During a maintenance inspection of a Pacific Aerospace CT4/B aircraft, registered VH-YCR, a significant crack was identified within the rear spar of the aircraft’s left wing. The Civil Aviation Safety Authority (CASA) requested technical assistance from the ATSB in the metallurgical examination of the spar. To facilitate this assistance, the ATSB initiated an external investigation under the provisions of the Transport Safety Investigation Act 2003.

The ATSB has concluded the metallurgical examination of the rear spar and provided the results of that work to CASA on 4 May 2022.

CASA is responsible for, and will administer, the release of any information from the ATSB’s examination. Any enquires relating to the matter should be directed to CASA at www.casa.gov.au.

Source: CASA

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The information contained in this update is released in accordance with section 25 of the Transport Safety Investigation Act 2003 and is derived from the initial investigation of the occurrence. Readers are cautioned that new evidence will become available as the investigation progresses that will enhance the ATSB's understanding of the accident as outlined in this update. As such, no analysis or findings are included.

Safety summary

What happened

On the afternoon of 6 July 2021, a Saab 340B aircraft, registered VH-ZLJ, departed Perth Airport for a scheduled passenger flight to Albany, Western Australia, with two flight crew, one cabin crew, and 16 passengers on board.

At about 1623, while climbing through an altitude of 6,000 ft, and before entering icing conditions, the crew activated the engine anti-ice and wing de-ice systems. Shortly afterwards, caution lights illuminated indicating a fault in the de-ice system. After levelling off at 7,000 ft, the crew actioned the relevant abnormal checklist, but the caution lights remained on. In response, the flight crew requested a descent to 5,000 ft to exit icing conditions and decided to return to Perth.

During the descent, the captain handed over control of the aircraft as pilot flying to the first officer. Over the next 2.5 minutes, air traffic control (ATC) communicated with the flight crew on multiple occasions, issuing a series of vectors and requesting flight information. As the aircraft was levelling off at 5,000 ft under autopilot control, ATC instructed the crew to make a right turn. About 20 seconds after beginning the turn, the aircraft’s aerodynamic stall warning stick shakers activated. The first officer initiated the stall recovery procedure before the captain took control as pilot flying to complete the recovery. The aircraft returned to Perth, landing at 1642.

What the ATSB found

The ATSB found that the aircraft’s right wing inboard de-ice boot probably delaminated shortly before encountering icing conditions, triggering the de-ice system fault that led to the flight crew’s decision to return to Perth.

During the return, the pilot flying became task saturated due to high workload and did not notice the aircraft’s reducing airspeed, which was also missed by the pilot monitoring due to a focus on other tasks until the stick shaker activated. The crew managed the recovery from the potential stall condition effectively and the aircraft returned safely to Perth.

What has been done as a result

The aircraft operator has amended flight crew training simulator sessions and related training material to include flight at minimum manoeuvring speeds – minimum airspeeds that provide a margin above a stall during aircraft manoeuvring.

Safety message

This stick shaker activation incident highlights that during periods of high workload, where there is an increased chance of making mistakes or errors, flight crews should prioritise monitoring critical flight parameters. Effective communication can help flight crew recognise a situation when their workload is becoming overwhelming, and consequently better manage the situation – for instance, giving themselves more time to complete the required tasks by discontinuing an approach, or deferring air traffic control requests appropriately.

The investigation

The occurrence

At 1619 Western Standard Time^[1] on 6 July 2021, a Saab 340B aircraft, registered VH-ZLJ (Figure 1) and operated by Regional Express, departed Perth Airport for a scheduled passenger flight to Albany, Western Australia, carrying 16 passengers. The crew comprised the captain (pilot flying),^[2] the first officer (pilot monitoring) and one cabin crewmember.

Figure 1: VH-ZLJ

Source: Supplied

At about 1623, the aircraft was climbing through 6,000 ft above mean sea level (AMSL) with the autopilot engaged. Consistent with operator procedures, the flight crew activated the engine anti‑ice and wing de-ice systems as the aircraft was entering icing conditions. Shortly afterwards, an ice protection master caution light, and TIMER light illuminated, indicating a fault in the de-ice system (see the section titled Airframe de-ice system). Soon after, the flight crew requested, and received, a clearance from air traffic control (ATC) to level off at 7,000 ft to avoid icing conditions. They then began actioning the TIMER light on abnormal checklist.

At 1629 the flight crew requested, and received, a diversion from ATC to avoid storm cells. Despite the crew actioning the checklist, the TIMER light remained on during the wing inboard de‑ice boot cycle, so at 1630 they commenced a descent to 5,000 ft to exit icing conditions. Shortly afterwards, the crew notified ATC that they would return to Perth.

During the subsequent descent, the captain handed over control of the aircraft as pilot flying to the first officer. Over the next 2.5 minutes, ATC communicated with the flight crew on eight separate occasions, issuing a series of radar vectors and flight information requests. At about 1632, the aircraft was levelling off at 5,000 ft with the autopilot engaged when ATC instructed the crew to make a right turn. About 20 seconds after beginning the turn, the aircraft’s aerodynamic stall warning stick shakers activated (see the section titled Stall warning system). The first officer initiated the stall recovery procedure before the captain took control as pilot flying to complete the recovery.

The aircraft returned to Perth without further incident, landing at 1642.

Context

Flight crew

The captain held an Air Transport Pilot Licence (Aeroplane), and had 4,695 hours of flying experience, of which over 4,474 hours were on the Saab 340B. The captain made the following comments and observations about the incident.

• The decision to return to Perth was based on the de‑ice system fault indication, the low freezing level along the route and no engineering support at the destination (Albany).
• As pilot monitoring during the descent from 7,000 ft to 5,000 ft, the captain notified the operator and communicated with the cabin crew and passengers regarding preparation for the return to Perth.
• During the descent their workload was relatively high, but the captain recalled feeling comfortable handling it at the time. However, in hindsight the captain felt that they did not monitor the first officer appropriately or focus enough attention on the aircraft’s airspeed and engine power levels.

The first officer held a Commercial Pilot Licence (Aeroplane), and had 605 hours of flying experience, of which over 386 hours were on the Saab 340B. The first officer made the following comments and observations about the incident.

• After taking over as pilot flying, the first officer became overly focussed on complying with ATC clearances since:
  • the captain was occupied and not available to perform standard clearance cross-checks
  • they were aware of previous instances of flight crew’s deviating from clearances because only one pilot had acknowledged them.
• The focus on ATC clearances, in combination with managing related communications, caused the first officer to feel ‘task saturated’^[3] and that the workload was ‘very high’.
• The first officer believed that the task saturation resulted in their instrument scan breaking down and not paying sufficient attention to the airspeed and engine power settings.
• The flight crew could have better managed the workload by giving themselves more time to complete tasks.

The ATSB found no evidence to indicate either flight crew were experiencing a level of fatigue known to affect performance.

Meteorological information

The relevant graphical area forecast indicated a freezing level of about 8,000 ft at Perth, reducing to about 6,000 ft at Albany. Moderate showers with broken^[4] cloud from 2,500 ft to above 10,000 ft, severe icing above 6,000 ft, and moderate turbulence below 7,000 ft were also forecast.

The flight crew reported rain and storm cells in the Perth Airport area and encountered occasional cloud at 7,000 ft, where the outside air temperature was 4° C (icing conditions).

Airframe de-ice system

The aircraft’s airframe de-icing system consisted of inflatable boots, located on the leading edges of the vertical and horizontal stabiliser, and the inboard and outboard section of the wings. The boots were rapidly inflated, using engine bleed air, to crack any accumulated ice and then deflated. A timer control unit regulated the boot inflation cycles in a sequence – stabiliser, outboard wing, and then inboard wing. Sensors monitored the boot cycles, and a TIMER light would illuminate together with an ice protection master caution light if a fault was detected with the de‑ice system.

Post-flight examination of the de-ice system revealed a delamination in the right wing inboard de‑ice boot on the underside of the wing (Figure 2). The aircraft operator stated that this was probably caused by an internal stitching failure, resulting in the loss of system pressure. The boot was replaced and the de-ice system was subsequently tested serviceable. The ATSB reviewed the aircraft’s maintenance history related to the de-ice system and found it compliant with the required maintenance.

Figure 2: Right wing inboard boot delamination

Source: Operator, annotated by ATSB

Stall warning system

The stall warning and identification system fitted to the Saab 340B included:

• two independent stall warning computers
• two angle of attack (AOA) sensors – one mounted on each side of the fuselage
• stick shaker device on each control column that provided a physical warning of an impending aerodynamic stall in the form of vibrations and aural clacker sound when activated
• stick pusher device that applied forward force to the control column to reduce aircraft AOA when a stall condition was identified.

The AOA activation level for the aircraft’s stall warning system was dependent on flap position, engine anti-ice operation, and airframe de-ice operation. Flight in icing conditions required the operation of engine anti-ice and boot de-ice systems. Accumulation of ice and/or operation of the wing boot de-ice system alters the stall characteristics of the wings. This was compensated for by the stall warning system activating the stick shaker at a lower AOA (earlier) when the aircraft was configured for flight in icing conditions. The stick pusher AOA activation was unchanged. There was no indication in the cockpit of the AOA, but if an AOA sensor activation level was exceeded, the stick shaker and aural clackers activated, and the autopilot (if engaged) disengaged. If the AOA sensor values increased further, the stick pusher was activated.

Post-flight testing revealed that the left AOA sensor triggered the stall warning systems about 1 or 2° earlier than the specified parameters. The left AOA sensor was replaced, and the stall warning system was successfully tested. The ATSB identified that the aircraft’s maintenance history related to the stall warning system was compliant with the required maintenance.

Recorded data

Data from the aircraft’s flight data recorder was downloaded, but the aircraft manufacturer identified that some data parameters (AOA and elevator angle) had been corrupted.

Figure 3 shows verified flight data for certain recorded parameters at the time of the incident. The data shows that during level flight at 7,000 ft, engine power was at about 60% torque. During the descent to 5,000 ft, engine power was reduced by the flight crew to about 15% torque. After levelling off at 5,000 ft, engine power remained at that level, however the aircraft’s pitch angle increased, while the airspeed decreased. The pitch increase and airspeed reduction continued after the turn was commenced. About 20 seconds later, the autopilot disconnected, and the flight crew initiated the stall recovery.^[5] Altitude lost during recovery was about 450 ft.

The investigation could not determine which AOA sensor triggered the stick shaker, but the flight data was consistent with the aircraft approaching a stalled condition, so the early triggering of the left AOA sensor did not affect the outcome.

Figure 3: VH-ZLJ flight data

Source: ATSB

Similar occurrences

In 2013, an ATSB research report^[6] identified that 245 stall warnings in high capacity aircraft had been reported between 2008 and 2012 in Australia. Almost all of those were low risk events of momentary duration and were responded to promptly and effectively by the flight crew to maintain control of the aircraft. However, there were also several higher risk incidents where stick shaker activation occurred on approach to land when aircraft were in a low speed, high AOA configuration. In these cases, the risk of a stall developing was increased by a lack of awareness of decreasing airspeed and increasing AOA prior to the stall warning, probably due to increased flight crew workload during this phase of flight. None of the reported occurrences resulted in an actual stall.

Safety analysis

Shortly after the aircraft departed Perth, the flight crew received cockpit indications of a de-ice system fault. The fault was probably triggered by a delaminated de-ice boot on the underside of the right wing that failed during its inflation cycle shortly before encountering icing conditions. With a low freezing level and forecast icing conditions along the planned route, the de-ice fault indication led to the flight crew’s decision to return to Perth.

While manoeuvring towards Perth, engine power was reduced to descend the aircraft from 7,000 ft to 5,000 ft. However, when the aircraft levelled off at 5,000 ft, engine power was not increased. Consequently, as the airspeed reduced due to the low engine power, the autopilot maintained the selected altitude (5,000 ft) by pitching the nose up, increasing the AOA and reducing the airspeed further. This condition went unnoticed until one of the AOA sensors reached the level required for stick shaker activation.

The first officer, the pilot flying in the time leading up to the stick shaker activation, probably became task saturated while managing flying tasks (changing flight state to descend, level flight and turn) as well as communicating with, and following ATC instructions. This task saturation reduced the attention that the first officer paid to managing the airspeed and engine power. At that time, the captain (pilot monitoring) was also not monitoring these key parameters due to a focus on other communication tasks related to the return to Perth. The crew’s reduced awareness of airspeed resulted in the potential stall going unnoticed until the stick shaker activated.

In addition, during that rapid sequence of events, neither pilot recognised the first officer’s high workload and task saturation. Consequently, no attempt was made to alleviate the situation, for example by discontinuing the approach or deferring ATC requests for information until the aircraft was straight and level. Such actions would have provided additional time and opportunity for the crew to refocus on flight instruments and key parameters.

Findings

From the evidence available, the following findings are made with respect to the stick shaker activation involving Saab 340B, VH-ZLJ, 30 km south-west of Perth Airport, Western Australia on 6 July 2021.

Contributing factors

• The aircraft’s right wing inboard de-ice boot probably delaminated shortly before encountering icing conditions, triggering the de-ice system fault that led to the flight crew’s decision to return to Perth.
• The pilot flying became task saturated due to high workload and did not notice the reducing airspeed, which was also missed by the pilot monitoring due to a focus on other tasks until the stick shaker activated.

Safety actions

Safety action by Regional Express

Regional Express has amended flight crew training simulator sessions and related training material to include flight at minimum manoeuvring speeds – minimum airspeeds that provide a margin above a stall during aircraft manoeuvring.

Note: Saab advised the ATSB that it intended to follow-up with Regional Express to obtain further details on the out of limits AOA vane and the delaminated de-ice boot.

Sources and submissions

Sources of information

The sources of information during the investigation included:

• the flight crew
• Regional Express
• Saab
• Airservices Australia
• Bureau of Meteorology.

References

ATSB aviation research investigation report AR-2012-172, Stall warning in high capacity aircraft: The Australian context, Australia.

Submissions

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

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

• Regional Express, including flight crew
• Saab
• Civil Aviation Safety Authority
• Airservices Australia.

Submissions were received from Regional Express, and the flight crew. The submissions were reviewed and, where considered appropriate, the text of the report was amended accordingly.

Purpose of safety investigations The objective of a safety investigation is to enhance transport safety. This is done through: identifying safety issues and facilitating safety action to address those issues providing information about occurrences and their associated safety factors to facilitate learning within the transport industry. It is not a function of the ATSB to apportion blame or provide a means for determining liability. At the same time, an investigation report must include factual material of sufficient weight to support the analysis and findings. At all times the ATSB endeavours to balance the use of material that could imply adverse comment with the need to properly explain what happened, and why, in a fair and unbiased manner. The ATSB does not investigate for the purpose of taking administrative, regulatory or criminal action. Terminology An explanation of terminology used in ATSB investigation reports is available here. This includes terms such as occurrence, contributing factor, other factor that increased risk, and safety issue. Publishing information Released in accordance with section 25 of the Transport Safety Investigation Act 2003 Published by: Australian Transport Safety Bureau © Commonwealth of Australia 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.

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1. Western Standard Time (WST): Coordinated Universal Time (UTC) + 8 hours.
2. Pilot Flying (PF) and Pilot Monitoring (PM): procedurally assigned roles with specifically assigned duties at specific stages of a flight. The PF does most of the flying, except in defined circumstances; such as planning for descent, approach and landing. The PM carries out support duties and monitors the PF’s actions and the aircraft’s flight path.
3. Having too many tasks to complete without enough time, tools, or resources to do them. This can lead to an inability to focus on what really matters. Task saturation can be insidious, and people can become too busy to recognise that they are overloaded.
4. Cloud cover: in aviation, cloud cover is reported using words that denote the extent of the cover – ‘broken’ indicates that more than half to almost all the sky is covered.
5. The flight data did not record stick shaker or aural warning activation. However, the airspeed increase, pitch angle reduction, and engine torque data was consistent with flight crew identifying the stall warning and initiating recovery procedures.
6. ATSB (Australian Transport Safety Bureau) (2013), AR-2012-172, Stall warnings in high capacity aircraft: The Australian context, Available from the ATSB website.

Safety summary

What happened

On 21 June 2021, a Boeing Company 787-9, registered VH-ZNH and operated by Qantas Airways, was prepared for a scheduled passenger flight from Sydney, New South Wales, to Perth, Western Australia. During initial climb, the flight crew selected the landing gear lever to UP. Shortly after, they received a warning, indicating that neither main landing gear had retracted to the ‘up and locked’ position. Despite consulting the aircraft’s electronic checklist, the flight crew were unable to resolve the retraction issue. The landing gear lever was then selected to DOWN, with positive gear extension indications, and the aircraft returned to Sydney for an uneventful landing.

What the ATSB found

The ATSB found that two of the five downlock pins, one in each main landing gear, had not been removed following towing of the aircraft to the domestic terminal aircraft bay. In addition, these gear pins were not identified during subsequent external inspections, prior to the departure. When the flight crew selected the landing gear to retract, the nose gear successfully retracted and locked in the up position. However, the two installed pins prevented any movement of the main landing gear. There was no damage to the main landing gear.

What has been done as a result

Following the occurrence, the operator distributed memos to engineering, flight and ramp crew, highlighting the quantity and location of the gear pins on the Boeing 787, and the importance of following the documented ramp, pre-flight and dispatch procedures.

The memo to engineering also emphasised the importance of checking the pin location, rather than relying on streamers for identification. In addition, training packages for engineering, ramp and flight crew were updated with additional detail. Further, the operator advised they were working to relocate the gear pin stowage to the flight deck, in line with other aircraft types, to enable ease of access to visually verify pin removal and stowage.

Safety message

‘Remove before flight’ streamers are a reminder to remove covers, or lockout devices, prior to flight. Failure to remove these devices and covers can prevent the functionality of certain aircraft systems. The streamers are subject to varying environmental conditions that can reduce their visibility.

Expectation can also affect identification of these warning devices. Put simply, the likelihood of detecting ‘remove before flight’ streamers is significantly reduced if they are not expected to be there. The same principle can also prevent the discovery of damaged and/or missing components.

The investigation

The occurrence

Pre-flight ground operations

On the morning of 21 June 2021, a Boeing Company 787-9 (787), registered VH-ZNH (ZNH) and operated by Qantas Airways, was being prepared for a scheduled passenger flight from Sydney, New South Wales, to Perth, Western Australia. At about 0745 Eastern Standard Time,^[1] ZNH was towed, by Qantas Engineering (engineering), from the aircraft parking location to domestic terminal bay 11. The tow crew on the ground consisted of the person in charge (PIC), two wing walkers and the tow‑motor driver.^[2] On board the aircraft was a 787 licenced aircraft maintenance engineer (LAME), in the role of flight deck operator (FDO)^[3] and an aircraft maintenance engineer (AME), who was undergoing informal general familiarisation training.

Upon arrival at bay 11, chocks were placed at the aircraft wheels and the tow‑motor was unhitched, to allow it to be used for another tow. The PIC removed the nose gear downlock pin (gear pin), then walked to the rear of the aircraft and removed one gear pin from the right main gear. At the same time, one of the wing walkers removed a gear pin from the left main gear.

The PIC and wing walker had not towed a 787 before and, as such, contacted the LAME via the aircraft intercom system, to enquire where the pins were stowed on this aircraft type. The AME, under instruction from the LAME, advised the PIC that the pins were stored in the electrical equipment centre (EEC) located just aft of the nose gear. The AME then relayed that the PIC could leave the removed pins on the nose gear and the LAME would stow them when the aerobridge^[4] arrived and they could exit the aircraft.

Despite the offer to leave the pins on the nose gear, the PIC identified a short ladder nearby and opened the EEC. The ladder was of insufficient height to see into the pin stowage location, so the PIC felt around and physically identified pin stowage holes. After stowing the three gear pins, the PIC closed the EEC, returned the ladder and departed, with the wing walker, to conduct another tow.

Unavailability of an aerobridge operator resulted in the LAME and AME being unable to leave the aircraft for about 20 minutes. When the aerobridge was manoeuvred into place, at about 0810, the LAME and AME exited the aircraft via the associated stairs. The LAME noted that the nose gear pin had been removed. The LAME reported that they then looked down toward the main gear and did not identify any streamers associated with the gear pins (see the section titled Landing gear downlock pins).

As there were no gear pins on the nose gear, the LAME directed the AME to confirm the gear pins had been stowed in the EEC, utilising the same nearby ladder previously used by the PIC. The ladder height was again insufficient to allow the AME to see into the pin stowage area, but they were able to physically feel the presence of the pins. After closing the EEC panel and returning the ladder, the LAME and AME waited at the aircraft until a car arrived at about 0819, to take them to the engineering office. The LAME signed for the removal and stowage of the landing gear pins on the electronic and paper technical logs (tech log). The LAME then returned the paper tech log to the aircraft at about 0842.

The flight crew, who arrived at the aircraft at about 0900, consisted of the captain, the first officer and a second captain, who was filling the role of relief pilot.^[5] The flight crew reviewed the tech log and noted the endorsement that the gear pins had been removed and stowed. As the third crew member, the relief pilot conducted the external inspection, between 0938 and 0945.

The relief pilot reported conducting the external inspection as per the flight crew operations manual (FCOM), with no anomalies identified, before returning to the flight deck to assist with the remainder of the pre‑flight preparations. The pre-flight, including landing gear system checks, were completed, with nil anomalies identified.

Aircraft dispatch for the 787 was conducted by two Swissport^[6] ground crew, a supervisor and a crew member undergoing training, who arrived at ZNH about 1020. Once all ground services had been completed, the supervisor conducted the final external inspection prior to pushback. The supervisor reported checking all doors and panels were closed and secured, and no streamers were identified. The aircraft was pushed back at about 1025.

Occurrence flight

ZNH was cleared to depart via runway 16R,^[7] initially heading to the south of the airport before making a westerly turn onto the planned route. The captain was the pilot flying (PF) and the first officer was the pilot monitoring (PM),^[8] with the second captain (relief pilot) seated in the flight deck for take-off.

At about 1032, shortly after take-off and with the aircraft established in a positive climb, the PM positioned the landing gear selector to UP. Ten seconds after selecting the landing gear up, the crew received a GEAR DISAGREE caution on the Engine Indication and Crew Alerting System (EICAS) and an associated aural alert. The flight crew observed indications that the nose landing gear had retracted however, both main landing gear continued to display a grey crosshatch symbol, indicating that they remained ‘in transit’ (see the section titled Landing gear operation).

The flight crew configured the aircraft for safe operation with the landing gear extended in accordance with the operator’s procedures. The PF then requested the PM commence the GEAR DISAGREE EICAS procedure through the aircraft’s electronic checklist. The flight crew advised air traffic control (ATC) of a landing gear problem and then levelled the aircraft at an altitude of about 9,000 ft, away from the airport and over water, to troubleshoot the issue.

The PF, who reported experiencing a degree of startle upon receiving the initial GEAR DISAGREE EICAS message, asked the PM to read out the electronic checklist procedure again, to confirm it was fully understood.

On completion of the GEAR DISAGREE checklist, the main landing gear continued to indicate ‘in transit’. The flight crew discussed cycling the landing gear, selecting DOWN and then UP, to troubleshoot the issue however, due their proximity to the airport, they decided to return to Sydney.

The flight crew reported that guidance for the continued management of the abnormal gear indication from the electronic checklist and Quick Reference Handbook was limited to noting airspeed and fuel duration considerations, and therefore decided to extend the gear via the normal gear selection. They further agreed to select landing gear down earlier in the approach than they normally would, to allow sufficient time to assess and resolve any abnormalities, noting the substantial fuel endurance available, if required. The landing gear lever was then selected to ‘DOWN’ and the crew received a positive ‘green’ indication on the EICAS that confirmed all of the landing gear was ‘down and locked’.

The flight crew reported that ATC asked if they wanted emergency services to be on standby for the landing however, they advised that this was not required. This decision was based on the aircraft’s landing gear now indicating normal extension. At 1106, ZNH touched down on runway 16R, for an uneventful landing. The aircraft was taxied to bay 11, and engineering subsequently identified that two landing gear pins were still installed, one in each main gear.

Context

Landing gear operation

The gear retraction sequence commences when the landing gear lever is placed in the UP position. The EICAS landing gear position indication changes from a green DOWN indication to a white crosshatch in-transit indication. When the landing gear has retracted, and is being held in place by uplocks, the landing gear hydraulic system is automatically depressurised. At this point, no landing gear indications are displayed on the EICAS.

The normal transit time for gear retraction is approximately 10 seconds. If any landing gear is not up and locked after about 40 seconds, the EICAS caution message GEAR DISAGREE is displayed. The EICAS gear position indication then displays an expanded non‑normal format. The flight crew can then see which gear is UP, in‑transit, or DOWN (if the gear never unlocked from the down position). In this instance, the flight crew were presented with an UP indication for the nose gear and in-transit indications for each of the main gear (Figure 1).

Figure 1: EICAS expanded message indication, showing nose gear up and locked, and main gear 'in-transit' (crosshatched)

Source: Supplied, annotated by ATSB

The EICAS checklist ‘objective’ for GEAR DISAGREE included for the flight crew ‘to extend the gear using an alternate gear extension’. The checklist also had a note to not exceed the ‘gear extended speed limit’ and that flight with the gear extended would increase fuel consumption. The flight crew reported that, as the nose gear retracted without issue, they did not suspect normal gear operation was affected. Therefore, they elected to attempt normal gear extension, before considering alternate procedures. The normal gear extension was completed without issue.

Landing gear downlock pins

The landing gear downlock pins (gear pins) were installed to prevent inadvertent gear retraction during maintenance or towing operations. The 787 has five gear pins, one for the nose gear and two for each main landing gear (Figure 2).

Figure 2: Typical left main gear showing pins and streamers installed.

Source: Supplied, annotated by ATSB

The gear pin is a quick release style and has a ‘REMOVE BEFORE FLIGHT’ streamer attached via a split ring. The aircraft maintenance manual (AMM) contained procedures for installation and removal of the gear pins. The main gear pins are located above head height and the AMM procedures recommend a 1.83m (6 ft) ladder, be utilised for installation and removal.

If the aircraft was required to be operated with the landing gear locked in the extended position, for example for maintenance purposes, the gear pins were to be secured as per the AMM. In that instance, a bolt and nut were to be installed on the end of the pin, with a large washer located between the bolt and the pin quick-release, to ensure retention of the pin in the landing gear.

The gear pin stowage box was located in the EEC, just aft of the nose gear, and was attached to the aircraft structure (Figure 3). The hinged door, which had receptacles for the four main gear pins, tilted outwards from the top and included a lanyard to limit swing. The box portion contained two receptacles, one for the nose gear pin and one for the steering bypass pin.^[9] Qantas engineering personnel reported that a ‘tall ladder’ was required to be able to see into the stowage box.

Figure 3: Gear pin stowage box showing hinged door with four main gear pin receptacles

Source: Supplied, annotated by ATSB

Airbus A330s and Boeing 737s were the aircraft types that Sydney Qantas engineering were most familiar with. These aircraft types have a total of 3 gear pins, one in the nose and one in each of the main gear. In addition, the gear pins on these aircraft types are stowed in the flight deck, readily accessible to flight and ground crew.

Gear pin streamers

Boeing advised that gear pins are classified as ground support equipment (GSE) and therefore not included in the type design of the aircraft. As a result, there is no minimum specifications, nor do they direct a maintenance or cleaning program.

Ground and flight crew described the streamers, of various aircraft types, as being different lengths and various states of cleanliness, which could reduce visibility in certain environmental and light conditions. Due to their installed location, the landing gear pin streamers were subject to contamination from oil, grease and grime. In addition, the streamers were known to wrap around the gear on occasion, particularly in wet and/or windy conditions.

An image of one of the missed main landing gear pins, upon return to Sydney, showed it to be dull and frayed however, it’s condition prior to the flight could not be determined (Figure 4). Examination of ZNH’s gear pin streamers noted degraded condition, particularly with respect to the normal intensity of the high-visibility colour.

Figure 4: Gear pin identified on landing (left) and VH-ZNH gear pins (right).

Source: Supplied, annotated by ATSB

CCTV footage showed that, when ZNH was towed into bay 11, prior to the flight, one streamer on each main landing gear was visible (Figure 5). It was these streamers that were identified and removed by the tow crew. The footage showed the wing walker and the PIC, climb the rear tyre of each main gear^[10] and remove a pin (with attached streamer) from the side braces. Streamers associated with the drag braces were not readily visible in the CCTV footage.

The footage also showed:

• evidence of recent rain when the aircraft was being towed to bay 11, but good light conditions
• some light rain at about the time the 787 LAME and AME, departed the flight deck, checked the EEC for the presence of pins and waited for a lift to the office
• the tow crew and AME used a 0.9 m (3 ft) 3-step ladder to access the EEC
• partly cloudy / sunny conditions when the relief pilot and dispatch crew conducted their respective external inspections, and during pushback.

Figure 5: VH-ZNH with visible main gear streamers

Source: Sydney Airport, annotated by ATSB

Procedures

Qantas engineering were responsible for aircraft towing operations, in accordance with the Towing section of the Qantas Engineering Procedures Manual. Section 7 Post aircraft tow, step 4 stated that it was either the tow crew PIC or the FDO’s responsibility to ‘remove and stow aircraft main and nose landing gear downlock pins’.

Swissport had been contracted by Qantas to carry out receipt and dispatch procedures for the 787, since its introduction in 2017. All other Qantas aircraft types had receipt and dispatch activities conducted by Qantas engineering at Sydney Airport. Qantas Ramp Operations Manual procedures were to be followed by Swissport staff, for receipt and dispatch of the 787. The aircraft dispatch procedure stated:

- Ensure the Steering By-pass pin is fitted

- Any landing gear downlock pins are also removed and stowed in the correct place

- Advise Engineering if Pitot covers are still present. Ensure they are removed prior to departure.

The section manage pins and covers identified:

There can be a total of five (5) downlock pins that can be fitted to the aircraft.

- One (1) nose gear downlock pin, and

- Up to Four (4) main gear downlock pins.

The ‘external inspection sequence’ included, ‘observe whether the main gear downlock pins have been removed’.

The flight crew were required to conduct their external inspection in accordance with the Qantas flight crew operations manual (FCOM) 787 Amplified procedures – exterior inspection. The section regarding the left and right main landing gear areas inspection included ‘gear pins – as needed’ (Figure 6)

Figure 6: FCOM external inspection of main gear areas

Source: Supplied

Awareness of five gear pins

Qantas ground crew

As a result of the COVID-19 pandemic travel restrictions, voluntary redundancies were offered to affected personnel. A subsequent restructure of Qantas engineering took place in February 2021, which resulted in certain engineers being transitioned into new roles, on new aircraft types.

Only one of the Qantas ground crew that spoke with the ATSB,^[11] the 787 LAME, advised they were aware that the 787 had five gear pins. In addition, it was the first time towing a 787 for all the ground crew except the 787 LAME. One of the wing walkers was a LAME on the 737, 747 and Airbus 330 (A330), while the PIC and the AME being trained by the 787 LAME, held category A licences^[12] on the A330.

Fight crew

All flight crew recalled undergoing computer-based training on external inspection procedures during their initial ground school (in 2018 and 2019), and then conducting an external inspection under supervision from a training captain, during initial flight‑line operations. Neither captain could specifically recall the number, nor exact location, of the main gear pins, from their training.

The first officer was aware of the five pins, due to their flying experience on the 767,^[13] which had a similar design of landing gear to the 787. The previous flying experience of the two captains was on aircraft types that had three gear pins. In addition, the second captain (relief pilot) and first officer advised they had never seen pins installed, as they were typically removed before the flight crew conduct their external inspection. Further, the flight crew reported their process was to look for the streamers during their external inspection, as opposed to sighting the actual pin locations.

Swissport dispatch crew

The Swissport crew consisted of a trainer and trainee. The trainer had experience dispatching 787 aircraft for several airlines, they advised that they were aware of the five gear pins on the 787 and had occasionally seen gear pins and streamers installed, for example, when aircraft were under tow.

The Swissport trainee, while experienced in dispatching other aircraft types at another Australian airport, was undergoing Sydney familiarisation training. The trainee advised that ZNH was only the second 787 they had dispatched, the first being a few hours earlier that day. The trainee recalled being aware of the five pins, from their training however, had never seen the pins installed. Further, as the trainer had conducted the external inspections that day, the trainee had not specifically looked out for them.

Both Swissport crew reported their dispatch procedures were to check all ground equipment was clear and inspect the aircraft for security of doors and panels, and presence of any streamers. The Swissport crew would install the steering bypass pin when the tow‑motor was connected, and then remove it when the tow‑motor was disconnected, following pushback. The steering bypass pin was located near the nose gear pin. The trainer advised that, had the nose gear pin still been installed, it would have been an alert to check all the other gear pins had been removed. However, as the nose gear pin was not installed, the trainer concluded that all pins had been removed, as they had not encountered a situation where only some of the pins had been removed.

Procedure if gear pin streamers identified

Both the flight crew and Swissport dispatchers reported that, if they identified any streamers during their external inspection, they were to contact Qantas engineering, who would then remove the associated pin or cover. Further, all reported being aware of the possibility that streamers can become caught up in, or stuck to, the landing gear.

Similar occurrences

Boeing advised they had received reports from other operators of inadvertent departures with gear pins installed. As the gear pins are classified as GSE, this type of event was not required to be reported to Boeing and subsequently that were not able to give an accurate estimate of how often situations like this may have occurred. Further, Boeing advised that, from the reports they did have, they were not aware of any outcomes more serious than a ‘return‑to‑base for a safe landing’.

The investigation identified two similar events involving Australian-operated 787s, in 2014 and 2021, noting this type of occurrence was not required to be reported to the ATSB. In 2014, the aircraft had been dispatched, and gear pin streamers were noted by the crew of another taxiing aircraft. The aircraft returned to bay and two gear pins were located, one in each main gear. In this occurrence, the gear pin streamers were noted to be ‘dirty’, short in length and ‘not as visible as new’ streamers.

On 19 June 2021, at about 2205 local time, two gear pin streamers were identified by the second officer during the flight crew external inspection. This was despite the tech log being endorsed that the pins had been removed and stowed. The second officer’s report stated that, when inspecting the right main gear from the front, nothing abnormal was noted. The second officer then moved to the rear of the main gear and used their torch to check the gear pin location holes. At this point they observed a gear pin streamer wrapped up and stuck to the main gear leg.

The second officer reported that, due to the wet and windy conditions, the streamer had been caught up on the main gear and, in combination with low light, it was difficult to see. Before returning to the flight deck to notify engineering, the second officer identified a gear pin streamer on the left main gear. The pins were subsequently removed by engineering and the aircraft departed as scheduled.

Safety analysis

In this occurrence, multiple factors led to an aircraft departing configured such that the flight crew were unable to retract the main landing gear. Specifically:

• The tow crew used the visible streamers to identify what they incorrectly believed were the only three gear pins installed the aircraft.
• While the LAME was aware the 787 had five gear pins, they did not confirm all of them had been removed and stored before signing the tech log. Instead, the AME physically checked for the presence of pins without knowing the number to expect.
• The ladder used to access the gear pin stowage location was not of sufficient height to allow visual confirmation of pin stowage. Sighting of ‘empty’ pin stowage receptacles would have provided a clear indication that not all pins had been removed from the landing gear.
• The flight and dispatch crews conducted their external inspection with no expectation of finding streamers indicating gear pins were still installed. This was likely due to the tech log being endorsed and a belief that the gear pins had been removed by engineering personnel.
• There was probably reduced visibility of the streamers, due to their degraded condition and the likelihood they were stuck on the gear, from a combination of grime and the recent wet and windy conditions.

Research has demonstrated that people are more likely to detect targets (such as gear pin streamers) when they are expected and less likely to detect targets that are not expected (Wickens and McCarley 2008). In addition, bias can occur when prior knowledge, combined with an expected outcome, influences decision making.

The tow crew were expecting to see the gear pin streamers, as they had just completed moving the aircraft. The tow crew then identified, and removed, three main landing gear pins, which was consistent with the aircraft types they had experience on. In contrast, as the gear pins were typically removed prior to the flight and dispatch crew external inspections, they were not expecting to see any gear pin streamers.

Findings

From the evidence available, the following finding is made with respect to the landing gear indication and return involving Boeing 787, VH-ZNH, near Sydney Airport, New South Wales, on 21 July 2021.

Contributing factor

• Two of the five landing gear pins were not removed as per the operator’s procedures, nor identified by engineering, flight crew or dispatch during pre-departure checks. This resulted in the aircraft departing without the functionality to retract the main landing gear.

Safety actions

Safety action by Qantas Airways Ltd

Following the occurrence, Qantas considered the viability of a maintenance program for ‘remove before flight’ streamers. However, it was determined that enhanced training and procedures would have greater benefit in reducing the risk of a similar occurrence. In response to an internal investigation, Qantas has advised the ATSB of the following actions:

• Release of memos to engineering, flight and ramp crew, highlighting quantity (five) and location (images) of gear pins on the 787, and the importance of following the documented procedures. The memo to engineering also emphasised the importance of checking the pin location, rather than relying on streamers. The memo to flight crew and ramp emphasised that engineering were to be contacted if any gear pins were identified, before continuing with the external inspection.
• Updated training packages for engineering, ramp and flight crew.
• Relocation of the pin stowage from the electrical equipment centre (EEC) to the flight deck, in line with other aircraft types, to enable ease of access to verify pin stowage.

Sources and submissions

Sources of information

The sources of information during the investigation included:

• Qantas engineering personnel involved in the tow
• Qantas flight crew
• Swissport dispatch crew
• Qantas Airways
• Boeing

References

Wickens, C.D. and McCarley, J.S (2008). Applied attention theory. Boca Raton, FL: CRC Press.

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:

• Qantas, including the involved engineering and flight crew
• Swissport, including dispatch crew
• Boeing and the United States National Transportation Safety Board.

Submissions were received from:

• Boeing
• Qantas

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

Purpose of safety investigations The objective of a safety investigation is to enhance transport safety. This is done through: identifying safety issues and facilitating safety action to address those issues providing information about occurrences and their associated safety factors to facilitate learning within the transport industry. It is not a function of the ATSB to apportion blame or provide a means for determining liability. At the same time, an investigation report must include factual material of sufficient weight to support the analysis and findings. At all times the ATSB endeavours to balance the use of material that could imply adverse comment with the need to properly explain what happened, and why, in a fair and unbiased manner. The ATSB does not investigate for the purpose of taking administrative, regulatory or criminal action. Terminology An explanation of terminology used in ATSB investigation reports is available here. This includes terms such as occurrence, contributing factor, other factor that increased risk, and safety issue. Publishing information  Released in accordance with section 25 of the Transport Safety Investigation Act 2003 Published by: Australian Transport Safety Bureau © Commonwealth of Australia 2021 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.  Eastern Standard Time (EST): Coordinated Universal Time (UTC) + 10 hours.
2. The PIC coordinates the tow with the ground crew via voice and hand signals, and with the flight deck via the aircraft intercom system. The wing walkers walk at each wing tip, monitor for clearance and can alert the PIC of impending danger, via hand signals or air horn.
3. The Flight Deck Operator (FDO), is a LAME who is licenced on the aircraft type and is required to ensure correct aircraft configuration throughout the tow duration.
4. Aerobridge – a moveable, elevated platform corridor connecting the aircraft to the terminal building.
5. The relief pilot, in this instance, was on board to allow the first officer a rest period during the flight. This was to ensure the first officer remained within flight and duty requirements for their return flight to Sydney later that day. The two captains were ending their duty in Perth.
6. Swissport provided ground services and cargo handling to Qantas, and other airlines, within Australia and globally.
7. Runway numbering: the number represents the magnetic heading closest to the runway (runway 16 at Sydney Airport is oriented 168° magnetic) and R indicates the right most of two parallel runways.
8. Pilot Flying (PF) and Pilot Monitoring (PM): procedurally assigned roles with specifically assigned duties at specific stages of a flight. The PF does most of the flying, except in defined circumstances; such as planning for descent, approach and landing. The PM carries out support duties and monitors the PF’s actions and the aircraft’s flight path.
9. When the steering bypass pin is inserted, the steering hydraulics on the landing gear are bypassed. This allows the aircraft to be moved by tow motor, without having to deactivate the entire aircraft hydraulics.
10. It was reported that ladders are typically not utilised for installation or removal of gear pins.
11. The ATSB did not interview the second wing walker or tow motor driver as they were not directly involved with the gear pins removal and/or stowage.
12. The category A licence gives the holder limited licensing privileges that are matched to the knowledge, competencies and assessments specified in the Civil Aviation Safety Regulations (CASR) Part 66 Manual of Standards for the category A licence.
13. The 767 is no longer operated by Qantas.

Executive summary

What happened

On 23 June 2021, a Cessna A150M Aerobat, registered VH-CYO, departed from the Sunshine Coast Airport, Queensland, with an instructor and student pilot on board. The purpose of the aerobatic training flight was to introduce and practice spin entry and recovery techniques.

The aircraft climbed to about 6,000 ft above mean sea level and arrived at the area intended to conduct aerobatics about 20 minutes after departure. Radar data showed that the aircraft then entered into a left spin that continued for about 55 seconds until the aircraft impacted terrain. The instructor and student were fatally injured, and the aircraft was destroyed.

What the ATSB found

Forward movement of the aircraft and the low angle of entry indicated that the aircraft was most likely in the process of recovering from the spin when it impacted with trees.

Examination of the aircraft did not identify any mechanical defect. However, the aircraft was significantly disrupted and therefore functionality of the flight controls was unable to be fully assessed. Pre- and post-accident medical information did not identify any underlying conditions in either pilot that may have contributed to the accident.

The aerobatics instructor was experienced in conducting spins, primarily in the Pitts Special aircraft type. However, it was likely that they had no experience in spinning a Cessna A150 Aerobat or any similar variant. The instructor’s theoretical spin training provided to the aerobatic student pilot (and another student at the same time) did not include instruction on the recovery technique as prescribed in the Aerobat pilot’s operating handbook (POH). Further, the ATSB established that it was likely the instructor intended to practice 2 spin recovery techniques. One of those techniques, broadly known as the Mueller/Beggs recovery method, has been shown to not recover a Cessna A150 Aerobat established in a spin to the left. The other method known as PARE, aligned closely with the aircraft’s POH and, if utilised, it would recover the aircraft from a spin.

The ATSB was unable to ascertain which of the recovery technique(s) was being utilised at the various stages of the spin recovery preceding the accident. For this reason, the ATSB was unable conclude if the use of an inappropriate recovery technique contributed to the accident.

What has been done as a result

The ATSB has issued a Safety Advisory Notice SAN (AO-2021-025-SAN-001) for aerobatic pilots and aerobatic instructors who conduct spins utilising the Mueller/Beggs spin recovery method, to raise awareness of its limitations.

Safety message

Although the reason for the accident could not be fully established, the investigation identified that one of the spin recovery methods that was to be practiced on the day of the accident would most likely not recover the Cessna A150M Aerobat from a spin.

This investigation presents a timely reminder that pilots should review the pilot’s operating handbook of the aircraft type that they intend to operate. Prior to intentionally spinning an aircraft, pilots should obtain instruction and/or advice in spins and recovery techniques from an instructor who is fully qualified and current in spinning that model. Further, aerobatic pilots and instructors should be aware and also teach the Meuller/Beggs method of spin recovery advantages, but most importantly its limitations in that it will not recover all aircraft types from a spin.

The occurrence

Aerobatics instructional flights

Two private pilots (students), who were members of the Sunshine Coast Aero Club, contracted an aerobatics instructor to provide aerobatic flight training in the aero club’s Cessna A150M Aerobat (Aerobat), registered VH-CYO. That training included theoretical and practical training aspects.

As the instructor did not work at the aero club, the aero club’s chief flying instructor (CFI) conducted a check flight with the instructor in the Aerobat to assess the instructor’s ability. The CFI was not rated in aerobatics, and the check flight was limited to an assessment of the instructor’s general handling and area knowledge. The CFI stated that the instructor performed the flight to a high standard and concluded that the instructor had the requisite skill and knowledge to conduct the flight training in the aero club’s Aerobat.

The students hired the aero club’s Aerobat for the practical flight training. The training was split into 2 days, commencing on the 16 June 2021. On that day 4 flights were undertaken, with 2 one-hour flights per student. The students undertook theoretical and practical instruction on:

• stall recovery techniques
• stall turns
• loops
• barrel rolls
• aileron rolls.

It was reported that, during the practical flight phase on that day, the instructor demonstrated each of the manoeuvres before handing control to the student.

Pre-flight briefing on the day of the accident

On the morning of 23 June 2021, the 2 students and the instructor continued the aerobatics training from Sunshine Coast Airport, Queensland, commencing with pre-flight theoretical instruction on spin training. The briefing contained information about:

• what is a spin^[1]
• inverted and upright spins
• what is a spiral dive^[2]
• difference between a spin and a spiral dive
• the Mueller/Beggs emergency spin recovery method
• the PARE method for spin recovery.

One of the students indicated that, during the pre-flight briefing, they were not instructed on what recovery method was recommended in the Aerobat Pilot’s Operating Handbook (POH), or that it closely aligned with the PARE method. Further, they were instructed on the advantages of the Mueller/Beggs method, but not on its limitations; namely, if the Mueller/Beggs method was utilised on an Aerobat, the aircraft would not recover from a spin to the left (see Aerodynamic spins).

Both students were instructed to write down the 2 spin recovery methods on a piece of paper for reference in flight when the practical component of the spin recovery was to be undertaken. One of the students indicated that they believed they were going to utilise both methods of spin recovery during their flight instruction. The first method written down on both students’ spin recovery notes was the Mueller/Beggs method.

Accident flight

At 1103 Eastern Standard Time,^[3] VH-CYO took off from the Sunshine Coast Airport, with the instructor and one of the aerobatic student pilots on board. The flight was being conducted under visual flight rules (VFR), and visual meteorological conditions existed during the flight. The accident flight was the first of 4 one-hour flights intended for that day (2 per student).

The aircraft departed to the south-west and climbed to about 6,000 ft above mean sea level (AMSL). Radar data showed that the aircraft arrived at the area intended to conduct aerobatics about 20 minutes after departure (Figure 1).

Figure 1: VH-CYO flight track radar data showing take-off point and accident site

Source: Google Earth, annotated by the ATSB

Figure 2 shows recorded radar data for the last 3 minutes of the flight. It indicated that, within the last 90 seconds, the aircraft conducted a 180° left turn, decelerated while maintaining altitude, and then descended rapidly, with the point of decent beginning at 5,800 ft above ground level (AGL). That manoeuvring was indicative of the planned entry into a spin.

At about 1122, 55 seconds after the initiation of the spin, the aircraft impacted terrain. The aircraft was destroyed, and the 2 occupants were fatally injured.

Figure 2: VH-CYO last 3 minutes of recorded flight data viewed from the left and above

Source: Google Earth, annotated by the ATSB

Figure 2 shows recorded radar data for the last 3 minutes of the flight. It indicated that, within the last 90 seconds, the aircraft conducted a 180° left turn, decelerated while maintaining altitude, and then descended rapidly, with the point of decent beginning at 5,800 ft above ground level (AGL). That manoeuvring was indicative of the planned entry into a spin.

At about 1122, 55 seconds after the initiation of the spin, the aircraft impacted terrain. The aircraft was destroyed, and the 2 occupants were fatally injured.

1.  Spin: a sustained spiral descent of a fixed-wing aircraft, with the wing’s angle of attack beyond the stall angle.
2.  Spiral dive: a steep descending turn with the aircraft in an excessively nose-down attitude and with the airspeed increasing rapidly.
3.  Eastern Standard Time (EST) was Coordinated Universal Time (UTC) + 10 hours.

Context

Pilot information

Instructor

Experience and qualifications

The instructor held a valid commercial pilot licence (aeroplane) that was issued on 10 August 2017. The licence included the following ratings and endorsements:

• single engine aeroplane class rating
• manual propeller pitch control, design feature endorsement
• aeroplane formation, spinning and aerobatics (low level) flight activity endorsement
• flight instructor rating with grade 2, spinning, formation (aeroplane) and aerobatics training endorsements
• aeroplane formation, spinning and aerobatics flight activity endorsements.

The instructor had their own aviation company that predominantly conducted aerobatic joy flights and instructional flights in the company’s 2 Pitts Special aircraft. The ATSB had access to the pilot’s logbook information up to 16 February 2020, at which point the instructor had accumulated 1,112.3 flight hours. The information in those logbooks indicated that the instructor had about 100 hours of flight experience in a Cessna 152 (a similar, non-aerobatic variant of the Aerobat), but none of that recorded experience was aerobatic in nature.

In the week prior to the accident, the instructor provided information to the Sunshine Coast Aero Club that they had about 100 hours experience in the Cessna 152. However, there was no mention of experience in the Cessna A150 Aerobat. The provided information was consistent with the information in the instructor’s logbook.

The ATSB was informed that, in recent times, the instructor had been utilising cloud-based pilot logbook software to record flight experience. The ATSB was unable to gain access to the cloud-based system.

The instructor’s initial and ongoing aerobatics training was conducted in the Pitts Special aircraft. Apart from the instruction flights in VH-CYO during the week prior to the accident, the ATSB was unable to identify any previous aerobatic experience in the Cessna A150 Aerobat or any other similar Cessna variants.

The person who conducted the aerobatics training to give the instructor a rating for aerobatics, and a rating to instruct in aerobatics, stated that they informed the instructor of the limitations in the Mueller/Beggs method during their initial aerobatics training. All of the practical flying training aspects were conducted in a Pitts Special.

Medical information and recent history

The instructor held a current class 1 medical certificate with no restrictions, and the accompanying medical records did not indicate any underlying medical issues at the time of the accident.

The instructor was reported to be fit and well on the day of the accident. There were no issues identified in the post-accident medical and toxicological results (including carbon monoxide) that may have affected the instructor’s operation of the aircraft.

Aerobatic student

Experience and qualifications

The aerobatic student pilot held a valid private pilot licence (aeroplane) that was issued on 13 June 2010. They also held a single-engine aeroplane class rating, and manual propeller pitch control and retractable undercarriage design feature endorsements. The student had a total of 248.5 flight hours experience.

The student had conducted an introductory aerobatic flight in an American Champion Aircraft Corp 8KCAB with an instructor in December 2014. That flight did not include spins.

Medical information and recent history

The aerobatic student pilot held a current class 2 medical certificate with no restrictions, and the accompanying medical records did not indicate any underlying medical issues at the time of the accident. The student was reported to be well rested and in good spirits on the morning of the accident. There were no issues identified in the post-accident medical and toxicological results (including carbon monoxide) that may have affected the student’s operation of the aircraft.

Operator information

The Sunshine Coast Aero Club was located at the Sunshine Coast Airport. At the time of the accident, the aero club had about 100 members and 3 aircraft: 2 Recreational Aviation Australia (RAAUS) registered Sling 2 aircraft and a Cessna A150 Aerobat (Aerobat), registered VH-CYO.

The Aerobat was recently purchased with the intent to conduct aerobatic instructional flights for its members. At the time of the accident, the aero club did not have a Civil Aviation Safety Regulation (CASR) Part 141 certificate to conduct flight training in a VH registered aircraft, nor was it required for an instructor to conduct spin or aerobatics flight training. There were no aerobatics-trained instructors at the aero club.

The aero club sought the assistance of a contracted aerobatics instructor to conduct the aerobatic flight training, utilising the instructor’s own flight training approval. The first aerobatic flight training conducted by the aero club utilising VH-CYO was the week prior to the accident with the flight instructor who was on board the accident flight.   

Aircraft information

General information

The Cessna 150 is a high-wing, 2-seat, single piston engine aeroplane designed for flight training. The Aerobat was a slightly modified model that was designed to conduct basic aerobatic training. The type of manoeuvres approved in the Aerobat Pilot’s Operating Handbook (POH) included spins.

VH-CYO

VH-CYO (Figure 3) was manufactured in 1976 and first registered in Australia in 1995. It had been owned and operated by the Sunshine Coast Aero Club since March 2021. However, it had not been utilised for aerobatics until the week prior to the accident.

Figure 3: VH-CYO Cessna A150M Aerobat

Source: Simon Coates

Maintenance information

The aircraft had a current certificate of airworthiness, certificate of registration, and maintenance release with no outstanding maintenance, or defects listed.

Subsequent to the accident, it was reported to the ATSB that the right-side radio push-to-talk switch had a defect which prevented radio calls from that position. Therefore, all calls had to be made from the headset and microphone plugged into the left-side jack point. It was also reported that the defect did not affect the intercom between pilots.

Rudder stop modification

The Cessna 150 and 152 series aircraft had a mandatory rudder stop modification identified as Single Engine Bulletin (SEB) 01-1. The Service bulletin was also mandated by Federal Aviation Administration Airworthiness Directive (AD) 2009-10-09 and therefore automatically mandated in Australia. The purpose as stated in the bulletin was as follows:

To provide an enhanced rudder stop, bumper, doubler and attachment hardware designed to assist in preventing the possibility of the rudder overriding the stop bolt during full left and/or right operation of the rudder.   

 VH-CYO had the rudder stop modification incorporated at the time of the accident.

Weight and balance

The aircraft’s published maximum take-off weight (MTOW) according to the Pilot Operating Handbook was 727.3 kg (1,600 lb). The aircraft’s weight for the accident flight was estimated to be about 14.3 kg over the MTOW on departure and about 7.1 kg overweight at the time of the accident.

Taking into consideration the aircraft’s calculated weights at take-off, and at the time of the accident, a centre of gravity (CG) calculation could not be carried out, as the aircraft’s weight was outside that of the published CG calculation limits (Figure 4). As the aircraft was over the MTOW, the data was extrapolated outside of the chart limits to get an estimate of the CG location at the time of the accident. The extrapolated value placed the CG aft of mid-range, but well forward of the aft limit.

Figure 4: Estimated weight and balance

Source: Cessna, annotated by the ATSB

Recorded information

The aircraft flight path was derived from primary^[4] and secondary^[5] surveillance radar data recorded by Airservices Australia. The data included the aircraft’s position with a time stamp and altitude above mean sea level (AMSL) at 5-second intervals.

Figure 5 shows the last 90 seconds of flight with the spin entry beginning about 55 seconds before impact with terrain. The decent rate varied between data points, with an average descent rate of about 5,000 ft/min. The radar returns stopped at about 1,200 ft above mean sea level (AMSL), which was 800 ft above ground level (AGL) at the accident site. That was most likely due to the aircraft descending below radar coverage.

The last 2 recorded data points without pins were considered to be predictive and not an accurate representation of the aircraft position.

Figure 5: Radar data with timestamp, airspeed, altitude and vertical decent rate labelled

Source: Google Earth, annotated by the ATSB

Site and wreckage examination

The accident site was located in a dense stand of trees that stood about 15–20 m high and straddled a creek line in a band about 50 m wide, with open areas of farmland on either side (Figure 6).

Figure 6: Area of accident site

Source: Google Earth, annotated by the ATSB

The wreckage trail extended about 50 m from the initial tree impact point, until the final piece of wreckage, oriented in an east-west direction. There were several notable tree impact points, including trees that had been broken in half or completely felled by the impact forces. Calculations of the tree impact damage heights indicated the final flight path angle was a descent of 12.8° (Figure 7).

Figure 7: Final flight path angle of entry

Source: ATSB

The main wreckage came to rest at the base of a tree that was struck at a height of about 10 m. The aircraft structure was significantly disrupted as a result of impacting several trees (Figure 8).

Figure 8: Aircraft main wreckage at the base of a large tree that was struck

Source: ATSB

The ATSB conducted an examination of the aircraft wreckage. The examination identified that:

• the disruption to the aircraft and foliage, coupled with the length of the wreckage trail, indicated that the aircraft had significant forward speed at impact
• the flaps were in the retracted position
• the aircraft had no evident pre-impact defects with the flight controls or aircraft structure
• the aircraft was intact prior to impact with terrain
• the engine had no obvious defects upon external examination, was free to rotate and had compression on all 4 cylinders
• the throttle setting was captured at an idle position (full out and bent to one side) during the accident sequence
• the propeller rotational damage signatures were minimal, indicating a low power setting
• both seats were in the full aft position.

Survivability aspects

General information

During the accident sequence, the cockpit area was completely disrupted due to significant impacts with trees, leading to the occupants’ liveable space being compromised. For this reason, it was considered unlikely that the accident was a survivable event.  

Flight notes and tracking overdue arrivals

The CASR Part 91 Manual of Standards (MOS) stated that for some types of visual flight rules (VFR) flights a pilot was required to submit a flight plan, nominate a SARTIME for arrival, or leave a flight note with a responsible person. These included air transport flights, a flight over water, a flight in a designated remote area, or a flight at night proceeding beyond 120 NM from the departure aerodrome. In other cases, a pilot could elect to submit a flight plan, nominate a SARTIME or leave a flight note.

If a flight note was left with a responsible person, then that person had to be over 18 years old, have access to at least 2 operative telephones, and satisfy the pilot that they know how to contact the Joint Rescue Coordination Centre (JRCC) and will do so immediately in the event that the pilot’s flight was overdue.

In summary, a flight note was not formally required for flights similar to that conducted in VH-CYO on the day of the accident. However, flight notes or another method of identifying if an aircraft is overdue is highly recommended.

The ATSB was informed that the Sunshine Coast Aero Club had a method of tracking estimated arrival times. That method involved instructors informing the aero club administration of estimated arrival times and aircraft movements. The ATSB noted that the instructor of VH-CYO did not inform the aero club administration about the estimated time of the aircraft’s return. It was considered likely that the instructor, being a contractor who had not worked with the aero club before, was not informed or aware that it was the aero club procedure to do so.

The aircraft accident occurred at 1122. It was scheduled to return to refuel at about 1200, and it was reported missing at about 1515 by the aero club chief pilot when the second student raised concerns about the aircraft not returning from its flight.

The post-mortem reports for the pilots indicated that the occupants’ chances of survival would not have improved if the location of the wreckage was identified sooner.

Emergency and personal locator beacons

The aircraft was not fitted with a fixed emergency locator transmitter (ELT), nor was it required to be under the current regulations. 

ATSB research into the effectiveness of ELT’s in aviation accidents (AR-2012-128) stated that:

Data from the ATSB database show that ELTs function as intended in about 40 to 60 per cent of accidents in which their activation was expected. Records of the Australian Maritime Safety Authority’s SAR incidents shows that search and rescue personnel were alerted to aviation emergencies in a variety ways including radio calls and phone calls, and that ELT activation accounted for the first notification in only about 15 per cent of incidents. However, these ELT activations have been directly responsible for saving an average of four lives per year.

A personal locator beacon (PLB) was identified on the accident site in an area that was away from and not likely to be located by the occupants of the aircraft (if they had survived the impact). The beacon was in date and passed a self-function test to indicate that it was serviceable.

The ATSB research report also mentioned PLBs with the following suggestion:

…carrying a personal locator beacon (PLB) in place of or as well as a fixed ELT will most likely only be beneficial to safety if it is carried on the person, rather than being fixed or stowed elsewhere in the aircraft.

Aerodynamic spins

General description

An aerodynamic spin is a sustained spiral descent in which an aircraft’s wings are in a stalled condition, with one wing producing more lift than the other. This difference in lift sustains the rotation and keeps the aircraft in the spin. The nose angle can also vary considerably. In a fully developed, upright, left spin, an aircraft will simultaneously roll to the left while yawing to the left, making a vertical corkscrew path through the air. A spinning aircraft will descend more slowly than one in a vertical or spiral dive and it will also have a lower airspeed, which may oscillate.

Intentional spins are normally entered from a stall in straight and level flight, with the reduction in power, the application of full back elevator and full rudder in the intended direction of rotation at the moment of stall.

When entering a spin, an aircraft’s motion through the air is irregular at first. This is known as the incipient phase of the spin. Though the nature of the incipient spin is heavily dependent on the aircraft type and the manner of entry, recovery may be more rapid and require less control input in this stage compared with recovery from a developed spin. After a number of rotations and depending on the aircraft type, loading, and control inputs, an aircraft in an incipient spin may then settle into a regular rotating descent, known as a developed spin. A spin may steepen (nose-down) or flatten (nose more horizontal) as it continues, potentially requiring different recovery techniques. Figure 9 shows the various stages from spin entry until recovery.

Figure 9: Various stages of a spin and recovery

Source: New Zealand Civil Aviation Authority, Spin avoidance and recovery

Recommended practices in preparation for spin

The CASA Flight Instructor Manual: Aeroplane stipulated:

The aeroplane must be clear of inhabited areas and normally in an area designated for the practice of such exercises. In addition, it should be at a height sufficient to ensure recovery by 3,000FT above ground level. The pre-spinning check will vary from aeroplane to aeroplane but will normally be similar to that used as a pre-stalling check in that particular aeroplane. In most aeroplanes flaps and undercarriage must be retracted during both the spin and spiral. … In all cases a 360° turn to ensure that all is clear around and below should be carried out immediately prior to commencing each exercise.

The information stipulated in the flight instructor’s manual was commonly referred to by the acronym HASELL, which is:

• Height – sufficient to recover by 3,000 ft AGL
• Airframe – wheels up / flaps up / CG ok / trim set
• Security – seat belt tight / no loose items in aircraft or pockets
• Engine – temperature and pressure / carburettor heat / mixture / fuel quantity and selection
• Location – aerobatic area / no built-up area or public gathering within 600 m / forced landing fields available
• Lookout – 360° turn or wingover.

Spin recovery techniques

Aircraft manufacturer spin recovery information

There was information provided by the aircraft manufacturer on spin recovery in 2 sections of the Cessna A150M Aerobat POH. This information was the same in each section, and the spin recovery technique stated that:

Should an inadvertent spin occur, the following procedure should be used:

1). Retard throttle to idle position.

2). Place ailerons in neutral position.

3). Apply and hold full rudder opposite to the direction of rotation.

4). Just after the rudder reaches the stop, move the control wheel briskly forward far enough to break the stall. Full down elevator may be required at aft centre of gravity loadings to assure optimum recovery.

5). Hold these control inputs until rotation stops.

6). As the rotation stops, neutralise rudder and make a smooth recovery from the resulting dive.

It also stated that:

Variations in basic airplane rigging or in weight and balance due to installed equipment or cockpit occupancy can cause differences in behaviour, particularly in extended spins. These differences are normal and will result in variations in the spin characteristics and in recovery lengths for spins of more than 3 turns. However, the above recovery procedure should always be used and will result in the most expeditious spin recovery.

Cessna also provided further information in a document tilted Spin Characteristics of Cessna Models 150, A150, 152, A152, 172, R172 and 177. Apart from reiterating the recovery procedure provided in the POH, it also stated information including:

Basic Guidelines for Intentional Spins

1). Know your aircraft thoroughly.

2). Prior to doing spins in any model aircraft, obtain thorough instruction in spins from an instructor fully qualified and current in spinning that model.

PARE spin recovery method

The PARE spin recovery method is generic and typical of most light single engine aircraft types. PARE is an acronym that stands for:

• Power, idle
• Ailerons, neutral (and flaps up)
• Rudder, full opposite to the spin direction and held in that position
• Elevator, forward

Hold these inputs until rotation stops, then:

• Rudder, neutral
• Elevator, easy pull to straight and level or climbing attitude.

A comparison between the Cessna A150 Aerobat recovery method and the PARE method indicated there was little difference between the 2 methods, with the exception that the Cessna method emphasised the use of the term ‘briskly’ in regards to the forward movement of the elevators, and that full forward elevator may be required.

Mueller/Beggs (emergency) spin recovery technique

The Mueller/Beggs recovery technique, sometimes referred to as the emergency spin recovery technique, was documented in an aerobatic article written by an aerobatic pilot, Eric Mueller, in the 1980s. The article stated that it was a technique designed to recover a Pitts Special aerobatic aircraft from an upright or inverted spin, even if the pilot was disorientated. The technique is as follows:

1. Power off

2. Remove your hands from the stick

3. Apply full opposite rudder

4. Neutralise the rudder and recover to level flight.

Another aerobatic pilot, Gene Beggs, popularised the recovery technique in a series of articles. Beggs’ reference manual titled Spins in the Pitts Special stated:

With this method you can quickly and easily recover from any spin in the Pitts Special. It is easy to remember and execute even if you are frightened or confused; furthermore, it is not necessary to know whether the spin is upright or inverted, the recovery is the same in either case.

In the Beggs course notes for advance spin recovery, the frequently asked questions section stated:

The question I hear most is “Will the emergency spin recovery work on all aircraft?” No, not exactly! Although I have found it works beautifully in the vast majority of cases, there are rare exceptions. You may occasionally encounter a spin mode in some aircraft in which you must physically apply nose-down elevator. This is extremely rare, and I assure you it will never happen in a Pitts Special.

A newsletter titled Spinoffs written by Beggs in 1985 indicated that the author was informed by another pilot that a Cessna A150 Aerobat would not recover using the emergency recovery method (Meuller/Beggs method). Beggs decided to conduct some spin testing in a standard Cessna 150. The following is a summary of that testing:

• The aircraft would recover using the emergency recovery technique (hands off) in fully developed spins to the right.
• The aircraft would not recover using the emergency recovery technique in fully-developed spins to the left, no matter how many turns the aircraft was allowed to do.
• If the elevator was pushed forward briskly during the emergency recovery technique to the left, the aircraft would always recover promptly in one additional turn with pitch attitude almost perfectly vertically down.
• In spins both to the right and left, the use of opposite aileron (out spin aileron) would produce a recovery from the spin. This was opposite to the results obtained in all other aircraft types (that had been previously spun by Beggs).
• In the Cessna 150, the use of in-spin aileron always increased the rate of rotation and steepened the pitch attitude. This was also opposite to the results obtained in all other aircraft types.

Beggs stated having conducted thousands of emergency spin recoveries in numerous aircraft types. The Cessna 150 was one of the very few aircraft that required the application of full forward elevator to recover.

Regulatory requirements and guidance

The CASR Part 61 MOS, Volume 2, Section 6, Unit FAE-8 – Spinning, described the skills and knowledge required to execute and recover from an upright spin.

Unit FAE-8, element 4, titled underpinning knowledge, stated that the following items were required to be imparted to students:

…

(o) standard spin entry and recovery techniques for the aircraft being flown;

(p) number of turns normally required for spin recovery in the aeroplane type;

…

(r) Mueller-Beggs spin recovery action and limitations on its application

(s) ‘g’ and any other limitations applicable to spinning for the aeroplane type.

The Civil Aviation Aeronautical Publication (CAAP) 155-1(0) Aerobatics was issued in 2007. In relation to spin recovery, it stated:

Modern aerobatic aircraft designs normally have predictable spin characteristics and respond to the standard spin recovery technique. However, older aircraft and non-certificated or amateur built aircraft may have special characteristics which require particular recovery procedures. Therefore, pilots need to be familiar with, and practised in, the spin recovery procedure specified for the particular aircraft type.

It also stated:

Spin recovery procedures will vary between aircraft types and situations. The aircraft flight manual should be the final authority for spin recovery procedure…

The CAAP also discussed the Mueller/Beggs spin recovery method. The ATSB requested CASA’s interpretation on the Mueller/Beggs spin recovery limitations referenced in the MOS. It stated:

Civil Aviation Advisory Publication (CAAP) 155-1(0) – Aerobatics, published January 2007 provides guidance to pilots on aerobatics operations. Section 7 - Risk management and TEM includes subsection 7.24 Mueller-Beggs Spin Recovery, which describes the Mueller-Beggs recovery technique and associated limitations. There is also reference to the techniques in the underpinning knowledge sections of the Units of competency in Appendix A of the CAAP from which the MOS references were drawn.

As stated in 7.24.1, the main limitation, as is that it is known, is the technique is not effective in a number of aircraft types. 7.24.4 advises pilots to determine the extent to which the technique has been tested and found to be reliable in a particular aircraft type. It also states pilots wishing to test the procedure should also be familiar with the normal spin recovery procedure specified for the type. While 7.24.5 states the technique is not recommended, it may prove to be useful in the event a pilot becomes disoriented.

Based on the above information CASA’s opinion of the limitations of the Mueller-Beggs technique are:

1. Application of the technique may not be effective for the aircraft in which the training is conducted,

2.Use of the technique will likely delay the recovery from the spin and consequently increase the height lost, perhaps to a point recovery cannot be achieved,

3. The technique might be in conflict with the aircraft manufacturer’s recommended technique.

Reference to the technique is included in the CAAP to make pilots aware of its existence as an alternative recovery technique. In the event they become disoriented from high rates of rotation, which can be encountered in an upright or inverted spin, the technique might effect a recovery if other recovery techniques applied are unsuccessful.

Associated with a range of regulatory changes in December 2021, the CAAP was removed from the CASA website in January 2022.^[6]

In April 2020, CASA issued Advisory Circular AC 61-16 v1.0 (Spin avoidance and stall recovery training). In addition to a variety of other guidance, it stated:

Before selecting an aircraft for stalling or spinning training, consult with the manufacturer and other users to establish what manoeuvres are safe to conduct, including steep turns, stalls, stalls with a wing drop and spinning.

It also stated that, prior to spinning any aircraft, pilots should:

- Comply with aircraft flight manual weight and balance and manoeuvre limitations, placards and, if provided, procedures and advice for each intended manoeuvre…

- Obtain thorough instruction in spins from an instructor fully qualified and current in spinning that model…

- Enter each spin at a high altitude. Plan recoveries to be completed well above the minimum legal altitude…

- Conduct all spin entries and recoveries in accordance with the procedures recommended by the manufacturer...

In the guidance for instructors, it stated:

- Ensure the aircraft is operated in accordance with the aircraft flight manual limitations and entry and recovery procedures for manoeuvres including stalling and spinning…

- Recognise and avoid the potential for negative training with a clear understanding of what the desired training outcome is for the lesson. The latent effects of negative training can stay with a pilot throughout their career…

The effects of centre of gravity on spins

The CASA Flight Instructor Manual: Aeroplane included a section for spins and how it is affected by the CG. It stated:

The effect of the position of the Centre of Gravity (CG) must be pointed out to the student if movement of this position within the limits laid down has a great effect on the spinning characteristics of the aeroplane. Normally a forward CG results in a steeper spin with a high rate of descent. A forward CG makes recovery much easier and may even prevent a spin altogether, resulting in a spiral dive. An aft CG tends to flatten the attitude resulting in a lower rate of descent. The recovery action to be taken when an aeroplane is spinning in a flat attitude is the same as the normal recovery technique with respect to the actual control movements. However, in the flat spin case it is essential to ensure that full control movement is applied in the recovery action and that this is maintained if necessary, for a much longer period than normal. In some aeroplanes it takes many turns to recover from a flat spin.

Related occurrences

Cessna A150 Aerobat (VH-CYO), Cairns, Australia, December 1995

The ATSB received a report from a previous pilot of VH-CYO about an incident that occurred in the aircraft involving a flat spin. The incident occurred near Cairns Airport in December 1995. A summary of that event was as follows:

• On the day of the incident, the aircraft (VH-CYO) was being operated as an aerobatic aircraft with a student and instructor on board. The purpose of the day’s instructional flights was stalls, spins and spin recoveries.  
• On the day of the training sequence, air traffic control (ATC) clearance was obtained to operate between 5,000 ft and 3,000 ft AMSL.   
• The spin training exercise commenced at 5,000 ft and consisted of showing recovery, student follow through, and finally student completing the entry and recovery. 
• As a final exercise, the student was instructed to commence the spin at about 5,000 ft, to allow the ‘spin’ to fully develop and recover from the spin when instructed.   
• The instruction to recover was given at about 4,300 ft and the student was observed to apply the correct Cessna A150 POH recovery technique. However, the aircraft failed to recover from the spin. The instructor took control of the aircraft and applied the POH spin recovery method, but the aircraft failed to recover from the spin. 
• As the aircraft descended towards the cleared level of 3,000 ft, the instructor believed the aircraft would not respond to the POH recovery method and may had entered a flat spin. The instructor attempted to force the nose down by commencing a backwards and forwards full deflection of the elevator motion. That action did not assist, so the instructor coordinated full throttle acceleration to elevator deflection with the thought that it might assist in getting a nose-down attitude. 
• The instructor regained some control of the aircraft as it passed 1,000 ft, with the aircraft exiting the spin and entering a spiral dive. At approximately 700 ft, recovery from the resulting dive was completed, ATC was advised that the aircraft had flown below the minimum specified altitude, and a clearance was obtained to return to Cairns Airport. 

A subsequent engineering inspection, which included a check of the aircraft rigging, did not identify any defects.   

The instructor of the 1995 flight advised the ATSB that, after some consideration, they believed that the issue was most likely one of a rear centre of gravity in the loading of the aircraft. The instructor stated that they were 182 cm and about 85 kg, with the student being at least 188 cm and about 90–95 kg.  Both seat positions were adjusted to the rear stop and the fuel load was from memory sufficient for about 3.0 hours total. 

The instructor of the 1995 flight stated that they had spoken to 2 other pilots, who had detailed that, while conducting spinning together in another C150, they had experienced difficulty in exiting a planned spin, and their experience seemed to have been very similar to what the instructor encountered. 

Cessna 152 accident, Concord, United States, 29 January 2018

A Cessna 152 aircraft, registered N93316, lost control and impacted terrain, fatally injuring the pilot. A subsequent inspection of the aircraft identified that one of the rudder cables had failed and the other had frayed to a point where about 50% of the strands had fractured.^[7]

4.  Primary radar returns are produced by radar transmissions that are passively reflected from an aircraft and received by the radar antenna. The received signal is relatively weak and provides only position information, not the aircraft’s altitude.
5.  Secondary radar returns are dependent on a transponder in the aircraft replying to an interrogation from a ground station. An aircraft with its transponder operating is more easily and reliably detected by radar and, depending on the mode selected by the pilot, the aircraft’s pressure altitude is also displayed to the air traffic controller.
6.  CASA advised that the CAAP was intended to be replaced by AC 61-18 Aerobatics.
7.  National Transportation Safety Board investigation WPR18FA075

Safety analysis

Introduction

Radar data indicated that, while being used to conduct spin training, the Cessna A150 Aerobat (VH-CYO) entered a spin at 5,800 ft above ground level and the spin was not fully recovered before the aircraft impacted terrain. Site and wreckage examination indicated that the aircraft had significant forward velocity, a low angle of entry, and the throttle was captured in the idle position. Those items of evidence indicated that the aircraft was most likely in the initial stages of recovery from the spin when the aircraft impacted terrain.

In previous training with the student on board, the instructor had demonstrated each manoeuvre before handing control to the student. The accident occurred during the first manoeuvre of the training session, and the ATSB was unable to ascertain which of the 2 pilots (instructor or student) was controlling the aircraft at various stages of the spin and for the initiation of the recovery.

This analysis discusses several possible reasons for the aircraft not being fully recovered from a spin before impacting terrain. These include:

• mechanical failure
• flight control obstruction
• aft centre of gravity and flat spin
• pilot incapacitation
• interference with the controls
• incorrect recovery technique.

Potential scenarios to explain absence of recovery from spin

Mechanical failure

A failure of the aircraft structure, the flight control system, or a rudder locking past the rudder stops have contributed to aircraft accidents in the past. However, examination of the aircraft structure and flight controls of the aircraft did not reveal any pre-impact defects. The aircraft also had a modification incorporated to prevent the rudder-stop locking issue that had contributed to some previous Cessna 150 accidents.

Further, there was evidence that the aircraft was in the early stages of recovery from the spin, which indicated that whatever had delayed the recovery had been overcome prior to impacting terrain.

Overall, it was considered unlikely that some type of mechanical failure of the flight controls contributed to the accident. However, due to the disruption and displacement of the wreckage, the ATSB was unable to completely rule out the possibility of a mechanical issue.

Flight control obstruction

Aircraft accidents have previously occurred where foreign object obstruction has led to flight controls becoming locked, preventing the pilots from controlling their aircraft. If an object had locked the controls of VH-CYO, the initial stages of the recovery evident before impact with terrain would indicate that the controls became unlocked, or more controllable, during the final stages of the descent.

The examination of the aircraft did not reveal any issues in relation to flight control locking due to foreign object fouling. However, due to the disruption and displacement of the wreckage, the ATSB was unable to rule out the possibility of a flight control obstruction, but it was considered to be unlikely.  

Aft centre of gravity and flat spin

The further aft the aircraft’s centre of gravity is, the more difficult it may be to lower the nose in order to recover from a spin. In this case, the aircraft was slightly over the maximum allowable take-off weight (MTOW) for the entire flight. Regarding the aircraft loading and centre of gravity (CG), and after interpolating the data (as the aircraft was outside its weight limit), it was considered to be within the desired CG range, trending towards aft of nominal.

It is possible that the spin entry or recovery actions created a flat spin, where the nose was comparatively high compared to a normal spin (with the nose slightly down). This can be exacerbated by an aft CG and can make the aircraft slower to respond to recovery techniques. Previous incidents in the same aircraft type have shown that flat spins can be very difficult to recover, even when the appropriate recovery technique is applied for an extended period.

In summary, it is possible that the aircraft entered a flat spin that was unable to be fully recovered, and that the aft CG may have exacerbated the difficulty in recovering from the spin. However, there was insufficient evidence to conclude that this occurred.

Pilot incapacitation

Both of the pilots were reported to be well at the time of the accident, and the pre and post-accident medical information did not identify any conditions or issues with either pilot that may have contributed to the accident. Also, as previously noted, the aircraft was most likely in the initial stages of recovery from the spin when the aircraft impacted terrain. Accordingly, the ATSB considered it unlikely that pilot incapacitation contributed to the accident.

Interference with the controls

The Cessna A150 Aerobat is a dual control aircraft. If an inexperienced pilot were to ‘freeze’ at the controls or make other inappropriate flight control inputs, it may be difficult for the instructor to regain control of the aircraft.

As previously noted, it was not possible to ascertain which of the 2 pilots (instructor or student) was controlling the aircraft at various stages of the spin and for the initiation of the recovery. In addition, during the previous week, the student conducted steep turns, stall recovery, loops, and barrel and aileron rolls. The student had also done a small amount of aerobatics several years before the accident and had a reasonable amount of flight experience. Overall, none of the available evidence indicated that the student was susceptible to freezing at the controls or making other inappropriate flight control inputs.

Incorrect recovery technique

The instructor owned, was trained on, and had significant aerobatic experience in the Pitts Special aerobatic aircraft. However, the ATSB could not identify any aerobatic experience for the instructor in the Cessna A150 Aerobat or similar variants, apart from the previous week’s instructional activities with the same students. That training did not include spin entry and recovery techniques.

The aircraft manufacturer’s guidance document on spin characteristics stipulated that, if the instructor was unfamiliar with the aircraft type’s spin characteristics, then they should obtain thorough instruction in spins from an instructor qualified and current in spinning that particular model aircraft. The Civil Aviation Safety Regulation (CASR) Part 61 Manual of Standards (MOS) stated that underpinning knowledge for spin training included the standard spin entry and recovery techniques for the aircraft being flown. Other CASA guidance highlighted the importance of being familiar with the spin recovery method specific to the aircraft type. However, the ATSB could not identify if the instructor had sought additional information about the Aerobat’s spin characteristics. It is possible that, due to the instructor’s general familiarity and experience on a similar, non-aerobatic variant (the Cessna 152), they did not consider that recovery techniques successfully utilised on other aircraft types would not work equally as effectively on the Cessna A150 Aerobat.

The theoretical spin recovery training conducted by the instructor on the morning of the accident included 2 recovery methods; namely the PARE and Mueller/Beggs methods. The PARE method was closely aligned with (but not exactly the same as) the method described in the Cessna A150 Aerobat Pilot’s Operating Handbook (POH) and the Cessna guidance document. The Mueller/Beggs method has proven to be a very effective method of spin recovery in most aircraft types, though there are a few aircraft types that will not recover using this method. The Cessna A150 Aerobat and similar variants are aircraft types that most likely will not recover from a spin to the left, as was the case in this accident.

The Part 61 MOS stated that the instructor should teach the students the method of recovery in the aircraft type that they will be operating in. It also stated that the limitations of the Mueller/ Beggs method should also be discussed. However, according to the second student who received the theoretical instruction, the instructor did not highlight to the student’s what recovery method was recommended in the POH, or that the Aerobat would not recover utilising the Mueller/Beggs technique.

Further, the instructor informed the students to write down both methods of recovery (Mueller/Beggs and PARE) on a piece of paper for reference during the flight. The second student was of the firm belief that they would be conducting both methods of spin recovery in the Aerobat, with the first method written down being the Mueller/Beggs method.

The ATSB considered it likely that the instructor was not aware or did not recall that the Aerobat would not recover utilising the Mueller/Beggs method in a spin to the left. Further, the evidence indicates that the instructor intended to utilise both methods of recovery in 2 separate spin sequences on the accident flight.

If the Mueller/Beggs method was being used for the first exercise, it would provide a viable explanation of the accident sequence. However, based on the available evidence, the ATSB was unable to establish if the Mueller/Beggs method was being utilised at the time of the accident, or if it contributed to the delayed recovery time.

Survival aspects

Management of overdue aircraft

Due to the nature of the impact, the accident was not survivable. However, the investigation noted that there were potential areas for improvement that could be relevant in other situations.

The Sunshine Coast Aero Club had a common practice for flight instructors to log an estimated arrival/return time with the aero club’s administrator prior to departing for a flight. However, that procedure was not utilised on the day of the accident. The ATSB considered it likely that the contracted flight instructor was not informed of the procedure and therefore did not inform the administrator of their estimated time for return. As a consequence, the aero club did not discover that the aircraft was overdue for some time, and subsequently reported the aircraft missing about 3 hours after it was due to return.

Although there is no regulatory requirement to do so for many types of flights under the visual flight rules, a standardised method to identify if an aircraft is missing would decrease the amount of time for the Joint Rescue Coordination Centre to be notified and for a subsequent search for the aircraft to commence.

Emergency locator transmitter and portable locator beacons

The aircraft was not fitted with a fixed emergency locator transmitter (ELT). Although a fixed ELT is not a regulatory requirement, they are an effective safety feature that have been shown to significantly reduce the amount of time between an aircraft accident and identifying the location of the aircraft by search and rescue.

A portable locator beacon (PLB) was identified in an area away from the aircraft occupants that would not likely have been located without an extensive search. Carrying a PLB would be much more beneficial to safety if it is carried on the person, rather than being fixed or stowed elsewhere in the aircraft.

Findings

From the evidence available, the following findings are made with respect to the collision with terrain accident involving Cessna A150 Aerobat registered VH-CYO on 23 June 2021.

Contributing factors

• While the student and instructor were conducting aerobatic spin training starting at 5,800 ft above ground level, for reasons that could not be established, the aircraft did not fully recover from a spin before impact with terrain.

Other factors that increased risk

• It is likely that the aerobatics instructor had no flight experience conducting spinning and/or spin instruction in the Cessna A150 Aerobat or similar variants. It was also considered probable that they did not seek advice from an experienced aerobatic instructor on the A150 type about the aircraft’s spin characteristics.
• The spin training theory provided by the instructor to the 2 aerobatics students was generic in nature and did not highlight the limitations of the Mueller/Beggs spin recovery technique or provide guidance on the method recommended in the Cessna A150 Pilot’s Operation Handbook, as stipulated in the Civil Aviation Safety Authority aerobatic instruction procedures and guidance material.
• It was likely that the aerobatics instructor intended to practice the Mueller/Beggs method of spin recovery during the accident flight in the Cessna A150 and was likely unaware that the aircraft type was one of the few types that would not recover from a spin to the left utilising that technique.
• On the day of the accident the aircraft operator was not utilising a flight following procedure to identify if an aircraft was overdue, nor were they required to under the current regulations. Therefore, the overdue aircraft was not identified and reported as missing for 3 hours after it was due to return.

Other findings

• The aircraft structure and flight controls were examined, and no pre-impact defects were identified.
• It could not be determined which pilot was controlling the aircraft during the various stages of the accident flight and spin recovery.
• The aircraft was not fitted with a fixed emergency locator transmitter, nor was one required by the regulations. Fixed emergency locator transmitters have been shown to be an effective safety feature to reduce the amount of time taken to identify an aircraft’s location, even if the occupants are incapacitated.

Safety actions

Safety Advisory Notice

Safety advisory notice to aerobatic pilots and instructors

The ATSB strongly encourages all aerobatic pilots and aerobatics flight instructors to be aware:

• the Mueller/Beggs method of spin recovery does not recover all aircraft types from a spin
• the Mueller/Beggs spin recovery method limitations should be emphasised during spin theory training
• the Mueller/Beggs method of spin recovery will not recover a Cessna A150 Aerobat or similar variants from a spin in some circumstances
• they should review the pilot’s operating handbook of the aircraft type that they intend to operate for the recommended spin recovery technique
• prior to doing spins in any model aircraft, they should obtain instruction and/or advice in spins from an instructor who is fully qualified and current in spinning that model.

Glossary

Sources and submissions

Sources of information

The sources of information during the investigation included the:

• Sunshine Coast Aero Club
• student pilot who underwent theoretical and practical training with the instructor
• the instructor’s aerobatics instructor
• Civil Aviation Safety Authority
• Queensland Police Service
• aerobatic subject matter experts
• Airservices Australia.

References

ATSB Research Investigation AR-2012-128, The effectiveness of emergency locator transmitters in aviation accidents.

New Zealand Civil Aviation Authority (2014) Spin avoidance and recovery.

Experimental Aircraft Association Inc. (1985) ‘Spinoffs-Gene Beggs’, International Aerobatic Club Sport Aerobatics Magazine.

Beggs G (2001) Aerobatics with Beggs: Spins in the Pitts Special (A guide and reference manual for aerobatic instructors and students).

Submissions

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

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

• the Sunshine Coast Aero Club
• the student pilot
• the instructor’s aerobatic instructor
• the Civil Aviation Safety Authority (CASA)
• the aircraft manufacturer.

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

Purpose of safety investigations The objective of a safety investigation is to enhance transport safety. This is done through: identifying safety issues and facilitating safety action to address those issues providing information about occurrences and their associated safety factors to facilitate learning within the transport industry. It is not a function of the ATSB to apportion blame or provide a means for determining liability. At the same time, an investigation report must include factual material of sufficient weight to support the analysis and findings. At all times the ATSB endeavours to balance the use of material that could imply adverse comment with the need to properly explain what happened, and why, in a fair and unbiased manner. The ATSB does not investigate for the purpose of taking administrative, regulatory or criminal action. Terminology An explanation of terminology used in ATSB investigation reports is available here. This includes terms such as occurrence, contributing factor, other factor that increased risk, and safety issue. Publishing information  Released in accordance with section 25 of the Transport Safety Investigation Act 2003 Published by: Australian Transport Safety Bureau © Commonwealth of Australia 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.

Executive summary

What happened

On the morning of 22 June 2021, the pilot of a Piper PA-32-300 Cherokee Six, registered VH‑CWK, prepared for a private flight at Moorabbin Airport. The pilot was the only occupant and intended to conduct several circuits during the flight to maintain experience in the aircraft type.

Between 1129 and 1200 Eastern Standard Time, the pilot conducted an engine run up and completed 3 circuits using runway 35 right without any incident or abnormal engine indications.

At 1200, as the aircraft climbed through 505 ft above ground level to complete a fourth circuit fuel flow to the engine significantly reduced and within 12 seconds, the engine lost power.

Soon after the engine power loss, the aircraft commenced descending. The pilot identified one of few clear areas available for a forced landing and manoeuvred the aircraft towards that area. As the aircraft approached the selected landing area, the pilot recognised that insufficient height remained to clear trees along the southern edge of the selected landing area. The aircraft impacted the trees before colliding with rising ground about 35 m beyond the trees. The aircraft was destroyed, and the pilot sustained serious injuries.

What the ATSB found

The ATSB found that as the aircraft climbed upwind from the departure runway, fuel flow reduced and the engine lost power. Despite extensive examination, the reason for the fuel flow reduction could not be determined.

It was also identified that the incorrect engine variant for the aircraft serial number was inadvertently fitted to the aircraft. This did not affect the operation of the aircraft or contribute to the power loss.

Safety message

This accident highlights the challenges pilots face when confronted with a loss of engine power at low level and with few suitable forced landing areas within the glide capability of the aircraft.

Pilots can best mitigate the effects of a power loss by forward planning, which reduces your mental workload under stress, and always maintaining control of your aircraft. Maintain glide speed and use no more than a moderate bank angle to avoid entering a stall and/or spin. During the forced landing, aim to arrive at the ground with wings level and the aircraft level with the ground, which improves your prospects of survivability. The ATSB research publication Managing partial power loss after take-off in single-engine aircraft provides further guidance, which is also applicable to a complete power loss.

The investigation also found that while in this case the fitment of an incorrect engine variant did not contribute to the accident, it underlines the importance of the correct interpretation of the manufacturer’s type certificate documentation. If the guidance is unclear, a maintainer should contact the Civil Aviation Safety Authority or the original equipment manufacturer for clarity on permitted action.

The investigation

The occurrence

On the morning of 22 June 2021, the pilot of a Piper PA-32-300 Cherokee Six, registered VH‑CWK, prepared for a private flight at Moorabbin Airport. The pilot was the only occupant and intended to conduct several circuits to maintain experience in the aircraft type.

Between 1129 and 1200 Eastern Standard Time (EST),^[1] the pilot conducted an engine run up and completed 3 circuits using runway 35 right without any incident or abnormal engine indications.

At 1200, the aircraft climbed through 505 ft above ground level (AGL) to complete a fourth circuit. At that time, as was the pilot’s usual practice, engine RPM was reduced from about 2,700 to the desired climb power of 2,500 RPM and the throttle was left at a full open setting. At the same time as the RPM reduced, fuel flow to the engine significantly reduced and within 12 seconds, the engine lost power. Soon after the power loss, the aircraft commenced descending and the pilot made a MAYDAY^[2] broadcast stating ‘…I’ve got a power loss’.

As the descent continued, the pilot targeted a glide speed of 90 kt and searched for a landing site within a 30° arc either side of the aircraft’s nose (Figure 1). The pilot identified one of few clear areas available for a forced landing within the gliding capability of the aircraft and manoeuvred the aircraft for a forced landing in that area (see the section titled Aircraft details).

As the aircraft approached the selected landing area, the pilot recognised that the aircraft was close to stalling and that insufficient height remained to clear trees along the southern edge of the selected landing area. The left wing subsequently impacted the trees about 14 m AGL and separated from the aircraft. The aircraft then rolled left and pitched nose down before impacting rising ground about 35 m beyond the trees. The aircraft was destroyed and the pilot sustained serious injuries, including to their head, which significantly impaired the pilot’s recollection of the flight.

Figure 1: Overview of the flightpath after the power loss

Source: Google Earth and OzRunways, annotated by ATSB

Note: Area ‘A’ was an excavated quarry. Area ‘B’ had been developed after the satellite imagery was captured and before the accident.

Context

Aircraft details

The Piper PA-32-300 Cherokee Six is a low‑wing, piston-engine aircraft with a two-blade variable‑pitch propeller, fixed tricycle landing gear and could be fitted with up to 7 seats. VH-CWK, serial number 32-7840052 (Figure 2), was manufactured in the United States in 1977 and first registered in Australia in 1978.

Prior to the accident flight, the aircraft had not flown for 4 weeks. On the morning of the accident, the aircraft was fitted with two overhauled magnetos, a test run of the engine was carried out and the aircraft was released for service.

Figure 2: VH-CWK

Source: David Carter

The ATSB estimated the weight of the aircraft at the time of the accident as 1,281 kg (1,542 kg maximum allowable). The information manual for the aircraft provided best range glide speeds of 87 kt for an aircraft weight of 1,542 kg and 78 kt for 1,315 kg. The information manual indicated that the maximum glide range from 505 ft AGL was 0.66 NM (no wind).^[3]

The aircraft was fitted with a main and a wingtip fuel tank in each wing. The combined capacity of the 4 tanks was 318 litres (315 litres usable). The aircraft was reported to have departed with full fuel in the right wingtip and two main tanks. The left wingtip tank had been used for the engine run earlier in the day and was reported to be close to full. The pilot recalled intending to use the right main fuel tank for the entire flight. This tank contained sufficient fuel for the planned flight.

Engine

The PA-32-300 was equipped with a fuel-injected Lycoming IO-540 series engine of 300 horsepower. The aircraft type certificate data sheet (TCDS) stated that the aircraft type could be fitted with either an IO-540-K1A5 or an IO-540-K1G5 engine variant.

During its operating life, VH-CWK had been fitted with both K1G5 (factory installed) and K1A5 variants. Including K1A5 variants fitted by several maintenance organisations. In July 2020, VH‑CWK was fitted with an IO-540-K1A5 that had been rebuilt following a propeller strike in another aircraft. Prior to the accident flight, this engine had completed about 55 hours since being fitted to VH-CWK, and a total of 1,413.3 hours in service.

The difference between the K1A5 and K1G5 engine variants was the fuel pump type. The K1A5 variant was fitted with a vane type fuel pump, the K1G5 was fitted with a diaphragm type. The K1G5 variant was also 1 pound (0.454 kg) lighter than the K1A5.^[4]Both variants operated in the same fuel pressure range and no fuel system or other airframe differences applied to the fitment of either variant.

The TCDS did not specify a specific serial number range for the fitment of a K1A5 engine variant, but did so for the K1G5 variant as follows:

PA-32-300

Engine

- Lycoming IO-540-K1A5, Bendix injector type RSA-10ED1

- Lycoming IO-540-K1G5 (See NOTE 12)

NOTE 12:

- Lycoming engine Model IO-540-K1G5 with Hartzell propeller HC-C2YK-1(F), Blade Model 8475D-4, S/N 32-7640066 (only) and S/N 32-7640072 through 32-7940290.

When reviewing the TCDS, the maintainer responsible for installation of the engine in July 2020 interpreted the allowable engine variants as follows:

…the K1A5 was an allowed engine as there was no notes or restrictions…while noting if using a K1G5 that could only be installed in certain serial range.

As a consequence of that interpretation, a K1A5 variant was fitted to the aircraft. Past fitment of this variant by several maintenance organisations indicated a similar interpretation of the TCDS.

However, the manufacturer stated the following as the correct interpretation of the TCDS:

The type design specifies the engine model IO-540-K1G5 for Piper Model PA-32-300 serial numbers 32-7640066, 32-7640072 and up (ending 32-7940290). All other PA-32-300 aircraft serial numbers had engine model IO-540-K1A5 defined.

This interpretation is summarised in Table 1.

Table 1: PA-32-300 engine variant serial number applicability

The Civil Aviation Safety Authority approved aircraft flight manual, the information manual and the illustrated parts catalogue also referred to a K1G5 variant as the appropriate engine for installation in VH-CWK.

Meteorological information

A meteorological report for Moorabbin Airport, recorded at 1200, included a northerly wind of 9 kt, visibility greater than 10 km, no cloud, and a temperature of 14 °C.

Wreckage information

The aircraft impacted the tree about 14 m (Figure 4) above its base with the wing flaps retracted.

The left wing contacted the tree first and separated from the aircraft. Ground impact scars were located on an upslope 35 m from the tree base, 10.2 m below the height of the tree impact. After ground impact, the right wing also separated from the fuselage. The engine and fuselage were the last items in the wreckage trail, coming to rest 55 m from the tree.

Figure 3: Accident site viewed in the direction of flight

Source: ATSB

Note: The red objects were tarpaulins provided by first responders to the accident.

Fuel system

First responders to the accident drained a significant amount of fuel from the right main fuel tank.

While examination of the fuel system was limited by accident damage, the on-site examination identified that the:

• left main fuel tank, along with both tip tanks, were breached during the accident and empty
• left main and both tip tank caps were fitted and secure
• right main tank was not breached
• right main tank was selector lever was in the right tank position and the selector valve inlet port was connected to the supply line from the right main tank.
• right main tank cap had been removed by first responders

In addition:

• all fuel tank vents were clear of obstructions
• the electric fuel pump switch was selected on and functioned correctly
• no pre-existing defects were found with the supply lines and hoses
• the in-cabin fuel sump drain lever was secured behind a fastened panel

The fuel selector valve and fuel filter were retained for further examination. Fuel collected from the right main tank and fuel selector was tested and found to be of the correct type and free of contaminants.

Engine controls and propeller

The engine struck the ground on its left forward cylinder area, separated from its mount and rotated 90° around the aircraft centreline. The throttle and mixture cables fractured and separated during the impact. The throttle lever was found in the full position and the propeller control was in 

the maximum RPM position. The mixture lever was positioned at about half of its range of travel. However, it could not be determined if the levers had moved from pre-impact positions as a result of impact forces or during efforts to extract the pilot.

The bending damage to the propeller blades indicated that little or no power was being delivered to the propeller at the time of impact.

The engine and associated accessories were retained for further examination.

Recorded information

The aircraft was fitted with a J.P. Instruments EDM-830 Engine Data Management system. Data recovered from this unit captured data points every 6 seconds and included the power loss (Figure 5).

The first abnormal indication was a reduction in fuel flow from 113 litres per hour (l/h) to 47 l/h at 1200:49 (A). At the same time, RPM reduced from about 2,700 to about 2,500 (B) and exhaust gas temperature (EGT) increased across all cylinders (C). The next data point at 1200:55 showed the fuel flow reduced further to 22 l/h (D) and all EGT values, along with RPM, reduced significantly as power was lost (E). Following the power loss, fuel flow varied between 20 l/h and 16 l/h in conjunction with changes in RPM from the windmilling propeller.

No abnormal cylinder head temperature (CHT), manifold pressure (MAP) or oil pressure (Oil Px) indications were recorded before or after the power loss.

Figure 4: Graphical representation of data recovered from VH-CWK

Source: ATSB

Airservices provided recorded surveillance data of the flight. The aircraft was recorded commencing descent at 1200:53 at a groundspeed of 80 kt (headwind component was at least 9 kt). During the descent the groundspeed reduced further to between 68‑60 kt.

Engine, fuel selector and filter examination

In December 2021,^[5] the engine was disassembled and examined at a CASA-approved engine overhaul facility under the supervision of the ATSB.

The engine condition was consistent with the engine’s recorded time in service since overhaul. No internal or external damage was identified that may have prevented the engine from operating normally prior to the accident. No defects were identified in the induction system components, core engine, or cylinder assemblies that may have affected its pre-accident operation.

The ATSB examined the control positions required to replicate the recorded RPM and fuel flow indications. It was determined that to reproduce a fuel flow of 20 l/h with the throttle fully open, the mixture control needed to be moved close to the cut-off position. The propeller control movement needed to reduce RPM from 2,700 to 2,500 was significantly less. However, it was noted that control rigging variations could produce slightly different control movement ranges.

The ignition system components and fuel system components, including both fuel pumps, were tested. No defect was identified with these components that could have contributed to the power loss.

The fuel selector was examined at the ATSB’s technical facilities in Canberra, and it was found to function as designed.

Safety analysis

Engine power loss and collision with terrain

During the fourth circuit in a session of circuits, as the aircraft climbed through about 505 ft above ground level, the engine lost power. Following the power loss, the pilot established a glide at a speed below that targeted, but close to the correct speed for the aircraft weight. This led to near optimum glide performance. However, few suitable landing areas were available within the glide capability of the aircraft. The pilot selected an open area, but the aircraft did not clear trees along the southern boundary of the area. The aircraft impacted these trees separating the left wing before impacting the ground.

The on-site examination of the wreckage and later engine examinations and analysis of the recorded data found no indications of an induction issue, including icing, an ignition system or fuel system problem.

The recorded data showed that a significant reduction in fuel flow led to the power loss. Notably, after the power loss, the fuel flow did not reduce to zero, but varied between 20 and 16 l/h (in conjunction with RPM changes) indicating that fuel starvation did not lead to the power loss. Further, wreckage examination, flight records and witness reports indicated that there was sufficient fuel on board, and in any tank, to power the engine.

The ATSB considered the possibility that the pilot inadvertently reduced the mixture control instead of, or at the same time, as manipulating the propeller control. However, the pilot’s head injuries greatly limited their recollection of actions taken before and after the power loss. The recorded data showed that RPM reduced at the time, and by the amount, that the pilot intended to reduce RPM. Therefore, it is almost certain that the pilot manipulated the propeller control as intended.

At the same time, the fuel flow reduced significantly from 113 l/h to 22 l/h. The mixture lever movement required to produce this fuel flow reduction was significantly larger than that associated with the intended RPM change and required the lever to be positioned near the cut-off stop. After the accident, the mixture lever was found to be at a mid-travel position, but as the impact had caused significant damage to the engine controls, including breaking the mixture control actuating arm, the pre-impact position could not be determined. Overall, there was insufficient evidence to determine if the mixture control was inadvertently moved.

While damage limited the examination of the fuel system, no defect was identified that could have led to the fuel flow reduction. The engine was dismantled, examined and all fuel system components were tested. These components functioned correctly when examined. In summary, a reason for the fuel flow reduction could not be determined.

Incorrect engine variant

The type certificate data sheet did not specify a specific serial number range for the fitment of a K1A5 engine variant but did so for the K1G5 variant. This led the maintainer to interpret the aircraft type certificate data sheet as permitting the fitment of an K1A5 to VH-CWK instead of the correct K1G5. Past fitment of the K1A5 variant by other maintenance organisations indicated they had similarly assessed the TCDS as permitting this combination of engine variant and aircraft serial number.

However, the aircraft flight manual and the illustrated parts catalogue stated the only applicable engine variant for VH-CWK to be a K1G5, which was also confirmed by the aircraft manufacturer.

The differences between the fitted variant and the correct variant were minor and did not affect the operation of the aircraft, nor did they contribute to the power loss and collision with terrain.

Findings

From the evidence available, the following findings are made with respect to the collision with terrain involving a Piper PA-32-300 aircraft, VH-CWK, near Moorabbin Airport, Victoria on 22 June 2021.

Contributing factors

• As the aircraft climbed through 505 ft above ground level, fuel flow reduced and the engine lost power. During the subsequent forced landing the aircraft collided with terrain. The reason for the fuel flow reduction could not be determined.

Additional finding

• The incorrect engine variant for the aircraft serial number was inadvertently fitted to the aircraft. This did not affect the operation of the aircraft or contribute to the power loss.

Sources and submissions

Sources of information

The sources of information during the investigation included:

• the pilot
• the aircraft owner and maintainer
• Piper Aircraft (aircraft manufacturer)
• Lycoming Engines (engine manufacturer)
• engine data monitor
• Airservices Australia
• OzRunways
• Bureau of Meteorology

References

Australian Transport Safety Bureau, Avoidable Accidents No. 3 - Managing partial power loss after takeoff in single-engine aircraft

Submissions

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

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

• the pilot
• the aircraft owner and maintainer
• Piper Aircraft
• Lycoming Engines

Submissions were received from:

• the pilot
• the aircraft owner and maintainer
• Piper Aircraft

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

Purpose of safety investigations The objective of a safety investigation is to enhance transport safety. This is done through: identifying safety issues and facilitating safety action to address those issues providing information about occurrences and their associated safety factors to facilitate learning within the transport industry. It is not a function of the ATSB to apportion blame or provide a means for determining liability. At the same time, an investigation report must include factual material of sufficient weight to support the analysis and findings. At all times the ATSB endeavours to balance the use of material that could imply adverse comment with the need to properly explain what happened, and why, in a fair and unbiased manner. The ATSB does not investigate for the purpose of taking administrative, regulatory or criminal action. Terminology An explanation of terminology used in ATSB investigation reports is available here. This includes terms such as occurrence, contributing factor, other factor that increased risk, and safety issue. Publishing information  Released in accordance with section 25 of the Transport Safety Investigation Act 2003 Published by: Australian Transport Safety Bureau © Commonwealth of Australia 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. Eastern Standard Time (EST): Universal Coordinated Time (UTC) + 10 hours.
2. MAYDAY: an internationally recognised radio call announcing a distress condition where an aircraft or its occupants are being threatened by serious and/or imminent danger and the flight crew require immediate assistance.
3. The glide range capability of an aircraft reduces with an increase in headwind.
4. VH-CWK was reweighed after the fitment of the K1A5 variant of engine.
5. Examination of the engine was delayed due to Coronavirus related travel and working restrictions. During the period between the accident and examination, the engine was inhibited and stored in a secure location.

The occurrence

At about 1126^[1] on 18 June 2021, a locomotive collided with the rear of a stationary coal train at Westwood, Queensland, located about 45 km west of Rockhampton.

The locomotive, operated by Queensland Rail (QR), was being used for route tuition^[2] on the Blackwater system^[3] in Queensland. It was being operated as a ‘light engine’ (that is, with no other rail vehicles attached) and it was assigned the train number LET0. The crew consisted of a tutor driver providing route tuition and two other QR drivers receiving route tuition. LET0 utilised a single QR class 2470 class locomotive (number 2471).

The intended route for the tuition was from Rockhampton to Bluff and then return (Figure 1). For the first leg of the route, the locomotive was long end leading (that is, operated in the reverse direction to normal operation, see Long end leading for further details).

Figure 1: Rail route on the Blackwater system showing the path of the locomotive and the collision point

Source: Google Maps, annotated by the ATSB

The three-person QR crew started and prepared the locomotive for traffic in Rockhampton yard. At 1041, LET0 left Rockhampton yard and entered the Blackwater system. One of the drivers receiving route tuition performed the role of the driver and the other driver receiving route tuition performed the role of co-driver.

Between Rockhampton and Bluff, there was an Up^[4] line and a Down line. LET0 travelled on the Up line until it reached Kabra, where the network control officer (NCO) routed it to the Down line to allow for the passage of a loaded coal train travelling east on the Up line.

At Westwood there was a common loop.^[5] There was a maintenance closure on the Down line to the west of Westwood, which meant all rail traffic in that area had to use the Up line, and the common loop at Westwood was used for passing traffic.

As LET0 approached Westwood, there was an Aurizon coal train (EE16) stationary in the common loop. EE16 was travelling westwards between Callemondah (Gladstone) and Ensham Mine (Comet), and it consisted of three Aurizon 3800 class locomotives and 102 empty coal wagons.

At 1107, the NCO set up the route for LET0 to travel to Westwood signal WD28, located to the east of Westwood (Figure 2). The NCO planned to route LET0 via the Westwood common loop and then for all traffic (EE16 and LET0) to travel via the Up line from Westwood to Windah. The signal interlocking system was set up to show a yellow (caution) aspect in the approach signal WD28P and a red (stop) aspect in WD28. That meant that LET0 would be required to stop at signal WD28 outside Westwood until EE16 had vacated the common loop, at which time the signal aspect in WD28 would change to proceed.

At 1119, while LET0 was travelling towards Westwood, the NCO set the 11 A/D points as planned from the Down line into the common loop at Westwood in preparation for the locomotive to enter the common loop after EE16 had departed (Figure 2).

Figure 2: The route of LET0 into Westwood common loop

The yellow solid line within the image shows the path of the locomotive on approach and after passing signal WD28. Source: Queensland Globe, annotated by the ATSB

The locomotive’s data logger showed that a partial application of the independent brake was initiated at 1125:42, as the locomotive entered a downhill gradient into Westwood yard.

At 1125:43, a SPAD (signal passed at danger) alarm was generated in the Aurizon network control centre, indicating that LET0 had passed signal WD28 while it was displaying a red (stop) aspect.

At 1125:46, LET0 entered the 11 A/D points. The locomotive’s data logger showed that it entered the 50 km/h turnout^[6] from the Down line to the common loop at approximately 72 km/h.

At 1125:49, in response to the SPAD alarm, the NCO made an emergency broadcast over the network control radio. There was no response from the crew of LET0.

At 1125:53, a full independent brake application was made. At this time the speed of the locomotive was approximately 60 km/h.

At 1125:59, LET0 collided with the rear of EE16 at a speed of approximately 44 km/h. The collision occurred just after the locomotive entered the Westwood common loop. Figure 3 shows the collision point between the locomotive and the coal train on the common loop (centre track) of the three-track Westwood yard.

Figure 3: Collision site at Westwood, Queensland

Source: Queensland Police Service, inserts by the ATSB

The locomotive and the last nine wagons of the coal train sustained significant damage from the collision. The driver was fatally injured, the co-driver sustained serious injuries and the tutor driver received minor injuries.

At 1130, after attempting to call for help using the radio, the tutor driver of LET0 called the network control centre via mobile phone to advise that LET0 had been involved in a collision. The NCO provided first aid and CPR instructions to the tutor driver. At 1132, another Aurizon NCO contacted the Queensland Ambulance Service, and the first emergency vehicle arrived on scene at 1201.

Context

Signal testing

Aurizon was the rail infrastructure manager for the Blackwater system. Remote controlled colour light signalling controlled train movements on the system and it was operated by the Aurizon network control centre at Rockhampton.

Testing of the signalling system by Aurizon found that, at the time of the accident:

• Approach signal WD28P was displaying a single yellow aspect, which indicated to a driver that the next signal, WD28 would be at red (stop).
• The dynamic speed indicator^[7] attached to WD28P was not illuminated.
• WD28 was displaying a red aspect.

Train crew information

Driver

The main role of a driver is to control the movement of the locomotive. The driver is also responsible for observing and obeying signal aspects and maintaining control of the speed of the locomotive.

The driver of LET0 had been qualified as a QR driver for about 4 months, and had both the safeworking^[8] and traction^[9] competencies required to drive the locomotive. The driver was receiving route tuition for the section of track between Rockhampton and Bluff.

Co-driver

One of the roles of a co-driver is to observe, announce and confirm the signal aspects as they are sighted. When driving long end leading, the structure of the locomotive on 2470 class and similar locomotives limits vision for the driver and they rely heavily on the co-driver for observing signals.

The co-driver on LET0 had been qualified as a QR driver for about 6 months, and had both the safeworking and traction competencies required to drive the locomotive. It was intended that the co-driver would perform the role of the driver (from the driver’s position) for a period during the tuition that day. The co-driver was receiving route tuition for the section of track between Rockhampton and Bluff.

Tutor driver

A tutor driver is responsible for instructing drivers on all aspects of controlling a locomotive, which includes teaching train handling and route knowledge.

The tutor driver on LET0 had qualified as a driver with another rail operator about 9 years previously. They had been qualified as a tutor driver about 5 years earlier, before joining QR in that role about 3 years before the accident. They had the safeworking, traction and route competencies to drive the locomotive from Rockhampton to Bluff, and were providing tuition on that route to both the driver and co-driver. 

Locomotive information

Locomotive 2471 was a Queensland Rail (QR) 2470 class locomotive with a single driving station at the front right of the cabin. The normal driving direction of the locomotive was with the cabin end leading (Figure 4).

Figure 4: Locomotive 2208D similar to a QR 2470 class locomotive

Source: ATSB

Figure 5 is a view from inside the cabin looking forward, showing the driver’s vision on the right and the co-driver and tutor driver’s view on the left when travelling in the normal direction.

Figure 5: View from inside the cab looking forward

Source: ATSB

Figure 6 is a plan view of the driver’s cabin with the seats in the normal position (driven cabin end leading). A driver seated in the driver’s seat has access to all the relevant controls. The only locomotive control available to the co-driver on a 2470 class locomotive is an emergency brake valve.

The tutor driver was positioned in a temporary seat (removable chair) located in the centre rear of the cabin, facing towards the front windows. From that position the tutor driver had a good view out the front of the train during normal operations. According to the tutor driver, it was normal practice for the tutor driver to take a position in the temporary seat at the centre rear of the cabin area when two drivers were undergoing route tuition. This would have been the configuration of the cabin for the return trip from Bluff to Rockhampton.

Figure 6: Plan view of the driver’s cabin in normal configuration

Source: Queensland Rail, annotated by the ATSB

Long end leading

‘Long end leading’ occurs when a locomotive travels with the driving cabin at the rear for the direction of travel. Figures 7 and 8 shows the limited view for the driver during this method of operation on a 2470 class locomotive, with a significant amount of the forward view being obstructed by the leading portion of the locomotive and the back wall of the cabin.

Figure 7: Driver's viewport when long end leading

Source: ATSB

Figure 8: View from inside the cabin from driver and co-driver perspective with long end leading

The image on the left shows the driver’s view from the locomotive’s active driving station when long end leading. The image on the right shows the view from the co-driver’s seat when long end leading. Source: ATSB

Figure 9 is a plan view of the driver’s cabin configured for long end leading. The driver’s position was such that they were required to face 90⁰ to the direction of travel to enable use of the driver controls. The driver’s attention was split between the driver controls, the gauge console and the view ahead.

The co-driver’s seat was rotated 180⁰. The co-driver was relied upon to convey observations to the driver because the driver’s view was obscured on the right side of the locomotive. When the co-driver was positioned this way, they could no longer reliably operate the emergency brake valve without moving from their seat.

On LET0, the tutor driver’s temporary seat was positioned as shown in Figure 9. They were facing rearward in relation to the direction of travel and had no forward view.

Figure 9: Plan view of driver’s cabin configured for long end leading

Source: Queensland Rail, annotated by the ATSB

Long end leading is conducted in the rail industry with many types of locomotives, usually for the purposes of manoeuvring to a location to turn around or for shunting wagons. Some types of locomotives are designed with additional controls at the rear of the cabin and cameras to facilitate long end leading operations. Some designs have eliminated long end leading by implementing driving cabins at each end of the locomotive.

QR used long end leading for tuition trains between Rockhampton and Bluff for its current training cohort since December 2020.

Safety action

On 21 June 2021, QR suspended all mainline long end leading operations both on its own network, and as an operator of its trains on other networks. Permitted operations for long end leading were limited to shunting, turning of a locomotive, setting back and propelling movements.

In addition, on 25 June 2021, the Office of the National Rail Safety Regulator issued a safety alert, requiring all rail infrastructure managers and rolling stock operators to review the risks associated with long end leading operations (if applicable) by the end of July 2021.

Further investigation

To date, the ATSB has:

• gathered and undertaken preliminary analysis of locomotive event recordings and network control and locomotive voice recordings
• conducted brake and operational control testing of the locomotive
• gathered information about the locomotives, rail infrastructure and operational procedures
• conducted a re-enactment of the event to identify visual limitations from long end leading operations, including on the curved section approaching signal WD28.

The investigation is continuing and will include:

• review and examination of the functionality and cabin ergonomics of the 2470 class locomotives for long end leading operations and other factors that may have influenced the crew’s performance
• review of the nature and extent of the use of long end leading for main line operations
• review of long end leading risk controls related to collision and authority exceedance (SPAD) hazards
• review of change management and risk management processes applicable to the use of long end leading for route tuition
• review of post incident procedures for managing emergencies on the network
• review and examination of the radio and signalling infrastructure and procedures on the Blackwater system
• review of the Westwood signal interlocking event recordings and associated circuit diagrams.

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

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

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 2021 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.  All time references in this report are in local time (Eastern Standard Time).
2. Route tuition involved learning the signalling, speeds, and dynamics of a section of a track prior to an assessment for route qualification for that section.
3. The Blackwater system was managed by Aurizon and included the section of track from Rocklands (3 km south of Rockhampton) to Nogoa (2.5 km east of Emerald), including the track at Westwood.
4. The Up direction on the Blackwater system was in a westerly direction. The Up line was the name applied to the left-hand duplicated track, facing westward. l
5. The common loop was the middle of the three tracks at Westwood.
6. Turnout: a combination of a set of points, V crossing and guard rails that permit traffic to turn out from one track to another.
7. A dynamic speed indicator is an illuminated numeric display attached to an approach signal that indicated the maximum speed which applied at the next signal. It is only illuminated when the next signal was not at stop (red) or green, and the approach signal it was attached to was at yellow.
8. Safeworking: an integrated system of operating rules and procedures that define the interaction between workers and engineered systems for the safe operation of a railway
9. Traction competency refers to the type of motive power (locomotive) driven.

Safety summary

What happened

On 10 June 2021, two SPENO Rail Maintenance Australia Road-Rail Vehicles (RRVs), FL18 and SP128, on-tracked at about the 196.012 km point, Binney Road level crossing, at Crystal Brook, South Australia, to undertake ultrasonic rail flaw detection. However, the track worker level 2 (TW) for the RRV travel inadvertently requested the protection limits for Train Running Information (TRI) travel from a location about 3 km in advance of where the RRVs were to on-track. The RRVs ontracked outside of the protection limits and travelled for about 3 km before protection for the movement was applied by the network controller (NC).

What the ATSB found

The TW incorrectly requested the signal for the protection limits for RRV travel as signal 24 Crystal Brook (current location), instead of signal 24 Rocky River, when communicating with the Australian Rail Track Corporation (ARTC) NC. In addition, there was no confirmation between the TW and the NC of where the RRV’s were to on-track while discussing the limits of protection required for the travel. Combined, these factors resulted in the NC applying Blocking Facilities from signal 24D at Crystal Brook to signal 3 at Coonamia and the RRV’s operating outside of the limits defined in the Train Running Information.

What has been done as a result

SPENO have undertaken a review and made amendments to processes for on-tracking of RRV’s. The proposed amendments include the provision to remove the single point of failure of the TW being responsible for identifying and communicating the location which RRVs would on-track in rail networks.

Safety message

This incident highlights the importance of identifying the location that travel or work on track will commence. Competent workers should provide all the information required for network controllers to identify and confirm that protection limits adequately cover the intended work site. Confirmation of location is especially important for providing Blocking Protection for RRV movements.

The investigation

The Occurrence

On 10 June 2021, SPENO Rail Maintenance Australia (SPENO) had planned to conduct ultrasonic rail flaw detection on the Australian Rail Track Corporation (ARTC) Port Augusta Line, South Australia. The testing was to be from the 196.030 km point at Crystal Brook to 94.960 km at Spencer Junction, (Figure 1). The maintenance was planned to be conducted with two Road Rail Vehicles^[1] (RRVs), the testing vehicle FL18 (Figure 2) leading, and the hand testing vehicle SP128 (Figure 3) following.

Figure 1: Location of Crystal Brook, South Australia

Source: Google Earth Pro, annotated by the ATSB

Figure 2: SPENO FL18 ultrasonic test vehicle (lead vehicle)

Source: SPENO Rail Maintenance Australia

Figure 3: SPENO SP128 ultrasonic test vehicle (second vehicle)

Source: SPENO Rail Maintenance Australia

To provide protection for the travel, a track worker level 2^[2] (TW) assigned to the SPENO RRVs planned the protection required using a Worksite Protection Plan and Worksite Protection Plan Map that was marked with the limits of protection for Train Running Information^[3] (TRI) travel (signal 24 Rocky River through the Westbound Mainline), RRV on-tracking location (196.012 km) and intended travel path denoted in light brown on Map (Figure 4).

Figure 4: Competent worker map of Crystal Brook showing intended limits of protection for RRVs

Source: Track Worker Level 2 Worksite Protection Plan Map Markup, annotated by ATSB

At about 0715^[4] the TW briefed the SPENO work crew on protection arrangements. The SPENO work crew who attended the pre-work brief by the TW acknowledged the pre-work briefing by signing the Pre-Work Brief Form. At about 0721 the TW contacted the network controller^[5] (NC) to initiate receiving TRI. During the initial conversation the NC asked the TW for their location, to which the TW replied, ‘Crystal Brook’. The TW and NC continued to exchange information, which included the limits for TRI travel. For the limits of protection, the TW requested signal 24 at Crystal Brook to signal 3 at Coonamia.

The NC noted Crystal Brook had a signal 24 and signal 24D and asked the TW if they required both the Eastbound Mainline and the Westbound Mainline for the intended work. The TW responded that they only required the Westbound Mainline for the travel, and the NC then stated that signal 24D was the protecting signal for that line.

After the signals for limits of protection were agreed, at about 0722 the NC placed Blocking Facilities^[6] from signal 24D at Crystal Brook to signal 3 at Coonamia (Figure 5).

Figure 5: Phoenix showing Blocking Facilities applied (blue section)

Source: Australian Rail Track Corporation, annotated by ATSB

After the TW received the TRI at about 0735, the SPENO crew prepared the RRVs and on-tracked at the 196.012 km point at the Binney Road Level crossing and proceeded towards Coonamia, conducting ultrasonic tests as they proceeded. On arrival at the number 20 points for the turnout^[7] to the Eastbound Mainline or Eastbound Mainline at Crystal Brook, located at 21.144 km^[8], the crew observed that the turnout was set for the Eastbound Mainline. The TW contacted the NC to request the number 20 points be set for their intended route to the Westbound Mainline.

The NC questioned the work crew’s current location, and after confirmation, the NC informed the crew that they were outside of the limits of protection. The TW then explained to the NC that they had on-tracked the RRVs at the 196.012 km Binney Road Level Crossing, which was about 3 km prior to the start limits of the protection applied by the NC. Figure 6 depicts the travel of the RRVs outside of their protection limits in red. The RRV end location and green section of track indicate the location of where the original protection limits started. (Figure 6).

Figure 6: Path of RRV’s outside of protection

Source: Google Earth Pro, annotated by the ATSB

Context

Track worker level 2

At the time of the occurrence, the TW had completed all the accredited and non-accredited course components and had been recertified, as of 21 May 2021, as current for Train Running Information and Code of Practice (CoP0 for the Defined Interstate Rail Network (DIRN), and the ARTC Addendum. The TW had undertaken Category 1 rail safety medical and had been deemed fit for duty subject to review on 10 December 2021. The review subject was not considered a factor in this occurrence. Alcohol and other drug tests were undertaken after the occurrence. The results were negative.

The work orders for SPENO for the planned scope of works had the times of 0600 – 1630 on two previous days and on the day of the occurrence. As the TW had adequate opportunities for rest prior to commencing work, fatigue was not considered to be a factor.

Network Rules and Procedures

When planning work or travel in a rail corridor, it is the TW’s responsibility to ensure that the work is planned, and the protection requirements are carried out according to network rules and procedures. In the case of the RRV travel for the ultrasonic testing, the applicable rules were governed by the CoP for the DIRN, ARTC Version 3.0: 01 July 2018 and the ARTC Addendum to the CoP for the DIRN Version 5.1: 02 July 2020.

Sections 3.11.22 and 3.11.23 of the CoP for the DIRN defined the requirements for initiation and format of a TRI. When a TW requested a TRI, the TW shall tell the NC their name and company, the location from which communications is made, type of vehicle or work to be undertaken and the TRI limits expressed as being between two locations which may include the following:

- kilometre locations
- signal locations or numbers
- a main track or crossing loop at a specific location
- the track where there are multiple tracks, and
- section name.

The Rail Industry Safety and Standards Board (RISSB) had a procedure within its suite of Australian Network Rules and Procedures (ANRP) that address the identification and verification of location for worksite protection. The RISSB procedure states:

Where worksite protection is primarily applied by the network control officer, the correct and accurate location of the worksite is critical in ensuring the safety of workers and rail traffic.

Further, the RISSB procedure has additional information the TW may use to identify that location, which included:

- Contact the Network Control Officer
- Communicate the proposed worksite location using the identifiers below in the following order

- track name, and
- station name or stations at both ends of the worksite, and
- One or more of the following:

- the signal/Block Limit Board identification number/s giving entry to worksite, or
- a points identification number located in the worksite, or
- a kilometre location in the worksite, or
- a permanent structure in the worksite that is visible on the Network Control Officer workstation

The ARTC rules and procedures did not specifically have a procedure for identification and verification of location. The ARTC Addendum to the CoP for the DIRN s23.1 had the following mandate under s23 Track Force Working:

23.1 Defining a Location and Train ID

A worker shall identify their location in km and m in a section whilst trains are to be identified as being from one location to another location.

Network Communication

The CoP for the DIRN had provisions for communications between rail safety workers. This included the requirement for a TW to establish communication with the relevant NC and provide sufficient detail to ensure adequate identification of location. The ATSB reviewed the voice recordings between the TW and NC during the establishment of the Train Running Information and noted that the communication of important safety information was informal, conversational and did not include the location that the RRVs would on-track. The TW included the location of Crystal Brook within the context of references to signal 24 and did not make any reference to signal 24 at Rocky River as the location required for the start of the protection limits.

The ARTC Train Notice (TN) 1928 - 2017 Track Worker Communication Protocol contains details for a competent rail safe worker (CRSW), to which a TW is aligned, is required to undertake to access the ARTC Rail Corridor.

The CRSW must on initial contact with Network Control, specify their physical location by stating:

- Location name and KM, or
- KM and Signal Number.

The RISSB has a CoP for safety critical communications, which states it is important that safety critical communication is transmitted accurately and effectively to all rail safety workers.

When arranging worksite protection, it is important that safety critical communications are transmitted accurately and effectively between the NCO [network control officer]^[9] and the PO [protection officer]^[10], and with other parties where applicable.

Road Rail Vehicles

The SPENO work order information had kilometrage from 196.030 km at Crystal Brook to signal 43 at Spencer Junction (Figure 7). The SPENO crew attended the TW pre work briefing at about 0715. The SPENO Supervisor stated that the TW had mentioned the limits of protection would be signal 24 Rocky River to signal 3 Coonamia.

After the TW had received the TRI from the NC, the SPENO crew prepared the RRVs for work by lowering the rail wheels onto the rails, which guide the RRVs, at the 196.012 km and proceeded towards Coonamia.

Figure 7: SPENO Work Order from Crystal Brook to Spencer Junction

Source: Australian Rail Track Corporation, annotated by ATSB

Safety analysis

On the morning of 10 June 2021, while preparing for scheduled maintenance work on a section of track between Crystal Brook and Spencer Junction, South Australia, the protection officer for the work crew contacted the network control officer to obtain train running information and establish protection limits. During the discussion between the track worker level 2 and network controller, the exact location that the work crew would on-track was not clearly communicated and confirmed. Inclusion of the on-track location would have also provided an opportunity for the network control officer to recognise that the requested protection was inappropriate for the area of work. Consequently, the RRV on-tracked outside the limits of protection.

In addition, the track worker level 2 requested the protection limits start at signal 24 Crystal Brook, instead of signal 24 Rocky River. Signal 24 Rocky River encompassed their planned start location of Binney Road at the 196.012 km, which was the location they briefed the work crew and had annotated on their work plan. This resulted in the network controller applying Blocking Facilities on the incorrect section of track.

Findings

From the evidence available, the following finding is made with respect to the RRV’s on-tracking outside of the limits of protection on the 10 June 2021.

Contributing factors

• The track worker level 2 incorrectly requested the protecting signal for the protection area required as signal 24 Crystal Brook (current location), instead of signal 24 Rocky River, when communicating with the network controller. Further, there was no confirmation of where the road-rail vehicles were to on-track while discussing the limits of protection required for the work.

Safety actions

Safety action by SPENO Rail Maintenance Australia

SPENO have undertaken a review and made amendments to processes for on-tracking of RRVs. The proposed amendments include the provision to remove the single point of failure of the TW being responsible for identifying and communicating the location which RRV’s would on-track in rail networks.

Glossary

ARTC               Australian Rail Track Corporation

CoP                 Code of Practice

CRSW             Competent rail safe worker

DIRN                Defined Interstate Rail Network

NC                   Network controller

TW                   Track worker

RRV                 Road-rail vehicle

TRI                   Train running information

Sources and submissions

Sources of information

The sources of information during the investigation included the:

• Protection Officer of the occurrence
• SPENO Rail Maintenance Australia
• Australian Rail Track Corporation
• Rail Industry Safety and Standards Board
• Office of the National Rail Safety Regulator

References

Department of Transport and Regional Services 2002, Code of Practice for the Defined Interstate Network, Volume 3, ARTC Version 3.0: 01 July 2018, pp.70-71.

ARTC Addendum to the Code of Practice for the Defined Interstate Rail Network 2020, Volume 5.1, s23.1, p.88.

ARTC Network Information Book, West CTC, Dry Creek North Junction (exc) to Spencer Junction (inc), OGW-30-09 2020, Version 1.3.

ARTC Train Notice 1928 - 2017, Track Worker Communication Protocols.

ARTC Network Communications Standard 2020, OPE-PR-043, Version 1.0.

Rail Industry Safety and Standards Board 2017, Identification and Verification of Location, Version 1.0.

Rail Industry Safety and Standards Board 2017, Code of Practice, Safety Critical Communications, Version 1.0, p.5.

Office of the National Rail Safety Regulator 2019, Guideline, Road Rail Vehicle Management & Operations, Version 1.0.

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:

• Railsafe SA Pty Ltd, Protection Officer of the occurrence
• SPENO Rail Maintenance Australia Pty Ltd, Ultrasonic Testing Supervisor
• SPENO Rail Maintenance Australia Pty Ltd, Operator of FL18
• SPENO Rail Maintenance Australia Pty Ltd, Operator of SP128
• Australian Rail Track Corporation, General Manager, Safety and Environment
• Australian Rail Track Corporation, Safety Assurance Manager
• Office of the National Rail Safety Regulator

A submission was received from the Australian Rail Track Corporation, Safety Assurance Manager, and, where considered appropriate, the text of the report was amended accordingly.

Purpose of safety investigations The objective of a safety investigation is to enhance transport safety. This is done through: identifying safety issues and facilitating safety action to address those issues providing information about occurrences and their associated safety factors to facilitate learning within the transport industry. It is not a function of the ATSB to apportion blame or provide a means for determining liability. At the same time, an investigation report must include factual material of sufficient weight to support the analysis and findings. At all times the ATSB endeavours to balance the use of material that could imply adverse comment with the need to properly explain what happened, and why, in a fair and unbiased manner. The ATSB does not investigate for the purpose of taking administrative, regulatory or criminal action. Terminology An explanation of terminology used in ATSB investigation reports is available here. This includes terms such as occurrence, contributing factor, other factor that increased risk, and safety issue. Publishing information Released in accordance with section 25 of the Transport Safety Investigation Act 2003 Published by: Australian Transport Safety Bureau © Commonwealth of Australia 2021 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 road vehicle fitted with retractable rail guidance wheels. Also referred to as 'hi-rail vehicle'.
2. A Competent Worker responsible for managing the rail safety component of worksite protection.
3. Information about rail traffic movement and frequency for a particular location.
4. All times are in Australian Central Standard Time (UTC + 10:30) and in 24-hour format.
5. A Competent Worker who authorises, and may issue, Occupancy Authorities, and who manages rail traffic paths to ensure safe and efficient transit of rail traffic in the Network.
6. A facility or device used by a competent worker to prevent either the unintended issue of an occupancy authority, or the operation of points or signalling equipment.
7. A combination of a set of points, V crossing and guard rails which permits traffic to turnout from one track to another.
8. Change of datum point between network kilometrage measurements.
9. A network control officer, in the context of this occurrence, is aligned to a network controller (NC) as defined in the RISSB Glossary of Terms.
10. A track worker level 2, in the context of this occurrence, is aligned to a protection officer (PO) as defined in the RISSB Glossary of Terms.

Safety summary

What happened

On the afternoon of 6 June 2021, a Babcock Mission Critical Services Australasia, AgustaWestland AW139 helicopter, registered VH-YXH, was conducting a medical retrieval flight from Yielima, Victoria to the Royal Melbourne Hospital. The helicopter was being operated under the instrument flight rules (IFR). At the same time, a Moorabbin Aviation Services Piper PA-44-180 Seminole aircraft, registered VH-HMQ, was operating an IFR training flight from Wagga Wagga, New South Wales to Mangalore Airport, Victoria.

As the Seminole tracked north along the RNAV-Z runway 36 approach to Mangalore Airport, the helicopter was about 10 NM north of Mangalore and tracking south to overfly the airport at 3,100 ft. At about 1555, the Seminole commenced a missed approach resulting in the helicopter’s traffic alerting and collision avoidance system (TCAS) displaying a traffic advisory, followed by a resolution advisory. Six seconds later, the aircraft passed in cloud 451 m (in a straight line) from each other with a minimum vertical separation of 543 ft and a minimum horizontal separation of 333 m. Both aircraft were in cloud throughout the occurrence.

The helicopter continued to Royal Melbourne Hospital while the Seminole diverted to Shepparton. Both aircraft landed without further incident.

What the ATSB found

The helicopter pilot did not consider the possibility of the pilot in the Seminole conducting a missed approach and that it could conflict with the helicopter’s flight path. The Seminole’s pilot reported not hearing broadcasts from the helicopter and misinterpreted traffic advice from air traffic control. Consequently, the Seminole pilot was not aware of the helicopter’s presence and that an incident had occurred.

The ATSB also found that the helicopter operator's traffic alert and collision avoidance knowledge was inadequate with respect to resolution advisory alert terrain considerations and the required intensity of response manoeuvring.

What has been done as a result

The Seminole operator implemented a non-technical skills education program. This included situational awareness, potential biases, and the dangers of student-instructional distractions, particularly during periods of high workload.

The helicopter operator issued a safety alert to flight crew of TCAS equipped aircraft, alerting pilots to the ground inhibit functions of the system and the control response requirements for resolution advisory manoeuvres. The safety alert also highlights the mandatory compliance requirements of resolution advisories. 

The helicopter operator has also updated the flight crew training courseware, syllabus and simulator program for 2022. The updated simulator program incorporates elements relevant to the occurrence along with simulator instructor guides.

Safety message

This incident shows that the effective use of radio remains a primary defence in avoiding mid‑air collisions. This is achieved by maintaining an effective listening watch and proactive communication. The ATSB publication A pilot’s guide to staying safe in the vicinity of non-towered aerodromes highlights some of the known challenges presented to pilots operating around uncontrolled airfields.

The incident also highlighted the importance of effective flight crew TCAS training. TCAS is a complex system which serves as a ‘last line of defence’ in airborne collision avoidance. Thorough knowledge of the system is critical in ensuring that crews respond appropriately to TCAS resolution advisories.

The ATSB also strongly encourages the fitment of ADS‑B transmitting, receiving and display devices as they significantly assist the identification and avoidance of conflicting traffic. The continuous positional information ADS‑B provides can highlight a developing situation many minutes before it becomes hazardous – a significant improvement on both point‑in‑time radio traffic advice and ‘see‑and‑avoid’. The ATSB also notes that ADS‑B receivers, for pilots operating under both the instrument or visual flight rules, are currently available within Australia at low cost and can be used in aircraft without any additional regulatory approval or expense.

It is also important to recognise that ADS‑B IN cannot be relied upon to display all nearby traffic so effective use of radio remains a primary defence in avoiding mid‑air collisions. In that context pilots need to make all required broadcasts detailed in the Aeronautical Information Publication, even if there is no known traffic, and respond to broadcasts if a potential traffic conflict is identified.

The occurrence

On the afternoon of 6 June 2021, a Babcock Mission Critical Services Australasia (Babcock MCS) AgustaWestland AW139, registered VH-YXH (Figure 1) was conducting a medical retrieval flight from Yielima, Victoria to the Royal Melbourne Hospital. The helicopter was being operated under the instrument flight rules (IFR) using the callsign HEMS3 with a pilot, two crewmembers and a patient onboard.

At the same time, a Moorabbin Aviation Services Piper PA-44-180 Seminole, registered VH-HMQ was operating an IFR training flight from Wagga Wagga, New South Wales to Mangalore Airport, Victoria. An instructor and a student were onboard the Seminole.

Figure 1: VH-YXH (left) and VH-HMQ (right)

Source: Tony Hanes and Grahame Bann

At 1531 Eastern Standard Time (EST),^[1] the student in the Seminole commenced a very-high frequency omni radio range (VOR)^[2] approach to Mangalore from 3,900 ft above mean sea level (AMSL). The approach was conducted entirely in cloud. During the approach, another helicopter (using the callsign HEMS1) transited the Mangalore common traffic advisory frequency (CTAF)^[3] broadcast area at 5,000 ft. The instructor in the Seminole communicated with the pilot of HEMS1 to coordinate adequate aircraft separation.

During the VOR approach, the instructor communicated with a third helicopter operating beneath their approach path. As the Seminole descended to about 1,800 ft, the instructor elected to discontinue the approach to ensure separation with that helicopter. The instructor took control of the aircraft and positioned it at waypoint MNGSI, 13 NM south of Mangalore, to commence the RNAV-Z^[4] approach (Figure 2) to runway 36^[5] . The missed approach procedure for the approach required the aircraft be climbed to at least 2,800 ft on a continuation of the approach track (358 degrees Magnetic).

Figure 2: Mangalore Airport runway 36 RNAV-Z approach chart

Source: Airservices annotated by the ATSB

At 1548, as the Seminole crossed MNGSI and tracked north along the approach, the helicopter HEMS3, was about 20 NM north of Mangalore and tracking south toward the airport in visual conditions at 1,400 ft. The pilot observed that cloud conditions to the south prevented visual flight and climbed the helicopter to proceed in instrument meteorological conditions (IMC). Due to concerns regarding the welfare of the patient, the pilot intended to operate at the lowest available altitude. A route proceeding to Mangalore and then southwest toward Puckapunyal provided a lowest safe altitude of 3,100 ft so the pilot climbed the helicopter to continue toward Mangalore at that altitude. This flight path conflicted with the Seminole’s missed approach path.

At 1550, when the Seminole was positioned about 10 NM south of Mangalore, the student asked the instructor a question. At the same time, air traffic control (ATC) contacted the Seminole to advise that a helicopter with the callsign HEMS3 would be overflying Mangalore from the north. The instructor reported that, due to the overlap of the student’s question with the ATC communication, the altitude and callsign information provided by ATC was not heard. As a result, the instructor misinterpreted the traffic advice as relating to HEMS1, the helicopter with which separation had been coordinated about 15 minutes earlier.

Shortly after, ATC contacted the pilot of HEMS3, advising that the Seminole was conducting the RNAV-Z approach. The helicopter pilot reviewed the runway 36 RNAV-Z approach chart, determined the Seminole’s flight path and assumed that it would land from that approach. The pilot did not consider the potential conflict with the RNAV-Z missed approach path and, hence, did not change their flight path or contact the instructor to coordinate separation between the two aircraft.

At about 15:52, the instructor in the Seminole broadcast on the Mangalore CTAF that the aircraft was 7 NM to the south of the airport and conducting the RNAV-Z approach to runway 36. The helicopter pilot heard the broadcast and reported broadcasting on the CTAF about a minute later that HEMS3 was 10 NM to the north and overflying Mangalore at 3,100 ft. The instructor in the Seminole, however, reported not hearing this broadcast.

The Seminole continued along the approach and, at 1555, descended to the minimum descent altitude of 990 ft.^[6] Cloud conditions prevented the instructor and student sighting the runway and, at 1555:32, the instructor commenced a missed approach from about 1.5 NM south of the airport. At that time, the helicopter was about 3.6 NM north of Mangalore at 3,100 ft. The instructor intended climbing the Seminole to 4,000 ft (the missed approach required a climb to at least 2,800 ft) and to divert to Shepparton Airport.

At 1556:18, the helicopter was about 1.8 NM to the north of Mangalore as the Seminole passed over the runway 36 threshold at an altitude of about 1,900 ft. At this time, the helicopter pilot observed the Seminole climbing toward the helicopter on the traffic collision avoidance system (TCAS) traffic display. Seven seconds later, the TCAS provided a traffic advisory alert to the pilot (see section titled Traffic alert and collision avoidance system). In response to the alert, the pilot commanded the autopilot to commence climbing the helicopter. Soon after, the instructor in the Seminole broadcast on the Mangalore CTAF that a missed approach had been commenced.

At 1556:39 the TCAS presented a resolution advisory alert to the pilot. The resolution advisory (RA) provided an aural alert ‘monitor vertical speed’ and presented a red ‘avoid’ indication on the vertical speed indicator (VSI) for descents of 500 ft per minute or greater (Figure 3).

Figure 3: Video capture of the resolution advisory indications during the occurrence

Source: Babcock MCS, annotated by ATSB

The pilot incorrectly perceived the RA as a descent instruction. At that time, the helicopter’s climb rate was increasing to 600 feet per minute and the pilot believed that transitioning to a descent could startle those onboard. The pilot also believed that following TCAS instructions could lead to a collision with terrain and therefore did not want to descend below the lowest safe altitude. Hence, the pilot attempted to increase separation by commencing a right turn away from the Seminole. By the completion of the turn, the climb rate had reduced to zero. The helicopter reached a maximum altitude during the event of 3,180 ft.

At 1556:45, six seconds after the RA, the two aircraft passed with a minimum vertical separation of 543 ft and a minimum horizontal separation of 333 m (451 m in a straight line).

At 1556:49, the TCAS alerted the pilot that the helicopter was clear of the conflict. The helicopter continued to the Royal Melbourne Hospital while the Seminole diverted to Shepparton. Both aircraft landed without further incident and no injuries resulted.

The crew of the Seminole, which was not equipped with TCAS or Automatic Dependent Surveillance Broadcast (ADS-B) IN, remained unaware of the incident until after the flight.

__________

1.  Eastern Standard Time (EST): Universal Coordinated Time (UTC) + 10 hours.
2.  Very-high frequency omni-direction Radio Range (VOR): A VHF radio navigational system which provides continuous indication of bearing from the selected VOR ground station.
3.  A CTAF is a radio frequency on which pilots operating in the vicinity a non-controlled aerodrome should make positional radio broadcasts.
4.  Area navigation (RNAV) approach: An approach flown along a path of GNSS waypoints.
5.  Runway number: the number represents the magnetic heading of the runway.
6.  If local atmospheric pressure information (QNH) was available, the MDA could be lowered by 100ft. QNH was available at the time via the Mangalore Aerodrome Weather Information Service.

Context

Meteorological information

Both the instructor in the Seminole and the pilot of the helicopter reported being in cloud during the occurrence. At 1600 (about the time of the incident), the Bureau of Meteorology’s automatic weather station at Mangalore Airport recorded overcast cloud with a base of 767 ft AMSL (300 ft above ground level).

Traffic alert and collision avoidance system

The traffic alert and collision avoidance system (TCAS II) fitted to the helicopter is designed to alert flight crews to possible conflicting traffic and to provide recommended escape manoeuvres. The TCAS identifies a three-dimensional airspace around the aircraft based on the closure rate of other transponder-equipped traffic.

TCAS alerts

If a potential conflict meets defined vertical and horizontal parameters, the TCAS generates a visual and aural alert. Two alert types are generated by the system, a traffic advisory (TA) and a resolution advisory (RA).

A TA is intended to assist a pilot in the visual acquisition of the intruder aircraft and prepare for a potential RA. This is presented to the pilot as a visual indication (Figure 4) supplemented by an aural alert.

Figure 4: Representation of the TCAS TA

Source: ATSB

The RA alerts provided recommended avoidance manoeuvres (in the vertical plane only) to either increase or maintain the existing vertical separation between aircraft. When generated, the recommended manoeuvring is displayed on the VSI (Figure 5). The target vertical speed may be displayed as a green line and the vertical speed range to be avoided is displayed in a red band. Some RAs only display the vertical speeds to be avoided and may not necessitate a change in flight path.

Figure 5: Example of a TCAS ‘monitor vertical speed’ RA

Source: ATSB

TCAS aural alerts are in the form a specific annunciation based on the nature of the conflict and response required of the pilot (Table 1).

Table 1: TCAS aural alerts (Federal Aviation Administration TCAS II booklet)

The helicopter operator’s procedures contained in the Babcock MCS Operations Manual (Part B) provided the following information for pilot response to TA and RA alerts:

Immediate manoeuvring is not required for Traffic Advisory (TA) information generated by TCAS II. Information on the display is provided as an aid to visually acquiring traffic. It is not a replacement for ATC instruction or ‘See and avoid’ techniques.

The recommended Pilot action on the activation of a Resolution Advisory [RA] is to immediately initiate a climb or descent as dictated by the TCAS II RA. The technique to achieve the requested profile will be dependent on the initial flight parameters such as airspeed, altitude, weight and guidance modes. On activation of an RA the Pilot should not initiate banking manoeuvres but attempt to fly the aircraft in accordance with the indication displayed on the vertical speed indicator.

Traffic display

The TCAS traffic display depicts the position of nearby traffic, relative to own aircraft. The information displayed includes vertical speed indications of traffic (Figure 6). Traffic are depicted using geometric symbols, depending on their threat status. A filled red square indicates an intruder that is the source of an RA.

An intruder’s relative altitude is displayed in hundreds of feet preceded by a plus (+) above the intruder symbol if it is above own aircraft or a minus (-) below the symbol if it is below own aircraft. When a target is reporting its altitude is changing by more than 500 feet per minute, an arrow to the right of its symbol indicates whether it is climbing (up arrow) or descending (down arrow).

Figure 6: Representation of the TCAS traffic display at the time of the RA

Note: The information generated for the Seminole shows it as an RA (red square) that is 500 ft below the helicopter (-5 below the red square) and climbing at more than 500 feet per minute (up arrow).

Source: Honeywell, annotated by ATSB

Resolution advisory inhibitions and manoeuvring

The United States Federal Aviation Administration (FAA) publication Introduction to TCAS II Version 7.1 describes the following inhibitions designed into the TCAS II system:

TCAS is designed to inhibit Increase Descent RAs below 1450 feet AGL; Descend RAs below 1100 feet AGL; and all RAs below 1000±100 feet AGL. If a Descend RA is being displayed as own aircraft descends through 1100 feet AGL, the RA will be modified to a Do Not Climb RA.

The TCAS aural annunciations are integrated with other environmental aural alerts available on the aircraft. The priority scheme established for these aural alerts gives windshear detection systems and ground proximity warning systems (GPWS) a higher annunciation priority than a TCAS alert. TCAS aural annunciations will be inhibited during the time that a windshear or GPWS alert is active.

The publication also describes the required response manoeuvring for an RA:

In modelling aircraft response to RAs, the expectation is the pilot will begin the initial 0.25 g^[7] acceleration maneuver within five seconds to an achieved rate of 1500 fpm. Pilot response with 0.35 g acceleration to an achieved rate of 2500 fpm is expected within 2.5 seconds for subsequent RAs.

The publication also stated:

During an RA, do not maneuver contrary to the RA.

The AW139 flight manual included a caution which stated:

The TCAS II may request climb or descent actions which would exceed aircraft limitation or put the aircraft in undesirable conditions (i.e. autorotation). The pilot should achieve a maximum climb or descent rate applicable for the aircraft condition and maintain this until the conflict is clear or an alternative manoeuvre is requested.

Helicopter operator training and knowledge

The helicopter operator’s pilots underwent TCAS training during AW139 type rating training and during recurrent (twice annual) simulator training. This training included both theoretical and practical components and incorporated various RA scenarios.

During the investigation, the ATSB discussed the pilot’s understanding of the required response manoeuvring and potential for this to result in a terrain collision with senior members of the operator’s flying operations and training department. The operator supported the pilot’s decision-making in manoeuvring contrary to the perceived descent RA. The operator also shared the pilot’s misunderstanding of the terrain inhibitions designed into the system and stated incorrectly that following an RA could jeopardise terrain separation. It was also stated that a flight path change from a high rate of climb to a descent is undesirable in a helicopter as it can cause a rotor over-speed. However, the aircraft flight manual states that in such a scenario, the instruction should not be disregarded, but instead ‘the pilot should achieve a maximum climb or descent rate applicable for the aircraft condition and maintain this until the conflict is clear or an alternative manoeuvre is requested’.

The ATSB reviewed the helicopter operator’s TCAS training program and materials. These were found to adequately address the system and recommended pilot response actions. However, the pilot’s reasoning during the occurrence and subsequent statements along with the operator’s statements indicated misunderstandings of the terrain inhibitions and required RA response manoeuvring.

Recorded data

The Seminole was not equipped with any form of flight data recording.

Helicopter

The helicopter (VH-YXH) was fitted with a digital flight data recorder and flight deck video recorder, both of which captured the occurrence. The aircraft’s TCAS unit also recorded occurrence data.

Flight data

The flight data showed activation of the TA at 15:56:25. At 15:56:33, the helicopter commenced climbing and, at 15:56:38, commenced a right turn. Two seconds after the turn commenced, the climb rate peaked at 608 feet per minute before reducing to zero 10 seconds after the turn had commenced. The helicopter climbed 84 feet during the conflict.

Figure 7: Graphical representation of flight data

Note: The resolution advisory was not captured as a 'Traffic Alarm’ by the flight recorder and is therefore presented as ‘False’ in the graphical representation of the flight data.

Source: ATSB

The data also captured the activation of the radio transmit switch from 15:52:49 until 15:53:02 (the selected radio frequency was not captured). At that time, the helicopter was about 10 NM north of Mangalore. This duration and timing was consistent with the broadcast stating the pilot’s intention to overfly Mangalore.

TCAS unit

The TCAS unit recorded the occurrence TA and RA alerts, the associated aural alerts (Traffic, Traffic, Monitor Vertical Speed and Clear of Conflict) and the intruder hexadecimal code^[8] from the Seminole’s transponder. Data indicates that at 15:56:45, separation between the aircraft reduced to a straight-line minimum of 451 m (543 ft vertically and 333 m horizontally).

Surveillance

Airservices provided surveillance data relating to the flight paths of the Seminole and the helicopter. The data captured both flights including the incident (Figure 8).

Figure 8: Representation of recorded surveillance data

Source: Airservices, Google Earth, annotated by ATSB

Communications

The Mangalore CTAF was not recorded.

Melbourne Centre air traffic control audio recordings for the time of the incident captured the crew of both aircraft being provided and acknowledging traffic information from ATC.

No broadcast was recorded on the Melbourne Centre frequency between 15:52:49 and 15:53:02, when the flight data from the helicopter showed a transmission being made. This indicates the broadcast made by the helicopter pilot at that time was very likely made on the Mangalore CTAF.

At 1556:25 (the same time as the TA), the air traffic controller contacted the helicopter pilot to confirm that the pilot had contacted the Seminole. The pilot responded ‘Just copied [the Seminole’s] last call (7 NM south of Mangalore) thanks. I’ve just got a traffic alert now, I’m going to climb to 5,000.’

__________

7.  G load: the nominal value for acceleration. In flight, g load represent the combined effects of flight manoeuvring loads and turbulence and can have a positive or negative value.
8.  The transponder fitted to VH-HMQ was programmed with a unique six-digit hexadecimal code.

Safety analysis

The incident

At 1553 on 6 June 2021, the helicopter (VH-YXH, HEMS3) was 10 NM north of Mangalore Airport tracking south to overfly the airport at 3,100 ft AMSL. At the same time, the Piper Seminole (VH-HMQ) was conducting the RNAV-Z runway 36 approach to the airport from the south.

The helicopter pilot was aware of the Seminole’s movements from its broadcasts and air traffic control (ATC) advice. Consequently, the pilot reviewed the approach chart and determined the Seminole’s approach path for landing. However, the pilot did not consider the possibility of a missed approach and did not recognise that the helicopter’s flight path conflicted with the Seminole’s missed approach path. Therefore, the pilot decided that it was not necessary to alter their flight path or communicate with the Seminole’s pilot to manage separation.

When ATC provided traffic information for the HEMS3 helicopter to the Seminole’s pilot, the timing of the student’s question resulted in the instructor not interpreting this information correctly. The instructor assumed the advice related to HEMS1, a helicopter with which separation had been coordinated about 15 minutes earlier.

The ATSB considered callsign confusion as a possible reason for the instructor’s misinterpretation of the traffic advice. The instructor in the Seminole did not hear the altitude or callsign of HEMS3 in the traffic advice provided by ATC. The ATSB determined that it was these factors, not callsign confusion, that led to the instructor incorrectly believing the traffic advice related to HEMS1.

Recorded flight and ATC data indicates the helicopter pilot very likely made a transmission on the Mangalore CTAF when 10 NM to the north. The pilot reported that this broadcast stated an intention to overfly the airport, the instructor in the Seminole reported not hearing this or any other broadcast from the helicopter.

Subsequently, the Seminole’s pilot (instructor) did not sight the runway at the missed approach point and conducted a missed approach, unaware of the approaching helicopter. The two aircraft passed 451 m of each other (in a straight line) during the missed approach.

Collision avoidance procedures

During the incident, the helicopter’s traffic alert and collision avoidance system (TCAS) generated a traffic advisory followed by a resolution advisory (RA). The TCAS was designed to inhibit RA alerts when response manoeuvring may lead to terrain conflict or RA aural alerts when ground proximity warning system alerts were being generated. Additionally, if RA response manoeuvring is required, this manoeuvring is not severe (0.25g up to 5 seconds after an alert is generated).

As the aircraft was climbing and the RA prohibited descents of 500 ft per minute or greater, the correct response to the RA generated in this case did not require any manoeuvring. However, the helicopter pilot misinterpreted the RA as commanding a descent toward the intruder (the Seminole). The pilot incorrectly believed that RA manoeuvring instructions could lead to terrain collision and therefore, did not want to descend below the lowest safe altitude. The pilot also thought that the manoeuvring to transition from the climb to a descent may startle others on board. As the intruder was below and approaching from the left, the pilot elected to continue climbing and turn right. While not prohibited by TCAS guidance, the turn reduced the climb rate, nullifying the intended climb away from the intruder.

While the pilot’s actions did not reduce aircraft separation or conflict with the RA presented, the reasons provided for not complying with the misinterpreted RA indicated that system inhibitions and required actions were not properly understood. Senior members of the operator’s flying operations and training department demonstrated a similar misunderstanding of the terrain inhibitions designed into the system. These personnel further stated incorrectly that the RA required response could have led to an undesired aircraft state, such as rotor overspeed. This demonstrated a misunderstanding of the intensity of the required response manoeuvring and the flight manual caution information. This flight manual caution advised pilots to adhere as closely as possible to TCAS instructions within aircraft limitations rather than to disregard the instruction when an adverse aircraft state could be encountered. While the training program and materials were found to adequately address the system, these misunderstandings, shared by both the pilot and the operator, indicate that the operator’s TCAS training with respect to RA alerts and response actions was ineffective in delivering these details to the operational flight crew.

When operating in non-controlled airspace (such as the current Class G airspace around Mangalore), whether under the instrument or visual flight rules, pilots hold responsibility for separation from other aircraft. A review of past occurrences indicates that self-separation using broadcast traffic advice has been a largely reliable procedure.

The ATSB does however note that the effectiveness of the current pilot-separation method relies on individual pilots:

• recognising a potentially unsafe situation
• formulating an effective separation plan that often requires coordination with the occupants of the other involved aircraft.

While on this occasion one of the involved aircraft was equipped with TCAS, this process is almost exclusively reliant on individual human actions without other mechanisms potentially acting as a safeguard and/or safety redundancy, and as such subject to human error, even when it involves experienced pilots. Furthermore, such errors often increase under high workload associated with, for example, instrument flying approach procedures, low experience or a busy airspace environment.

Of note, the airspace surrounding Mangalore Airport accommodates a complex mix of aircraft types and operations, while also being located close to several other non‑controlled airports.

In that context, while the available evidence in this investigation does not support a conclusion that the present self‑separation system is unsafe, there is an opportunity to potentially reduce safety risk further. 

In consideration of the above and the recently completed ATSB investigation AO-2020-012, mid-air collision south of Mangalore Airport, the ATSB supports systemic enhancements to the overall air traffic system that have been assessed by regulatory and air traffic specialists, in keeping with their obligations as providing a net overall safety increase. Key examples of such enhancements include:

• the increased use of controlled airspace and ADS‑B aircraft surveillance data (both by air traffic services and in‑cockpit)
• improved monitoring of air traffic movements (both quantity and complexity) to assist the identification of increasing risk areas.

With respect to this occurrence, had the aircraft been operating in controlled airspace they would have been positively separated, likely preventing the occurrence.

In September 2021, the CASA Office of Airspace Regulation (OAR) announced an aeronautical study into the airspace within a 25 NM area of Mangalore Airport, up to an altitude of 8,500 ft. The scope of this study involves:

• a review of traffic type and density over the previous 5 years
• an evaluation of the suitability and efficiency of the airspace
• review of the equitability of access to the airspace, the appropriateness of the airspace classification and the suitability of the existing services and facilities provided by Airservices Australia.

As of May 2022, this aeronautical study was still in progress.

Findings

From the evidence available, the following findings are made with respect to airborne collision alert system warning involving AgustaWestland AW139 helicopter, VH-YXH, and Piper PA-44-180 Seminole aircraft, VH-HMQ, overhead Mangalore Airport, Victoria on 6 June 2021

Contributing factors

• The helicopter pilot did not consider the possibility of the pilot in the Seminole conducting a missed approach and that it could conflict with the helicopter’s flight path.
• The Seminole’s pilot reported not hearing broadcasts from the helicopter and misinterpreted traffic advice from air traffic control. As a result, the pilot was not aware of the helicopter’s presence and that an incident had occurred.
• During the Seminole’s missed approach, aircraft separation reduced and resulted in the helicopter’s collision avoidance system generating alerts.

Other factors that increased risk

• The helicopter operator's traffic alert and collision avoidance system knowledge was inadequate with respect to resolution advisory alert terrain considerations and the required intensity of response manoeuvring. (Safety issue)

Safety issues and actions

Inadequate traffic alert and collision avoidance training 

Safety issue number: AO-2021-023-SI-01 
Safety issue description: The helicopter operator's traffic alert and collision avoidance system knowledge was inadequate with respect to resolution advisory alert terrain considerations and the required intensity of response manoeuvring.

Safety action not associated with an identified safety issue

Proactive safety action by Babcock Mission Critical Services Australasia

The helicopter operator has updated the flight crew training syllabus to include:

• A safety alert reminding all flight crew of the importance of proactive traffic separation management. This includes considering both the intended flight path of the conflicting traffic, and the possibility of a missed approach.
• Simulator training sequences developed that include consideration of a missed approach flight path to ensure traffic separation.
• Development of a simulator instructor guide. This guide includes scenario set up, teaching methods, and briefing topics to address threat and error management competencies related to flight crew consideration of conflicting traffic missed approach flight path.

Proactive safety action by Moorabbin Aviation Services

The Seminole operator implemented a non-technical skills education program. This included situational awareness, potential biases, and the dangers of student-instructional distractions, particularly during periods of high workload.

Glossary

Sources and submissions

Sources of information

The sources of information during the investigation included the:

• Seminole instructor
• helicopter pilot
• Seminole operator
• helicopter operator
• Honeywell Aerospace
• Airservices Australia
• United States Federal Aviation Administration
• the helicopter flight data recorder
• the helicopter flight deck video recorder

References

United States Federal Aviation Administration 2011, Introduction to TCAS II Version 7.1, Washington DC, USA.

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:

• Babcock Mission Critical Services Australasia
• Moorabbin Aviation Services
• Helicopter pilot
• Seminole instructor
• Airservices Australia
• Civil Aviation Safety Authority

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

Purpose of safety investigations The objective of a safety investigation is to enhance transport safety. This is done through: identifying safety issues and facilitating safety action to address those issues providing information about occurrences and their associated safety factors to facilitate learning within the transport industry. It is not a function of the ATSB to apportion blame or provide a means for determining liability. At the same time, an investigation report must include factual material of sufficient weight to support the analysis and findings. At all times the ATSB endeavours to balance the use of material that could imply adverse comment with the need to properly explain what happened, and why, in a fair and unbiased manner. The ATSB does not investigate for the purpose of taking administrative, regulatory or criminal action. Terminology An explanation of terminology used in ATSB investigation reports is available here. This includes terms such as occurrence, contributing factor, other factor that increased risk, and safety issue. Publishing information  Released in accordance with section 25 of the Transport Safety Investigation Act 2003 Published by: Australian Transport Safety Bureau © Commonwealth of Australia 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.