Collision with terrain

​Executive summary

What happened

On the morning of 23 February 2022, a Piper Aircraft Corporation PA-25-235/A9, registered VH‑SEH, was conducting agricultural spreading operations from a private landing area located near Seaview, Victoria. At 0711, the pilot commenced take-off for the first load of the day. The aircraft accelerated along the prepared strip and briefly became airborne. The outboard section of the aircraft’s left wing impacted trees and detached from the aircraft. The aircraft rolled to the left, pitched down, and collided with terrain. The pilot, who was the sole occupant, was fatally injured and the aircraft was destroyed.

What the ATSB found

The ATSB found that the take-off was attempted at an aircraft weight that likely did not permit sufficient performance to clear the trees at the end of the strip. Although the pilot had conducted take-offs using the Seaview runway strip in previous years, the increased height of trees at the northern end of the strip were found to have reduced safety margins to some extent.

It was also identified that engine power during take-off may have been slightly lower than normal. This may have been due to the water content of the air, carburettor ice, or the carburettor heat selector may have been inadvertently left on during the take-off. However, a conclusion regarding the existence of these scenarios could not be drawn with any certainty.

The ATSB also found that the pilot likely initiated a jettison of the hopper contents shortly after becoming airborne, but any effect this had on the aircraft’s performance was probably negligible.

Safety message

Aircraft operators and pilots are reminded of the hazards associated with operations from small landing areas that are not prepared as permanent runways. In any case, pilots should ensure aircraft loads are within specified limits, appropriate for the environmental conditions, and will result in the required performance to maintain safety margins.

The investigation

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

The occurrence

On 23 February 2022 at about 0650 local time, the pilot of a Piper Aircraft Corporation PA-25-235/A9, registered VH-SEH, departed Leongatha Aerodrome, Victoria, for a positioning flight to a private landing area[1] situated 25 km to the north in the locality of Seaview. The aircraft was reportedly carrying full fuel (170 L) prior to take-off.

The aircraft landed at about 0700 in preparation for the aerial spreading of superphosphate pellets. The pilot had been tasked to spread 41,000 kg of superphosphate fertiliser at 6 nearby properties. It was anticipated this would take about 80 loads and 8 hours to complete.

The loader driver[2] for the day’s activities arrived at the Seaview landing area at about 0705. On arrival, the loader driver found VH‑SEH parked with the engine stopped and the pilot out of the aircraft. The pilot had filled the loader’s bucket with superphosphate prior to the arrival of the loader driver.

The loader driver and the pilot had a short conversation and the pilot returned to the aircraft. The loader driver transferred the superphosphate to the aircraft’s hopper with the pilot on board the aircraft. The loader driver could not see how much superphosphate had been loaded into the bucket, and the weighing system in the loader only indicated weight at the time of filling the bucket.

The loader driver then parked the loader at the southern end of the landing area and prepared for the next load. A short time later, the pilot started the aircraft’s engine and remained at the southernmost point of the landing area for about 5 minutes.

Based on local weather observations and a witness’s video recording of the take-off, the weather at the time of the accident was fine with the wind likely calm. The loader driver described the weather conditions at the time as good.

According to witness reports, the pilot was wearing a 4-point harness and a helmet. Data from an onboard GPS device showed that the pilot commenced the take-off on the prepared runway strip at about 0711 (Figure 1).

The runway strip went downhill, and then uphill, where it branched into 2 sections. According to the 2 witnesses and the recorded video, the aircraft accelerated along the strip and traversed the right section where the strip divided.

The aircraft briefly became airborne at a point at the end of the strip where the terrain dropped away. The outboard section of the aircraft’s left wing then impacted trees and separated the left outboard section of wing. The aircraft rolled to the left, pitched down, and collided with terrain about 30 m beyond the trees (Figure 2). The pilot was fatally injured and the aircraft was destroyed.

Figure 1: Runway strip overview

Source: ATSB

Figure 2: End of runway strip and impact points

 Source: ATSB

Context

Pilot information

The pilot held a valid class 1 aviation medical certificate and a commercial pilot licence (aeroplane), having completed a flight review and an aerial application proficiency check on 11 November 2021. At the time of the accident, the pilot had about 12,350 hours total aeronautical experience. The pilot was the owner and chief pilot of the aerial work operator, which conducted mostly aerial application activities.

The pilot was reported to be fit and healthy and there was no indication they were experiencing a level of fatigue known to affect performance. The post-mortem and toxicology examinations did not identify any indicators of incapacitation or substances that could have affected the pilot’s capacity to perform the flight.

Aircraft information

General information

The aircraft was a 2-seat Piper Pawnee PA-25-235/A9 with a 6-cylinder, normally aspirated Textron Lycoming O-540-H2A5 engine driving a 2-blade McCauley Propellers 1A200/FA8452 fixed-pitch propeller (Figure 3). This propeller was designed for increased efficiency during cruise compared with other propeller options, but also resulted in decreased climb performance and increased the take-off distance required. The propeller was first installed on the aircraft in March 2019.

Figure 3: A similar Piper PA-25-235/A9 configured for agricultural spreading

Source: ATSB

The aircraft was originally manufactured as a single-seat PA-25-235 in 1974. In 1988, the aircraft was involved in an accident while conducting herbicide spraying near Deddick Park, Victoria. The outboard section of the right wing collided with a tree. The aircraft climbed steeply then descended in a nose-down attitude and impacted terrain.[3]

In 1989, the aircraft was rebuilt and converted to an ‘A9’ variant. This conversion included the installation of a second seat (in a side-by-side configuration), replacement of the fabric-covered wings with metal wings, the installation of a larger chemical hopper, and the fitment of a larger Lycoming O-540-H2A5 engine. Flying controls were on the left side.

The engine was last overhauled in March 2021, and the last periodic inspection was carried out in July 2021 with no defects recorded. At the time of the accident, the aircraft had accumulated 9,543.5 hours total time in service, and the engine had accumulated 159 hours since overhaul.

Aircraft hopper

The hopper was located between the instrument panel and the engine firewall. It was constructed from fiberglass and had a 544 kg maximum permissible load. Its volume (200 gallons, or 757 L) was sufficient to hold up to about 800 kg of superphosphate pellets. There was a clear section in the cockpit, with graduations in gallons, to enable the pilot to see how much volume of product was in the hopper.

The quantity of superphosphate on board the aircraft during the take-off could not be determined. Those familiar with the recent operating practices of the pilot of the accident flight reported that, if weather and strip surface conditions were favourable, it was normal for the pilot to take a full load of superphosphate on the first flight from a landing area. Otherwise, the pilot would normally opt to take a reduced load on a first flight. A typical reduced load for this pilot was reported as being about 400 kg.

The aircraft was fitted with an emergency hopper dump mechanism. The mechanism allowed a pilot to dump all or part of the hopper contents if the aircraft did not achieve the required performance. To do so, the pilot would push a button on the spread/dump lever (to enable the lever to move past a gate) and move the lever past the spread selection to the full forward position. This would fully open the hopper door located on the underside of the aircraft fuselage. A full load of superphosphate was expected to completely jettison in about 4 seconds. Dumping the hopper load would significantly, and almost immediately, reduce the aircraft’s weight and increase performance.

The total elapsed time from the aircraft becoming airborne to impacting the trees was 2 seconds.

Performance

The approved flight manual for VH‑SEH contained take-off performance charts that could be applied to calculate a performance-limited maximum take-off weight using aircraft and environmental parameters for a given flight. These charts included a wet or dry surface and long or short grass. Such charts had reduced applicability for landing areas with significant changes in slope, and rough surface conditions were not captured by the charts. The aircraft operator’s operations manual (OM) contained the responsibilities for company pilots. The OM stated:

In determining that an operation can be conducted safely, the pilot will consider:

 

a) carriage of heavier than manufacturers’ recommended weights

b) strip length and conditions, particularly in relationship to the performance parameters of the particular aircraft used by the Company

c) strip altitude and density altitude

d) wind speed and direction, especially any downwind component

e) obstacles

The OM also stated:

Pilots are responsible for the safety of the aircraft. Many accidents have loading as a causal factor. That is, the aircraft may have flown off the same landing area with the same load but slightly different environmental conditions. The decision to dump a load may be relatively cheap when compared to repairing an aircraft. The ability to dump the load is the last line of defence in the accident chain but it remains a very good defence and should be used as required. Pilots should make a conscious decision on each take off about how much load they will take and at what stage they will either abort take-off or dump the load in the event that the aircraft fails to become airborne at the expected time. To make this decision, pilots should have firmly in their mind where the aircraft should get airborne.

The ATSB undertook performance calculations using known and estimated aircraft and environmental information, including fuel and hopper loads. It was estimated that the aircraft was probably near the performance-limited maximum take-off weight for a level (no slope) strip the same length as the actual strip, without any load in the hopper. Using an estimated weight range for the hopper load of 400–544 kg, the aircraft would have been over the performance-limited maximum take-off weight for an equivalent-length level strip. This range of hopper loads would have resulted in a take-off weight of about 1,400–1,544 kg. The aircraft’s maximum take-off weight was 1,315 kg.

Carburettor heat

Carburettor icing occurs when water vapour freezes within an engine’s carburettor due to a decrease in temperature and pressure within the carburettor. The likelihood of carburettor icing increases with humidity and at partial power settings (for example, when idling). If ice accumulates within a carburettor, the flow of air to the engine (and, ultimately, available power) reduces.

A carburettor heat control was available in VH‑SEH. When selected, warm air was directed from a heat exchanger on the exhaust system to the carburettor inlet, melting any ice in the carburettor. The operator’s other pilots reported that it was standard practice to apply carburettor heat during ground operations, selecting it off just prior to commencing the take-off. The purpose of this practice was to prevent carburettor ice build-up during engine idling.

It was reported that the application of carburettor heat in VH‑SEH would result in a propeller speed reduction of about 100 RPM and, if inadvertently left on during take-off, would significantly increase the take-off distance required. Due to the level of damage, the ATSB could not determine the position of the carburettor heat control at the time of the accident or whether carburettor icing occurred during the take-off.

Water vapour and engine performance

High concentrations of water vapour within the air (a high relative humidity) can impact engine performance. The water vapour alters the fuel to air ratio, causing enrichment, as well as reducing the burning and cooling efficacy of the engine. This reduces the power output of engine and may increase the take-off distance required. The ATSB could not determine the relative humidity at the landing area at the time of the accident (see also Weather information).

Runway strip

The runway strip at Seaview was prepared annually for aerial agricultural operations by the operator of VH‑SEH. The prepared strip had been mowed into a ‘Y’ configuration by the pilot of the accident flight in the days before the accident. It consisted of mowed grass and the surface was hard and rough from previous cattle movements. The strip was at an elevation of about 1,100 ft above mean sea level (AMSL) and each branch provided about 360 m take-off and landing distance on the ground.

Take-offs were always conducted in the same direction due to the more downwards slope. In this direction, the strip followed the natural terrain, with a downwards then upwards slope before dropping steeply towards the stand of trees. The left branch was oriented to the left of the trees and the right branch was oriented directly towards the trees (Figure 4).

Figure 4: Runway strip ‘Y’ intersection showing the left and right branches with the trees at the runway’s end

Source: ATSB

The pilot had not operated from this strip for at least 2 years prior to the accident. It was reported that the trees at the end of the strip had grown about 3–10 ft during that time. The pilot was reportedly aware of the hazard presented by the trees, having commented on their growth over the years. In the days prior to the accident, the pilot had communicated their intent to use the right side of the prepared strip for the day’s operations. Another of the operator’s pilots reported preferring the left branch of the strip in order to avoid the trees. The reasons for the accident pilot’s preferred use of the right branch could not be determined.

Site and wreckage

The wreckage was located about 30 m north of the stand of trees at the northernmost end of the strip. The trees were about 90 ft in height above ground level (AGL). Damage to the trees indicated the left wing impacted the trees at a height of about 74 ft AGL. Examination of the accident site indicated the aircraft impacted the ground inverted with an angle of entry of about 50° with the left wing low, and came to rest about 8 m from the initial impact point. The cabin sustained significant damage (Figure 5). Significant curved compression damage was evident on the leading edge of the left wing consistent with tree impact damage (Figure 6).

Figure 5: Aircraft wreckage

Source: ATSB

Figure 6: Outboard section of left wing with tree impact damage

Source: ATSB

The hopper door was open, and superphosphate had spilled from the hopper with most in the vicinity of the fuselage. Superphosphate was also found in smaller quantities near the initial impact point with the trees and scattered from halfway between the aircraft’s point of take-off to the wreckage site. The scattered pellets were consistent with a pilot-initiated release (and not post-impact scatter); however, it could not be determined if the mechanism had been activated in the spread or emergency dump position. The position of the spread/dump lever at the time of impact could not be determined.

Examination of the propeller, along with ground marks, indicated the propeller was rotating under power at the time of impact.

External examination of the engine did not identify any obvious defects. The engine tachometer displayed a needle ‘slap mark’[4] indicating about 2,240 RPM.[5] The throttle position at the time of impact could not be determined due to disruption of the controls.

There were no evident pre-impact defects with the aircraft structure and flight control continuity was confirmed as far as possible. The flap handle was in the top notch, indicating full flap. The operator’s other pilots reported that it was normal practice to apply full flap at the lift-off point, followed by a gradual reduction of flap setting as the aircraft climbed away.

ATSB analysis (based on estimates of the aircraft’s speed, impact angle and damage to the aircraft) indicated the impact forces for this type of accident would normally be expected to result in fatal injuries irrespective of any safety equipment worn.

Weather information

Recorded meteorological data for the landing area was not available. The weather conditions captured on the video recording made by a nearby witness included no cloud, visibility greater than 10 km and wind calm.

At the time of take-off, there was no fog at the landing area, there was a layer of fog in a nearby valley below the landing area. Given the proximity of the fog (saturated airmass), it indicates that conditions conducive with reduced engine performance and/or carburettor icing may have been present at the landing area. Recorded information

Accident video

The video recording captured by the witness was 30 seconds in length and commenced 6 seconds prior to the initiation of the take-off roll, ceasing 1 second after the aircraft impacted trees. No anomalies were evident in engine sound recorded on the video, such as rough running or power reduction during the take-off roll.

Audio spectrogram analysis of the video recording indicated that the aircraft’s propeller speed was likely about 2,357–2,587 RPM during the take-off roll, and this was maintained until the collision with the trees. The operator’s other pilots indicated that a typical propeller speed for VH‑SEH during take-off was about 2,500 RPM.

Global positioning system

A Tracmap Aviation TMA384 GPS device was recovered from the accident site and the stored data was downloaded. The data captured the aircraft’s arrival at the Seaview landing area, and the moments prior to take-off, but the device did not capture the subsequent take-off or the accident sequence. This was probably due to power supply disconnection during impact, preventing data being written to the memory card.

Safety analysis

The accident flight was the first load of the day and the aircraft had almost full fuel on board. Although the amount of superphosphate loaded onto the aircraft could not be determined, it was likely that the aircraft’s weight exceeded the performance-limited maximum take-off weight for the strip as well as the aircraft’s documented maximum take-off weight. This likely degraded the aircraft’s take-off performance significantly and contributed to the aircraft being unable to clear the stand of trees downslope of the lift-off point.

Additionally, the tachometer slap mark and the audio spectrogram analysis of the video recording indicated the power generated by the engine during the take-off may have been slightly lower than normal. No obvious defects were identified with the engine and the propeller was rotating under power at the time of impact. The relative humidity at the time of take-off could not be established. However, it is possible the aircraft’s engine performance was negatively impacted by the volume of water present within the air, affected by carburettor ice, or the carburettor heat selector may have been inadvertently left on during the take-off. Although these scenarios could explain a reduced propeller speed, there was insufficient evidence available to determine whether these events took place.

Although the pilot had conducted take-offs using the Seaview runway strip in previous years, the increased height of trees at the northern end of the strip had reduced safety margins to some extent. The aircraft struck the trees about 16 ft from the top, which meant that even without their estimated 3–10 ft extra height, there would not have been sufficient clearance for a safe take-off.

The investigation was unable to determine why the pilot elected to prepare, and use, a strip orientated directly towards the trees when an alternate take-off option was available.

A limited number of superphosphate pellets were found scattered between the aircraft’s point of take-off and the location where the aircraft impacted the ground. This indicated the pilot likely attempted to jettison the hopper contents around the time of becoming airborne. However, the effect this jettison would have had on the aircraft’s performance was probably insufficient for it to clear the trees, given that it would have had to gain about 16 ft in 2 seconds with some of the load still on board.

Findings

ATSB investigation report findings focus on safety factors (that is, events and conditions that increase risk). Safety factors include ‘contributing factors’ and ‘other factors that increased risk’ (that is, factors that did not meet the definition of a contributing factor for this occurrence but were still considered important to include in the report for the purpose of increasing awareness and enhancing safety). In addition ‘other findings’ may be included to provide important information about topics other than safety factors.  These findings should not be read as apportioning blame or liability to any particular organisation or individual.

From the evidence available, the following findings are made with respect to the collision with terrain involving Piper PA-25, VH-SEH, near Seaview, Victoria, on 23 February 2022.

Contributing factors

• The take-off was attempted at an aircraft weight that did not permit sufficient performance to clear a stand of trees downslope of the lift-off point. As a result, the aircraft impacted the trees and collided with terrain.

Other factor that increased risk

• Although successful take-offs had been made using the prepared strip in previous years, the increased height of trees at the end of the strip reduced the safety margins over time.

Other findings

• The pilot likely attempted to jettison the hopper contents shortly after becoming airborne. However, the jettison would have only been partially completed by the time the aircraft collided with the trees, and there had probably been insufficient time for the aircraft to gain enough height to clear them in the intervening period.

Sources and submissions

Sources of information

The sources of information during the investigation included the:

• Bureau of Meteorology
• operator, 2 of the operator’s other pilots and loader driver
• Civil Aviation Safety Authority
• Victoria Police
• maintenance organisation
• witness and witness video.

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 Civil Aviation Safety Authority
• the operator.

A submission was received from a party familiar with the operator’s activities. The submission was reviewed and, where considered appropriate, the text of the report was amended accordingly.

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

Read the Safety Advisory Notice: UH-1H helicopter main drive shaft failure

The investigation

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

The occurrence

On the morning of 19 December 2021, at the Redcliffe aircraft landing area, Queensland, a Rockwell International 114 aircraft, registered VH‑WMM, was being prepared for a local private flight under visual flight rules.[1] On board for the flight were the pilot and 3 passengers. The weather conditions and visibility were good, with light winds from the east.

Closed circuit television (CCTV) showed the pilot conducting a pre-flight inspection of the aircraft. This included draining a small amount of fuel from each fuel tank drain to check for any water contamination and using a dipstick to check the fuel tank quantity of each tank. 

A passenger video (see Appendix - Sequence of events) was recovered from a mobile phone which showed portions of the taxi, before take-off checks, and the accident flight. Several witnesses at the airfield, in boats near the airfield, and in other aircraft also observed the flight of VH-WMM (Figure 1).

Before the take-off, passenger video showed the pilot conducting before take-off checks (from memory) and did not show the use of any written checklists. While conducting the engine run-ups, the pilot perceived a technical difficulty with the aircraft, and the checks were paused. After notifying a ground crew member by phone, the pilot taxied back toward the ground crew who was walking towards the aircraft on the taxiway. The ground crew member recalled that through hand signals, the pilot identified the issue as misidentification of the mixture control for the propeller pitch control and communicated that they had identified and corrected the problem.

The pilot then taxied again for runway 07 without continuing or restarting the interrupted before take-off checks and continued direct to the runway holding point. The occupants of VH-WMM then discussed where other traffic was in the circuit, before entering and backtracking to the end of the runway. VH-WMM then turned and commenced the take-off at 0908 local time.

After take-off from runway 07,[2] the aircraft’s undercarriage and flaps were retracted, and 62 seconds later, while in a left climbing turn, the engine RPM started to fluctuate, followed by a large drop in engine power 3 seconds later. The (adult) passenger, seated on the rear-right side of the aircraft then asked the pilot about fuel coming out of the top of the right wing; however, the pilot did not respond to the question. The video also did not indicate the pilot conducting any engine troubleshooting activities. The pilot made 2 further left turns, which were consistent with manoeuvring the aircraft back toward the western end of runway 07 (Figure 1), and the stall warning sounded twice. About 17 seconds after the power reduction (1 minute 31 seconds after take-off), the engine stopped. 

Four seconds later, the video recorded the undercarriage warning bell followed by the stall warning. Based on the recorded sounds, it is likely the pilot responded by lowering the landing gear. Another pilot who was on final approach for runway 07 heard the pilot of VH-WMM broadcast on the radio that they were returning to the airfield.[3] 

Figure 1: Redcliffe aircraft landing area and VH-WMM approximate flight path and accident site

Source: Google Earth, annotated by the ATSB

Over 24 seconds, the stall warning sounded another three times, followed by a turn directly toward the runway and then further stall warnings, two successive drops of the right wing and then the sounding of the ‘stall’ voice alert.

Three seconds later, as the aircraft neared the mangrove tree line to the north of the airfield, it contacted the water, about 170 m from the shoreline. The aircraft overturned and came to rest inverted in about 2 m of water. 

The pilot of another aircraft that was inbound to Redcliffe who had also heard the pilot of VH‑WMM make the returning to the airfield call, was alerted to the possibility of an accident from an unknown person on the radio upon arrival. After observing an aircraft in the water, the pilot contacted Brisbane air traffic control (ATC) to advise them of the accident. The pilot remained overhead the accident site while boats arrived at the scene and continued relaying information to ATC. 

Witnesses at the airfield and on nearby boats contacted emergency services and the Australian Volunteer Coast Guard. After being notified by a witness on a kayak, a nearby vessel made its way to the aircraft, arriving about 5 minutes after the accident. Following the impact with water, the inverted orientation of the aircraft meant that the door handles were submerged. First responders reported that it was difficult to locate the handles to open the doors from the outside. When inverted on the seabed in mud and silt, the upper door latches were also unable to be located. The disturbance of the mud/silt further reduced visibility of the exits and their operating handles. 

A coast guard vessel arrived onsite; however, the crew were also unable to gain access into the aircraft’s cabin. Queensland Police Service divers arrived at the aircraft about 2 hours after the accident. They observed the water to be about 1.5 m deep. Upon entering the water, police observed that visibility was very poor. The pilot’s door was shut and could not be opened. The right door was unlocked and slightly ajar, and police were able to open the door with some difficulty. The pilot and 3 passengers were fatally injured, and the aircraft was destroyed. 

Context

Pilot information

The pilot held a valid Private Pilot Licence (Aeroplane) and a Class 2 aviation medical certificate, valid until February 2023. The pilot held single and multi‑engine aeroplane ratings and endorsements for manual propeller pitch control, retractable undercarriage, and formation flying. At the time of the accident, the pilot had logged 334.3 hours in VH-WMM and had about 505 hours total aeronautical experience. 

The flight instructor who conducted the pilot’s last flight review in July 2021 stated that the pilot was assessed on engine failure after take-off. They also described that the assessed procedures on that review were similar to the accident flight, insofar as location of engine power loss and the actions that were to be taken as a result. During the flight review, the pilot had performed all actions to a satisfactory level.  

Pilot medical history

A review of the pilot’s Civil Aviation Safety Authority (CASA) medical file identified that the pilot had disclosed a hypertension condition and that they had been prescribed medication for it but did not list any other health issues or concerns.

Discussion with the pilot’s next-of-kin and general practitioner (GP) identified that the pilot was a long term, type 2 non-insulin dependent diabetic. The pilot had been prescribed medication for at least 10 years with medical records indicating tracked blood glucose readings back to January 2003, and an immediate family history of non-insulin dependent diabetes. The pilot had also been diagnosed with high cholesterol and had been prescribed medication for its treatment. The GP was also aware of a family history of heart disease. 

Of the last 3 CASA aviation medical examinations, the pilot had not declared their high cholesterol, diabetic status, and diabetes medication to their CASA designated aviation medical examiner (DAME), however had disclosed family history of both diabetes and heart disease to the DAME. Regarding the question in relation to diabetes on the pilot’s pre-examination medical history, the pilot indicated ‘unsure’, which was later changed by the DAME to ‘no’ during the examination.

Toxicology reports showed that the pilot of VH-WMM had detectable quantities of several substances, including a prescribed medication, paracetamol, and an over-the-counter sedating antihistamine. A carbon monoxide concentration of less than 5% was also detected in the analysis.

The ATSB sought advice from a specialist toxicologist regarding the potential effects the detected substances may have had on the pilot during the accident flight. The advice indicated that the level of antihistamine detected in the samples was low and suggested the drug had been used between 12 and 24 hours prior to the accident. They also reported that although the medication the pilot had been prescribed may have increased the sedating effects of the antihistamine, given the low levels detected it was unlikely there was any significant impairment of the psychomotor skills[4] required to fly an aircraft.

The specialist toxicologist also identified that there may have been an interaction between the multiple antihypertensive medications that the pilot had been prescribed[5] to lower blood pressure. However, from the passenger video it was noted that the pilot did not appear to be physically incapacitated, so it is very unlikely the pilot experienced any form of incapacitation prior to the accident.  

Aircraft information 

General information

The Rockwell International 114 is a 4-seat, single-engine aeroplane with fully retractable, trailing link undercarriage. It is powered by a 6-cylinder Lycoming IO-540 fuel-injected engine and is fitted with a 3-blade constant-speed propeller. Passenger and pilot access is by a door on each side of the aircraft cabin (Figure 2).

VH-WMM was manufactured in the US in 1977 and was first registered in Australia in May 2013. The last periodic inspection was conducted on 7 July 2021. At the time of the accident, VH-WMM had accrued a total time in service of 3,431.4 hours and had flown about 11 hours since the last inspection.

Figure 2: VH-WMM

Source: Nathen Sieben, annotated by the ATSB 

Fuel system

The Rockwell 114 fuel system consists of 2 integral (wet wing)[6] fuel tanks, 1 in each wing, with a fuel gauge for each tank located in the cockpit. The fuel capacity is 132.5 L for each tank, with 128 L considered usable. Both fuel tanks supplied the engine through the fuel selector, gascolator,[7] electric fuel pump and an engine driven fuel pump. The fuel selector valve had 5 positions, which allowed the pilot to select OFF, LEFT, BOTH, RIGHT and OFF positions. 

The last refuelling of VH-WMM occurred before a flight on 16 October with an uplift of about 120 L of AVGAS, taking the total quantity to about full tanks. VH-WMM was then operated for about 2.2 hours over 2 flights, prior to the accident flight. On the day of the accident, the ATSB calculated that about 115 L of fuel remained on board, equivalent to about half tanks. 

CCTV at Redcliffe airfield showed that prior to the flight, the wings of VH-WMM were not level while parked on the tarmac. The right wing at the tip was about 60 cm lower than the left, indicating a fuel imbalance, where the right wing contained a greater fuel quantity than the left wing. The right-wing low condition indicated that fuel crossflow from the left to right fuel tanks may have occurred while VH-WMM was hangered. 

It is a known issue with the Rockwell International 114 that when the fuel selector is not placed in the OFF position when parked, fuel can flow from one tank to the other. Once a crossflow has started, the increasing fuel weight will also increase the lean of the aircraft, further promoting the fuel crossflow. This results in further uneven fuel distribution, and sometimes an overflow of fuel through the wing tank fuel vents when this imbalance fills one tank completely. The ‘local fix’ amongst the Rockwell 114 community to prevent the crossflow was to set the fuel selector to OFF when the aircraft was parked for an extended period of time. The possibility of fuel crossflow in VH-WMM was also known to the pilot. 

A review of the aircraft’s logbooks showed that in April 2011, a maintenance intervention was performed on the fuel system due to a crossflow defect occurring when the fuel selector was set to BOTH fuel tanks. The fuel selector position of VH-WMM was unknown prior to the day of the accident, however it is likely that it was not selected to the OFF position.

Undercarriage system

The Rockwell 114 is equipped with a hydraulically operated undercarriage. The aircraft is fitted with an undercarriage warning system. A switch is mounted on the throttle quadrant which connects to an undercarriage warning bell, activating whenever the throttle is brought to idle while the undercarriage is retracted. 

Stall warning

The Rockwell International 114 is fitted with an aural stall warning system, that provides an audible tone to indicate that the aircraft speed is slowing to a speed that it can no longer produce lift in flight.

On board video recorded the stall warning sounding 13 seconds after the engine experienced the large drop in power. The stall warning continued sounding intermittently throughout the remainder of the flight, indicating that the aircraft was only marginally maintaining airspeed above the stall speed. The stall warning horn activated multiple times during the final approach until impact with water. This indicates that the aircraft would have been within 3-4 kt of the straight and level flapless stall speed of about 63 kt.

VH-WMM was also fitted with a voice alert system. This unit was an electronic device which detected the activation of the existing aircraft stall and undercarriage warning systems. It was configured to place a voice warning directly into the pilot headset and through a built-in speaker in the unit itself. In this situation, a pilot who may not hear the aircraft-generated stall warning horns because of noise cancelling headsets, will have an electronic voice annunciation of the warning. 

A witness who had flown with the pilot previously described the system as functional and that it was an effective warning tool. The passenger video detected one annunciation of ‘stall’ from the built-in speaker, just prior to impact. It is unknown if the system was alerting the pilot through the headsets during the flight, however it is likely that the system was functioning, as other pilots who had been on board for previous flights had observed its operation.

Engine information

The engine fitted to VH-WMM was last overhauled in July 1998 and had accrued about 988 flight hours in operation. The overhaul schedule as listed in Lycoming Service Instruction SI 1009BE was 12 years or 2,000 hours, whichever occurred first.  

Although the engine had exceeded the calendar schedule of the manufacturer’s time between overhaul, this was permissible when the engine was maintained in accordance with the CASA on‑condition[8] requirements. At the last annual inspection in July 2021, the maintenance organisation had completed a piston engine condition report verifying the engine serviceability, which then permitted the engine to continue in service.

Site & wreckage information

Onsite examination

The wreckage was located about 1 km north of the Redcliffe airfield, on a tidal flat (Figure 3). The accident occurred about 40 minutes before high tide, and the water depth at the time of the accident was about 2 m. The aircraft impacted the water on a heading of about 218° in an upright, slight right-wing low, nose-down attitude, with the undercarriage in the extended position, and with the wing flaps retracted. 

Ground scars observed on the tidal flat indicated that after entering the water, the aircraft nose wheel and propeller contacted the seabed leading to the aircraft overturning, resulting in sudden deacceleration and the aircraft coming to rest inverted. Witnesses described the water directly around the aircraft to be murky due to the mud and silt seabed having been disturbed by the aircraft impact. The left door (pilot door) was in a closed and latched condition when the ATSB arrived onsite. The right door was found by police divers to be slightly ajar, and difficult to open during the recovery operation. 

Figure 3: VH-WMM accident site at low tide

Source: ATSB

The aircraft fuselage underside and right wing showed evidence of hydraulic[9] compression from impacting the water surface, and the engine had separated from the aircraft. The impact to the fuselage underside damaged the fuselage skins forward and aft of the wing main spar carry‑through, resulting in a large hole. The engine firewall had been punctured by the engine and the left rear side window was broken. The identified damage would have allowed water ingress into the fuselage. Fuel was visibly leaking from the right underwing fuel vent, and a strong fuel smell was evident at the site. 

Wreckage examination

The wreckage was recovered to a secure storage facility for a detailed examination. ATSB investigators established flight control continuity before the rear of the fuselage and empennage were separated to facilitate transport from the recovery point.  

A further flight control examination was performed with no defects noted. All components of the aircraft were identified and accounted for, and no pre-existing defects were noted with the airframe or engine.

Fuel system examination

Examination of the aircraft fuel system was carried out and found that the fuel selector was set to the LEFT tank at the time of the accident, and the auxiliary fuel pump was switched OFF. The gascolator was disassembled and contained water. After recovery of the wreckage, the fuel tanks’ contents were drained and consisted of:  

• right wing: about 85 L of AVGAS recovered, with no visible water
• left wing: about 25 L of water, with no visible AVGAS.

Engine & propeller examination

The engine and propeller displayed no pre-existing damage. The propeller damage was indicative of low rotational energy at the time of impact and exhibited damage to the blades and spinner due to impact with the seabed. The engine was externally examined, all components were accounted for, and the engine was able to be rotated. The engine was disassembled and examined at a CASA-approved engine overhaul facility under the supervision of the ATSB. The engine showed no evidence of pre-impact mechanical discontinuity or defects which would inhibit normal operation. 

Examination and testing of the engine fuel system was performed at a separate CASA-approved overhaul facility under ATSB supervision. Some system components had internal corrosion; however, this was most likely due to saltwater immersion. After removal of the corrosion, the system components tested correctly for operation. 

The fuel control unit (FCU) initially could not be tested. A disassembly of the FCU found internal corrosion within the regulating system and the centre body seal was found to be separated. The centre body seal was examined at the ATSB’s technical facilities in Canberra. ATSB determined that the internal seal separation had occurred when the FCU was disassembled for examination and was not a prior defect. 

Rockwell 114 procedures

Before take-off checklist 

At each critical phase of aircraft operation, pilots refer to checklists to guide them through specific items to configure the aircraft for the next planned phase of the flight. The Rockwell 114 pilot’s operating handbook (POH) [10] stated in 3 separate checklists,  ‘interior’, ‘before starting engine’, and ‘before take-off’ checklists, that the fuel selector valve is to be set to the BOTH position before the aircraft is ready for take-off.

Figure 4 shows the Rockwell 114 ‘before take-off’ checklist as detailed in the POH. Annotations highlight where the interruption occurred at the beginning of the accident flight, and the steps not completed as identified in the passenger video. The POH was located at the accident site at the rear of the pilot seatback, and passenger video showed that it was not accessed during the before take-off checks or during the flight.

Figure 4: Before take-off checklist

Source: Rockwell 114 pilot’s operating handbook, annotated by the ATSB

Third-party checklists

CCTV footage showed the pilot passing a folder to the adult passenger who placed it into the rear of the pilot seatback prior to engine start. This folder was found on-site in the rear of the pilot seatback pocket and contained the third-party checklists inside. Both of these checklists had interpretations of the Rockwell 114 POH checklists and had differences to the approved manufacturer’s documentation. This included changes in the checklist sequence, and omissions of some elements including the absence of one of the fuel selector checks. 

CASA issued AC 91-22v2.0 Aircraft checklists, in November 2021 to provide guidance on establishing and using aircraft checklists and is derived from Civil Aviation Safety Regulation 91.095 Compliance with flight manual. This stated that any third-party checklists ‘must concisely convey each procedural step in correct sequence’ to ‘ensure aircraft are operated in a way that meets flight manual requirements and limitations.’ 

The US Federal Aviation Administration released a safety alert for operators (SAFO) 17006, in April 2017, warning pilots and operators of the risks of using commercially available and personally derived, third-party checklists. 

An acquaintance who had regularly flown with the pilot reported that the pilot would also use generic mnemonic checklists that had been committed to memory, instead of the POH or the third‑party checklists. The commonly used mnemonic covered some, but not all of the checks required by the POH checklist.  

Engine failure management

The Rockwell 114 POH emergency procedures checklist for an in-flight engine failure stated that the glide speed of 82 kt should be adopted, the auxiliary fuel pump selected on, mixture full rich, and the fuel selector be placed on the fuller tank to rectify possible fuel starvation. 

Maintaining the published glide speed in flight gives the optimal amount of lift for the least amount of drag, thereby giving the greatest glide distance for the amount of height lost during the descent.

Rockwell 114 ditching procedure 

A ditching is a controlled emergency landing on water. The Rockwell 114 POH ditching procedure identified that on approach to a ditching, the airspeed should be maintained at 82 kt. 

The procedure followed on to list: transponder (if installed) set to 7700, and a mayday call should be made. The emergency locator transmitter should be activated if installed, seats, seatbelts, shoulder straps and loose objects should be secured, flaps should be up, cowl flaps closed, and the undercarriage retracted. 

On final approach, flaps should be set to 20°, airspeed reduced to 74 kt, the undercarriage should remain retracted, and propeller set to high RPM. On touchdown, the elevator should be full aft, and the fuel selected to OFF.

Ditching guidance

In 2004 the ATSB made recommendation R20010258 which stated:

The Australian Transport Safety Bureau recommends that the Civil Aviation Safety Authority educate industry on procedures and techniques that may maximise the chances of survival of a ditching event. Part of that education program should include the development of formal guidance material of the type contained in the UK CAA General Aviation Safety Senses leaflet 21A Ditching.

In response to the recommendation CASA published CAAP 253-1(1) Ditching. This guidance was reissued in the form of AC 91-09 v1.0 and included but was not limited to the following safety advice about conducting a ditching:

For an aeroplane, it is likely to end up in a nose down vertical position after impact. Opening a forward door in these circumstances to escape may cause rapid water entry. Planning for this circumstance should include consideration of which exit might be opened prior to and after impact and briefing passengers on precautions when releasing seat belts. Any briefing should consider the prospect that the pilot may not be able to assist due to their prominent position where impact forces may be concentrated. An able-bodied passenger near an accessible exit would be the best resource for survivability in this situation.

The guidance also recommended unlatching a door prior to impact and providing passengers with a briefing, which included the brace position.[11]

Survival aspects

Passenger seating, exit location, and operation

The pilot (P) was seated in the front left seat location. The 3 passengers consisted of an adult and 2 children.[12] One child (C) was seated in the forward right seat next to the pilot and another child (C) was seated in the left-rear behind the pilot. The adult (A) passenger was seated in the rear‑right (Figure 5). Both aircraft doors were at the front row.

Figure 5: Seating positions

Source: Rockwell annotated by the ATSB

Figure 6 shows the aircraft doors, which were designed as both normal and emergency exits. Both doors had the same operation, which required 2 opening mechanisms to be manipulated, both when operating from inside or outside. One handle was located above the passenger/pilot head that needed to be rotated downwards to unlatch. The second handle was fitted to the forward lower part of the door and was a lever type arrangement, which was required to be pulled inwards to unlatch the 2 lower latches. Each door needed to be pushed outwards to open. There was no emergency jettison mechanism. 

Figure 6: Location of door interior operating handles

Source: ATSB

CASA produced guidance for the allocation of passengers to exit row seats in multi-part advisory circular (AC) Passengers seated in emergency exit row seats for parts 121, 133 and 135 operators, however this AC was not applicable to private flights. 

In addition to passenger suitability, the AC identified risks associated with seating inappropriate persons at exits and recommended that operational procedures should be used to address this risk. 

Applicable risks included:

• exits being opened when they should not be e.g., a passenger opens the exit without assessing the outside conditions 

• operation of exits by passengers who are not aware of the instructions specific to that exit e.g. how to open, remove and discard the exit 

• passengers seated in an emergency exit row having an adverse reaction to the emergency due to inadequate briefings 

• passengers that are not suitably able-bodied, lacking the strength and ability to remove the exit, attempting to open the exit, and delaying or impeding an evacuation process. 

In addition, CASA guidance[13] identified that pilots should consider the possibility of incapacitation, and seat and brief an able-bodied person accordingly. However, passenger composition and operational considerations such as weight and balance must always be considered to determine passenger seat allocation. 

Pre-flight, exit and emergency briefings 

Civil Aviation Safety Regulations (CASR) 1998 Part 91 (General Operating and Flight Rules) manual of standards, Division 20.3 Passenger safety briefings and instructions which came into effect just prior to the accident on 2 December 2021,[14] required, among other things, that passengers be briefed on:

(f)    how and when to adopt the brace position;

(g)   where the emergency exits are, and how to use them;

(p)   the requirement that:

             (i)  passengers seated in emergency exit rows must be willing and able to operate the exit in the event of an emergency; and

            (ii)  such passengers must not have a condition that will cause them to obstruct the exit or hinder an emergency evacuation

While they had to be briefed, there was no legislative requirement to assess the suitability of a person[15] in an exit row for a private flight.

Guidance[16] on passenger safety briefings relevant for small aircraft operators included: 

• to include the brace position in the pre-flight safety briefing
• to advise passengers to adopt the brace position in an emergency
• if the flight involves overwater operations, passengers are briefed on ditching procedures.

Briefings in practice

A witness who the accident pilot regularly flew with reported that the pilot would normally provide a briefing about the seatbelts and the operation of the aircraft exits. The instructor who assessed the pilot in their most recent flight review provided confirmation of consistent elements normally included in the pilot’s briefing.

The ATSB was unable to determine what information was provided to the passengers prior to flight on the day of the accident. Video footage captured during the emergency showed that the pilot did not provide an in-flight emergency briefing to passengers about the nature of the emergency or what actions to take.

Occupant injuries

A post-mortem examination of the pilot and passengers was conducted on behalf of the Queensland Coroner. The examination found all occupants had sustained injuries which may have caused some incapacitation but were insufficient to have been fatal. The reports found that the deaths were consistent with drowning. The report also detailed evidence of injuries consistent with being caused by wearing a harness or seatbelt.

Other information

Pilot medical requirements

As outlined above, of the last 3 CASA aviation medical examinations, the pilot had not declared their diabetic status or diabetes medication to their CASA designated aviation medical examiner (DAME).

The disclosure to DAMEs was required due to the nature of type 2 non-insulin dependent diabetes and its effect on aviation participants. The CASA Clinical practice guidelines for type 2 diabetes website stated their concerns:

Effect of aviation on [diabetes] condition:

• Difficulty with regular blood-sugar monitoring

• Irregular meal and sleep times

• Sedentary occupation

• Access to emergency sugar

Effect of [diabetes] condition on aviation:

• Overt incapacitation

- Cardiovascular event

- Cerebrovascular event

• Subtle incapacitation - end-organ damage

- Visual impairment (fields, low contrast sensitivity, colour)

- Impaired motor and sensory nerve function

- Impaired autonomic function (hypoglycaemia awareness). 

Pilots are permitted to hold a licence after a diabetes diagnosis. The CASA website further stated:

Type 2 diabetes is an aeromedically significant medical condition. Pilots and [air traffic] controllers who have been diagnosed with Type 2 Diabetes are required to ground themselves and notify this condition to their DAME.

In cases where the condition can be managed appropriately, and once cleared by the DAME, in accordance with the CASA guidelines, ongoing monitoring of the diabetes must be provided to CASA to prove that it is able to be managed and does not affect the pilot’s ability to fly. 

Safety analysis

Introduction

Shortly after take-off, VH-WMM likely experienced fuel starvation leading to a complete loss of engine power. During the attempted return to the airfield without power, the pilot did not maintain an adequate glide speed, and the undercarriage was extended, thereby reducing glide range, which resulted in the aircraft colliding with water before it reached the airfield and becoming inverted about 170 m from shore. 

This analysis will explore the power loss on take-off, flight planning and decision making of the pilot in command, and post impact survivability factors.

Checklist use

The passenger video identified that the pilot became distracted with a perceived engine problem during the before take-off checks and taxied back towards the groundcrew member. However, after realising that they had mis-identified the wrong engine control, the pilot then proceeded to the runway and conducted the take-off, without further completion of the required checks.

One essential aspect of the POH checklist stated that the fuel selector was to be set to BOTH. This ensures a positive supply of fuel can be delivered to the engine from both fuel tanks during take-off. There were two versions of the checklists on board the aircraft: the official aircraft POH included this item in 3 separate checklists, while the third-party checklists included it twice. While it is likely that the distraction affected the pilot’s completion of the ‘before take-off’ checklist items, the fuel selector was also not set to BOTH on the ‘interior’ or ‘before starting engine’ checks. 

Should a third-party checklist be used, it must be checked to ensure that it contains the correct information that is applicable for the aircraft being operated and that the checklist is verified against the approved POH checklists. The ATSB was advised that the pilot sometimes referred to the third-party checklists, however it is unlikely that the third-party checklists were referred to on the day of the accident as the folder containing the checklists were located in the pilot seat back pocket and not readily at hand.

The POH was carried on board the aircraft on the day of the accident, and the passenger video showed it was not referred to during the flight. 

On this basis, it is likely the pilot performed the before take-off checks from memory or used a mnemonic checklist to perform the before take-off checks which were ultimately interrupted. Before take-off, there is no time pressure (as there was inflight after the engine power loss), so there was opportunity to consult the written checklists to ensure all steps were completed. Conducting aircraft checks from items committed to memory can lead to checks being skipped or an assumption that a check has been completed when it has not. Also, when a checklist is interrupted, the habit of restarting from the beginning is a means of ensuring that all steps to be performed are done so in order and the checklist is complete.

Fuel imbalance

Analysis of CCTV imagery indicated it was likely that VH-WMM had a substantial quantity of fuel in the right wing, and that the pilot would have been aware of the imbalance after physically using a dipstick to check the aircraft fuel tanks during the pre-flight checks on the ground outside the hangar.

The fuel selector was found to be on the left tank after the accident and there was no video evidence of the pilot changing it during the flight. Therefore, the fuel selector was likely on the left tank during take-off. Due to the fuel imbalance, the left tank likely had minimal fuel to sustain engine operation during the climb out, which would result in the engine being starved of fuel, lose power, and begin to surge, and eventually stop. This is consistent with no fuel being found in the left tank after the accident. 

If the fuel selector was placed on BOTH tanks, then it is likely, even with one fuel tank having most of the fuel and the other almost empty, that fuel supply to the engine would remain unaffected. Excess fuel in the right tank may have led to the observed fuel coming from the right wing during the flight.

Therefore, with the aircraft’s remaining fuel supply most likely in the right tank, and with the fuel selector likely set to LEFT prior to take-off, the engine became starved of the available fuel supply in the aircraft’s right fuel tank, leading to the engine stopping. 

Engine power loss management

ATSB found that few, if any, initial emergency actions took place in response to the loss of engine power to rectify a possible fuel starvation as per the Rockwell 114 procedures. The aircraft had sufficient fuel for flight in the right wing, but the fuel selector was found to be selected to the now empty left tank, and the auxiliary fuel pump was off during the emergency. 

In addition, the pilot did not maintain the published glide speed of 82 kt as demonstrated by the numerous stall warnings that sounded repeatedly, indicating a speed within 3-4 kt of the straight and level flapless stall speed (63 kt). Airspeed management was made more difficult by the extension of the landing gear, which may have been an automatic reaction by the pilot in response to hearing the undercarriage warning bell sound while the pilot was managing the emergency.

Not maintaining the glide speed and the landing gear extension increased the vertical rate of descent and reduced the glide range of the aircraft. However, video evidence suggests the pilot continued with their initial plan to glide to the runway. In addition, the extended landing gear was an unfavourable configuration for the subsequent collision with water.

There was no available evidence to indicate that the pilot’s response (actions and inactions) to the emergency was affected by a medical issue, or similar factors. However, the pilot was making decisions during the emergency under a high level of stress and time pressure. A substantial amount of research has shown that people often do not make optimal decisions in such situations.

Some commonly reported effects of stress and/or time pressure include attentional narrowing, with people searching fewer information sources (Staal 2004) and focusing on cues that are perceived to be the most salient or threatening (Burian and others 2005, Wickens and Hollands 2000). Working memory and the ability to perform complex calculations is impaired (Burian and others 2005), and the ability to retrieve declarative knowledge (or facts) from long term memory is affected (Dismukes and others 2015). In addition, a person under stress and time pressure will generally consider fewer alternatives, and not be as systematic when evaluating alternatives (Dismukes and others 2015, Staal 2004).

Collision with water

It is likely that the pilot never intended to ditch the aircraft. Rather, the reduced speed of the aircraft below the glide speed, exacerbated by the undercarriage extension, led to a reduced glide range and inability to reach the runway at Redcliffe. The sounding of the ‘stall’ alert just before the collision indicates the aircraft could no longer maintain lift and the aircraft collided with water 3 seconds later. 

It is likely that under the stress of the situation, the pilot’s attention narrowed and their focus on landing back on the departure runway likely hampered their ability to consider a forced landing on water (ditching). Had the pilot recognised that the aircraft would not be able to glide to the runway, there was a brief opportunity (about 30 seconds) to attempt a controlled landing on water before the aircraft’s speed reduced to the stall speed.

If this had been the case, there were several actions the pilot would have had to remember (due to the limited time remaining) and complete to ensure a safe ditching. From the Rockwell 114 POH procedure, key actions were to ensure the undercarriage was retracted and the flaps were selected to 20° on the final approach to land on the water. 

Use of flap in the final stages of the ditching would have provided a reduced stall speed, therefore allowing the aircraft to touch down at a lower, controlled speed. Touching down on the water while not at the appropriate speed, and with the undercarriage extended, contributed to the aircraft inverting after colliding the water.

Further, although there was no reference in the POH to the pre-impact position of emergency exits (cabin doors) prior to a ditching, unlatching of cabin doors can allow quick egress from the aircraft after ditching. In this accident, given the brief opportunity available for such considerations, it was not considered feasible that all actions were possible. 

Due to the inverted orientation of the aircraft during the crash sequence and its submersion in murky water, the aircraft occupants were probably panicked, confused, and disorientated following the collision. Once the cabin filled with water, visibility would have been extremely low, which would have further reduced the likelihood of occupants being able to visually locate and operate the aircraft door handles. With the aircraft inverted, it is likely the occupants would have also been disoriented to the extent that it made opening the closed doors more difficult, reducing their ability to escape.

Pre-flight and emergency briefings 

Research has shown that more knowledgeable passengers perform better in an emergency (Meng-Yuan, 2014). It could not be determined what information was provided to the passengers prior to flight, however based on accounts from persons who had flown with the pilot previously, including their flight instructor, it is likely that any briefing given did not include any information about the brace position or what to do in the event of a ditching. This meant that the passengers were likely unaware of actions that may assist survival such as opening the aircraft door or adopting a brace position.   

Video footage recorded during the accident sequence showed that the pilot also did not provide passengers an in-flight emergency brief or instruct them on any actions they should take. This accident highlights the importance of providing instructions to passengers before a flight commences as often emergency situations are time limited and there may not be an opportunity to do so once something occurs.  

Providing information on the adoption of the brace position or how to, and when to open an emergency exit in a ditching situation will increase the likelihood of passengers taking appropriate action in an emergency. 

Passenger seating and emergency exit operation

Post-mortem examinations identified that the occupants of the aircraft were not fatally injured during the accident sequence. There was no readily available assistance nearby the accident site, and therefore the occupants would have had to extricate themselves from the aircraft.

The 2 emergency exits available to the occupants were more accessible to persons seated in the front of the aircraft. The exits required manipulation of both a handle on the door and a latch at the top. For the rear passengers, it is likely that they would have had difficulty (particularly with their seatbelt on) to reach the latch at the top of the door if required to operate the exit. The rear seat occupants would have also been restricted in accessing the doors and exiting the aircraft due to the presence of the front seat occupants. 

After the accident, police divers were unable to open the pilot’s left door, and only opened the other (right) door with difficulty. For the injured pilot and right front seat occupant of VH-WMM, who was a child, it is highly unlikely they would have had the post-accident capability to open the doors. The right door was observed unlocked and ajar by police divers following the collision, suggesting the possibility that an attempt had been made to open the door.

Guidance suggests that pilots should determine the most appropriate person to assist in an emergency and to brief that person accordingly, therefore, in this case, seating a child who has less physical and mental capability rather than an adult next to an exit, meant that the most suitable person (the adult) was not in the best position to assist themselves and others in the event of an emergency. 

Diabetes

The pilot had been diagnosed with type 2 non-insulin dependent diabetes which was managed with prescription medication by the pilot’s GP. A review of the pilot’s CASA aviation medical information indicated that this significant medical condition was disclosed in the pilot medical history as ‘unsure’ to the CASA DAME in the previous 3 aviation medical renewals, all of which were changed to ‘no' at the DAME examination prior to submission to CASA.

It was important to note that having type 2 non-insulin dependent diabetes did not mean that this condition would be an immediate disqualification of the pilot’s licence. However, due to the aeromedically significant nature of diabetes, it was important for this to be fully disclosed with the pilot’s DAME and to CASA. Without this interaction, it was a missed opportunity for the pilot’s condition to be monitored at a safe level required to exercise the privileges of a pilot’s licence. 

Findings

ATSB investigation report findings focus on safety factors (that is, events and conditions that increase risk). Safety factors include ‘contributing factors’ and ‘other factors that increased risk’ (that is, factors that did not meet the definition of a contributing factor for this occurrence but were still considered important to include in the report for the purpose of increasing awareness and enhancing safety). In addition, ‘other findings’ may be included to provide important information about topics other than safety factors.  These findings should not be read as apportioning blame or liability to any particular organisation or individual.

From the evidence available, the following findings are made with respect to the fuel starvation and collision with terrain involving a Rockwell International 114, VH-WMM, 1 km north of Redcliffe aircraft landing area, Queensland, on 19 December 2021. 

Contributing factors

• An unsafe condition was created by not referring to the approved checklists in the pilot operating handbook. Checklists located in the pilot operating handbook would have prompted the pilot on 3 occasions to set the fuel selector to BOTH prior to take-off.
• A perceived engine problem distracted the pilot during the conduct of pre-take-off checks. After rectifying the issue, they did not complete the remaining pre-take-off checks (including fuel tank selection) before departure.
• A fuel imbalance and likely an incorrect fuel tank selection prior to take-off, led to fuel starvation and engine stoppage soon after take-off.
• The pilot, likely experiencing the effects of stress and time pressure following the engine power reduction and then stoppage, did not conduct initial emergency actions and attempted to return to the runway for landing but did not maintain glide speed, and the aircraft impacted shallow water prior to reaching the airfield.
• During the return to the airfield, the pilot extended the undercarriage, contributing to the aircraft inverting when it collided with water. This likely resulted in occupant disorientation, difficulty in operating the exits, and reduced their ability to escape.

Other factors that increased risk

• It is very likely that the passengers did not receive pre-flight information about the brace position or what to do in the event of a ditching. In the limited time available inflight after the power loss, the pilot also did not provide an emergency briefing or any instructions to passengers prior to impact with the water.
• While the pilot was primarily responsible for the operation of the aircraft exits in an emergency, seating a child, who may require assistance, adjacent to an exit instead of an adult meant that a less suitable passenger was available to operate the exit if required.
• The pilot had a diagnosed type 2 diabetic condition and did not directly declare this to the DAME during multiple medical renewals. 

Sources and submissions

Sources of information

The sources of information during the investigation included:

• Civil Aviation Safety Authority
• Queensland Police Service
• Australian Volunteer Coast Guard
• accident witnesses
• CCTV footage
• passenger mobile phone recordings
• the pilot’s general practitioner
• the pilot’s designated aviation medical examiner
• the flight review instructor
• maintenance organisation

References

Australian Government 2021, AC 91-22 Aircraft checklists v2.0, Civil Aviation Safety Authority, Canberra, ACT, viewed 18 December 2023, < AC 91-22 v2.0 - Aircraft checklists (casa.gov.au)>

Australian Government 2022, Type 2 Diabetes - Non-insulin dependent - Low risk of hypoglycaemia, Civil Aviation Safety Authority, Canberra, ACT, viewed 7 February 2022, < Type 2 Diabetes - Non-insulin dependent - Low risk of hypoglycaemia | Civil Aviation Safety Authority (casa.gov.au)>

Australian Government 2023, Avoidable Accidents No. 3 - Managing partial power loss after take-off in single-engine aircraft, Australian Transport Safety Bureau, Canberra, ACT, viewed 8 February 2022, < Avoidable Accidents No. 3 - Managing partial power loss after take-off in single-engine aircraft | ATSB> 

Australian Government 2023, AC 91-09 Ditching v1.0, Civil Aviation Safety Authority, Canberra, ACT, viewed 25 January 2022, < AC 91-09 v1.0 - Ditching (casa.gov.au) >

Australian Government 2023, Part 91 (General Operating and Flight Rules) Manual of Standards 2020, Civil Aviation Safety Authority, Canberra, ACT, viewed 25 January 2022, Part 91 (General Operating and Flight Rules) Manual of Standards 2020 (legislation.gov.au)> 

Australian Government 2023, Passenger safety information, Civil Aviation Safety Authority, Canberra, ACT, viewed 25 January 2022, < Multi-Part AC 91-19, AC 121-04, AC 133-10, AC 135-12 and 138-10 - Version 1.1 (casa.gov.au)>

Australian Government 2023, Passenger safety information, Federal Register of Legislation, Canberra, ACT, viewed 24 January 2022, <Civil Aviation Order 20.16.3 - Air service operations - Carriage of persons (02/12/2004) (legislation.gov.au)>

Burian BK, Barshi I & Dismukes K 2005, The challenge of aviation emergency and abnormal situations, National Aeronautics and Space Administration Technical Memorandum NASA/TM-2005-213462. 

Casner SM, Geven RW & Williams RT 2013, ‘The effectiveness of airline pilot training for abnormal events’, Human Factors: The Journal of the Human Factors and Ergonomics Society, vol. 55, pp.477-485.

Chaiken, S. R., Kyllonen, P. C., & Tirre, W. C. (2000). Organization and components of psychomotor ability. Cognitive Psychology, 40(3), 198-226.

Dismukes RK, Goldsmith TE & Kochan JA 2015, Effects of acute stress on aircrew performance: Literature review and analysis of operational aspects, National Aeronautics and Space Administration Technical Memorandum NASA/TM-2015-218930.

United States Government 2017, Safety Concerns with Using Commercial Off-the-Shelf (COTS) or Personally Developed Checklists, Federal Aviation Administration, Washington, DC, viewed 10 January 2024, < SAFO 17006: Safety Concerns with Using Commercial Off-the-Shelf (COTS) or Personally Developed Checklists (faa.gov)>

Kahneman D 2011, Thinking, fast and slow, Allen Lane London.

Klein G 1998, Sources of power: How people make decisions, Massachusetts Institute of Technology.

Landman A, Groen EL, van Passen VV, Bronkhorst AW & Mulder M 2017, ‘The influence of surprise on upset recovery performance in airline pilots’, The International Journal of Aviation Psychology, vol. 27, pp.2–14.

Lycoming Engines 2021. Service Instruction No 1009BE Time Between Overhaul (TBO) Schedules, viewed 7 December 2021, Lycoming Engines <Service Instruction No. 1009 BE | Lycoming>. 

Meng-Yuan, L. 2014, An evaluation of an airline safety education program for elementary school children. Evaluation and Program Planning, Science Direct, viewed 21 January 2023, < An evaluation of an airline cabin safety education program for elementary school children - ScienceDirect>

Precision Airmotive Corporation 20200, Training Manual RSA Fuel Injection System, viewed 6 June 2023, <15-812_b.pdf (precisionairmotive.com)>

Precision Airmotive Corporation 2020, RSA Fuel Injection system schematic wallchart, viewed 24 March 2022, < precisionairmotive.com/wp-content/uploads/2019/06/WALLCHART_rsa.pdf>

Staal MA 2004, Stress, cognition, and human performance: A literature review and conceptual framework, National Aeronautics and Space Administration Technical Memorandum NASA/TM-2004-212824.

Wickens CD & Hollands JG 2000, Engineering psychology and human performance, 3rd edition, Prentice-Hall International Upper Saddle River, NJ.

Wikipedia 2023, Rockwell Commander 112/114 family, viewed 14 January 2022, Wikipedia < Rockwell Commander 112 - Wikipedia>

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 Civil Aviation Safety Authority
• the National Transportation Safety Board
• the pilot’s last flight review flight instructor
• the pilot’s ground crew member
• medical subject matter experts.

Any submissions from those parties was reviewed and, where considered appropriate, the text of the draft report was amended accordingly.

Appendix

Sequence of events

The sequence of events below lists the key activities and audio from the passenger recorded video. This recording was started at 0902 and 25 seconds. The time listed in the table below is added to this time stamp. The video began during the taxi back toward the ground crew after the perceived engine problem.

Table 1: Sequence of events from accident flight video 

Time (m:ss) from recording start	Time (m:ss) after take-off commencement	Activity	Comment
1:50		Stop at holding point	Discussing location of other traffic
2:18		WMM enters and backtracks runway 07
3:00 – 3:21		Take-off
3:30	0:09	Undercarriage retracts	Motor heard during gear retraction
3:56	0:35	Left turn	Aircraft over water
4:05	0:44	Engine RPM decrease	Pilot reduces power after take-off
4:09	0:48	Flaps seen retracting	Captured on video
4:15	0:54	Left turn	WMM now about 90° to runway heading
4:32	1:11	Engine RPM fluctuating	Distinct rise and fall of engine RPM
4:35	1:14	Large drop in engine RPM
4:38	1:17	Passenger asks pilot about fuel coming out of right-wing fuel cap
4:38 & 4:42	1:17 & 1:21	Two left turns	WMM now on downwind leg to airfield
4:48 & 4:51	1:27 & 1:30	Stall warning sounds
4:52	1:31	Engine stops	Distinct ‘whomp’ sound from engine, usually heard when a piston engine stops
4:56	1:35	Undercarriage warning bell followed by stall warning	‘Click’ sound, followed by a wind noise. Gear extension most likely set here.
5:02	1:41	Pilot speaking	Radio call for return to runway
5:18, 5:20 & 5:24	1:57, 1:59, & 2:03	Stall warning sounds
5:25	2:04	WMM turns directly toward runway
5:26 to 5:40	2:05 to 2:19	Stall warning multiple sounds
5:40	2:19	Right wing drops
5:42	2:21	Right wing drops Electronic voice calls “stall” Aircraft stall warning remains on	Electronic voice is an alert from the Voice Alert System – heard only once
5:45	2:24	Aircraft impacts water

Source: ATSB based on passenger mobile phone recording

Purpose of safety investigations The objective of a safety investigation is to enhance transport safety. This is done through:  identifying safety issues and facilitating safety action to address those issues providing information about occurrences and their associated safety factors to facilitate learning within the transport industry. It is not a function of the ATSB to apportion blame or provide a means for determining liability. At the same time, an investigation report must include factual material of sufficient weight to support the analysis and findings. At all times the ATSB endeavours to balance the use of material that could imply adverse comment with the need to properly explain what happened, and why, in a fair and unbiased manner. The ATSB does not investigate for the purpose of taking administrative, regulatory or criminal action. Terminology An explanation of terminology used in ATSB investigation reports is available here. This includes terms such as occurrence, contributing factor, other factor that increased risk, and safety issue. Publishing information Released in accordance with section 25 of the Transport Safety Investigation Act 2003 Published by: Australian Transport Safety Bureau © Commonwealth of Australia 2024 Ownership of intellectual property rights in this publication Unless otherwise noted, copyright (and any other intellectual property rights, if any) in this report publication is owned by the Commonwealth of Australia. Creative Commons licence With the exception of the Coat of Arms, ATSB logo, and photos and graphics in which a third party holds copyright, this publication is licensed under a Creative Commons Attribution 3.0 Australia licence. Creative Commons Attribution 3.0 Australia Licence is a standard form licence agreement that allows you to copy, distribute, transmit and adapt this publication provided that you attribute the work. The ATSB’s preference is that you attribute this publication (and any material sourced from it) using the following wording: Source: Australian Transport Safety Bureau Copyright in material obtained from other agencies, private individuals or organisations, belongs to those agencies, individuals or organisations. Where you wish to use their material, you will need to contact them directly.

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

ATSB investigation report findings focus on safety factors (that is, events and conditions that increase risk). Safety factors include ‘contributing factors’ and ‘other factors that increased risk’ (that is, factors that did not meet the definition of a contributing factor for this occurrence but were still considered important to include in the report for the purpose of increasing awareness and enhancing safety). In addition, ‘other findings’ may be included to provide important information about topics other than safety factors.  These findings should not be read as apportioning blame or liability to any particular organisation or individual.

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

SAN number:

AO-2021-025-SAN-001

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

AC	Advisory circular
AGL	Above ground level
AMSL	Above mean sea level
ATC	Air traffic control
CAAP	Civil aviation advisory publication
CASA	Civil Aviation Safety Authority
CASR	Civil Aviation Safety Regulations
CFI	Chief flying instructor
CG	Centre of gravity
ELT	Emergency locator transmitter
IAS	Indicated airspeed
MOS	Manual of standards
MTOW	Maximum take-off weight
PARE	Spin recovery method that is generic and typical of most light single engine aircraft types
PLB	Personal locator transmitter
POH	Pilot operating handbook
VFR	Visual flight rules

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 & publishing information

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.

What happened

On 10 July 2019, a Robinson Helicopter Co model R44 helicopter, registered C-FJLH, with two persons on board, collided with terrain near Lac Valtrie, Quebec, Canada. Both persons died as a result of the accident.

The Transportation Safety Board of Canada (TSB) investigated the accident and released a public report on 31 March 2021 (A19Q0109). Subsequently, the helicopter manufacturer (Robinson) formally requested that the TSB reconsider its reported findings in relation to the role of the helicopter's main rotor blades (specifically the localised disbonding of the lower aerofoil skin of one blade) in the development of the accident.

ATSB involvement

In support of this request, on 13 May 2021, the TSB Chair formally requested assistance from the ATSB Chief Commissioner in the conduct of an independent review of the TSB report’s findings relating to the main rotor blades' role in the accident. Supporting materials were provided, including the TSB's laboratory report on the blade examination and, with the permission of the helicopter manufacturer, the submissions it provided on the laboratory, draft and public reports.

To support the review and ensure appropriate protections were afforded to the information provided, the ATSB commenced an External Aviation investigation (AE-2021-019) under the Australian Transport Safety Investigation Act 2003 (TSI Act). As such, all information received from the TSB was classified as Restricted Information in accordance with Section 60 of the TSI Act.

Investigation outcomes

The ATSB has completed its review of the TSB investigation and provided detailed feedback to the TSB management and Board under the provisions of s.62 of the TSI Act.

As such, all inquiries regarding the outcomes of this review should be directed to the Transportation Safety Board of Canada via their website: General enquiries - Transportation Safety Board of Canada (tsb.gc.ca)

Safety summary

What happened

In the early afternoon of 13 April 2021, a Cessna R172K aircraft registered VH-DLA (DLA) departed Canberra Airport, Australian Capital Territory, with a pilot and observer onboard to conduct powerline survey work to the north of Sutton township, New South Wales.

About 3 hours into the flight, while conducting powerline inspection in the vicinity of Tallagandra Lane, nearby witnesses observed the aircraft flying low above the trees before commencing a left turn that continued in to a steep descent and collision with terrain. The pilot and the observer were fatally injured, and the aircraft was destroyed.

What the ATSB found

The ATSB found that while manoeuvring to align the aircraft to inspect a powerline, the aircraft aerodynamically stalled and entered a spin at a height that was insufficient for recovery prior to the collision with terrain.

What has been done as a result

Following the accident, the operator amended the training and checking section of their Operations Manual to incorporate Threat and Error Management (TEM) and Situational Awareness (SA) training modules for powerline low‑level survey operations. The amendments enhanced existing topics in the operator’s crew resource management training and stipulated learning outcomes and assessment criteria specific to TEM and SA.

The operator also advised that they intended to introduce an airspeed ‘manoeuvre margin’ to take in to account the increased stall speed associated with steep turns.

Finally, the operator plans to modify their aircraft to include an angle of attack indicator to supplement the installed stall warning and a g‑meter with recording and data download capability to enable post flight review.

Safety message

This accident highlights the need for pilots to manage airspeed and bank angle to minimise the risk of an aerodynamic stall. This is particularly important when operating in close proximity to the ground, such as during take-off, landing and when conducing low-level air work, as recovery may not be possible.

The investigation

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

The occurrence

On 13 April 2021 at 1324 Eastern Standard Time,^[1] a Cessna R172K aircraft registered VH-DLA (DLA) departed Canberra Airport, Australian Capital Territory, with a pilot and observer onboard to conduct powerline survey work to the north of Sutton township, New South Wales.

At 1622 DLA crossed Tallagandra Lane (Figure 1) and the observer proceeded to inspect powerlines servicing properties to the east of the lane. Following the completion of two orbits, the pilot initiated a right turn and tracked to the north‑north‑east.

Witnesses in the area described that, following the right turn, the aircraft was flying low above the trees before commencing a left turn that continued into a steep descent and collision with terrain. The witness reports, including one from an experienced pilot, were consistent with a loss of control and entry into a spin preceding the ground impact. The pilot and the observer were fatally injured and the aircraft was destroyed.

Analysis of the final segment of recorded Garmin GPS^[2] and OzRunways^[3] flight data (see the section titled Recorded data) identified that the last Garmin GPS data point at 1624:48 showed the height of the aircraft was about 164 ft above ground level (AGL) about 115 metres from the accident site. The final OzRunways data point, recorded at 1624:50, was about 80 metres from the accident site and indicated that the aircraft was about 80 ft AGL (Figure 1).

Figure 1: Recorded flight path data shown relative to the accident site

Image description: DLA flight path – Garmin data is primarily referenced due to its higher sample rate and increased vertical accuracy. The final segment of OzRunways data is included as it provided the closest data point to the accident site.

Source: Google, with Garmin GPS and OzRunways data, annotated by the ATSB

Context

Pilot information

The pilot of VH-DLA (DLA) held a Commercial Pilot Licence (Aeroplane) issued in December 2019. The pilot also held a single engine aeroplane class rating, and a manual propeller pitch control design feature endorsement. The pilot completed a low-level aeroplane operational rating on 28 November 2019, valid for 2 years, and a single‑engine flight review on 15 March 2021, valid until 31 March 2023.

The pilot held a Class 2 Aviation Medical Certificate issued by the Civil Aviation Safety Authority, without medical restrictions, which was valid until 1 November 2023.

The operator’s records indicated the pilot had a total flying experience of 968.8 hours to the last recorded flight on 12 April 2021, of which about 572 hours were in the Cessna 172. In the previous 90 days, the pilot had flown 164.6 hours on type, and in the previous 30 days the pilot had flown 66.4 hours on type.

The pilot completed the operator’s low-level proficiency check on 9 February 2021 and was issued with a low-level, aerial survey certificate of competency to conduct powerline inspections without supervision. The pilot’s accumulated flight time conducting powerline survey work, following the operator’s approval, was about 135 hours.

Workload and fatigue

The operator had identified that aerial powerline survey work could be fatiguing for pilots and observers. To manage this, the operator applied work time limitations for pilots with fewer than 200 hours of powerline survey experience. Those pilots were limited to 6 hours of survey flight time per day with flights, conducted in sorties of 2‑3 hours duration.

After having 2 days off, the pilot had ferried the aircraft from Albury, New South Wales on the day prior to the accident and then logged about 5 hours of survey flight time over two sorties. On the day of the accident, the pilot had flown an earlier survey sortie of 1.3 hours duration and had been flying for about 3 hours when the accident occurred.

In flight, it was normal practice for the observer to direct the pilot to fly a pre-prepared route while the observer inspected the powerlines. To facilitate the observer’s work, the pilot was required to make constant changes to the aircraft’s heading and power setting to manoeuvre the aircraft into the optimum position for the observer. This resulted in a higher sustained pilot workload than that involved in flying an aircraft in straight and level flight. The operation of the aircraft at low level and relatively slow speeds also left little room for error. Research has shown that when an individual has to detect specific types of targets or stimuli over an extended period, their performance will decrease (Wickens and Hollands 2000).

The ATSB considered the effect of the sustained attention to flight parameters over the final sortie, but there was insufficient evidence to establish whether the pilot was affected by a level of fatigue that may have impacted their performance.

Post-mortem examination

The post-mortem and toxicology examinations did not identify any indicators of incapacitation or substances that could have affected the pilot’s capacity to perform the flight.

Aircraft information

DLA was a single engine, Cessna R172K aircraft. It was manufactured in the United States in 1977 with serial number R1722809 and was first registered in Australia in 1978. It was a four-seat, high-wing aircraft, with a non-retractable tricycle undercarriage. The aircraft was powered by a Teledyne Continental Motors IO-360, six-cylinder, fuel‑injected piston engine, driving a two-blade, constant speed propeller.

A maintenance release for the aircraft was issued following the completion of scheduled inspections on 2 March 2021 for day VFR^[4] operations, at an aircraft time in service of 16,488.5 hours. There were no open defects recorded on the maintenance release and no outstanding or overdue maintenance was noted.

The aircraft’s maintenance records also showed that in the 6 months prior to the accident, DLA’s:

• pitot static system had been checked for leaks
• pressure altimeter had been checked for serviceability
• fuel quantity system had been calibrated.

The airspeed indicator was tested in October 2018 and found to be serviceable. At the time of the accident, the instrument had accumulated 283 hours, time-in-service.

A weight and balance assessment identified that, at the time of the accident, the aircraft’s weight was about 979 kg, 178 kg below the aircraft’s maximum gross weight limit of 1157 kg, and the aircraft’s centre of gravity was within limits.

Aircraft stall and spin behaviour

The Pilot’s Operating Handbook for the Cessna R172K specified that, depending on the aircraft’s centre of gravity position, at its gross weight limit and with 10° of flap selected, the aircraft would stall^[5] at between 41‑43 knots indicated air speed. The altitude loss during recovery from a wings level stall could be up to 160 ft.

A spin can result when an aircraft simultaneously stalls and yaws.^[6] The yaw can be initiated by rudder application or by yaw effects from a range of factors that include aileron deflection, torque (engine power setting) and engine/propeller effects. A spin is characterised by the aircraft following a downward, corkscrew path and requires significantly more altitude for recovery compared to a wings level stall. The Cessna R172K Pilot’s Operating Handbook specified that at least 1,000 ft should be allowed for a one turn spin and recovery.

Further, should a stall occur during a turn, the aircraft’s behaviour becomes dependent on which wing stalls first. That is, it is possible for the upper wing to stall resulting in the aircraft rolling and yawing in the opposite direction to the turn.

Wreckage and impact information

The accident site was located about 10 km to the north-west of the township of Sutton in an open field about 30 metres east of Tallagandra Lane. From the accident site, the terrain sloped up to the north‑west by about 240 ft over a distance of about 600 m. The terrain dipped slightly to the east of the site, dropping about 50 ft over a distance of about 500 m.

Most of the aircraft wreckage was located next to the initial impact point. Larger items, including the propeller and the right undercarriage leg were found next to the fuselage. Items from the luggage locker were located within five metres of the aircraft’s initial impact point. The most distant item from the main wreckage was the aircraft battery which was found near the edge of Tallagandra Lane. The limited spread of wreckage indicated that the aircraft impacted the terrain with little horizontal speed.

Examination of the wreckage showed that the aircraft impacted the ground in a near‑vertical, nose‑down attitude. Damage signatures on the wing leading edges indicated that the right wing impacted the terrain first. The outboard section of the right wing, leading edge, near the tip was slightly deflected up, which was consistent with the aircraft spinning to the right at impact.

Compression damage to the forward fuselage reduced the available cabin space. While the occupants were secured with 4-point harnesses, the accident was non‑survivable.

Site and wreckage examination did not identify any aircraft defects that could have contributed to the accident and there was no evidence of birdstrike.

It was noted that the aircraft’s wing flaps were extended. Assuming a correctly rigged flap system, examination of the flap actuator screw jack extension determined that the flaps were set in the down position, at 18-20°.

Inspection of the aircraft’s stall warning system established that, other than damaged tubing attributed to the accident sequence, the warning horn sounded when suction was applied. The system was therefore considered serviceable prior to the accident.

Operational information

Powerline survey

The role of the observer was to coordinate the powerline survey work. The observer monitored the survey’s progress on a map depicting the electrical distribution network and directed the pilot to the sections of powerline to be inspected (Figure 2). The map was marked with warnings and cautions associated with network specific features and areas to avoid (no-fly areas) associated with dwellings, livestock and/or hazardous features.

The sequence in which the survey progressed was a combination of the flight crew’s pre‑departure planning and in-flight variations as determined by the observer. The pilot would fly the aircraft in response to the observer’s directions provided it was safe to do so. The observer would photograph any observed powerline defects and annotate their location on the distribution network map.

Figure 2: Aircraft flight path and electrical powerline network in the vicinity of the accident site

Source: Google, with operator supplied powerline network distribution map, and Garmin GPS and OzRunways data, annotated by the ATSB

To provide the right‑seat observer with the best opportunity to detect defects, the pilot would position the aircraft to keep the powerline to the right of the observer, at a height of about 150 ft above ground level and 150 ft horizontally from the powerline. According to the operator, the speed of the aircraft would preferably be maintained above 70 kt to maintain a margin above the aircraft’s stall speed and slow enough for the observer to note defects. The operator further advised that during survey operations the aircraft flaps were normally set at 10°.

The operator’s Aircrew Operational Procedures Manual instructed pilots that when surveying T‑Offs,^[7] from a main distribution line that may require significant manoeuvring, the pilot should initiate a partial orbit of 270° commencing in the opposite direction to the T-Off orientation (Figure 3).

Figure 3: Powerline survey T-Off positioning manoeuvre (partial orbit)

Source: Oberon Aviation Services and annotated by the ATSB

This was a standard re-positioning procedure that would result in a lower bank angle and wing load factor^[8] while orientating the aircraft in the direction of the target T‑Off.

With respect to aircraft aerodynamics, the wing load factor or g-force on the wings varies with the angle of bank in a level turn and has a direct influence on the aircraft stall speed. Specifically, as the angle of bank increases, the load factor and the stall speed of the aircraft also increases.

To turn, an aircraft must roll in the desired direction, which increases the aircraft's angle of bank. Turning flight lowers the wing's vertical lift component. To compensate (and prevent the aircraft from descending), the lift force must be increased by pulling back on the control yoke to increase the angle of attack of the wings. If the angle of attack reaches a critical angle, loss of lift and increased drag occurs, and the wing will aerodynamically stall.

Final flight segment

On completing the survey work to the east of Tallagandra Lane, the pilot conducted a turn to the north-north-east and momentarily tracked parallel to the main distribution line that ran beside the lane (Figure 4). Based on flight path data and progress notations on the electrical network distribution map, the next powerline to be surveyed was the branch to the north-west which departed the main distribution line near the accident site.

 Figure 4: VH-DLA flight path in the vicinity of the accident site

Source: Google, with operator supplied powerline network distribution map, and Garmin GPS and OzRunways data, annotated by the ATSB

The operator advised the ATSB that the standard procedure to establish the aircraft to survey that branch would have been for the pilot to conduct a partial right orbit through 270° prior to intercepting the powerline. However, the witness accounts indicated that the aircraft banked left towards the branch immediately before the accident. The operator was unable to provide advice as to why the orbit manoeuvre was not performed at this point. Flight path data showed the pilot had performed the 270⁰ partial orbit manoeuvre in similar situations earlier in the flight.

The ATSB considered whether the final turn may have been an evasive action by the pilot to avoid birdlife, however there was insufficient evidence to determine if that may have influenced the turn.

Meteorological information

The forecast meteorological conditions for the Canberra Airport area indicated winds from the north-west at 12-14 kt and no cloud below 5,000 ft AGL. Visibility was forecast to be 10 km or greater. The METAR^[9] for Canberra Airport issued at 1600 was consistent with the forecast conditions, with recorded wind from the west-north-west at 10 kt with visibility of 10 km or greater and a temperature of 18⁰ Celsius.

Witnesses in the accident area reported that visibility was unlimited, and there was little to no wind.

Recorded data

DLA was not equipped with a flight data or cockpit voice recorder, nor was it required to be. Flight path data from the OzRunways application and Airservices Australia secondary surveillance radar was provided to the ATSB. Data was also retrieved from an on-board Garmin Aera 500 GPS and a Garmin GPSMAP 60Cx portable GPS unit for analysis.

Speed and position data from the Garmin 60Cx unit was used in the analysis of the aircraft’s movement as it offered better resolution and was recorded at a higher sampling rate than the other sources.

Due to a gap in data between DLA’s final recorded GPS position and the accident site, data from previous turns was used to estimate the performance of the aircraft during the final turn where the loss of control occurred.

Estimated values for speed, bank angle and stall margin during the final turn were derived from the analysis of data associated with a selection of turns conducted during the day’s flying. Turns with a distinct radius, generally through greater than 90° were identified and selected for analysis. Turns that displayed an irregular radius or inconsistent data points were excluded from the analysis. The final group of 19 turns that were analysed included all five turns prior to the accident turn, plus selected turns at various points earlier in the flight. The group also included three turns that met the selection criteria and related to the flight conducted earlier in the day.

Indicative values of DLA’s airspeed, angle of bank and stall margin were derived (Table 1). To facilitate the analysis, it was assumed that each turn was coordinated, at a constant altitude and at a constant speed. The aircraft weight and a wing flap position of 18° were also factored into the analysis.

The ATSB acknowledged the difference between the forecast winds and the local wind conditions observed by the witnesses. However, the analysis assumed nil wind speed as it was not possible to incorporate large changes in aircraft direction in the calculations. In order to assess the aircraft’s performance, it was also necessary to convert the Garmin GPS ground speed data to calibrated airspeed by correcting for density altitude.

Table 1: Flight path data analysis

Time[10]	Time to accident	Speed (kt)[11]	Angle of bank (deg)	Normal load factor (g)[12]	Calculated stall speed (kt)[13]	Stall margin (kt)
1053:14[14]	5:31:38	72	41	1.33	55	17
1101:1214	5:23:40	53	33	1.19	52	1
1119:0214	5:05:50	68	34	1.21	52	16
1421:09	2:03:43	64	36	1.23	52	12
1445:52	1:39:00	61	30	1.16	51	10
1456:20	1:28:32	65	42	1.34	54	11
1544:21	0:40:31	58	38	1.26	52	6
1547:35	0:37:17	57	40	1.30	53	4
1608:07	0:16:45	62	32	1.18	50	12
1610:37	0:14:15	58	44	1.38	54	4
1618:06	0:06:46	69	24	1.09	48	21
1618:48	0:06:04	79	46	1.44	55	24
1620:45	0:04:07	78	33	1.20	50	28
1621:02	0:03:50	69	35	1.23	51	18
1622:52	0:02:00	75	31	1.16	50	25
1623:11	0:01:41	60	31	1.16	50	10
1623:45	0:01:07	57	34	1.20	50	7
1624:17	0:00:35	60	31	1.17	50	10
1624:45	0:00:07	56	33	1.19	50	6

For DLA’s final turn after its last recorded Garmin GPS position at 1624:48, and assuming that the speed of the aircraft did not vary from the previous turn, the analysis indicated that DLA was likely being manoeuvred in a 50° banked turn to the left and was flying at a speed that was very near to the stall speed (Table 2).

In contrast to the other analysed turns, the load factor during the final turn was also found to be the highest and had the lowest stall margin that was demonstrated in the other turns. Had the wind direction and strength been similar to conditions recorded at Canberra Airport the stall margin in the final turn would have been greater.

Table 2: Estimated values for DLA’s speed, bank angle and stall margin during the final turn

Time	Time to accident	Speed (kts)	Angle of bank (deg)	Normal load factor (g)	Calculated stall speed (kts)	Stall margin (kts)
1624:50	0:00:02	56[15]	50[16]	1.56	57	-1

Operator’s response to the accident

Following the accident, the operator amended their Operations Manual (Training and Checking) to incorporate Threat and Error Management (TEM) and Situational Awareness (SA) training modules as applicable to low-level, powerline survey operations. The amendments enhanced existing topics in the operator’s crew resource management training and stipulated learning outcomes and assessment criteria specific to TEM and SA.

The TEM module was intended to assist pilots and observers with the identification and management of threats associated with:

• weather
• operational considerations (including terrain, density altitude and power network complexity)
• aircraft performance
• time pressures
• decision making
• Go-No Go and escape options.

The SA training aimed to increase the maintenance of situation awareness as it related to the:

• obstacle environment
• aircraft performance and energy management
• speed and manoeuvre management (continual management and monitoring of aircraft attitude, critical airspeeds and balance).

It was intended that the training would be initially delivered to the operator’s Training and Checking pilots who, in turn, would deliver briefings to pilots and observers at a standard equivalent to that of a flight instructor. An additional aircraft handling or ‘fly safe’ check will be conducted on all pilots and observers prior to the start of each powerline survey season.

The operator also provided detail of intended amendments to their low-level procedures to implement an airspeed ‘manoeuvre margin’ that will take in to account the increased stall speed associated with steep turns. The manoeuvre margin will be calculated by the pilot, and independently verified by the observer before each flight as part of the crew’s risk assessment procedure and recorded in the daily operations diary. For the pilot’s and observer’s in-flight reference, the minimum manoeuvre airspeed will be temporarily marked on the airspeed indicator.

Further, the operator plans to modify their aircraft to include an angle of attack indicator and a g‑meter with recording and data download capability. The instruments will supplement the aircraft’s stall warning device by providing additional warning of an impending stall. A record of the maximum and minimum in-flight readings will be downloaded post flight for review by the Chief Pilot.

Other occurrences

Between 2011 and 2021, the ATSB investigated 21 fatal accidents involving piston engine aeroplanes flown in visual meteorological conditions that involved a loss of control and collision with terrain. While none of the 21 accidents involved aircraft engaged in powerline survey work, 11 involved single engine aeroplanes that aerodynamically stalled at a height from which recovery was probably impossible before ground contact.

Safety analysis

Introduction

The pilot and observer onboard VH-DLA (DLA) were conducting powerline survey work to the north of Sutton, New South Wales. Following the completion of two orbits over properties to the east of Tallagandra Lane, the pilot initiated a right turn and tracked to the north‑north‑east. The aircraft was then observed by witnesses to commence a left turn to the north‑west followed by a steep descent and ground impact. Witness observations and wreckage characteristics were consistent with a loss of control and entry into an aerodynamic spin prior to the collision with terrain.

The ATSB found that the pilot was qualified to conduct low-level powerline survey work and was suitably rested to conduct the task. Further, while acknowledging that powerline survey work was more demanding on pilots than other flight activity, there was insufficient evidence to indicate that the sustained workload created a level of fatigue that affected the pilot’s performance.

Site and wreckage examination did not identify any aircraft defects that may have contributed to the accident. This analysis will examine possible reasons for, and the nature of, the manoeuvring that preceded the accident.

Manoeuvre to the north-west

Following the turn to the north-north-east, the pilot would likely have been receiving directions from the observer based on progress of the survey work, which was being monitored with reference to the electrical network distribution map.

The ATSB established that, on completion of the turn, the T-Off immediately to the left of DLA’s track linking a relatively short section of powerline to the north‑west was likely chosen as the next section to be surveyed. The witness reports and flight data indicated that a direct turn towards that T-Off was initiated, rather than the partial orbit advocated by the operator. While the reason for this could not be established, a review of the manoeuvring prior to the accident indicated that partial orbits had been previously used to position the aircraft parallel to other branch lines.

Significantly, the direct turn towards rising terrain probably resulted in a higher bank angle/wing load factor, and therefore a higher stall speed, than aligning the aircraft via a partial orbit.

Loss of control

From the recorded data and witness accounts, DLA transitioned from a level, right turn to the north-north-east into a tighter, possibly climbing, left turn. From the ATSB’s analysis of the turns conducted by the pilot earlier in the flight, it was estimated that the final turn was likely conducted at a comparatively high angle of bank and closer to the stall speed of the aircraft.

As the manoeuvre continued, the aircraft likely exceeded the critical angle of attack for the wing, causing the wing to stall. While no fault was identified with the aircraft’s stall warning system, had the manoeuvring been relatively dynamic, there may only have been a small time interval between the activation of the warning and the actual stall.

Analysis of the recorded flight data identified that the aircraft had been operated relatively close to the stall speed during previous turns without a consequential loss of control. However, from the available evidence it was not possible to determine why control was maintained during those earlier turns.

Following the stall, the aircraft entered a steep, nose down aerodynamic spin that continued until the collision with terrain. The reason for the lower airspeed than used in the majority of the previous turns could not be determined however it may have been the result of deceleration associated with manoeuvring and/or initiation of a climb due to approaching rising terrain. Although the wind appears to have been relatively light, it could also not be ruled out that the aircraft encountered some turbulence in the lee of the rising ground that may have contributed to the accident.

The collision point was to the north-west of DLA’s last recorded flight position and adjacent to the T‑Off. When the aircraft entered the spin, it was significantly below the required height above ground specified by the aircraft manufacturer for recovery from a spin.

Findings

ATSB investigation report findings focus on safety factors (that is, events and conditions that increase risk). Safety factors include ‘contributing factors’ and ‘other factors that increased risk’ (that is, factors that did not meet the definition of a contributing factor for this occurrence but were still considered important to include in the report for the purpose of increasing awareness and enhancing safety). In addition ‘other findings’ may be included to provide important information about topics other than safety factors. These findings should not be read as apportioning blame or liability to any particular organisation or individual.

From the evidence available, the following findings are made with respect to the loss of control and collision with terrain involving Cessna R172K, registered VH-DLA near Sutton, New South Wales on 13 April 2021.

Contributing factors

• While manoeuvring to align the aircraft to inspect a powerline, control of the aircraft was lost at a height that was insufficient for recovery prior to the collision with terrain.

Sources and submissions

Sources of information

The sources of information during the investigation included:

• Airservices Australia
• Bureau of Meteorology
• Civil Aviation Safety Authority
• OzRunways
• the operator
• the aircraft manufacturer
• recorded data from the portable GPS unit in the aircraft
• a number of witnesses.

References

FAA 2016, Airplane Flying Handbook, FAA-H-8083-3B, U.S. Department of Transportation, OK 73125

Wickens CD & Hollands JG, 2000, Engineering psychology and human performance, 3rd edition, Prentice-Hall International Upper Saddle River, NJ

Submissions

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

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

• Civil Aviation Safety Authority
• the operator.

A submission was received from the operator. 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.

__________

1. Eastern Standard Time (EST): Coordinated Universal Time (UTC) + 10 hours.
2. GPS: Global Positioning System. A satellite-based radionavigation system.
3. OzRunways: An electronic flight bag application providing subscriber flight information and navigation service.
4. Visual Flight Rules (VFR): a set of regulations that permit a pilot to operate an aircraft only in weather conditions generally clear enough to allow the pilot to see where the aircraft is going.
5. Aerodynamic stall: occurs when airflow separates from the wing’s upper surface and becomes turbulent. A stall occurs at high angles of attack, typically 16⁰ to 18⁰, and results in reduced lift.
6. Yawing: the motion of an aircraft about its vertical or normal axis
7. T-Off: A junction in the power line distribution network branching from a main line.
8. Load factor: the ratio of the aerodynamic force on the aircraft to the gross weight of the aircraft.
9. METAR: a routine aerodrome weather report issued at routine times, hourly or half-hourly.
10. Local time at midpoint of turn.
11. Calibrated airspeed assuming nil wind.
12. Assumed a steady level coordinated turn,
13. Calculated from a MTOW, wings level, 18° of flap, stall speed of 50 kt (calibrated airspeed).
14. Prior flight.
15. No recorded data. Assumed from previous turn.
16. Calculated from an assumed arc starting tangential from the last known point to the accident location.

The occurrence

Appendix B – Engine examination

The engine was disassembled and examined at a Civil Aviation Safety Authority (CASA) approved engine overhaul facility under the supervision of the ATSB.

Some impact damage was identified; however, the main engine components were found generally in working order.

Review of the engine systems found that the left carburettor was missing a clip that attached the float needle valve to the float hinge bracket (Figure B 1 and Figure B 2). During multiple tests under controlled conditions, the left carburettor flooded[8] repeatably. It was later determined that this was likely due to the presence of significant amounts of corrosion on the float needle valve, its seat, and a deposit on the on the valve tip (Figure B 3).

Figure B 1: Carburettor components

Source: BRP-Rotax, modified by the ATSB

Additionally, both carburettor float bowls were contaminated. The floats fitted to both carburettors were the original type (Figure B 4), which were required to be replaced as part of a mandatory service bulletin. Pre-service bulletin floats could lose buoyancy and increase the likelihood of carburettor flooding, also characterised by the presence of fuel odour. 

The float bowl of the right carburettor was also contaminated, and one of the float guide pins was bent, causing a float to contact the side of the bowl.

A number of fuel lines were destructively inspected. The internal surfaces in some fuel lines were perished and had become brittle, compromising the security of their end fittings. Some of the fire sleeves covering the fuel lines had marks where securing clamps had previously been removed.

Figure B 2: VH-SIP left carburettor condition

Source: ATSB

Figure B 3: VH-SIP left carburettor float needle valve and seat

Source: ATSB

Figure B 4: Left carburettor float condition

Source: ATSB, BRP-Rotax, modified by the ATSB

Carburettor contamination

ATSB technical analysis found that the contamination on the left carburettor float needle valve showed that it was corrosion, and the deposit on the valve tip was a carbon-based material. The contamination in the bowls of both carburettors was considered a likely corrosion by-product from the bowls.

The engine manufacturer advised the ATSB that faultless function of the engine could not be guaranteed if contaminants were found in the carburettor bowls. Corrosion on the float needle valve, and the absence of the clip that attaches the float needle valve to the float hinge bracket further increased the risk that the engine would not satisfactorily perform. The engine manufacturer also advised that the deposit on the left carburettor float needle valve could cause flooding and engine rough running at low power settings.

Service bulletins from the manufacturer recommended that if any contamination was found within the carburettor bowl, that the entire fuel system must be inspected and cleaned.

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