that were subsequently injured interpreted the hard landing instruction to mean they needed to crouch down deep into the basket and brace.

Landing positions

The landing position on the operator’s safety briefing cards was a similar position to that recommended by the United Kingdom Civil Aviation Authority (CAA)^[5] for the double T-partitioned basket and required a passenger’s back to be facing the direction of travel with knees bent at an angle of less than 90 degrees (Figure 5). The research conducted to support the CAA recommendation^[6] found the backwards facing landing position reduced the risk of injury compared to the sideways facing position (Figure 6) during heavy and tip-over landings.^[7]

Figure 5: Recommended landing position (double T-partitioned basket)

Source: United Kingdom Civil Aviation Authority, annotated by ATSB

Figure 6: Sideways landing position (double T-partitioned basket)

Source: United Kingdom Civil Aviation Authority, annotated by ATSB

Flight camera images showed the passengers facing sideways during the pre-flight briefing, and before the initial touchdown. Just before this touchdown, the two passengers that were subsequently injured lowered themselves further into the basket than the other passengers who remained more upright. The long side of the basket was orientated perpendicular to the direction of flight during the initial touchdown as shown (Figure 6). After the first touchdown, the two injured passengers, and another one, lowered themselves further into the basket, probably crouching in a deep squat position with the knees bent more than 90 degrees. They remained in those positions during the final landing.

The basket contained internal padding to support passengers’ backs during landing but did not extend all the way to the basket floor. One of the injured passengers reported that one foot slid under the padding during the hard landing and possibly contributed to the injury.

The Australian Ballooning Federation Pilot Training Manual stated that a descent rate greater than 400 feet per minute on landing could cause personal injury and damage the equipment. The ATSB determined that during the final landing the average descent rate was at least 470 feet per minute. Just before the balloon landed, the balloon had turned such that the long edge of the basket was orientated about 50° from the direction of travel (Figure 7).

Figure 7: Basket orientation during final landing

Source: United Kingdom Civil Aviation Authority, annotated by ATSB

Number of passengers

The balloon’s flight manual included the following passenger limitations:

Partitioned baskets are limited to a maximum of 6 people per passenger compartment and 2 flight crew in the pilot compartment.

All occupants must have access to a minimum of one hand hold eg: rope handle or tank rim.

All occupants must have reasonable space to achieve a safe landing position and reasonable comfort levels during the flight.

The operator’s OM included information on the maximum ‘passenger seats’ available for each balloon within the fleet. The passenger capacity for VH-BSW was 17. The operator advised that the following factors were used when determining the maximum passenger capacity:

• maximum total passenger weight for each balloon envelope based on its condition.
• number of rope handles – minimum of 2 handles per passenger
• flight manual considerations

The camera images showed that there were 4 passengers located in each passenger compartment, and review of the passenger load charts were all within balloon weight limitations.

The pilot stated that the passengers were instructed into sideways facing landing positions during the pre-flight briefing because the number of passengers on board meant that they physically could not adopt a backwards facing position. A review of the camera images confirmed that it was unlikely that all passengers could have physically achieved a backwards facing landing position. The images and passenger weights indicated that some passengers were of above average size, and some below average, so combined represented a typical group of passengers.

The pilot reported instructing passengers into the backwards facing position for previous flights on VH-BSW as there were less passengers and enough space for them to achieve this position.

Balloon landing considerations

The United States’ FAA Balloon Flying Handbook, Chapter 8 – Landing and Recovery provided the following advice on landing considerations:

When selecting a landing site, three considerations in order of importance are: safety of passengers, as well as persons and property on the ground; landowner relations; and ease of recovery.

The best landing site is one that is bigger than the balloon needs and has alternatives. If the balloon has three prospective sites in front of it, the pilot should aim for the one in the middle in case the surface wind estimate was off. If the balloon has multiple prospective landing sites in a row along its path, the pilot should take the first one and save the others for a miscalculation. Unless there is a 180° turn available, all the landing sites behind are lost.

When faced with a high wind landing, the balloon pilot must remember that the distance covered during the balloon’s reaction time is markedly increased… A pilot who is not situationally aware and fails to recognize hazards and obstacles at an increased distance may be placed in a dangerous situation with rapidly dwindling options.

The balloon’s flight manual also stated the following regarding the approach to land:

A suitably large landing site should be selected, free of obstacles such as power lines, buildings and livestock. The overshoot area (downwind of the landing) should be free from high obstacles where possible in case the landing has to be aborted.

When a fast landing is anticipated extra space will be required for the potential drag and deflation of the balloon and a low approach should be favoured to minimise the vertical speed during landing.

Landowner relationships

Much of the land within the Yarra Valley suitable for hot air balloon use was privately owned, potentially containing the source of the livelihood of the landowners (for example, livestock and crops). In order to avoid problems such as trespassing, commercial balloon operators developed good relationships with landowners to permit take-offs, landings, and recovery of passengers and equipment from their properties. Some properties were approved for landing while others were not. Balloon pilots generally avoid landing in fields with livestock and crops to maintain good landowner relationships.

Information on maintaining positive landowner relationships was contained in the operator’s OM:

Good landowner/farmer relationships are imperative for the continued operation of Picture This Ballooning.

Maintain a map marked with the landing sites wherein the owner has given approval where practicable.

Select a landing field that should cause the least possible inconvenience to the landowner.

The pilot stated that in an emergency, the primary concern was the safety of passengers, and a landing could be made at any place considered practical – even if this occurred on a property not approved by a landowner. If there was no emergency, landing a balloon on a crop or a non‑approved property could create problems for future balloon operations.

Potential landing sites

The pilot acknowledged that apart from the final landing location, there were other potentially suitable landing sites along the balloon’s path but did not consider that the wind conditions warranted an attempt to land in these fields. These sites were rejected as one had cattle, another had locked gates that would have posed logistical problems with passengers and balloon retrieval, while others had been seeded for crops (Figure 8). These fields were longer than the final landing site and had no power lines nearby.

The pilot also stated that the final landing field was the last known landing site along the balloon’s path, and that beyond this, the potential landing fields were smaller. A review of the flight track indicated that built up suburban areas were about 3 km further along the flight path from the balloon’s final landing location.

Figure 8: Flight track with potential landing sites

Source: Google Earth, annotated by ATSB

Power lines

The Australian Ballooning Federation ABF Pilot Training Manual, Part 5 – Aerostatics and Airmanship included the following information regarding power lines:

Contact with power lines should be very carefully avoided. Any voltage can cause fatal or very serious injuries.

IF IN DOUBT, RIP OUT. If there is any doubt about your ability to clear the wires, make an emergency landing without hesitation. Pull the ripline as you warn passengers to hold on for landing, and turn off pilot lights and vent fuel hoses if there is time. There is considerably less risk of injury, fire and electrocution if the envelope contacts the wires than if the basket does.

The pilot was aware of the location of power lines downwind of the final landing field before committing to land in that field. The pilot stated that although using the parachute vent was standard procedure during an approach to land, its use during the final landing sequence might not have descended the balloon fast enough to avoid contacting the power lines. Further, attempting to ascend over the lines would be dangerous given the balloon’s distance and height from the lines. The pilot considered that the immediate use of the rip line was necessary to avoid contacting the power lines.

Similar occurrences

ATSB Investigation AO-2011-045

On 2 April 2011, during a scenic charter flight and while operating at low level, the pilot of a Kavanagh Balloons E‑210 hot-air balloon, registered VH-OTZ, was unable to arrest the balloon's descent and initiate a climb in time to avoid powerlines, requiring an emergency descent and landing. The balloon landed hard in a paddock with the basket not orientated correctly to the direction of flight. It bounced, dragged and inverted along a distance of 60 m, resulting in injuries to the occupants and minor damage to the basket.

ATSB investigation AO-2018-016

On 8 February 2018, a Kavanagh Balloons B-350, registered VH-EUA, departed Glenburn, Victoria for a scenic charter flight with a pilot and 15 passengers on board. About 45 minutes into the flight, over the Yarra Valley, the balloon experienced a sudden wind change with associated turbulence. The pilot decided to land immediately resulting in a hard and fast landing. Eleven passengers were injured, 4 of them seriously.

Although some passengers were provided with a safety briefing prior to boarding the balloon, the operator’s normal safety briefing for passenger’s post boarding was not conducted. In addition, the briefing prior to boarding was not effective in ensuring all passengers understood the required landing position to use for an emergency landing. The ATSB identified a safety issue with the operator’s risk controls which did not provide assurance that all passengers would understand the required procedures for emergency landings.

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2. That balloon pilot had reportedly received this weather information from the BoM.
3. The BoM had not retained a copy of the Yarra Valley Meteogram available on the morning of the flight. However, a Meteogram was generated for the investigation using archived weather data.
4. Civil Aviation Safety Regulation Part 131 was released on 2 December 2021. However, because the Part 131 Manual of Standards was deferred, CAO 95.53 was still effective at the time of the accident which included the requirement to comply with CAO 20.11.
5. United Kingdom Civil Aviation Authority (2007), Balloon Notice 1/2007, Passenger Landing Position Guidance to Operators, available from the UK CAA website
6. United Kingdom Civil Aviation Authority (2006), CAA Paper No. 2006/06, Evaluation of and Possible Improvements to Current Methods for Protecting Hot-Air Balloon Passengers During Landings, available from the UK CAA website.
7. When an obstacle is hit in the double T-partitioned basket, the backwards landing position was found to increase the risk of injury when compared to the sideways facing position. However, heavy and tip-over landings were found to be more common, so the backwards facing position was considered the overall safest position to adopt. A heavy landing was defined as having a horizontal speed of 10 kt and descent rate of 500 feet per minute. A tip-over landing was defined as having a horizontal speed of 10 kt and descent rate of 300 feet per minute.

Safety analysis

On 31 December 2021, a Kavanagh B-350 hot-air balloon, registered VH BSW and operated as a scenic charter flight by Picture This Ballooning (PTB), was being prepared near Glenburn, north of the Yarra Valley, Victoria, with one pilot and 16 passengers. The pilot conducted a pre-flight safety briefing and departed shortly after, intending to land near Yarra Glen.

About 42 minutes into the planned 1‑hour flight, the pilot received a report that the surface wind near the landing area was increasing. The pilot assessed multiple landing options over the next 17 minutes while the wind was increasing. The pilot then made an approach to a landing field and the balloon landed hard with 2 passengers seriously injured.

Landing areas

The forecast weather indicated that the conditions were suitable for the flight. However, after descending into the valley, the balloon’s relatively high speed at low level indicated that the inversion layer had started to break down earlier than forecast. Despite this, the wind conditions were still suitable to conduct a safe landing.

Since the wind conditions would probably degrade further, it would have been prudent for the pilot to select a large field with minimal obstacles and alternative landing sites nearby as a backup. However, the pilot rejected several large landing sites to avoid probable logistical difficulties with passenger and balloon retrieval or perceived negative impact on future operator-landowner relationships, which progressively reduced the number of safe landing sites available. Rejecting these landing sites, particularly the last two large seeded fields, in favour of a relatively small field with fences, power lines downwind, and no known alternate sites, increased the risk of obstacle collision and a hard landing in the prevailing wind conditions.

Hard landing

The final approach to land was initially complicated by the balloon descending faster than intended and touching down unintentionally in a seeded field before rising back into the air. Whether this descent was from excessive use of the parachute vent during the approach, insufficient burner application, the turbulent wind on the leeward side of the small hill, or a combination of all three, could not be determined.

The burner application to arrest the initial descent would have slowed the vertical descent rate, which was desirable, but also filled the balloon with hot air, increasing the rate of ascent after the touchdown and risk of contacting the power lines. After the balloon rose back into the air, the normal landing procedure was to use the parachute vent, and then pull the rip line when the balloon was close to the ground. However, the pilot started pulling immediately on the rip line to quickly descend the balloon and avoid the power lines. Although different to standard procedure, the use of the rip line was reasonable in the situation, but reduced control of the balloon’s final rate of descent.

Further complicating the situation was the late identification of a fence during the approach. This fence needed to be manoeuvred over and probably contributed to an increase in the maximum height that the balloon reached after the first touchdown. With the relatively high wind conditions and the distance to the powerlines reducing, the pilot pulled the rip line further resulting in the rapid descent and hard landing. While undesirable, the hard landing was the safer option instead of risking contact with the power lines.

During the final landing sequence, the balloon turned so that the long side of the basket was not orientated optimally, ideally with the direction of flight, possibly due to the wind or rapid loss of air through the vent. This orientation during the hard landing probably reduced the effectiveness of the handholds and landing position in preventing passenger movement, increasing the risk of injury. Further, although the pilot might have visually checked the passenger positions during the initial approach to land, it is unlikely the pilot re-checked their positions after the initial balloon touchdown. While rechecking passenger positions and orientating the basket correctly would have reduced the risk of injury, there was little time available, and the pilot was focussed on the more important task of controlling the balloon to avoid hazardous obstacles.

Pre-flight briefing

On every balloon flight, passengers need to adopt a specific body position during landing to reduce the likelihood and severity of injury. There are limited opportunities for a pilot to demonstrate or reinforce this briefing during flight so passenger preparation during the pre-flight briefing is critical. Although the pilot provided a verbal briefing of the landing position to the passengers before the flight, the required passenger landing position demonstration and use of briefing cards were omitted. The pilot probably missed these important steps because of time pressure and an incorrect assumption that all passengers would fully understand a verbal briefing.

This incomplete briefing reduced the likelihood of all passengers understanding the landing position, and probably resulted in some passengers not adopting the instructed body position during the hard landing, resulting in injuries to 2 passengers who adopted a deep squat position.

Passenger landing positions

Being able to achieve a safe landing position is an important consideration for every flight. Although the passengers:

• represented a typical group of adult passengers
• had sufficient handholds
• were within the balloon’s weight limitations
• were within the operator maximum passenger limits

the operator’s required safe landing positions (backwards facing) could not be physically achieved by all the passengers. Consequently, during the pre-flight briefing, the pilot instructed all the passengers to take a sideways facing landing position. This positioning in that type of basket increased the risk of injury during landing. However, since all the passengers were in a sideways facing position during the hard landing without any reported injuries, except for the 2 passengers injured who were also crouching down in a deep squat position, it is unlikely that the sideways facing position contributed to their injuries.

Findings

From the evidence available, the following findings are made with respect to the hard landing involving Kavanagh Balloons B-350, VH BSW, 2 km south of Lilydale Airport, Victoria on 31 December 2021.

Contributing factors

• The pilot rejected several suitable landing fields to avoid possible post-landing logistical and operational difficulties. This progressively reduced the safe landing sites available to the pilot.
• The field in which the pilot decided to land contained fences not previously known to the pilot, powerlines downwind, and no known landing sites further along the balloon's track. This landing site presented high risks in the prevailing windy conditions.
• The landing was complicated by the balloon descending faster than intended, bouncing off the ground back into the air, and then manoeuvres to clear fences. This, in combination with the prevailing winds and nearby power lines, led to the pilot descending the balloon rapidly from an excessive height resulting in the hard landing.
• All required actions of the pre-flight passenger safety briefing were not completed, probably due to time pressure and the pilot’s assumption that all passengers would understand an abbreviated briefing. The incomplete briefing probably resulted in 2 passengers adopting a deep squat position during the hard landing, causing their injuries.

Other factors that increased risk

• The balloon landed hard with the basket not orientated optimally to the direction of flight, increasing the risk of injury.
• The maximum number of passengers that the balloon operator allowed to be carried meant that there was insufficient room in the basket for them to adopt the landing position specified in the operator's procedures to reduce the risk of injury. (Safety issue)

Safety issues and actions

Passenger brace positions

Safety issue number: AO-2022-003-SI-01
Safety issue description: The maximum number of passengers that the balloon operator allowed to be carried meant that there was insufficient room in the basket for them to adopt the landing position specified in the operator's procedures to reduce the risk of injury.

Glossary

AGL                 Above Ground Level

AMSL               Above Mean Sea Level

BoM                 Bureau of Meteorology

CAA                 Civil Aviation Authority (United Kingdom)

CASA               Civil Aviation Safety Authority

EM                   Emergency Procedure’s Manual

GPS                 Global Positioning System

OM                   Operation’s Manual

Sources and submissions

Sources of information

The sources of information during the investigation included the:

• pilot
• passengers
• Picture This Ballooning (the operator)
• Civil Aviation Safety Authority
• Bureau of Meteorology
• video images from the accident flight
• recorded data from the GPS unit on the aircraft.

References

ABF (Australian Ballooning Federation) (2019), ABF Pilot Training Manual, ABF

FAA (Federal Aviation Administration) (2008), Balloon Flying Handbook, FAA-H-8083-11A, FAA

CAA (Civil Aviation Authority) (2006), Evaluation of and Possible Improvements to Current Methods for Protecting Hot-Air Balloon Passengers During Landings, CAA Paper No. 2006/06, CAA United Kingdom

CAA (Civil Aviation Authority) (2007), Passenger Landing Position Guidance to Operators, Balloon Notice 1/2007, CAA United Kingdom

CASA (Civil Aviation Safety Authority), (2021), Manned free balloons – Operations, Advisory Circular AC 131-02v2.0, CASA

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:

• pilot
• Picture This Ballooning (the operator)
• Civil Aviation Safety Authority
• Australian Ballooning Federation
• the injured passengers.

Submissions were received from:

• Civil Aviation Safety Authority
• the injured passengers.

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

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Overview of the investigation

On 27 December 2021, a Fokker F100, registered VH-FNU, was being operated on a scheduled passenger flight between Newman and Perth, Western Australia. There were 5 crew and 7 passengers on board.

During cruise at flight level (FL) 340 (34,000 ft), a cabin crew member began to feel unwell and was treated with portable oxygen by the other cabin crew members. Suspecting air sickness due to light turbulence, the flight crew climbed to FL350. A few minutes later the other two cabin crew members also began feeling unwell and reported to the flight crew that they suspected possible hypoxia.

The first officer later reported that they also felt light-headed and experienced slight nausea. As a precaution, the flight crew donned oxygen masks, manually deployed the passenger oxygen masks and conducted an emergency descent to 10,000 ft. The aircraft landed at Perth Airport and one cabin crew member was taken to hospital for assessment. The passengers did not report any symptoms to the crew.

As part of its investigation, the ATSB:

• interviewed the flight and cabin crew
• analysed recorded data from the aircraft’s flight data recorder (FDR)
• reviewed the aircraft maintenance records
• reviewed air traffic control recordings
• reviewed other depressurisation occurrences involving Fokker 100 aircraft
• reviewed post-occurrence testing and evaluation reports from the aircraft manufacturer for the cabin indication panel
• reviewed the material safety data sheets and the possibility of a dangerous goods spill.

Additional information

Recorded data

According to the FDR data, about 50 minutes after establishing cruise at FL340 the aircraft climbed to FL350, which took about 1 minute. The aircraft remained at this level for 3.5 minutes and then descended to 10,000 ft over a 5-minute duration (during the emergency descent). This aligned with flight crew and cabin crew recollections.

The parameters that were available for analysis from the FDR did not include the cabin altitude or cabin differential and did not provide detail about the cabin altitude at the time of the event. The FDR recorded any cabin altitude warnings; none activated during the flight. 

Pressurisation system

• The normal cabin altitude for the Fokker F100 at FL350 is 8,000 ft.
• The flight crew recalled that the cabin altitude reached about 8,300 ft.
• The excessive cabin altitude warning (which activates at 10,000 ft) did not activate during the flight.
• The drop-down cabin oxygen masks automatically deploy at a cabin altitude of 13,500 ft on the Fokker F100 aircraft. The masks did not automatically deploy and were manually deployed by the flight crew.

Maintenance inspection results

Inspections and tests were conducted in accordance with the aircraft maintenance manual and in consultation with the aircraft manufacturer. Although there were defects identified, none were considered contributory to a depressurisation event or to the symptoms and subsequent incapacitation reported by the crew members. Several components were changed as a precaution.

ATSB comment

The available evidence indicates that the aircraft’s cabin altitude remained below 10,000 ft. The reasons for the cabin crew and flight crew symptoms could not be established.

The decision by the flight crew to don oxygen masks and descend to a safe altitude was sound. If there is any doubt as to whether the flight crew’s ability to operate the aircraft may be affected by a possible oxygen supply problem, the safest course of action is to go onto oxygen as soon as possible.  

Reasons for the discontinuation

Based on a review of the available evidence, the ATSB considered it was unlikely that further investigation would identify any systemic safety issues or important safety lessons. Consequently, the ATSB has discontinued this investigation.

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