Collision with terrain

On 4 December 2021, the pilot of an Air Tractor AT-400 aircraft, registered VH-ACQ and operated by Aircair Aviation Operations (Aircair), was conducting aerial application (spraying) operations on a property 75 km west-south-west of Moree, New South Wales.

At 0604 Eastern Daylight-saving Time,[1] the aircraft departed Moree Airport and tracked to the property’s airstrip, 43 km south-west of Moree Airport. A loader was stationed at the property’s airstrip, whose role was to mix and load chemical into the aircraft’s hopper, and to refuel the aircraft.

A GPS tracker onboard the aircraft recorded data at 15-second intervals. The data showed that commencing at 0632, the aircraft took off from the property airstrip and sprayed 11 loads over the course of the morning.

For the first 8 loads, the aircraft remained within sight of the loader. Those loads were sprayed using a racetrack pattern (Figure 1). Each of the 8 loads took about 20 minutes, except the third load, which took 32 minutes as it included clean-up spray runs (across the direction of the pattern) and tracking to the next target area. Each time the aircraft landed at the airstrip, the loader mixed chemical and water totalling 1,250 L into the hopper. On 2 of those occasions, the loader refilled the aircraft fuel tanks.

Figure 1: Racetrack spray pattern

Source: ATSB

At 0914, while the pilot conducted the seventh load, the operations manager sent the pilot a text message advising that 4 of the target fields marked on the map were no longer to be sprayed (marked in orange in Figure 2). On the next (eighth) load, the pilot overflew an area marked on their map to be sprayed that day, which was adjacent to a river and under water due to flooding. As a result, the pilot radioed the operations manager to ask whether to spray the flood-affected area. The operations manager reported that they contacted the property owner but were subsequently unable to communicate with the pilot via radio to provide a response. 

Figure 2: Operating area including target spray blocks, location of airstrip, property boundary and neighbouring house 

Source: Aircraft operator information overlaid on Google Earth, annotated by the ATSB

At 1053, the aircraft took off with the tenth load and continued to fly north-south racetrack patterns from the western side of blocks 127 and 128, followed by an inspection of the northern end of the target area, before returning to land at the airstrip again at 1120. The loader then filled the aircraft with fuel and loaded 1,250 L of chemical into the hopper. While the loader did those tasks, the pilot had a snack and a drink, and conducted a walk-around of the aircraft, which they had done consistently during refuelling breaks throughout the day.

At 1126:15, the aircraft departed on the eleventh load and tracked again towards blocks 127 and 128 to recommence spraying the next run from where they had left off (as can be seen in Figure 3), in the racetrack pattern. The pilot commenced a run to the south, but before reaching the target crop, the aircraft climbed and turned left. The aircraft then overflew the northern boundary of block 127, which was also the property boundary. The operations manager heard the pilot on the radio expressing concern about the potential for chemical spray to drift towards a house on the neighbouring property due to the wind. The aircraft then tracked north and again overflew the flood-affected area (top of Figure 2 and Figure 3), before returning to the north‑eastern end of block 127 (Figure 3).

Figure 3: GPS data showing the aircraft’s track on the accident load

Source: Aircraft operator TracPlus data overlaid on Google Earth, annotated by the ATSB

A witness reported that on the first and second runs along the eastern boundary, which were towards the south and north respectively, the pilot used smoke to assess the drift from the wind, before commencing spraying on the next (third) run. Instead of a racetrack pattern, the pilot conducted back-to-back spray runs with a procedure turn at each end. In a procedure turn, the aircraft is initially turned away from the direction of the turn, usually about 45°, before reversing the direction and completing the turn to position the aircraft on the reciprocal heading for the next spray run (Figure 4).

Figure 4: Back-to-back patterns with procedure turns

Source: Aerial Application Pilots Manual (Aerial Application Association of Australia, 2011), annotated by the ATSB

After the two ‘smoker’ runs, the aircraft sprayed 4 runs. At 1145, the aircraft commenced a spray run towards the south, at the end of which the aircraft climbed. The aircraft’s last recorded position was at 1145:30 about 170 m beyond the southern end of the field and 180 ft above the ground.

A witness (‘Witness 1’, Figure 5) located in the neighbouring paddock to the east, observed the aircraft turn slightly left then enter a right turn, consistent with a procedure turn. During the turn, the witness observed the aircraft’s nose pitch down and it descended rapidly, right‑wing low, then disappeared behind trees. The witness reported seeing a black plume of smoke rise almost immediately afterwards.

Figure 5: Aerial photo of target spray area taken 10 December 2021, showing accident site and witness location  

Note: The yellow lines represent the block boundaries.

Source: Aircraft operator, annotated by the ATSB

Another witness positioned about 1 km south of the accident site, observed the aircraft’s distinct yellow colouring as it descended among trees and impacted the ground. The witness estimated this was followed within about 2 seconds by flames and smoke. The pilot was fatally injured, and the aircraft was destroyed.

Context

Pilot information

Medical, licence and qualifications

The pilot held a valid Class 1 Aviation Medical Certificate issued on 15 October 2021 with no recorded medical issues and was reported to have been fit and healthy. The pilot’s Commercial Pilot Licence (Aeroplane) was issued on 30 March 2021.

The pilot also held ratings for:

• single-engine aeroplane
• low-level
• aerial application[2]

and endorsements for:

• tailwheel
• manual propeller pitch control
• gas turbine engine.

The pilot attained Spraysafe accreditation[3] through the Aerial Application Association of Australia (AAAA) on 2 July 2021 and had been issued a Pesticide Licence by the New South Wales Environment Protection Authority on 24 August 2021.

At the start of the accident day, the pilot had accumulated 372.5 flying hours, 203.3 of which were conducting aerial application operations (including training), 31.7 of which were in VH-ACQ. 

Recent history

The pilot’s recent sleep-wake and work history was determined from a combination of interviews, text messages, logged flight times and recorded flight data.

The pilot lived about 30 km from their assigned base and about 70 km from the operator’s Moree base. In late November, the pilot’s commute was increased by about 1 hour as a road was inaccessible due to flooding.

On 2 December 2021 (2 days prior to the accident), the pilot left home at about 0600, returned at 2000 for dinner and was in bed by 2100. That day, the pilot recorded 13 hours of duty time and 8 hours of flight time. The pilot had described this as a huge day – the most spraying so far in one day – and was very tired at the end of the day.

The day prior to the accident, the pilot was awake by 0412 and left for work at 0530. That day, the pilot recorded 13 hours of duty time and 7.9 hours of flight time. At 1816, the pilot sent a text message to a friend stating that they were about to fall asleep in the aeroplane (but did not advise the operator), before ferrying the aircraft to Moree Airport for maintenance, arriving at about 1900. Rather than drive home, the night before the accident, the pilot stayed with another company pilot in Moree. The company pilot reported that the accident pilot was happy and was proud of having sprayed 1,100 hectares that day and 1,000 hectares the previous day. They went out for dinner at about 2100 and went to bed between 2200 and 2215. Others described the pilot that evening as a bit tired but nothing out of the ordinary.

The accident day was the pilot’s ninth consecutive day of duty. That morning, the pilot was awake by 0510 and picked up another company pilot at 0530. They purchased breakfast, snacks and lunch from a petrol station before heading to Moree Airport. The company pilot recalled that the pilot reported having had a good sleep, appeared fresh and not tired, and was very happy that morning. Other company pilots who had seen the pilot in the 24 hours prior to the accident reported that the pilot did not seem overwhelmed or stressed.

For the 3 days prior to the accident, the recorded flight times were the longest consecutive logged by the pilot (7.7, 8.0 and 7.9 hours) and the longest duty times (12, 13 and 13 hours).

Flight training

The pilot completed their commercial pilot licence flight test on 24 March 2021 with 166 hours total flying time. The pilot had completed an integrated training course, combining ground theory training with practical flight training for their private and commercial pilot licences. During this training, the pilot was described as a good student who was well-prepared, focused and dedicated. The pilot’s non-technical skills were assessed as being very good, and their aircraft handling skills were described as exceptional – including maintaining the aircraft well within the required tolerances in steep turns, practice forced landings and circuits. 

Aerial application training

The pilot commenced training for aerial application and low-level ratings on 15 June 2021, and achieved those, along with a tailwheel endorsement, on 30 June 2021. At that time, the pilot had accrued 204.3 hours total flying time. This included the aerial application rating training, which consisted of 31.1 hours dual (including test) and 5.5 hours solo aerial application flight time, conducted in a Piper PA-25 two-seat dual-control aircraft.

The instructor who conducted the pilot’s aerial application rating and endorsement, noted in the second lesson (16 June) that the pilot had carried out stalls in all configurations at 1,000 ft above ground level. The pilot was reported to have handled these well for their total flying experience and achieved a good standard in recovery from stalls during climbing turns with left- and right-wing drops.

The lesson conducted on 20 June was conducted on a field similar to the accident field – with a diagonal boundary and trees – and included conducting back-to-back runs with procedure turns (Figure 6). On the training day, the wind was about 5 kt in the downwind direction at the diagonal boundary. The lesson notes indicated the pilot initially had difficulty lining the aircraft up on the spray run after the turn. The notes from the following day’s lesson (21 June) included ‘needs to back off on turns, pulling too tight…at times near stall’. A similar comment was made on 28 June. The instructor reported providing feedback to the operator of VH-ACQ (Aircair), to keep an eye on this aspect, but overall assessed that the pilot flew very well when taking into account the limited hours of experience at that time. 

Figure 6: Diagonal boundary paddock example  

Source: ATSB

Employment at Aircair

The pilot was inducted into Aircair Aviation Operations (Aircair) in July 2021, and initially commenced working as ground crew – mixing and loading chemical. On 9 September, the pilot satisfactorily conducted an operational proficiency check flight with the chief pilot in a Cessna 185 aircraft. The pilot’s first aerial application job at Aircair was on 15 September 2021 in a Cessna 188B (C188B) aircraft – a conventional single-seat, piston-engine, strut-braced low-wing agricultural aircraft – having completed 2.4 hours of familiarisation in the aircraft in the previous 2 days. The pilot’s emergency dump training[4] in the C188B aircraft was assessed satisfactory on 21 October 2021, although recorded in the pilot’s logbook as 13 October.

The pilot then conducted aerial application in the C188B aircraft and on 22 November 2021, the chief pilot signed off that the pilot had completed the required 110 hours of aerial application under supervision. At that time, the pilot had accrued 321 hours of flying time.

The pilot was described as having a natural ability to pick things up quickly, flew very nicely and did everything they were asked to. The chief pilot and general manager of Aircair assessed that the pilot was then ready to progress to turbine-engine aircraft.

Gas turbine design feature endorsement

On 26 November 2021, the pilot commenced gas turbine engine endorsement training. The Civil Aviation Safety Regulations Part 61 Manual of Standards Schedule 2 detailed the skills and knowledge required to operate a gas turbine powered aircraft on the ground and in the air during normal and abnormal operations. The elements specified in the Schedule were starting, stopping and managing a gas turbine engine, and managing abnormal and emergency actions applicable to a gas turbine engine.

The endorsement required the pilot to complete ground (theory) components including studying the applicable flight manual, and then submit a written exam on the engine and aircraft to the examiner, which the pilot completed on 26 November 2021.

The pilot also received ground familiarisation of the engine and aircraft, followed by 7.5 hours of flight time in a two-seat dual-control turbine Air Tractor AT-504 aircraft. This included normal and abnormal situations, stalls and steep turns, and aerial application operations. The pilot’s stall training in the AT-504 aircraft consisted of climbing to a safe height, at which the supervising pilot demonstrated a straight and level stall, with the accident pilot following on the controls. The supervising pilot pointed out the stall buffet and the stall stick position, then demonstrated recovery from the impending stall, by reducing back pressure on the control stick. The supervising pilot commented that the AT-504 always tended to drop the right wing about 5° in the stall. The accident pilot then conducted two stalls. On the second of those, during the recovery, the aircraft nose lowered, and, assuming the aircraft had recovered from the stall, the pilot reapplied back pressure. However, as the wing was still stalled at the time, this action resulted in a secondary stall, from which the pilot performed a successful recovery.

Having demonstrated the ability to identify and recover from stalls, the pilot then conducted their first aerial spraying activity under supervision in the AT-504. The supervising pilot reported that the pilot had initially applied too much back pressure on the control stick (‘pulled too hard’) during the turn. This was due to trying to keep the aircraft too close to the paddock and led to a stall buffet during the turn. The supervising pilot reported that they reiterated the importance of the stall stick position, and the need to reduce back pressure on the control stick. The amount of force required on the control stick depended on the trim setting. If the aircraft was trimmed such that forward pressure was required during a spray run, the back pressure required to stall the aircraft was small.

The supervising pilot also reported advising the pilot to increase the amount of initial turn (‘fade’) away from the direction of the turn in the procedure turn, so the resulting turn was not as tight. They commented that the pilot subsequently flew the spray pattern ‘beautifully’.

The pilot received their gas turbine endorsement on 27 November 2021. The pilot had completed the requirements of the endorsement; however, it was noted that the theory examiner had signed off the endorsement although the flying component was conducted by a different pilot. At the time the theory component was conducted, a dual-seat aircraft was not available to conduct the in-flight competencies, and as a result, the examiner would have had to observe the pilot solo in a single seat aircraft from the ground. The operator assessed it would be more effective and safer to wait until the dual-seat aircraft was available. The theory examiner was not available when the dual-seat aircraft became available and the flying component was supervised by a pilot whose instructor rating was not current as it had not been renewed, primarily due to COVID restraints. They had however, previously conducted 5 gas turbine endorsements before their rating lapsed, and subsequently renewed their instructor rating in 2022.

Transition to the AT-400

On the morning of 28 November, the pilot conducted circuits in the AT-504 in preparation for transitioning to the single-seat AT-400 aircraft.

The operator reported that they had put many less-experienced pilots in VH‑ACQ over the last 40 years, primarily because it never lacked take-off performance, even when fully loaded. They assessed that the biggest differences the pilot would have found in transitioning from the C188B to the AT-400, were that the operating speed of VH-ACQ was about 20 kt faster, it was heavier and had more inertia. Due to its inertia, it would take longer to recover from an impending stall than the C188B. The operator noted that the cockpit layout of VH-ACQ was very similar to the C188B but more ergonomic. The main difference was the Satloc GPS display, which had a touchscreen in the C188B, but a keypad in the AT-400. The pilot had reportedly noted during their endorsement that this was something they would have to get used to.

Before the accident pilot’s first flight in the AT-400 (VH-ACQ), the Aircair general manager reported briefing the pilot about the aircraft. This included cautioning the pilot to keep the airspeed up in the turns because of the shorter wings, without Hoerner wing tips (Appendix A – Hoerner wingtips), and higher wing loading[5] than the AT-504. As a result, VH-ACQ tended to give less pre-stall buffet indication before stalling. However, the general manager advised the pilot that the stall characteristics were similar to the AT-504, in that the AT‑400 would likely drop a wing in a stall and stall recovery required the pilot to reduce back pressure on the control stick. This was consistent with descriptions by other pilots who had flown VH-ACQ. They described it as providing a stall buffet later in an impending stall than an AT-502. Additionally, that it tended to drop a wing when close to the stall, and that all Air Tractors can produce a significant wing drop when close to the stall in an unbalanced turn.

On 29 November, the pilot conducted familiarisation and circuits in VH-ACQ, before commencing revenue operations with a reduced hopper load (1,000 L), mentored from the ground by the chief pilot. The next day, the chief pilot approved an increase to 1,200 L hopper loads for 3 days, before assigning a maximum hopper load of 1,300 L on 3 December. That was still the pilot’s assigned limit on 4 December.  

The chief pilot reported that the pilot appeared to be coping well with the transition to VH-ACQ. The pilot had described the transition to the AT-400 as ‘like learning to fly again’ and had remarked that they loved flying VH-ACQ. The pilot had reportedly commented that because of the air conditioner in VH-ACQ, they did not get as tired as when flying the C188B. The pilot and chief pilot had spoken each day that the pilot flew VH-ACQ, up to the accident day. The chief pilot reported that this included discussion of general management of the turbine engine, and that the pilot had not indicated any deficiency in operating the aircraft.

Ongoing supervision and mentoring

During the pilot's flights at Aircair, they were typically supervised either by the chief pilot or the general manager flying in the same area or observing from the ground. Regardless of having completed the mandatory supervised hours, the chief pilot advised that inexperienced pilots were typically ‘spoon fed’ up until 800–900 hours of agricultural flying.

The pilot had been conducting aerial spraying on the same property on the 2 days before the accident. The chief pilot had briefed the pilot at the end of the day prior to the accident, and discussed what blocks had been done, which to do next and the expected weather noting the wind direction and forecast high temperature. The chief pilot was absent on the accident morning and did not speak to the pilot.

The chief pilot reported that they would have been on the radio with the pilot if they had not been called away on leave that day. As a result of that leave, on the day of the accident, the pilot was unsupervised for the first time. However, the Aircair general manager radioed the pilot at 0645 to check how they were going, and the pilot responded that they were good and had a plan for the day’s operation.

Aircraft information

VH-ACQ

VH-ACQ was an Air Tractor Incorporated AT-400 single-seat low-wing tailwheel agricultural aircraft manufactured in the United States (US) in 1980. It was first registered in Australia – to Aircair – in November 1980 to operate in the Agricultural category, and was later operated in the Restricted category.[6] The Certification basis was US Federal Aviation Regulation (FAR) 21.25(a)(1) and the aircraft met the structural requirements of FAR 23, basis February 1, 1965, through Amendment 23-9. The flight criteria, propulsion, system and equipment items met the requirements of Appendix B, Civil Aeronautics Manual (CAM) 8, November 15, 1951, as amended through January 10, 1956.

The aircraft was powered by a Pratt & Whitney PT6A-15AG turboprop engine, which drove a Hartzell HC-B3TN-3D three-blade constant speed reversible pitch propeller.

The aircraft was fitted with two fuel tanks, located in the inboard section of each wing and an integral part of the wing structure. Both tanks gravity fed into a small header tank, located behind the hopper. Their combined total fuel capacity was 476 L, of which 454 L was usable. This equated to a maximum usable fuel weight of 363 kg (using a specific gravity of 0.8 for Jet A1 fuel). The aircraft was also fitted with dispersal equipment for spraying and spreading, and a system that allowed the hopper contents to be dumped if required. The hopper had a capacity of 1,514 L.

Maintenance history

The aircraft was maintained by a Civil Aviation Safety Authority (CASA)-authorised maintenance organisation in accordance with a CASA-authorised system-of-maintenance. A periodic inspection, including annual, 150 and 300-hourly, was completed on 28 September 2021, with the current maintenance release issued at that time. Scheduled and preventative maintenance conducted during this time included:

•  engine overhaul and fitment of an overhauled propeller assembly
•  replacement of lower spar caps (due life limit), with wing disassembly allowing for wing repairs and hopper refurbishment
•  testing of the airspeed indicator, altimeter, compass and pitot/static system
•  corrosion treatment and repainting.

At the time of the accident, the aircraft had accrued 18,869.2 hours total time in service. The aircraft had flown 4 hours 42 minutes since maintenance, having undergone a scheduled 75-hour inspection the evening prior, which included checking air and fuel filters, tyres, brakes and governor. The maintenance release had likely been destroyed in the post-impact fire and was not recovered from the accident site. However, there was no report of any aircraft defects prior to the accident. Furthermore, a general review of the maintenance records did not identify any anomalies.

Aircraft operating weight

The AT-400 type certificate data sheet[7] specified a maximum weight of 2,722 kg (6,000 lb). For VH-ACQ to operate above that weight, Air Tractor Service Letter 304 – Establishing and operating with a special purpose operating weight for Air Tractor aircraft, applied. The Service Letter referenced methods described in CAM 8 to enable operations up to a maximum recommended weight of 3,565 kg (31% overload). A placard affixed to the aircraft stated the maximum take-off weight as 3,565 kg. The Service Letter stated:

When operating at weights above the certificated maximum weight, please note that the stall speeds will increase from the published stall speed numbers in the Airplane Flight Manual. For example, when operating at a 31% overload weight, the stall speed will be approximately 15% higher than at the certificated maximum weight. During the required flight check, the new stall speeds should be determined.

On 23 October 2018 at 18,098.2 hours total time in service, the airframe logbook included an entry stating that the aircraft was flight checked on that day in accordance with CAM 8.10-3(e). It was found to be safely controllable and to operate satisfactorily with the hopper load of 1,356 kg and aircraft total weight of 3,565 kg.

Accident load weight and balance

The Airplane Flight Manual (AFM)[8] for VH-ACQ included a load data sheet to calculate the aircraft’s weight and balance. The sheet contained a table with entries for the weight, arm and moment of the aircraft with sprayer and spreader configurations, pilot, baggage, hopper and fuel. The table also provided forward and aft centre of gravity (CG) limits for weights up to 2,269 kg and for 2,722 kg, with a straight-line variation between those points.

For the accident load, VH-ACQ had been refuelled to full and the hopper loaded to about 1,250 L. Using a fuel consumption rate of 225 L/hr for spraying based on the company’s operations manual, the probable fuel remaining was approximately 387 L (310 kg). The pilot had completed 4 spray runs about 1,700 m long at an 18 m wide swath, using a chemical application rate of 18 L/ha, which left about 1,030 L in the hopper. The accident weight was therefore approximately 3,066 kg, below the demonstrated maximum gross weight of 3,565 kg, and the CG was about 534 mm aft of the datum. This was within extrapolated CG limits.

The hopper load calculation table for VH-ACQ stated that with full fuel, the maximum permissible hopper load was 1,348 kg.

Fuel tank certification and testing

For the aircraft’s certification, CAM 8.3052 Tank Tests required that all fuel tanks should be pressured tested to 3.5 PSI to provide an indication of the ability of the tank to resist distortion and leakage under vibratory, accelerating, and surging loads, which may be encountered in flight and landing conditions.

FAR 23.967 (e)(1) stated that the fuel tank must withstand 9 G ultimate fore and aft load from emergency landing conditions. Air Tractor simulated this in testing by converting the acceleration to an internal pressure. Air Tractor provided an extract of the engineering report covering the fuel tank testing. Their testing found that using 20 PSI, the fuel tanks were capable of withstanding 27 G before leaking.

These two requirements were for flight, landing and emergency landing conditions, but did not assess the tank for tolerance to direct impingement. There was no requirement in the design standards for normal category aeroplanes to be tested for fuel tank crashworthiness.

Installed GPS systems

Systems

The aircraft was fitted with a TracPlus surveillance system, which provided real-time tracking through a satellite or mobile phone network. It reported position, altitude, and speed at set time periods, in this case every 15 seconds. The ATSB obtained TracPlus data for the accident day and several previous flights.

A Satloc aerial guidance system provided the pilot with guidance commands to fly accurate spray patterns. It was set to record at 2-second intervals. The Satloc data from the accident flight was unrecoverable due to extensive fire damage to the Satloc unit. However, the ATSB obtained Satloc data for several of the pilot’s previous flights. 

Satloc increase/decrease

The Aircair Air Tractor fleet all had the same control stick switch configuration. The Satloc stick switch (button) provided a ‘remote’ function to increase or decrease the run number, which could also be done on the Satloc keypad (Figure 7).

Figure 7: Satloc stick switch and keypad

Source: ATSB

The Satloc keypad could be set to either increase or decrease the run numbers. When set to increase, pressing the stick switch (button) once, increased the run number by one, and when set to decrease, pressing the stick switch once decreased the run number by one. When a pilot had set up the Satloc GPS to spray a racetrack pattern, then changed to fly a back-to-back pattern, they would then be spraying every second run number (with the alternate numbers on the other side of the programmed racetrack pattern). Therefore, the next parallel spray run required the switch to be double-clicked at the end of each run to spray the adjacent, parallel run.

The stick switch could only make the run numbers go one way: up if increase was set or down if decrease was set. Therefore, if a pilot inadvertently clicked the button too many times and needed to go back, that would have to be done using the keypad.

When the Satloc was set to decrease, this swapped the direction function of the keypad buttons: the up arrow on the keypad (labelled ABC) would then decrease the run number and the down arrow on the keypad (labelled DECR) would increase the run number. Reportedly, this frequently resulted in pilots pressing the incorrect (for example, up arrow) button first, then having to press the correct one (for example, down arrow) multiple times. This would require ‘head in cockpit’ time and the potential for distraction from controlling the aircraft. The US Federal Aviation Administration (FAA) Advisory Circular 137-1A stated that pilots should ‘use extreme caution when using GPS swath-marking equipment to prevent diverting attention away from the task of flying the aircraft safely’. 

Meteorological information

Bureau of Meteorology

Between 0600 and 1145 on the accident day, the pilot was operating within the NSW - West subdivision of the Bureau of Meteorology Graphical Area Forecast.[9]. The forecast for NSW - West issued at 0323 on 4 December and valid 0400–1000 was for visibility greater than 10 km and no cloud. The graphical area forecast issued at 0325 and valid 1000–1600 included scattered high cloud above 10,000 ft and, from 1100, isolated cumulonimbus clouds with visibility reducing to 2,000 m in isolated thunderstorms and rain. Moderate turbulence below 10,000 ft was forecast in thermals and dust devils[10] from 1200.

The nearest Bureau of Meteorology weather station was at Moree Airport, 80 km east-north-east of the property airstrip. The aerodrome forecast[11] for Moree Airport issued at 0424 and valid from 0600–1900 included wind from 360° at 8 kt, changing from 1100 to 240° at 14 kt and CAVOK.[12] Between 1100 and 1500, there was a 30% probability of variable winds at 20 kt gusting to 40 kt with visibility reducing to 2,000 m in thunderstorms with rain and associated scattered cloud at 800 ft above aerodrome elevation. The maximum temperature was forecast to reach 34 °C.

Oz Forecast

For more accurate local weather information (temperature and wind speed/direction), company pilots usually referenced the closest Oz Forecast weather station. The wind was measured 2 m above ground level and recorded in km/h and degrees true (°T). The nearest Oz Forecast weather station was located 11 km west of the property airstrip. Data from that weather station recorded at 15-minute intervals and converted to kt, is shown in Table 1.

Table 1: Weather recorded at 15-minute intervals from 0600–1200 EDT

Source: Oz Forecast

At the time of the accident (1145), the wind was from the south-west at 10 kt gusting to 18 kt and the temperature was 32.6 °C. On the last spray run, as the aircraft had been tracking south, the wind was primarily a headwind. As the aircraft started to turn, it initially encountered more of a crosswind. The accident occurred as the wind became a quartering tailwind, but before completion of the turn to the north.

Other observations

A witness described the wind at about the time of the accident as ‘chopping and changing directions, was more stop and start again…gusts on and off’. The loader also described the weather as ‘windy’ and reported that the wind had become stronger throughout the morning.

At the time of the accident, the Aircair general manager was flying near Moree Airport, where the temperature was about 32 °C. They described the flying conditions as starting to get ‘bumpy and uncomfortable’ and about 30 minutes after the accident, as ‘quite windy and rough’. They reported that on the accident day, the wind had started from the north-east and went around to the north-west during the morning, in the usual summer pattern, but that it was stronger than normal, and increased around the time of the accident.

Another company pilot operating in the area that day recalled that it was the first hot, rough day of the season.

The chief pilot reported that on the evening before the accident flight, during their briefing with the pilot, they discussed the forecast 35 °C temperature. This included discussion of the associated increased thermal activity, which may lead the pilots to cease spraying operations.

At the time of the accident, the sun was not in a position to affect the pilot’s visibility.

Operational information

Work orders

The pilot had operated at the same property on 2–4 December. The blocks allocated to the pilot to be sprayed were depicted on multiple work orders for the property, one of which is depicted in Figure 8. Of the blocks depicted in Figure 8, on 4 December the pilot sprayed blocks M10, M11, M24, M25, M118, before commencing blocks 127 and 128. Block 117 was the wet area along the river and 123, 124 and 125 were not to be sprayed (although as they had powerlines in them, the pilot had been told not to spray them anyway).

Figure 8: Work order map depicting areas to be sprayed and location of the accident site

Source: Aircraft operator, annotated by the ATSB

Field selection

The operator reported that they selected blocks for spraying appropriate to a pilot’s experience and ability – including the block shape and whether there were powerlines in or near the target area. The accident pilot had not yet sprayed a block with a powerline in it, but had sprayed blocks with a powerline along one edge in the previous two weeks. Although not documented, it was reported that when any new aspects of the spraying task were introduced, the chief pilot or general manager would be there to mentor the pilots – either on the ground or flying next to them. The gradual progression to more complex blocks continued with the pilot’s transition to a more powerful, faster, heavier aircraft.

The field the pilot was spraying at the time of the accident (127 and 128 – Figure 8) was selected by the chief pilot because it was considered suitable for the pilot’s level of experience, with no powerlines or difficult obstacles. The blocks sprayed by the pilot the previous day were irrigated blocks – squarer and more defined. The accident field was a dry-land block with a few small trees. The field was near rectangular, but it had a diagonal border at the southern end, and the eastern and western fence lines were not quite parallel. The diagonal border angled down toward the western side, which would have made the back-to-back spray runs with a procedure turn at each end slightly more difficult for the pilot when incrementing runs from east to west. This is because with a diagonal end, each subsequent time the pilot pulled the aircraft up to make the procedure turn, the aircraft had to be further beyond the boundary to allow enough distance to line up for the next run (Figure 6).

Back-to-back pattern

According to the AAAA Aerial Application Pilot’s Manual (2011), the back-to-back pattern was the most common pattern flown prior to the availability of on-board GPS systems. It was usually the first pattern pilots learnt in their initial aerial application rating training. Flying back-to-back patterns was the preferred pattern when working around a hazard, such as a powerline, tree, susceptible crop, or house. This was because in a back-to-back pattern, the aircraft would be gradually moving towards a hazard. In contrast, when flying a racetrack pattern, the aircraft moves away from the hazard, which could be more easily forgotten on the next run. In a back-to-back pattern, during the procedure turn at the end of each run, the aircraft is turned through 180°. During the turn, ‘most of the speed is squandered and you arrive back on the same [reverse] heading at which you started the turn, with time and speed both going in the wrong direction’ (AAAA, 2011).

The operator reported that during a procedure turn, pilots judge how far to turn away (fade) by using the GPS light bar for guidance, counting (for example, for 3 seconds) in their head, or by feel, before banking the opposite way around the turn. If they do not get it right, it can be difficult to line up on the next run. In that case a pilot would normally skip that run and write the missed run number on their hand. They would then either return to spray it later or leave it and advise the operations manager at the end of the day, so that it would get done another day. The chief pilot reported having previously seen the pilot with missed run numbers written on their hand.

In a procedure turn, after the fade, as a pilot banked to turn the aircraft in the opposite direction, they would extend some flap during the turn, usually up to about 15° in the Air Tractor aircraft. They would then retract the flap as the aircraft lined up for the next spray run. The chief pilot reported that the key instrument referenced by a pilot during the turn was the airspeed indicator, while also cross-referencing the GPS light bar, and using the turn and balance indicator (ball) to ensure a balanced turn. The target airspeed they were referencing on the airspeed indicator depended on the aircraft weight.

Flight and duty review

Aircair flight and duty time limitations were in accordance with Civil Aviation Safety Regulations Part 137.Q. The key limitations were:

• maximum flight time of 170 hours in 28 days and 1,200 hours in 365 days
• daily tour of duty limit of 14 hours including a rest period of at least 8 hours after a duty of 10 hours or less, or 10 hours after a duty of more than 10 hours
• following a tour of duty of more than 10 hours, a pilot was permitted to recommence after 9 hours off duty, if they believed they were mentally and physically fit to do so and would not breach any other regulation in the subpart
• at least 36 hours continuous off duty in any 14 days
• 44 hours cumulative duty time limit in 3 days (72 hours) and 98 hours in 7 days (168 hours). 

The Aircair Administration and Policy Manual stated that for aerial application operations, duty time was calculated from 30 minutes prior to the flight to 15 minutes after the flight. The regulations defined flight time as commencing when ‘the aircraft first moves under its own power for the purpose of taking off’.

On the accident morning, the aircraft engine started at 0553, take-off roll commenced at 0559 and it took off at 0600. According to Aircair’s procedures, recorded duty time would commence no later than 0529, although the pilot arrived at the airport at about 0550. According to the operator’s flight and duty records, the pilot had been on duty for 13 hours the previous day, having commenced duty at 0700 and ended at 2000. Recorded data showed the aircraft was shut down at 1919 that evening and duty time should therefore finish no earlier than 1934.

As the previous day’s duty time exceeded 10 hours, the pilot was required to have a rest period of 10 hours, but could recommence duty after 9 provided the pilot assessed themselves ‘mentally and physically fit to do so’. The pilot’s start time was close to the 10-hour rest period, accounting for imprecision of the recorded duty times. It could not be determined whether the pilot made this assessment, however, regulations required pilots to ensure they were fit for duty prior every flight. Civil Aviation Safety Regulation 137.300 described that a pilot was not fit for duty if they had not had adequate rest, food or drink; or was adversely affected by a medical condition or a psychoactive substance.

The pilot commenced flying for Aircair on 9 September 2021 and flew 15.5 hours total for the month. In October, the pilot flew 54.8 hours in the C188B aircraft, over 18 days, with the longest flight time 7.3 hours on 6 October followed by 6.3 hours on 7 October. From 1 to 24 November, the pilot conducted 50.4 hours in the C188B. In that period, the longest flight time was 6.6 hours on 16 November which was also the longest duty day of 10.5 hours. The previous longest flight time recorded was on 6 October (7.3 hours). Both those days had been preceded by significantly shorter flight times.

The pilot’s most recent day off work prior to the accident was 25 November. After their day off, on 26 November the pilot commenced the transition to turbine-engine aircraft. Figure 9 and Table 2 show the pilot’s flight and duty records from 26 November to 3 December. The first time (ever) that the pilot flew VH-ACQ, was 5 days before the accident on 29 November. On that day, the pilot was awake at 0454 and home at 2126, having logged 5.6 hours of flight time in VH-ACQ.

Figure 9: Recorded flight and duty times from 26 November to 3 December 2021

Source: Aircraft operator data analysed by the ATSB

Table 2: Flight and duty records from 26 November to 3 December 2021

In the 8-day period since the pilot’s last rest day, there were some discrepancies between the logged flight and duty times and the recorded GPS data for the aircraft. On 3 December, the aircraft was rolling at 0647, 13 minutes prior to the recorded duty commencement. On 29 November, the aircraft landed at 1841 and on 26 November, the aircraft landed at 1932, both times after the recorded end of duty period. It was the pilot’s responsibility to enter the flight and duty times and it could not be determined how the inconsistencies occurred. The chief pilot reported that they checked the entered data occasionally.

Operational tempo

A review of text messages the pilot sent to a friend (but not to the operator) showed that since October and throughout November, the pilot had often mentioned that they felt tired, and had frequently been awake at or before 0500, and getting to bed after 2100. 

The accident pilot had flown more than 30 hours in VH-ACQ in the 4 days prior to the accident. The chief pilot commented that the company pilots had been doing a lot of flying and were approaching the flight and duty limits every day. Other company pilots reported that they had been working long, but not excessive, days. Further, that although they had early starts, they were not finishing very late.  

On the day before the accident, the chief pilot had reported being worried about the company pilots with the workload ahead. The chief pilot sent a text message to check they were all managing the workload and reminding them to work together with each other and the ground crew, stick to the routine and keep it simple. Later that day, a company aircraft struck a powerline, which resulted in minor damage and no injuries to the pilot.

In response, on the morning of the accident flight, the chief pilot sent a message to all company pilots, reminding them, among other things, to be aware of the effects of successive early starts and late finishes. The message advised pilots to manage their time and rest when they could, consider load sizes particularly following refuelling, maintain wire awareness, and to be safe, have fun and keep it simple.

Communications

The UHF radio in VH-ACQ had malfunctioned on the day prior to the accident and been fixed that evening. The UHF radio was used to communicate with the operations manager, other company pilots in the area and normally, with the loader. However, the loader did not have a radio that day as they were not driving a (company) vehicle fitted with one. Normal procedure involved the pilot communicating with the loader via radio so the loader could prepare the next chemical load prior to landing. The operator also had a procedure for loaders to operate with an unserviceable UHF, which required the loader to either mix load by load only, or to continue mixing until further notice, and to have a mobile phone. The loader had a mobile phone.

During refuelling prior to the accident load, the pilot sent a text message to the operations manager and received an immediate response. After departing with the accident load at about 1130, a company pilot operating in the area heard the accident pilot on the radio to the operations manager advising of their concern about drift onto neighbouring property and that the wind was picking up. That company pilot later reported that they thought the pilot sounded nervous. The operations manager reportedly responded suggesting they could spray a different area or cease operating.

Analysis of recorded data

The TracPlus data for 4 December 2021 indicated that the pilot had not flown a hazard check of any block before commencing spraying or conducting clean-up runs. This meant the pilot had not overflown the south-eastern area of the block (127 and 128) where the accident occurred.

For the accident load, several data points were recorded at the northern and southern ends during the turns. Analysis of these points indicated the maximum height reached during the turn at each end of the field was about 250 ft above the ground.

Analysis of Satloc data from the pilot’s flight the day prior to the accident, showed that in more than 75% of procedure turns, the peak angle of bank was 50–70° and peak acceleration was between 1.5 and 1.9 G. The angle of bank exceeded 80° three times and the peak G on average occurred at about the same time as the peak angle of bank. In the turn technique described in the AAAA’s Aerial Application Pilot’s Manual (AAAA, 2011), the peak G would be reached before the peak angle of bank:

A key pilot technique in aerial application is to unload the aircraft from excessive G before applying aileron to initiate a turn. This is most likely to be relevant during a pull out of a paddock at the end of a run. Pull back to get out of the paddock and establish the aircraft in a climb, unload the G, and then initiate the turn. 

The Satloc data from the day prior to the accident also showed that during back-to-back spray runs with procedure turns, the aircraft was usually lined up (within half a swath width) on the next spray run about 200 m prior to the crop boundary.

Aerodynamic stall

A wing generates lift when the airflow around the upper and lower surfaces results in a pressure difference between those surfaces. At a certain angle of attack (the relative angle between the chord line of the wing and the approaching airflow), which is a characteristic of the wing design, the flow over the upper surface of the wing separates from the surface. This condition is known as an aerodynamic stall (or simply a stall) and results in a rapid reduction in the lift generated and an increase in drag. Due to the sudden reduction in lift from the wing and rearward movement of the centre of lift, an uncommanded nose-down pitch ensues.

A wing drop occurs when one wing stalls before the other, which can be exacerbated by uncoordinated (or ‘unbalanced’) flight. A cross-control stall occurs when the critical angle of attack is exceeded while aileron is applied in one direction and rudder in the opposite direction.

As a loss of altitude also occurs during recovery from a stall, it is possible to stall with insufficient height above the ground to recover. The AFM for VH-ACQ stated the altitude loss from a wings-level stall was 220 ft at 2,722 kg gross weight. The main indications of an impending stall in the AT-400 are airframe buffeting (vibration) and an aural stall warning (horn).  

Aerofoils of the type used on aircraft such as the AT-400, typically stall at angles of attack of around 16°. This critical angle of attack can be exceeded at any airspeed, any (pitch) attitude and any power setting. As most small aircraft do not have an instrument that indicates the aircraft’s angle of attack, the angle of attack at which the stall occurs may be referenced to an airspeed. The AFM for VH-ACQ provided stall speeds at 2,722 kg gross weight, power off, wings level (0° angle of bank), in a balanced level turn at selected angles of bank, and with the flaps up (retracted) and flaps down (fully extended) (Table 3).

Table 3: Angle of bank and stall speed at 2,722 kg, power off (adapted from AFM)

However, the airspeed at which a stall will occur is not fixed to a single value, and varies with weight, centre of gravity, load factor,[13] and power setting. Tight turns and rapid pull-ups increase the load factor and therefore increase the stall speed. A stall that occurs at a stall speed greater than the +1 G stall speed, such as when turning or pulling up, is termed an accelerated stall. Increasing an aircraft’s weight by 25% will result in the stall speed being about 12% faster.

At the probable aircraft weight at the time of the accident (3,066 kg), the stall reference speeds in the AFM (Table 3) would increase by a factor of 1.06. For the referenced angle of bank stall speeds, if the pilot did not move the control stick aft to maintain level flight, and the aircraft descended while turning, (at the same radius), the G would be less, therefore the stall speed would be lower than when maintaining a level turn.

The primary control for angle of attack is the aircraft’s elevator. Pulling back on the control stick will increase the angle of attack and pushing forward will decrease the angle of attack. If a pilot pulls the stick too far back and deflects the elevator too far, it will increase the angle of attack of the wing to the critical angle and stall it. The elevator control stick (or column) position at which the critical angle of attack is reached is independent of factors including airspeed, angle of bank, power, and pitch attitude. Recovery from a stall requires reducing the angle of attack by moving the control stick forward, which normally means lowering the aircraft nose (pitching down). A secondary stall can result following a stall if, during the recovery, the pilot again pulls the stick past the position at which the critical angle of attack is reached in an effort to regain horizontal or climbing flight too quickly.

As VH-ACQ was the ‘first of type’ AT-400 registered in Australia, flight tests were conducted at Ballarat airfield, Victoria, on 31 October and 2 November 1980. At the flight-tested weight of 3,042 kg, the report concluded that the handling characteristics were acceptable. It found the airframe (pre-stall) buffet was felt at 76 kt indicated airspeed (IAS) with the flaps up (fully retracted) and was ‘not violent’. There was a ‘clear and distinctive’ stall warning onset at 80 kt IAS with flaps up (fully retracted) and at 68 kt with flaps down (fully extended). The stall characteristics were described as ‘satisfactory’.

Human performance considerations

Workload

Workload is defined as the sum of task demands placed on an individual’s cognitive resources that are used for attention, perception, decision making and action (Skybrary, 2010). Humans are limited in the amount of new information the brain can process at once. Once the limit of cognitive resources has been reached, performance starts to decline with increased error rates and/or delayed responses. Factors that can increase workload include excessive task demands, time pressures, a lack of operator skills and knowledge, or environmental conditions (NASA, 2010).

Task complexity and an individual’s level of experience and knowledge can have a significant impact on their workload (Li and others, 2021). Less experienced pilots typically have a higher cognitive workload compared to those that are more experienced due to their continual learning and development of skills. A more experienced and knowledgeable individual can rapidly interpret a situation based on past experiences and knowledge, and subconsciously pattern-match. This frees up cognitive capacity for a pilot to maintain vigilance and monitor performance, and, if they choose, reflect on their actions, whereas a less experienced individual may not (Byrne and others, 2013).

Green and others (1996) described the effect of practice on motor skills such as flying an aeroplane. With experience, skill acquisition progresses from the cognitive phase, in which the learner has to think consciously about the action, through the associative phase and on to become automatic, and the skill can then be executed without conscious control. Until this occurs, central processing capacity is needed to perform the task. Thus, a pilot with fewer hours in an aeroplane type would be expected to experience a higher workload than a more experienced one for the same task.

The instructor who conducted the pilot’s aerial application rating described the increase in workload for a pilot progressing from the C188B to the AT-400 as: ‘The workload is just so high for [the AT-400 aircraft] – they’re fast, nippy in the turn. If you are going to fly it on the edge, things are going to happen. It has more than double the weight and inertia’ of the C188B. They further reported that aerial application work is ‘not mundane’, that the pilot would be concentrating all the time, and has to consider other factors such as drift and temperature, in addition to flying. To conduct effective aerial application, while manoeuvring the aircraft at low altitude, a pilot must visually scan external cues and monitor internal resources (NTSB, 2014).

High workload is associated with increased error rates and reduced safety margins (Harris, 2011). It also leads to a degradation in performance and at extremely high levels of workload, important information may be missed due to the narrowing or focussing of attention onto only one aspect of the task (Green and others, 1996).

Fatigue

Overview

The Civil Aviation Safety Regulations define fatigue for a flight crew member (FCM) as:

a physiological state of reduced alertness or capability to perform mental or physical tasks, which:

• may impair the ability of the FCM to safely operate an aircraft
• is caused by 1 or more of the following: 
  • the FCM’s lack of sleep;
  • the FCM’s extended wakefulness;
  • the FCM’s circadian phase at any relevant time;
  • the FCM’s workload of mental activities, or physical activities, or mental and physical activities at any relevant time.’

The International Civil Aviation Organization (ICAO) (2020) defines fatigue as:

… a physiological state of reduced mental or physical performance capability resulting from sleep loss or extended wakefulness, circadian phase, or workload (mental and/or physical activity) that can impair a person’s alertness and ability to perform safety-related operational duties.

Factors that can cause fatigue include (CASA, 2012):

• emotional strain
• mental workload
• strenuous or sustained physical exertion
• inadequate food and fluid intake
• adverse environmental conditions, such as extremes of temperature, low light levels, vibration and confined spaces
• disrupted and lost sleep.

Mental fatigue results from long periods of cognitive activity. Its effects can include reduced concentration and manual dexterity, increased reaction time, performance monitoring, error management and decision making (Boksem and others, 2005; Bafna & Hansen, 2021, CASA, 2012; Heywood 1999).  

Self-assessment of fatigue

Although there are some known limitations of self-rated fatigue, research on airline flight crew has shown correlation between self-rated fatigue and performance in vigilance tasks, for example using the Samn-Perelli 7-point fatigue scale[14] (Garwon, 2016, Petrilli, 2007 and Roach, 2012). There was no regulatory or operator requirement for pilots to determine (or provide) a standardised fatigue estimation prior to, or during, operations.

Sleep and time of day

Inadequate quantity and quality of sleep is a contributor to fatigue. Most people generally require 7–8 hours of sleep to achieve a maximum amount of alertness and performance. Sleep debt can be cumulative and can result in degraded performance and uncontrolled sleep episodes (Orlady & Orlady, 1999; Hawkins, 1993). The pilot’s 72-hour history indicated they had adequate sleep opportunities in the preceding nights and the pilot was reported to have no sleeping issues.

Circadian rhythms are the body’s internal clock that regulates the sleep-wake cycle and repeats roughly every 24 hours. According to the International Civil Aviation Organization (2016) there are two times of peak sleepiness within a 24-hour cycle. The main peak is in the early morning between 0300–0500 known as the window of circadian low, another smaller peak around 1500–1700 is known as the afternoon nap window. For each individual these times can vary. The period between when the pilot arrived at Moree Airport and the accident was outside these peak sleepiness times.

Effect of multiple long days

The instructor who conducted the pilot’s aerial application rating, when asked what the effect of the previous long days would be, reported that it was not just the last couple of days; the season had effectively continued since July without a break. Research has found self-ratings of fatigue (Rithemeister and others 2021) and risks of successive incidents both increase for each consecutive day worked (Folkard and Akerstedt 2004).

As documented by ICAO (2020) biomathematical modelling is ‘a computer programme designed to predict aspects of a schedule that might generate an increased fatigue risk for the average person, based on scientific understanding of the factors contributing to fatigue…All bio-mathematical models have limitations that need to be understood for their appropriate use.’ Biomathematical models can only forecast the effects of sleep and circadian rhythms[15] on performance and cannot account for other factors known to impact performance such as training, experience, stress and illness. Additionally, the models were not designed for aerial agricultural operations and did not consider the pilot’s cognitive workload.

The ATSB used two software programs, Sleep Activity Fatigue Task Effectiveness-Fatigue Avoidance Scheduling Tool (SAFTE-FAST) and Fatigue Assessment Tool by InterDynamics (FAID) Quantum, which are biomathematical models to assess fatigue based on the pilot’s duty hours and sleep opportunity in the days leading up to the accident. Each model has specific applications and limitations.

SAFTE-FAST predicts future performance based on the recent sleep history of the projected population or individuals. The output is a performance score indicating a percentage of cognitive effectiveness at a point in time. The lower the performance score, the higher the effect of fatigue. The model is based on biological determinants of fatigue such as: hours of sleep, hours of wakefulness, current sleep debt, the circadian process and sleep fragmentation (awakenings during a period of sleep) that reduce quality (Hursh and others 2004). SAFTE-FAST indicated that the pilot’s performance was not affected by sleep history and circadian processes.

FAID uses work hours as its input to predict the effect on fatigue and performance of different duty periods or work schedules. The FAID output is a score indicating different levels of fatigue exposure for different work hours. The higher the FAID score, the higher the fatigue exposure. The FAID score is based on the following biological determinants of fatigue: time of day of work and breaks, duration of work and breaks, work history in the preceding 7 days, and biological limits on recovery sleep (InterDynamics n.d). FAID indicated a high fatigue exposure risk for the pilot on the accident day, but lower (although still high) at the time of the accident than the start of the day.

The outputs of the two models were inconsistent. The differences in results can be explained by the underlying parameters in each model.

Time on task

Agricultural operations are known to place high demands on the pilot’s attention for sustained work periods, which can result in a degradation of performance, even if the pilot has obtained adequate sleep. This is due to the continuous, repetitive, low altitude flying associated with this type of operation, while also managing the spray application (NTSB, 2014).

Rosa and others (2020) found that during a simulated 11-hour flight mission, participants' self-ratings of fatigue increased over time and their response time was slower after 7 hours. This demonstrates that sustained attention and vigilance were adversely affected by time on task.

Having started the aircraft’s engine at 0553, the pilot had been operating for nearly 6 hours when the accident occurred at 1145. Consistent with previous days and normal operations, the pilot took short breaks while the loader was refuelling, to get out of the aircraft, eat and drink. These breaks occurred approximately every hour and would last about 10 minutes. One fatigue countermeasure is activity breaks. These can reduce the impact of accumulating workload and alertness and performance will improve briefly due to providing a mental break from a continuous task (Caldwell 2008; Mallis and others 2022). Therefore, breaks can be temporarily beneficial in reducing the effects of fatigue.

Combined effects of workload and fatigue

Fatigue and workload can have similar effects on vigilance, perception and reaction/response times. A study of workload and fatigue in rail workers (Fan & Smith, 2017) found that both high workload and fatigue were associated with performance impairments. High workload was also found to increase fatigue, which then leads to a reduction in performance. The United Kingdom Civil Aviation Authority Flight-crew human factors handbook – CAP 737 (2016) described symptoms of increasing workload, including attentional and task focusing, task shedding, increased fatigue, and chance of error. It stated that:

Sustained workload contributes to fatigue. Very high workload (particularly fast onset) and feelings of not coping with the workload can cause high arousal or stress. All these things make error more likely.

The handbook lists effects of fatigue, similar to those associated with mental fatigue described earlier, including reduced awareness, easy distraction and increased slips and mistakes.

Accident site and aircraft damage  

Accident site and impact

The wreckage was located at the southern end of a stand of trees and had been subject to a significant post-impact fuel-fed fire. There were no powerlines in the area and there was no evidence the aircraft struck a tree or bird prior to the collision with terrain.

On-site examination of the wreckage and surrounding ground marks indicated that the aircraft impacted terrain upright, in a nose-down attitude of about 40°, with the right wing down about 10°. The propeller, main wheels and wing leading edge impacted the ground first (Figure 10), during which the fuselage right bottom longeron[16] fractured and punctured the right wing main spar (Figure 11). Two propeller blades were located at the engine point of impact.

Figure 10: Initial impact points – right wing, main landing gear and propeller

Source: ATSB

Figure 11: Fuselage frame longeron fracture and associated impact damage with main spar damage to right wing

Source: ATSB

Forward momentum then collapsed the forward section of the fuselage and resulted in the main spar rotating about 120° and separating from the fuselage. The aircraft then continued a short distance rotating to the right, consistent with a right turn/spin, and came to rest facing approximately east.

The engine fractured in half around the flange ‘C’ area (ring of bolts joining the exhaust casing to the gas generator casing), with the gas generator module remaining near the fuselage. The propeller hub, with propeller blade, the engine power section module, including power turbine wheel, was recovered about 27 m from the impact point, in the direction of the target crop (north). The liberated compressor turbine disc was found a further 30 m beyond the hub in a similar direction (north-east), and at the edge of the fire zone (Figure 12).

The flame front and debris trail were in the direction of the wind (towards the north-east) and towards the target crop (north). The propeller hub displacement and fire zone were consistent with the aircraft’s trajectory prior to the loss of control, and with ignition at the final resting place. There was no evidence of fire at the initial impact point.

Figure 12: Overview of accident site and fire zone

Source: ATSB

Wreckage examination

Although the throttle position could not be determined from the wreckage, examination of the damage to the engine and propeller blades was consistent with the engine producing power at impact. Seat frame distortion was consistent with a nose-down attitude at impact. Although impact and fire/heat damage precluded inspection of some control tubes and cables, flight control continuity was established via examination of connections, for example steel rod ends securely attached to bellcranks.

Aircraft configuration

Flap actuator measurement and corresponding flap setting indicated the flaps were extended about 18°. Due to impact damage, the position of the dump lever and of the hopper door could not be determined.

Fuel testing

A fuel sample was collected from the operator’s fuel tank at the property. The fuel was tested for the presence of water with none identified. A visual inspection did not identify any particulate matter in the fuel. There were also no reports of fuel quality concerns with the operator’s other aircraft using the same fuel source.

Survivability

Post-mortem and toxicology results

An autopsy report was prepared for the NSW Coroner. The report provided to the ATSB included the results of a post-mortem examination conducted by a forensic pathologist and toxicology testing.

The post-mortem examination found one minor fracture and multiple heat-related injuries, with no (life-threatening) traumatic injuries identified. No natural disease pathology was identified and no substances likely to have contributed to the accident were found in the toxicology results. The cause of death was found to be the effects of fire.

Restraint and helmet

The pilot’s seat was fitted with a 4-point harness, the webbing of which was destroyed by the fire. Despite this level of damage, the left and right lap belt attach points were found secured and the lap belt and shoulder harness steel buckle was secured. Additionally, the lap belt and shoulder harness webbing had been replaced in January 2020, and therefore would be very unlikely to have failed due to deterioration.

The pilot was always known to wear a helmet and was almost certainly wearing it at the time of the accident.

Impact force analysis

The ATSB analysed deformation of the pilot’s seat frame to determine peak impact deceleration. The pilot’s seat frame was bent at the two seat attachment locations, but the seat pan was undeformed. This indicated that the angle of deceleration was mostly forward rather than vertical. It was assessed that the seat rail was at the lowest height adjustment. The 4-point restraint was being worn at impact.

In conducting a dynamic loads analysis, a conservative evaluation of the peak deceleration for the pilot seat was 75 G. Based on a stall speed with flaps retracted of 60 kt, this equates to a square wave deceleration pulse[17] duration of 42 milliseconds.

The Aircraft crash survival design guide Volume 2 – Impact conditions and human tolerance (Coltman and others, 1989) placed this forward deceleration in the ‘area of severe injury’. Severe injury included life-threatening injuries such as major haemorrhages, spinal, abdominal and thoracic injuries, multiple fractures, concussion and long-time unconsciousness (Eiband, 1959). This was based on experiments of whole-body impact tolerance conducted on human volunteers to (mostly) subcritical levels, and test animals. Whole-body tolerance criteria were assessed with subjects seated in the upright posture and wearing full-torso restraints (and in some cases head restraint). The tolerable magnitude of accelerative force is a function of the duration; higher G were tolerated for a shorter pulse duration.

Post-impact fire safety

Post-impact fire and survivability

A potentially survivable accident is one in which the impact forces are within the limits of occupant tolerance, the aircraft structure preserves the required survival space, and the occupant restraint is adequate. As detailed below, for aircraft (including fixed and rotary wing) with a maximum certified take-off weight of 5,700 kg or less, post-impact fire (PIF) has been shown to contribute significantly to injuries and fatalities in accidents that are otherwise potentially survivable (TSB, 2006).

Aircraft certification requirements

Aircraft certification is found primarily in three regulatory structures: the US Federal Aviation Regulations (FARs), the Canadian Aviation Regulations, and the European Aviation Safety Agency requirements. These requirements are harmonised such that light aircraft manufactured in the US, Canada and Europe all meet basically the same standards.

Part 23 of the FARs prescribes the airworthiness standards for aeroplanes in the normal, utility, aerobatic, and commuter categories. There are only three FAR 23 fuel system certification requirements designed to reduce the risk of PIF. These specifically apply to aircraft with retractable landing gear in the event of a wheels-up landing.

The AT-400 aircraft was certificated under FAR 21 in the restricted category. It met the structural requirements of FAR 23, and the flight criteria, propulsion, systems and equipment items of CAM 8, Appendix B (FAA TCDS A9SW).

Fuel tanks in accident impacts

In an accident impact, metal fuel tanks are prone to rupturing, allowing fuel to spill. The rupture of the tank causes the fuel to escape at high pressure and velocity which in turn causes the fuel to form a fine mist, which can be ignited by a source such as a hot engine or electrical arcing, and produces a very intense fire.[18]  

The rupturing of the tanks results from high fluid pressures caused by inertial accelerations during the impact. The pressure distorts the tank walls and rupture will occur when the strain[19] of the distortion reaches the rupture strain (also known as the ‘ultimate’ or ‘fracture’ strain) of the tank wall material.

To improve crashworthiness, fuel bladders and cells have been constructed of materials that are less prone to rupturing, that is, they have a higher rupture strain. These are able to withstand more deformation and a puncture is less likely to expand or tear and form a larger opening from which fuel can escape.   

The rupture strain for airframe aluminium (2024-T3 alclad sheet) is about 18%. Elastomers[20] tolerate severe deformation without rupturing – for a typical elastomer, the rupture strain is about 300% – significantly higher than metals. Additionally, even if elastomeric walls are punctured, the probability of fuel misting is very low because the flow rate for the puncture is much less than through a split tank wall. As an example, Robinson R44 helicopter bladder tanks are elastomer.

The resistance of elastomers to rupture and puncture can be substantially increased by incorporating high-strength fibres, such as Kevlar, into the material. For ultimate post-crash fire resistance (as in motor racing), fuel tanks (or cells) use double elastomeric walls with material such as Kevlar in the outer layer. This substantially reduces the probability of tank wall rupture, puncture and of fuel misting.

Prevention of post-impact fires

The US National Transportation Safety Board (NTSB) special study report General Aviation Accidents: Postcrash Fires and How to Prevent or Control Them (NTSB, 1980), found that PIF occurred in about 8% of the 22,002 general aviation accidents in the US during 1974–1978. Fatalities resulted from about 59% of the accidents involving PIF and 13.3% of the accidents without fire. The study tested the hypothesis that PIF occur more often in severe accidents. Severe accidents included collisions with the ground or objects such as trees/poles, stall/spin accidents, and some following engine failure/malfunction. These made up almost 80% of fatal accidents. In severe accidents, fatalities occurred in 18% of the accidents without PIF, but in more than 60% with PIF. For non-severe accidents, less than 1% involved fatalities without PIF and 19% involved fatalities with PIF. The report summarised that fire, rather than impact, was the major contributor to fatalities in general aviation accidents involving PIF.

The study found that PIF was occurring in survivable accidents. It noted that in contrast to civil aviation, the US Army had used fuel containment technology to dramatically reduce fire injuries and deaths. A crash resistant fuel system is designed to absorb energy in controlled failures of sacrificial structures to minimise impact loads on the fuel tank and eliminate the escape of flammable fluid in a crash. The intent was that the aircraft occupants would then have sufficient time to escape or be rescued without the threat of fire.

The report identified that technology for crash-resistant fuel systems existed (in 1980) suitable for general aviation aircraft. The 1980 NTSB special study report stated that ‘the concept of fuel containment is both feasible and achievable now’. The report Tests of Crash-Resistant Fuel System for General Aviation Aircraft (Perrella, 1978) concluded that lightweight, flexible, crash-resistant fuel cells used in combination with self-sealing break-away fuel-line couplings can effectively reduce PIF in general aviation aircraft equipped with wing tanks. Safety fuel cells were developed in the 1960s to prevent post-crash fuel-fed fires in race cars to improve survivability.

However, aircraft design and certification regulations did not reflect the technologies available. In response, the US NTSB issued 6 recommendations to the US Federal Aviation Administration (FAA) to implement regulations aimed at addressing the issue of post-crash fires – A-80-90 to A-80-95.

On 17 September 1985, the FAA issued an advance notice of proposed rulemaking that informed the public of the FAA’s intent to formulate rules to improve the crash-resistance of small airplanes' fuel systems and requested economic and technical information to assist in economic analysis and technical decisions for future rulemaking.

After several years of studies and discussions, on 20 May 1988, the FAA advised the NTSB that they had drafted a notice of proposed rulemaking (NPRM). On 14 February 1990, the FAA issued an NPRM proposing changes to the airworthiness standards to improve the crash resistance of fuel system on normal, utility acrobatic, and commuter category airplanes. These proposed design changes were to limit fuel spillage near ignition sources and would provide additional time for survivors of an accident to evacuate the aeroplane.

After some changes and review of the NPRM, in 1995, the FAA concluded that the recommendations could not be justified on a benefit-to-cost basis and therefore planned to take no action on these recommendations.

In 1996, the NTSB assessed that no tangible action had occurred in the 16 years since the issuance of these recommendations, and classified recommendations A-80-90 to -92 as closed with unacceptable safety action.

Since that time, crash-resistant fuel bladders/tanks have been introduced in rotorcraft. Crash-resistant fuel system technologies have also advanced significantly, particularly in motor sports.

Regulation of helicopter fuel systems

In 1994, US helicopter standards FAR 27.952 and FAR 29.952 introduced fuel system crash resistance tests and features for new design certification. These were introduced because it was estimated at the time that 5% of occupants in survivable rotorcraft accidents were killed or injured by PIF. There were no equivalent test requirements for fixed wing aircraft.

Research for ATSB investigation AO-2013-055, found that in Australia from 1993 to 2013, PIF occurred in 7 of 47 impact-related accidents (with usable fuel remaining) involving Robinson R44 helicopters not fitted with bladder tanks. Six of those accidents resulted in fatalities. The investigation found that PIF occurred in a significantly higher proportion of accidents involving R44 helicopters without bladder-type tanks than in other similar helicopter types. In response to ATSB safety recommendation AO-2013-055-SI-01, in April 2013, CASA issued an airworthiness directive requiring Australian operators of R44 helicopters to comply with the manufacturer’s service bulletin to replace all-aluminium fuel tanks with bladder-type tanks on R44 helicopters. Since then, there have been 68 R44 and R44 II accidents in Australia, 4 of which had PIF. There were no recorded fatalities as a result of PIF in R44 helicopters in that period.

Transportation Safety Board of Canada safety issues investigation

The Transportation Safety Board of Canada (TSB) conducted a safety issues investigation – Post‑impact fires resulting from small-aircraft accidents. The investigation examined TSB data for the 13,806 accidents involving aircraft weighing 5,700 kg or less, that occurred between 1976 and 2002. The TSB determined that PIF had occurred in 521 (3.8%) of those accidents, resulting in 728 (22%) of the 3,311 total fatalities. Of the 728 fatalities, 205 were assessed as due to fire as were 80 of the 231 total serious injuries. The aircraft included 382 production aeroplanes, 94 production helicopters, 27 amateur-built aeroplanes, 2 amateur-built helicopters, 1 gyroplane and 17 ultralights. Two of the accidents were mid-air collisions between 2 aeroplanes.

The investigation found that PIF presented a significant risk of fire-related injuries and fatalities to the aircraft occupants following a collision because of:

• the proximity of fuel to the occupants
• limited escape time
• limited energy-absorption characteristics of the airframes in crash conditions
• high propensity for immobilising injuries
• inability of firefighters to suppress PIFs in time to prevent fire-related injuries and fatalities.

The investigation concluded that there should be improvements to prevent PIF and reduce fire-related injuries in otherwise survivable accidents. It found that ‘the most effective defence against post-impact fire is to prevent the fire from occurring at impact, either by containing fuel or preventing ignition, or both’.

The investigation also reviewed the history of post-impact fire safety action and identified that previous attempts to amend certification requirements for small aircraft had been unsuccessful. The report stated that post-impact fire-resistant fuel system technology had been demonstrated to be effective in race car and automotive applications, and in certified civilian helicopters. However, there was no requirement to incorporate these engineering countermeasures into new or existing small aeroplanes (or helicopters certified before November 1994).

While acknowledging the difficulty of implementing design improvements in new and existing (FAR 23 and equivalent) aircraft, the investigation found that doing so would reduce the incidence of fire-related injuries and significantly increase the rate of occupant survival.

ATSB post-impact fire occurrences

Post-impact fire data

As not all accidents were likely to have a post-impact fire risk, ATSB identified a subset of accidents, which were impact-related and therefore expected to be more likely to result in fire. The ATSB occurrence database held records of 316 collision with terrain or controlled flight into terrain (CFIT) accidents involving VH-registered (fixed-wing) aeroplanes between 2012 and 2021.

PIFs occurred in 34 (11%) of these accidents. Of the 316 accidents, 81 resulted in fatal injuries, 24 of which had PIF, in 36 the highest injury level was serious, 5 of which had PIF, and 199 resulted in only minor or nil injuries, 5 of which had PIF. As a proportion of PIF accidents, 71% were fatal, 15% were serious injury accidents and 15% resulted in minor or nil injuries. By comparison, 20% on non-PIF accidents were fatal, 11% resulted in serious injuries and 69% in minor or nil injuries.

Figure 13: Proportion of accidents with and without PIF

The 316 accidents resulted in a total of 137 fatalities and 61 serious injuries. The 34 PIF accidents accounted for 35 of the fatalities (26%) (similar to the TSB issues investigation which found 22%), and 10 (16%) of the serious injuries (Table 4).

Table 4: Number of fatal and serious injuries in PIF vs all aeroplane accidents 2012-2021

Survivability analysis

The ATSB analysed available information from the 34 PIF accidents to determine which fatalities and serious injuries were due to fire or impact. Information sources included post-mortem reports, coroners’ reports and published ATSB investigation reports. Post-mortem reports were not available for all the fatal accidents and were generally only of flight crew (not passengers). Further, for non-fatal injuries, recorded details of the injuries were limited. For this analysis, the severity was assessed as having been increased due to fire only where burns or smoke inhalation were specifically mentioned. Where information was unavailable, these were not counted as fire-related injuries/fatalities. As the NTSB found, fire rather than impact was the major contributor to fatalities in general aviation accidents involving PIF.

There were 2 accidents in which the cause of death was a combination of multiple injuries and fire, and where the injuries included head/skull injuries. These were assessed as probably not survivable because head injuries and skull fractures were significantly associated with mortality in studies of falls from heights and motor vehicle accidents (Liu and others, 2009, Papadimitriou-Olivgeris and others, 2020).

In 5 of the 34 PIF accidents (15%), a total of 5 fatalities were assessed as a result of fire following survivable injuries received in the impact. This was about 4% of all the VH-registered aeroplane impact-related accident fatalities. Two additional accidents resulted in a total of 4 serious injuries due to fire. Detail of the analysis is in Appendix B. In summary, analysis of the 34 PIF accidents found:

• 5 were considered survivable without the post-impact fire, where occupants were fatally injured
• 18 in which the accident impact was not considered survivable or were probably not survivable
• 2 resulted in serious fire-related injuries
• 9 in which occupants egressed and survived without further injury.

Five of those 34 accidents with a post-impact fire occurred during aerial application operations:

• 2 were probably not survivable as the occupants sustained multiple injuries including skull fractures
• 1 in which the occupant survived and exited the aircraft before it was destroyed by post-impact fire
• 1 in which the pilot died from the effects of fire
• 1 in which the pilot died from the effects of fire and sustained injuries that would probably have prevented the pilot extricating themselves from the wreckage.

Fuel tank type

Three types of fuel tanks were used in the accident aircraft – integral, rigid and bladder tanks:

• Integral fuel tanks are part of the aircraft structure. They are manufactured by assembling parts of the aircraft structure with sealant to form a fuel-tight compartment, most commonly in the wings.
• A rigid tank can be made of various materials including aluminium alloy, steel or composites. They are usually removable and mounted into the airframe structure.
• A bladder type fuel tank is a rubber/elastomer cell dependent on the structure of the cavity it sits in to support the weight of the fuel within it. Bladder (or ‘bag’) tanks have historically been installed in the wing in lieu of sealing the structural components but not made of crash-resistant materials. Crash-resistant materials are capable of providing impact and puncture resistant fuel bladders and cells such as those used in helicopters and racing cars.

For the aircraft involved in the 34 PIF accidents:

• Non-crash-resistant bladder tanks were fitted in 2 aircraft involving 6 fatalities. No serious injuries were recorded for those aircraft and neither accident was survivable.
• Rigid tanks were fitted in 9 of the aircraft involving 7 fatalities, none of which were survivable. Two resulted in serious injuries that were not fire related.
• Integral tanks were fitted in 23 of the aircraft involving 22 fatalities, 5 occupants of which would have survived without for the fire. In those aircraft, 8 serious injuries occurred, 4 of which were attributable to fire.

Organisational information

Aircair overview

Aircair was founded in 1980 and was one of the largest aerial application operators in Australia. The CASA-issued Air Operator’s Certificate current at the time of the accident was re-issued to Aircair on 11 June 2021, valid until 30 June 2024. Under the certificate, Aircair was authorised to conduct aerial application and aerial work operations. At the time of the accident, Aircair had a fleet of 13 aircraft conducting application operations and engaged 12 pilots. As well as VH-ACQ, the aircraft fleet included a radial-engine Air Tractor AT-301, turbine-engine AT-502, AT-504 and AT-802 type aircraft, and a piston-engine Cessna 188B, which the company had purchased specifically for the accident pilot to operate during their initial supervised hours of aerial application operations.

Safety management

At the time of the accident, although Aircair was not required to have a safety management system, they had implemented the AAAA’s Aerial Improvement Management System (AIMS). AIMS was designed to meet the safety management and quality assurance requirements of the multiple regulators that an aerial application employer is bound by, including CASA. AIMS incorporated safety management of all facets of the business, including aviation, and was designed to integrate with the company’s Operations Manual.

The AIMS section associated with planning and conducting an application detailed that the operations manager or general manager could select a particular pilot for a given application based on their experience. The section also included a detailed drift risk assessment, which was to be followed by a plan to manage the application risks, including identifying if a forecast temperature would result in a decision to cease spraying. There was no requirement for the risk assessment to be documented or retained. The chief pilot reported having discussed the application plan and forecast with the pilot the evening prior to the accident, and the pilot had confirmed the temperature spray limit with the operations manager while the aircraft was being refuelled shortly before the accident. 

The AIMS section also required the pilot to complete a hazard check on arrival to the treatment area.

Similar occurrences

Loss of control in flight

The CASA Advisory Circular 61-16 – Spin avoidance and stall recovery training (CASA, 2020), stated that stall-spin accidents accounted for about a quarter of all general aviation accidents worldwide. Further, that other than those which occurred during dual flight instruction, most of those losses of control occurred at a height too low for recovery.  

The ATSB occurrence database recorded 269 accidents that occurred due to a loss of control between 2010 and 2020 involving (fixed-wing) aeroplanes. Of those accidents, 32 occurred while manoeuvring or conducting airwork, 17 of which resulted in fatal injuries. Of the 32 accidents that occurred during manoeuvring/airwork, 14 were conducting aerial application or mustering operations.

The following is a sample of ATSB investigations into fatal accidents that resulted from an aerodynamic stall at a height too low to recover before the aircraft impacted terrain.

AO-2008-069

The pilot of a Piper Aircraft PA36-375 Pawnee Brave was conducting aerial baiting operations in the Pilton Valley, Queensland when the aircraft collided with terrain. The aircraft was seriously damaged by impact forces and a post–impact, fuel- and magnesium-fed fire. The pilot was fatally injured.

The investigation found that the topography of the area and the strong gusty wind conditions at the time, probably resulted in turbulence that increased the hazardous nature of the low-level application task. It is likely that the pilot lost control of the aircraft as a result of that turbulence, at a height from which recovery was not possible before the aircraft struck the ground.

AO-2009-070

The pilot of a Cessna A188B aircraft was fatally injured when the aircraft impacted terrain during spraying operations. The investigation determined that the aircraft stalled at an altitude from which the pilot was unable to recover before the aircraft impacted terrain.

AO-2011-082

A PZL-Mielec M18A Turbine Dromader aircraft impacted terrain on a cotton station near Dirranbandi, Queensland while conducting aerial spraying. The pilot was fatally injured, and the aircraft was destroyed by impact forces.

The ATSB found that, for reasons that could not be determined with certainty, the aircraft departed from controlled flight during a turn at low height and the pilot was unable to recover before impacting the ground.

AO-2012-059

The owner-pilot of a Cessna 150 aircraft was aerial stock mustering on a cattle station about 55 km north-east of Bourke, New South Wales. The aircraft was observed circling over an area (where cattle were not moving,) then entered a steep descent followed by the sound of an impact. The aircraft was seriously damaged, and the pilot sustained fatal injuries.

The ATSB found that, while manoeuvring at low level, the pilot inadvertently allowed the aircraft to aerodynamically stall, resulting in a high rate of descent and collision with terrain. There was insufficient information about pilot control inputs to establish the factors that precipitated the stall.

AO-2014-192

On 29 December 2014, a Cessna 172S aircraft departed Cambridge Airport, Tasmania to photograph yachts participating in the 2014 Sydney Hobart race. On board the aircraft were the pilot and a photographer.

At about 1815, the aircraft commenced low-level photographic runs on yachts. Shortly after completing a run on one yacht at a height of about 50 ft, the aircraft entered a steep climbing turn. The aircraft had almost completed a 180° turn when the upper (right) wing dropped sharply while the aircraft’s nose pitched down to almost vertical. The aircraft impacted the water’s surface in an almost vertical nose down attitude with wings about level. Both aircraft occupants were fatally injured, and the aircraft was substantially damaged.

As a result of the steep climbing turn, the aircraft’s upper wing aerodynamically stalled, resulting in a rapid rotation out of the turn. The steep pitch attitude indicated that, because of the stalled upper wing, the aircraft entered a spin. There was insufficient height for the pilot to recover the aircraft.

Addressing loss of control in flight occurrences

The US FAA Airplane Flying Handbook (2021) chapter 5 Maintaining aircraft control: upset prevention and recovery training, stated that a loss of control in flight (LOC-I) is the leading cause of fatal general aviation accidents in the US and commercial aviation worldwide. The text listed situations that increase the risk of loss of control, including uncoordinated flight, distraction, turbulence and poor risk management. It further stated that in situations where a LOC-I can occur, pilots must recognise when the aircraft is approaching a stall or has stalled and execute the correct procedure to recover the aircraft. This requires training that includes slow flight, stalls, spins, and unusual attitudes.

US FAA Advisory Circular 120-109 – Stall prevention and recovery training was aimed at reducing LOC-I accidents and incidents. The circular stated that a ‘recurring causal factor in LOC-I accidents and incidents is the pilot’s inappropriate reaction to impending stalls and full stalls’. Further, the circular advised that reducing the angle of attack was the most important pilot action to recover from an impending or full stall and therefore this should be emphasised in stall training. 

Safety analysis

Introduction

On the morning of 4 December 2021, after completing the fifth spray run of the eleventh chemical load on a property near Moree, New South Wales, VH-ACQ was observed to climb, enter a right procedure turn, then descend rapidly and impact terrain, followed almost immediately by an intense fuel-fed fire.

The investigation found no evidence of a bird or tree strike, or anything likely to have jammed the flight controls affecting controllability. Continuity of the flight controls was established, the main wing spar was intact, and the engine was making power and driving the propeller when the aircraft impacted the ground. At the time of the accident, the aircraft was below the maximum take-off weight approved for aerial application operations and the centre of gravity was within the extrapolated limits.

This analysis will discuss development of the accident sequence and the effect of the environmental conditions. The pilot’s experience and how this contributed to workload and fatigue will also be examined. Further, it will consider the management of flight risk and factors affecting survivability.

Loss of control

Witness observations of the aircraft turning and descending rapidly were consistent with an aerodynamic stall and loss of control in flight. These observations were consistent with the accident site, in which the aircraft wreckage was confined in a small area, with evidence of a high vertical impact and low forward speed.

The last recorded GPS position left of the last spray run and about 180 ft above the ground, was consistent with the pilot conducting a right procedure turn – a shallower turn about 45° to the left, followed by a steeper right turn – at the end of the spray run. That last recorded height was very likely not the maximum reached, as the data from previous turns showed the aircraft generally climbed to about 250 ft above the ground.  

The loss of control in flight was consistent with a rapid entry to the stall. That stall was a result of the angle of attack being too high from moving the elevator control stick position too far aft while increasing the bank angle during the turn. The stick force experienced by the pilot on the elevator control depended on the trim position, which could not be determined. Regardless of the stick force, the stick position that a pilot needs to set to recover from a stall will be the same. Stall prevention requires monitoring the position of the elevator control stick, awareness of its position at which the aircraft will stall, and to maintain the control stick forward of that position. Stall warning or buffet should alert the pilot to move the stick forward, but the pilot may have had very little warning. The pilot reportedly had the stall stick position demonstrated, and although they had on occasion pulled the stick back too far in a turn during training, this was a common training error, which the pilot had been observed to have rectified. Analysis of recorded GPS data from the pilot’s flights prior to the accident, showed the pilot generally employed sound technique in the turns.  

The Airplane Flight Manual stated that the aircraft would lose 220 ft in recovering from a straight and level stall at the published maximum weight, based on flight testing. Recovery height would be increased by an accelerated stall and uncoordinated turn. Accident site analysis showed the aircraft impacted the ground nose-down and wings almost level, which suggested the pilot had acted to recover from the stall but had insufficient height to complete the recovery.

Effect of field shape

As evidenced by the recorded GPS data, the pilot had not flown hazard checks on the accident day. The operator assessed that as the pilot had overflown the accident block several times in the previous days, they were probably familiar with it. However, it could not be determined whether the pilot had identified the uneven southern boundary and shape of crop to be sprayed before commencing the accident turn.

Due to the shape of the target block, the pilot needed to turn the aircraft further beyond the southern boundary or wider than the previous turns, to line up on the next spray run at a suitable height to commence spraying. Consideration of additional turn radius was also required due to the 10–18 kt gusty south-westerly wind becoming a tailwind during the turn, thereby pushing the aircraft closer to the crop.

The recorded GPS data from the pilot’s flights on the day prior to the accident showed that the aircraft was usually lined up on the next spray run about 200 m prior to the crop boundary. The location of the accident and the position where the loss of control occurred was about 110 m south of the target crop. At that point, the aircraft was too high and too close to the southern boundary to manoeuvre safely to commence spraying the crop at the start of the next spray run. From this position, the pilot likely attempted to tighten the turn rather than miss the additional crop (and skip that spray run).

Experience, workload, and fatigue

Experience

The pilot had commenced aerial application training immediately after attaining a commercial pilot licence in the minimum timeframe. On achieving their aerial application and low-level ratings, the pilot commenced aerial application operations as an employee of the aircraft operator, in September 2021. The pilot then conducted the required supervised aerial application flight time in a piston-engine aircraft. One week before the accident, the operator assessed that the pilot was ready to transition to turbine-engine Air Tractor aircraft.

Although the pilot had demonstrated competence in the aircraft and aerial application to a high level of skill for their experience, at the time of the accident, they were still relatively inexperienced in overall flight time, aerial application, and particularly in the AT-400 aircraft. This inexperience likely affected many facets of the operation, including aircraft handling, workload and fatigue.

Workload 

Agricultural pilots operating at low altitudes must visually scan external cues to control the aircraft and avoid obstacles, while also monitoring inside the cockpit including instruments, spray systems and property maps. Due to the close proximity to obstacles, terrain and the airspeeds at which the aircraft are flown, agricultural pilots have less time to respond to abnormal situations. As a result, any lapse in concentration or imprecision in control input could lead to catastrophic consequences (NTSB, 2014).

During the morning, the increased temperature, change in wind direction and increase in wind strength and gust speed, made the flying conditions increasingly turbulent. The conditions half an hour after the accident were described as quite windy and rough. Turbulence has been found to increase physical and mental workload, which can lead to degradation in the pilot’s ability to safely and effectively operate the aircraft. This is due to human perceptual systems breaking down, as a result performance can diminish, leading to fatigue, motion sickness and reduced mental performance. (Dodd and others, 2014). These conditions increased the pilot’s workload through additional physical aircraft handling and discomfort.

The pilot’s text message regarding the temperature, radio call regarding drift, and the aircraft’s track on the accident load, were indicative of the pilot making decisions in response to the changing conditions. While such decision-making is a usual part of spraying operations, it requires cognitive resources, thereby increasing workload. The pilot’s radio call about 20 minutes before the accident, suggested the pilot was experiencing stress and high workload. During the morning, the pilot had been in radio contact with the operations manager and other company pilots including the Aircair general manager. However, resources usually available to assist in managing the pilot’s workload and aid in decision‑making, were diminished on the accident day as the loader had no radio and it was the first day that the chief pilot was not supervising the pilot.

Without these resources to assist, the pilot was possibly assessing whether to cease flying due to the conditions, further adding to their cognitive load. Making such a decision may also have been more difficult while other company pilots were continuing to operate.

The pilot’s concern about drift precipitated a change of plan, whereby the pilot elected to move from the western to the eastern boundary, abandon the incomplete racetrack pattern and resume spraying in a back-to-back pattern. The change in spray pattern briefly required the pilot’s focus inside the cockpit to change GPS settings, introducing the potential for distraction and increasing workload. However, there was no evidence to demonstrate this distraction occurred at the time of the accident.

Due to a combination of inexperience, the environmental conditions, decision-making, and absence of supervision, the pilot’s workload was likely at a level known to increase error rates, reduce performance and lead to important information being missed (Green and others, 1996).

Fatigue

The pilot had several early starts and long days in the month prior to the accident, consistently reporting to a friend (but not to the operator) being very tired at the end of each day. As the accident day was the pilot’s ninth day of duty, there was an increased risk of cumulative fatigue. In the 3 days prior to the accident, the pilot had recorded their longest consecutive flight and duty times since commencing aerial application operations. Additionally, the pilot’s commute by car to and from the base was extended due to recent flooding, which reduced the opportunity for recovery between flight duties.  

All the pilot’s recent flight time was cognitively demanding low-level aerial application with short breaks during refuelling. Additionally, the cognitive demands would have been higher than for a more experienced pilot, particularly the pilot’s very limited flight time in the turbine-engine aircraft. At the time of the accident, the pilot had been operating for approaching 6 hours, with several short (10-minute) breaks during refuelling, including one about 15 minutes prior to the accident. Research on sustained attention during a task has shown that decreases in performance and self-rating experiences of fatigue increase over time (Rosa and others, 2020). However, work breaks can be temporarily beneficial in reducing the effects of fatigue (Caldwell 2008; Mallis and others 2022).  

The pilot’s sleep history and the accident time of day were unlikely to have affected the pilot’s performance. However, the consecutive long flight and duty times in the days leading up to the accident, in what would have been a high cognitive workload environment for the pilot, likely resulted in the pilot experiencing fatigue at a level known to affect performance.

Effects of workload and fatigue

Several factors increased the pilot’s workload at the time of the accident, including the conditions and inexperience. Those same factors and the high workload itself, combined with long flight and duty times in the preceding days, also likely contributed to the pilot experiencing fatigue.

The pilot had probably encountered similar environmental conditions while flying a piston-engine Cessna 188B aircraft in the previous weeks, but had more experience in that aircraft. That aircraft also had more docile stall characteristics and gave more warning of an impending stall. After commencing flying VH-ACQ 5 days before the accident, the pilot had demonstrated competence in that aircraft and operated it effectively, including spraying over 1,000 hectares in the previous 2 days. However, on the accident day, the pilot mishandled the aircraft during the turn. This handling error was likely a result of fixating on making the crop, and not monitoring the aircraft state or allowing adequate margin for the conditions. These errors and impaired awareness were consistent with the effects of both overload and fatigue.

Flight risk management

Management of fatigue is a shared responsibility between the aircraft operator and the pilot. Although the pilot had self-assessed as being tired on many occasions in the previous weeks, including the evening prior to the accident, there was no evidence this had been reported to the operator. Additionally, this tiredness had been noted in the evenings, following which there was a sleep opportunity for the pilot to recover (to some extent) before commencing the next morning.

Based on the regulatory duty time limitations, had the pilot been off duty for between 9 and 10 hours when they commenced on the morning of the accident, they were within a discretionary period that required a self-assessment of being mentally and physically fit to fly. The pilot commenced on the accident day close to the 10-hour rest period and it was unknown whether the pilot conducted this self-assessment. However, pilots were required to ensure they were fit to fly prior to every flight. There was also no evidence that the operator was aware the pilot had commenced duty on the accident day within or approaching the discretionary duty time window.

The aircraft operator’s operations manual stipulated that fatigue be managed in accordance with Civil Aviation Safety Regulations, which provided maximum flight and duty times (and minimum rest periods) for aerial application operations. However, there was no consideration of environmental conditions or experience – total aeronautical experience, aerial application flight hours, or hours in an aircraft model – nor how this may affect fatigue. Given inexperience and environmental conditions can increase fatigue, these factors in combination should be considered as part of fatigue risk.

Furthermore, fatigue risk is just one component of overall flight risk. A flight risk assessment provides a comprehensive assessment of factors that increase risk and the effect of combination of these factors. Although it was not required by regulations at the time, the aircraft operator had a safety management system. However, it did not include a flight risk assessment tool, which is a key component of a safety management system (FAA, 2016).

The 2014 US National Transportation Safety Board Special investigation report on the safety of agricultural aircraft operations outlined that risk management guidelines and best practices specific to agricultural aircraft operations were necessary to help operators and pilots mitigate their unique risks. These practices should include information and checklists for performing pre-flight risk assessments and identifying mitigation strategies.

A flight risk assessment tool specific for aerial application operations should include consideration of pilot (experience, recency, supervision, fitness to fly), aircraft (including role equipment), environment (weather, task, chemical, hazards) and operational pressures. Use of a flight risk assessment tool before commencing a flight also acts as a prompt for a pilot to reassess the risk when the considered factors change. Although the operator was attempting to manage the risk associated with inexperience, having a formal process may have integrated all the hazards present on the accident day. Had a flight risk assessment tool been available to the pilot on the accident morning, the combination of the weather conditions, inexperience, complexity of the task, absence of supervision, and probable fatigue, would have been expected to generate an elevated risk rating that would have required mitigation and/or approval for the pilot to conduct or continue the flight.

Survivability

The post-mortem examination identified that the pilot succumbed to the effects of fire. The fire was likely a hot, flash-over fire resulting from the rupture of the fuel tanks and misting of the fuel. Local workers who witnessed the accident were on site within minutes of the accident, however, the fire erupted within seconds of impact.

The tolerance of the human body to accident impact is a function of many variables, including individual characteristics, such as age, sex and general health. The restraint system significantly contributes to the overall probability of survival in an accident (Coltman and others, 1989). Contact injuries are reduced by 4-point (and 5-point) restraints and aviation-standard helmets. Restraints, energy-absorbing structure and seats reduce acceleration injuries. If these injuries do occur, they can contribute to fire-related fatalities and more serious injuries, by preventing self-extrication from an aircraft in the event of a post-impact fire.

An estimate of the impact forces, based on the bending of the pilot seat frame, indicated the accident would have likely resulted in severe injury. However, the pilot did not sustain impact-related injuries likely to have contributed to mortality. The pilot was almost certainly wearing a helmet and a 4-point restraint, and the cockpit maintained survivable space around the pilot’s torso. The crushing of the hopper and forward section of the aircraft likely absorbed a significant amount of the of the forward impact, aiding in reducing acceleration injuries.

Crash-resistant fuel systems

Air Tractor aircraft, like many others, use the aircraft wing structure as an integral fuel tank. The AT-400 fuel tank met or exceeded the certification requirements. In an impact with the ground, traditional aircraft wing structures are comparatively rigid and will rupture, allowing their fuel contents to escape. Due to the high fluid pressures generated inside the fuel tank in ground impacts, fuel forced through these ruptures tends to mist into a large cloud, which increases the risk of ignition and conflagrates quickly into a large encompassing fire.

An aircraft fuel tank lined with a crash-resistant bladder can be more resistant to spilling or leaking due to its ability to retain its contents if distorted. Being flexible, the bladder can withstand changes to its shape without rupturing or splitting. The bladder is also more tolerant of penetrating objects being able to deform around the intruding body to some extent. There have been no fatal or serious injuries to occupants as a result of post-impact fire in Robinson R44 helicopters in Australia since fitment of bladder tanks was mandated after a fatal accident in 2013. Prior to that time, accidents involving Robinson R44 helicopters without bladder tanks resulted in a significant proportion of post-impact fires. Of the (fixed-wing) aeroplanes involved in fatal accidents with post-impact fire in Australia between 2010 and 2022, 2 were fitted with fuel bladders. However, these were not made of crash-resistant materials.

Bladder tanks are one technology designed to improve crashworthiness of fuel systems. Crash‑resistant fuel systems reduce the risk of post-impact fire and provide occupants with more time to escape or be rescued. VH-ACQ was not fitted with crash-resistant fuel tanks or systems. The certification standards at the time the aircraft was manufactured did not require it, nor did the fixed-wing aircraft standards at the time of the accident. This differed from the requirements for rotary-wing aircraft.

The US National Transportation Safety Board and the Transportation Safety Board of Canada found a significant risk associated with post-impact fires in general aviation aircraft. As a result, they made recommendations to the US Federal Aviation Administration aimed at addressing the crashworthiness of fuel systems in these aircraft. A review of VH-registered aeroplane accidents in the ATSB occurrence database from 2010–2022 found a significant risk for post-impact fire fatalities, consistent with that previously identified in the US and Canada. Nearly 4% of the fatalities (5 fatalities in 10 years) in general aviation accidents in Australia were solely the result of the post impact fire. A fatality percentage of 5% was used by the Federal Aviation Administration to justify fuel system crash resistance tests and features for new helicopter designs.

The design principles and technologies for crash-resistant fuel systems exist and have been proven effective in helicopters and the automotive industry. Incorporating these in aeroplane design would reduce the risk of impact-induced fire in otherwise survivable accidents.

Findings

From the evidence available, the following findings are made with respect to the loss of control and collision with terrain involving Air Tractor AT-400, VH-ACQ, 75 km west-south-west of Moree, New South Wales, on 4 December 2021.  

Contributing factors

• The aircraft was too close to the start of the spray run during the turn, which probably resulted in the pilot tightening the turn. This almost certainly resulted in an aerodynamic stall at a height too low to recover before colliding with the ground.
• The pilot was likely experiencing high workload and fatigue due to long flight and duty times, inexperience, the complexity of the task and the weather conditions. The combined effects of these factors probably resulted in the pilot mishandling the turn.
• The aircraft’s integral fuel tanks ruptured during the accident sequence. This resulted in a fire which led to the pilot’s fatal injuries.

Other factors that increased risk

• The aircraft was not fitted nor required to be fitted with a crash-resistant fuel system under the current standards or those in place at the time of manufacture. As a result, post-impact fire presents a significant risk of fire-related injuries and fatalities to aircraft occupants. (Safety issue)

Other findings

• A flight risk assessment tool is used in some aerial work operations, however for aerial application operations it is not a requirement and generally not used. A flight risk assessment tool tailored to aerial application would likely have identified an elevated risk on the day of the accident, due to the combination of the pilot’s inexperience, weather conditions, complexity of the task, absence of supervision and probable fatigue.
• The pilot was almost certainly wearing a helmet and 4-point restraint increasing their chances of survival in an accident.

Safety issues and actions

Crash-resistant fuel system

Safety issue number: AO-2021-052-SI-01

Safety issue description: The aircraft was not fitted nor required to be fitted with a crash-resistant fuel system under the current standards or those in place at the time of manufacture. As a result, post-impact fire presents a significant risk of fire-related injuries and fatalities to aircraft occupants.

Safety recommendation description: The ATSB recommends that the United States Federal Aviation Administration take action to address certification requirements for crash-resistant fuel systems for fixed wing aircraft to reduce the risk of post-impact fire.

Safety action not associated with an identified safety issue

Additional safety action by Aircair Aviation Operations Pty Ltd (Aircair)

Aircair has considered whether there could be a risk associated with fatigue that does not necessarily correlate to flight and duty hours worked. As such, they are investigating if other means of measuring fatigue risk can be developed, such as a point score system that includes any other contributory factors such as conditions, experience, overall wellbeing and difficulty of the task. Further, they intend to explore technology available in modern cars and machinery that measures operator fatigue.

In August 2022, Aircair’s pilot group underwent advanced stall and spin prevention, recognition and recovery training with an experienced aerobatic instructor. Due to its success, Aircair is investigating ways of incorporating such training into its new pilot induction program.

Aircair recommended that the risks associated with mobile phone use in the cockpit (as referenced in the Aircair Operations Manual) are reiterated to pilots on a regular basis by way of pilot meetings and safety notices.

Aircair intends to ensure that pilots are regularly reminded of the possibility of becoming distracted by guidance systems and the impact this may have on safe operations. As part of this process, pilots should be reminded to only attend to GPS related issues when at a safe height above the ground.

Pre-application field inspections form a critical component for a safe application operation (particularly for unfamiliar fields). The requirement to conduct such inspections is set out in the Aircair Operations Manual and is tested during Aircair Operator Proficiency Checks (OPC). The importance of pre‑application field inspections will be reinforced to pilots on a regular basis by way of pilot meetings and safety notices.

Glossary

AAAA               Aerial Application Association of Australia

AFM                 Airplane Flight Manual

AIMS                Aerial Improvement Management System

CAM                 Civil Aeronautics Manual

CAR                 Canadian Aviation Regulation

CAS                 Calibrated airspeed

CASA               Civil Aviation Safety Authority

CASR               Civil Aviation Safety Regulations

CG                   Centre of gravity

EDT                  Eastern Daylight-saving Time

FAA                  Federal Aviation Administration

FAR                  Federal Aviation Regulation

FCM                 Flight crew member

IAS                   Indicated airspeed

ICAO                International Civil Aviation Organization

LOC-I                Loss of control in-flight

NASA               National Aeronautics and Space Administration

NPRM               Notice of proposed rule making

NTSB                National Transportation Safety Board

PSI                   Pounds per square inch

SMS                 Safety management system. A systematic approach to organisational safety encompassing safety policy and objectives, risk management, safety assurance, safety promotion, third party interfaces, internal investigation and SMS implementation.

TSB                  Transportation Safety Board (of Canada)

UTC                  Coordinated Universal Time

Sources and submissions

Sources of information

The sources of information during the investigation included the:

• aircraft operator and chief pilot
• other company pilots
• Civil Aviation Safety Authority
• New South Wales Police Force
• aircraft manufacturer
• aircraft maintainer
• accident witnesses
• recorded data from the aircraft’s GPS units
• Bureau of Meteorology and Oz Forecast.

References

Air Tractor (2012). Service letter 304: Establishing and operating with a special purpose operating weight for Air Tractor aircraft.

Australian Transport Safety Bureau (2017). ATSB Safety Investigation. Canberra, Australia: ATSB.

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Boksem, M. A. S., Meijman, T. F., & Lorist, M. M. (2005). Effects of mental fatigue on attention: An ERP study. Brain research. Cognitive brain research, 25(1), 107-116. doi: 10.1016/j.cogbrainres.2005.04.011

Byrne, A. J., Murphy, A., McIntyre, O., & Tweed, N. (2013). The relationship between experience and mental workload in anaesthetic practice: an observational study. Anaesthesia, 68(12), 1266-1272. doi: 10.1111/anae.12455

Caldwell, J. A., Caldwell, J. L., & Schmidt, R. M. (2008). Alertness management strategies for operational contexts. Sleep medicine reviews, 12(4), 257-273. doi: doi:10.1016/j.smrv.2008.01.002

Civil Aviation Safety Authority (2012). Fatigue Management Strategies for Aviation Workers: A Training & Development Workbook.

Civil Aviation Safety Authority (2020). Advisory Circular AC 61-16 v1.0: Spin avoidance and stall recovery training.

Coltman, J. W., Van Ingen, C., Johnson, N. B. & Zimmerman, R. E. (1989). Aircraft crash survival design guide: Volume II – Aircraft design crash impact conditions and human tolerance. US: United States Army Aviation Applied Technology Directorate.

Dawson, D., & Reid, K. (1997). Fatigue, alcohol and performance impairment. Nature, July 1997, 388:235.

Dodd, S., Lancaster, J., Miranda, A., Grothe, S., DeMers, B., & Rogers, B. (2014). Touch Screens on the Flight Deck: The Impact of Touch Target Size, Spacing, Touch Technology and Turbulence on Pilot Performance. Proceedings of the Human Factors and Ergonomics Society 58th Annual Meeting, 58(1), 6-10. https://doi.org/10.1177/1541931214581002

Eiband, A. M., Human tolerance to rapidly applied accelerations: A summary of the literature, NASA Memorandum 5-19-59E, National Aeronautics and Space Administration, Washington, D.C., June 1959.

Faber, L. G., Maurits, N. M., Lorist, M. M., & de Lange, F. P. (2012). Mental Fatigue Affects Visual Selective Attention. PloS one, 7(10), e48073-e48073. doi: 10.1371/journal.pone.0048073

Fan, J., & Smith, A.P. (2017). The impact of workload and fatigue on performance. Conference Paper in Communications in Computer and Information Science, June 2017. doi: 10.1007/978-3-319-61061-0_6

Federal Aviation Administration (2021). Airplane Flying Handbook, FAA-H-8083-3C. US: FAA. Retrieved from: Airplane Flying Handbook | Federal Aviation Administration (faa.gov)

Fletcher, A., Lamond, N., van den Heuvel, C., & Dawson, D. (2003). Prediction of performance during sleep deprivation and alcohol intoxication by a quantitative model of work-related fatigue. Sleep Research Online, 5(2), 67-75.

Fletcher, A. (1999). Measurement and management of work-related fatigue: Development and preliminary validations of a predictive model. Ph.D. Thesis, 1999, The University of South Australia.

Folkard, S., & Åkerstedt, T. (2004). Trends in the risk of accidents and injuries and their implications for models of fatigue and performance. Aviation, space, and environmental medicine, 75(3), A161-A167.

Gawron, V. J. (2016). Overview of self-reported measures of fatigue. The International Journal of Aviation Psychology, 26:3-4, 120-131. doi: 10.1080/10508414.2017.1329627  

Goode, J. H. (2003). Are pilots at risk of accidents due to fatigue?. Journal of safety research, 34(3), 309-313. doi: 10.1016/s0022-4375(03)00033-1

Green, R. G., Muir, H., James, M., Gradwell, D., & Green, R. L. (1996). Human Factors For Pilots (2nd ed.), Ashgate, England.

Harris, D. (2011). Human Performance on the Flight Deck. Ashgate, England.

Hawkins, F.H. (1993). Fatigue, Body Rhythms and Sleep. In H.W. Orlady (Eds.), Human Factors in Flight (2nd ed., pp. 56-83). Ashgate.

Heywood, B. (1999). Pilot Fatigue and the Limits of Endurance, Flight Safety Australia (1999, April). Retrieved from: https://skybrary.aero/sites/default/files/bookshelf/1080.pdf.

Hursh, S. R., Balkin, T. J., Miller, J. C., & Eddy, D. R. (2004). The fatigue avoidance scheduling tool: Modeling to minimize the effects of fatigue on cognitive performance. SAE transactions, 111-119.

InterDynamics (n.d.). FAID® Quantum Version 1.1 User Guide.

International Civil Aviation Organization (2020). Manual for the Oversight of Fatigue Management Approaches (Doc 9966).

Li, P. C., Wang, Y. X., Chen, J. H., Luo, Z. H., Dai, L. C. (2021). An experimental study on the effects of task complexity and knowledge and experience level on SA, TSA and workload. Nuclear engineering and design, 376, 111112. doi: 10.1016/j.nucengdes.2021.111112

Liu, C-C., Wang, C-Y., Shih, H-C., Wu, J. J-K., Huang, C-I., Hsu, H-S., Huang, M-H., Huang, M-H., Huang, M-S. (2009).  Prognostic factors for mortality following falls from height. Injury, International Journal of the Care of the Injured, 40 (2009) 595–597.

Mallis, M., Banks, S., Dorrian, J., & Dinges, D. F. (2022). Aircrew fatigue, sleep need, and circadian rhythmicity. In Keebler, J.R., Wilson, K.A., Lazzara, K.H., & Blickensderfer, E.L. (eds) Human Factors in Aviation and Aerospace (pp. 309-339). Academic Press.

National Aeronautics and Space Administration (2010). Human Integration Design Handbook (HIDH). Retrieved from: https://www.nasa.gov/sites/default/files/atoms/files/human_integration_design_handbook_revision_1.pdf

National Transportation Safety Board (1980). General Aviation Accidents: Postcrash Fires and How to Prevent or Control Them (NTSB-AAS-80-02).

National Transportation Safety Board (2014). Special Investigation Report on the Safety of Agricultural Aircraft Operations (NTSB/SIR-14/01). Retrieved from: https://www.ntsb.gov/safety/safety-studies/Documents/SIR1401.pdf

Orlady, H.W., & Orlady, L.M. (1999). Human Factors in Multi-Crew Flight Operations. Ashgate, England.

Papadimitriou-Olivgeris, M., Panteli, E., Koutsileou, K., Boulovana, M., Zotou, A., Marangos, M., Fligou, F. (2021). Predictors of mortality of trauma patients admitted to the ICU: a retrospective observational study. Brazilian Journal of Anesthesiology, 71 (2021) 23-30.

Perrella, W.M. Jr. (1978), Tests of Crash-Resistant Fuel System for General Aviation Aircraft, (FAA-RD-78-28), interim report prepared for the US Department of Transportation, Federal Aviation Administration.

Petrilli, R.M.A., Roach, G.D., Dawson, D., & Lamond, N. (2007). The sleep, subjective fatigue, and sustained attention of commercial airline pilots during an international pattern. Chronobiology International, 23(6): 1347–1362. doi: 10.1080/07420520601085925

Riethmeister, V., Matthews, R. W., Dawson, D., de Boer, M. R., Brouwer, S., & Bültmann, U. (2019). Time-of-day and days-on-shift predict increased fatigue over two-week offshore day-shifts. Applied ergonomics, 78, 157-163. doi: 10.1016/j.apergo.2019.02.010

Roach, G.D., Petrilli, R.M.A., Dawson, D., & Lamond, N. (2012). Impact of layover length on sleep, subjective fatigue levels, and sustained attention of long-haul airline pilots. Chronobiology International, 29(5): 580–586. doi: 10.3109/07420528.2012.675022

Rosa, E., Eiken, O., Grönkvist, M., Kölegård, R., Dahlström, N., Knez, I., ... & Willander, J. (2020). Effects of fatigue on cognitive performance in long-duration simulated flight missions. Aviation Psychology and Applied Human Factors, 10(2), 82. doi: 10.1027/2192-0923/a000191

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Tucker, A. (2015). JHC Commanders’ Guide to Fatigue Management. Retrieved from: https://www.aviation.govt.nz/assets/licensing-and-certification/medical/jhc-commanders-guide-to-fatigue-management.pdf

Submissions

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

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

• the aircraft operator
• the aircraft maintainer
• Civil Aviation Safety Authority
• US National Transportation Safety Board
• Transportation Safety Board of Canada
• Pratt & Whitney Canada
• US Federal Aviation Administration
• Air Tractor Incorporated
• Satloc.

Submissions were received from;

• the aircraft operator
• the aircraft maintainer
• Civil Aviation Safety Authority
• US National Transportation Safety Board
• US Federal Aviation Administration
• Pratt & Whitney Canada
• Transportation Safety Board of Canada
• Air Tractor Incorporated
• Satloc.

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

Appendix A – Hoerner wingtips

Executive summary

What happened

On 8 October 2021, a Kavanagh Balloons E-240 balloon, registered VH-LUD and operated by Floating Images Aust. Pty Ltd was conducting a morning scenic flight about 45 km south‑west of Brisbane, Queensland. On board was a pilot and 9 passengers. About 55 minutes into the flight, the pilot commenced a descent to locate a suitable landing area. During the descent, the balloon entered an area of localised fog where visibility reduced to 10 m.

The pilot continued the descent into the fog until a tree was observed in the path of the balloon. The pilot attempted to avoid the tree by initiating a climb, but the balloon collided with, and came to rest on the side of the tree, damaging the lower part of the balloon envelope. The pilot subsequently climbed the balloon off the tree and above the fog. The flight continued to an uneventful landing in a nearby paddock that was clear of fog. There were no injuries.

What the ATSB found

The ATSB found that, contrary to the visual flight rules visibility requirement, the pilot entered an area of reduced visibility in which the visibility was 10 m. This did not allow sufficient time to complete an avoidance manoeuvre when an obstacle was observed, as a result the balloon collided with a tree and the balloon envelope was damaged.

Safety message

In some circumstances, balloons are permitted to fly in significantly lower visibility than other types of aircraft. While this is mainly due to their inherently low flight speed, it also considerably reduces the available time to see obstacles. Additionally, as balloons can only manoeuvre vertically and significant time may be required to transition from a descent to a climb, they have limited capability to avoid obstacles.

Therefore, to reduce the collision risk if a balloon enters an area of visibility less than that permitted by the visual flight rules, pilots should ensure that an immediate recovery is commenced.

The investigation

The occurrence

On 8 October 2021, the pilot of a Kavanagh Balloons E-240 balloon, registered VH-LUD, was preparing for a morning scenic charter flight for 9 passengers from a location 45 km south‑west of Brisbane, Queensland. The pilot reported releasing a small helium balloon from the Ipswich Visitor Information Centre, located about 6 km to the east of RAAF Base Amberley (Figure 1), at 0425 Eastern Standard Time,[1] to observe wind speed and direction. The pilot also checked the wind observations recorded at the nearby RAAF Base, which were variable[2] at 3 knots.

Following an assessment, via the observation balloon, that the wind was from the west‑north‑west, the pilot planned the flight to commence at Rosewood Golf Club with an intent to track south-east, to the south of RAAF Base Amberley, and continue towards Yamanto (Figure 1). The pilot commented that there was no fog present at the departure time.

The 9 passengers arrived at the Ipswich Visitor Information Centre at about 0425 and they were taken to Rosewood Golf Club. The passengers were briefed on the 3 stages of balloon flying: inflation, flight, and landing. The pilot then inflated the balloon, and the passengers were boarded.

Although the pilot planned the flight in non-controlled Class G airspace[3] around RAAF Base Amberley, they made a telephone call to RAAF Amberley air traffic control and left a message on their answering machine with details of the balloon flight. The pilot reported that this was in case RAAF Amberley airspace became active during the period of the balloon flight and the airspace reverted to military Class C airspace[4] (see the section titled Airspace).

The balloon took off at around 0520 and tracked towards the east-south-east as expected from the wind observations. The pilot reported clear skies with some localised fog present to the south‑east of the RAAF base. The pilot estimated the fog to be from the surface to a height of 500 ft.

Figure 1: Flight path of VH-LUD

Source: Google Earth, annotated by the ATSB

After about 55 minutes of flight time the pilot commenced a descent to visually identify and select a suitable landing area. As the balloon descended below 1,000 ft the wind backed[5] to a south‑westerly. As a consequence of that wind change, the balloon began tracking north-east towards the previously‑identified fog bank (Figure 2).

The pilot approached the fog expecting to be able to maintain visual requirements for landing. However, upon entering the fog, the pilot recalled observing that it was significantly thicker than they expected or had flown in before with visibility of about 10 m. The pilot continued to descend at approximately 200 feet per minute into the fog until they sighted a tree directly ahead of them. In response, the pilot immediately commenced burning on all 3 burners to arrest the descent and transition to a climb, but the balloon collided with the tree at a speed of about 4 knots. The balloon came to rest on the side of the tree at a height of about 60 ft above the ground. 

Figure 2: Descent of VH-LUD to Yamanto

Source: Google Earth, annotated by the ATSB

The pilot continued operating the burners and the balloon commenced a climb away from the tree. The pilot climbed the balloon until they were out of the fog and conducted an uneventful landing in a nearby paddock, clear of the fog. There were no injuries to the pilot or passengers, however multiple sections of the lower portion of the balloon envelope required repair or replacement due to damage by tree branches. The balloon returned to service 7 days later.

Context

Pilot experience

The pilot held a Civil Aviation Safety Authority (CASA) Commercial Pilot Licence (Balloon) that was issued in January 1995. At the time of the occurrence the pilot had accrued a total flying time of 2,904 hours with approximately 2,000 hours on type. The pilot held a current CASA class 2 aviation medical certificate.

The pilot also held a CASA Maintenance Authority to conduct maintenance on the Kavanagh balloon.

Balloon information

VH-LUD was a Kavanagh Balloons E-240 manned free balloon manufactured as serial number E24-527 in 2016 by Kavanagh Balloons Australia Pty Ltd. The E‑240 balloon has an envelope capacity of 240,000 cubic feet and a maximum take-off weight of 2,000 kg. It is powered by three burners connected to two independent fuel systems. At the time of the occurrence VH‑LUD had accumulated a total time of 492.8 hours in service.

Flight conditions

The pilot obtained weather observations, noting isolated fog was forecast and that the wind was variable at 3 knots. The pilot also commented that if there was visible fog at their nearby residence prior to departure, as a general practice they would reschedule the flight.

An Amberley terminal area forecast (TAF) was issued at 0209 EST for the 24 hours from 0300 with an amendment issued at 0318 (Figure 3). A further TAF was issued at 0515, about the same time the balloon took off. All 3 forecasts predicted variable winds at 3 knots and a 30% probability of fog, in which visibility would reduce to 500 m.

Figure 3: RAAF Amberley terminal area forecast

Source: Airservices Australia, annotated by the ATSB

Airspace requirements

RAAF Base Amberley is surrounded by Class G non-controlled airspace, which allows aircraft to operate without air traffic control (ATC) permission. This airspace becomes military Class C when the air traffic control tower is active. Permission is required from Amberley ATC to operate in Class C airspace. At the time of the flight, the air traffic control tower was not active, therefore, Class G airspace procedures applied.

The pilot reported telephoning RAAF Base Amberley air traffic control and leaving a message on their answering machine with the balloon flight details. The pilot had conducted this process for a number of years. The pilot also reported monitoring the Amberley common traffic advisory frequency for traffic during the flight.

In Class G airspace, the required visibility for a balloon operating below 1,500 ft above ground level and clear of cloud, is 5,000 m. However, a balloon operating below 500 ft above ground level and beyond 10 NM of an aerodrome with an approved instrument approach procedure only requires 100 m visibility.

On this occasion, as this flight was conducted within 10 NM of RAAF Base Amberley, an aerodrome having approved instrument approach procedures, the balloon was required to maintain at least 5,000 m visibility and remain clear of cloud irrespective of its operating height.

Balloon performance

The pilot reported that at the time the tree was observed the balloon was descending at a rate of about 200 feet per minute and was flying at a velocity of about 4 knots. As soon as the pilot saw the tree, they commenced burning on all three burners.

The pilot stated the balloon took 20-30 seconds to arrest the descent and commence climbing. The pilot reported the balloon ‘settling’ on the side of the tree in a slow speed collision.

Damage to balloon

The balloon envelope consisted of a total of 460 sewn panels in a combination of four differing sizes. A total of 19 panels were damaged during the occurrence. These panels were either repaired or replaced by the operator in accordance with the Kavanagh Balloons maintenance manual.

Safety analysis

The RAAF Base Amberley TAF listed a 30% probability that fog would be present in the area, in which visibility would be 500 m. The pilot reported that during flight preparation there was no fog present. During the flight, fog was observed in a localised area to the south-east of RAAF Base Amberley.

The flight was conducted in Class G airspace within 10 NM of the RAAF Base. Due to the RAAF Base having an approved instrument approach procedure, the balloon operating under the visual flight rules was required to remain clear of cloud and maintain a minimum visibility of 5,000 m.

The pilot commenced a descent with the intention of locating a suitable landing area. During this descent, the wind backed, and the balloon began tracking towards the area of localised fog. Instead of remaining above the localised fog and descending in the clear air beyond, the pilot continued the descent and entered the fog believing that adequate visibility would exist for the landing. The visibility subsequently reduced to 10 m.

The pilot observed a tree, and in an attempt to prevent a collision, lit the burners to transition to a climb. However, due to the 20-30 seconds required before the descent could be arrested and a climb commence, there was insufficient time for the tree to be avoided due to the limited visibility. Given the climb performance of the balloon, even if the circumstances around the airspace allowed for the flight to be conducted in visibility conditions down to 100 m, the collision would still have occurred.

After the collision, the pilot climbed the balloon off the tree and up into clear air. The balloon was then flown to the edge of the localised fog and an uneventful landing was carried out.

Findings

From the evidence available, the following finding is made with respect to the collision with terrain involving Kavanagh E-240 Balloon, VH-LUD, at Yamanto, Queensland.

Contributing factors

• Contrary to the visibility requirement for visual flight rules flight, the pilot entered an area of fog that did not permit sufficient time to see and avoid obstacles. As a result, the balloon collided with a tree, damaging the balloon's envelope.

Sources and submissions

Sources of information

The sources of information during the investigation included:

• the pilot of VH-LUD
• Civil Aviation Safety Authority
• RAAF Base Amberley air traffic control.

Submissions

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

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

• the pilot of VH-LUD
• Civil Aviation Safety Authority.

Submissions were received from:

• the pilot of VH-LUD
• Civil Aviation Safety Authority

The submissions from those parties were reviewed however, they did not result in any amendment to the text of the draft report.

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]     Variable: used when the forecasting of mean wind direction is not possible. Usually due to low wind velocity.

[3]     Class G: This airspace is not subject to air traffic control (ATC). Both instrument flight rules and visual flight rules aircraft are permitted and neither require ATC clearance.

[4]     Class C airspace: Controlled airspace surrounding major airports. Both instrument flight rules and visual flight rules aircraft are permitted, but pilots must obtain a clearance to operate and maintain continuous radio contact with air traffic control.

[5] Backed: A counter‑clockwise shift in the wind direction.

Executive summary

What happened

On the evening of 11 February 2021, the pilot of a Robinson R22 Beta II helicopter, registered VH‑HKC was conducting a private flight near his property,110 km NNW of Hughenden, Queensland. During the flight, the weather conditions in the direction of his return to the homestead deteriorated. While avoiding weather, the pilot landed at an adjacent property to refuel and obtain directions. The pilot however continued flying away from their homestead arriving at another station about 24 minutes later. After refuelling, and 5 minutes prior to last light in dark night conditions, the pilot departed in a northerly direction. When the helicopter became overdue and unable to be contacted, a search for the helicopter was commenced. The following morning, the pilot was found fatally injured and the helicopter destroyed adjacent to an unsealed road 36 km from their Reedy Springs station.

What the ATSB found

The ATSB found that the pilot of VH-HKC, who did not hold a night visual flight rules (VFR) rating, instrument rating or had night flying experience, continued flying towards his destination in a remote area after last light.

Planning, operational and navigational decisions made by the pilot before and during the flight did not adequately address the risk of visual flight into dark night conditions. Notably, the pilot had a number of opportunities to discontinue the flight before last light when he refuelled his helicopter at other stations in the area.

The pilot continued flying through the period of civil twilight into astronomical twilight then, in dark night conditions and without local ground lighting, inadvertently allowed the VFR-only equipped helicopter to descend into terrain.

The ATSB found that the pilot likely navigated at low-level over a sealed road in poor light conditions which likely resulted in the helicopter contacting a powerline. Failure of the powerline resulted in a loss of ground lighting in the direction of flight. Then, shortly after turning onto an unsealed road in overcast, moonless conditions the helicopter departed the road after a bend in the road before flying over open grassland and colliding with trees and terrain in a left bank, nose-down attitude.

Safety message

This accident highlighted the inherent high risk of night flying in remote areas due to the absence or degradation of the visual references for establishing an aircraft’s attitude and position. This risk is increased when night flying is attempted by pilots without night VFR or instrument flying qualifications. To avoid disorientation and the possibility of loss of control of their aircraft, day VFR pilots need to plan to arrive at their destination at least 10 minutes before last light and to have a realistic alternate plan if it becomes apparent that an intended flight cannot be completed in daylight.

The ATSB has previously published material as part of safety publication Avoidable Accidents No 7 - Visual flight at night accidents. The information contained in this document and supporting material is reiterated on release of this report.

The investigation

The occurrence

On the morning of the accident, 11 February 2021, the pilot was briefly visited at their Reedy Springs homestead, Queensland, by close family members who were moving cattle by truck to an adjacent property. They advised that they may visit again later during their return journey if time allowed, although stormy weather in the area might prevent this. At 1600 Eastern Standard Time[1] the pilot started getting anxious when his family members had not arrived at the station as expected.

Departure from Reedy Springs Station

The weather in the area was reported as overcast with occasional showers. At 1715, during a clearing in the weather, the pilot departed the homestead in their Robinson R22 Beta II helicopter, VH-HKC, to search in an area near Cargoon Station, about 23 km east of the Reedy Springs homestead. The pilot was reported as leaving the homestead in a hurry.

Flight to Camden Park Station

At 1827, VH-HKC arrived at Camden Park Station, which is 35 km west-south-west of Cargoon and 18 km south-west of Reedy Springs.

On arrival at Camden Park Station, the pilot flew at low level over the entrance road towards the homestead, landing beneath a powerline (Figure 1). The pilot advised the owner he was lost, looking for Reedy Springs and that the helicopter’s low fuel[2] light was on.

Figure 1: Photo from 1829 EST - VH-HKC and pilot following arrival at Camden Park Station, property powerline indicated and southerly cloud conditions visible

Source: Camden Park Station owner, modified by the ATSB

The owner of Camden Park assisted the pilot to refuel the helicopter to full and provided directions for return to Reedy Springs to the north. The pilot appeared confused, disoriented and ‘bushed’ and appeared to not believe the directions provided. The owner offered to contact the pilot’s son at Pretty Plains Station[3] to confirm the directions, the pilot responded that he would be fine and not to worry about it. The helicopter departed Camden Park at about 1835 and headed south towards Hughenden, the direction described as a line of dark, low cloud by the Camden Park owner (Figure 1). Following VH-HKC’s departure the owner rang both the pilot’s spouse at Reedy Springs and a son who lived at Pretty Plains advising of the situation. The son, also a Robinson R22 pilot advised they couldn’t depart to try to find their father since it was raining at Pretty Plains (Figure 2).

Flight to Wongalee Station

At 1910, VH-HKC arrived at Wongalee[4] Station about 61 km south of Camden Park. The average ground speed in a direct line from Camden Park was calculated to be about 58 kt (106 km/h). The pilot spoke to a building contractor working at the property saying he had been avoiding storms and landing at stations. The pilot asked the contractor if it was Wongalee Station. When confirmed, the pilot flew to the hangar and was assisted to refuel the helicopter.[5] The contractor, unaware of the pilot’s intended destination, offered the pilot a meal and overnight accommodation. The pilot declined. The contractor observed that the pilot was disoriented although not anxious. At about 1920, after refuelling, VH-HKC departed Wongalee to the north in the direction of a storm (Figure 2).

Figure 2: VH-HKC accident flight - known locations and general direction of travel

Source: Google Earth, modified by the ATSB

Flight over Kennedy Developmental Road – Collision with powerline

Kennedy Developmental Road (Highway 62) was a remote unlit road heading north from Wongalee Station (Figure 2), recently sealed with side and centreline markings (Figure 3). The road was described by the contractor at Wongalee Station as not a busy road. The road was unlit.

Ergon Energy reported that at about 1954 EST, a high voltage powerline,[6] strung 6.8 m above the Kennedy Developmental Road (KDR), [7] 68 km north of Wongalee Station by road, was tripped. The poles supporting the wire on either side of the road were found bent towards the north and inwards with the easterly pole snapped near the base. The 3-strand single wire was broken directly above the road (Figure 3). The break in the line resulted in loss of power  to nearby Mount Sturgeon and Pretty Plains Stations. This meant exterior and station lighting in the area was then not available to assist the pilot of VH-HKC.

Based on the nature and location of the wirestrike and accident location it was very likely that the pilot was initially flying above the sealed Kennedy Developmental Road (marked with a centreline and sidelines) then the unsealed Pretty Plains to Camden Park Road and using these roads for navigation to his intended destination. Both of these roads were in a remote rural area and not illuminated by street lighting.

Figure 3: Powerline above the Kennedy Developmental Road showing location of break and direction of supporting pole movement

Source: Queensland Police Service, modified by ATSB

Search and rescue - Collision with terrain

When VH-HKC did not arrive at Pretty Plains or Reedy Springs that evening, search and rescue authorities were alerted. The helicopter was located the following morning, 8 km north-east of the broken powerline and 160 m south of the unsealed Pretty Plains Camden Park Road (Figure 4). This location was 11 km by road from the powerline break and 4.5 km west of the Pretty Plains homestead. The pilot was fatally injured and the helicopter was destroyed.

Figure 4: Aerial view of accident site showing Pretty Plains Camden Park Road

 Source: Queensland Police Service, modified by ATSB

Context

Pilot information

Qualifications and experience

The flight was conducted as a private category operation under the visual flight rules (VFR).[8] The pilot held a Civil Aviation Safety Authority (CASA) Private Pilot Licence (Aeroplane) that was first issued in 1960. This license was converted to Part 61 on 29 January 2020. The pilot was not rated for instrument flying or night VFR operations.

The pilot’s family reported that he had undertaken pre-license helicopter training in Cairns many years ago, however, the pilot’s license was not endorsed for helicopter operations.

The pilot had owned and operated two helicopters and had been flying helicopters for over 40 years. As the sole owner and pilot of VH-HKC, he had accrued flying time of 1,870.2 hours since 2006.

Recent history

The pilot flew VH-HKC almost exclusively over his Reedy Springs property using the helicopter for mustering cattle, attending to fences and water infrastructure maintenance. The only time the pilot left the property was for helicopter maintenance at Charters Towers.

Medical information

The pilot held a Class 2 medical valid until 19 July 2021, and his most recent aviation medical examination was on 15 July 2019. Restrictions on the certificate were for distance vision correction to be worn and reading correction to be available.

The pilot was described as a very fit and aware 82-year-old. The pilot had well-managed Crohn’s disease and had recently developed asthma following a chest infection. The pilot used medication for treatment of the condition as well as an asthma reliever and preventer.

The witness at Wongalee Station observed the pilot as ‘not puffing or panting’ on the day of the accident. The pilot’s glasses and a Ventolin (asthma) inhaler were located at the accident site.

The pilot’s autopsy identified that salbutamol (Ventolin) was not detected in the toxicology examination. In response to a suggestion that the pilot may have suffered an asthma attack prior to the accident the autopsy reported ‘there were…no features that could confirm a serious acute exacerbation of asthma.’

In response to a concern on whether a recent head injury whilst shopping in Charters Towers (described below) potentially contributed to the circumstances of his death, it was reported that ‘there were no features of significant recent (pre-crash) head injury identified at autopsy, although…difficult to completely exclude subtle pre-existing head injury’.

Events prior to the accident flight

In the two weeks leading up to the accident the pilot was in Townsville, Queensland. On 10 February 2021, the day before the accident, the pilot travelled about 350 km by road from Townsville to his homestead at Reedy Springs cattle station. During the journey, the pilot visited a Charters Towers hardware store. At about 1342, closed circuit television video footage recorded the pilot falling backwards to the ground when attempting to dismount from the tray of a utility vehicle. The pilot stood up from the fall within 10 seconds, before briefly talking to another customer and driving from the carpark. The pilot arrived at Reedy Springs at 1600 and reported he had lost balance on the utility vehicle and fell backwards onto concrete. He reported hitting the back of his head on the tyre of an adjacent vehicle in the carpark but did not have a lump on their head. After unpacking the vehicle, the pilot had a 30-minute rest before dinner at 1900. The pilot retired at about 2130 and had a normal night’s sleep.

On the day of the accident, the pilot woke about 0600 and then had a normal day, working around the Reedy Springs homestead eating both morning tea and lunch.  

Aircraft information

VH-HKC was a Robinson R22 Beta II helicopter manufactured in the USA in August 2004. Initial registration of VH-HKC to the pilot was effective from February 2006. At the time of the accident, the helicopter had completed 1870.2 hours in service, and was certified for day VFR flight only. The last 100-hourly inspection was completed on 3 December 2020 at 1858.9 hrs, 11.3 hours prior to the accident, with all maintenance requirements completed.

The helicopter was equipped with two landing lights installed in the nose of the aircraft just below the canopy, and UHF/ VHF radios. In addition, it had an inertia reel lap/sash restraint fitted to the only installed seat.[9] R22 helicopters are not fitted with a wire strike protection system (cable cutter) on the front of the helicopter.

Recorded information

No flight plan was submitted by the pilot. VH-HKC was not visible on recorded radar data and no communications from the helicopter were recorded by Airservices Australia. The aircraft had no onboard recording equipment. The pilot carried a satellite phone and a dual frequency (406/121.5 MHz) personal locator beacon on the aircraft. Neither of these communication devices were activated.

Accident site information

The ATSB did not attend the accident site. The following is based on an assessment of accident site photos and statements provided by Queensland Police Service.

The area near the accident site was open grassland and grassland with trees. The initial impact point was coincident with the tree line at the edge of an open grassy area about 160 m south of the unsealed Pretty Plains Camden Park Road. The site was 4.5 km west of the Pretty Plains Homestead. The wreckage trail extended in a south-westerly direction of over an area of about 50 m long and 20 m wide.

Figure 5: Overview of VH-HKC accident site

Source: Queensland Police Service, modified by ATSB

Both landing gear skid tubes were broken off at the initial impact point just prior to the main cabin impact crater evident in the soft ground (Figure 5), with main rotor blade strikes forward and to the left of the area of impact. The impact captured the airspeed indication at 38 kt (70 km/h) and the vertical speed indication at -870 ft/min (-16 km/h). This correlated to a flight path angle of 13 degrees nose-down with a groundspeed of 37 kt (68 km/h).

Figure 6: Initial impact location

Source: Queensland Police Service, modified by ATSB

The tail rotor gearbox, blades and empennage were located close to the initial impact. The remainder of the tail boom remained attached to the main fuselage which was 27 m further along the wreckage trail (Figure 5 and Figure 6). The engine was located at the end of the wreckage trail (Figure 6).

Figure 7: Overview of accident site

Source: Queensland Police Service, modified by ATSB

One main rotor blade separated during the impact sequence; the other blade remained attached to the hub at the main wreckage. Both blades were deformed in a manner indicative of powered rotation on impact. The wreckage trail and damage pattern were consistent with a high-energy nose-down impact, likely in a left skid-low attitude.

The front landing skid cross tube and shattered Perspex canopy, both of which are common wirestrike locations, were unable to be examined for evidence of a wirestrike.

R22 Wirestrike collisions

A review of the ATSB occurrence database showed a number of occurrences where a Robinson R22 helicopter had contacted a powerline that did not result in damage or collision with terrain. Of these occurrences, 22% resulted in nil or minor damage to the helicopter and the pilot was able to continue with no loss of control.

Weather and environmental information

Storms

Witnesses at Reedy Springs, Camden Park and Wongalee Stations reported storms and rain in the area during the time of the flights. An image taken at 1756 at Camden Park (Figure 8) captured the prevailing conditions.

Figure 8: Image taken at Camden Park and captioned ‘Another storm is coming’ sent via WhatsApp at 1756 EST about 30 minutes before VH-HKC arrival at Camden Park

Source: Camden Park Station owner

The storm clouds to the south were evident at the time of the pilot’s arrival at Camden Park (Figure 1). The pilot reported to at least one witness that they had been avoiding storms. The Bureau of Meteorology satellite infrared imagery shows the presence of clouds and storms in the area of the route taken by the pilot (Figure 9). The white and purple-blue colours in Figure 9 represent a scale of cloud-top temperatures. The colder the cloud-tops, the higher they are.^[10] The red and orange patches in Figure 9 were overlaid lightning strike data.^[11] The image indicated that there was lightning in the discrete storm cells over Northern Queensland in the vicinity of VH-HKC and also showed the purple colour relating to the very high cumulonimbus cloud tops associated with the storms.

Figure 9: Satellite Infrared imagery[12] at 1830 showing extent of clouds and storms in the area visited by VH-HKC

Source: Bureau of Meteorology, modified by the ATSB

Light conditions[13]

On 11 Feb 2021 the moon phase at Wongalee Station was a waning crescent with 1% of the moon's visible disk illuminated. Moonset was at 1851 and sunset was at 1902.[14] For aviation purposes, night is defined as the period of darkness commencing at the ‘end of evening civil twilight’,[15] also known as last light. The pilot landed at Wongalee Station at 1910, 15 minutes prior to last light.[16] VH-HKC departed Wongalee at 1920 EST during the period of civil twilight, about 5 minutes prior to last light (Figure 10).

Figure 10: Regions of twilight relative to VH-HKC location at Wongalee Station 1920 EST

Source: in-thy-sky.org/twilghtmap

The end of evening nautical twilight[17] was 1951. At this time, it was dark. Both the collision with the powerline on Kennedy Developmental Road and collision with terrain adjacent to the Pretty Plains Camden Park Road occurred in the period of astronomical twilight[18] (Figure 11).

Figure 11: Regions of twilight relative to VH-HKC accident location at 2000 EST

Source: in-thy-sky.org/twilghtmap

The flight involving the collisions was conducted during astronomical twilight, moonless and in overcast conditions (no starlight) in a remote area with limited terrestrial lighting. This was considered to be a dark night with minimal light available. The collision with the powerline exacerbated the situation by extinguishing the Pretty Plains Station terrestrial lighting in the direction of travel.

Visual flight rules requirements

A VFR flight must not be conducted at night, unless the pilot in command is authorised under CASR Part 61 to conduct a flight under the instrument flight rules (IFR) or at night under the VFR and the aircraft is appropriately equipped for flight at night or under the IFR.,..[19]^,[20] A pilot who does not hold a night visual flight rules rating or an instrument rating must not depart unless the estimated arrival time for the destination (or alternate) is at least 10 minutes before last light allowing for any required holding. [21]

Risks of flying in areas of reduced visual cues

Night flying in remote areas is an inherently high-risk operation due to the absence or degradation of the visual references for establishing an aircraft’s attitude and position. This risk is increased to unacceptable levels when night flying is attempted by pilots without night VFR or instrument flying qualifications.

The attempt to continue to the intended destination in fading or absence of daylight in this case, might have been reinforced by the availability of a well-marked but unlit road that could to some extent compensate for the navigational difficulties usually associated with degraded visibility. The pilot reportedly did not have any previous night flying experience.

The ATSB has previously highlighted the risk associated with VFR flight in dark environmental conditions. The ATSB Avoidable accidents booklet, ‘Visual flight at night accidents: What you can’t see can still hurt you’ (AR-2012-122) describes that on average between 1993 and 2012, there were nearly two accidents per year as a result of visual flight at night. Importantly, accidents at night tend to be unforgiving, with 75% of these accidents resulting in fatal outcomes. For the accidents during night visual conditions, half involved a loss of aircraft control, most likely due to the influence of perceptual illusions caused by the lack of visual cues. The other half involved controlled flight into terrain, where the pilot probably did not know of the terrain’s proximity immediately before impact. Nearly all of these accidents occurred on dark nights.

Similar occurrences

AO-2011-087

On the evening of 27 July 2011, the owner-pilot of a Robinson R22 helicopter was conducting a local flight from Big Rock Dam to Brooking Springs homestead near Fitzroy Crossing, Western Australia. The pilot was reported missing and the wreckage of the helicopter was located the following day, 14 km north-west of Fitzroy Crossing township. The helicopter was seriously damaged and the pilot sustained fatal injuries.

The pilot was attempting to fly visually at low level on a dark night in an area that did not contain any local ground lighting. About halfway into the flight, the pilot inadvertently allowed the helicopter to develop a high rate of descent, resulting in a collision with terrain.

The ATSB investigation found that the pilot was operating at night without the appropriate training or qualification in a helicopter that was not suitably equipped. An examination of the helicopter found no evidence of any pre-existent defects or anomalies.

AO-2014-144

On the afternoon of 25 August 2014, the pilots of two Robinson R22 helicopters were ferrying the helicopters from Yeeda to Springvale via a refuelling stop at Leopold Downs, within the Kimberley region of Western Australia. The pilot who was ahead by about 10 NM (18 km) arrived at Springvale about 40 minutes after last light but the pilot of the second helicopter did not arrive as expected.

A search using helicopters began early the next morning and the overdue helicopter was found in a seriously damaged state, close to the intended track and 25 NM (46 km) west of Springvale. The pilot had been fatally injured.

The ATSB found that the pilot, who did not hold a night visual flight rules (VFR) rating or instrument rating, continued flying towards the destination after last light (end of civil twilight), then in dark night conditions without local ground lighting, inadvertently allowed the helicopter to descend into terrain.

AO-2016-031

On 7 April 2016, the pilots of two Robinson R22 helicopters flew from Mossman, Queensland to various fishing locations to the north with a passenger in each helicopter. Late in the afternoon, the pilots commenced the direct return flight to Mossman. However, the pilots encountered weather and winds that slowed their progress and required them to refuel at Cooktown.

The pilots departed Cooktown at last light intending to track via the coast to Mossman. As the flights progressed, the light available from the sun continued to decrease and there was no moon. There were also patches of cloud and rain in the general area.

Shortly after passing Cape Tribulation, in dark night conditions, one of the helicopters collided with the sea. The passenger was injured in the accident but was able to reach the shore and notify emergency services. Unaware of the accident, the occupants of the other helicopter continued to Mossman. A search was initiated and the missing helicopter was located on 9 April 2016 in about 400 m offshore in about 10 m of water. The pilot was not located.

The ATSB found that the pilot, who was only qualified to operate in day-VFR conditions, departed on a night flight and continued towards the destination in deteriorating visibility until inadvertently allowing the helicopter to descend into water.

These fatal collisions all involved pilots of R22 helicopters attempting to fly visually at low-level on dark nights in areas that did not contain any local ground lighting.

Safety analysis

The speed of the impact in a nose-down, left-skid-low attitude indicated that the pilot collided with terrain with substantial energy. This, along with the helicopter rotor damage, were consistent with delivery of engine power to the rotors and at least some control. The following analysis examines the circumstances of the occurrence to identify the contributing factors and any safety implications.

Flying at low-level and collisions

Powerline

The timing and physical appearance of the severed powerline on the Kennedy Development Road was consistent with contact with the helicopter. The distance from Wongalee Station to the severed powerline along the Kennedy Development Road was about 68 km, which was consistent with a speed of about 64 kt (119 km/h) had the pilot been following the road. It was likely that in the dark conditions, the pilot navigated by following the road centreline illuminated by the helicopter’s landing lights.

Assuming the pilot was aware he had flown through a powerline, it should have served as an additional warning that he was flying with reduced visibility and risked a collision with terrain at this time.

Terrain

VH-HKC collided with terrain after departing from flight shortly after a bend above the unsealed and unmarked Pretty Plains Camden Park Rd. The pilot was almost certainly using this road for navigation. In the absence of ground lighting and a poor reflective surface after leaving the road, therefore losing his visual reference, the pilot left the SE heading road and flew at low-level over open grassland in a SE direction with a line of trees to the left until inadvertently descending into terrain at a speed of about 37 kt on a flight path angle of about 13 degrees nose down. The collision occurred at about 2000 EST which was in the period of astronomical twilight (after dark).

Operation at night

The pilot’s family advised that the pilot avoided flying at night and predominantly only flew over their own property. CASA flight crew licensing information showed that the pilot did not hold a night VFR or instrument rating. The logbook for VH-HKC confirmed that the helicopter was not certified for instrument flight rule (IFR) or night VFR operations and was not equipped with suitable instruments for this type of operation.

Within 5 minutes of departure from Wongalee, the pilot was flying at night, with no illumination being provided by the moon or stars. There was very minimal terrestrial lighting with the roads unlit and homesteads sparsely located. The remote Kennedy Development Road carries a low level of traffic. A collision with a powerline over the road occurred 29 minutes after last light (1954) and the collision with terrain about 35 minutes after last light (2000). In such conditions and in particular after the loss of power to local stations as a result of the cut powerline, the available visual references for establishing an aircraft’s attitude and position were degraded or absent.

The conditions on 11 February 2021 were particularly dark after departure from Wongalee Station. It was after moonset and sunset with the moon only 1% illuminated and in overcast weather. The flight after this time continued through the entire periods of civil and nautical twilight.

In very dark conditions such as rural areas, the skills needed to fly an aircraft at night are vastly different to day VFR flights, and may even exceed the capabilities of some pilots trained in night VFR operations.

Pilot’s operational decision making and opportunities to discontinue flight

The pilot did not assess that weather conditions in the vicinity of Reedy Springs and Cargoon were unsuitable for flight in a helicopter only equipped for flight under the visual flight rules (VFR). The pilot’s decision to depart Reedy Springs during a clearing in the weather was made in a hurry and without consideration of an alternate plan. The pilot subsequently became lost and close to fuel exhaustion before flying at low-level under powerlines at Camden Park Station.

The pilot did not consider suggestions at both Camden Park and Wongalee stations to discontinue his flight. Despite arriving at the familiar Wongalee Station within the prescribed 15 minutes before last light, the pilot elected to continue to his destination, likely by navigating at low-level, using a sealed highway. The pilot continued flying despite colliding with a powerline above the highway and flying into the night in dark conditions without the assistance of ground lighting.

The pilot also had opportunities to land the helicopter at a safe location and communicate by satellite phone or activate the personal locator beacon to obtain assistance.

The decisions that the pilot made both before departing Reedy Springs and during the flight both at Camden Park and Wongalee Station, including importantly, the decision to continue towards his destination despite offers of accommodation and attempts at discouraging continuing flight resulted in the pilot flying in dark night conditions where the eventual collision with terrain would have been difficult to avoid.

No helicopter endorsement

CASA flight crew licensing information indicated that the pilot’s license was not endorsed for helicopters. The pilot had considerable experience flying helicopters over many years but predominantly over his own familiar property during day visual meteorological conditions. At the time of the accident the pilot was operating outside the regulations without a helicopter endorsement and in night conditions.

Findings

From the evidence available, the following findings are made with respect to the collision with terrain in dark night conditions involving Robinson R22 Beta II helicopter, registered VH-HKC, which occurred 87 km north of Hughenden, Queensland on 11 February 2021. The findings should not be read as apportioning blame or liability to any particular organisation or individual.

Contributing factors

• While attempting to fly visually at low level, on a dark night without local ground lighting, the pilot inadvertently allowed the helicopter to descend, resulting in a collision with terrain.
• The pilot was operating at night without the appropriate night flying qualification or experience, in a helicopter that was not suitably equipped for night operations.
• The pilot continued flying towards the intended destination after last light (end of civil twilight), then in dark night conditions without local ground lighting despite opportunities available to discontinue the flight.

Other factors that increased risk

• The pilot made a decision to depart on the flight without prior planning. A number of operational and navigational decisions made by the pilot during the flight did not adequately address the risk of visual flight into dark night conditions.
• It was very likely that the helicopter struck a powerline above the Kennedy Developmental Road while flying at low-level in poor light.

Other (key) findings

• The pilot held a private pilot's license for aeroplane operations, however, was not endorsed for helicopter operations.

Sources and submissions

Sources of information

The sources of information during the investigation included:

• Civil Aviation Safety Authority
• Queensland Police Service (Hughenden Police and Townsville Forensic Crash Unit)
• the next-of-kin of the pilot
• witnesses from Camden Park and Wongalee Stations, Queensland
• Ergon Energy, Queensland
• the maintainer of VH-HKC
• Robinson helicopters

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
• Queensland Police Service (Hughenden Police and Townsville Forensic Crash Unit)
• the next-of-kin of the pilot
• witnesses from Camden Park and Wongalee Stations, Queensland
• Ergon Energy, Queensland

Submissions were received from;

• Civil Aviation Safety Authority
• Queensland Police Service (Hughenden Police and Townsville Forensic Crash Unit)

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

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

Executive summary

What happened

On 28 December 2020, at about 1438 local time, a Dynaero MCR-01 VLA, registered VH-SIP, departed Serpentine Airfield, Western Australia, to conduct a post-maintenance check flight. At about 300 ft above ground level, the engine began to run rough, however continued to operate. The pilot commenced a turn to the left, and the aircraft appeared to decelerate in a nose-high attitude without gaining height. Shortly after, the aircraft was observed to aerodynamically stall, pitch nose-down, and impact terrain. The pilot, who was the sole occupant, was fatally injured, and the aircraft was destroyed.

What the ATSB found

The ATSB found that multiple tasks in the aircraft’s return to service after a significant period of inactivity were not adequately carried out, and that the left carburettor of the aircraft’s engine was missing a component and contained a significant amount of contamination. This likely resulted in over-fuelling of the carburettor at a low power setting, and likely produced subsequent engine rough running at high power settings.

The pilot was unfamiliar with the aircraft and engine type, which increased the risk of not being able to adequately manage an inflight emergency. During the partial power loss on take-off, the pilot turned the aircraft in a likely attempt to land on another runway, when the aircraft stalled.

The ATSB found that the pilot had probably consumed a significant amount of alcohol the night before the accident, which increased the risk of post-alcohol impairment.

Safety message

Ongoing maintenance of an aircraft’s fuel system is essential to ensure fault-free operation of its engine. In particular, the reliability of carburettors is dependent on their condition, and by following the manufacturer’s maintenance requirements and service bulletins.

The ATSB encourages pilots to review and practice the conduct of a pre-take off safety brief before each flight, and highlights the importance of preparedness for possible emergencies on take-off leading to an off-airfield landing. The ATSB further encourages pilots to review the recommended partial power loss procedure in the aircraft pilot operating handbook if available, and cautions against turning back towards the runway unless in controlled situations where sufficient altitude exists. Further information can be found in the ATSB booklet, Avoidable Accidents No.3: Managing partial power loss after take-off in single engine aircraft AR-2010-055.

Pilots transferring from one type of aircraft to another are reminded that there is as much risk in moving to lower performance aircraft, as there is moving to higher performance aircraft. The ATSB encourages pilots to manage this transition using a risk-based approach such as Federal Aviation Administration (FAA) advisory circular AC90-109A – Transition to Unfamiliar Aircraft (U.S. Department of Transportation Federal Aviation Administration, 2015).

This accident is also a reminder that blood-alcohol can persist the day after significant alcohol consumption, and the residual effects of alcohol may impair performance, especially in demanding and time critical situations.

The occurrence

Overview

On 28 December 2020, at about 1438 local time, a Dynaero MCR-01 VLA, registered VH-SIP, departed Serpentine aircraft landing area (ALA), Western Australia, to conduct a post-maintenance check flight. At about 300 ft above ground level, the engine began to run rough, however continued to operate. Shortly after, the aircraft was observed to aerodynamically stall,[1] pitch nose-down, and impact terrain. The pilot, who was the sole occupant, was fatally injured, and the aircraft was destroyed.

Aircraft return to service

Post-maintenance flight checks

On 27 December 2020, the new owner and a flight instructor were a conducting post-maintenance check flight of VH-SIP at Serpentine ALA, after undergoing maintenance after an extended period of inactivity (see Return to service tasks). As they departed from runway 05[2] on climb, at about 200–300 ft above ground level (AGL), the engine lost power and began to run rough. The instructor, who was the pilot in command, reported that they lowered the nose and reduced power, which cleared the rough running and allowed the aircraft to continue flight. There was sufficient power available to continue a reduced climb and conduct a circuit back onto runway 05.

The instructor recalled they then initiated a missed approach on short final approach to runway 05 and commenced a full power climb. While the aircraft engine power initially responded, rough running was again experienced at about 200–300 ft AGL. The instructor again reduced power, cleared the rough running, and conducted a slow climb before making a final landing back on runway 09. Both occupants identified the smell of fuel in the cockpit at the time.

The instructor, the new owner and several other people including the pilot of the accident flight (pilot) assisted a licenced aircraft maintenance engineer (LAME) with troubleshooting the engine rough running that afternoon. Numerous engine-runs were conducted on the ground with multiple witnesses stating that they were able to replicate the rough running and partial power loss during the static full power tests on the ground, both with and without the electric fuel pump assistance. The owner stated that the engine seemed to run smoother with the electric fuel pump on, however engine coughing and rough running was replicated on all of the full power runs to varying degrees. Other witnesses recalled the engine stopping when the throttle was reduced after the engine runs, one capturing the stoppage on video.

Engine troubleshooting

To try and diagnose the problem, basic fuel system troubleshooting was conducted by another LAME on behalf of the original LAME, who was no longer at the airfield. This included the draining and cleaning of the fuel filter on direction of the original LAME by phone. A witness described the contaminants within the fuel drain sample and filter as a significant amount of ‘brown gunk’. The engine troubleshooting continued until early evening, when the aircraft was then hangered for the night with the original LAME scheduled to conduct troubleshooting on the aircraft the next day.

The owner and instructor made the decision to return back to Queensland without the aircraft and have the aircraft ferried over when the rectification work was completed. The pilot, who was known to the LAME, volunteered to ferry VH-SIP from Serpentine to Queensland after working with the LAME to correct the engine problem. The owner accepted the offer before departing Serpentine Airfield back to Perth.

Evening activities

That evening, the local aero club held a dinner at the airfield (see social function). Witnesses confirmed that the pilot attended the event, retiring to their accommodation at about 0200 the following morning.

Accident flight

On 28 December 2020, the pilot and LAME met at the airfield at about 1100. The LAME did not recall the pilot was any different to usual, however did remark that the pilot was consuming significant amounts of water. The pilot assisted the LAME with the running of the engine and mentioned that they had never flown an aircraft as small or light before and had not operated a Rotax engine previously. Subsequently, the LAME explained the absence of a mixture control, use of ignition systems and the operation of the electric inflight adjustable propeller.

The LAME removed the aircraft cowls and inspected the engine compartment for a fuel leak before replacing a newly installed mechanical engine driven fuel pump with the old pump to test positive fuel flow without any blockages as part of the troubleshooting sequence. The LAME identified that the fuel flow increased with the activation of the electric fuel pump.

The pilot conducted a troubleshooting check flight in VH-SIP at about 1415, with the support of a number of ground crew including several LAMEs. On return from the first flight, the pilot reported that the engine was not developing full power (5,500 RPM),[3] and was not able to produce much greater than 4,000 RPM. The LAME provided an additional brief to the pilot on the use of the automatic propeller system and requested further ground runs of the engine.

At about 1438, the pilot conducted a further post-maintenance troubleshooting flight from runway 09 (Figure 1). The LAME stated that they expected the aircraft operation to be a high-speed ground run. At about 300 ft AGL, witnesses described audible changes in the aircraft engine noise, and observed a noticeable change in aircraft performance. They observed the aircraft visibly slow and begin a left turn. Further change in the engine noise was heard before the aircraft was described to commence another left turn towards runway 23. At about 200 ft AGL, witnesses described the left turn beginning to tighten and the aircraft visibly slowing with a nose-high attitude. At about 150 ft AGL, the aircraft’s left wing dropped and the aircraft entered a steep rotating descent to the left. The pilot was unable to recover control of the aircraft before it impacted with terrain.

Figure 1: Aircraft’s flight path and accident site location

Source: Google Earth, modified by the ATSB

Context

Pilot information

Licencing

The pilot held an air transport (Aeroplane) pilot licence. This licence was for single and multi-engine aircraft, with endorsements for tailwheel aircraft, manual propeller pitch change, gas turbine engines, pressurisation and for aircraft with retractable undercarriage.

Aeronautical experience

General experience

The pilot’s logbook showed a total flying experience of 5,999.8 hours, up to the last recorded flight on 31 November 2019, when the pilot ceased airline flying with a carrier in the US, before moving back to Australia.

Aircraft specific experience

The majority of the pilot’s total flight time was conducted in multi-engine, piston and turbine aircraft operations. However, since the pilot’s return to Australia, they had conducted a tailwheel design feature endorsement, an aeroplane flight review, and a number of private flights of the local aeroclub aircraft based at Serpentine ALA.

Although the pilot had considerable experience, a review of the pilot’s logbook records found that they had not previously flown Rotax-powered aircraft or the Dynaero MCR-01 VLA.

Medical

The pilot held a valid class 1 and class 2 medical certificate, with the last examination conducted on 23 January 2020. The pilot’s class 2 medical was valid until 23 January 2022 and included restrictions requiring the wearing of distance vision correction and additionally, that reading correction must also be available whilst exercising the privileges of the licence.

Recent history

The night before the accident, a number of airfield members met for an informal social dinner at the clubhouse facilities. It was reported that a number of people attended the dinner, and that alcohol was consumed as part of the social event. Witnesses reported seeing the pilot drinking alcohol during the dinner, 1 witness recalled that the pilot engaged in a ‘fairly heavy’ drinking session consuming a significant quantity of alcohol. The witness recalled the pilot being in a good state of mind, being exceptionally chatty and, later on, recalled them stating that the pilot was ‘really drunk’.

The social function ended at about 0130 on the morning of the accident. Another witness recalled seeing the pilot shortly before driving home from the airport at about 0147, but did not believe that the pilot was significantly impaired by alcohol at that time. The pilot’s quantity and quality of sleep could not be determined.

Post-mortem and toxicology

A post-mortem indicated that the cause of death was due to multiple injuries that were sustained as a result of the collision with terrain. Toxicology indicated low levels of carbon monoxide, consistent within normal levels, and did not detect any common drugs. Toxicology did not detect levels of alcohol within either blood or urine samples.

Aircraft information

General

The Dynaero MCR-01 VLA is a low-wing, high performance, experimental amateur-built aircraft. It was supplied in kit form and VH-SIP was constructed for the education and recreation of the previous owner. The Dynaero MCR-01 VLA was promoted as suitable for cross-country flying, with an airspeed range from 56 to 200 kt. It could be operated between +3.8 g and -1.5 g,[4] however aerobatic flight and intentional spinning of the aircraft were prohibited.

Airworthiness and maintenance history

The aircraft was constructed from a kit and had a special certificate of airworthiness issued on 15 May 2003, and was first flown on 22 May 2003. The aircraft was powered by a horizontally opposed, 4-cylinder, dual carburettor, Rotax 912 ULS-FR, that was manufactured in May 2002.

On 6 November 2003, the canopy of VH-SIP shattered while the aircraft was in flight. This led to a loss of control and the aircraft entering a spin at altitude. After recovering controlled flight, the pilot conducted a forced landing into a paddock, which resulted in significant damage to the aircraft. VH-SIP was repaired over a period of about 18 months, and during this time, the carburettors were removed, cleaned and refitted. The aircraft was returned to service in April 2005.

Among other work carried out on the aircraft, the logbook recorded that, in September 2006, the carburettors were again cleaned and refitted. The aircraft did not fly between November 2009 and November 2013 (4 years). In August 2013, the original owner conducted maintenance on the aircraft for the last time. The aircraft was flown on 4 occasions in 2014, and then was inactive for over 5 years.

On 13 January 2019 the aircraft logbook indicated that work had been conducted on the fuel system and carburettors of VH-SIP, including a new fuel drain valve, removal and cleaning of the carburettors, the installation of new idle jets, O rings and new carburettor float bowl gaskets. Oil and oil filter replacements were also carried out, and the fuel system was flushed with 10 L of aviation gasoline (AVGAS) before being ground run.

In 2020, the aircraft was offered for sale. A pre-purchase inspection was undertaken on 22 May 2020 by a Recreational Aviation Australia Level 2 maintenance engineer on behalf of a prospective buyer. The engineer did not consider the aircraft to be in an airworthy condition due to contaminants in the carburettors, unactioned carburettor float service bulletins, and the mandatory rubber component replacement requirements had not been carried out. Subsequently, the condition of the aircraft was reported to the prospective buyer and the sale did not proceed.

The licenced aircraft maintenance engineer (LAME) at Serpentine ALA was contacted by another prospective buyer in early December 2020 to conduct a pre-purchase inspection before the aircraft was due to be auctioned. The LAME advised the prospective owner that they considered the aircraft to be in good condition, however it would require an annual inspection. Several days later the LAME was contacted by the buyer and advised of the successful acquisition of the aircraft and requested that the LAME carry out the work required to issue a maintenance release. The last entry in the aircraft maintenance log was on 27 December 2020, the day prior to the accident. It showed the most recent work conducted by the LAME.

Engine preservation and return to service

Preservation and storage requirements apply to aircraft engines fitted to an aircraft, as well as uninstalled engines. The Rotax operator’s manual had preservation and storage requirements for long out-of-service periods that were required to be repeated every year the engine was inactive. This included inhibiting the engine both internally and externally and covering all of the engine’s openings to protect it from dirt and humidity. The line maintenance manual limited the storage period for engines to 24 months, and if this period had been exceeded, the engine required overhaul.

The engine manufacturer had an aircraft engine return to service schedule for Rotax 912 engines after a prolonged period or during preservation. These requirements included conducting the normal 100-hour inspection before flight if the engine has been preserved for greater than 12 months.

Return to service tasks

At the request of the new owner, the LAME performed the return to service over a period of several days. The LAME recalled that, during this work, the floats were removed from the carburettor bowls and weighed for discrepancies, refitted, and a carburettor balance was conducted. The LAME also recalled conducting a fuel calibration by draining and replacing the fuel at set increments to ascertain if the fuel quantity markings were correct. Additional work carried out included a periodic inspection, instrument and systems checks, a compression test, engine idle adjustment, and engine ground runs.

Logbook entries detailed that the airframe was inspected in accordance with the Dynaero schedule and considered airworthy along with entries stating:

• the propeller was inspected and found to have nil defects evident
• the engine was inspected in accordance with the BRP-Rotax 912 maintenance manual and CASA AD/ENG/4 with nil defects evident
• service bulletins for the flaps, main landing gear attach, trim tab attach, and canopy attach were carried out
• pitot-static leak tests
• engine-driven fuel pump was replaced
• the 5-year carburettor rubber part and coolant hose replacement was carried out in addition to fitting a new fuel pump and spark plugs.

A maintenance release was issued by the LAME on 27 December 2020 at an aircraft time in service of 439.3 hours. There were 3 endorsements on the maintenance release:

• an engine oil and filter change at 489.3 hours
• a periodic inspection by 539.3 hours or 26 December 2021
• the oil and fuel hoses to be changed by February 2021.

The LAME recalled that the oil and fuel hose replacement entry had been added because the required parts were not available to be sourced and therefore could not be fitted during the aircraft’s return to service.

The other required parts were supplied by the engine importer directly to the LAME in mid-December 2020. Some of these parts were replaced during the return to service, however a few unused parts in their original packaging were found in the aircraft at the accident site.

After the aircraft was returned to service, it underwent a number of other maintenance troubleshooting checks the day prior to, and the morning of the accident. These checks included the removal and replacement of key parts, such as the refitting the original time-expired engine‑driven fuel pump for troubleshooting purposes, however these changes were not documented.

The pilot also conducted several ground runs along runway 09 before becoming airborne and conducting a circuit.

Fuel

The aircraft operated on AVGAS and had the capacity to carry 79 L of usable fuel, in one 80 L main tank. The aircraft was reportedly refuelled prior to the proposed departure from Serpentine ALA the day before the accident, and the new owner estimated that about 60-65 L would have been on board at the time of the accident. ATSB investigators confirmed a strong smell of fuel at the accident site.

Weight and balance

Weight and balance information retrieved from the accident site indicated the aircraft had an empty weight of 261 kg and a maximum take-off weight of 490 kg. The difference left about 229 kg of useable payload for the pilot and fuel. Weight and balance calculations placed the centre of gravity towards the forward limit of the envelope, and within limits.

Amateur-built aircraft

Pilots and passengers of experimental aircraft in Australia accept the risk that the aircraft may not meet the same airworthiness safety standards as certified aircraft, and operate these aircraft on the basis of informed participation.[5] Most amateur-built aircraft are constructed in Australia for the owners education and leisure, however in time many are sold to other private operators.

Operating limitations

Aircraft operating limitations were contained within the aircraft flight manual and the relevant stall airspeed limitations are detailed in Table 1.

Table 1: Stall speeds at 400 kg maximum take-off weight

Bank angle	0° flaps,[6] power off, knots indicated airspeed (KIAS)	10° flaps, power off, KIAS	25° flaps, power off, KIAS
0º	58	51	44
30º	62	53	47
60º	81	72	62

The flight manual also described the recommended glide speed of the Dynaero MCR‑01 VLA of 70 KIAS with a 13.4:1 glide ratio,[7] indicating that the Dynaero MCR-01 VLA has a higher glide speed compared to many other low inertia aircraft in a similar weight category.

Aerodynamic stall speeds considerably increase beyond a 30° angle of bank turn (Table 1). Pilots should be aware these of characteristics during emergency manoeuvring.

The Dynaero MCR-01 VLA flight manual indicates the emergency procedure for an engine failure after take-off (Figure 2). Specifically mentioned, for engine failures immediately after take-off, is not to attempt a 180° turn to return to the runway.

Figure 2: Engine failure on take-off procedure

Source: Dynaero MCR-01 VLA flight manual

Meteorological information

Bureau of Meteorology graphical area forecast for the Serpentine local area indicated that at the time of the accident, that visibility was greater than 10 km with nil significant weather issues. However, moderate turbulence was expected below 10,000 ft over land in thermals and dust devils.

At about the time of the accident, Jandakot Airport, about 30 km to the north of Serpentine, recorded an easterly wind of about 13 kt with visibility greater than 10 km and no significant cloud or weather.

Witnesses at the airfield described the weather as a ‘belting easterly’ and similar to the previous day with hot, dry and windy conditions.

Wreckage information

Site and wreckage examination

The accident site was located in relatively flat and open farmland (Figure 3), about 200 m east of the threshold of runway 23 at Serpentine ALA. The ATSB conducted an examination of the site and wreckage and identified:

• ground impact marks indicated that the aircraft had impacted terrain nose-down, upright and with left rotation
• flaps were in the retracted position.

No pre-impact defects were identified with flight controls or aircraft structure. The fuel tank, located between the cockpit and engine compartment, had ruptured and a quantity of fuel had leaked into the soil. There was no pre- or post-accident fire.

A damaged GPS device, instrumentation including a fuel flow indicator, the engine, propeller, and fuel lines, were recovered from the accident site for further technical examination by the ATSB.

Figure 3: Accident site

Source: ATSB

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. Apart from impact damage, the main engine components were generally in good condition.

Testing and dis-assembly of the carburettors and fuel system identified:

• the left carburettor was missing a clip that attached the float needle valve to the float hinge bracket
• corrosion was identified in both carburettor bowls and on both sets of carburettor floats
• significant corrosion deposits were found on the float needle valve, seat and on the valve tip
• carburettor floats were the incorrect type
• the right carburettor float guide pin was bent, causing float contact with side of carburettor bowl
• fuel line internals were perished and brittle with splitting at the securing end.

Further details relating to the engine teardown can be found in Appendix B – Engine examination.

Partial power loss

Partial power loss on take-off

The ATSB booklet, Avoidable Accidents No.3: Managing partial power loss after take-off in single engine aircraft (AR-2010-055) (Australian Transport Safety Bureau, 2013), describes partial engine power loss as a situation when the engine provides less power than commanded by the pilot, but more power than idle thrust:

This kind of power loss is more complex than a complete failure, and it can be much harder to stay ahead of the aircraft. The pilot is thrust into a situation where the engine is still providing some power; however, the power may be unreliable, and the reliability may be difficult to assess. As a result, pilots are uncertain about the capabilities of their aircraft, and what their options are.

Partial engine power loss can range from providing very little power to almost full power, with varying levels of reliability of the remaining engine power. When faced with a partial power loss, pilots should not try to diagnose the engine problems at the expense of maintaining aircraft control.

On take-off, once the aircraft climbs to a point where it does not have enough runway to land straight ahead, but is not high enough to safely return to the aerodrome for a landing, it has reached a ’no return’ to the runway decision point (Figure 4). From this point, until the aircraft climbs to a height allowing safe return to the runway, the pilot is faced with conducting a forced landing beyond the prepared surface of the airfield. Decisions made by the pilot in command can be critical to the safety of flight at this point. 

Figure 4: No return decision point

Source: Google Earth, modified by the ATSB

In the event of any emergency during critical phases of flight, such as below 200 ft above ground level (AGL) on take-off in a single engine aircraft without runway remaining, pilots should focus on the priorities of:

• Aviate: maintain glide speed and assess whether the aircraft is maintaining, gaining or losing height to gauge aircraft performance
• Navigate: fly the aircraft to make a landing, if height and power are limited, then an into wind landing, 30° left or right of the centreline is a safer option
• Communicate: Mayday call as appropriate.

Pre-take-off safety brief

The pre-take-off safety brief is a verbal and mentally prepared response, through the pre-visualisation of an emergency on take-off and is generally conducted once all engine run-ups are complete and prior to entering the runway. The brief mentally prepares a pilot with pre-programmed responses to possible unexpected events during this critical phase of flight when decision making time is short.

These anticipated actions in response to certain stimuli, assist pilots in making better decisions in accepting emergency circumstances and safely managing emergencies, especially when an off-airfield landing may be the safest option.

The briefing should include the pilot in command’s intentions in the event of an engine related problem during the take-off roll and after take-off, both with runway remaining and without. This formulates pre-existing mental models of possible actions should an emergency arise. 

A pre-take off safety brief should include:

• consideration of the runway in use, it’s length, surface, boundary fencing and possible forced landing areas beyond the runway, including terrain and obstacles
• wind direction and strength, which will indicate the safest into wind turning options to safely maintain airspeed and provide a lower groundspeed in case of a forced landing beyond the airfield boundary
• consideration of required height and direction of turn, to conduct a turn back to the runway

The ATSB Avoidable Accidents booklet provides sound guidance to pilots on this subject and concludes that:

Generally speaking, if you self-brief your plan of action just before flight, you have more chance of ‘staying ahead’ of the aircraft and being able to concentrate on flying.

The turn back

The turn back is described as the conduct of an emergency manoeuvre to reverse the direction back towards the take-off runway, to either conduct a landing on the reciprocal runway or to land at another runway at the original departure point.

During this critical time, the pilot must assess four main considerations for the safe conduct of a turnback:

• Is the height sufficient to safely turn the aircraft back to the runway?
• Is there remaining power available to continue to climb or maintain height?
• Can a safe airspeed be maintained during the turn, taking into account the increased stall Speed associated with an increased angle of bank to prevent aerodynamic stall?
• assuming that the engine may fail at any time, is the remaining power reliable?

The ATSB Avoidable Accidents booklet noted:

A turnback requires accurate flying during a period of high stress to prevent a stall and possibly a spin occurring. If an aerodynamic stall and or spin occurs, given that these circumstances are likely to be at low level, there is little likelihood of a successful recovery.

There are many scenarios where it might be considered inappropriate to conduct a turnback. For example, consideration should be given to additional hazards such as other aircraft, obstacles, an unfavourable wind component, increased stall risk during a low-level turn and surrounding terrain.

Pilot decision making during partial power loss

The ATSB Avoidable Accidents booklet also detailed influences on decision making affecting pilots:

The course of action chosen following such a partial power loss after take-off can be strongly influenced by the fact that the engine is still providing some power, but this power may be unreliable. As the pilot, you may also have a strong desire to return the aircraft to the runway to avoid aircraft damage associated with a forced landing on an unprepared surface.

Based on an analysis of partial power loss accidents after takeoff, the booklet further noted that pilot decision making is also influenced by the amount of power loss experienced. In situations where power loss is substantial, pilots are more likely to recognise this as being close to a complete loss of power and typically conduct a forced landing outside of the runway environment. However, if the remaining power is sufficient to continue climb, albeit at a reduced rate, pilots were able to take advantage of increased options, such as a continuing a circuit or conducting a turn back towards the runway.

However, the ATSB identified a period between these 2 areas that represented a region of heightened uncertainty (Figure 5). In this region, excess power was not available to climb but there was sufficient power to prevent appreciable descent, resulting in a period of flight uncertainty where the aircraft may not be able to maintain height without bleeding off airspeed, eventually resulting in the aircraft slowing to maintain or gain height and increasing the risk of aerodynamic stall.

Figure 5: Region of heightened uncertainty during partial power failures on take-off

Source: ATSB

The ATSB identified that 8 out of 9 partial power loss accidents resulting in fatal injuries occurred with mid-range power loss. Inconsistent power or engine surging from high to low RPM present complex problems to the pilot. Inability to maintain height with partial power loss usually leads to aircraft stall and loss of control, mostly resulting in collision with terrain.

Transition to unfamiliar aircraft

General competency

In order for a pilot to operate a different aircraft type already covered by their licence category and class rating, they need only be satisfied that they are competent under Civil Aviation Safety Regulation (CASR) 1998.

CASR 61.385 Limitations on exercise of privileges of pilot licences – general competency requirement stated:

(1) The holder of a pilot licence is authorised to exercise the privileges of the licence in an aircraft only if the holder is competent in operating the aircraft to the standards mentioned in the Part 61 Manual of Standards for the class or type to which the aircraft belongs, including in all of the following areas:

(a) operating the aircraft’s navigation and operating systems;

(b) conducting all normal, abnormal and emergency flight procedures for the aircraft;

(c) applying operating limitations;

(d) weight and balance requirements;

(e) applying aircraft performance data, including take-off and landing performance data, for the aircraft.

Guidance on transition

While no definitive Australian guidance provided advice on the transition of pilots to unfamiliar aircraft, the Federal Aviation Administration (FAA) advisory circular AC90-109A – Transition to Unfamiliar Aircraft (U.S. Department of Transportation Federal Aviation Administration, 2015) is a widely recognised and utilised publication providing a sound basis to consider the hazards of transitioning to unfamiliar types of aircraft, whether certified or experimental.

The AC recognises the importance of providing guidance to pilots transitioning between aircraft types, or to experimental aircraft with differing design features to high performance and complex aircraft. It recommends that pilots’ should develop a training strategy (Figure 6) for mitigating the risks of operation of an unfamiliar aircraft type.

The FAA AC recommend that:

Prior to flying an unfamiliar airplane, all pilots should review the hazards and risks outlined in this AC, and complete the training recommended before operating the airplane. Accident data has shown that there is as much risk in “moving down” in performance as “moving up.” For example, consider a pilot who has substantial experience in high-performance corporate, airline, or military airplanes. The knowledge and skills used to safely fly at high speeds, high altitudes, and over long flights will, by themselves, not prepare the pilot for the challenges of a low-inertia, high-drag airplane.

Figure 6: FAA recommended airplane transition training approach

Source: FAA AC90-109A

The guidance recommends firstly that pilots should consider undertaking flight training with a qualified flying instructor in the proposed transition aircraft, the same make and model or an aircraft that exhibits the same design features or characteristics of the transition type. If instruction is unavailable, seek another experienced pilot to conduct a familiarisation flight; however, if unwilling, at least discuss the differences and expected characteristics of the transition aircraft.

The guidance further recommended that pilots take a risk management approach to formally identify the hazards and mitigate any known or elevated risks identified.

These may include:

• specific type training in the transition aircraft or similar type/design features
• safety equipment such as helmets, fire extinguishers or parachute
• condition, maintenance and history of the transition aircraft
• review of aircraft operating limitations
• plan transition flights to conservatively build up manoeuvres and aircraft experience
• conducting initial flights in benign weather conditions

Fitness for flight

Regulatory requirements

CASA identifies that any amount of alcohol in your body may affect a pilot’s fitness to safely operate an aircraft.

Subparagraphs 91.520(2)(b)(i), (ii) and subregulation 91.520(5) of CASR outlines a crew member for a flight (pilot) commits an offence if they consume alcohol at any time during the period of 8 hours ending when the flight begins, or if a test of a body sample of the crew member to determine the level of alcohol in the sample was taken at the time of carrying out the duty (and) the test reveals that the permitted level for alcohol (within the meaning of Part 99) is exceeded.

Part 99 of CASR defines –

permitted level means:

• (a)    for a testable drug—a level of the drug specified in subregulation (2A) for the purposes of this paragraph; and
• (b)   for alcohol—a level of alcohol of less than 0.02 grams of alcohol in 210 litres of breath.

This means pilots should give considerable and reasonable thought to the amount and rate of alcohol consumption in order to determine if residual alcohol levels may affect cognitive functions, such as decision making, reduced attention and physical ability during the intended flight.

Post alcohol impairment

Post-alcohol impairment (PAI) has been defined as performance impairment after alcohol is no longer detectable. While the performance decrement of pilots under the influence of alcohol is well known and documented, the effect of post-alcohol impairment, commonly known as a ‘hangover’, is less tangible.

Although pilots must not operate an aircraft within 8 hours of the consumption of alcohol, a pilot’s ability to make normal and emergency decisions may be impaired even after the blood alcohol concentration (BAC) has returned to zero.

Research conducted for the ATSB (Newman, 2004) into alcohol and human performance highlighted that:

In simple terms, alcohol impairs human performance…

It has detrimental effects on cognitive functions and psychomotor abilities. Risk taking behaviour may result, and a full appreciation of the consequences of a planned action may not be possible… Adverse effects can also persist the day after alcohol ingestion, with reductions in alertness, concentration and vestibule-ocular function, and increases in anxiety all being reported…

Alcohol has been shown to impair registration, recall, and organisation of information, leading to increased reaction times and/or a greater number of errors…

…performance has also been found to suffer most when an unexpected or unanticipated event occurs.

A study found that 14 hours after alcohol ingestion leading to a BAC of at least 0.10%, pilots performed much worse at a flight simulator task at a time when their BAC had returned to 0 (Yesavage & Leirer, 1986). Pilot performance was measured and found worse on almost every level, with detriments to precision and accuracy being highlighted. It was also found that pilots were not able to accurately judge their own degree of impairment and concluded that such performance effects would still be measurable sometime after 14 hours.

The ATSB study (Newman, 2004) also found that:

The alcohol-induced impairment of cognitive performance becomes more evident when the nature of the flying task becomes more complex and demanding, such as in an emergency situation. A pilot suffering from the effects of post-alcohol impairment may not handle such a high-workload emergency appropriately, due to reduced attention, a slower rate of information processing, increased reaction time, and poor decision-making. All of these could ultimately result in an accident.

Safety analysis

Introduction

On 28 December 2020, the pilot of a Dynaero MCR-01 VLA, registered VH-SIP, was conducting post-maintenance troubleshooting check flights at Serpentine Airfield, Western Australia. While at about 300 ft above ground level (AGL), on the second flight for the day, the engine began to run rough. Shortly after, and while most likely attempting to return to the airfield, the aircraft’s left wing was observed to drop, the nose pitched down, rotate to the left, and impact terrain.

This analysis will explore airworthiness considerations pertaining to VH-SIP, its return to service, the pilot’s experience on the aircraft type and its effect on emergency management, and the effects of post-alcohol impairment.

Return to airfield and stall

A partial power loss occurred at about 300 ft AGL on take-off from runway 09. Although alternative ‘off-runway’ landing areas were available, the pilot elected to continue flight while manoeuvring the aircraft towards the eastern end of runway 15. 

Manoeuvring an aircraft to return to the airport during critical periods of the initial climb, with inconsistent and unreliable power output, significantly increases risk.

With a combination of turning downwind, marginal power and performance, potentially an attempt to maintain altitude, probably led to the aircraft decelerating. During a further left turn towards runway 15, this decrease in airspeed likely resulted in the left-wing stall at about 200 ft AGL, that did not afford the pilot an opportunity to successfully recover.

Airworthiness of VH-SIP

Return to service

VH-SIP had 3 periods of inactivity, about 18 months, 4 years, then 5 years. There was no record in the logbooks for VH-SIP to indicate its engine had been preserved, however the logbook states the carburettors were cleaned on 3 occasions, with the most recent being in January 2019.

The requirement to replace time-limited components every 5 years was partially carried out. Some of the fuel lines that were not replaced were found to be in poor condition when examined at the overhaul facility after the accident. However, it could not be determined if this contributed to the engine rough running prior to, and on the day of the accident.

Engine defects and partial power loss

The preliminary examination of the engine at the accident site, and the subsequent engine examination at an overhaul facility did not identify any pre-impact mechanical defects. However, both carburettors were found to contain contamination, most likely forming during the aircraft’s extended periods of inactivity.

This contamination that was not rectified prior to the aircraft being released for service, or during the subsequent troubleshooting of the engine rough running. Additionally, there was no record of the fuel system being inspected and cleaned in accordance with the manufacturer’s requirements when carburettor contamination has been identified.

The flooding that was observed during multiple tests of the left carburettor, was the result of significant contamination on its float needle valve and seat. Given the amount of contamination, the left carburettor was likely flooding prior to the accident, and as carburettor flooding is known to result in fuel odour, would have been the likely source of the reported fuel smell.

It’s possible the contamination in both carburettors, along with the absence of the clip that attached the float needle valve to the float hinge bracket, resulted in the rough running of the engine at high power settings.

Ongoing maintenance of an aircraft’s fuel system is essential to ensure fault-free operation of its engine. In particular, the reliability of carburettors is dependent on their condition, and by following the manufacturers maintenance requirements and service bulletins.

Unfamiliarity with aircraft type

Although experienced in passenger transport operations and heavier multi-engine aircraft, the pilot was not as experienced in flying lighter general aviation aircraft, with even less experience in very light, low inertia aircraft such as the Dynaero MCR-01 VLA.

The safe conduct of post maintenance flights and troubleshooting of aircraft systems requires pilot familiarity and experience in the aircraft type, its design features and its normal and emergency operating parameters.

Although appropriately licenced, the pilot had never flown a Dynaero MCR-01 VLA previously and had limited experience with low inertia aircraft, as well as the engine and the propeller type fitted to VH-SIP.

The conduct of a post maintenance flight with limited pilot experience and knowledge in the aircraft and its systems, increased the likelihood that the pilot would be unable to effectively manage any in-flight emergency.

Post alcohol impairment

Post-alcohol impairment is of particular importance in aviation. While regulations require a minimum time between drinking and flying, there is considerable evidence that pilot performance may be impaired for much longer periods. Post-alcohol impairment can increase the potential for spatial disorientation for up to 48 hours. While a pilot may be legally able to fly eight hours after drinking, the residual effects of alcohol may seriously impair their performance when they need it most, such as during an emergency.

Witness accounts of reported alcohol consumption the night before the accident, increased the likelihood that the pilot would have been experiencing some level of post alcohol impairment that may have contributed to reduced cognitive function which could have affected the pilot’s decision making during the partial power loss after take-off.

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 partial power loss and collision with terrain involving, Dynaero MCR-01 VLA, VH-SIP near Serpentine Airfield, Western Australia, on 28 December 2020.

Contributing factors

• Shortly after take-off, the engine experienced a partial power loss. The pilot turned the aircraft to the left most likely in an attempt to return for landing.
• At about 200 ft above ground level, with low airspeed and no flap selected, the left wing aerodynamically stalled. This resulted in the aircraft entering into an upright spin, at an altitude that limited an effective recovery.
• Multiple tasks in the aircraft’s return to service after a significant period of inactivity were not carried out adequately before the aircraft was released to service.
• The left carburettor contained contamination that likely resulted in flooding at low power, and rough running at high power settings.
• The pilot did not adequately manage the risk of transitioning to an unfamiliar aircraft type, further increasing the risk of not being able to adequately manage in-flight emergencies during post maintenance flights.

Other factors that increased risk

• The pilot had probably consumed a significant amount of alcohol the night before the accident, which increased the risk of post-alcohol impairment.

Glossary

AGL                  Above ground level

ALA                  Aircraft Landing Area

ATSB                Australian Transport Safety Bureau

AVGAS             Aviation gasoline

BAC                 Blood alcohol concentration

CASA               Civil Aviation Safety Authority

FAA                  Federal Aviation Administration

GPS                 Global positioning system

KIAS                 Indicated airspeed

LAME               Licenced aircraft maintenance engineer

PAI                   Post alcohol impairment

RPM                 Revolutions per minute

VFR                  Visual flight rules.

Sources and submissions

Sources of information

The sources of information during the investigation included the:

• witnesses that operated the aircraft the day before the accident flight
• Civil Aviation Safety Authority
• Western Australian Police Service
• aircraft manufacturer
• engine manufacturer
• maintenance organisation
• Airservices Australia
• Bureau of Meteorology
• accident witnesses
• video footage of VH-SIP the day before the accident flight and other photographs and videos.

References

Australian Transport Safety Bureau. (2013). Avoidable Accidents No. 3 Managing partial power loss after takeoff in single-engine aircraft. Canberra: Australian Transport Safety Bureau.

Newman, D. G. (2004). Alcohol and Human Performance from an Aviation Perspective: A Review. Canberra: Australian Transport Safety Bureau.

U.S. Department of Transportation Federal Aviation Administration. (2015, July 06). AC 90-109A Transition to Unfamiliar Aircraft. Washington DC: U.S. Department of Transportation Federal Aviation Administration.

Yesavage, J. A., & Leirer, V. O. (1986). Hangover effects on pilots 14 hours after alcohol ingestion: a preliminary report. American Journal of Psychiatry, 1546-1550.

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 Bureau d'Enquêtes et d'Analyses pour la sécurité de l'aviation civile
• engine manufacturer
• a LAME witness
• the aircraft owner
• maintenance organisation.

Submissions were received from:

• Civil Aviation Safety Authority
• A LAME witness.
• the Bureau d'Enquêtes et d'Analyses pour la sécurité de l'aviation civile

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

Appendices

Appendix A – Sequence of events

Source: ATSB
 

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.

Executive summary

What happened

On 22 December 2020, the pilot of a Robinson R44 II helicopter was conducting aerial agricultural spray operations on a property about 13 km south-east of Clare Valley Aerodrome, South Australia. After completing numerous spraying runs throughout the morning, the pilot started a gentle descending turn to the landing site to replenish with chemical product when a loud bang emanated from the rear of the helicopter. The pilot reported that the helicopter descended rapidly, and the flight controls appeared to be jammed. The helicopter collided heavily with the loading vehicle, coming to rest on its side. The pilot and ground crewman were uninjured, and the helicopter was substantially damaged.  

What the ATSB found

The ATSB found that the forward yoke of the helicopter’s clutch shaft had failed due to an undetected fatigue crack that originated from an indent in one of the arms of the yoke. This resulted in loss of drive to the main and tail rotor systems. The unrestrained clutch shaft caused the displacement of the hydraulic reservoir and the loss of fluid. The loss of hydraulic fluid removed hydraulic power assistance to the flight control servos leading to increased control stick forces to operate the helicopter.

The pilot experienced difficulties in controlling the helicopter and executed an emergency descent from a low height without hydraulic power assistance and no tail rotor control. The pilot was presented with a compound emergency for which no training had been provided and for which they had no prior experience.

The ATSB found that the helicopter manufacturer’s maintenance instructions requiring verification that no cracks, corrosion or fretting were present on the yoke, lacked specific instructions on the method to be employed. The visual inspection that was employed increased the risk that a crack in the yoke arm may not be detected.

What has been done as a result

The helicopter manufacturer, the Robinson Helicopter Company, introduced new maintenance inspection requirements for the clutch shaft forward yoke at the 2,200/2,400-hourly inspection for the R44 helicopter. This included replacement of yokes of earlier revision status (A through G) and for later revision (H and subsequent), the option of replacement, or a more detailed examination that included a magnetic particle inspection. This update was included in the R44 maintenance manual in August 2022. The manufacturer also changed the paint colour of the yokes at the forward flex coupling from dark grey to white. This was to enhance the visibility of fretting dust during inspections, in the event of loose hardware.

Following the accident, the ATSB issued a Safety Advisory Notice, AO-2020-064-SAN-014 advising operators of R44 helicopters that based on the preliminary finding of fatigue cracking, to look for the presence of corrosion, fretting or cracking, which may not be visually obvious during all inspections of the clutch shaft yoke.

The Civil Aviation Safety Authority issued an Airworthiness Bulletin, AWB 63-010 advising industry of the failure of the yoke based on the ATSB investigation preliminary finding. It advised pilots and maintenance personnel to exercise vigilance for any signs of deterioration in the helicopter drive train components. This was further supported by the release of similar bulletins by the European Union Aviation Safety Agency and the US Federal Aviation Administration.

Safety message

This occurrence highlighted how non-life limited components such as a drive train yoke may still develop defects and fail in-flight. Aircraft owners and maintenance personnel are reminded of the importance of applying inspection and maintenance criteria specified in the aircraft manufacturer’s publications. Should maintenance information be lacking or unclear, the manufacturer or authorised representative should be contacted for appropriate, additional information.

The occurrence also serves as a reminder to pilots and maintenance personnel that when conducting inspections to be prepared for the unexpected, and to remain vigilant for defects in parts with an established history of reliability.

The occurrence

On the morning of 22 December 2020, the pilot of a Robinson Helicopter Company R44 II, registered VH-HOB, prepared the helicopter for aerial agricultural spray operations to be conducted on a property located about 13 km to the south-east of Clare Valley Aerodrome, South Australia. The pilot completed the daily inspection and departed the Clare Valley hangar at 0652 Central Daylight-saving Time[1] for the short flight to the loading zone, from where operations would be based.

The pilot arrived at the loading zone at 0700 and departed at 0702 with the property owner on board to conduct a short survey flight of the area to be sprayed, returning to the loading zone at 0708. Following the arrival of the ground crewman, the helicopter was loaded with chemical product, and at 0728 the pilot departed and conducted a series of spraying runs.

Numerous spraying runs were completed during the morning between 0728 and 0920 with the pilot returning to the loading zone periodically to replenish with chemical product and to refuel the helicopter. The pilot reported that the operation proceeded smoothly, and the long spray runs with minimal obstacles made for ideal spraying conditions. 

During the final descent to the loading zone at about 0926, the pilot momentarily increased altitude to gain a better view of a light shower approaching from the south-west, and to assess its potential impact on further spraying operations. The pilot slowed the helicopter, and once satisfied that the shower did not pose a threat, started a gentle, right descending turn at 0926:20 towards the ground loading vehicle with the intent to land alongside as on previous occasions (Figure 1).

Figure 1: VH-HOB flight path showing return to loading zone and descent and inset providing accident location

Source: Google and DGPS data, annotated by the ATSB

About 10 seconds into the turn, at 0926:30, a loud bang from the rear of the helicopter was heard, followed by vibrations from the rotor systems. The ground crewman recalled looking up and seeing that the tail rotor had stopped turning. The pilot reported that the cockpit flight controls appeared to have jammed and of not being able to move the tail rotor pedals. The helicopter’s rate of descent increased to 550 ft/min and as reported by the pilot, its movement towards the ground loading vehicle was generally unaffected by the pilot’s attempts at control inputs. The helicopter’s flight path continued until its landing gear impacted the vehicle’s roof, which resulted in it rolling onto its right side and colliding with terrain at 0926:46.

The pilot was not injured in the collision and was assisted from the helicopter wreckage by the ground crewman. There was no post-impact fire, and the helicopter was substantially damaged.

Context

Pilot information

The pilot of VH-HOB held a Commercial Pilot Licence (Helicopter) and a Private Pilot Licence (Aeroplane), both issued in March 2015. The pilot held class ratings included single engine helicopters and helicopter low-level rating. From 2017, the pilot also held an aerial application rating for helicopter operations.

The pilot completed an aerial application proficiency check for single engine helicopters and a night Visual Flight Rules (Helicopter) flight review for Robinson R44 helicopters on 23 July 2020. Both were valid until 31 July 2021.

The pilot held a Class 2 Aviation Medical Certificate issued by the Civil Aviation Safety Authority (CASA), without medical restrictions, which was valid until 23 January 2023.   

The pilot’s logbook indicated that at the time of the accident, the pilot had a total flying experience of about 6,521 hours. Of these, about 1,337 hours were in the Robinson R44 helicopter and 1,018 hours conducting aerial application work. The pilot had flown about 105 hours on type in the previous 90 days, and about 54 hours on type in the previous 30 days.

Aircraft information

VH-HOB was a Robinson Helicopter Company R44 II helicopter that was manufactured in the United States in 2005 with serial number 10801. It was first registered in Australia in 2005.

The R44 II is a single-engine, light utility and training helicopter with a semi-rigid, two-bladed main rotor, a two‑bladed tail rotor and skid type landing gear. It had an enclosed cabin with two rows of side‑by‑side seating for a pilot and three passengers.

The helicopter was powered by a Textron Lycoming IO-540-AE1A5, 6-cylinder, fuel-injected piston engine and was fitted with hydraulic servo-actuators providing hydraulic power assistance to the main rotor, flight control system.

VH-HOB was configured for aerial application work that included a belly-mounted storage tank and laterally mounted spray booms for chemical product dispersal.

The helicopter’s current maintenance release was issued on 20 October 2020, about 92 flight hours prior to the accident. It was valid for 12 months or 100 hours, whichever occurred sooner. At the time of the accident, VH-HOB had accumulated about 4,579 hours, total time-in-service. There were no open defects recorded on the maintenance release and no outstanding or overdue maintenance was noted.

Maintenance records also showed that about 188 flight hours prior to the accident, at an aircraft time-in-service of 4,391.0 hours, an airframe 2,200-hour/12-year inspection was completed.

Meteorological information

The forecast meteorological conditions for Clare Valley Aerodrome (13 km north-west of the accident site) area, indicated winds from the south-south-west at 19 kt and a temperature of 12 ⁰C. Visibility was forecast to be greater than 5 km with isolated showers of rain and broken cloud above 1,200 ft.

The METAR[2] for Clare Valley township issued at 0930 recorded wind from the south-west at 7 kt and a temperature of 14 ⁰C. This was consistent with witness in the accident area who reported that some cloud was present with isolated showers to the south.

Wreckage information

The ATSB did not attend the accident site and based assessment of the helicopter on imagery and reports supplied by the operator, maintenance personnel, interview records and witness account.

The helicopter presented as relatively intact with the tailboom broken aft of its forward mount point. The operator’s examination identified that one of the arms of the clutch shaft forward yoke had fractured resulting in loss of drive to the main and tail rotor systems. The tubular steel structure surrounding the shaft was damaged by the rotation of the unrestrained clutch shaft. The hydraulic reservoir was also found displaced from its mounting base and was located within the wreckage (Figure 2).

Figure 2: VH-HOB following the collision with inset showing clutch shaft with upper drive sheaves and displaced hydraulic reservoir

Source: Supplied, annotated by the ATSB

Following the accident, attending maintenance personnel reported they conducted a functional check of the flight control system and found the cyclic[3] and collective[4] controls had full and free movement. However, one of the tail rotor control tubes exhibited bending damage that was likely the result of contact with the unrestrained clutch shaft.

Both the pilot and the ground crewman reported that the engine stopped operating shortly before the collision. Images showed that a cutting action of the unrestrained clutch shaft forward yoke (see R44 rotor drive system below) penetrated the engine upper firewall and damaged the engine fuel system flow divider located on the engine below. The yoke perforated the flow divider top housing, which likely interrupted fuel flow to the engine, resulting in engine stoppage.

Both of the fuel tanks were found intact and there was little external distortion of the auxiliary tank following the impact with the ground.

At interview, the ground crewman commented that the helicopter was observed to approach at a low rate of descent, and had it not struck the vehicle, the landing would likely have resulted in significantly less damage to the helicopter.

R44 rotor drive system

The clutch shaft forward yoke assembly is part of the R44 rotor drive system. The R44 pilot’s operating handbook provided the following description of the main and tail rotor drive system and is illustrated in Figure 3.

A vee-belt sheave is bolted directly to the engine output shaft. Vee-belts transmit power to the upper sheave which has an overrunning clutch contained in its hub. The inner shaft of the clutch transmits power forward to the main rotor and aft to the tail rotor. Flexible couplings are located at the main gearbox input and at each end of the long tail rotor drive shaft.

Figure 3: R44 drive train with inset showing clutch shaft forward yoke and flex plate providing input power to the main and tail rotor gearboxes

Source: Robinson Helicopter Company R44 maintenance manual, annotated by the ATSB

Images provided by maintenance personnel showed that during the accident sequence, the vee‑belts had dislodged from the upper sheave.

A manual, cable operated rotor brake was mounted on the aft end of the main gearbox and when applied via the pull handle in the cabin ceiling, friction pads of the braking mechanism would contact the main gearbox input yoke to stop the rotor system. Images showed that the actuating cable was displaced from its guide pulley and was disconnected from the braking mechanism (Figure 4).

Figure 4: Rotor brake mechanism minus actuating cable attached and trapped wire material around the main gearbox input yoke shaft

Source: Maintenance organisation, annotated by the ATSB

The action of separating the cable from the braking mechanism likely caused the rotor brake to be momentarily actuated, and while considered minimal, may have affected the speed of the main rotor system.

R44 II hydraulic system

The R44 II hydraulic system consists of a pump mounted to the main rotor gearbox, a servo at each of the control tubes connecting the cockpit controls to the swashplate, a reservoir assembly, hydraulic fluid and interconnecting flexible hoses (Figure 5). Should a loss of hydraulic pressure occur, the servos contain an irreversible feature to reduce main rotor feedback forces to the pilot’s controls. However, in the absence of hydraulic pressure, the manufacturer advised that the cyclic control system is harder to move in the fore-and-aft and lateral planes, while the collective control can be easily lowered, but becomes harder to raise.

Following the accident, the hydraulic system was provided to the ATSB for further examination. Without hydraulic pressure applied, examination of each servo showed that the irreversible feature was functional. The forces required to move each servo were noted to be slightly higher in comparison to new servos but were considered acceptable.  

The hydraulic reservoir had separated from the hydraulic manifold mounted to the tubular frame likely from the clutch shaft striking the manifold (mounting location circled, Figure 5). This resulted in significant loss of hydraulic fluid. The ATSB’s examination of the hydraulic reservoir revealed multiple impact marks attributed to striking, or being struck repeatedly by a rotating component, likely the main gearbox input yoke.

Figure 5: Hydraulic system and main gearbox installation from VH-HOB

Source: Maintenance organisation, annotated by ATSB

Yoke examination

The clutch shaft with the fractured yoke arm, the forward flex plate and the attaching hardware were provided to the ATSB for detailed examination (Figure 6). A portion of the flex plate that remained connected to the yoke and the separated section of the arm was also provided for examination.             

The yoke presented with one arm intact, to which a portion of the forward flex plate and its attaching hardware were present. The opposite arm had fractured at the bolt hole that secured the arm to flex plate.

The surfaces of the yoke presented with scoring marks and indentations to the painted surfaces. Mechanical impact damage and gouging was also present with smearing damage to the arm fracture surfaces obscuring some of the original fracture features.

Figure 6: Fractured forward yoke arm with inset showing clutch shaft assembly and flex plate

Source: ATSB

A detailed visual inspection of the yoke arms using an optical microscope and a magnetic particle inspection of the yoke surfaces and bolt hole regions, did not identify additional cracks.

Red-coloured corrosion products were observed on the forward face of the yoke where it contacted the bonded stainless-steel washer from of the forward flex plate (Figure 7). Fretting damage was present on the aft face that was in contact with the attaching hardware. Microscopic examination of the red-coloured product identified it to have been produced from general corrosion/oxidation of the underlying steel surface. There were no indications of pitting corrosion.

Figure 7: Fractured yoke arm and separated section front and rear surface condition

Source: ATSB

Visual examination of the fracture surfaces on either side of the bolt hole showed evidence of fatigue fracture. The fracture surface showed concentric beach marks indicative of a progressive crack mechanism, which radiated outwards from the likely origin at the inner bolt hole surface on the front face of the yoke (Figure 8). The fatigue crack had propagated from the front to the aft face, and initially obscured from view by the presence of the attaching hardware.

Crack propagation continued across a substantial portion of the cross section (about 98% of fracture # 1 and about 80% of fracture #2), with a visible portion on the rear face of about 6 mm before final overstress fracture and separation occurred. 

Figure 8: Separated yoke tip with fracture features identified

Source: ATSB

A scanning electron microscope (SEM) was used to further qualify the fracture surfaces at high magnifications. The SEM examination confirmed:

• many hundreds of crack progression bands were observed, which indicated crack growth occurred as a result of high-cycle fatigue[5]
• surface damage (an indent) approximately 0.10 mm in depth at the fatigue crack origin of fracture #1 had likely influenced the initiation of cracking within the yoke arm at the point of fracture
• a clear boundary on the fracture surface existed between the region of corrosion and the region that was not corroded (Figure 9).

Figure 9: Fracture surface of separated section showing corrosion boundary with inset showing crack surface discoloration

Source: ATSB

Metallurgical, chemical and dimensional analysis established that the yoke conformed to the manufacturer’s specification for material type, hardness, and physical dimensions.

Overall corrosion protection had been specified by the manufacturer that was for the yoke to be cadmium-plated, primed and then painted. These corrosion protection schemes were confirmed during metallurgical examination of the yoke.

Manufacturer’s clutch shaft forward yoke inspections

The manufacturer’s instructions for continuing airworthiness of the clutch shaft forward yoke (part number C907) were contained in the Robinson R44 II pilot’s operating handbook (POH) and the aircraft maintenance manual. The following was noted:

• At each daily or pre-flight inspection, the yoke flanges[6] (yoke arms) were to be checked. No cracks were permitted.
• At each 100-hour or annual airframe inspection, the yoke was to be checked for condition and to verify no cracks, corrosion or fretting was present. The yoke was also to be checked for security and operating clearance.
• At each 2,200-hour inspection, a 100-hour or annual inspection is also conducted, and the yoke was to be checked for condition. Additionally, the aircraft maintenance manual provided a list of components that were to be replaced with new or overhauled exchanged parts when they had accumulated 2,200/2,400-hours time‑in‑service. There was no requirement for the yoke to be replaced with a new or overhauled part once those hours had accumulated.

Other than for unscheduled maintenance, the yoke was only separated from the forward flex plate (see Figure 3 insert) when parts were replaced at their assigned 2,200/2,400-hour service interval. The yoke was treated as an ‘on-condition’ item and was not assigned an operating time‑in‑service, fatigue, or calendar life-limit.

Maintenance personnel reported that when installed, the yoke can be viewed on a daily inspection via an access panel located on the right side of the helicopter. During the 100-hour or annual inspection, the yoke can also be inspected from above when the upper panel between the fuel tanks was removed. It was noted that cracking on the front face of the yoke arm would not be visible during these inspections as there was no requirement to remove the yoke from the flex plate.

The aircraft maintenance manual specified a range of examination methods for the detection of defects and identified specific parts that warranted examination above that provided by visual inspection means. Higher levels of examination for nominated parts included the use of a suitably powered magnifying glass, and fluorescent penetrant and magnetic particle inspection processes. However, the yoke was not included in the nominated parts list.

Maintenance practices

The pilot reported that on the day of the accident, a pre-flight inspection was completed, and no defects were noted. Maintenance personnel also reported that no defects associated with the forward yoke were noted during the 100-hour inspection that was conducted 92 hours prior to the accident.

During the most recent 2,200-hour inspection, the helicopter’s main rotor gearbox was refitted, and the three flex plates of the rotor system drive train were replaced with new items.

Records showed that the engine-to-gearbox clutch shaft assembly had been replaced about 701 hours prior to the 2,200-hour inspection with the forward yoke transferred to the replacement shaft. This may have provided another opportunity for detailed inspection of all yoke surfaces.

Maintenance personnel involved in the 2,200-hour inspection reported that at the time of replacing the flex plates, following separation from the forward flex plate, the yoke surfaces were visually examined for defects and the yoke was determined to be serviceable.

The manufacturer advised that yokes were commonly removed from service due to the presence of corrosion or fretting damage, but not due to cracks. When forward yokes were returned to the manufacturer as part of the clutch shaft for overhaul, the surface finish was removed, and a magnetic particle inspection for defects would be completed prior to release to service.

Helicopter emergency procedures

Hydraulic system normal and emergency procedures

The R44 II POH advised pilots that for training purposes, a hydraulic system failure may be simulated by switching the hydraulic system off by using the cyclic-mounted hydraulic switch. With hydraulics switched off, controlling the helicopter in a hover may be difficult due to control system feedback forces.

The handbook also advised pilots to expect control stiffness and feedback when conducting hydraulic systems checks or pre-take off control checks with the hydraulic system switched off.

The handbook described the symptoms for a hydraulic system failure as indicated by heavy or stiff cyclic and collective controls, and loss of hydraulic fluid may cause intermittent and/or vibrating feedback in the controls. Should that occur, the POH stated that control of the helicopter would be normal except for the increase in stick forces. Additionally, if hydraulic power was not restored after verifying that the hydraulic switch is in the ‘ON’ position, the pilot is to switch hydraulics to ‘OFF’ and to land as soon as practical.

Engine power loss or loss of tail rotor function

In the event of an engine or drive system failure, the POH advised pilots to immediately lower the collective lever and enter autorotation[7] while observing airspeed requirements. Pilots were also instructed to enter an autorotation if loss of tail rotor thrust in forward flight occurs.

An autorotation is typically conducted at a specified forward airspeed and rotor RPM at which a power-off glide is most efficient. Autorotation airspeed and RPM is different for each helicopter type and is characterised as a controlled descent. The flight controls are used to manoeuvre the helicopter during the autorotation, through to completion of the landing sequence.

Although the tail rotor is used to counteract the yawing effect of the main rotor at low speed, a loss of tail rotor control or drive to the tail rotor, is manageable provided adequate airspeed is maintained, as directional stability is provided by the helicopter’s vertical and/or dorsal fin.

Pilots are trained to perform autorotational descents, and autorotational capability is a certification requirement for helicopters.

At interview, the pilot reported that simulated engine failures, tail rotor system malfunctions and hydraulic failures were practised during training and flight reviews. However, they were trained and assessed as independent emergencies and were never conducted simultaneously as a compound emergency.

Recorded data

VH-HOB was not equipped with a flight data or cockpit voice recorder, nor was it required to be. Differential GPS[8] flight path data from the on-board SatLoc Bantam[9] aerial application tracking device was provided to the ATSB.

Speed and position data from the SatLoc device was used in the analysis of the helicopter’s movements in the final 3 minutes of flight (Table 1).

Table 1: Key events involving VH-HOB during the final minutes of flight with approximate values of flight behaviour