[2]     The air temperature inside the envelope is directly related to the buoyancy force acting on the balloon which is generated by the heated air within the envelope. As the internal envelope air temperature increases compared to the ambient air temperature outside the envelope, the upwards pressure on the vent panel also increases.

[3]     When liquid fuel quantity diminished, so did fuel pressure. This decreased burner heat output and therefore capability for climbing to clear obstacles or arrest descents.

[4]     The Civil Aviation Safety Authority (CASA) classifies balloons into three classes. Class 1 – Hot air balloons that have a volume of not more than 260,000 cubic feet. Class 2 – Hot air balloons that have a volume of more than 260,000 cubic feet. Class 3 – Gas balloons.

[5]     Operating above the maximum temperature limits can cause a rapid decrease of the fabric strength and porosity of the envelope fabric.

[6]     A ‘minor change’ has no appreciable effect on the mass, balance, structural strength, reliability, operational characteristics, operational suitability data, or other characteristics affecting the airworthiness of the product or its environmental characteristics. All other changes are ‘major changes’.

[7]     A Design Organisation Approval is the recognition that a Design Organisation complies with the requirements of Part 21 Subpart J of the EASA Commission Regulations. This subpart details the elements required of a design organisation in order to hold the Design Organisation Approval. The approval grants privileges for the organisation to design new products, product modifications or repairs and may include approval for these designs.

[8]     CASA can issue type acceptance certificates for aircraft manufactured in a foreign country based on a foreign type certificate being issued for the aircraft type by the national aviation authority of a recognised country. CASA recognised EASA as a national aviation authority of a recognised country.

[9]     A person appointed by CASA to perform authorised functions for the purposes of a regulation subject to any conditions stipulated in an Instrument of Appointment.

[10]    Manned free balloon: a free balloon that can carry 1 or more persons and is equipped with controls that enable the altitude of the balloon to be controlled. Manned free balloons consist of four major components; the envelope, the burner, the basket, and fuel tanks. The CoA is issued to the complete balloon.

[1]     Circuit: the specified path to be flown by aircraft operating in the vicinity of an aerodrome.

[2]     Touch-and-go: a manoeuvre in which an aircraft conducts an approach, touches the runway, and immediately takes off again.

[3]     The upper torso restraint (shoulder harness) was physically attached to the roof of the cabin at one end, and when in use, the other end is secured to the lap portion of the restraint.

[4]     Runway numbering: represents the magnetic heading closest to the runway orientation (for example, runway 29 is oriented 292º magnetic).

[5]     The shoulder harness and/or restraint is referred to as an upper torso restraint in this report.

Pre-flight

In the morning of 16 April 2022, the pilot of a Beechcraft B58 Baron (B58) registered VH-NPT (NPT) arrived at Aviair Pty Ltd, at Broome Airport to prepare for a regular charter flight to several remote locations in northern Western Australia. The operator’s duty maintenance officer (maintainer) reported that the pilot contacted them by phone before the flight, reporting a ‘fuel kind of smell’ in the aircraft’s cockpit. The maintainer recalled discussing the basics of the aircraft’s fuel system and asking the pilot to monitor the situation and report back if the smell did not go away.   

The flight

The flight, with one passenger, seated in the rear right seat, and 4 boxes of cargo onboard, was planned to transit through the East Kimberley Regional Airport at Kununurra (Figure 1), refuel, then continue to Halls Creek where the passenger was to disembark, Fitzroy Crossing to unload cargo and then return to Broome via Derby.

Figure 1: Flight area with planned stops

Source: Google Earth annotated by the ATSB

The aircraft departed Broome at 0613 local time and climbed to 9,000 ft while tracking to the north-east. The maintainer, reported that at 0628 the pilot contacted them again, advising that the ’fuel like smell’ detected on the ground was no longer present.

At 0749 the pilot contacted air traffic control (ATC) and requested traffic for a direct track to waypoint Kununurra Whiskey Foxtrot (KNXWF) for an approach to runway 12 at Kununurra (Figure 2). At 0817 the pilot of NPT contacted ATC advising that they were leaving their cruising altitude of 9,000 ft on descent for Kununurra.

Figure 2: NPT flight path and Brisbane Centre radio calls

Source: Google Earth and AvPlan annotated by the ATSB

The approach

Seventeen minutes later NPT joined a straight in approach to runway 12. The pilot recalled slowing the aircraft, extending the first stage of flaps, and attempting to extend the landing gear.

Upon selecting the landing gear handle to the down position, the gear down and locked indicators (3 green lights) illuminated immediately. The pilot reported that this was unusual, as normal operation required a few seconds for the landing gear to extend and the lights to illuminate. However, no sound was heard from the landing gear motor and no decrease in aircraft performance was felt that would indicate gear had extended. The pilot also recalled, co‑incident with the landing gear handle activation, that the landing gear warning horn erroneously activated. The pilot stated that these unusual indications were followed immediately by an electrical burning smell and smoke emerging from below the left side of the aircraft instrument panel, forward of the pilot’s circuit breaker panel.

About a minute later, at 0836, the pilot made a PAN-PAN[1] call on the Brisbane Centre frequency advising of smoke and suspected fire in the cockpit. The pilot then activated the SOS[2] function on a dash mounted Spider Tracks[3] unit. The pilot recalled switching off the electrical power to the aircraft, in accordance with the electrical smoke and fire emergency procedure. They also reported switching off the avionics master switch (see the section titled Electrical system) as an additional precaution. By that time flames were emanating from the same location as the previously observed smoke.

The pilot then expended the entire contents of the aircraft’s handheld portable fire extinguisher, while continuing the straight in approach to runway 12 (Figure 3). However, the fire almost immediately returned, emanating from the same location, with flame and significant smoke in the cockpit. The pilot reported difficulty maintaining control of the aircraft as their left hand and leg were exposed directly to the flames and the smoke prevented them seeing both the instruments and the outside environment. In response, they opened the aircraft’s storm window[4] in an attempt to clear the smoke and obtain a visual reference.

Figure 3: NPT approach to East Kimberley Regional Airport

Source: Google Earth, AvPlan and Airservices Australia, annotated by the ATSB

As the aircraft approached the Ord River, multiple airborne witnesses reported that it appeared to be below the standard approach profile and ‘skimming the treetops.’

Recorded flight data indicated that, at 0837, the aircraft started diverging left of the extended runway centre line, crossing the Ord River at low level approximately 1.5 km from the threshold of runway 12. The aircraft subsequently collided with terrain, coming to rest inverted about 600 m beyond the river and about 800 m from the runway 12 threshold (Figure 3) and was consumed by a significant post‑impact fire.

Several pilots who were listening to the Brisbane Centre frequency reported hearing a transmission of static at the approximate time of the collision with terrain.

Post impact actions

The pilot reported difficulty in releasing themselves from the restraint and exiting the inverted aircraft. After exiting the aircraft, they attempted to access the passenger through the rear doors but were unable to due to the presence of significant smoke and flame. The pilot then re‑entered the aircraft through the crew door and located the passenger who was still secured in their restraint. The pilot, with limited assistance from the semi‑conscious passenger, undid the restraint and proceeded to extract the passenger from the aircraft. Shortly after the pilot and passenger exited the aircraft, the pilot collapsed, and operator personnel arrived and moved them to a safe distance from the wreckage.

The passenger succumbed to their injuries at the accident site. The pilot suffered serious injuries and was airlifted from the site to East Kimberley Regional Airport for transfer to the Kununurra Hospital before being transferred to Darwin for further treatment.

Context

Aircraft Information

NPT was a Beechcraft B58, low-wing, twin engine aircraft (Figure 4). It was manufactured in the United States in 1996 and first registered in Australia in 2012. The aircraft was fitted with 2 Continental IO-550-C piston engines, driving 3‑blade constant‑speed propellers.

Figure 4: VH-NPT at the time it was purchased by the operator

Source: Operator

NPT was acquired by the operator in 2019. It was configured for charter operations with seating for up to 4 passengers in a club[5] configuration and seating for 2 pilots. The aircraft was configured with dual flight controls.

Access to the aircraft was through one of 2 doors, a crew door located on the front right of the aircraft next to the co-pilot’s seat, providing access to the front seats. Two rear or ‘barn doors’ on the right side of the aircraft provide access to the rear cabin for the loading of persons and freight (Figure 5). The aircraft was also fitted with an emergency exit window on the left side of the aircraft next to the left rearward facing passenger seat. This window could be opened by a passenger in the event of an emergency. The pilot reported that instruction on its operation was included in the pre-flight briefing to the passenger.

Figure 5: Aircraft schematic identifying location of key elements

Source: Manufacturer annotated by the ATSB

Weight and balance

Prior to departure the pilot determined that the aircraft would be within weight and balance limitations for each leg of the flight using the operator’s approved spreadsheet for NPT. The ATSB obtained a copy of the approved spreadsheet for NPT and confirmed the pilot’s calculations. This assessment also indicated that for the legs of the flight that the passenger was onboard, the aircraft remained within balance limits irrespective of the seat occupied by the passenger.

Fire suppression

In accordance with the manufacturer’s requirements, NPT was fitted with a handheld portable 2 kg halon fire extinguisher for emergency use by the crew. The extinguisher was located centrally between the pilots’ seats and the rearward facing passenger seats. The extinguisher was inspected and reweighed as part of the last 100 hourly inspection in accordance with Civil Aviation Safety Authority requirements.

The pilot commented that, while they were able to access and utilise the extinguisher, its positioning made it more difficult to access in the event of an emergency than in other aircraft within the fleet.

Electrical system

Aircraft power was supplied by a single battery and an alternator fitted to each of the aircraft’s 2 engines. These power sources could be connected and disconnected individually using 3 separate switches on the pilot’s sub‑panel labelled ‘MASTER’ (Figure 6). To protect the avionics from electrical damage when the master switches were being operated, a separate ‘AVIONICS MASTER’ switch (Figure 6) controlled power to these devices. The ‘AVIONICS MASTER’ was dependant on the ‘MASTER’ switches in the control hierarchy, meaning that if the ‘MASTER’ switches were off, the ‘AVIONICS MASTER’ was not able to be powered.

Figure 6: Schematic of the pilot’s subpanel showing master power and landing gear controls

Source: Manufacturer annotated by the ATSB

Electrical power was supplied to several systems including drive motors for the landing gear and flaps, aircraft lighting, avionics and communications. A circuit breaker panel on the pilot’s left side protects the circuits from overload and damage. Wiring was routed from the circuit breaker and instrument panels down along the left side of the aircraft in a series of looms. Figure 7 shows the area forward of the circuit breaker panel and below the pilot’s instrument panel in an exemplar aircraft.

Figure 7: Circuit breaker and instrument panel of an exemplar B58 showing the position of wiring looms.

Source: Operator annotated by the ATSB.

Based on the pilot’s report of the abnormal landing gear behaviour, the ATSB conducted a detailed examination of the system function. The landing gear system consists of:

• a motor driving the gear between the extended and retracted positions
• an indicating system that identifies to the pilot when the gear is retracted, extended or in transit
• an aural alert that the gear is not extended if the aircraft is otherwise configured for landing.

Landing gear motor

The landing gear handle (Figure 6) acts as an electrical switch closing either the retract or extend landing gear motor circuit and powering the motor. Current flows through the switch and landing gear limit switches[6] to the motor relays. They are connected to the pilot’s circuit breaker panel by wiring on the left side of the aircraft and protected by a 5-amp circuit breaker. The relays operate a separate 30-amp circuit providing power directly to the landing gear motor. The switches and relays within the gear motor system provide power, with the motor constantly grounded. The landing gear motor is located below the floor of the aircraft between the crew and passenger seats.

Landing gear indication

The landing gear indication system consists of 4 lights, including one for each of the left, right and nose gears indicating they are in the down and locked position. A fourth light indicates that the gear is in transit. The lights are positioned above the gear handle on the instrument panel on the pilot’s subpanel assembly (Figure 6).

The lights are connected to down-lock and up-lock switches on each of the gear.  The in-transit light is illuminated when either the down-lock or up-lock switches on any of the gear are not depressed. Once the down lock switches on each gear is closed, the light for that gear is switched on and once all 3 down lock switches are activated, the in-transit light switches off. These lights are connected to a 5-amp power supply and are switched on by grounding the circuit through these switches.

Landing gear warning

The landing gear warning system warns the pilot if the aircraft is incorrectly configured for landing due to the gear not being extended. The system consists of a warning horn connected to flap, throttle, and landing gear position switches. The horn will activate if the flaps are extended to full and the throttles are retarded while the landing gear is selected up.

The wiring for these systems, and several other electrical systems, are bundled together in the area where the pilot reported the fire started. The ATSB’s review of the aircraft electrical wiring schematics was not able to identify a single point of failure, either through a short between systems or to ground or an open circuit, which could have caused all 3 symptoms that the pilot reported. However, the bundling of multiple wires and the possibility of live circuits contacting one another meant that a multiple point failure in the landing gear, or within other electrical circuits, leading to the symptoms the pilot reported was possible.

Other electrical anomalies

After the pilot selected the landing gear to the down position and the fire commenced, the pilot reported switching off the aircraft’s electrical power and that the aircraft’s avionics screens went black. Spider Tracks data (see the section titled Recorded data) ceased shortly after this, however the aircraft’s ADS-B transponder continued to transmit (see the section titled Recorded data) until just before the aircraft collided with terrain. Following the PAN-PAN, no radio transmissions from the aircraft were recorded on the Brisbane Centre frequency. However, multiple pilots operating in the area at the time reported significant static on this frequency at approximately the time the aircraft collided with terrain, possibly indicating that NPT’s radio was powered.

Cabin heater

The B58 is fitted with a fuel‑burning cabin heater in the nose of the aircraft (Figure 5). Maintenance records indicated that the heater was infrequently used, and the pilot advised that the heater was not utilised during the accident flight. In the 12 months leading up to the most recent 100 hourly inspection the heater had been used for 102.5 of the aircraft’s accumulated 1,077 hours, of which only 3.3 had been accrued in the last 6 months. The heater’s hour count following the 100 hourly inspection was unable to be determined due to the post impact fire.

The heater is supplied with fuel via a direct line from the left-wing leading-edge fuel tank. The fuel line is attached to the tank at the wing root and traverses internally along the lower left fuselage. It passes through the aircraft cockpit below the pilot’s circuit breaker panel (Figure 6). The line then enters the aircraft’s nose-wheel bay and connects to the heater. The line fills with fuel as the tank is filled and will remain full of fuel at all normal flight attitudes. The line is secured at multiple locations with clamps to prevent damage from contact with the aircraft’s structure.

When the heater is running, fuel flows through the line at a rate of about 4 litres per hour.

Maintenance history

The last 100 hourly inspection was completed 9 days prior to the accident flight. Since that time, and prior to the accident flight, the aircraft had accrued 18.7 hours of flight time.

Concurrent with the 100 hourly inspection, additional maintenance tasks were carried out on NPT. One of these tasks was a repair to the leading-edge fuel tank in the aircraft’s left wing. A leak was identified during a post maintenance fuel leak check and traced to a gasket on the tank. Maintenance records indicated that the fuel bladder was manoeuvred to access and replace the leaking gasket. Records did not indicate if the line to the cabin heater was disconnected prior to the maintenance taking place. Following the repair to the gasket a further post maintenance leak check was carried out with nil defects identified. The aircraft manufacturer’s 100 hourly inspection required that the heater be inspected in accordance with the heater manufacturer’s manual. The manual required an operational check of the heater, including at least 2 operational cycles.

The ATSB reviewed the aircraft’s logbook and maintenance release, no references were identified to a fuel leak or a potential fuel smell in the cockpit between the time the 100 hourly was completed and the accident flight.

Restraints

NPT was fitted with 2 types of restraints, 4-point harnesses for the crew seats and 3-point harnesses for both the forward and rearward facing passenger seats in the main cabin. The 4‑point harnesses fitted to the crew seats were not original equipment and had been retrofitted to the aircraft prior to its purchase by the operator, replacing the existing 3-point harnesses. These restraints were in accordance with or exceeded regulatory requirements (see the section titled Survivability - Restraints).

Flammability resistance

The B58 was certified under Part 3 of the United States Civil Air Regulations as amended in 1956, which required that materials making up the cabin interior be ’flash resistant’, or ’flame resistant’ if the compartment could be used for smoking.

The type certificate data sheet for the B58 required placarding that the aircraft was non-smoking for serial numbers TH-2173 and later. The interior of NPT, being an earlier serial number, was required to meet the standard for a flame-resistant interior.

Flame resistant materials are required to resist flame advance of more than 4 inches per minute. Flash resistance required average flame advance to be less than 20 inches per minute.

These progression rates are tested under controlled conditions in accordance with FAA advisory circular 23-2A. The tests are conducted on the materials in isolation and do not account for accelerants being present.

Site and wreckage information

The initial collision point with terrain was approximately 45 m from the main wreckage location with the aircraft tracking approximately 117° and becoming inverted during the impact sequence.

Despite the aircraft being consumed by a post impact fire some of the aircraft’s contents, including several documents and personal effects were ejected during the impact sequence, leaving them largely unaffected.

Due to the severity of the post‑impact fire, the ATSB was not able to conduct a complete wreckage examination. However, there was evidence of engine rotation prior to the collision with terrain and no evidence found of pre-existing defects in the engines or flight control components that could have contributed to the accident. The landing gear was observed in the stowed position and no landing gear impact marks were visible at the accident site.

Aircraft windscreen

During the impact sequence the aircraft’s windscreen fractured and was liberated from the fuselage in multiple pieces. Some of these pieces, were clear of the post‑impact fire and were located nearby in long grass with their internal surfaces facing down.

The ATSB was able to reassemble almost the entire windscreen on-site (Figure 8). Once reassembled a soot trail was visible on the internal surface of the left side of the windscreen. The trail, emanating from the bottom of the windscreen, was approximately 34 centimetres from the left edge. The soot was of sufficient thickness that a clearly visible trail was able to be wiped into it. At the point where the soot trail initiated, the windscreen material exhibited a different failure mode, likely associated with significant heat.

Figure 8: Reassembled aircraft windscreen showing soot trail outline and heat damage

Due to environmental conditions on-site the soot trail was not easily visible in captured image. The outside surface of the windscreen was subsequently marked on site with yellow paint marker identifying lateral extremities of the soot trail.

Source: ATSB

The upper, aft corner of the pilot’s storm window surround (Figure 9) was located with the outer surface down, closer to the post‑impact fire than the windscreen. Soot was located on both sides with the external surface, consistent with soot being drawn out of the window by the airflow.

Figure 9: Smoke and soot indications on window surfaces adjoining the pilots storm window

Source: ATSB

Flaps

Due to fire damage to the flap actuators, the specific position of the flaps at impact was unable to be determined. The aircraft’s flap tracks were recovered for further examination at the ATSB’s technical facilities in Canberra. Impact markings on the flap tracks indicated that the flaps were likely extended to the first of the 2 flap positions (15°) at the time of impact (Figure 10). This corresponded with both the pilot’s report of having extended the flaps one position prior to activating the landing gear and the operator’s procedures that required first stage flap extension as part of the setup of the aircraft for the approach.

Figure 10: Left inboard flap track with markings indicating likely flap position at impact

Source: ATSB

Possible tree strike

In response to witness reports that the aircraft skimmed trees prior to the ground collision, the operator conducted an airborne search on the western side of the Ord River. This search identified a grouping of 4 trees in the approach to runway 12 that had damage consistent with aircraft contact.

The trees were approximately 500 m west of the river and 60 m north of the extended runway 12 centreline (Figure 11). Their position was consistent with the aircraft’s approach path, and were close to the lowest point in the aircraft’s flight path data on the western side of the Ord River. Tree damage was between 15 and 20 ft above ground level and the direction of the breaks and fallen limbs were consistent with the aircraft’s direction of travel.

Figure 11: Possible tree strike location

Source: Google Earth, Operator, AvPlan and Airservices Australia, annotated by the ATSB

Other than evidence of a collision with a number of small trees at the accident site, no additional tree strikes were identified, and no evidence of a foliage strike was located on the wreckage, however the significant fire damage prevented a detailed examination.

Pilot information

The pilot held a current Commercial Pilot License (Aeroplane), with their last flight review conducted in December 2021. They also held a:

• Class 1 aviation medical certificate, valid until January 2023
• multi engine aircraft instrument rating with retractable undercarriage and manual propellor pitch control endorsements.

Prior to the accident flight, the pilot had accumulated approximately 2,482 hours of aeronautical experience, of which just over 120 hours were in command of the B58. The pilot had completed their most recent operational proficiency check on 9 January 2022 and a line check in the B58 was carried out on 25 January 2022.

Meteorological information

An aerodrome meteorological report (METAR[7]) was issued by the automatic weather station at East Kimberley Regional Airport approximately 7 minutes before the accident. The report showed fine weather, with winds from the north at 2 kt, visibility greater than 10 km and nil cloud detected.

The ATSB also reviewed CCTV footage from the East Kimberley Regional Airport, which captured the smoke plume from the accident. Figure 12 shows the location of a camera covering the regular public transport apron. The camera image showed a smoke plume rising near-vertically from the accident site approximately 3 minutes after the accident indicating little to no wind immediately after the accident, consistent with the METAR.

Figure 12: Location of CCTV camera

Source: Google Earth annotated by the ATSB

Survivability

In reviewing the survivability aspects of this accident, the ATSB sought expert guidance from the Royal Australian Air Force Institute of Aviation Medicine (IAM). Their report formed the basis of the following section.

Restraints

Injuries to aircraft occupants arising from traumatic contact with aircraft structure occur at least 5 times more often than acceleration‑related injury. Within small aircraft that have confined interiors, lap belts and upper torso restraints are critical to crash survivability for both crew and passengers. The restraint of the upper body serves 2 purposes:

• reducing the likelihood of impacting structures by minimising body flailing
• distributing forces more widely across the body, making them more likely to be survivable.

Upper torso restraints can be provided with a single shoulder strap, like that used in a car seatbelt or 2 straps, one over each shoulder. Figure 13, below, shows the difference between 2-, 3- and 4-point restraints. The image also shows a 5-point restraint that has a crotch strap which provides additional protection for the wearer, preventing them from ‘submarining’ or sliding under the lap portion of the restraint.

Figure 13: Aircraft restraint types.

Source: United States Department of the Interior via IAM

Both 3- and 4-point harnesses restrain the upper torso. However, the 3-point only provides lateral restraint in one direction, if the person flails to the unrestrained side they may come out of the shoulder strap rendering it ineffective. Additionally, with only one strap over the torso, the 3‑point restraint has a smaller surface area than the 4-point, increasing the force exerted to the restrained area on the wearer.

In accordance with Civil Aviation Safety Regulation (CASR) 90.105 the flight crew seats must be fitted with a restraint that consists of a lap belt and at least one shoulder strap. Requirements for occupant restraints are outlined in CASR 90.110 and require all occupant seats for aircraft with less than 10 seats and manufactured after 13 December 1986 to be fitted with an approved seat belt and shoulder harness.  

Seating

It is generally accepted that in the event of a frontal impact a rearward facing seat will increase survivability in two ways.

• Spreading the impact force over the entire surface of the back rather than specific areas where a restraint is positioned.
• Limiting the movement of the head through flexion and extension of the neck, provided the seat is fitted with an appropriately positioned headrest.

There is no Australian regulatory requirement for the use of rearward facing seats. Their use is subject to availability and based on a range of operational considerations. These include weight and balance, emergency egress, other payload items (cargo), company procedure and passenger and pilot comfort. The ATSB recovered all seat frames from the aircraft wreckage. However, due to the severity of the post‑impact fire the ATSB was not able to conduct a detailed assessment and determine their effectiveness in attenuating impact forces and any subsequent effect on survivability.

Injuries

IAM reviewed the hospital and post-mortem records of the pilot and passenger respectively and provided a summary of their injuries. Both the passenger and the pilot received injuries attributable to both the fire and the collision with terrain. While there were some similarities in the injury profiles, the passenger’s injuries included more severe burns and trauma to the neck and chest, consistent with a single shoulder restraint and flailing within the aircraft, that the pilot did not suffer.

Recorded data

Spider Tracks

The last non-SOS Spider Tracks data point, available to the nearest minute was recorded at 0835. Immediately after this, still at 0835, two ’SOS Opened’ data points were recorded, indicating that the SOS function has been activated. No further data was received by the operator.

The SOS function increases the frequency of the data transmissions to 10-15 second intervals rather than the standard 2 minutes. Data from the pilot’s electronic flight bag (EFB) application indicated that the aircraft collided with terrain at 0837. If the Spider Tracks unit had remained powered after the 2 SOS data points at least 8 further transmissions should have been received. If the activation of the SOS function had not triggered the increase in data frequency, then one more point may have been received at 0837, depending on the exact time that the 0835 data point was transmitted.

The operator advised that the Spider Tracks unit was connected to aircraft power and the loss of signal from the Spider Tracks indicated a loss of electrical power to the aircraft.

Electronic flight bag

The operator utilised the AvPlan EFB application for pilots to undertake flight planning tasks, access electronic information, such as charts or relevant documentation and depending on the settings, display nearby traffic. The application can also record aircraft position information at 5‑second intervals. The pilot of NPT had a device with the application installed and active for the flight, for which the ATSB received data. This provided multiple flight parameters including ground speed and tracking details for the aircraft from the time of take-off until it collided with terrain.

The device was powered by an internal battery. However, it could be connected to aircraft power to keep the battery charged. The loss of aircraft power would not reduce the functionality of the device or effect the data recorded while the battery maintained its charge.

ADS-B

The aircraft was fitted with a transponder that broadcast ADS-B[8] data to ground stations and nearby aircraft fitted with ADS-B IN. The ATSB retrieved the data transmitted by this unit from ground stations operated by both Airservices Australia and other third-party receivers, including one at the East Kimberly Regional Airport.

Data obtained from the receivers operated by Airservices Australia and several third-party receivers, recorded the aircraft’s location from Broome until 0835 when the aircraft started the approach to runway 12 at East Kimberley Regional Airport. The signal was then lost, likely due to the aircraft’s descent taking it below the coverage altitude for these receivers.

An ADS-B receiver at the East Kimberley Regional Airport received data from the aircraft between 0834 and 0837. This recorded the aircraft passing KNXWF and commencing the approach to the East Kimberley Regional Airport. The final position report was received at 0836:43. Between 0836:43 and 0837:12 eight more data packets were received containing NPT’s mode S transponder code, however position information was not included.

The aircraft was fitted with a GTX33 ADS-B transponder unit, which was not equipped with an internal backup battery.

Related occurrences

The ATSB identified one occurrence in Australia and 3 in the United States that had similarities to this accident. These 4 occurrences involve in-flight fires accelerated by combustible hydrocarbons that were initiated by damaged electrical wiring. Each of these fires were different, with 2 relating to direct feeding fuel and oil gauges (which NPT was not fitted with), one was an engine fire, and one was a cockpit fire that was controllable. While different in detail, they all demonstrate the risks when electrical wiring and combustible hydrocarbons such as fuel and oil are in proximity.

AO-2014-040

On 26 February 2014 at about 1645 local time, a Beech 58 aircraft, registered VH‑SBS, departed Darwin for Gove, Northern Territory, on a private ferry flight with a supervising pilot and pilot in‑command-under-supervision (ICUS) on board.

At about 1815, the pilot flying ICUS saw smoke and flames by their left leg adjacent to the circuit breaker panel and immediately switched off the electrical master switch. The supervising pilot seated in the right seat took control of the aircraft and commenced an immediate descent. The pilot ICUS retrieved the fire extinguisher from underneath their seat and extinguished the fire.

An engineering inspection found electrical wiring penetrated through the heater supply fuel line causing it to arc and burn a hole in the fuel line. The wires had been bundled together and were rubbing on the fuel line.

NTSB investigations

Between 1983 and 2022 the NTSB’s public database identified 7 investigations where an inflight fire or explosion was listed as a factor. Of these, 3 were identified to be of particular relevance and are summarised below.

MIA00FA221

On 17 July 2000, approximately 7 minutes after departing Memphis Tennessee, the pilot of a B58 aircraft registered N158MT, serial number TH-1186, contacted ATC reporting that they had an electrical fire and were going to switch off the master. Following two further communications with ATC the aircraft collided with water at Arkabutla Lake. Witnesses reported seeing a ’vapor trail’ or ’dust’ coming from the aircraft. The pilot was fatally injured, and the aircraft was destroyed.

The NTSB investigation identified that the fire was likely the result of arcing of an electrical wire behind the pilot’s instrument panel and associated heat‑related cracking to fuel and oil lines that feed direct reading pressure gauges for fuel and oil pressure in the cockpit. The investigation also identified that the pilot had not switched off the engine alternator switches in accordance with the electrical smoke and fire emergency checklist.   

SEA02FA023

During take-off, on 2 January 2002, the pilot of a B58 aircraft registered N132Z, serial number TJ‑284, identified a fire in the aircraft’s left engine. The pilot reduced power and landed the aircraft on the remaining runway. The pilot and the passenger evacuated the aircraft, which sustained substantial damage.

Further inspection identified that an improper clearance had allowed an alternator wire to chafe against a pneumatic line in the engine bay. The exposed wire subsequently arced to the aluminium line igniting fuel vapor. The most probable cause of the accumulated fuel vapor was from a fuel cell leak that had previously been repaired.

ERA11FA312

On 25 May 2011, a B58 aircraft, registered N77AR, serial number TH-757, with a pilot and 3 passengers on board was conducting a flight from Atlanta, Georgia to Hazard, Kentucky. At 1612 local time the pilot contacted ATC to advise they were declaring an emergency due to a fire on board. No further radio transmissions were received. ATC recorded 7 further transponder and 2 primary radar returns. Several witnesses observed the aircraft in its final stages of flight before it collided with terrain at approximately 1613 local time. The 4 occupants were fatally injured, and the aircraft was consumed by a post‑impact fire.

The NTSB investigation identified that an in-flight fire likely initiated in the right front cockpit area forward of the instrument panel and below the glare shield. While the NTSB was unable to conclusively determine the origin of the fire, their analysis notes that the speed of the fire’s advance was consistent with a fuel fed fire. The analysis also identified that the area where the fire was believed to have initiated was an area that is near the direct‑reading oil pressure gauges.  

This report noted that B58 and 58A models with serial number TH-001 through TH-1193 were fitted with direct‑reading fuel flow and pressure indicators in the cockpit. Direct‑reading pressure indicators use a direct line from the engine to the cockpit for presentation of engine fuel pressure. The report noted that aircraft with serial number TH-1194 and later (NPT serial number TH-1769) were fitted with remote fuel flow indicators, removing the need for fuel lines to go directly to the cockpit.

Safety analysis

Introduction

At 0834 local time on 16 April 2022, the pilot of B58 Baron aircraft registered VH-NPT commenced a straight in approach to runway 12 at the East Kimberley Regional Airport at Kununurra. During the approach the pilot declared a PAN-PAN to air traffic control reporting smoke and suspected fire in the aircraft’s cockpit.

The pilot continued the approach, diverging from the runway centreline track as they crossed the Ord River. The aircraft collided with terrain on the eastern side of the Ord River approximately 800 m from the runway 12 threshold. The passenger sustained fatal injuries and the pilot sustained serious injuries.

The following analysis will examine the in-flight fire, looking at the sources of initiation and acceleration, the pilot’s loss of visual cues and factors that affected survivability.

In-flight fire

The pilot reported that smoke and subsequently flame emerged from below the left side of the instrument panel, below and forward of the circuit breaker panel. The pilot attempted to extinguish the fire with a portable handheld fire extinguisher. The extinguisher suppressed the fire, however once removed, the fire returned vigorously.

Within 90 seconds of the pilot declaring the PAN-PAN, the aircraft had collided with terrain. The pilot sustained serious burns to their left side and the pilot and passenger sustained fire‑related respiratory injuries.

Materials used in the interior trim of NPT were required to be flame-resistant. The fire progressed at a speed greater than what would be expected of flame-resistant materials, consistent with the fire being fuelled by an accelerant.

Acceleration

Several lines and multiple looms of electrical wiring pass through the area where the pilot reported that the fire initiated. The lines contain pitot and static air for instruments, air conditioning system gasses and the fuel line to the aircraft’s cabin heater. Of these, the fuel line to the cabin heater provided the only source for flammable liquid to accelerate the fire.

A breach in the fuel line forward of and below the pilot’s circuit breaker panel would allow fuel to enter the area behind the side wall trim panel, possibly being absorbed by the fibreglass insulation. This would provide a high energy acceleration source capable of overcoming the flammability resistance of the trim materials. A direct examination of the line, surrounding insultation and the trim panel was not possible due to the post impact fire. As a result, the integrity of the heater line was unable to be established.

Two possible scenarios were considered for when a breach in the fuel line may have occurred. The first was that the leak was initiated at the time the pilot detected the smoke. This would show significant similarity to the previous Australian occurrence (AO-2014-040) whereby the breach in the fuel line initiated and provided an accelerant for the fire. However, in the 2014 occurrence, the leak was small, and the fire was comparatively controllable. In the event of a larger breach, or the line fracturing, fuel would be liberated more quickly, decreasing the chances of controlling the fire effectively.

The second scenario considered fuel to have been leaking for some time prior to the initiation of the fire. If the fuel had been leaking previously this would allow accelerant to accumulate behind the trim panel and in the insulation. In this scenario a smaller leak could lead to the same issues controlling the fire as a larger breach occurring due to the accumulated fuel.

The pilot’s report of a ‘fuel like smell’ in the cockpit on the morning of the accident may support the line having been breached at some point prior to the aircraft taking off. However, the pilot reported that the smell was no longer present once airborne. Additionally, there was no reported evidence of fuel spillage on the ground and the aircraft had passed its fuel leak check following maintenance 18 flight hours earlier.

Due to the post impact fire damage the ATSB was unable to determine which of the 2 scenarios were more likely. However, once the fire was initiated, given its location, it would very likely have quickly burned through the heater line liberating fuel that remained in the line further accelerating the fire and contributing to its rapid return after the pilot suppressed it with the portable handheld fire extinguisher.

Initiation

The electrical burning smell reported by the pilot immediately before the smoke and subsequent flames were observed supports the fire being initiated by a fault in the electrical system. The pilot reported that all systems had been operating normally until the landing gear handle was selected to the down position. Following the operation of the landing gear handle the pilot reported that the landing gear did not extend and there were multiple abnormal landing gear system indications.

Wiring for both the indication and operational systems are contained in wiring looms that pass through the area where the pilot first observed the smoke. These looms run near one another and the aircraft structure. Undetected damage could occur to or within the wiring looms, providing an ignition source from chafing, overheating of wiring or wires shorting to another wire or the airframe. Due to the destruction of the aircraft wreckage the ATSB was not able to determine the exact sequence of events that led to the electrical fault, the initiation of the fire and the other electrical anomalies that occurred.

Despite that, previous occurrences in both Australia and the United States show the danger that damaged electrical wiring can pose in areas with flammable liquid lines.

Loss of visual cues

As the fire advanced it generated a large amount of heat and smoke in the cockpit as reported by the pilot and evidenced by the soot on the internal surfaces of the aircraft windscreen and the pilot’s storm window surround, both of which were separated from the post‑impact fire. The extent of this smoke likely prevented the pilot from being able to see visual cues external to the aircraft or to effectively use the instruments as a reference. That situation, combined with the direct heat of the fire, meant that the pilot was presented with significant difficulty retaining control of the aircraft.

Following the PAN PAN call the aircraft descended below the normal approach profile; however, the pilot was able to maintain the approach track until crossing the Ord River when the aircraft diverged to the left of the extended runway centreline. The pilot was subsequently able to regain the approach heading prior to the aircraft colliding with terrain.

Survivability

The survivability of the accident can be broken down into the environment within the aircraft prior to and after the collision and the impact forces related to the collision.

The fire generated significant heat and smoke in the aircraft’s cockpit. The reports of the pilot and the respiratory injuries to both occupants indicate that they were unable to effectively vent the smoke.

With the pilot able to self-extract after the collision, the passenger continued to be exposed to the environmental conditions within the aircraft until the pilot was able to re-enter the aircraft to extract them. This likely reduced the passenger’s chances of survival.

The pilot reported that they and the passenger were secured in their restraints at the time the aircraft collided with terrain. The pilot, in the left control seat was in a 4-point harness and the passenger, in the rear right seat, was in a 3-point harness. Generally, the 4-point harness improves survivability in 2 ways. Firstly, it better attenuates the impact forces, by spreading them more broadly over the body. Secondly, it secures the occupant more effectively laterally reducing flailing. This decreases the likelihood of injuries due to contact with obstructions or structure of the aircraft.

The primary difference in injuries between the 2 occupants of the aircraft was the chest and other trauma present in the passenger. This trauma was consistent with the differences between the use of a 3-point and 4-point restraint. The 3-point restraint did not distribute forces as evenly across the body and allowed significant multi-directional movement (flailing) inside the aircraft.  

Based on advice from the manufacturer, operator and ATSB research a 4-point restraint is not available for the rear seat of B58 aircraft. However, this accident demonstrates the fitment of the 4-point harness to the crew seats, can improve survivability over the 3-point restraint that is required under the regulations.

Seating position

NPT was fitted with a club passenger seating configuration, with 2 forward facing and 2 rearward facing seats. As the pilot and passenger were seated in forward facing seats a comparison of injury profiles due to forward or rearward facing seats was not possible. However, the available literature supports that in the event of a frontal impact the rearward facing seat will provide better restraint of the occupant. By both spreading impact force more evenly over the whole back and reducing the potential for flailing by forcing the body into the seat.

For this flight, the ATSB reviewed the weight and balance documentation, determining that the aircraft remained within limits regardless of where the passenger or the cargo were positioned. Additionally, due to the size of the cabin, the passenger’s emergency egress route would not have been altered by changing positions.

Recognising that, when flight planning, pilots have many operational considerations when it comes to passenger positioning, in the event of a frontal impact, such as a collision with terrain, a rearward facing seat will generally better protect the occupant and increase their chances of survival.
 

Findings

From the evidence available, the following findings are made with respect to the In-flight fire and collision with terrain involving Beechcraft B58 Baron, VH-NPT near East Kimberley Regional Airport, Kununurra, Western Australia on 16 April 2022.

Contributing factors

• On approach to runway 12 at Kununurra, a fault associated with the landing gear electrical system likely ignited fuel from the cabin heater supply line, resulting in a significant and sustained cockpit fire.
• Due to smoke in the cockpit, the pilot lost visual reference to both the instruments and outside environment. This, combined with the direct exposure to flames, led to a divergence from the extended runway centre line and the aircraft impacting terrain off the airfield.

Other findings

• The 4-point harness that was installed for the pilot provided better restraint and attenuation of impact forces compared to the best available option of a 3-point restraint in the rear, leading to less severe impact related injuries.
• The aircraft’s passenger cabin had a ‘club’ configuration with 2 forward and 2 rearward facing seats. Although not a requirement, positioning the passenger in rearward facing seat would have likely improved survivability from frontal impact‑related injuries.

Safety action

Safety action by Aviair Pty Ltd

In response to this accident the operator reported that they

• commenced a program to install 4-point restraints in the crew seats of all their B58 aircraft
• installed an additional fire extinguisher in each of their B58 aircraft,
• incorporated additional 100-hourly fuel line and wiring inspections in the vicinity of the heater fuel line and circuit breakers adjacent to the pilot’s seat.

Safety advisory notice to operators of B58 aircraft

In conjunction with the preliminary report released on 21 September 2022, the ATSB issued a Safety Advisory Notice to all B58 operators encouraging them to:

• note the circumstances of this accident and previous ATSB investigation AO‑2014‑040

conduct a detailed examination of the wiring and fuel line on the left side of the aircraft forward of, and below, the pilot’s circuit breaker panel.

A copy of the Safety Advisory Notice can be found on the ATSB website here.
 

Glossary

ATC                 Air traffic control

ADS-B             Automatic Dependent Surveillance - Broadcast

CASA              Civil Aviation Safety Authority

CASR              Civil Aviation Safety Regulations

CCTV              Closed-circuit television

EFB                 Electronic Flight Bag

FL                    Flight level

KNXWF           Approach point Kununurra Whiskey Foxtrot

METAR            Aerodrome meteorological report

IAS                  Indicated airspeed

IAM                  Royal Australian Air Force Institute of Aviation Medicine

Sources and submissions

Sources of information

The sources of information during the investigation included the:

• pilot and operator
• Civil Aviation Safety Authority
• Western Australia Police Service
• aircraft manufacturer
• Airservices Australia
• accident witnesses
• CCTV footage and ADS-B data recorded at the East Kimberley Regional Airport
• recorded data from AvPlan electronic flight bag application on the pilots iPad.
• Royal Australian Air Force Institute of Aviation Medicine

Submissions

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

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

• pilot of the accident flight
• operator
• Civil Aviation Safety Authority
• aircraft manufacturer
• Royal Australian Air Force Institute of Aviation Medicine

Figure 2: Damage to upper engine cowl of VH-AAX

Source: ATSB

Figure 3: Damage to the engine combustion chamber, turbine section, and exhaust assembly

Source: ATSB             

Context

Pilot information

The pilot held a Private Pilot (Aeroplane) Licence and had a total flying experience of 1,078 hours, of which 540 hours were on the de Haviland Canada DHC-2/A1 Beaver. In the previous 90 days, the pilot had flown 154 hours total and 140 hours on the Beaver. The pilot was also employed by the operator as a licence aircraft maintenance engineer.

Aircraft information

General

VH-AAX was a de Havilland Canada DHC-2/A1 Beaver high-wing aircraft, with a single turboprop engine. At the time of the incident, the aircraft’s total time-in-service was 17,039.2 hours. The aircraft was last serviced 70 hours prior and there were no outstanding maintenance items recorded on the maintenance release.

Engine information and history

The engine fitted to VH-AAX was a Honeywell International Inc (formerly AlliedSignal, Garrett, and AiResearch) model number TPE331-2-201A, turbo-propeller engine (Figure 4), serial number P90018C. It consisted of:

• a 2-stage centrifugal compressor
• an annular combustion chamber
• a 3-stage axial turbine
• a reduction gear and shaft section.

The turbine section contained the 1st, 2nd and 3rd-stage turbine wheels. The exhaust assembly was considered part of the turbine section.

Figure 4: Schematic of Honeywell TPE331-2-201A Engine

Source: Honeywell, annotated by the ATSB

On 18 June 2009, the engine was overhauled and the engine components were certified with zero cycles at this time. On 14 August 2014, new 1st and 2nd-stage turbine wheels were fitted and a hot section inspection[6] was performed.

On 2 September 2019, the engine was removed from VH-AAX and sent for preservation to allow for an airframe rebuild by the new owner. Up until this time, the engine had been primarily maintained by a single organisation, the ‘first maintainer’. The engine was reinstalled in VH-AAX on 18 August 2020 and operated without issue until the date of the incident. The most recent 100‑hourly maintenance inspection was performed on 21 February 2022 by the ‘current maintainer’. The owner had arranged for the 1st, 2nd, and 3rd-stage turbine wheels to be replaced during an upcoming scheduled maintenance event as, according to the engine logbooks, the 3rd‑stage turbine wheel, part number 868630-9, was approaching the component life-limit.

Engine examination

The engine was transported to a Honeywell facility in the United States for a teardown and detailed examination supervised by the National Transportation Safety Board. The examination found that:

• there was evidence of rotational instability in the engine while the engine was running
• the main shaft and the torsion shaft had fractured
• a fragment of turbine wheel was lodged in the outwards rupture of the combustion case; this fragment (Figure 5) was consistent with the specified material of the 3rd-stage turbine wheel. No other parts of the 3rd stage turbine wheels were found in the engine
• evidence of low-cycle fatigue cracking[7] was identified on the fragment of the 3rd-stage turbine wheel found lodged in the combustion case (Figure 5 and Figure 6)
• the 2nd stage turbine wheel was not present
• the aft turbine bearing and bearing support, aft sump scavenge pump, aft bearing support struts, turbine nut, and tail cone were missing
• there was ‘no uncontainment’ of the combustion case.[8]

Both Honeywell and the National Transportation Safety Board concluded that the most likely reason for the engine failure was a low-cycle fatigue failure of the 3rd-stage turbine wheel.

Figure 5: Recovered fragment of 3rd-stage turbine wheel found lodged in the combustion case viewed from the aft (left) and forward sides (right)

Source: Honeywell, annotated by the ATSB

The photograph in Figure 6 shows the fracture surface on the 3rd-stage turbine wheel fragment. The fracture surface is in the radial plane located at a rivet hole. The crack initiation area has been indicated.

Figure 6: Fracture surface on the 3rd-stage turbine wheel fragment

Source: Honeywell, annotated by the ATSB

The scanning electron microscope image in Figure 7 taken of the fracture surface, showed features consistent with fatigue cracking. The direction of crack growth (white dash arrows), informed by the striations, indicated that the crack originated from the reduction in diameter of the rivet hole.

Figure 7: Microscopic fracture surface features adjacent to the fracture initiation area indicating fatigue crack growth

Source: Honeywell, annotated by Honeywell and the ATSB

Equivalent cycles in special operations

On 9 August 2006, the United States Federal Aviation Administration issued airworthiness directive (AD) 2006-14-03, applicable to Honeywell TPE331 series turboprop and TSE331-3U model turboshaft engines. The AD was issued to prevent an uncontained engine failure resulting from fracturing of the turbine rotor[9] due to low-cycle fatigue. This AD was developed in response to several reports of uncontained turbine rotor separation[10] that had resulted in metal fragments either penetrating the engine case or exiting the tail pipe, on engines used in ‘special-use’ operations. Special-use operations was defined as those aircraft that make multiple take-offs and landings without an engine shutdown, such as parachute and agricultural spraying operations. The additional take-offs and landings result in the life-limited parts accruing low-cycle fatigue damage at a faster rate when compared with passenger and freight transport flights.

The previously established cycle counting and life limits for life-limited parts used in Honeywell TPE331 turboprop engines were based on a cycle that consisted of an engine start, aircraft take‑off, cruise, landing, and engine shutdown (Figure 8). This is typical of a passenger transport flight. Applying this, an engine component such as a turbine wheel, would accrue a single cycle for each engine start/shutdown, irrespective of how many landings occurred.

Figure 8: Example of a passenger transport flight corresponding to a single engine cycle

Source: ATSB

The AD required implementation of a new flight cycle counting method, which involved tracking ‘equivalent cycles’ for turbine wheels in aircraft undertaking special-use operations (Figure 9). An equivalent cycle incorporated a damage fraction factor for each additional landing that occurred with no engine shutdown followed by a take-off. This was in addition to the cycle for one landing associated with the start/shutdown as shown in Figure 8. Total equivalent cycles were the sum of equivalent cycles for all operational flights.

Figure 9: Example of a special-use operation requiring an equivalent cycle calculation

Note: Schematic showing hypothetical day of operation for an aircraft used for ‘special-use’ operations. This example shows a total of 2 shutdowns and 5 landings.

Source: ATSB

The AD also referred to the use of Honeywell service bulletin TPE331–A72–2111, first issued in 2002, to determine the total equivalent cycles for TPE331-2 model engines. This included the engine fitted to VH-AAX, which was overhauled after the introduction of the AD and was reportedly always involved in special-use operations. The method outlined in the service bulletin for determining equivalent cycles for a turbine wheel in this engine, used the equation:

Where, the damage fraction applicable to the 1st, 2nd and 3rd-stage turbine wheels was 0.5, 0.6 and 0.2, respectively. For the part numbers fitted to the incident engine, the ‘turbine wheel removal schedule’ specified for the retirement of the 1st, 2nd and 3rd-stage turbine wheels was at 5,700, 5,400 and 6,000 total equivalent cycles, respectively.

Shutdowns and landings recorded by the operator

Operators conducting special-use operations, which included parachuting flights conducted in VH‑AAX, recorded the number of landings associated with each start/shutdown cycle to monitor the accumulation of equivalent cycles. The operator of VH-AAX recorded the total number of shutdowns and the total number landings performed in a day of operation as part of the daily line item on the maintenance release. The total number of equivalent cycles accrued by engine components was not calculated at the end of each shutdown as described in Honeywell service bulletin TPE331–A72–2111. Instead, the calculation was performed by the maintenance organisation at scheduled maintenance events.

The operator used their parachuting manifest to accurately record the number of landings that occurred in a day. The number of engine shutdowns was estimated by the operator at the end of each day, rather than by a pilot record being made at the time of each shutdown.

Equivalent cycles calculations by the maintenance organisations

Two maintenance organisations, the ‘first maintainer’ and the ‘current maintainer’, were primarily responsible for the maintenance of the engine since it was rebuilt in 2009. There was another maintenance organisation, the 'second maintainer’, that was only briefly responsible for maintenance of the aircraft. The maintenance organisations used the maintenance release to calculate total equivalent cycles accrued by engine components. At a scheduled maintenance event, the maintainer would sum the number of shutdowns and the number of landings for the period of the maintenance release. Then they would calculate the cycles accrued by a component over that period according to the following equation:

Where shutdowns was the total number of engine shutdowns recorded on the maintenance release, landings was the total number of landings recorded on the maintenance release, and damage fraction was 0.5, 0.6 and 0.2, for the 1st, 2nd and 3rd-stage turbine wheel, respectively. The maintainer would then add the equivalent cycles for the latest maintenance release period to the previous total recorded to obtain the new value.

The ATSB completed a review of the equivalent cycle counting recorded by the 3 maintainers, for the time from the engine rebuild in 2009 until the engine failure (Table 1). Comparison of the engine logbook and maintenance release identified errors in the total equivalent cycles and engine components recorded by the first maintainers. Calculation of the accurate number of cumulative equivalent cycles for the 3rd-stage turbine indicated that the turbine had completed 477.6 more equivalent cycles than recorded, resulting in the part having exceeded the retirement limit by 357.6 cycles at the time of the engine failure (red text in Table 1). The first maintenance organisation stated that a single individual was tasked with calculating and recording cycles and that there was no secondary check by another worker.

Another discrepancy between recorded and corrected total equivalent cycles related to the second maintainer appeared to be related to rounding.

The current maintainer did not record the total equivalent cycles accrued by engine components in each logbook entry, instead the remaining cycles was calculated in the work packs. The remaining cycles, rounded down to a whole number, were then communicated to the operator. No errors were identified in the total equivalent cycles recorded by the current maintainer.

Table 1: Number of equivalent cycles accrued by the engine and turbine wheels fitted to VH-AAX

Safety analysis

Low-cycle fatigue crack

When a low-cycle fatigue crack on the 3rd-stage turbine wheel, grew to a critical size, a fragment of the wheel was liberated under load, which initiated the engine failure. The fragment impacted the combustion case and became lodged. The separation of this wheel fragment resulted in significant rotational imbalance, which led to fracturing of the main and torsion shafts. Detached turbine section components then exited the engine, damaging the exhaust assembly. There was no evidence that any turbine wheel fragments exited through the combustion case with sufficient energy to cause a hazard to the aircraft. As such, the failure was deemed to be contained.

When the engine failure occurred, the pilot was descending from FL 145 above the airport, so had sufficient time to conduct all engine failure checks and prepare for a forced landing. The decision to land on runway 18, despite the tail wind, reduced the risk the aircraft posed to the parachutists.

Cycle counting error for 3rd-stage turbine wheel

The ATSB’s examination of the engine logbooks and available maintenance releases determined that the aircraft’s first maintainer made a number of traceable errors when calculating and recording engine cycles, and engine component equivalent cycles. There was limited opportunity to avoid these errors as the calculations were performed by one individual and no independent checking was incorporated into the process.

The cumulative effect of the errors meant that the 3rd-stage turbine wheel had accrued 477.6 equivalent cycles more than the reported value. Consequently, at the time of the engine failure, the 3rd-stage turbine wheel had exceeded its component life-limit by 357.6 equivalent cycles. The operator had planned to replace the 3rd‑stage turbine wheel upon reaching the life-limit (as recorded in the engine logbook). If the equivalent cycles had been correctly recorded, the part would have been replaced before an engine failure occurred.

Number of engine shutdowns estimated

The operator’s method for estimating engine shutdowns on a day of operation also introduced a potential source of error in accounting for cycles. The estimation of the number of shutdowns at the end of each day, combined with delaying the calculation of total equivalent cycles until a scheduled maintenance event, deviated from the method for monitoring equivalent cycles described in Honeywell service bulletin TPE331–A72–2111.

The maintainers relied on the record of landings and shutdowns in the maintenance release for the calculation of total equivalent cycles accrued by a component. In practice, if the information recorded on the maintenance release accurately reflected the operation of the aircraft, there would have been no difference between performing the calculation after each start/shutdown cycle or using the total number of landings and starts shutdowns for the period of the maintenance release. It was not possible for the ATSB to quantify the errors, if any, introduced by the operator’s estimation method without a record to compare the estimated and actual shutdowns.

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 engine failure involving de Havilland Canada DHC-2 Beaver, registration VH-AAX, overhead Moruya Airport, New South Wales, on 4 April 2022.

Contributing factors

• A low-cycle fatigue crack, which had initiated on the 3rd-stage turbine wheel, grew to a critical size liberating a fragment of turbine wheel. Following this, the engine failed, requiring the pilot to shut down the engine and conduct a forced landing.
• Errors in cycle counting made by a previous maintainer resulted in the 3rd-stage turbine wheel remaining in-service beyond the component life-limit.

Other factors that increased risk

• The operator estimated the number of engine shutdowns conducted each day based on recollection only, which increased the likelihood that cycles recorded were incorrect.

Safety actions

Whether or not the ATSB identifies safety issues in the course of an investigation, relevant organisations may proactively initiate safety action in order to reduce their safety risk. The ATSB has been advised of the following proactive safety action in response to this occurrence.

Safety action by the first maintainer

In response to the incident, the first maintainer has implemented the following safety action:

• They have conducted an audit of the calculations of engine cycles and engine component total equivalent cycles for the in-service turbine engines they maintain, and any errors were corrected.
• They introduced new procedures for the calculation of engine cycles and engine component total equivalent cycles. The procedures included an independent check of input variables and calculation results. In addition, the maintainer will conduct 6-monthly internal audits of calculations.

Safety action by the operator

In response to this incident, the operator has introduced a flight log for the pilot to record each flight, including whether there was an engine start associated with the flight. The total number of flights and engine starts on the flight log are then used to populate the maintenance release with verifiable accurate information.

Safety action by Honeywell

Honeywell had been analysing engine performance data from aircraft with TPE331 engines in both agricultural spraying and parachuting operations. They found that, while agricultural spraying operations incur damage at a higher rate than the United States Federal Aviation Administration procedure originally used to set the cycle limits of the turbine wheels, parachuting operations incur damage at an even higher rate. Honeywell, working with the Federal Aviation Administration, is in the process of issuing a revised cycle counting methodology that will address the operating characteristics of parachuting and agricultural spray applications.

Sources and submissions

Sources of information

The sources of information during the investigation included the:

• pilot of VH-AAX
• operator of VH-AAX
• maintenance organisations for VH-AAX
• Civil Aviation Safety Authority
• Honeywell International Inc
• United States National Transportation Safety Board.

References

Aerospace Industries Association (2010) AIA Project Report on High Bypass Ratio Turbine Engine Uncontained Rotor Events and Small Fragment Threat Characterization 1969-2006, Volume 1, published January 2010, accessed 11 April 2023. https://www.faa.gov/regulations_policies/rulemaking/committees/documents/media/App%20B%20-%20Vol1%20AIA%20Rotor%20Burst%20Small%20Fragment%20Committeee%20Report%20Fina%20r1%20(2).pdf

Federal Aviation Administration (1997) Design considerations for minimising hazards caused by uncontained turbine engine and auxiliary power unit rotor failure, Document Number: 20-128A (Advisory Circular), published 25 March 1997, accessed 29 March 2023. https://www.faa.gov/documentLibrary/media/Advisory_Circular/AC_20-128A.pdf

Federal Aviation Administration (2006). AD 2006-14-03, Document Number: 06-5929, Published 7 July 2006. Effective 9 August 2006. Accessed 6 January 2023. https://www.federalregister.gov/documents/2006/07/05/06-5929/airworthiness-directives-honeywell-international-inc-tpe331-series-turboprop-and-tse331-3u-model

Honeywell International Inc. (2002) ALERT Category 1: Safety ENGINE – SERVICE LIFE – SERVICE LIFE LIMITS OF CRITICAL LIFE LIMITED COMPONENTS – SPECIAL USE OPERATION – PARTIAL CYCLE COUNTING, Document Number: TPE331-A72-2111 (Service Bulletin), published 12 November 2002.

Submissions

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

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

• pilot and operator of VH-AAX
• maintenance organisations for VH-AAX
• Civil Aviation Safety Authority
• Honeywell International Inc
• United States National Transportation Safety Board.

Submissions were received from Honeywell International Inc. 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.

[1]     At altitudes above 10,000 ft in Australia, an aircraft’s height above mean sea level is referred to as a flight level (FL). FL 150 equates to 15,000 ft.

[2]     Uncontained failure of a turbine engine was any failure that resulted in the escape of turbine rotor fragments from the engine that had sufficient energy to create a hazard. An industry report differentiated between fragments breaching the engine casing and tail-pipe debris (including material passing through the wall of the tailpipe), which was considered lower energy and lesser risk (Aerospace Industries Association 2010).

[3]     Feathering is the rotation of propeller blades to an edge-on angle to the airflow to minimise aircraft drag following an in-flight engine failure or shutdown.

[4]     MAYDAY is an internationally recognised radio call announcing a distress condition where an aircraft or its occupants are being threatened by serious and/or imminent danger and the flight crew require immediate assistance.

[5]     The torsion shaft, which is coupled to the reduction gear section, is positioned concentrically inside the main shaft, which, along with the compressor impellors and turbine wheels, formed the rotating assembly.

[6]     A hot section inspection involves examination of components in the hot section of the engine, which includes the combustion, turbine, and exhaust sections. Typically, the condition of several key engine parts, including the turbine blades, the combustion chamber, the stators, the vane rings, the compressor impellers, and the shroud segments are examined.

[7]     Low-cycle fatigue cracking is associated with relatively high-loads, which produce elastic strain as well as plastic strain during each cycle. This is distinguished from high-cycle fatigue cracking, which is associated with relatively low-loads where the strain resulting from each cycle is primarily elastic. High-cycle fatigue cracking, nominally, requires more than 10⁴ cycles to failure.

[8]     ‘No uncontainment’ is equivalent to stating that the engine failure was contained.

[9]     The turbine wheels are referred to as rotors in AD 2006-14-03 (Federal Aviation Administration 2006).

[10]    In this context, ‘turbine rotor separation’ means the breaking apart, and fragmentation, of a turbine wheel.

[1]      Ground power unit: an external generator that provides power to the aircraft.

[2]      Motoring: rotating an engine (usually gas turbine) by means of its starter for a purpose other than starting.

[3]      Interstage turbine temperature: the temperature of the gases between the high-pressure and the low-pressure turbines.

[4]      The flight attendant later indicated that they knew that 4 chimes was an evacuation signal, but that it did not ‘register’ at the time because bells and chimes are common during flight preparation.

[5]      R1 was an emergency exit. The main door, used for normal boarding and disembarkation, as well as emergencies, was Left 1 (L1).

[6]      Crash alarm: an emergency is declared when an aircraft is experiencing problems and there is a reasonable certainty of a threat to the safety of the aircraft.

[7]      Gas-turbine rpm at which, during start cycle, external cranking (battery or GPU) is no longer needed.

[1]     Visual flight rules (VFR): a set of regulations that permit a pilot to operate an aircraft only in weather conditions generally clear enough to allow the pilot to see where the aircraft is going.

[2]     Eastern Standard Time (EST): Coordinated Universal Time (UTC) + 10 hours.

[3]     Cloud cover: in aviation, cloud cover is reported using words that denote the extent of the cover – ‘scattered’ indicates that cloud is covering between a quarter and a half of the sky, ‘broken’ indicates that more than half to almost all the sky is covered.

[4]     Emergency locator transmitter (ELT): a radio beacon that transmits an emergency signal that may include the position of a crashed aircraft, activated either manually or in the crash.

[5]     Instrument meteorological conditions (IMC): weather conditions that require pilots to fly primarily by reference to instruments, and therefore under Instrument Flight Rules (IFR), rather than by outside visual reference. Typically, this means flying in cloud or limited visibility.

[1]     Piball: an abbreviation of ‘pilot balloon’, which is a small, helium-filled free balloon with a light attached. It is released and visually tracked to determine the wind at different altitudes.

Overview

On 31 March 2022, 2 Airbus Helicopters EC130 T2 helicopters, registered VH-WVV (WVV) and VH-XWD (XWD), and operated by Microflite under the visual flight rules, departed the Batman Park helicopter landing site (HLS), Melbourne, Victoria, for the destination of Ulupna, Victoria. Each helicopter had a pilot and 4 passengers on board. While tracking overhead Mount Disappointment towards Ulupna, the pilots of both helicopters encountered instrument meteorological conditions. The pilot of WVV was in the lead and called for a U-turn and exited from the conditions. The pilot of XWD attempted to follow WVV with a U-turn but entered cloud and lost control of the helicopter, which resulted in a collision with terrain that fatally injured the 5 occupants and destroyed the helicopter.

Positioning flight to Batman Park helicopter landing site

At about 0709 local time, XWD departed Moorabbin Airport for Batman Park HLS about 10 seconds behind another company helicopter, WVV.^[1] Their task was to transport a charter group from the Batman Park HLS in the city, north to Ulupna on the border with New South Wales.

The pilot of WVV later recalled that the weather forecast had been a concern the night before and again on the morning of the accident as the forecast for Melbourne Airport included scattered^[2] cloud at 1,500 ft above the aerodrome from 0700. This was 30 minutes before their scheduled departure time from Batman Park and indicated that they would not be able to transit through the ranges to the north below cloud. The recommended visual flight rules (VFR)^[3] route, for a track north outside controlled airspace, was through Kilmore Gap, which had an elevation of 1,200 ft. The pilot of WVV believed the Melbourne Airport forecast would not allow them to maintain their minimum legal height if they attempted to track via Kilmore Gap below cloud. Therefore, they planned to take a more direct track to their destination, over Mount Disappointment (elevation of 2,605 ft), about 12 NM (22 km) to the east of Kilmore Gap. Figure 1 depicts the key locations.

Figure 1: XWD accident flight and key locations

Note: The 2 purple pins depict the ends of the recommended VFR route.
Source: Google Earth and OzRunways, annotated by the ATSB

The recording from the Appareo^[4] camera fitted onboard XWD showed that, after start at Moorabbin Airport, the pilot erected the main artificial horizon (AH)[5] on the helicopter’s instrument panel but did not turn on and erect the standby AH. Therefore, the standby AH presented the helicopter’s attitude as a 90° roll to the left with a red off flag in the top right corner.

After take-off from Moorabbin, the pilots assessed the weather and observed the forecast cloud was not yet established over the ranges (refer to section titled Meteorological information). Therefore, they considered the route over Mount Disappointment would be suitable for the planned charter flights and continued to Batman Park to collect their passengers. At about 0717, the helicopters landed at Batman Park and were shut down (Figure 2). The pilots then proceeded to the operator’s HLS office to meet their charter group of 8 passengers for their business trip to Ulupna. They escorted the passengers to the helicopters where they were divided into 2 smaller groups of 4 passengers for each helicopter and provided a safety briefing.

Figure 2: XWD (left) and WVV (right) at Batman Park HLS

Source: Operator, through Victoria Police

Departure from Batman Park helicopter landing site

At about 0741, XWD departed from Batman Park 30 seconds behind WVV. The standby AH in XWD remained off and continued to indicate a 90° left roll attitude (Figure 3). Both helicopters were operating VFR outside controlled airspace without a flight plan.[6] The helicopters initially headed east to remain outside controlled airspace before turning north toward Ulupna. As they tracked east and then north, the lower limit of controlled airspace increased,[7] and the helicopters climbed from 1,500 ft above mean sea level to 2,500 ft and then to 3,500 ft. The pilots reportedly discussed the weather over the radio and noted the conditions to the west were consistent with the forecast, but that the conditions to the north had not deteriorated, and they continued to track northbound.

Figure 3: XWD take-off from Batman Park HLS

Source: ATSB (from the Appareo)

While tracking north towards Mount Disappointment, the helicopters climbed above a layer of scattered cloud that the pilot of WVV estimated to have a top of about 2,500-3,000 ft and below a layer of broken cloud with an estimated base of about 4,500 ft. The pilot of WVV later recalled that they could see areas of sunlight striking the ground ahead of them, and therefore considered the weather ahead suitable to climb on top of the scattered layer of cloud, rather than attempt to cross Mount Disappointment underneath the cloud layers.

As they approached Mount Disappointment, XWD was about 1.5 NM (3 km) behind WVV, and the helicopters were cruising at an altitude of about 3,500 ft with a 120 kt ground speed. At this time, the pilot of WVV noted the layer of scattered cloud below them was becoming broken, that the tops were rising, and that the base of the cloud above them appeared to be lowering, resulting in the 2 layers of cloud appearing to converge ahead of them. They tracked around a rising cloud top, that otherwise would have forced them to climb into controlled airspace. Once around that cloud top, the pilot of WVV could still see spots of sunlight striking the ground ahead. Therefore, they were confident to continue.

Mount Disappointment

Before they crossed Mount Disappointment, the pilot of WVV was confronted with a ‘wall of cloud’ in front, and to the left and right of their intended track, and so broadcast to XWD their intention to turn around. The pilot of WVV knew that XWD was nearby and wanted to ensure that the pilot of XWD understood WVV would be making a U-turn. The pilot of WVV reported that the pilot of XWD was initially confused as to why WVV was turning around and might have thought the conditions were suitable to continue. The pilot of WVV then broadcast ‘U-turn, U-turn, U-turn’ to XWD. At 0756:30 (Figure 5), the pilot of WVV conducted a sharp left turn onto a southerly track at 3,635 ft. At that time, XWD was at 3,582 ft, with 100 kt indicated airspeed (KIAS), and a first limit indicator (FLI)[8] power setting of about 5.

At 0756:54, while maintaining 3,600 ft with FLI 5, the Appareo camera recording showed that the cloud through the windscreen of XWD appeared to change from broken to overcast. Over the next 5 seconds, the FLI reduced to 2 and XWD started to descend at about 500 ft/min.[9] The pilot also started actively scanning to the left and above.

At 0757:00, WVV had turned onto a southerly track (186°), climbed to 3,967 ft with a ground speed of 73 kt, and was close to passing abeam XWD, which was at 3,504 ft tracking north (359°), with a ground speed of 116 kt. The pilot and passengers onboard WVV sighted XWD when they passed above and abeam the left-side of XWD. This was the last visual contact with XWD. Figure 4 depicts the meteorological conditions from XWD shortly after the helicopters passed abeam each other at 0757:09.

Figure 4: Footage of weather conditions from XWD at 0757:09

Source: ATSB (from the Appareo)

At 0757:10, XWD briefly rolled left about 30° with a FLI indication of 2, before returning to a level attitude. Three seconds later, the pilot looked across to the right side of the instrument panel. At that time, the helicopter was pitched 10° nose down, wings level, at 70 KIAS and 3,500 ft, and with a FLI indication of 4. The pilot then reached across the instrument panel, grasped the standby AH knob momentarily and then released it, with no change to it indicating a 90° left roll with the off flag still visible in the top right corner.

At 0757:20, at an altitude of about 3,300 ft at 75 KIAS with a FLI indication of 1 and while descending at 1,300 ft/min, XWD rolled left to about 60° angle of bank with the nose pitched 5° down. One second later, the nose down attitude had reached 15°, the airspeed had reduced to about 70 KIAS, and the rate of descent increased to 1,400 ft/min with FLI 1.5. Within 3 seconds, the horizon disappeared off the top right corner of the main AH, such that only ground was visible on the instrument, with a 1,500 ft/min rate of descent and FLI 2.

At 0757:26, the vertical speed indicator reached the full-scale descent deflection of 3,000 ft/min. The main AH still displayed full ground nose down attitude, but the angle of bank had reduced to about 30° left. The airspeed was about 85 KIAS with a FLI indication of 1. The Appareo global positioning system data indicated the helicopter’s rate of descent exceeded 5,000 ft/min from 0757:23 to 0757:28 and peaked at about 5,700 ft/min at 0757:25 (Figure 5.).

At 0757:29, at an altitude of about 2,700 ft, with a low FLI setting and the vertical speed indicator still at full-scale deflection, trees became visible in the cloud. In the last second of footage, the helicopter pitched significantly nose up while the altimeter continued to decrease from 2,700 ft to 2,600 ft. The vertical speed indicator remained at full-scale deflection, the airspeed decayed by 20 KIAS, there was no significant change in the FLI indication, and the LIMIT^[10] caution light activated twice. The Appareo cabin area microphone also detected the rotor overspeed warning activate and the sound of the rotor blades striking the trees. The collision with tree occurred at 0757:31. The flight track for XWD is presented in Figure 5.

Figure 5: XWD flight track and accident site

Source: Google Earth and OzRunways, annotated by the ATSB

After WVV completed the U-turn onto a southerly heading, the pilot found a clearing through the cloud and turned back northbound with a clearance from air traffic control to climb to not above 5,000 ft after reporting they were in instrument meteorological conditions. After a few minutes, the pilot and passengers onboard WVV attempted to contact the pilot and passengers onboard XWD, initially with the helicopter radio, then with their mobile phones, with no success. The pilot then contacted the Microflite operations manager, which started the search and rescue process. WVV diverted to Mangalore Airport and landed without further incident.

The emergency locator transmitter fitted to XWD did not activate after the accident and low cloud in the area initially hampered the search. The wreckage site was located at about midday at an elevation of 2,359 ft (719 m). The 5 occupants were fatally injured and the helicopter was destroyed.

VH-WVV passenger reports

The passenger in the front middle seat had flown regularly with the pilot of WVV and considered the pilot to be very cautious regarding the weather. The passenger recalled that, during the flight, the pilot radioed XWD about the approaching weather. A ‘wispy cloud then went past us, and it felt like a heavy white cloud came down and dumped on us’.

The passenger in the front right seat had flown in helicopters for about 30 years. The passenger recalled that, as they crossed Mount Disappointment, heavy cloud rolled in resulting in ‘a white‑out[11] with ground visibility no longer evident’. The pilot radioed XWD and said words to the effect of ‘U-turn, U-turn, U-turn’. Then the pilot of WVV immediately completed a U-turn. The pilot of XWD radioed back with words to the effect ‘aren’t we going to cut through?’ The passenger then saw XWD pass just below them.

The passenger seated behind the pilot had flown once previously with the pilot of WVV and found them to be very professional and relaxed. During the flight, the passenger was reading emails, but noted as they approached Mount Disappointment that the pilot’s body language had changed, which gave the passenger the feeling that something was not right. The passenger looked outside and saw cloud in front and to the left, and then heard the pilot announce they were going ‘hard left’. When the passenger next looked outside, they ‘could not see anything, it was like a white‑out’. The passenger then felt the helicopter in a hard left turn.

Context

Pilot information

Qualifications and experience

The pilot of VH-XWD (XWD) held a Commercial Pilot Licence (Helicopter) (CPL(H)), issued 22 February 2016, with a single-engine helicopter class rating and a Class 1 Aviation Medical Certificate with an expiry date of 28 February 2023. In addition, the pilot held an aerial application rating and a low-level rating with a sling endorsement. The Civil Aviation Safety Authority (CASA) had no record of the pilot holding a gas turbine endorsement[12] but noted that the pilot had conducted several flight reviews with an authorised instructor in turbine-powered helicopters since being issued with the CPL(H) in 2016.

The pilot was initially employed as a line pilot conducting scenic flights in the Northern Territory from March 2016 until April 2019. The pilot then moved to another employer in south-east Queensland from May 2019 before joining Microflite in December 2019.

The pilot received company approval by Microflite to conduct visual flight rules (VFR) charter operations on 22 December 2019. According to the operator’s records, the pilot had accumulated 3,005.8 flying hours on helicopters, which included 330.6 hours on the EC130, 2,507.3 hours total turbine, and 2,866.8 hours in command. Their records indicated the pilot had no instrument flying,[13] simulated instrument flying or night flying experience.

Since joining Microflite, the pilot had completed operator VFR proficiency checks[14] on 21 December 2019 (EC130), 21 April 2020 (EC120),[15] 14 October 2020 (AS350),[16] 25 May 2021 (EC120), and 31 October 2021 (AS350) to a pass standard with no remedial training required. According to the operator’s training manual, the proficiency checks included ‘flight planning, refuelling, aircraft weight and balance, passenger briefing, forced landings and all emergency operations.’ The instrument flying unit of competency was optional and not tested on any of the checks.

The pilot had completed the following ground school courses with Microflite:

• Microflite fatigue management policy questionnaire – 4 December 2019
• Controlled flight into terrain / Approach and landing accident reduction – 23 December 2019
• Wire and obstacle environment awareness – 10 July 2020
• Drug and alcohol management plan awareness – 12 August 2020
• Human factors training for helicopter flight crew – 5 September 2020
• Dangerous goods by air – 7 January 2022
• Pilot maintenance approval – 23 February 2022.

Flight and duty period limits

According to the Microflite operations manual, the company operated to Civil Aviation Order 48.1 Instrument 2019 (Appendix 4) for their air transport operations, which provided prescriptive flight and duty period limits. A review of the pilot’s flight and duty periods from 1 March 2022 up to, and inclusive of 30 March 2022, found the pilot recorded 169.2 hours of duty with 47.8 flight hours and had 11 rostered days off. In the previous 90 and 365 days, the pilot accumulated 108.5 and 274.5 flight hours respectively. On 30 March 2022, the day prior to the accident, the pilot was on duty from 1030 to 1825 (7.9 hours) and recorded 2.2 flight hours. On the day of the accident, the pilot’s duty started at 0630. There was no evidence to indicate that the pilot had exceeded any of the flight or duty period limits set in appendix 4.

Pilot of VH-WVV

The pilot of VH-WVV (WVV) was issued with a CPL(H) in 2016 and held a low-level rating. At the time of the accident, the pilot had reportedly accumulated about 2,500 hours, which included about 1,500 hours on the EC130, EC120 and AS350 single-engine turbine helicopters. The pilot joined Microflite as a day VFR line pilot in 2019 with about 3 years prior experience of charter operations in Victoria and Queensland and had no instrument or night flying experience. The pilot of WVV reportedly paired with the pilot of XWD about 10 times in the previous 2 years, noting that tasks for 2 helicopters were the exception and single helicopter taskings were the norm.

The chief pilot noted that while the pilot of XWD had slightly more flying hours experience and qualifications than the pilot of WVV, the pilot of WVV started with Microflite before the pilot of XWD. Therefore, the chief pilot considered the 2 pilots to be of equivalent experience for the task and there was no operator appointed hierarchy or ‘lead’.

Helicopter information

General information

The accident helicopter was an Airbus Helicopters EC130 T2 manufactured in France in 2017 and equipped with a Safran Helicopter Engines Arriel 2D turboshaft engine, 3-bladed main rotor and Fenestron^[17] tail rotor (Figure 6). The helicopter was registered VH-XWD in Australia in August 2019 in the night VFR operational category. At the time of the accident, XWD was owned by and registered to Asian Pacific Building Corporation Pty Ltd and operated by Microflite under a cross‑hire agreement. The helicopter was in a 7-seat configuration, with 3 seats in the front row and 4 seats in the rear row. Dual flight controls were fitted. The flight controls operated in the conventional sense with hydraulic assistance. No stability augmentation system or autopilot was fitted (refer to section titled The stabilisation problem).

Figure 6: VH-XWD

Source: Dylan Noveski

Instrumentation

The supporting Manual of Standards for the Civil Aviation Safety Regulations (CASR) Part 133 Air transport operations-rotorcraft stipulated that rotorcraft operating under VFR by day were required to be fitted with the following flight instruments: indicated airspeed, pressure altitude, magnetic heading, time, slip, and outside air temperature. Additional instruments such as attitude and standby attitude (artificial horizon (AH)) were required for night VFR and IFR operations. XWD was approved for night VFR operations.

The instrument panel had a conventional layout with analog flight instruments on the left, a vehicle and engine multi-function display (VEMD) in the middle, and a standby AH on the right. The pilot’s seat was on the left side and the centre console was fitted with a Garmin GTN 750 touch-screen global positioning system, which was used for navigation and communications.

The AHs were electrically powered. The main AH was powered on when the battery was turned on, but the red off flag would not clear until generator power (28 V) was supplied. After power on, the pilot was required to erect the gyro with a cage knob to align it with local gravity. The standby AH had a push-button switch located on the centre console to provide power. The red off flag would not clear unless it was powered on, at which stage the pilot could erect the gyro as per the main AH.

Setting each of the AHs after start for flight was not specifically stated in the checklist. There was a step for: ‘all necessary instruments…on – tested’ after engine start. Therefore, which instruments were set for flight would depend on the specific helicopter configuration, regulatory requirements, and pilot’s requirements for the planned role.

Weight and balance

The helicopter weight and balance were calculated for the accident flight at the time of take-off and at the top of the final descent, and it was determined to be within the published limits. Therefore, helicopter performance was not considered to be a factor in this accident.

Following a request from the ATSB to analyse the development of the nose low attitude in the final turn, Airbus Helicopters conducted an aerodynamic analysis of the helicopter’s response to lateral cyclic input for a 60° angle of bank turn to the left, and provided the following comments:

Emergency locator transmitter

The emergency locator transmitter (ELT) was a KANNAD 406 INTEGRA transmitter, factory fitted to a mounting bracket in the rear baggage bay, left side, aligned with the normal axis. It is set in the ARM position for flight so that the G-switch[20] will provide impact-activation. The G-switch orientation is 45° below the longitudinal axis, so that it will detect a component of longitudinal and normal accelerations. After the G-switch is activated, the ELT will conduct a self-test before the first transmission is made about 65 seconds after activation. If the ELT or its antennae connection are destroyed within the initial 65 second period, no signal will be transmitted. According to Airbus Helicopters, the shock accelerations qualification defined in the regulations (for ELT) are consistent with a survivable impact and typically different than cockpit voice and flight data recorder equipment, which is by design more robust to an impact. There was no ELT activation detected.

Engine overspeed protection

According to Safran Helicopter Engines, a power turbine overspeed[21] may occur if the engine is delivering power and there is a rupture in the power transmission chain at the reduction gearbox, or transmission shaft, or the engine to main gearbox driveshaft. To avoid a power turbine disc bursting from an overspeed condition, the engine incorporates a power turbine blade-shedding system. This is set by the design of the power turbine blades to occur below the disc burst speed with a safety margin. The engine is designed to contain the energy from blade-shedding, but not a disc burst. It is also a certification requirement for aircraft engines to prevent disc burst.

Safran published a service bulletin (SB 292 73 2210), applicable from January 2019, on the subject: Electronic Engine Control Unit (EECU). Modification of software (V603). Application of modification TU 210. The SB applied to the Arriel 2D engine and included the following warning:

The purpose of modification TU 210 was to modify the engine control software to:

• improve detection of a slow decrease in performance of the fuel low pressure pump
• signal a sudden interruption of the fuel supply at engine inlet
• limit damage associated with a power turbine overspeed.

According to the SB, if the engine speed exceeded 120%, the engine control system would send an activation command to the engine stop electro-valve. This would allow engine shut‑down provided the associated Airbus Helicopters hardware SB modification had been incorporated.

On 22 August 2019, the European Union Aviation Safety Agency issued safety information bulletin (SIB) 2019-10 on the subject: Power turbine over-speed protection on Arriel 2D engines. The SIB explained that the extra thermal energy released from the engine during blade-shedding was a potential source of ignition for a post-impact fire. While the ignition source for post-impact fires was not always determined, the introduction of an electronic overspeed protection (TU 210) aimed to limit blade-shedding and reduce the potential for post-impact fire.

At the time of the release of the SIB, the concern was not considered to warrant airworthiness directive action.[22] However, the SIB recommended operators incorporate the engine and helicopter modifications into their affected helicopters.

A review of the maintenance records for XWD revealed the EECU was manufactured, and software downloaded in May 2016. The EECU was installed in August 2016 and the records indicated there had been no modifications incorporated since manufacture. On review, Safran confirmed the TU 210 modification was not embodied in the accident EECU.

The operator reported that they had complied with the relevant SBs from Safran and Airbus Helicopters. The operator’s helicopters with a build date prior to 2019 received the EECU software update in May 2019 when a Safran technician attended their facility (the hardware and training required to comply with the SB was not available in Australia prior to the date of the accident). XWD was assembled in September 2019 and therefore not available for that modification at the time of the Safran visit but was scheduled for a later update within the compliance period for the Safran and Airbus SBs. Their helicopters with a build date from 2021 received the update in the factory.

Wreckage and impact information

Accident site

The ATSB’s site survey established that XWD had impacted a large old growth tree, which broke the upper tree trunk and significantly disrupted the cabin. Cabin debris, including the overhead panel with the rotor-brake handle, was littered around the base of this tree. The helicopter then descended at an angle of about 45° on a southerly trajectory to the ground. Figure 7 and Figure 8 depict the old growth tree break from overhead the main wreckage site.

Figure 7: Overhead view of old growth tree break and main wreckage site

Source: ATSB

Figure 8: View to the north of old growth tree break from overhead the main wreckage site

Source: ATSB

The vegetation surrounding the accident site comprised of 2 distinct levels of growth. A new growth canopy with a height of about 24 m, and old growth trees with a height of about 70 m, as measured by a remotely piloted aircraft system. The elevation of the base of the old growth tree was 718 m, which indicated that the elevation of the top of the tree was about 788 m. The tree break was 41 m above ground level at an elevation of 759 m. Therefore, the tree impact very likely occurred at an altitude of 2,490–2,585 ft (759–788 m).

General crash survival requirements include maintaining a liveable volume, keeping occupants restrained and the impact loads within human tolerance, and providing the means and time to escape (Fox, 1989). Given the breakup of the cabin on impact with the old growth tree and associated height above ground level, this was not considered to be a survivable accident.

Wreckage examination

The helicopter was subject to a post-impact fire, resulting in the destruction of some components. However, from the components available there was no evidence of any pre-existing defect that would have prevented normal operation.

The engine had disconnected from both the main rotor and Fenestron driveshafts. The Fenestron driveshaft exhibited significant scoring damage, which indicated it was rotating at high speed during the accident sequence. Damage to the leading edges of the engine compressor blades was also characteristic of high-speed rotation (Figure 9) and the power turbine exhibited blade shedding. The rupture of the engine to main gearbox transmission drive shaft and flexible coupling,^[23] with its screws sheared on the main gearbox side, was consistent with a sudden over‑torque. Overall, the damage observed indicated that the engine was producing power at the time of impact.

Figure 9: Damage to engine compressor blades

Source: ATSB

The centre console push-button switch for the standby AH was found in the off position (push‑button out). The other push-button switches on the same row as the standby AH were in the correct position for flight – off (out) for the fuel pump (the electric fuel pump is a booster pump for engine start and is switched off after start), off for the dome light, and on (in) for the avionics.

The ATSB retrieved the pilot’s electronic flight bag (iPad), an Appareo cabin-mounted camera, the vehicle and engine multi-function display (VEMD), a Garmin GTN 750 global positioning system, the EECU, and the central warning panel for further analysis. The engine data recorder was not able to be recovered due to fire damage.

Recorded information

The pilot’s iPad, Appareo camera and VEMD were successfully downloaded by the ATSB. The pilot’s iPad contained 1-second flightpath data and the Appareo memory included the positioning flight to the Batman Park HLS, the accident flight, and some footage of flights on the previous day. There were 2 audio channels on the Appareo for the intercom system and cabin area microphone. However, only the cabin area microphone successfully recorded.

A review of the available logs on the VEMD indicated there were no faults, failures or limits reached until the beginning of the impact sequence when a high rotor speed value of 410 rotor revolutions per minute was recorded, which was consistent with the Appareo download. The EECU and Garmin GTN750 global positioning system were not attempted to be downloaded due to significant fire damage and it was considered unlikely that they would have provided additional information. The central warning panel did not contain a memory module and did not provide any evidential data.

Medical and pathological information

A full post-mortem examination of the pilot was conducted. No soot was found in the airways and the cause of death was recorded as ‘Multiple injuries sustained in a helicopter incident (pilot)’. Further, the pilot’s toxicological results did not identify any substances that could have impaired their performance.

An external examination with computed tomography scan was performed on the passengers. The post-mortem reports for the passengers stated, ‘A reasonable cause of death would appear to be: Multiple injuries and effects of fire sustained in a helicopter incident (passenger)’. However, the forensic pathologist assisting the Victorian Coroner confirmed to the ATSB that the pilot’s cause of death, which did not include the effects of fire, was the most reliable indicator for all the occupants.

Meteorological information

Graphical area forecast

According to the Bureau of Meteorology, the graphical area forecast (GAF) is designed primarily to meet the needs of pilots flying in the airspace between the surface and 10,000 ft above mean sea level (AMSL). They provide information on weather, cloud, visibility, icing, turbulence, and freezing level in a graphical layout with supporting text.

The GAF for Victoria, current at the time of the departure from the Batman Park HLS, was issued at 0321 on the morning of 31 March 2022 and was valid from 0400-1000. The GAF divided the state into 4 areas, identified as A, B, C and D, with sub-divisions in areas A, B and C, separated by green scalloped lines (Figure 10). The flight was planned to start in area C2, transit area C1 (including Mount Disappointment), A1 and end in area A. The destination of Ulupna is located 8 NM (15 km) west of Tocumwal (YTOC in Figure 10).

Figure 10: GAF with direct track from Melbourne to Ulupna west of Tocumwal (YTOC)

Source: Bureau of Meteorology, annotated by ATSB

For the flight route, from departure to the planned destination, the GAF specifically stated that:

• All of area C was forecast to have a broken layer of stratus cloud from 2,000-3,000 ft and a broken layer of cumulus/stratocumulus cloud from 3,000-8,000 ft with visibility greater than 10 km. In addition, area C included scattered showers of rain with cloud tops up to 10,000 ft.
• Kilmore Gap, identified as a critical location on the GAF, was in area C1. The cloud forecast for Kilmore Gap was for a broken layer of cumulus/stratocumulus at 3,000 ft with TEMPO (temporary) conditions from 0600-1000 for a broken layer of stratus at 1,200 ft with the note ‘CLD ON GND’ [cloud on the ground].
•  Area A was forecast to have few cumulus/stratocumulus cloud from 3,000-5,000 ft.

The grid point wind and temperature forecast, valid from 0500, indicated the wind was 13 kt from 180° at 2,000 ft and 32 kt from 140° at 5,000 ft.

Melbourne Airport forecast

Melbourne Airport was north of the departure point and nearby the intended route (Figure 10). It has an elevation of 434 ft, and as an international airport, it provides a 24-hour aerodrome forecast. An aerodrome forecast is valid for a radius of 5 NM (9 km) from the aerodrome reference point. It includes cloud bases, visibility, weather, and surface wind. However, it does not include the height of cloud tops.

The forecast valid for the departure of the accident flight included wind from 180º at 10 kt, visibility greater than 10 km, light showers of rain, scattered cloud with a base of 1,500 ft above the aerodrome and broken cloud with a base of 2,500 ft. The forecast scattered cloud base of 1,500 ft above the aerodrome was 1,934 ft AMSL. This was consistent with the 2,000 ft cloud base on the GAF. The forecast for broken cloud at 2,500 ft above the aerodrome (2,934 ft AMSL) was consistent with the 3,000 ft cloud base on the GAF.

Kilmore Gap weather station and camera

The Bureau of Meteorology Kilmore Gap weather station and web camera was located 19 km west-north-west of the accident site (Figure 11). At 0750, 8 minutes prior to the accident, the camera depicted cloud overhead Mount Disappointment (Figure 12). Shortly after the accident, at 0800 and 0810, the camera showed extensive development of low cloud in the area (Figure 13 and Figure 14).

Figure 11: Kilmore Gap webcam view looking east on 3 May 2022

Source: Bureau of Meteorology, annotated by the ATSB

Figure 12: View towards Mount Disappointment at 0750 (8 minutes before the accident)

Source: Bureau of Meteorology, annotated by the ATSB

Figure 13: View towards Mount Disappointment at 0800 (2 minutes after the accident)

Source: Bureau of Meteorology, annotated by the ATSB

Figure 14: View towards Mount Disappointment at 0810 (12 minutes after the accident)

Source: Bureau of Meteorology, annotated by the ATSB

The weather station recorded a relative humidity of 93-95% from 0730-0830. From 0730 until 0741, the time the accident flight departed the Batman Park HLS, the lowest cloud at Kilmore Gap was 590 ft above ground level and the coverage was fluctuating between scattered and broken. At about 0758, the temperature and dewpoint were 9.7 °C and 8.9 °C respectively, and the wind was 17 kt from 171°. There was few cloud at 394 ft and broken cloud at 3,510 ft above ground level. At about 0811, 13 minutes after the accident, the cloud became broken at 394 ft and 3,510 ft. The cloud conditions continued to deteriorate through to 0830, at which time the cloud was broken at 295 ft.

Accessing weather forecasts

The National Aeronautical Information Processing System (NAIPS) is a multi-function, computerised, aeronautical information system that allows users, such as pilots, to obtain weather information and submit flight plans into the air traffic system. The pilots of XWD and WVV were using a NAIPS mobile app developed by OzRunways.[24] This app included a location briefing, area briefing and a chart selection icon. According to the app developer, only the first person to request a specific chart via the chart icon (such as the GAF) will be recorded by the NAIPS system as the requestor. The chart is then saved to cache memory on their server and all subsequent requests to view that chart via the app chart icon will result in retrieval of the chart from their server, rather than the NAIPS server. Therefore, while the submission of a location and/or area briefing request would be recorded on the NAIPS system, the selection of an area forecast via the chart icon would not necessarily be recorded on NAIPS.

Interpretation of the forecast

The pilot of WVV reported that the weather was a concern both the night before and in the morning. From the Melbourne Airport forecast, there was scattered cloud at 1,500 ft at 0700. As they were scheduled to depart 30 minutes after that, they were concerned that the weather was ‘already going to be established’ and they would not be able to get over the range. They elected to assess the actual conditions on their way to the Batman Park HLS.

The pilot further stated that the flight was planned as a VFR flight outside controlled airspace, which did not require a flight plan, and none was submitted. Consequently, they intended to remain below the controlled airspace steps that surrounded Melbourne Airport on their route from the HLS to Ulupna. The pilot of WVV also indicated that they were concerned about the cloud height above ground level at Kilmore Gap, where the terrain is at 1,200 ft AMSL. The forecast cloud at 1,500 ft indicated to the pilot that they would not be able to transit Kilmore Gap at their minimum height above ground of 500 ft.

Operational information

Visual meteorological conditions

Visual meteorological conditions (VMC) are expressed in terms of flight visibility and distance from cloud (horizontal and vertical) and are prescribed in the Civil Aviation Safety Regulations (CASR) Part 91 (General Operating and Flight Rules) Manual of Standards 2020: 2.07 VMC criteria. In addition to visibility and distance from cloud, VMC may also be subject to operational requirements. There are a variety of criteria for the different altitudes and airspace that a VFR flight is operating in.

For aircraft operating below 10,000 ft in class G airspace (uncontrolled airspace), the VMC criteria were a minimum flight visibility of 5,000 m, horizontal distance from cloud of 1,500 m and vertical distance from cloud of 1,000 ft. For aircraft operating in class G airspace below 3,000 ft AMSL, or 1,000 ft above ground level, whichever is higher, the distance from cloud is reduced to ‘clear of cloud’, provided the aircraft is operated in sight of ground or water. For a helicopter operating below 700 ft above ground level, the visibility can be reduced to 800 m.

A VFR flight can be conducted above cloud provided VMC can be maintained for the entire flight, including climb, cruise, and descent.[25] The CASA Visual Flight Rules Guide included the following note for VFR flight above cloud:

The accident flight was conducted in class G airspace and climbed to about 3,500 ft AMSL, which was above 1,000 ft above ground level, before reaching Mount Disappointment. Therefore, while the minimum visibility remained at 5,000 m, the distance from cloud increased from ‘clear of cloud’ while they were below 3,000 ft and in sight of the ground, to 1,000 ft vertical and 1,500 m horizontal distance as soon as they climbed above 3,000 ft. Figure 15 provides a visual depiction of the VMC criteria below 10,000 ft (excludes helicopter VMC below 700 ft) from the CASA Visual Flight Rules Guide.

Figure 15: VMC criteria below 10,000 ft

Source: Civil Aviation Safety Authority

Flight planning

Regulatory requirements

According to CASR Part 91 (General Operating and Flight Rules) Manual of Standards 2020: 7.02 Forecasts for flight planning, an authorised weather forecast must cover the whole period of the flight, and include a wind and temperature forecast and, for a flight at or below 10,000 ft AMSL, a GAF or general aviation meteorological^[26] area forecast. In addition, CASR Part 133 Air transport operations-rotorcraft, subpart 133.130: Flight preparation requirements, stated:

Microflite requirements

The Microflite operations manual section 2B1.1: Planning and briefing materials, detailed the pre‑flight requirements for a pilot in command, which included the following:

Section 2B1.7: Minimum safe altitudes / lowest safe altitude (LSALT), provided the following advice for their day VFR pilots:

Section 2C3.3 Diversions due weather, provided the following guidance for handling deteriorating weather in-flight:

Chief pilot’s expectation

The chief pilot reported that the pilots had a company issued iPad (electronic flight bag) that provided them with up‑to‑date access to the booking information on the company calendar. In addition, they were issued with a credit card, which could be used to purchase their flight planning apps subscriptions. The chief pilot provided the following explanation for the flight planning sequence:

The chief pilot acknowledged the client on board WVV was an important client, being a regular client, but that this should not have changed the conduct of the flight. The chief pilot also recognised that perceived pressure to deliver for a client was normal within the industry and it was not limited to charter, it could also occur in aerial work operations. However, from a company management perspective, they attempted to provide support for their pilots by not applying pressure to conduct a flight, using client services staff to liaise with clients, and organising alternate transport (road vehicles) for clients if a flight cannot proceed or a pilot decides their planned destination cannot be reached. The chief pilot had not flown with the client for the accident charter group, and therefore did not know the client as well as the pilot of WVV. From their own interactions with the client, they did not believe they would have pressured the pilots to proceed on the accident flight.

Accident pilot

The accident pilot accessed NAIPS on 30 March 2022 (the day prior to the accident flight) at 1506,[28] via the OzRunways app and requested meteorological and notice to airmen[29] information for Melbourne Airport. At this time, the pilot was at Warragul, from where a return flight was conducted to Moorabbin Airport via Lancefield and the Batman Park HLS. The request was limited to a location briefing for Melbourne Airport and did not include an area briefing (GAF) request. This was the only request recorded on NAIPS for the 24 hours prior to the accident.

The pilot did not submit any NAIPS location requests on 31 March 2022. Examination of the pilot’s iPad found that the OzRunways and WillyWeather^[30] apps were running at the time of the accident. The pilot accessed the WillyWeather app at 0633 and it continued to run. The WillyWeather app support reported that they did not offer any features specific to aviation, but did offer most of the data required, such as cloud cover, wind, temperature, and predicted rainfall. When selecting a location, the app also provided a link to the nearest weather radar station feed.

In the week prior to the accident, the pilot submitted a location briefing request for Melbourne Airport at 2212:46 on 24 March 2022. The following day, the pilot conducted a passenger transport return flight in XWD between Moorabbin Airport and the Cathedral Lodge Golf Course, which is about 55 NM (102 km) north-east of Moorabbin and 32 NM (59 km) east-north-east of the accident site, on the north side of the ranges. The outbound flight was 0836-0910 and the return flight was 1612-1650. There was no record of a briefing request submitted either on the morning prior to departure, or in the afternoon prior to the return flight. However, as described earlier, it was possible the pilot viewed a GAF chart without it being recorded by the NAIPS system.

Pilot of VH-WVV

According to the pilot of WVV, the 2 pilots accessed the weather information independently on 30 and 31 March 2022, but then discussed it together. The pilot of WVV accessed NAIPS via OzRunways on 30 March 2022, the day before the accident, to submit a meteorological and notice to airmen request for the locations Moorabbin, Essendon, Melbourne, Avalon, and Coldstream. This occurred at 1103, 1111, 1118 and 1124, and they departed from Moorabbin Airport at about 1219 to collect their charter group from the Batman Park HLS. The same request was made at 1242 before departure from Batman Park, at 1506 before departure from Warragul, at 1602 and 1618 before departure from Lancefield, at 1751 before departure from Batman Park for the return flight to Moorabbin, and at 1950 after arrival.

On the morning of the accident, the pilot resubmitted the request for the locations Moorabbin, Essendon, Melbourne, Avalon, and Coldstream at 0545, 0559 and 0628. At interview, the pilot reported that they would have checked the GAF but not the grid-point wind and temperature chart, and demonstrated to the ATSB how they used their NAIPS app to check the current GAF.

The pilot stated that the Melbourne Airport forecast would be consulted the evening before a client services flight as it provided a 24-hour forecast, and therefore, provided an indicator of the potential conditions for the next day. Normally, the company operations staff would consult one of the pilots at about 1630 to check on the likelihood of weather cancellations the following day. If the weather looked unsuitable, then client services would contact the client and confirm if they wished to hold their booking, noting the risk that it could be cancelled, or arrange alternative transportation.

The pilot reported that the client on the day of the accident had never pressured them to conduct a flight in marginal weather and that there were numerous occasions when a service was cancelled due to weather. The pilot could not provide a specific example of a weather cancellation, but explained that, due to the elevation of Melbourne and the built-up area, they would cancel a client pick-up from the city [Batman Park HLS] if the cloud was forecast to be below 1,400 ft AMSL or there was reduced visibility, and that ‘it happens a lot’.

Former company pilot

The ATSB spoke to a former Microflite pilot during the investigation. This pilot provided similar information to that provided by the pilot of WVV and the company’s chief pilot. They reported that for flight planning, they would look at the Melbourne Airport forecast the night before to get an indication of the weather for the Melbourne Basin[31] the next day. The company operations staff might ask a pilot at the close of business if the weather was going to be acceptable the next day for client liaison purposes. For operations around the basin, the pilot would use the location forecasts and weather radar, but if they planned to fly over the ranges, then they would ‘get everything’ including location forecasts either side of the ranges, the GAF, grid point wind and temperature chart, and check the web cameras.

The pilot reported that, if conditions were marginal or even instrument meteorological conditions (IMC),[32] then pilots might take-off if the weather at Mangalore was clear. There were several areas that they would go to assess the actual weather and if it was possible to pass through the ranges, which included Kilmore Gap to the north.

The pilot confirmed that the company would stand between their pilots and the clients if required, provided they were aware of marginal weather the evening prior to the service. They reported that the company has clients whose businesses could be negatively impacted if they missed a meeting due to a flight cancellation, which is why the operations staff proactively checked the risk of a weather cancellation. The pilot was able to recall an instance of rejecting a task due to weather while working for the operator.

Weather cancellations

The operator provided a copy of their flight cancellation records for the period 1 January 2021 to 31 March 2022. There were 895 cancellations recorded and they reported that 1,917 flights were conducted. This indicated that 32% of their planned flights were cancelled during this period. Of these flights, 331 (37%) were cancelled for COVID-related reasons. A total of 145 flights (119 charter flights) were cancelled due to weather-related reasons, which was about 16% of all cancellations and 5% of the planned flights. However, it was noted that 20% of the cancellations did not have a code, and therefore, it was possible that the actual percentage of weather-related cancellations was higher than recorded.

Organisational information

Microflite

The operator, Microflite Pty Ltd, trading as Microflite Helicopter Services, was founded in 2000 and purchased by the current owners in 2004, with company headquarters at Moorabbin Airport. The company structure included a Chief Executive Officer, Executive General Manager, Head of Flying Operations (chief pilot), Head of Operations (chief flying instructor) and Head of Aircraft Airworthiness and Maintenance Control. They conducted flight training, passenger transport (charter), special aerial work operations and commercial freight operations with their fleet of 18 single and twin-engine turbine helicopters. Their operations included day and night VFR (including aided night VFR with night vision imaging system), and IFR. They were also an approved maintenance organisation.

Safety risk management

Microflite was re-issued with their Air Operator’s Certificate, that included charter operations, on 25 May 2020 with an expiry date of 31 May 2022. With the transition from Civil Aviation Regulations to the Civil Aviation Safety Regulations (CASR), helicopter charter operations became CASR Part 133­–Australian air transport operations–rotorcraft, on 2 December 2021. While the Part 133 regulations did not require an operator to have a safety management system at the time of the accident, the Microflite manual suite included an Integrated Management System Manual, which contained the elements of safety and quality management. This included a section on risk management with the following introduction:

Risk management of adverse weather

On 1 September 2015, Microflite raised a risk assessment for air transport operations - Risks associated with general charter operations from Company known and frequently used locations. The risk assessment included the following weather threat:

The initial risk assessment, without controls, was assessed as ‘high’ risk. According to their manual, this level of risk was unacceptable and required a treatment plan to reduce it to at least a tolerable level (medium risk). It was treated with the following controls:

The controls were assessed as ‘effective’ and ‘fully implemented’, which reduced the likelihood of the risk to ‘rare’, thereby lowering the risk from ‘high’ to ‘low’. The result was an acceptable level of risk that required no further action from the management team. The consequence for this risk was ‘catastrophic’, which was consistent with a loss of VMC accident for a VFR pilot. However, the definition for ‘unlikely’ (one level above ‘rare’) included that it ‘has happened before in the industry’. Use of ‘unlikely’ would have elevated the risk from ‘low’ to ‘medium’ but would not have required any further action as the risk was assessed as low as reasonably practicable.

The ATSB found that the operator’s pilots were issued with iPads and each had a budget to purchase the flight planning app of their choice. In addition, the ATSB received evidence that flights were routinely cancelled due to weather and an instance when their helicopters could not proceed due to weather, landed out-field, and ground transport was arranged for their clients. This was consistent with their documented risk controls.

Their risk of ‘loss of VMC’ was managed by cancelling operations. While the controls did not refer to how this would be managed in-flight, the company had published several procedures in their manual suite relevant to this risk. They included controls that could mitigate the risk of ‘loss of VMC’ through prevention and recovery, such as section 2B1.7 Minimum Safe Altitudes / Lowest Safe Altitude (LSALT), section 2C3.3 Diversions due weather, and in their training and checking manual Inadvertent Entry into IMC Recovery Training:

The accident pilot and pilot of WVV had not conducted the Inadvertent Entry into IMC Recovery Training. In addition, the lowest safe altitude instructions for day VFR flights were published as a ‘should’ rather than a ‘shall’, indicating that it was not mandatory.

The Microflite operations manual volume 2C5: Adverse weather operations, did not include any reduced VMC operating procedures or inadvertent IMC recovery procedures. The company did have a procedure for inadvertent IMC under volume 2D1.18: Formation flying. The goal of this procedure was to ensure safe separation of the formation aircraft after an inadvertent IMC entry and was therefore not applicable as a risk control for their day VFR charter pilots.

Assessing pre-flight risk

The risk assessment performed at an operator’s management level is by design a high-level assessment that does not necessarily capture the circumstances for each particular flight. In a multi-crew airline environment, there are multiple checks in the system and the junior flight crewmembers will spend years learning decision-making from senior flight crewmembers before they progress to the role of pilot in command. This system of learning and oversight is generally not available in the single-pilot sector by the nature of the task. Consequently, there has been a growing adoption of easy-to-use pre-flight risk assessment tools, which can help inform pilots of the cumulative level of risk to their operation at the planning stage and can be employed in the commercial sector to escalate decision-making to management for oversight. In 2014, this was introduced by the United States Federal Aviation Administration (FAA) into their helicopter air ambulance regulations under Code of Federal Regulations 135.617: Pre-flight risk assessment. Later, in 2016, the FAA Safety Team released their flight risk assessment tool, based on scoring predefined criteria, with the introduction:

Civil Aviation Safety Authority requirements

The ATSB reviewed the CASR Part 133 and the corresponding Manual of Standards to determine the regulatory expectation on operators for managing the risk of VFR into IMC and any subsequent loss of control or controlled flight into terrain. While the ATSB was unable to identify any CASR Part 133 specific requirements for managing the risk of VFR into IMC that were additional to what would already be expected for all pilots under CASR Part 91, including private/pleasure flights, it was noted that CASA can stipulate additional conditions to manage specific risks through the safety regulations and standards. For example:

• CASR Part 133 required operators to include risk assessments in their expositions, for CASA approval, for any planned performance class 2 with exposure operation (a Category A rotorcraft flight where failure of an engine or system does not permit continued safe flight and does not ensure a forced landing into a suitable forced landing area).
• To reduce the risk of controlled flight into terrain, larger rotorcraft being operated on passenger or medical transport flights under IFR were required to be fitted with a terrain awareness and warning system.
• CASR Part 135 (air transport operations – smaller aeroplanes) operators were required to include procedures for low-visibility operations and stabilised approach criteria in their exposition to mitigate the risk of approach and landing accidents.

Civil Aviation Safety Authority oversight

In 2023, the ATSB requested a copy of the last 5 CASA surveillance activities of Microflite, which included a:

• September 2022 surveillance report for passenger and cargo air transport operations in single‑engine helicopters
• 29-30 March 2022 surveillance report for flight training operations
• November 2018 surveillance report for passenger handling at the Batman Park HLS
• March 2018 surveillance report for low flying operations
• 2017 investigation report for an alleged breach of low flying at a sport event.

There were no reports of ramp checks provided, which would have captured flight planning activities.

The November 2018 surveillance of passenger handling started as an unannounced event and the CASA inspector reported that all flying was initially cancelled due to the weather in the morning. When flying commenced, the inspector noted the operator maintained positive control of the passengers and positive separation between the helicopters. There was only one safety finding from the 4 surveillance reports, which was for training records. The September 2022 surveillance activity was a follow-up to this accident to determine if any changes had been made. The inspector recorded that the operator reported an increased focus on instrument flying during training and proficiency checks, and the implementation of a flight risk assessment tool.
 

Basic instrument flying standards

Microflite pilot proficiency checks

Proficiency checks are intended to assess a pilot’s flying skills and operational knowledge in carrying out normal, abnormal, and emergency procedures. This ensures the pilot is competent to conduct the flights the operator has assigned that pilot. According to the chief pilot, the accident pilot’s initial check to line as a charter pilot would have covered general handling, and emergency procedures for flying around Melbourne, Yarra Valley, and coastal scenic routes. The chief pilot reported that instrument flying would only be conducted during proficiency checks for night and instrument rated pilots, and that for their day VFR pilots, the flight review could be completed without an instrument flying component.

According to the pilot of WVV, the operator’s proficiency checks included a ground theory component, and they were required to obtain a detailed weather briefing, including location forecasts, GAF and grid-point wind and temperature forecasts. They were then checked to ensure they understood all the information they were presented with. The pilot of WVV and a former Microflite pilot both reported that they were never trained or checked for instrument flying because it was not a requirement.

The chief pilot reported that when the accident pilot’s aerial application rating for fire-fighting training was done in October 2021, they would have conducted training in the hills around Melbourne. This would have included dealing with mountain flying in adverse weather conditions. The chief pilot could not confirm if any specific exit manoeuvres for adverse weather were included and reported that they had discussions about the subject previously within the company but could not provide a specific procedure for all situations that might be encountered. They did not believe there was any ‘one-size-fits-all’ rule being taught by their instructor staff and that it was a matter of their pilots adapting to the circumstances and ensuring they always have an exit route.

International Civil Aviation Organization

The International Civil Aviation Organization’s (ICAO) Annex 1: Personnel Licensing foreword stated:

Section 2.4 described the general requirements for the issue of a commercial pilot licence. Under the specific requirements for the helicopter category, section 2.4.4.1.1.1 (c) stated the applicant shall have completed, in helicopters, not less than 10 hours of instrument instruction time of which not more than 5 hours may be instrument ground time. Section 2.4.4.2 stated the instructor shall ensure that the applicant has operational experience in at least the following areas to the level of performance required for the commercial pilot: (i) basic flight manoeuvres and recovery from unusual attitudes by reference solely to basic flight instruments.

ICAO Annex 6 Part III – International Operations – Helicopters (July 2016), section 7.4.3 Pilot proficiency checks stated:

Civil Aviation Safety Authority

Integrated and non-integrated training programs

There were two types of commercial pilot licence training courses:

• intensive integrated courses, through Part 142 flight training operators
• non-integrated courses, through Part 141 flight training operators.

The Integrated training meant an intensive course of training:

According to CASR Part 61(Flight crew licensing), instrument flying training is a requirement for a CPL(H) under an integrated training program. The aeronautical experience required under Part 61.595 (Aeronautical experience requirements for grant of commercial pilot licences—helicopter category) was 10 hours instrument time with a minimum of 5 hours instrument flight time in a helicopter. The instrument flight time included full panel (IFF)[33] and limited panel (IFL).[34] Both IFF and IFL included basic instrument flight manoeuvres and recovery from unusual attitudes and inadvertent IMC (IIMC). However, under a non‑integrated training program for a CPL(H), there was no instrument flying training required. Both IFF and IFL were required for an aeroplane CPL. In addition to recovering from unusual attitudes and IIMC, on 21 November 2023, in response to the draft report, CASA reported:

The pilot’s CPL(H) flight test report recorded the IFF and IFL units of competency as ‘not tested’ and CASA confirmed the flight test form indicated it was a non‑integrated training program. The pilot of WVV stated that they did not do any instrument flying training as it was not required for their licence. Another former Microflite pilot also reported that they did not do any instrument flying training, but that they were advised to complete the instrument rating theory examination after completing their CPL(H) training in case they ever had ambition to work in the offshore helicopter industry. That pilot completed their theory examination but no instrument flying.

Flight review[35]

The Part 61 Manual of Standards single-engine helicopter flight review competency standards indicated instrument flying was ‘optional’. In comparison, the flight review competency standards for single and multi-engine aeroplane, and multi-engine helicopter, all required basic instrument flying sequences. However, under CASR Part 133 Air transport operations-rotorcraft, subpart 133.370: Composition, number, qualifications and training, it stated the following:

In addition, according to CASR Part 133.370(4), the Part 133 standards may prescribe requirements related to training and checking that must be completed by a flight crew member for a flight. However, the Part 133 standards Chapter 12 – Flight crew member training and checking, did not require an operator’s proficiency check of a day VFR pilot to include any instrument flight or IIMC recovery exercises.

History of the integrated and non-integrated syllabi

With the commencement of CASR Part 61 – Flight Crew Licensing in 2014, CASA introduced a requirement for applicants of a CPL with a helicopter category rating, to complete flight training and basic instrument flight, to comply with the standards specified by ICAO Annex 1: Personnel licensing.

To give industry time to develop the capability to conduct such training, transitional regulation CASR 202.277B provided relief from the new requirements by continuing to recognise the previous requirements for the grant of a CPL(H) as specified under Civil Aviation Regulation 5.127. This did not require instrument flying training until 31 August 2017. A subsequent amendment to the CASR in 2017 extended the time for transition until the end of August 2018. The accident pilot’s training was completed prior to the end of this transition period.

Prior to the end of the transitional period, CASA undertook a review of the instrument flight time experience requirements, which resulted in an amendment to CASR Part 61 in 2018. The amendment to CASR 61.615 continued the previous requirements specified for the grant of a CPL(H). An explanation of that amendment was included in the Explanatory Statement associated with that amendment: Civil Aviation Safety Amendment (Flight Crew Licensing Measures No. 1) Regulations 2018 (legislation.gov.au)

The review undertaken by CASA included a survey of the helicopter industry. The Explanatory Statement rationale for making the instrument flight time experience requirements optional for a non-integrated training course was in response to the survey results and as follows:

ATSB review of CASA industry survey

The ATSB requested a copy of the 2018 helicopter industry survey responses and noted that 87% (55/63) of respondents opposed basic instrument flying training when asked about the introduction of this for ICAO compliance purposes. The reasons provided included the rationales listed in the following Table 1.

Table 1: Rationales for opposing basic instrument flying training

Several respondents indicated that they did not believe CASA had made a safety case for the introduction of this requirement. Some supporters and opponents indicated that 2-3 hours of flying training to teach recovery from unusual attitudes should be sufficient. One opponent indicated that if the requirement was to teach recovery from unusual attitudes on instruments, instead of compliance with ICAO licencing requirements, they might have supported the proposal. One supporter of the requirement indicated that as the rules allow helicopter flight in visibility reduced to 800 m, some basic instrument flying skills are required.

In consideration of the industry objections published by CASA in their Explanatory Statement:

• The ATSB reviewed a manufacturer’s website for one of the most popular piston-engine training helicopters and noted they were offered for sale without an attitude indicator in their most basic configuration. This was consistent with 25% of respondents reporting that a lot of training helicopters in use at the flying schools were not fitted with the minimum instruments required to teach instrument flying.
• While 5% of respondents indicated there were insufficient instructional staff qualified to teach instrument flying, a 4-year transition period was provided to upgrade instructional staff.
• Throughout the course of this investigation, the ATSB found no research to demonstrate a link between basic instrument flying training and overconfidence resulting in VFR into IMC accidents.

Foreign jurisdictions  

United States

The US Code of Federal Regulations, Part 61.129 prescribed the aeronautical experience required for a CPL. The instrument flying required for the helicopter rating under Part 61.129 (c)(3)(i) stated:

Commercial helicopter pilots, employed for commuter and on demand operations (CASR Part 133 equivalent), operate under Part 135. Subpart 135.293 initial and recurrent pilot testing requirements stated:

European Union and United Kingdom Civil Aviation Authority

The European Union Aviation Safety Agency and United Kingdom Civil Aviation Authority content for their skill test for the issue of a CPL(H) included instrument flying training. Their recurrent training and checking syllabus for operator proficiency checks in accordance with the Organisational Requirements for Air Operations – Flight Crew – ORO.FC.230 (b) Operator proficiency check, included ‘(1) Each flight crew member shall complete operator proficiency checks as part of the normal crew complement to demonstrate competence in carrying out normal, abnormal and emergency procedures.’ Their acceptable means of compliance (AMC1 ORO.FC.230) included (1) recovery from unusual attitudes, and (2) IMC autorotation[37] techniques.

Canada

The Transport Canada aviation regulations flight test requirements for issuing a CPL(H) (Schedule 6 of Standard 428) included instrument flying in the airwork section of the syllabus and minimum safe altitude operations in the navigation section. In addition, air taxi (Standard 723.28) and commuter (Standard 724.24) (CASR Part 133 equivalent) helicopter pilots who operated to the reduced VFR visibility limits in uncontrolled airspace were to receive initial and annual recurrent flight training in reduced visibility procedures specified in the company operations manual. The manual was to contain low visibility operational procedures and pilot decision-making considerations, which included weather and the potential for white-out. However, Transport Canada had not introduced basic instrument flight sequences into their flight review requirements.

Research into VFR into IMC accidents

Introduction

Accidents from VFR into IMC are normally the result of either controlled flight into terrain or loss of control. Loss of control events can be the result of spatial disorientation, which is the inability of a pilot to correctly interpret aircraft attitude, altitude, or airspeed in relation to the Earth or other points of reference. This can lead to a pilot making incorrect control inputs or responding incorrectly to attitude changes. If flight path information is available it may be possible to conclude whether the aircraft was on a controlled or erratic path prior to the accident, indicating either controlled flight into terrain or loss of control occurred, respectively. However, flight data information is generally required to determine if an aircraft attitude change either preceded or followed pilot input in a loss of control event.

United States Helicopter Safety Team

In 2021, the US Helicopter Safety Team published a study that examined 221 fatal helicopter accidents that occurred between 2009 and 2019 in the US. An analysis of these events found that unintentional IMC events were one of the top causes of fatal accidents. Notably, they determined that a helicopter pilot operating under VFR who unintentionally continued flight into IMC would very likely lose control and collide with terrain within an average of 56 seconds. They have also released a video showing how rapidly a pilot could lose control when attempting to continue visual flight into IMC. They have also developed a ‘56 Seconds to Live Course’, which provides pilots with scenario-based training designed to teach them to employ pre-flight risk assessments and en route weather minima decision points to reduce the chance of an inadvertent IMC accident.

Transportation Safety Board of Canada Aviation Safety Study 90-SP002

A 1990 Transportation Safety Board (TSB) of Canada safety study on VFR into adverse weather (report 90-SP002) was prompted by the disproportionately high number of fatalities each year from these accidents. Their study identified 352 accidents in Canada between 1976 and 1985, which accounted for 6% of the total number of recorded accidents, but 23% of all fatal accidents. While 12.7% of the total accidents in this period were fatal, VFR into IMC accounted for a significantly higher proportion of fatal accidents (50.2%). The TSB report noted that in uncontrolled airspace in Canada, reduced visibility of 1 statute mile (1,609 m) was allowed, which ‘implicitly assume that orientation by other than reference to a natural horizon may be required to maintain control during VFR flight’.

The report also explored VFR into IMC specifically for the category of commercial helicopter pilots. Of the 33 helicopter accidents, they found that 27 were the result of white-out conditions in which the pilots were unable to maintain visual reference to the ground. Only 1 of the pilots held an instrument rating, and of the remaining, only 2 had acquired some instrument flying experience, but this was less than 20 hours for each of them.

The report noted that, from July 1987, the commercial helicopter pilot licence required 20 hours of actual and simulated instrument flying training, but before this, no instrument flying training was required. Consequently, the accidents identified in the study involved pilots who were not required to have instrument training to have obtained their helicopter licence. Therefore, the lack of instrument flying experience among the general population of commercial helicopter pilots was ‘expected to lead to a continuation of weather-related accidents in whiteout conditions’. This was also evident in the comparison between Canadian and US pilots with the following finding:

In addition, at the time of the TSB (1990) report, there was no requirement for commercial helicopter pilots to conduct recurrent basic instrument flying training as a condition of their licence. Therefore, the TSB noted that recently licenced pilots ‘will find that their instrument flying skills will deteriorate if not practised.’ They concluded that an evaluation of basic instrument flying skills during a pilot’s annual proficiency check would ensure commercially-employed helicopter pilots demonstrated ‘proficiency in skills necessary for coping with the major cause of VFR helicopter accidents in adverse weather.’ Noting that the annual proficiency checks for commercially‑employed pilots focussed on aircraft handling skills and technical knowledge, the TSB made the following finding and recommendation:

They also recommended to the Canadian Department of Transportation that all commercially‑operated helicopters be equipped with appropriate instrumentation, specifically an attitude indicator, for the conduct of basic instrument flying.

United States National Transportation Safety Board SS-05/01

In 2005, the US National Transportation Safety Board published a safety study into the Risk factors associated with weather-related general aviation accidents, highlighting that:

The study examined 72 general aviation accidents that occurred between August 2003 and April 2004 (report NTSB/SS-05/01). When an accident occurred, they contacted pilots of flights operating in the vicinity at the same time as the accident, which added 135 non-accident flights to their study for statistical comparison. One of their findings was that not having an instrument rating was associated with significantly higher accident risk. Specifically, ‘pilots who did not hold an instrument rating were found to be 4.8 times more likely than instrument-rated pilots to be involved in a weather-related accident.’

The stabilisation problem

Introduction

The prevalence of loss of control helicopter accidents in degraded visual environments (DVE) has resulted in several research studies into helicopter handling qualities and the associated pilot effort and performance in DVE. They include the US FAA (Hoh, 1990), the United Kingdom Civil Aviation Authority (2007) and Crognale & Krebs (2011), detailed below. A helicopter cannot be certified for instrument flight rules unless it complies with the airworthiness stability criteria for helicopter instrument flight, which is generally achieved with a stability augmentation system (artificial stabilisation). The success of these certification standards and the continued loss of control accidents in the light helicopter sector led to the US Helicopter Safety Team publishing a white paper on this issue (Oltheten & Trang, 2021). For the purposes of this section, the tasks requiring pilot attention are divided into control (managing the attitude), guidance (managing the flight path), and navigation (managing the route).

The effects of degraded visual cueing and divided attention on obstruction avoidance in rotorcraft

Hoh (1990) reported that a deterioration in the effective rotorcraft flying qualities[39] occurred in DVE. The pilot workload in such conditions was observed to be very high for aircraft control. This left the pilot with very little excess attentional capacity to maintain situational awareness.[40] The US Army experiments reported by Hoh (1990) found that the addition of artificial stabilisation improved flying qualities in DVE, which increased the pilot’s available capacity to maintain situational awareness.

Helicopter flight in degraded visual conditions

The United Kingdom Civil Aviation Authority (2007) reported that the inherent instability of many small and some medium helicopters can rapidly lead to excessive pilot workload when attempting to fly in DVE. Their performance study found that a key factor was the division of attention between the guidance and stabilisation [control] tasks, and there was a strong interdependency between handling qualities and visual cues. They also established that ‘attitude command‑attitude hold’ stabilisation systems were essential for safer operations in DVE. Their conclusions from simulator trials included the following:

Performance of Helicopter Pilots During Inadvertent Flight Into Instrument Meteorological Conditions

Crognale & Krebs (2011) tested 20 commercial instrument rated helicopter pilots on a US FAA approved flight simulator running a program for a Bell 206 helicopter that they were all qualified to fly. Each participant conducted 5 runs at varying altitudes and speeds and their results depicted a distinct change in pilot control inputs when external visual references were lost, indicating an increase in pilot workload to maintain control of the helicopter. The only accident during the study was a controlled flight into terrain when one of the participants was given a simulated air traffic control radar vector towards a mountain.

Figure 16 depicts the raw data for bank angle (left panel) and lateral cyclic[43] control movements (right panel) for a participant with 7,600 hours experience on their first run. The arrows at the bottom of each panel in the figure indicate where the visibility was reduced to 1 mile and then zero to simulate entering cloud. The right panel depicts large changes in lateral cyclic control input when the visibility reduced to zero, with associated bank angle changes on the left panel.

Figure 16: Bank angle (left) and lateral cyclic movement (right)

Source: Crognale and Krebs (2011)

Loss‐of‐control in‐flight mitigation through installation of stability augmentation and autopilot systems in light helicopters

In 2021, Oltheten and Trang published their report for the US Helicopter Safety Team’s helicopter safety enhancement number 70, output number 3. The purpose of the report was to encourage the use of technologies to reduce the risk of fatal helicopter accidents.

The report specifically stated that helicopters are generally more susceptible to loss of control accidents than aeroplanes due to their inherent instability and lack of mechanical trim. The need for inherent stability and trim are not as essential when operating in VMC. However, as conditions deteriorate, this need becomes increasingly essential to assist pilots with maintaining positive control during a temporary loss of visual cues or if they become disorientated.

Therefore, many loss of control accidents could be avoided if all helicopters were designed to meet some of the instrument flight rules stability requirements. They noted that the systems used in the transport category[44] sector have proven their effectiveness and safety for flight in IMC over 30 years but most of them were too heavy or complex to integrate into light helicopters. However, emerging technologies reduce the weight, complexity, and cost of these systems, which are now available for the light helicopter industry. Therefore, their paper advocated for industry and the US FAA to encourage the development and installation of these systems in light helicopters.

Civil Aviation Safety Regulations Part 133

Under CASR Part 133 rotorcraft air transport, an automatic pilot or automatic stabilisation system was required for instrument flight rules or single pilot night VFR without external visual references. While the accident helicopter was not in the instrument flight rules category, Airbus Helicopters reported there was a stability augmentation and autopilot system available for the EC130 T2 helicopters, which provided attitude stabilisation, altitude hold and heading fly‑to and maintain capability.[45]

ATSB database review

Occurrence data

A review of the ATSB accident and incident (occurrence) database for the period 2008-2022 was conducted to identify helicopter VFR into IMC and engine failure or malfunction events. The category of ‘engine failure of malfunction’ was selected for comparison as managing engine failures is a licencing and flight review requirement for helicopter pilots. In contrast, recovery from VFR into IMC requires instrument flying skills that were not required under the previous Civil Aviation Regulation 5 and not required on the current non-integrated syllabus.

The results, provided in Table 2, were consistent with findings from other jurisdictions that helicopter accidents from VFR flight into adverse weather have a high proportion of fatalities. In this period, engine failures (13%) accounted for a greater proportion of the total helicopter accidents (all categories) compared with VFR into IMC (1.3%). However, there were nil fatal accidents for engine failure or malfunction. In contrast, most VFR into IMC accidents resulted in a fatal outcome (83%), accounting for 14% of all helicopter fatalities for this period. If VFR dark night collision with terrain accidents were included in the VFR into IMC category, together they would represent 3.2% of all helicopter accidents and 29% of all helicopter fatalities.

Table 2: ATSB database review, 2008-2022

Another comparison (Table 3) was made between helicopter and aeroplane VFR into IMC accidents for the period 2008-2022. The comparison noted that the fatal outcome of a VFR into IMC accident was similar for both aircraft categories. However, of significance was that there was a notably lower percentage of VFR into IMC occurrences that resulted in an accident for aeroplanes, when compared with helicopters.

Table 3: VFR into IMC comparison between helicopters and aeroplanes

A Fisher’s exact test^[46] was applied to the helicopter and aeroplane VFR into IMC occurrences for accident and non-accident outcomes. The association between the groups (helicopter and aeroplane) and their outcomes (accident and non-accident) was found to be statistically significant, which indicated the difference in the proportion of accident outcomes between these 2 groups was not due to chance.^[47] The previously cited research indicated to the ATSB that the 2 main issues likely contributing to the difference between these groups, in their ability to recover from IIMC, were a lack of instrument flying training for helicopter pilots and the control difficulties associated with operating helicopters without stabilisation. As day VFR helicopters and aeroplanes are not required to be equipped with an artificial horizon, and they are not required to plan a lowest safe altitude, these were not identified as differences between the 2 groups.  

Accident summaries

A more detailed breakdown of the 6 helicopter accidents is provided in Table 4.

Table 4: VFR into IMC helicopter accidents

* Although classified as a private flight, this was the transport of the helicopter owner by a pilot employee.

The pilot involved in AO-2009-077 survived the accident and stated that he did not consider using the flight instruments as a means of recovering from being in cloud as the pilot was a VFR pilot and did not feel adequately trained to use them. Following the accident, the New South Wales National Parks and Wildlife Service proposed introducing requirements for helicopters to be in the night VFR category, pilots to be night VFR rated, and for operators to demonstrate that they have provided guidance to pilots for ‘action to take if inadvertent instrument conditions are encountered’. However, at an industry forum held on 27 July 2010, ‘feedback was very negative and overwhelmingly indicated that this would not only be practically unachievable but would likely significantly decrease safety levels.’ Therefore, the proposal was not actively pursued.

Likewise, the pilot of AO-2010-076 survived the accident. The pilot reported that, after inadvertently entering IMC while attempting to turn away from the weather ‘he became spatially disoriented and attempted to level out and fly through the cloud with the aid of the helicopter’s flight instruments.’ The helicopter exited the base of the cloud with about 41° left wing-low and 4,300 ft/min rate of descent. The pilot had time to flare the helicopter and reduce airspeed before it collided with trees.

The pilot of AO-2011-085 overcontrolled the helicopter after inadvertent IMC, which resulted in loss of control and inflight break-up. The ATSB’s investigation report specifically noted that ‘...The pilot was not trained or qualified for instrument flight, nor was the helicopter equipped with the required instruments, such as an artificial horizon. In those circumstances the pilot probably became spatially disoriented, leading to inappropriate control inputs…’.

In AO-2015-131, there was no flight tracking data available immediately prior to the collision with terrain. Therefore, it could not be determined if it was a loss of control or a controlled flight into terrain event. However, the ATSB found that the pilot likely encountered reduced visibility conditions leading to loss of visual reference leading to the collision with terrain.

In AO-2022-017, the ATSB found that, having encountered forecast low cloud and reduced visibility conditions, the pilot landed the helicopter at an interim landing site. Later that day, the helicopter then departed into cloud and visibility conditions unsuitable for visual flight. During the flight, recorded data showed that the helicopter had commenced a rapid climb and shortly after, entered a left turn descent that exceeded 3,800 ft/min followed by a collision with terrain. It was highly likely the cloud and visibility conditions resulted in the pilot experiencing a loss of visual reference and probably becoming spatially disoriented.

Non-accident occurrences

The 6 non-accident occurrences were reviewed for how the pilots exited IMC. Two reported climbing above cloud and in one of those cases it was to the lowest safe altitude in accordance with the operator’s IIMC procedure. In three cases they reported a descent below the cloud, and in one of those cases the helicopter was VFR over the top of cloud and had to descend through the cloud layer that was overcast below them. The last occurrence received assistance from air traffic control but the reporter did not describe how the helicopter exited from IMC.

Geographical distribution

The geographical distribution of the accidents was consistent with the east coast ranges through Victoria and New South Wales. Orographic uplift cloud from a moist maritime airmass at these locations can produce cloud bases at or near ground level. The Appendix figures depict the geographical distribution of accidents and reported occurrences for helicopters and all aircraft types for the 15-year period 2008 to 2022.

Intervention strategies

Many recommendations have been made to reduce the risk of VFR into IMC accidents from various accident investigation, regulatory and industry bodies. This section presents 2 industry papers that capture a significant number of the recommendations, including the key historical themes for how to reduce the risk of an inadvertent IMC encounter and accident.

Helicopter pilots in inadvertent IMC situations

The International Helicopter Safety Team has published several fact sheets about IIMC that are available from the US Helicopter Safety Team website. Their fact sheet, Helicopter pilots in inadvertent IMC situations, acknowledges that these encounters are the ‘most demanding, disorienting, and dangerous conditions a pilot can experience’ and result in the highest percentage of fatal injuries from helicopter accidents. Therefore, the combined use of flight simulators and ground instruction to improve instrument flying skills and proficiency is emphasised. This provides an opportunity to apply policies and procedures, and practice IIMC recovery, noting that these skills are considered perishable.

The fact sheet explained the immediate actions required by pilots in IIMC stating that:

If IIMC occurs, helicopter pilots can follow the 4 ‘Cs’: control, climb, course, and communicate, which need to be immediate memory recall items for a pilot who encounters IIMC:

In addition to recovering from IIMC, their fact sheet provided the following preparations for avoiding IIMC:

Helicopter accident trends in 8 ISASI [International Society of Air Safety Investigators] countries and how we might improve the fatal accident even further

Matthews, Alexander, and Stone (2017) conducted an analysis of fatal helicopter accidents across 8 jurisdictions with large helicopter fleets for the period 2001 to 2015. Their analysis of VFR into IMC accidents included the following:

When discussing the importance of IIMC recovery training, the report emphasised that ‘one-off training efforts’ had little or no effect as instrument flying skills are perishable. Instead, to be effective, repeated training reflecting an operator’s procedures and risk assessments was required. Further, regulators can contribute by increasing their surveillance of an operator’s procedures or helping in the development of these procedures and risk assessment programs. Their paper concluded with a comprehensive list of recommended training, process, and technology interventions with an accompanying explanation for each.

Safety analysis

Introduction

On the morning of 31 March 2022, 2 Airbus Helicopters EC130 helicopters, operated by Microflite, commenced a passenger transport flight from the company’s Batman Park helicopter landing site in Melbourne to Ulupna on the northern border of Victoria. Recorded data and interviews established that the first helicopter, VH-WVV (WVV) performed a U-turn overhead Mount Disappointment to avoid entering cloud. The second helicopter, VH-XWD (XWD), entered a high rate of descent and collided with terrain while attempting to follow WVV with the U-turn. The 5 occupants were fatally injured and the helicopter was destroyed.

This analysis will discuss the circumstances leading to the collision with terrain, including the route planning, entry into cloud, loss of control, instrument flying experience of the pilot, benefits of autopilot and artificial stabilisation, and the state of the standby artificial horizon. It will also examine how the risk of an inadvertent instrument meteorological conditions (IIMC) encounter was being managed in terms of recovery training, proficiency checks, a pre-flight risk assessment, and the operator’s risk management approach to adverse weather. Further, it will discuss the need for the regulator to provide greater safety assurance for passengers in the rotorcraft air transport sector.

The terms ‘VFR into IMC’ and ‘IIMC’ are used interchangeably in the analysis to reflect the nomenclature used by the respective references.

Route planning

The weather forecast for the Mount Disappointment area indicated broken stratus cloud at 2,000‑3,000 ft above mean sea level (AMSL) and a mixture of broken cumulus/stratocumulus cloud at 3,000-8,000 ft. The peak of Mount Disappointment is 2,605 ft and the upper limit of uncontrolled airspace was 3,500-4,500 ft. This indicated that cloud was forecast to develop below visual meteorological conditions (VMC) from ground level up into controlled airspace. This made the route over Mount Disappointment under the controlled airspace steps unsuitable for visual flight rules (VFR) planning purposes. Further, there were scattered showers of rain with cloud up to 10,000 ft forecast over the ranges, but north of the ranges was forecast to be clear.

The forecast for Kilmore Gap, the recommended VFR route to the north, included broken cloud at 3,000 ft with temporary periods of cloud on the ground from 0600-1000. This indicated a route via Kilmore Gap was an option with the caveat that the forecast included periods that it could be impassable. This option would have kept the pilots in sight of ground, which would have provided them with visual references for a turn-back and potential emergency landing sites if they could not proceed or turn-back. However, it was the Melbourne Airport forecast of cloud at 1,500 ft above that aerodrome that resulted in the pilots’ assessment that they might not be able to transit through Kilmore Gap below cloud. Instead, they selected a more direct route over Mount Disappointment above the lower layer of cloud. This plan was confirmed during their flight into the city from Moorabbin where they observed that the forecast cloud was not established over the ranges.

From interviews, it was reported to be common practice to use the 24-hour forecast for Melbourne Airport to assess the suitability of conditions for the following day’s taskings. While this forecast was useful for the Melbourne basin, it did not provide the height of the cloud tops (as available on the graphical area forecast) and was not valid for a cross-country flight. Although the pilot of WVV reported that they would have checked the graphical area forecast, the information provided on the Melbourne Airport forecast was a deciding factor in the pilots’ route selection. The ATSB was unable to determine why the Melbourne Airport forecast was more influential than the graphical area forecast for their assessment of the Kilmore Gap route. The fact that the pilot of WVV had made multiple location requests for weather and had concerns regarding the Melbourne Airport forecast, and the accident pilot had the WillyWeather app running from 0633 indicated that both pilots were conscious of the weather but were not able to associate the risk of their plan with the forecast conditions.

Entry into cloud

After departing the Batman Park helicopter landing site, with WVV in lead and XWD in trail about 30 seconds behind, the pilot of WVV could see the ranges and sunlight striking the ground ahead, indicating to them the cloud cover ahead was scattered. Consequently, they elected to proceed over the top of the cloud rather than divert via the recommended VFR route. On reaching 3,500 ft, the cloud coverage below gradually increased from scattered to broken but the pilot could still see patches of sunlight striking the ground and continued. The pilot’s repeated references to sunlight striking the ground ahead as they approached Mount Disappointment suggested that this visual indicator supported their plan.

The increasing cloud cover was starting to concern the pilot of WVV as the layer below was starting to rise towards their upper limit of uncontrolled airspace at 3,500 ft. There was also a layer above at about 4,500 ft, and these 2 layers appeared to be converging ahead over Mount Disappointment. The Appareo footage from XWD was consistent with the description of the conditions provided by the pilot of WVV and the forecast for the Mount Disappointment area.

As the minimum vertical clearance from cloud had increased from ‘clear of cloud’ to 1,000 ft when the helicopters climbed to the 3,500 ft upper limit, it was likely shortly after this that they encroached the criteria for VMC. However, the changing conditions had not yet triggered a decision for the pilots to divert.

As the cloud ahead continued to deteriorate, the pilot of WVV was eventually confronted with a wall of cloud, consistent with the passenger observations of white-out conditions. As they could not manoeuvre around the cloud while remaining outside controlled airspace, they advised the pilot of XWD they were turning around. The query from the pilot of XWD about the need for a U‑turn suggested the conditions had also not yet triggered a decision for them to divert. The pilot of WVV broadcast the U-turn manoeuvre so that the pilot of XWD would know to do the same. However, the pilot of XWD started a descent and waited to visually sight WVV pass abeam before attempting the turn. It could not be determined why the pilot of XWD delayed the turn, but it was possible they were either concerned about a mid-air conflict or were waiting to follow WVV.

As the pilot and passengers onboard WVV reported that they sighted XWD after the U-turn, the helicopters were not in cloud at this stage. However, shortly after the helicopters passed abeam each other, the footage showed that the main artificial horizon (AH) on XWD started to wander 10º in pitch and 30º in roll, which indicated the pilot had very likely lost external visual references at this stage.

Loss of control

After WVV passed abeam XWD, the footage showed that the pilot of XWD encountered IIMC. For the U-turn, the pilot attempted a steep left turn at about 60° angle of bank with low power, as indicated by the low FLI setting. While a steep turn would have facilitated exiting the cloud conditions quicker, it also required more significant changes to the flight control inputs than a small angle of bank turn for the pilot to maintain control of the vertical profile (climb, descent or level as necessary). After rolling into the left turn, the nose down pitch attitude increased, such that the main AH indicated ground only. The rate of descent subsequently increased significantly with at least a 3,000 ft/min full scale deflection observed on the vertical speed indicator and a peak of about 5,700 ft/min from the global positioning system data. This was about 10 times the normal descent rate stipulated by the operator for passenger charter operations. The significant deviation of the pitch attitude during the turn was likely unintentional and the result of inadequate pilot control due to a lack of instrument flying training and artificial stabilisation.

The pilot’s setting of the main AH before take-off and control of the angle of bank to enter the final turn, during the turn and exit from the turn, indicated they had developed some ability to read the bank angle on the AH. However, the loss of control and high rate of descent was consistent with other helicopter VFR into IMC accidents.

The pilot reversed the roll to about 10º angle of bank to the right as the helicopter reached its reciprocal heading, at which point the trees became visible in the cloud. A significant pitch-up was applied but could not prevent the collision.

Instrument flying experience

An IIMC event presents the risk of either controlled flight into terrain or loss of control and collision with terrain. The goals of instrument flying training for day VFR pilots include recovering from unusual attitudes and recovering to visual conditions after an IIMC event. Their ability to do this is dependent on receiving initial and recurrent training.

As the pilot had completed the non-integrated Commercial Pilot’s Licence (Helicopter) (CPL(H)), they had not been trained in basic instrument flying, which was supported by their flight test report. Likewise, the operator’s copy of the pilot’s logbook showed that the pilot had accumulated about 3,000 hours total experience but had not recorded any actual or simulated instrument flying. This was consistent with the pilot’s operator proficiency checks, which indicated instrument flight sequences were not assessed, in-line with the operator’s requirements for the day VFR pilots. Consequently, there was no recorded evidence that the pilot had ever been trained to manage or demonstrated an ability to safely recover a helicopter from an IIMC event. The pilot of WVV and a former company pilot also reported no instrument flying experience and therefore this was not unique to the accident pilot.

Autopilot and stabilisation

The accident helicopter, XWD, was not equipped with an autopilot or stability augmentation system and had an excessive rate of descent during the attempted U-turn in cloud when the nose down pitch attitude increased significantly after the turn entry. As established through tests and research, the handling qualities of helicopters without artificial stabilisation deteriorated in degraded visual environments to the extent that the pilot’s full attentional resources were required to maintain control of the helicopter. Consequently, a pilot may not have spare attentional capacity for either the guidance (managing the flight path) or navigation (managing the route) of the helicopter in IMC. Conversely, if their attention is diverted to guidance, they may not have sufficient capacity to maintain control (managing the attitude).

Consequently, helicopter certification for instrument flight rules includes stability characteristics, which can be met with a stability augmentation system. In addition, the Civil Aviation Safety Regulations (CASR) Part 133 for rotorcraft air transport require either an autopilot or automatic stabilisation system for helicopters engaged in instrument flight rules or single-pilot night VFR operations without external visual references.

In this case, if the helicopter had been equipped with an autopilot or stability augmentation system, and the pilot was trained to use the equipment, the attitude control and guidance provided by these systems would have reduced the risk of the loss of control. As emphasised by Oltheten and Trang (2021), many loss of control accidents could have been avoided if the helicopters met some of the instrument flight rules stability requirements. Therefore, the ATSB encourages the adoption of these systems wherever feasible.

Standby artificial horizon

Video footage showed that the pilot erected the main artificial horizon (AH) on start up at Moorabbin Airport but did not erect the standby AH. Likewise, the footage showed that the standby AH remained off on departing the Batman Park Airport, which was consistent with the position of the corresponding push-button switch found in the wreckage.

Immediately after WVV had completed the U-turn due to the deteriorating weather conditions and passed abeam XWD, the pilot of XWD looked across the cockpit at the standby AH that had a red ‘OFF’ flag visible and was indicating a 90º roll to the left. The pilot reached across and attempted to erect the standby AH and then released it with no change in the indications. As the pilot had not switched the power on to the instrument, the AH could not be erected. Consequently, this would have presented conflicting attitude information to the pilot, which they were unable to correct at about the same time they lost external visual references. Conflicting attitude information increases the risk of a pilot experiencing spatial disorientation. However, while the pilot was temporarily distracted by the standby AH, as they did not appear to scan this instrument during the accident turn, it was not considered to be a contributing factor.

Engine service bulletin

In 2019, the European Union Aviation Safety Agency issued a safety information bulletin describing the blade shedding design of the Arriel 2D engine for preventing turbine disc burst from an overspeed condition. The purpose of the bulletin was to explain the risk of thermal energy being released during blade shedding potentially contributing to post-crash fires and that Safran Helicopter Engines and Airbus Helicopters were working on the introduction of a fuel shut-off modification to prevent blade shedding events. They had introduced service bulletins for the hardware (Airbus) and software (Safran) requirements.

At the time a representative from Safran attended the operator’s facility to incorporate the software modification for their fleet, XWD was not available. In addition, the Airbus hardware modification had not yet been embodied for their fleet. However, both modifications were scheduled to be embodied within their respective compliance periods. Consequently, blade shedding as the design control for overspeed conditions still applied to XWD. This likely occurred when the engine to main gearbox drive shaft ruptured during the collision. However, the accident was of a severity that was not considered survivable, and the damage associated with the tree and ground impacts suggested a fire was likely to occur irrespective of the blade shedding. Therefore, the absence of the service bulletin was not considered to be a contributing factor.

Inadvertent instrument meteorological conditions recovery procedure and training

The International Helicopter Safety Team fact sheet – Helicopter Pilots in Inadvertent IMC Situations explained that it is the immediate actions after an IIMC encounter that will usually determine the outcome of the event. Furthermore, this emphasised that ‘pilots who possess a plan of action prior to encountering it are more likely to experience a successful outcome than those who are less trained and less proficient in the recognition and recovery procedures.’ The 4 immediate actions they advocated were control, climb, course, and communicate.

These actions represent the emergency procedure steps required following an IIMC encounter, which need to be immediate memory recall items. Without a published procedure for passenger operations, Microflite was reliant on individual pilots to identify the need and develop their own procedure. In contrast, the operator had published an IIMC procedure for formation flying, which was part of their formation pre-flight briefing. This indicated that the operator recognised IIMC as a potential in-flight risk and that immediate memory recall was required to minimise the likelihood of it being mishandled during a formation flight.

The operator had also published in their training manual that IIMC recovery training was available and conducted in their simulator. However, it was only a recommended sequence and neither the pilot of XWD or WVV had undergone this training. Statistics have shown that a loss of control and collision with terrain from IIMC could occur in about 56 seconds. In this accident, the pilot rolled the helicopter to a 60° angle of bank after encountering IMC, followed by a significant nose down attitude and rate of descent. This resulted in a collision with terrain in less than 30 seconds.

Successful recovery from an emergency requires a pilot to recognise what the problem is and what decisions and actions are required in response. In the IIMC avoidance and recovery scenarios the pilot needs the recognition, decision-making and basic instrument flying skills to handle degraded visual conditions. As noted by the United States Helicopter Safety Team, having standardised procedures ensures an enhanced level of safety by providing structure and preparing pilots to respond to normal and abnormal situations.

While the operator had a system that could have delivered training to their pilots for IIMC avoidance and recovery in accordance with a published procedure, they had not developed a procedure or mandated the training. If the pilot had received the technical and procedural training to recover from IIMC, this would have reduced the risk of this accident.

Operator proficiency checks

The Civil Aviation Safety Authority CPL(H) was divided into 2 syllabi, identified as the integrated syllabus and the non-integrated syllabus of training. The non‑integrated syllabus did not require instrument flying training, as was required for an aeroplane licence. Therefore, while the flight review for the aeroplane licence required an assessment of instrument flying, this was only optional for a helicopter flight review. Consequently, the operator did not conduct any basic instrument flying skills checks on their pilots who were employed as day VFR charter pilots.

The first action required to recover from IIMC is to control the helicopter with reference to the flight instruments, which requires the pilot to transition from an external visual scan to an internal scan of the primary flight instruments. Initial training is required for the pilot to develop the understanding and skill for how to control the helicopter by sole reference to instruments. However, instrument flying skills, like engine failure handling skills, are perishable skills and therefore regular practice and competency checks are required to maintain and assure proficiency.

The 6 previous helicopter IIMC accidents reviewed in this investigation found none of the pilots were likely proficient in basic instrument flying, having had no recent experience or no experience at all. This was supported by the report from one pilot with basic instrument flying training 18 months prior to their accident that they did not feel adequately trained to use their flight instruments. Proficiency checks provide operators with the opportunity to assess if their pilots have the decision-making and handling skills to perform their normal and emergency procedures to the required standard. Likewise for the pilot under assessment, feedback from the assessor can confirm if their decision-making and actions were appropriate.

While the operator’s decision not to assess instrument flying skills was consistent with regulations and the helicopter industry’s historical opposition to basic instrument flying training, research into IIMC accidents has shown that these encounters often result in fatalities from a loss of control or controlled flight into terrain. Therefore, as noted by the International Helicopter Safety Team, those pilots who are trained and proficient in IIMC recognition and recovery procedures are more likely to experience a successful outcome. As the accident pilot had neither been trained or subjected to a basic instrument flying skills check, this increased the risk of a loss of control while attempting to recover from the IIMC encounter over Mount Disappointment.

Pre-flight risk assessment

As noted by Matthews, Alexander, and Stone (2017), VFR into IMC accidents can involve a lack of pre-flight planning and/or risk assessment. The accident flight was a Part 133 rotorcraft day VFR passenger air transport operation with the pilots conducting their flight planning and preparation independent of direct oversight. While neither of the pilots were inexperienced, this sector of the industry is predominantly a single-pilot operational environment (the pilot’s flying experience indicated about 95% of flight time as pilot in command). Therefore, pilots have significantly less opportunity to learn operational decision-making from more experienced pilots than they would in a multi-crew environment.

In the Transport Safety Board of Canada’s safety study of IIMC accidents, they noted that technical piloting skills were not found to be deficient in the history of accident pilots’ check flights. Rather, the problem was with their decision-making in situations not traditionally assessed. In this case, the accident pilot had passed several proficiency checks with the operator and expanded their technical flying skills and qualifications with a low-level rating with sling endorsement and an aerial application rating.

The single-pilot passenger transport environment poses the challenge to operators for how to manage the oversight of planning activities conducted by their line pilots and afford them the decision-making learning experience from senior pilots that is available in the multi-crew environment. A tool that can assist with this is a pre-flight risk assessment that provides an escalation process commensurate with the level of risk. Weather is one of the key elements of a pre-flight risk assessment and provided the tool is designed to trigger an escalation if conditions are marginal for a VFR flight, then it will provide an operator with a risk-based approach to oversight flight planning. This process has been extensively used throughout the helicopter emergency medical services sector.

The operator did not have a process in place for independent checks of their line pilots’ flight planning activities. However, an oversight process could be made available with the use of a fit‑for-purpose pre-flight risk assessment tool with the records saved for verification and validation purposes. In this case, if a conversation had taken place with a manager or instructor pilot prior to the accident flight there likely would have been more scrutiny of the graphical area forecast and the recognition that a route via the Kilmore Gap was a lower risk option.

Risk management of inadvertent instrument meteorological conditions

In 2015, the operator had raised a risk assessment for air transport operations for the purpose of identifying the risks associated with their general charter operations from company known and frequently used locations. This included the threat of poor weather conditions, such as the risk of loss of VMC. The controls associated with this threat were cancelling operations if the forecast weather was below company minima, the arrangement of ground transport, and that all their pilots were issued with an iPad to access and assess the weather. During the investigation, the ATSB found evidence that the operator’s controls for the threat of poor weather conditions were being practiced and that charter flights had been routinely cancelled due to weather. However, the risk assessment did not consider how this threat would be managed in-flight.

The ATSB identified several recommended controls in the operator’s manual suite that could have been employed to mitigate the in-flight risk of IIMC. These included the use of minimum safe altitudes and recovery training for IIMC. However, they were not mandatory and therefore they were not effective risk controls. The operator’s client services management process and procedure for diversions due to weather were also missing from their risk assessment. Combined, this indicated the loss of VMC preventive controls were incomplete.

Despite the published preventive controls, the accident flight was planned and continued along a route forecast to be below VMC. This highlighted that a pilot’s weather assessment and diversions would not necessarily prevent a route planning mistake escalating into IIMC. The various optional and existing controls indicated the operator understood the risk, but that the regulatory environment for day VFR helicopter pilots likely meant that no further action was considered necessary as their published risk controls were in accordance with these requirements.

The operator’s approach to the risk of IIMC was consistent with the 2018 CASA helicopter industry survey, where most respondents opposed basic instrument flying training. However, this did not recognise that air transport safety has built and relied on multiple layers of controls to reduce the risk of single-point of failure accidents.

Civil Aviation Safety Regulations Part 133

The day VFR helicopter and aeroplane industry sectors typically range from private flying, flying training, aerial work activities, to air transport operations, which includes scheduled and non‑scheduled passenger transport, scenic flights and medical transport. The regulatory framework and expectations of the level of safety across these categories is graduated with separate rule sets, which facilitates the development of regulations that can be tailored to each specific sector. In the passenger air transport sector, there is a public and industry expectation that the flights will be operated to a higher safety standard than other sectors of the aviation industry. However, this distinction is not always captured within the regulations and standards for known risks, such as VFR into IMC.

In terms of a comparison between aircraft categories, helicopters and aeroplanes both had a high percentage of fatal VFR into IMC accidents, consistent with other jurisdictions, but helicopters were more likely to be involved in an accident following a VFR into IMC occurrence. Despite this, there was a notable difference between helicopter and aeroplane licencing and training requirements. The aeroplane CPL syllabus included a requirement to teach basic instrument flying (as did the integrated CPL(H) syllabus), which included recovery from IIMC as one of the units of competency. These perishable skills were required to be checked on flight reviews for aeroplane pilots. In contrast, the training was optional for the non-integrated CPL(H) and consequently the instrument flying flight review requirements were optional for all CPL(H). As such, it was very likely that VFR pilots from the non-integrated syllabus conducting passenger air transport operations would not have been trained to recover from IIMC.

There is a variety of risk controls that could be implemented to reduce the risk of an IIMC accident. They include equipment, such as artificial stabilisation and autopilots, warning devices, such as terrain awareness and warning systems, IIMC recovery training, pre-flight risk assessments, flight plan reviews, minimum safe altitudes, and supporting procedures. Noting these risk controls and the training differences described above, the ATSB reviewed the regulations and standards to determine how the Civil Aviation Safety Regulations (CASR) Part 133 air transport passenger operators were expected to manage the risk of a day VFR pilot experiencing IIMC.

The CASR Part 133 (air transport operations - rotorcraft) and associated Part 133 Manual of Standards set the helicopter air transport specific requirements for operators to prepare their exposition, to demonstrate how they intend to comply with the legislative requirements and how they will manage safety. This may include risk assessments, procedures, and equipment for the various categories of flight. Therefore, while operational risk identification is traditionally the domain of the operator, CASA can require the assessment of specific risks through the safety regulations and then audit against them for safety assurance purposes.

As an example, CASR Part 133 required operators to include risk assessments in their expositions, for any planned performance class 2 with exposure operation. Similarly, CASR Part 135 (air transport operations—smaller aeroplanes) operators were required to include procedures for low-visibility operations and stabilised approach criteria in their exposition to mitigate the risk of approach and landing accidents.

Further, in terms of the primary flight instruments required for controlling an aircraft when experiencing IIMC, this would include instruments providing airspeed, altitude, and attitude information. The requirements stipulated in the Part 133 Manual of Standards for day VFR operations included flight instruments for indicated airspeed and pressure altitude, but there was no reference to having attitude (artificial horizon) or standby attitude instruments. Additional flight instruments were required for night VFR and instrument flight rules (IFR) operations.

Likewise, an autopilot or automatic stabilisation system that would assist with controlling the helicopter in normal flight and reduce the risk of loss of control in IIMC was only required for IFR and some night VFR operations. A terrain awareness and warning system, alerting pilots when in hazardous proximity to terrain to reduce the risk of controlled flight into terrain, was only required for larger rotorcraft conducting passenger flights or medical transport operations, both operating under IFR.

The ATSB often finds that optional risk controls related to the occurrence under investigation were not implemented at the time of the occurrence. The pilots involved in this accident completed the non-integrated syllabus and therefore optional basic instrument flying training was not done. The operator’s risk controls for loss of VMC met the regulatory requirements. Hence, their IIMC recovery training was optional, and the pilots involved had not done it.

Part 133 does include some procedural controls, such as fatigue management, minimum flight crew experience for the pilot in command and additional training and checking requirements that are in addition to the general requirements of Part 91. However, the investigation found that the controls being employed to manage the risk of IIMC within the context of a Part 133 operation were broadly aligned with the requirements of Part 91 for a weather assessment and compliance with VMC criteria and found no evidence of any stricter criteria for forecasts of marginal VMC or recovery controls from an IIMC event. Hence, the regulations for day VFR rotorcraft air transport did not offer a higher level of passenger safety than a private flight for this specific risk. While voluntary guidance and educational resources are useful for both private and commercial pilots, they will not provide assurance for passenger safety.

Findings

From the evidence available, the following findings are made with respect to the VFR into IMC, loss of control and collision with terrain involving a Microflite Airbus Helicopters EC130 T2, registered VH-XWD, near Mount Disappointment, Victoria, on 31 March 2022.

Contributing factors

• The pilots of the two helicopters selected a route that was forecast to be unsuitable for visual flight. This was based on an incorrect assessment of the weather before and while in-flight.
• The pilots of both helicopters continued flight towards deteriorating cloud and into reduced visual cues, below the required visual meteorological conditions. These conditions were consistent with the area forecast for the Mount Disappointment area.
• While conducting a 180 degree turn without visual cues to exit from instrument meteorological conditions, the pilot could not maintain adequate control of the pitch attitude of the helicopter, which resulted in the development of a high rate of descent and collision with terrain.
• The pilot was not trained to fly the helicopter by sole reference to the instruments and almost certainly did not have any instrument flying experience, nor was it required by the regulations.
• The helicopter was not equipped with an autopilot or stability augmentation system, nor was it required to be. This equipment would have reduced the risk of a loss of control when the pilot attempted to exit from instrument meteorological conditions.
• Microflite had not published an inadvertent instrument meteorological conditions (IIMC) recovery procedure for their day visual flight rules pilots and their IIMC recovery training was not mandatory, nor were they required by the regulations. The provision of this procedure and training would have reduced the risk of a loss of attitude control following an IIMC encounter. (Safety issue)
• The Microflite Operator Proficiency Checks did not include a mandatory instrument flight component for their day visual flight rules pilots, nor was it required by the regulations. This would have reduced the risk of a loss of control event following an inadvertent instrument meteorological conditions encounter. (Safety issue)
• Microflite did not provide, nor require, their pilots to complete a pre-flight risk assessment for their taskings. A pre-flight risk assessment would have provided pre‑defined criteria to ensure consistent and objective decision-making and reduced the risk of them selecting an inappropriate route. (Safety issue)
• The Microflite air transport operations risk assessment for poor weather conditions did not consider the risk controls required for inadvertent instrument meteorological conditions. Rather, it relied on their pilots using the actual or forecast conditions to cancel their operations to manage the threat of poor weather. (Safety issue)
• The Civil Aviation Safety Authority's Part 133 (air transport - rotorcraft) exposition requirements did not adequately address the risk to passenger safety from a visual flight rules inadvertent instrument meteorological conditions event. (Safety issue)

Other factors that increased risk

• The standby artificial horizon was not turned on and presented conflicting information to the main artificial horizon. This resulted in a momentary distraction to the pilot when visual cues were reduced and increased the risk of spatial disorientation.
• The operator was in the process of modifying their fleet of helicopters in accordance with the service bulletins for overspeed protection to reduce the likelihood of blade shedding. However, this was not accomplished for the accident helicopter at the time of the accident, which increased the risk of a post-impact fire.

Safety issues and actions

Operator proficiency check requirements

Safety issue number: AO-2022-016-SI-01

Safety issue description: The Microflite Operator Proficiency Checks did not include a mandatory instrument flight component for their day visual flight rules pilots. This would have reduced the risk of a loss of control event following an inadvertent instrument meteorological conditions encounter.

Inadvertent instrument meteorological conditions recovery procedure and training

Safety issue number: AO-2022-016-SI-02

Safety issue description: Microflite had not published an inadvertent instrument meteorological conditions (IIMC) recovery procedure for their day visual flight rules pilots and their IIMC recovery training was not mandatory. The provision of this procedure and training would have reduced the risk of a loss of attitude control following an IIMC encounter.

Pre-flight risk assessment

Safety issue number: AO-2022-016-SI-03

Safety issue description: Microflite did not provide, nor require, their pilots to complete a pre-flight risk assessment for their taskings. A pre-flight risk assessment would have provided pre‑defined criteria to ensure consistent and objective decision-making and reduced the risk of them selecting an inappropriate route.

Risk management of inadvertent instrument meteorological conditions

Safety issue number: AO-2022-016-SI-04

Safety issue description: The Microflite air transport operations risk assessment for poor weather conditions did not consider the risk controls required for inadvertent instrument meteorological conditions. Rather, it relied on their pilots using the actual or forecast conditions to cancel their operations to manage the threat of poor weather.

Civil Aviation Safety Regulations Part 133 requirements

Safety issue number: AO-2022-016-SI-05

Safety issue description: The Civil Aviation Safety Authority's Part 133 (air transport - rotorcraft) exposition requirements did not adequately address the risk to passenger safety from a visual flight rules inadvertent instrument meteorological conditions event.

Safety recommendation description: The Australian Transport Safety Bureau recommends that the Civil Aviation Safety Authority takes safety action to further address the risk to rotorcraft air transport (Part 133) passenger safety from a visual flight rules inadvertent instrument meteorological conditions event.

Safety action not associated with an identified safety issue

Additional safety action by Microflite

During the investigation, Microflite advised the ATSB they had initiated the following proactive safety action.

Introduction of autopilots

Microflite are modifying their AS350 and EC130 helicopters with the Garmin GFC 600H helicopter flight control system. The AS350 has approved data for this modification but approval for the EC130 was not available at the time of the investigation.

Flight instrument upgrades to the fleet

Microflite are upgrading their fleet of EC130 and AS350 helicopters with the Garmin G500H primary flight display and multifunction display, incorporating synthetic vision and a terrain alerting functionality to improve pilot situational awareness in a degraded visual environment.

ICARUS flying hoods

Microflite has acquired 2 ICARUS (instrument conditions awareness recognition and understanding system) instrument flying training hoods, one for the left-seat of the EC130 and one for the right-seat of the AS350, to enhance the transition training from visual to instrument flight conditions.

Inadvertent instrument meteorological conditions avoidance training

Microflite required all their pilots to complete the Helicopter Association International online academy ’56 Seconds to Live’ training. The stated goal of this course was for pilots to ‘Recognize and avoid the trap of departing into, or continuing VFR flight into deteriorating weather conditions’.

Task rejection policy

Microflite introduced a company ‘Task rejection’ policy statement into their operations manual. The policy requires their pilots to cancel VFR flights if it is determined that VMC cannot be assured for the planned flight. It also provides management support to their pilots for cancelling their flights if the risk profile is deemed unsafe by the pilot in command.

Airbus helicopter training centre approval

Microflite obtained an Airbus Helicopter Training Centre approval. This approval provides them with greater access to the manufacturer’s technical resources for training their staff and operating and maintaining their helicopter fleet.

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