Collision with terrain

Preliminary report published: 8 October 2019

This preliminary report details factual information established in the investigation’s early evidence collection phase and has been prepared to provide timely information to the industry and public. Preliminary reports contain no analysis or findings, which will be detailed in the investigation’s final report. The information contained in this preliminary report is released in accordance with section 25 of the Transport Safety Investigation Act 2003.
 

What happened

On 6 August 2019, at 1103 Eastern Standard Time,^[1] a Liberty XL-2, registered VH-XLK (XLK), departed Moruya Airport, for a rural property near Braidwood, New South Wales (Figure 1). The pilot was the sole occupant and had been flying in company with another pilot and his aircraft on a social, multi-day touring flight of the New South Wales hinterland, alpine and southern coast regions.

The accompanying pilot landed his aircraft on a private landing area at the Braidwood property about 15 minutes prior to the arrival of XLK. That pilot advised the pilot of XLK that the landing area was undulating and not suitable for his aircraft type. At about 1126, witnesses on the ground (which included the accompanying pilot) observed XLK circling the landing area. On the second orbit, the aircraft was observed to slow and begin to lose height. At about 500 ft above ground level, and after crossing the marked end of the landing area, the left wing dropped and the aircraft entered a steep rotating descent. The pilot was unable to recover control of the aircraft before it impacted terrain.

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

The witnesses at the landing area were first to arrive at the scene, however the pilot had sustained fatal injuries. The aircraft was destroyed.

Site and wreckage examination

The accident site was located in relatively flat and open farmland, approximately 9 km north-east of Braidwood (Figure 2). The ATSB conducted an examination of the site and wreckage and identified that the:

• ground impact marks indicated that the aircraft had impacted terrain nose‑down, upright, with counter‑clockwise rotation
• left wing separated from the airframe on impact with the terrain
• flaps were in the retracted position.

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

A damaged electronic flight bag was recovered from the accident site and an engine control unit was removed from the aircraft and taken to the ATSB’s technical facility in Canberra for examination.

Figure 2: Accident site

Source: ATSB

Further investigation

The investigation is continuing and will include:

• analysis of the downloaded data from the engine control unit and other electronic devices
• examination of the aircraft flight instruments and a stabiliser trim component
• examination of the pilot’s qualifications, experience and medical history
• assessment of the aircraft’s flight performance characteristics
• examination of aircraft maintenance and operational records.

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

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 2019 Ownership of intellectual property rights in this publication Unless otherwise noted, copyright (and any other intellectual property rights, if any) in this report publication is owned by the Commonwealth of Australia. Creative Commons licence With the exception of the Coat of Arms, ATSB logo, and photos and graphics in which a third party holds copyright, this publication is licensed under a Creative Commons Attribution 3.0 Australia licence. Creative Commons Attribution 3.0 Australia Licence is a standard form licence agreement that allows you to copy, distribute, transmit and adapt this publication provided that you attribute the work. The ATSB’s preference is that you attribute this publication (and any material sourced from it) using the following wording: Source: Australian Transport Safety Bureau Copyright in material obtained from other agencies, private individuals or organisations, belongs to those agencies, individuals or organisations. Where you wish to use their material, you will need to contact them directly.

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1. Eastern Standard Time (EST): Coordinated Universal Time (UTC) + 10 hours.

On 13 June 2019, a BRM Aero Bristell NG5, registered G-OJCS, departed Kilrush Airfield, County Kildare, Ireland, for a local flight. Subsequently, recovered data showed that, after a series turns, the engine power was reduced as the aircraft maintained about 3,200 ft, with a reducing airspeed. The aircraft rapidly lost height, and impacted terrain about 30 seconds later. Both occupants were fatally injured and the aircraft was destroyed. There was no fire.

To assist with evidence collection, the Air Accident Investigation Unit (AAIU) Ireland requested an Accredited Representative from the Australian Transport Safety Bureau (ATSB) be appointed. To facilitate this request, the ATSB initiated an external investigation under the provisions of the Transport Safety Investigation Act 2003.

The AAIU has completed its investigation and the final report is available on its website.

Any enquires relating to the investigation should be directed to the Air Accident Investigation Unit Ireland.

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The information contained in this update is released in accordance with section 25 of the Transport Safety Investigation Act 2003 and is derived from the AAIU’s investigation of the occurrence.

Safety summary

What happened

On 22 June 2019, a Robinson Helicopter Company R22, registered VH-HHQ, departed Kutchera Station, Queensland to perform mustering operations. During mustering, as the pilot was manoeuvring the helicopter, the right tail rotor (or anti-torque) pedal cracked and became stuck. The pilot was unable to dislodge the pedal and prepared for an immediate landing in accordance with the stuck pedal procedure. Just prior to landing, the helicopter struck a tree and became uncontrollable. The aircraft impacted the ground and although the pilot was uninjured, the helicopter was substantially damaged.

What the ATSB found

Following examination of the helicopter by the maintenance organisation, a significant fracture was noted at a weld located on a right angle join between two sections of tube. The right pedal was removed from the helicopter and sent to the ATSB for further examination and testing. The ATSB found that the pedal had fractured as a result of a fatigue failure, which had initiated at the welded joint, and progressed until the remaining section of the tube could no longer sustain the in‑service loads. It was considered likely that a pre-existing crack had initiated at the highest stress part of the component, and had opened up following the load applied during the manoeuvre described by pilot, rendering the pedal unserviceable.

The tail rotor pedal had been recently inspected as part of routine maintenance and while it was considered likely that the developing crack was present, it was not detected at that inspection. However, it was considered that this was due to the inherent difficulties associated with inspections at the location of the cracking.

What has been done as a result

While not required as part of the routine inspections, the maintenance organisation has added the tail rotor pedals to the list of components that undergo magnetic particle inspection at each 2,200‑hour overall.

Safety message

The location of the fatigue crack in this accident highlighted the need to be vigilant when performing inspections in difficult or hard to reach places. In the case of the tail rotor pedal, the inspection was made difficult due to the location, and required a torch and mirror to inspect a matte black surface.

Additionally, the quick thinking actions of the pilot following the failure resulted in a good outcome, with no injuries reported.

The investigation

The occurrence

On 22 June 2019, the pilot of a Robinson Helicopter Company R22 helicopter, registered VH‑HHQ, departed Kutchera Station, Queensland to perform mustering operations. While mustering, the pilot applied a small amount of right tail rotor (or anti-torque) pedal^[1] to manoeuvre the helicopter to turn back in the opposite direction. During this time, and as the pilot reported repositioning in the seat, the right pedal cracked, which caused it to bend forward and become stuck. The pilot grabbed the right pedal in an attempt to free it and allow the use of the left pedal, but was unable to do so. The pilot continued the flight to the nearest safe cleared area to land and commenced the jammed pedal procedure.^[2]

When about 50 ft above ground level, as the pilot was preparing to perform a running landing,^[3] it was reported that a gust of wind hit the helicopter from an angle, causing it to spin. The helicopter then hit a tree and then became uncontrollable before coming to rest on the ground. The pilot shutdown the helicopter and exited. There were no reported injuries, however, the helicopter was substantially damaged.

Following examination of the helicopter by the maintenance organisation, a significant fracture was noted on the right tail rotor pedal assembly at a weld located on a right angle join between two sections of thin walled tube (Figure 1). This join was between the vertical section of tube where the pilot places their foot, and the horizontal tube connecting to the tail rotor controls, and sits slightly below the cabin floor. The pedal was removed from the helicopter and sent to the ATSB’s technical facilities in Canberra for further examination and testing.

Figure 1: Fractured right tail rotor pedal as installed on VH-HHQ

Source: Operator, annotated by the ATSB

Context

Tail rotor pedal examination

The ATSB’s initial examination of the right tail rotor pedal (part number A330-1), which had a matte black surface, found that:

• The weld had fractured on the side of the pedal closest to the pilot seat (Figure 2).
• While the fracture was not through the entire section of the tube, the pedal assembly was no longer capable of maintaining loads and transferring pilot inputs.
• The pedal did not show any evidence of dints, scratches or other signs of mechanical damage.
• Wear, in the form of missing paint and a shiny smooth surface, was observed on the pedal surface in contact with the pilot’s foot.

Some evidence of corrosion product was observed within the tubes. Robinson advised that this was the first known occurrence of internal corrosion. As part of the manufacturing process, to ensure the removal of any residual moisture, a small breather hole was left open, and the entire assembly heated to remove any internal moisture, before the breather hole was welded shut. Robinson also advised that the amount of corrosion observed appeared to be more than residual moisture from manufacture. They stated that, as the tubes were completely sealed, there was no inspection to detect internal corrosion.

Figure 2: Right tail rotor pedal as received by the ATSB, showing the location of the fracture

Source: ATSB

Following the initial examination, the pedal was fractured in the ATSB laboratory to separate and expose the two fracture surfaces. The majority of the fracture surface was discoloured and exhibited evidence of pre-existing cracking consistent with a fatigue failure (Figure 3). While the surface features were difficult to distinguish, the discolouration was indicative that the crack had been present for some period of time prior to the failure. While it appeared that the crack had initiated along the edge of the weld, no exact origin could be identified. However, the location of cracking was coincident with the location where the pilot input on the vertical tube was transferred to the horizontal tube, which is connected to the tail rotor push-pull tube assembly. As such, this area was subject to the largest torsional bending stress.

Figure 3: Right tail rotor pedal fracture surface following fracture by the ATSB

Source: ATSB

Following the examination of the fracture surface, it was then sectioned in the region adjacent to the likely origin for further inspection. The general fracture surface profile was consistent with a fatigue fracture. While the internal surface of the tube exhibited some evidence of pitting and general corrosion, there was no evidence that the crack initiated at one of these locations. Additionally, as the tubes were completely sealed, it was more likely that the corrosion product was the result of moisture ingress following the initiation of the fatigue crack.

The microstructure of the weld and tube was consistent with a low alloy steel in the heat-treated condition. A microhardness traverse test was conducted from the fracture surface through the weld heat affected zone into the parent metal and was consistent with the material type in the heat-treated condition. These observations complied with the information provided by the manufacturer.

Maintenance history

The helicopter (serial number 4071) had accumulated 5,828.4 hours total time-in-service at the time of the accident. Inspection of the tail rotor pedals was performed at both the 100-hourly inspection and 2,200-hour overhaul. The most recent 100-hourly inspection was performed 37.2 hours prior to the failure, while the 2,200-hour overhaul was completed in February 2017. At the 100-hourly inspection, the maintenance manual task for the pedals stated:

Inspect condition. Verify no cracks. Verify security and operating clearance.

There was no requirement to remove the bearing block cover plates, an access cover on the floor of the cabin, covering the horizontal portion of the rail rotor pedal. While the location of cracking in this occurrence was slightly under the cabin floor, Robinson advised that the affected weld would normally be visible using a torch and a mirror during the inspection. They also advised that the pedal needed to be moved forward and backward to see both sides. In addition to the 100-hourly inspections, at each 2,200-hour overhaul the pedals were removed for closer inspection.

The manufacturer further advised that, where maintenance was undertaken at a field service centre, as was the case for VH-HHQ, the pedals were subject to visual inspection only. However, if the overhaul was performed at the Robinson factory (not available in Australia), the pedals would be examined using a magnetic particle inspection (MPI).^[4] This technique would be more likely to identify surface defects, as the paint would be removed prior to the testing, and the contrasting nature of the test medium would mean that cracks would be highly visible.

Similar failures

Robinson advised that they were aware of previous in-service fractures near the weld, however, the cause was either attributed to a modification to the assembly which involved some type of pedal extension (one case) or impact/mechanical damage. A search of the Civil Aviation Safety Authority’s defect report service and ATSB occurrence databases for the previous 10 years did not identify any other similar failures.

Safety analysis

While manoeuvring during mustering operations, the right tail rotor pedal failed and became stuck. The pilot elected to land immediately, but during this, the helicopter struck a tree. The helicopter became uncontrollable and impacted the ground, resulting in substantial damage.

The tail rotor pedal failed as a result of a fatigue failure at a right angle welded joint between two sections of thin walled tube. While the ATSB’s examination identified that the fatigue failure had initiated adjacent to the weld line, the exact origin could not be determined. This location of the cracking was also coincident with the point of maximum torsional bending stress in normal operation. The microstructure and hardness of the tube and weld were consistent with the requirements as specified by the manufacturer.

The pedal had undergone a visual examination at the most recent 100-hourly inspection. While it was likely the crack was present at this inspection, the nature and location of the crack would have made it inherently difficult to detect. The developing fatigue crack would have initially presented as a hairline feature, and it was located on a matte black surface, at a change in section slightly below the level of the cabin floor.

Findings

From the evidence available, the following findings are made with respect to the tail rotor pedal failure and collision with terrain involving Robinson R22 helicopter, VH HHQ near Kutchera Station, Queensland, on 22 June 2019.

Contributing factors

• While conducting mustering operations, the right tail rotor pedal failed due to fatigue cracking. During the subsequent emergency landing, the helicopter struck a tree and became uncontrollable, before coming to rest on the ground.
• Due to undetermined reasons, a fatigue crack had initiated adjacent to a weld at a high stress location on the pedal. It was likely that the crack had been present at the most recent maintenance inspection, but the location of the weld may have made it difficult to detect in-situ.

Safety actions

Increased maintenance inspections

As a result of this accident, the maintenance provider has advised that, although not required by the maintenance manual, the tail rotor pedal assembly will now be included with other components that are sent for magnetic particle inspection at every 2,200-hourly overhaul.

Sources and submissions

Sources of information

The sources of information during the investigation included the:

• the pilot
• Robinson Helicopter Company
• the helicopter owner and maintainer.

References

United States Federal Aviation Administration (2019), Helicopter Flying Handbook, FAA-H-8083-21B.

Submissions

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

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

• the pilot
• the helicopter owner
• the helicopter maintainer
• Robinson Helicopter Company
• National Transportation Safety Board
• Civil Aviation Safety Authority.

Any submissions from those parties were reviewed and, where considered appropriate, the text of the draft 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 2020 Ownership of intellectual property rights in this publication Unless otherwise noted, copyright (and any other intellectual property rights, if any) in this report publication is owned by the Commonwealth of Australia. Creative Commons licence With the exception of the Coat of Arms, ATSB logo, and photos and graphics in which a third party holds copyright, this publication is licensed under a Creative Commons Attribution 3.0 Australia licence. Creative Commons Attribution 3.0 Australia Licence is a standard form licence agreement that allows you to copy, distribute, transmit and adapt this publication provided that you attribute the work. The ATSB’s preference is that you attribute this publication (and any material sourced from it) using the following wording: Source: Australian Transport Safety Bureau Copyright in material obtained from other agencies, private individuals or organisations, belongs to those agencies, individuals or organisations. Where you wish to use their material, you will need to contact them directly.

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1. The tail rotor pedal is used to change the pitch of the tail rotor, in order to control the torque of the main rotor and to provide movement about the yaw axis of the helicopter.
2. This procedure is required where a mechanical failure leads to the inability of the pilot to change or control tail rotor thrust even though the tail rotor is still capable of producing anti-torque thrust. The Robinson Helicopter Company R22 Pilot’s Operating Handbook did not include any guidance related to jammed (or stuck) pedals. The United States Federal Aviation Administration Helicopter Flying Handbook included a generalised description of procedures when more specific procedures were not available:
   The landing profile for a stuck neutral or a stuck right pedal is a low-power approach terminating with a running or roll-on landing. The approach profile can best be described as a shallow to normal approach angle to arrive approximately 2–3 feet landing gear height above the intended landing area with a minimum airspeed for directional control. The minimum airspeed is one that keeps the nose from continuing to yaw to the right.
3. A running landing is used to transition from forward flight to landing on the surface when there may not be sufficient power available to sustain a hover. This manoeuvre may also be conducted in some emergency situations such as certain tail rotor failures or stuck pedals.
4. Magnetic particle inspection is a non-destructive testing process widely used to inspect ferromagnetic materials, such as iron, nickel, cobalt and some of their alloys, for surface and shallow sub-surface discontinuities.

Preliminary report published 19 July 2019

This preliminary report details factual information established in the investigation’s early evidence collection phase and has been prepared to provide timely information to the industry and public. Preliminary reports contain no analysis or findings, which will be detailed in the investigation’s final report. The information contained in this preliminary report is released in accordance with section 25 of the Transport Safety Investigation Act 2003.

Sequence of events

On 5 June 2019, a Yakovlev Aircraft Factories Yak-52, registered VH-PAE, was conducting a private flight from Southport airfield, Queensland. The aircraft departed the airfield at about 0945 Eastern Standard Time (EST),^[1] with a pilot and one passenger on board. The flight was intended to take about 30 minutes, and include a low-level scenic flight north along the coast from Broadbeach to the Jumpinpin channel area, and then seawards off Jumpinpin for some aerobatic manoeuvres, before returning to Southport airfield (Figure 1). A second passenger was waiting at the airfield to complete a similar trip once the aircraft had returned.

When the aircraft had not returned by the designated time, the second passenger became concerned and started asking members at the Southport Flying Club if they had heard anything. At about 1310, a representative from the club contacted Airservices Australia about the overdue aircraft and at 1400, the Australian Maritime Safety Authority’s Joint Rescue Coordination Centre initiated search and rescue operations. At about 1630, part of the propeller was located on the eastern side of South Stradbroke Island. In the following days, additional wreckage was also recovered from the same location, as well as the pilot and passenger, both of whom had been fatally injured.

Figure 1: Map highlighting locations of interest for the proposed flight of VH-PAE

Source: Google earth, annotated by the ATSB

Pilot information

The pilot held a current Private Pilot Licence (Aeroplane) issued on 23 May 2016. The pilot also held a Class 2 Aviation Medical Certificate that was valid until 1 May 2021. The available information from the pilot’s logbook indicated that he had about 490 hours total aeronautical experience, including 38 hours in VH-PAE. The pilot had received both a spinning and aerobatic endorsement in January 2019.

Aircraft information

The Yakovlev Aircraft Factories Yak-52 was an all-metal, two-seat, low-wing aircraft, powered by an air-cooled radial M-14P engine driving a two-bladed, variable-pitch wooden propeller. VH-PAE (Figure 2) (serial number 822001) was manufactured in 1982 and first registered with the Civil Aviation Safety Authority on 5 April 2017. The aircraft was registered to the pilot on 5 July 2018.

The most recent entry on the maintenance release was 5 days prior to the accident (on 31 May 2019) and showed that the aircraft had accumulated 1,164.2 hours’ total time‑in‑service.

Figure 2: VH-PAE

Source: Matthew Coughlin

Wreckage information

The items of wreckage recovered were taken to a secure facility by the Queensland Police Service for examination by the ATSB. These items included:

• a section of the left side of the fuselage and the tail section (Figure 3)
• a section of the right wing
• two seat cushions
• pneumatic system cylinders
• a number of wooden propeller pieces.

The initial examination found that the tail of the aircraft exhibited significant damage on the vertical and right horizontal stabilisers, and it had remained attached to the fuselage by flight control cables. The significant disruption to the aircraft was indicative of a high-speed impact.

The ATSB removed a number of components from the wreckage for further examination, including various instruments from the fuselage section. The aircraft was not equipped with a flight data or cockpit voice recorder, nor was it required to be.

Figure 3: Some of the recovered pieces of VH-PAE

Source: ATSB

Ongoing investigation

The investigation is continuing and will include consideration of the following:

• recovered aircraft components
• aircraft maintenance documentation
• pilot qualifications, experience, and medical history
• weather conditions
• witness observations
• research and similar occurrences.

Acknowledgements

The ATSB acknowledges the support of the Queensland Police Service for their assistance during this investigation.

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

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 2019 Ownership of intellectual property rights in this publication Unless otherwise noted, copyright (and any other intellectual property rights, if any) in this report publication is owned by the Commonwealth of Australia. Creative Commons licence With the exception of the Coat of Arms, ATSB logo, and photos and graphics in which a third party holds copyright, this publication is licensed under a Creative Commons Attribution 3.0 Australia licence. Creative Commons Attribution 3.0 Australia Licence is a standard form licence agreement that allows you to copy, distribute, transmit and adapt this publication provided that you attribute the work. The ATSB’s preference is that you attribute this publication (and any material sourced from it) using the following wording: Source: Australian Transport Safety Bureau Copyright in material obtained from other agencies, private individuals or organisations, belongs to those agencies, individuals or organisations. Where you wish to use their material, you will need to contact them directly.

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1. Eastern Standard Time (EST): Coordinated Universal Time (UTC) + 10 hours.

Safety summary

What happened

On 21 May 2019, while engaged in a planned cull of feral animals in Kakadu National Park, Northern Territory, a crew of three were using a Bell 206B3 JetRanger helicopter for aerial platform shooting. While the helicopter was operating at about 50 ft above the ground, the engine decelerated to idle, resulting in an immediate loss of power, and subsequent collision with terrain. The three occupants (pilot, shooter and spotter) were seriously injured.

What the ATSB found

The engine power loss was due to a leak created by a loose union on an engine reference air line. During maintenance 4 days prior to install a power turbine governor (PTG), the union, which was downstream of the work completed, had not been checked for tightness. Potentially associated with distractions in the hangar at the time, an independent inspection following installation of the PTG was probably not conducted, and document verification processes did not detect that the independent inspection had not been recorded.

The cabin was not well prepared for the subsequent collision with terrain, with a range of factors exacerbating the occupants’ injuries or increasing risk. For example, the Director of National Parks required shooters and spotters to wear helmets, but helmets were not provided or used on a routine basis. Safety issues were also identified with the ambiguous wording of the instrument permitting harness use (issued by the Civil Aviation Safety Authority), and renewal of aerial platform shooting approvals without recurrent emergency training.

Additionally, the ATSB found that the Director of National Parks did not actively manage the risk of the aerial culling task, or effectively supervise the operation. As a result, an increase in the number of crew, a change in helicopter type and change of helicopter operator all progressed without requisite risk management. This exposed crew to avoidable harm during low-level aerial shooting operations.

What has been done as a result

The operator ordered an immediate fleet wide check of the security of all flexible and rigid reference air lines in its engines. Additionally, the approved maintenance organisation improved delivery of human factors training for engineers by contracting an external provider to deliver the course.

The Civil Aviation Safety Authority (CASA) has planned action to resolve the ambiguity associated with the instrument permitting harness use, and to require operators to ensure task specialists are trained in normal and emergency procedures. In addition, the operator has taken action to ensure all crew members are aware of the risk associated with using only a harness instead of a seat belt.

The Director of National Parks (DNP) immediately suspended aerial culling activities. In December 2019, the DNP commenced an internal review of standards of practice relating to aerial culling activity and personal protective equipment, and reaffirmed its requirement for the use of helmets during any future culling activities. The DNP has also undertaken a specialist aviation safety review into its aerial culling operation and is conducting ongoing review of its risk management policy and related aspects.

Safety message

Assured airworthiness and preparation of aircraft operating at low-level is paramount. Knowing that maintenance activities carry risk of error, independent inspection is a vital risk control. Inspections must be designed and conducted in a way that will capture critical issues, and visual inspections will not always be enough.

Any organisation that requires staff to engage in high-risk aviation activities should obtain professional advice on task design, actively manage risk, and provide appropriate equipment.

The occurrence

Prior to departure

On 21 May 2019, a Bell B206B3 JetRanger helicopter, registered VH-FHW and operated by Jayrow Helicopters, was being used for an aerial (feral animal) culling task in Kakadu National Park (KNP), Northern Territory (Figure 1). The helicopter operator provided helicopters and pilots under contract to the Director of National Parks (DNP), and the other crew involved in conducting the tasks were employees of Parks Australia.

Maintenance was conducted on VH-FHW by the helicopter operator in Darwin on 16 May 2019, and the helicopter had flown 4.7 hours since that maintenance. The helicopter was repositioned to Jabiru and then Mary River Ranger Station on the afternoon of 20 May and used for aerial culling tasks.

The plan for 21 May was to use the helicopter again as an aerial platform to shoot feral animals in a prescribed area within KNP. The pilot reported that, prior to departure, they refuelled the helicopter and conducted a pre-flight inspection, and no defects were observed. The two aerial culling crew, a shooter and a spotter, both licensed aerial platform shooters and KNP rangers, loaded the helicopter with the weapons, ammunition, and supplies.

Before departure, the pilot engaged the spotter and shooter in a safety briefing. The spotter then sat in the front left seat, the pilot in the front right, and the shooter in the rear right. The pilot and spotter both wore a four-point seatbelt with upper torso restraints. The shooter wore a fall arrest harness (harness) to allow flexibility of positioning in the open doorway for the shooting task.

Figure 1: Kakadu National Park and location of accident

Source: Google Earth, annotated by the ATSB.

Accident flight

At about 0913 Central Standard Time,^[1] the helicopter departed Mary River Ranger Station. The search for animals was conducted at 500 ft above ground level (AGL).

At 0923 the crew found a mob of feral horses, and the animals were mustered into a favourable location. The crew reported that this task went smoothly, and the animals were easy to manoeuvre. The mustering was conducted at about 300 ft AGL. Once the animals were in position, the crew began the culling task, and the shooting took place at about 50 ft AGL (Figure 2).

Figure 2: VH-FHW flight path

Source: Google Earth and the operator, annotated by the ATSB

At about 0957, 44 minutes into the flight, the helicopter was at a height of about 50 ft AGL over a lightly wooded area. The pilot reported that the helicopter’s engine started decelerating to idle, and the spotter recalled hearing the engine surge. The pilot’s immediate response was to ensure the throttle was fully open (which it was). The pilot quickly diagnosed the situation as a genuine emergency.

The pilot announced ‘we’re losing power and going over there’, referring to a small clearing slightly left of the nose in their direction of travel. The pilot managed the rotational energy remaining in the rotor system and the forward speed of the helicopter to reach the clearing.

The right side of the helicopter impacted a tree on the edge of the clearing, and then landed heavily in a level attitude. All three occupants were seriously injured, and the helicopter was destroyed (Figure 3).

Post-impact events

The spotter recalled, after impact, being covered in fuel and having heavily restricted movement in the neck and body. The spotter exited the helicopter and noted that the pilot and shooter were unconscious.

The spotter reported attempting to activate a handheld emergency position indicating radio beacon (EPIRB), but given that their corrective glasses were lost, the activation instructions were unable to be read. The spotter returned to the helicopter as the pilot and shooter became conscious. The pilot and spotter between them ensured the helicopter’s emergency locator transmitter (ELT) was on, and the spotter tried to make the pilot comfortable.

The spotter tried to assist the shooter in the back of the helicopter but was unable to do so. The rifle was still in the helicopter, and the barrel had punctured the floor of the cabin. The spotter made the weapon safe by removing the magazine and selecting the safety catch. The spotter located a daypack, which contained a park radio, then made a MAYDAY call which initiated the emergency response from KNP personnel.

The joint rescue coordination centre (JRCC) detected the signal from the ELT and tasked a passing Royal Australian Air Force (RAAF) C130J to search for the source. The RAAF aircraft’s crew found the wreckage of VH-FHW and directed a nearby helicopter to the scene. The crew on the second helicopter were able to provide immediate assistance. Meanwhile, the RAAF aircraft was also in communication with an inbound emergency medical service (EMS) helicopter.

The EMS helicopter arrived at the accident site about 5 minutes later. Medical professionals on board were winched from the helicopter to care for the injured personnel and prepare them for transport.

Following news of the event, the fuel supply at Jabiru was closed for testing as a precaution. This prevented the EMS helicopter from refuelling at Jabiru. Combined with limited access to site, the delays in refuelling meant extraction of the injured crew took longer than desired. The crew eventually reached hospital in Darwin at around 1900, about 9 hours after the collision with terrain.

Figure 3: VH-FHW following collision with terrain

Source: Northern Territory Police

________________

1. Central Standard Time: Coordinated Universal Time (UTC) + 9.5 hours.

Context

Personnel information

Pilot

The pilot held a valid Commercial Pilot Licence (Helicopter), and a current Class 1 Aviation Medical Certificate. Over a 40-year career, the pilot had accumulated over 18,000 hours flight time. The pilot first worked for the operator on a full-time basis in 1994, before then flying for other operators. More recently, the pilot was inducted to the operator as a contractor in 2014.

The pilot had a significant level of experience in low-level and remote area helicopter operations, including extensive experience in aerial shooting programs. The last proficiency check in single engine helicopters was conducted on 26 March 2018 (valid to 31 March 2020), and the last proficiency check for low-level helicopter operations was conducted on 1 November 2018 (valid to 1 November 2020). No problems were noted during either proficiency check.

Shooter and spotter

The shooter was a highly experienced Kakadu National Park (KNP) ranger who was first licenced for aerial platform shooting in 2002.

The spotter had over 30 years’ experience as a KNP ranger, and became a licenced aerial platform shooter in 2000.

Both the spotter and shooter had been trained in aerial platform shooting. The Civil Aviation Safety Authority (CASA) had issued permission to both personnel for carriage and discharge of a firearm from an aircraft. The conditions of permission required that, before shooting from an aerial platform, they must:

1. have completed training a syllabus of training by an accredited aerial platform shooting training organisation; or by the pilot in command for the type of aircraft to be used (aeroplanes or helicopters); and
2. retain a copy of this training course and evidence of its completion…; and
3. within the previous 2 years:
4. have conducted shooting from an aircraft; or
5. requalified under the training course mentioned above.

The permissions were valid for 3 years. The aerial platform shooting course was only undertaken once by both crew for the initial issue of their permissions. Permissions were then renewed by shooting from aircraft within the 2-year period. The crew also completed ground-based firearms safety courses. The spotter and shooter had not refreshed their emergency training for aerial platform shooting since the initial issue of their permissions in 2000 and 2002, respectively. They also had not conducted drills on the ground simulating a forced landing to prepare them for an actual event.

Organisational and management information

Kakadu National Park management

The Kakadu National Park (KNP) Board of Management developed, drafted, and monitored management plans for the park. The majority of land in the park was leased to the Director of National Parks (DNP) for management as a Commonwealth reserve. The KNP Board of Management worked with the DNP under a joint management framework.

The DNP was a corporate Commonwealth entity that existed under Part 19 of the Environment Protection and Biodiversity Conservation Act 1999. This entity administered, managed, and controlled the park. The DNP was supported in carrying out its functions by the Parks Australia Division of the Department of Agriculture, Water, and the Environment.

Parks Australia staff operated in the KNP as rangers under direction from the DNP and with oversight from the Board of Management.

Helicopter operator

Jayrow Helicopters held an air operator’s certificate (AOC) that authorised it to conduct a wide range of low-level aerial work activities using a wide range of helicopter types. These activities included aerial spotting and feral animal control (aerial culling).

The DNP tendered for helicopter services in late 2016 and contracted the helicopter operator to support a range of park activities under a deed of standing offer in May 2017.

The operator had provided helicopter services in remote areas of Australia for 55 years. Adaptations to the environment underpinned the expansion of its business into remote areas in the early days. Since then, its services expanded to all areas of onshore and offshore helicopter operations. The operator had a quality management system and safety management system, with a full-time safety and quality manager.

The helicopter operator’s operations in KNP were conducted from Jabiru, with management based in Darwin. The head office of the operator was in Melbourne, Victoria.

The DNP engaged aviation industry auditors to conduct second-party audits of the helicopter operator.

Approved maintenance organisation

The approved maintenance organisation was owned and operated by the same entity that operated the helicopters. The engineering manager, and the head of aircraft airworthiness and maintenance control, were based at head office in Melbourne. A senior base engineer and three full-time engineers were in place at the Darwin base. A contract engineer was temporarily employed to support a busy period of work at the time of the accident.

It was normal for most maintenance of the operator’s helicopters to take place in Darwin.

Helicopter and maintenance information

General information

VH-FHW was one of two helicopters taking part in the aerial culling program. VH-FHW was a Bell Helicopter Company 206B3 JetRanger, serial number 2838. It was manufactured in the United States in 1979, and first registered in Australia in 1980. VH-FHW had seating for a pilot and four passengers, and it was powered by one Rolls-Royce 250-C20J turboshaft engine. At the time of the accident the helicopter had accumulated about 16,916 hours total time in service (TTIS).

For the aerial shooting task, the rear right door of the helicopter was removed.

Wreckage inspection

The ATSB did not conduct an on-site examination of the wreckage. On 30 May 2019, under the guidance of the ATSB, and supervision of the Northern Territory Police, the police, Parks Australia rangers and the operator returned to the accident site to inspect the wreckage.

During the inspection of the wreckage, it was found that an engine reference air line^[2] union between the power turbine governor and the accumulator was loose (Figure 4). No other pre-existing problems with the helicopter were reported to be found during the wreckage examination.

Figure 4: Loose reference air union

Source: Operator, annotated by the ATSB

Maintenance information

The helicopter underwent scheduled maintenance in Darwin on 16 May 2019, 5 days prior to the accident. At that time, the helicopter had accumulated 16,911 hours TTIS. The planned maintenance included a clean of the tail rotor assembly, a 100-hour airframe inspection, and a 150-hour engine inspection.

All planned maintenance activities were recorded in a work pack. The package was prepared in advance of the maintenance and outlined the tasks to be completed. The work was conducted by four licenced aircraft maintenance engineers over a full day. The engineers signed each element as it was completed.

During this maintenance, it became apparent that the power turbine governor (PTG) and linear actuator required replacement due to stiff operation. As the PTG change was introduced on the day of maintenance, a separate work sheet was produced for that task.

Requirements of PTG install

The PTG is designed to keep the power turbine rotating assembly in a gas turbine engine rotating at a constant speed throughout changing power demands. The PTG senses engine speed changes by sensing engine reference air pressure (from the engine compressor), and it sends a signal to the fuel control unit (FCU) to adjust the fuel flow to the engine accordingly. A linear actuator assists the PTG by linking it to the pilot’s controls, allowing the PTG to adapt to changing power demands more efficiently.

The maintenance instructions for the replacement of the PTG included a warning in relation to the installation (Figure 5). The engine manufacturer (Rolls-Royce) advised that this warning was repeated throughout its 250-C20 Series Operation and Maintenance manual and applied to all union connections. This included both ends of all lines installed on the PTG. A loose union could create a leak, which would in turn cause engine power loss.

Figure 5: PTG installation warning

Source: Rolls-Royce 250-C20 Series Operation and Maintenance Manual

Replacing the PTG requires removing the air carrying flexible hose and pipes from the old unit and replacing them on the new unit. It is normal practice in maintenance to disconnect the PTG and loosen the other end of the lines (such as the engine reference air line) to allow manipulation of the lines for removal and refitting.

Replacement of the PTG on VH-FHW

The maintenance engineer that conducted the PTG replacement was a licenced aircraft maintenance engineer (LAME) with 27 years’ experience in Australia and overseas. They had maintained the operator’s fleet at the remote base in Darwin for 4 years.

The engineer stated that it was not necessary to loosen the other end of the flexible engine reference air line when replacing the PTG and that the reference air line adjacent to the accumulator was not touched at any point during the maintenance on 16 May 2019.

Other recent activities that could have loosened or dislodged the reference air line union were a turbine module change on 3 July 2015, a compressor module change on 6 July 2015, and a PTG change on 3 May 2018.

Human factors in engineering

The approved maintenance organisation had self-paced human factors training material for its engineers. The LAME that conducted the PTG replacement on 16 May 2019 completed that training on 12 January 2016.

In a Civil Aviation Safety Authority (CASA) published guide (Safety behaviours: human factors for engineers), the stated average rate of leaving a loose nut during maintenance was one in 250. The guide stated that such lapses were most commonly encountered when a distraction was introduced to the maintenance task.

The engineer that replaced the PTG stated that distraction and interruption were existent at the engineering facility where the maintenance was conducted. Such interruptions were witnessed by ATSB investigators during the course of the investigation.

Independent inspection requirements

Civil Aviation Regulation (CAR) part 42G (Flight control systems: additional requirements), mandated that an aircraft’s flight controls required independent inspection following maintenance activities. No other systems were required by regulation to undergo independent inspection. The qualification requirements of people conducting independent inspections were detailed in schedule 8 of CAR 42ZC (Maintenance on Australian aircraft in Australian territory). The qualified parties were essentially licenced engineers and pilots.

The maintenance organisation’s Engineering Procedures & Control Manual allowed appropriate persons to conduct independent inspections as per CAR 42G. It stated that the certifying LAME was responsible for ensuring the person conducting the independent inspection was qualified, trained, and briefed. It was the engineer’s responsibility to brief the pilots, and train them to conduct the independent inspections required. This was managed on an as needed basis without standardisation or formal support.

As human factors principals have been increasingly applied to the practice of aircraft maintenance over the years, the aviation industry has recognised the benefit of expanding the use of independent inspections beyond flight controls. Accordingly, many maintenance organisations have increased independent inspection requirements beyond the regulatory requirements to all critical maintenance tasks. Additionally, the Flight Safety Foundation’s voluntarily adopted Basic Aviation Risk Standard (BARS) required registered operators (of that standard) to identify critical maintenance tasks (CMT), and stated:

Maintenance tasks that involve assembly or disturbance of any system that may affect the flight path, attitude or propulsive force, which, if errors occurred, could result in a failure, malfunction, or defect that would endanger the safe operation of the aircraft must be considered as a CMT.

The maintenance organisation’s Engineering Procedures & Control Manual, last updated 10 January 2018 and valid at the time of the accident, stated that ‘second inspection’ requirements were added to the manual on 7 October 2008. The manual specified additional independent inspection requirements over and above the requirements of CAR 42G. These included:

1. Main rotor, tail rotor systems and drive-train components.
2. All powerplant controls, including MFCUs, AFCUs, FCUs, EECUs, etc
3. All powerplant electrical connectors
4. All closed areas prior to refitment of panels/assemblies/components, etc.
5. Fluid line fittings.

Note: Whether the complete system or only part of a system has been disturbed, the independent inspectors should thoroughly check the system and adjacent areas, ensuring that all tools, equipment and materials have been accounted for and removed.

Independent inspection of maintenance on 16 May 2019

The work pack generated at the time of maintenance on 16 May 2019 carried space for signing off after independent inspection of critical maintenance tasks. Two tasks relating to the reassembly of the tail rotor pitch control were identified for independent inspection. These items were signed as carried out by the LAME who completed the work and signed as inspected by a second LAME.

There was no documentary evidence to show independent inspection of the PTG install had taken place. The LAME that conducted the task stated that a pilot had conducted a visual inspection of the installation, and that due to distraction from unrelated operational demands the signing of the paperwork was missed.

The pilot who was nominated as having done the inspection stated that they had done duplicate inspections at times for the engineers, but it was not a common occurrence. They could not recall conducting a visual inspection of the PTG installation or any other aspect of VH-FHW during its maintenance on 16 May.

Verification of maintenance activities

The logbooks for all aircraft were held at head office in Melbourne. All maintenance documentation from the Darwin base was sent to Melbourne for verification prior to a maintenance release being issued for an aircraft. Following the maintenance on 16 May 2019, a maintenance release was issued for VH-FHW without the required independent inspection requirement being signed as completed for the PTG installation.

The last audit commission by the DNP on the helicopter operator and its maintenance organisation in September 2018 included the following observation:

An inspection of a recent work pack for the last service completed for (a company helicopter) showed records to be completed thoroughly and correctly. Logbooks are not kept on site and all records are scanned and sent electronically to the head office. (The operator) meet(s) the requirements of … the Deed of Standing Offer.

Torque seal

As a visual indicator of alignment, and an aid to indicate when an item has been secured, aircraft engineers often applied torque seal to that item. Pilots conducting visual inspections in the field could check the torque seal for cracks or movement. A crack or movement could indicate that the item was potentially not secure (Figure 6). However, torque seal is a hard lacquer and is not a perfect indicator. It can flake and crack due to heat or exposure to the elements (potentially providing false indications of movement), or if there is only slight movement it may only indicate hard to detect hairline cracks.

Orange torque seal had been applied to the several areas around the PTG, and these areas corresponded to the parts the engineer stated were manipulated when installing the PTG (Figure 6). There was yellow torque seal applied where the loose reference air line was located and it was observed to be cracked following the accident (Figure 6). Yellow torque seal was also present on some other parts that were not manipulated during the last maintenance.

Figure 6: Torque seal on air line unions as found on VH-FHW

Source: Operator, annotated by the ATSB

Subsequent inspections of the helicopter

Pilot inspections involved a visual check of the unions at the end of the air lines in the engine compartment, including the condition of the torque seal on air lines in-line with the PTG. However, the PTG lines were one of many components to inspect that would have torque seal applied (that is, there could be dozens of items with torque seal applied that needed to be checked during a daily inspection or similar pilot inspection).

Several visual inspections were made of VH-FHW by qualified people in the normal course of operation following the 16 May 2019 maintenance and none identified any defect. More specifically:

• On 17 May 2019, after the scheduled maintenance and replacement of the PTG had been conducted, a functional check of the helicopter’s engine and aircraft was conducted on the tarmac at the operator’s Darwin base. Inspection was required before the helicopter was operated, and was also done during the ground run. No defects were reported.
• On the morning of 20 May 2019, VH-FHW was flown to Jabiru and then used on a stream sampling job nearby. The pilot who conducted these flights reported that the daily inspection of the helicopter identified no defects and that the helicopter performed well.
• On the afternoon of 20 May 2019, the helicopter was left in Jabiru for the pilot contracted for the aerial culling task to collect. That pilot inspected VH-FHW before departing Jabiru for Mary River Ranger Station and stated that the helicopter presented no defects. The afternoon was spent using the helicopter for aerial culling tasks. The pilot reported that the check conducted at the end of the day identified no issues.
• On the morning of 21 May 2019, the pilot reported having ample light and time to conduct a thorough daily inspection. The pilot stated that the daily inspection was conducted, and no defects were identified.

Emergency procedures

Regarding the Rolls-Royce 250-C20J engine, if the PTG fails on the high side (high RPM), and puts too much fuel into the engine, the engine will overspeed. The pilot can decrease the throttle to reduce the fuel flow and therefore manage RPM.

As in the case of the accident on 21 March 2019, if the PTG fails on the low side (low RPM), and restricts the amount of fuel going to the engine, there is no adjustment the pilot can make to increase the fuel flow for this engine type. The pilot must instead treat the problem like an engine failure. When operating at a low height above ground, this means controlling rotor RPM with collective pitch and cyclic and managing the helicopter for the best available outcome.

Meteorological conditions

The pilot reported that there was limited internet connectivity at the Mary River Roadhouse so was unable to obtain updated weather information online. The pilot was familiar with the area and, given the conditions, they were satisfied that the weather was suitable for the planned flight.

The Bureau of Meteorology (BoM) provided automated weather reports for Jabiru for the morning of 21 May 2019. The reports indicated an east to north-easterly wind at 12 kt, nil cloud, temperatures from 28 °C to 30 °C, and visibility greater than 10 km. The weather was typical for the Northern Territory dry season and conducive to flying.

Cabin safety information

Occupant injuries

All three occupants of VH-FHW received serious injuries. The pilot received serious back and foot injuries, as well as chemical burns to the body from leaked fuel. The spotter received a serious back injury, a gash to the outside of the lower right leg, and damage to the right arm. The shooter received chemical burns from fuel, and serious injuries to the back, right hip, and scalp.

Seatbelts and harness

VH-FHW was fitted with four-point seatbelts with upper torso restraints (UTRs) in all seating positions. For the KNP shooting operations in B206B3 JetRanger helicopters, the pilot and the spotter both wore the four-point aircraft seatbelts.

The helicopter operator provided a harness for the shooter, which the shooter did not use. For reasons of comfort, the shooter instead used a harness supplied by Parks Australia, attached by way of a non-energy absorbing, webbing restraint strap of around 1 m to a specified anchor point.

The harness’s design complied with ATSO-C1003^[3] and was a quick release type, that could be released under load using two distinct movements (Figure 7), and it was approved under Civil Aviation Safety Regulation (CASR) 21 (Certification and airworthiness requirements for aircraft and parts). It was attached to the aircraft with an adjustable strap. Figure 8 shows the location of the anchor point installation in VH-FHW, which was approved by an authorised engineer under CAR 35 (Approval of design of modification or repair). The anchor point design required it to be installed on the left side of the cabin for use at the rear right door.

Both the shooter’s harness and the anchor point in VH-FHW carried a caveat. Figure 9 shows the harness manufacturer’s statement:

Not approved for take off or landing.

Additionally, the flight manual supplement for the approved anchor point stated:

The camera person/hoist operator must be restrained by his standard seat belt for take-off and landing.

The harness used by the shooter did not fail in the accident sequence, though it was noted after the accident to be past its 10-year retirement date by 3 weeks (Figure 7). The operator took immediate steps to prevent third parties using expired equipment aboard their aircraft after discovering this post-accident.

Harnesses are commonly worn in many aircraft applications. They are designed to prevent people from falling within, and from, the aircraft. They are not designed to protect the occupant during a collision or impact sequence.

Figure 7: Shooter’s harness, rear view

Source: Northern Territory Police, annotated by the ATSB

Figure 8: Harness anchor point

Source: Operator, annotated by the ATSB

Brace positions and emergency response

The operator specified brace positions for passengers in seats fitted with a lap belt and for seats fitted with a lap belt and UTR (Figure 9).

During the occurrence, the seatbelt with UTR kept the pilot in place while they flew the aircraft for as long as they could to achieve the best outcome.

Although the spotter was aware of the brace position, and the UTR held the spotter in their seat, they reported that they lifted their legs prior to impact. In contrast, the specified brace position required the occupant’s feet to be flat on the floor, as depicted in Figure 9.

Figure 9: Brace position information provided by operator

Source: Operator via the Director of National Parks

There was no universally recommended brace position for a crew member in a fall arrest harness, and the operator had not provided procedures or guidance for a brace position for a shooter wearing only a harness. The shooter reported that they crouched down as much as possible, as if they were wearing a lap belt.

A document on helicopter ditching produced by the North Atlantic Treaty Organisation (NATO) in 1989 recommended:

Those unrestrained or on a long tethered harness prior to impact, should if at all possible strap into the nearest seat and assume (a standard brace position). Otherwise they should immediately lie face down flat on the floor with their heads buried in the crook of their arms.

Those actions require time and space, which may not be available when responding to an emergency at a low height above the ground in a small helicopter.

Reducing the flail envelope of an occupant is a vital part of reducing harm in an impact sequence. Even short single-point restraints have been demonstrated to allow significant flail injury to occupants (see for example AO-2014-053). Figure 10 shows the estimated flail envelopes for the occupants of VH-FHW at the time of the accident. The shooter, with a single-point restraint, had a much larger flail envelope than the two front seat occupants.

In the event of an emergency (such as an impending impact), the shooter was required to throw their weapon out of the exit. The shooter advised that they understood this requirement. However, on this occasion they brought the live rifle into the cabin and pointed the barrel down.

Figure 10: Estimated flail envelope for occupants of VH-FHW

Source: ATSB

Harness use instrument

The use of seatbelts is mandated in CAR 251 (Seat belts and safety harness). It stated:

• Subject to this regulation, seat belts shall be worn by all crew members and passengers:
• during take-off and landing…
• when the aircraft is flying at a height of less than 1,000 feet above the terrain…
• CASA may direct that a type of safety harness specified in the direction shall be worn in place of a seat belt in the circumstances set out in the direction…

Civil Aviation Order (CAO) 20.16.3 (Air service operations – carriage of persons) detailed technical requirements to support CAR 251. It stated:

3.1     Each crew member and each passenger shall occupy a seat of an approved type:

(a)   during take-off and landing; and …

(c)   when the aircraft is flying at a height less than 1000 feet above the terrain;  ….

4.1     … safety harnesses, or seat belts where safety harnesses are not fitted, shall be worn by all persons at the times listed in paragraph 3.1…

Airworthiness bulletin (AWB) 25-007 issue 3 (Personnel Harnesses, Restraint Straps and Approved Attachment Points) alerted operators to safety issues surrounding the use of harnesses. The AWB did not offer guidance with respect to a brace position for personnel wearing only a harness.

In November 2018, CASA issued the instrument CASA.EQUIP.0029 under CAR 251(3) to the helicopter operator, exempting the operator from CAR 251(1) when certain conditions were met. It stated:

… approved safety harnesses may be worn in lieu of seat belts in a helicopter during take-off and landing and when the helicopter is flying at a height less than 1,000 feet above the terrain.

The instrument also specified various conditions and requirements, which included:

General conditions

The direction to use the harness is applicable only to the conduct of those tasks where the assistance of the otherwise unrestrained crew member is vital to the operational safety or to the conduct of specific aerial work functions as detailed in the operator's operations manual…

The harness must be worn in place of the seat belt for the minimum time commensurate with flight safety;…

Procedures, drills, operating crew duties and recency requirements covering both normal and emergency operations whilst wearing a safety harness, or swapping between seat belt and safety harness, must be defined and published in the operator's operations manual…

Crew requirements

Before flight, the pilot in command must brief crew members in regard to the responsibilities applicable to both normal and emergency operations whilst wearing a safety harness or swapping between seat belt and safety harness. The briefing must include the procedures to be adopted to afford the best protection to crewmembers in the event of a forced landing…

Conduct of flight

An approved seat and seat belt, for use in an emergency, must be available at all times to the occupant of the safety harness…

Transfer between a seat belt and a safety harness during flight must only occur above 1,000 feet AGL, where practicable, and with the cabin doors closed. These restrictions apply only if the occupant is not secured by either system during the transfer…

Notwithstanding the requirements of [previous paragraph], the occupant must not be secured by more than one (1) restraint system for other than the actual transfer (Ref CAO 108.42 para 3.6) except during the conduct of specific power line aerial work functions as detailed in the operator's operations manual.

Operator's responsibilities

…The Operator must further ensure that any person wearing a safety harness pursuant to the provisions of this direction is fully apprised as to the inherent limitations and potential risks involved in the use of such a harness, when it is worn in place of a seat belt or other restraining device of a type that would otherwise be required in accordance with the provisions of CAR 251.

This instrument was a common exemption to seatbelt requirements for operators conducting aerial work in Australia. Jayrow Helicopter’s instrument was initially issued in 2004.

CASA informed the ATSB that, despite the wording of the instrument, caveats on the specific equipment used (see Seatbelts and harness ), and conditions of the instrument requiring equipment to be approved for take-off and landing, meant that a harness could not be worn in lieu of seatbelts during take-off and landing. CASA also stated that, while the wording appeared otherwise, the instrument was never intended to allow the use of a harness during take-off and landing instead of a seatbelt.

CASA advised that no risk analysis had taken place regarding the potential use of the harness instead of a seatbelt for take-off and landing when issuing this instrument, as it had not anticipated that the instrument could be interpreted that way.

CASA provided renewals of the operator’s instrument every 3 years. Renewals relied on the existence of an antecedent instrument, and upon the content of the operator’s operations manual providing the means to fulfil the conditions of the instrument.

Harness use below 1,000 ft

There were three distinct phases of flight mentioned in CAR 251 and instrument CASA.EQUIP.0029: take-off, landing, and flight below 1,000 ft. The use of a harness below 1,000 ft was essential for completion of the shooting task, and the operator had published aerial culling procedures and harness use procedures in its operations manual. The harness use procedures included:

• annual recertification of equipment
• visual inspection of harness and anchor point
• pilot briefing on use by senior base pilot
• instructions on proper assembly of the quick release mechanism.

The helicopter operator stated that all crew involved in the shooting tasks had received a mass brief at the beginning of the aerial culling program, and regular briefings before flights at the aircraft. The manager in Darwin advised that the mass brief included the use of the harness, operation of the quick release, and shooting procedures as well as normal flying operations. The pilot reported that the pre-flight briefings at the aircraft included avoidance of rotating parts, how seatbelts and doors worked, and location of emergency equipment, as well as task-specific points such as coordination of turning with shooting.

Parks Australia staff members reported that, aside from the method of attachment and release from the harness, there was no other guidance or information provided to the aerial culling personnel about precautions or risks when utilising the harness, with or without the aircraft seatbelt fitted.

As noted above, the CASA instrument required a person wearing a harness to be made aware of the increased level of risk they are assuming when wearing a harness and not wearing a seatbelt. Parks Australia staff members stated they did not feel this was sufficiently communicated to them.

Harness use on take-off and landing

The pilot recalled that, on the day of the accident, the shooter was wearing only the harness on departure from the ranger station. The pilot reported a preference for crew to use the seatbelt, and on this occasion allowed the shooter to use the harness for comfort.

The shooter recalled wearing the seatbelt (lap belt) over the harness during the take-off and throughout the flight. Following the accident, the shooter was found to be only wearing the harness.

Interviews with the operator’s personnel and Parks Australia staff members confirmed that, in the B206B3, shooters would usually remain in the harness attached to the helicopter with the restraint strap at all stages of flight. Flight crew and Parks Australia personnel also reported that, if the aircraft seatbelt was used, it was normal to use the lap belt portion of the seatbelt in addition to the safety harness.

As noted above, the CASA instrument stated that the occupant must not be secured by more than one restraint system for other than the transfer between restraints.^[4]

Ancillary radio install

In 2015 an ancillary radio system was installed in the front passenger footwell of VH-FHW, in accordance with a CAR 35 engineering order. The installation protruded about 8 cm into the footwell (Figure 11). The radio system was a marine VHF/UHF radio, and it was not required for the aerial culling tasks. It had sharp small radii corners, and was not padded.

The spotter reported that the ancillary radio’s placement made it difficult to use the push-to-talk foot switch for the intercom system. Additionally, the large laceration to the spotter’s right leg matched the small radius, metal corners and edges of the ancillary radio installation.  

VH-FHW, serial number 2838, was a Bell 206B manufactured in 1979. The Bell 206B model was certified in the normal category in 1971, and its certification basis was the US Civil Aviation Regulation 6, dated December 1956, with various amendments. In terms of emergency landing conditions, that design standard stated:

The structure shall be designed to give every reasonable probability that all of the occupants, if they make proper use of the seats, belts, and other provisions…will escape serious injury in the event of a minor crash landing In which the occupants experience the following ultimate inertia forces… Upward 1.5g (downward 4.0g)…Forward 4.0g… Sideward 2.0g.…

Consequently, modifications to the aircraft (such as for the radio installation in VH-FHW) needed only to comply with the original design standard.

From 1989, the US Federal Aviation Regulation (FAR) 27.561 requirement for helicopter types certified in the normal category were required to be designed to protect up to 16 g forward, 20 g downward, 8g sideward and 4 g upward. From 1984, FAR 27.785 also required that:

Each seat, safety belt, harness, and adjacent part of the rotorcraft at each station designated for occupancy during take-off and landing must be free of potentially injurious objects, sharp edges, protuberances, and hard surfaces and must be designed so that a person making proper use of these facilities will not suffer serious injury in an emergency landing…

The Bell 206B3 is piloted from the right seat, however dual controls can be made available for pilot training and proficiency checks. This would require an instructor or check pilot to fly the helicopter from the left seat. US CAR 6 also required that:

…the pilot will be able to perform all of his duties and operate the controls in the correct manner…

The pedals at the front left seat of VH-FHW were disconnected from the flight control system. That position can be equipped with flight controls for tasks that require two pilots. The protrusion of the radio installation in VH-FHW over the pedals would likely prevent a pilot from effectively operating the controls. The engineering order for the installation did not prohibit a second pilot from flying the aircraft from the left seat.

Figure 11: Exemplar radio installation showing approximate position in footwell

Source: Maintenance organisation, annotated by the ATSB

The aerial culling task

Low-level operations

Helicopters are used extensively in low-level operations to support numerous industries in Australia. These notably include emergency services, fire suppression, and management of national parks. Low-level operation is defined as any operation below 500 ft, aside from take-off and landing.

Low-level flight brings several significant complexities to the operation, and pilots require training and approval to operate helicopters at low-level. One such complexity is management of forced landings. Both time and availability of suitable forced landing areas are significantly reduced.

During a forced landing, a helicopter can descend at around 2,000 ft/minute. From 1,000 ft, this provides around 30 seconds for preparation of the cabin for a forced landing. From 50 ft, the time is reduced to a few seconds, leaving very little (if any) effective time for warning or preparation.

Low-level flight also vastly reduces the availability of forced landing sites (Figure 12)  At best glide speed (69 kt in a B206B3), a glide ratio of around 4:1 is achievable. Low-level work ordinarily occurs at lower speeds than that, and in aerial culling the pilot must match the speed of the animals, further reducing choice of forced landing areas.

Figure 12: Theoretical choice of forced landing area at best glide speed

Source: ATSB

Task design

The primary purpose of the aerial culling activity was to care for Country and protect the habitat and people in the park from damage caused by feral animals.

It was normal practice across industry that an aerial culling task was performed with just two people on board the helicopter: a pilot and a shooter. For example, the successful brucellosis and tuberculosis eradication campaign in Australia ran for 27 years and made extensive use of aerial culling with two crew. In addition, the Northern Territory government’s aerial platform shooting course guide, under which the Parks Australia shooters were trained, did not mention observers or spotters being on board an aircraft.

The pilot of VH-FHW, who had 30 years’ experience in aerial culling, had ordinarily conducted shooting tasks with just two people on board. Experienced aerial shooters interviewed after the accident also stated a preference for carrying just the pilot and shooter on board to reduce risk to crew, carry more fuel to improve endurance, and do more work.

Parks Australia employees advised that aerial culling tasks in KNP were conducted in Robinson R44 aircraft with just a pilot and shooter up until 2016. In 2017, the DNP switched to a different helicopter operator, which provided a range of services using the larger Bell 206 JetRanger and Airbus Helicopters EC120B aircraft.

The DNP used the higher capacity of the larger helicopter to include the spotter position and improve data collection (in terms of information about the species, number and location of kills). A Parks Australia representative stated that it was critical that the spotter was carried for the success of the shoot, and to counter the risk of not having data for stakeholders. Accordingly, since 2017, the DNP designed the aerial culling task for three people. It required a spotter on board the helicopter in addition to the shooter and the pilot. Prior to 2017, when using the R44 helicopter, data collection was performed by the shooter.

Safe operating procedures

The DNP amended its safe operating procedures (SOPs) issued for aerial platform shooting in November 2016. The procedures included information relevant for conducting the task in an R44 and in a JetRanger and rated the risk to crews as high. For example, the SOPs accommodated the inclusion of the spotter (only relevant to a JetRanger), and required the shooter to wear a seatbelt at all times (which was applicable to the R44 but not how the operation was conducted in a JetRanger).

The SOPs required the spotter to have training in:

• map reading and navigation
• aerial animal welfare assessment
• locating the animals and counting kills from a helicopter.

During shooting, the pilot positioned the helicopter to the left of the mob of horses, and matched the speed and track of the helicopter to that of the animals. In a JetRanger, the spotter (seated in the front left seat) could not see what was happening on the right side of the helicopter where the shooting was taking place. The spotter would therefore require the input of the pilot and shooter to conduct the count (Figure 13).

Figure 13: Estimated firing zone and visibility

Source: ATSB

The SOPs also stated that safety equipment for the task included a flight helmet with intercom. No flight helmets were provided to the aerial shooting crew. The shooter and spotter on the accident flight reported that they were not wearing helmets and did not generally wear helmets during shooting operations. The pilot provided and wore their own helmet.

The spotter reported that they wore a headset for communicating with the pilot and shooter. The shooter reported that they also wore a headset but pushed it back when shooting, so that the earcups would not interfere with manipulation and aiming of the rifle.

Oversight of contracted helicopter operator

On award of the contract for helicopter services, and annually thereafter, the DNP commissioned an independent aviation auditing company to conduct an audit of the helicopter operator and its co-owned maintenance organisation. The audit examined the operator’s ability to provide the service while observing aviation regulations, as well as observing the terms of the contract entered into between the parties.

An audit conducted in September 2018 resulted in three findings, two related to sling load equipment and aircraft parking, and a third due to the operator’s emergency response plan at Jabiru not including relevant emergency contact details. The operator added the emergency contacts to its emergency response plan at the time of audit.

Oversight of shooting operations

There was limited oversight of shooting operations by the DNP. The aircraft travel plan was a document relied on by the park manager and aerial culling team for authorisation of the task, and it was detailed in the DNP aircraft safety policy as being ‘a very important safety factor’. This document was required to be completed for each task, but the template had not been updated since the change in helicopter operator in late 2016. It carried emergency contact details of the previous helicopter operator, and no contact details for the current helicopter operator.

A Parks Australia representative stated that they did not have visibility of the aerial platform shooting management process and that high turnover in the management role over the preceding years had hampered Parks Australia’s ability to provide oversight in that regard. The culling team had no permanent manager in place. A manager was temporarily seconded to the team to help prepare for the culling task in the lead up to the current program, yet risk management documentation for the operation, which was to be completed at manager level, was not conducted and had last been addressed in 2015.

This situation was accepted by management because the crew were all licenced, and local debriefs took place to manage the risk. However, the SOPs did not require a debrief after shooting and there was no record of crew debriefs, no indication of what the content should be, and no internal procedures to verify they were taking place.

Risk management

The date of the DNP’s last risk assessment for aerial culling was 3 August 2015, with a stated duration of 12 months. Since that time, a number of aerial culling tasks had taken place. In addition, the helicopter operator, helicopter type, crew configuration, and SOPs had all changed.

The introduction of a new helicopter operator introduced changes to elements such as:

• the integration of the standard operating procedures of the operator and the DNP’s SOPs
• task management documentation (trip plan details for example)
• emergency response planning
• emergency contacts.

The helicopter type had changed from an R44 to B206B3s (JetRangers) and EC120B helicopters. This introduced changes to the:

• seating position of the shooter
• shooting position of the shooter
• restraints used by the shooter (fall restraint harness in JetRanger instead of a seatbelt in R44)
• management of role equipment
• inclusion of the spotter.

The inclusion of the spotter introduced changes to:

• available fuel load
• number of people exposed to low-level helicopter operations.

None of these changes had been formally analysed by the DNP for their effect on the risk assessment, and the risk assessment as it stood was not equipped to capture the changes. Additionally, the risk assessment did not discuss protection of the crew through provision of personal protective equipment. Also, there was no formal risk analysis of the inclusion of the spotter position, or consideration of the potential benefits of improved data collection when weighed against operational difficulties in recording data, reduced efficiencies in operation, and increased exposure of employees to risk.

Additionally, the park’s radio network was cited as a mitigator for:

• injury to person on ground from stray bullet or ricochet
• inappropriate storage or transport of firearms
• incursion of people on ground into the shooting area.

However, KNP personnel reported that the park’s radio was only available 10 per cent of the time to the crew in flight, and the radio network was reported by a Parks Australia representative to be in need of maintenance and upgrade, yet upgrade required resources they did not have. If the aerial culling crew on a helicopter needed to talk to their ground support personnel, they had to land by the road to talk face-to-face. The risk management plan did not document these limitations with the mitigator or identify treatments to address the situation.

____________

2. Reference air line: This line provides compressor discharge pressure to the fuel control unit (FCU). If this line leaks, the air pressure signal to the FCU is reduced or lost, resulting in the engine idling, or flaming out.
3. ATSO-C1003 is the Australian technical standard order for external personnel lifting devices used in aviation applications.
4. To be secured by more than one approved system can increase time taken to evacuate an aircraft in the event of an emergency.

Safety analysis

Introduction

While the helicopter was operating at about 50 ft above the ground for the aerial culling task, the engine lost power and the pilot was required to conduct an emergency landing with limited options available. As a result of the collision with terrain, the three occupants (pilot, shooter and spotter) were seriously injured.

This analysis will initially discuss the factors associated with the engine power loss, including the loose reference air line and the associated inspections of this component. It will then discuss various factors that increased the risk of injury to occupants, including the preparation of aircraft for low-level operations, and design and management of the low-level aerial culling task.

Loss of engine power

Based on the available evidence, the direct initiator of the engine power loss was the loose reference air line connected to the accumulator downstream from the power turbine governor (PTG). The reference air union was found loose at the accident site, and it was considered very unlikely that this would have loosened during the impact sequence.

In addition, a loose reference air union is consistent with the descriptions of the engine power loss. It would have vented air pressure from between the PTG and the fuel control unit, which the fuel control unit recognised as a signal to reduce fuel flow to idle. Reducing fuel flow to idle would have decreased the power generated by the engine.

In summary, the ATSB concluded that the loose union on the engine reference air line unscrewed in flight, creating a leak, and this leak resulted in a loss of engine power.

There was no manual override for a low-side governor failure available to the pilot. Therefore, the reduction in engine power deprived the pilot of the power required to keep the helicopter airborne, leading to the forced landing and collision with terrain.

It is virtually certain that the union at the accumulator end of the flexible hose from the PTG would stay fastened if the attachment points were serviceable and the nut was sufficiently torqued. A failure of the attachment point would result in a crack in the hose end fitting, and no cracks were reported. Therefore, it is extremely likely that the nut was loosened at some point and not correctly retightened. It could not be definitively determined when this occurred.

The PTG was replaced on 16 May 2019, 5 days (and 4.7 flight hours) prior to the accident. The engineer who replaced the PTG reported that the engine reference air line union was not manipulated during that maintenance. They stated it was not necessary to do so, as the flexible hose could be manoeuvred at the PTG end. Regardless of whether it was intended, it is possible that the union loosened while the engineer manoeuvred the PTG end of the hose.

The warning in the PTG installation documentation, regarding tightening of fittings and tubes, meant that all lines and unions at both ends should have been checked for tightness. As the hose-to-accumulator union was not touched, it was not intentionally loosened, yet neither was it physically checked for tightness. It is likely that such a check at that time would have identified the loose union.

Maintenance, inspection, and verification

There were three opportunities for the loose air line union to be detected before release to service:

• the engineer’s own verification of the PTG installation
• independent inspection by another person
• verification of completeness of the relevant documentation.

Secondary checks by installing engineers and independent inspection by other trained parties are designed to catch lapses as part of an error-tolerant system. It is common practice for engineers to double check the tightness of unions to verify their own work. It is, however, notoriously difficult to detect issues in your own work (Sarter and Alexander 2000), and research has shown that errors of omission relating to fastenings are particularly difficult to detect (Reason and Hobbs 2003).

As already noted, the engineer that conducted the PTG replacement stated that the other end of the flexible hose was not touched. As such, self-verification of the installation concentrated on the PTG end of the flexible hose and the rigid pipes. It is noted that none of the unions on the PTG end loosened.

Given the likelihood of errors during procedural tasks such as maintenance, an independent inspection is a major part of capturing problems. Accordingly, the maintenance organisation’s procedures required independent inspections to be conducted for a range of activities in addition to the minimum regulatory requirements, including for fluid line fittings. In this case however, the independent inspection probably did not occur. The engineer and pilot provided differing accounts of the conduct of the inspection, and there was no paperwork to verify it had taken place.

Even if the independent inspection occurred, it is not certain that it would have identified the problem. The inspection specified was visual, and the only way to detect the loose union would be to demonstrate tightness of all unions, including unions downstream of the PTG. Tightness can only be assured by placing a spanner on the union and checking it for tightness during independent inspection. Accordingly, a thorough, well-designed independent inspection at the time of maintenance is vital in ensuring the continued airworthiness of an aircraft.

Verification of completeness of paperwork is an opportunity to detect tasks or activities that were potentially missed. Following that step, the issuance of a maintenance release is a trusted signal to all parties that the maintenance was carried out as required and that the aircraft is airworthy.

In this case, the independent inspection documentation was supplied as part of the work package, however, being a separate sheet, it may have been overlooked in the review. On this occasion, the verification of the documents did not detect that the independent inspection of the PTG installation had not been signed. As a result, a maintenance release was issued, and the aircraft was returned to service without full assurance of continued airworthiness.

Torque seal, such as was present on the engine reference air line union, would ordinarily be applied after independent inspection and demonstration of tightness. In this case, torque seal had been applied to the air line union, and it was cracked. However, the torque seal was consistent with that used on a maintenance task prior to 16 May 2019, and not consistent with the torque seal applied during the 16 May 2019 PTG replacement task.

The exact meaning of this evidence is not clear, and a range of possibilities exist. In particular:

• torque seal was applied to a loose union an at undetermined time
• torque seal was correctly applied to a tight union that was later loosened.

If the torque seal had been applied to a loose union, this would have potentially obscured a missed step in tightening the union. However, if the loose union existed prior to the 16 May 2019, it seems unclear why it would have taken so long to manifest into a leak.

Regardless of when the torque seal was applied, cracks in the torque seal were not identified during the 16 May 2019 maintenance or on other occasions. This could also be due to a variety of reasons, including:

• the torque seal was cracked but the crack was not readily detectable
• the torque seal was noticeably cracked but missed by all who later inspected the aircraft.

Following maintenance, there were further opportunities to detect a problem in the daily inspections and other inspections conducted by pilots. There are dozens of fastenings to inspect when preparing an aircraft for flight, and it is comparatively rare to find a problem. The high number of fastenings and low expectancy of a fault can predispose people inspecting aircraft to miss items. As all inspections carried out by pilots following the release of the aircraft to service were visual, they would not have detected the fault unless they sighted clearly broken torque seal on the relevant union.

In summary, an independent inspection following installation of the power turbine governor was probably not conducted, and document verification processes did not detect that the independent inspection had not been recorded. As a result, the helicopter departed for low-level operations without assurance of continued airworthiness. The exact reasons why these errors occurred could not be determined. However, errors of omission such as omitting the independent inspection, and not completing the associated documentation, can be associated with distractions, and the investigation noted that distractions were potentially associated with work in the hangar at the time,

Preparation of aircraft and crew operating at low-level

Introduction

To conduct the shooting task, the helicopter was periodically required to operate at a height of about 50 ft over a lightly wooded area. Accordingly, the configuration of the cabin and crew at any point in such a low-level operation is likely to be the configuration for impact with terrain should anything occur. Consideration must therefore be given to:

• cabin suitability
• personal protective equipment (PPE)
• restraints
• brace positions
• other emergency procedures
• awareness of risk.

Cabin suitability

The spotter’s injuries were worsened by the radio installation in the front passenger footwell. Although adopting a brace position, with feet flat on the floor would have helped reduce the injury risk, it is very likely that the spotter would have had a lower level of injury without the radio installation in that location.

It should also be noted that the crashworthiness of small helicopters and aeroplanes has improved over the years with changes in certification and manufacturing requirements. This includes improvements in requirements related to impact forces, injurious objects, restraints, fuel tanks and other aspects to reduce the risk of fire. Organisations who have personnel involved in low-level operations can consider these aspects when deciding what types of helicopters should be used for their activities.

Personal protective equipment

Personal protective equipment (PPE) should be used as the last resort to minimise injury risk, but for some aviation operations it is not possible to reduce the risk to an acceptable level without also including PPE. Low-level flight is one of those aviation operations.

Only the pilot wore a helmet, which they provided themselves. Although the pilot was unconscious following collision with terrain, they had no further head injuries.

Although helmets were required by the Director of National Parks’ (DNP’s) safe operating procedures (SOPs) for aerial culling crews, they were not supplied to the crews, and not worn on a routine basis. It is very likely that the shooter’s level of head injury would have been reduced if they were wearing a helmet.

Restraints

The seatbelts with upper torso restraints (UTRs) worn by the pilot and the spotter likely played a role in minimising the severity of upper body and head injuries.

Unfortunately, for some helicopters, such as the B206B3 JetRanger, use of a fall-arrest harness for the shooter was necessary to conduct the shooting task and a seatbelt could not be worn at the same time. However, in the event of a forced landing when in low-level flight, the shooter has no time to transfer to the seatbelt. This exposed the shooter to a higher level of risk due to the increased flail envelope. In this case, possibly due to the movement afforded by the harness, the shooter received a serious injury to their head and right hip.

Brace positions

The helicopter operator provided detailed information about brace positions for seats fitted with UTRs and seats fitted with just lap belts. In this case, probably associated with the limited time available and the surprise of the unfolding events, the spotter did not keep their feet firmly on the floor. This increased their risk of injury, particularly to their lower legs. More specifically, if they had adopted the specified brace position, it is likely the severity of their leg injury (contacting the radio installation) would have been reduced.

Under the Civil Aviation Safety Authority (CASA) instrument for using a fall-arrest harness, the helicopter operator (via the pilot) was required to provide a briefing on the procedures to be adopted to afford the best protection to crewmembers in the event of a forced landing. In this case, the aerial culling crews reported that they were not provided with any such briefing information. While briefings regularly took place, a brace position specific to a harness was not communicated.

It is acknowledged that there is very little information available, provided by CASA or other regulators, about suitable brace positions for a person wearing only a harness. Nevertheless, there is still a requirement on the operator to research and provide information on a suitable position. The extent to which a suitable brace position would have been able to reduce in jury risk in this case could not be determined.

Emergency procedures training for low-level flight

Renewal of the CASA-issued approvals for discharging firearms from an aircraft only required that the applicant had to complete an initial aerial-platform shooting course, and then have shot from an aircraft within the last 2 years.

The shooter and the spotter (who was also a shooter) had not conducted a full or refresher aerial platform shooting course, which included safe practices around helicopters, in almost 20 years. Although they had received pre-flight safety briefings numerous times, such briefings do not cover some of the essential procedures necessary to minimise risk in the aerial shooting task. Had the spotter and the shooter regularly trained and practiced in helicopter safety and emergency procedures, it is likely that they would have both been better prepared for the forced landing.

In particular, the shooter knew the rifle should be thrown from the helicopter yet had not practiced for such an event. There was very little time for the shooter to think about throwing the rifle clear of the helicopter, and the rifle remained in the cabin. Although the barrel was pointed down, the live firearm being in the helicopter increased the potential consequences of the accident. If the action of throwing the weapon in response to an emergency had been rehearsed or drilled, it would have been more likely to be ejected from the aircraft.

Awareness of risk

The CASA instrument also required the helicopter operator to advise personnel using a harness of the ‘inherent limitations and potential risks involved in the use of such a harness’. Aerial culling personnel using the harnesses reported that they were not made aware of the risks associated with harness use, nor precautions to be taken such as brace positions.

The high time aerial culling crew involved in this accident had a good understanding of the risks of the operation and revision of the risks from the operator would probably not have altered their intent to participate. However, another crew may not have been so experienced.

Harness instrument

The language of the CASA instrument regarding use of safety harnesses appeared to allow the use of a harness in lieu of seatbelts for take-off and landing. Equipment approved under CASA regulations (such as anchor points and harnesses) can be reasonably understood to meet the conditions of the instrument. However, CASA advised that the manufacturers’ caveats on use of these items of equipment meant that a seatbelt still had to be worn for take-off and landing.

CASA advised that the instrument was never intended to allow safety harnesses to be worn in lieu of seatbelts during take-off and landing, and that the conditions of the instrument prevented this from occurring. There appeared to be two specific meanings of the word ‘approved’ which could cloud interpretation of the instrument; one in the sense of the equipment being approved under Civil Aviation Safety Regulation 21, and the other of the equipment manufacturers approving their products for certain activities. The equipment requirements of the instrument did not make this distinction clear.

Both the language of the instrument and conflicting use of ‘approved’ opened the instrument to misinterpretation. The language and conditions of the instrument should be improved. Operators and pilots should be aware that, even though an instrument may appear to permit an activity, the limitations of the equipment used must be observed.

Risk management of aerial culling activities

Significant changes had been made to the Director of National Parks’ aerial culling operations in the KNP in the near 4-year period between the risk management plan development in 2015, and the undertaking of the aerial culling program in May 2019. This included, in 2016, the DNP designing the aerial culling task for three crew, introducing a spotter.

Given the increased complexity and risk in low-level operations, the number of crew should be kept to a minimum. That is, only personnel essential for conducting the task should be carried. In this case, the spotter was added to the crew without any formal or systematic consideration of the increased safety risk.

When pursuing a course of action, if one particular stakeholder risk presents the greatest threat, decision makers are prone to adopt a risky strategy which directly addresses the immediate threat to the detriment of other stakeholders (Jawahar and McLaughlin 2001). The spotter had been built into the program, primarily to collect data for stakeholders. Requiring a spotter to be on board mitigated a corporate stakeholder engagement risk, yet exposed the spotter to a high-risk aviation activity. Expanding the crew beyond the industry proven two crew model should have been a trigger for a formal risk analysis and assessment of controls.

A method of data collection designed for two crew or data collection managed through communication with ground crew would have exposed less people to risk. However, no alternative methods of data collection were explored, and the quality of data between two and three crew operations was not assessed. Therefore, the DNP did not know if lower risk options for data collection were available, or know if the added value to the operation warranted the increased risk exposure.

Additionally, there was no documentary evidence of consideration of the impact of changes in helicopter or operator on the operation. The 2015 aerial culling task risk analysis indicated limited consideration of aviation safety risk, and it is likely that the implications of further changes to the operation were not well understood.

When designing aviation operations, organisations without aviation expertise should seek outside information and expertise.  Although the DNP contracted an aviation auditor, their scope of work was to audit against the deed of standing offer. Likewise, the helicopter operator was contracted to deliver services as required by the DNP. Both organisations could have provided valuable input into risk analysis and task design, and neither was called upon to do so.

Furthermore, there was no evidence of a working process to build lessons learned into the aerial culling program. The SOPs did not require task debriefs, and hazard management was not conducted. For example, the aerial culling crew and park management knew that the radio network was unsuitable for the aerial culling task, and that they were unable to remedy it. Being such an important risk control, another solution should have been documented and implemented as an alternative.  

Other controls were also not managed or reviewed for effectiveness. Specifically, incorrect emergency contact details on KNP documentation used to authorise the task, expired equipment remaining available for use, and PPE being unavailable to the crew.

High turnover in the role of park manager, and the aerial-culling crew not having a line manager, were reported as reasons for there being no supervision or active management of risk. This limited level of risk management restricted the DNP’s ability to eliminate or minimise risk to the crew, meaning safety risk was not managed, nor was safety assured at an organisational level.

Findings

From the evidence available, the following findings are made with respect to the engine power loss and collision with terrain of VH-FHW on 21 May 2019.

Contributing factors

• A loose union on an engine reference air line unscrewed, creating a leak. The leak caused loss of engine power in flight, resulting in a forced landing.
• During installation of the power turbine governor, 4 days prior to the accident, an adjacent downstream attachment of the engine reference air line union was loose and not checked for tightness.
• Potentially associated with distractions in the hangar at the time, an independent inspection following installation of the power turbine governor was probably not conducted, and document verification processes did not detect that the independent inspection had not been recorded. As a result, the helicopter departed for low-level operations without assurance of continued airworthiness.
• Although compliant with regulatory requirements applying to the helicopter being used, bulky, non-task related equipment was installed in the front left passenger footwell, which increased the level of injury to the spotter during the collision with terrain.
• Although the Director of National Parks’ safe operating procedures required shooters and spotters to wear helmets during aerial culling tasks, helmets were not provided or used on a routine basis. (Safety issue)
• Associated with the limited time to prepare for the forced landing, the spotter did not adopt the brace position, with feet on the floor, increasing the level of injury to their lower legs.
• The Director of National Parks did not actively manage the risk of the aerial culling task being conducted in the Kakadu National Park, or effectively supervise the operation. As a result, an increase in the number of crew, a change in helicopter type and change of helicopter operator all progressed without requisite risk management. This exposed crew to avoidable harm during low-level aerial shooting operations. (Safety issue)

Other factors that increased risk

• Associated with the limited time to prepare for the forced landing, the shooter did not eject the rifle in readiness for a forced landing. As such, the cabin was not prepared for a forced landing.
• Recurrency training and drills in aircraft emergencies were not required for reissue of an aerial platform shooting permission. Some shooters last conducted training about 20 years prior, during initial issue of their permissions. (Safety issue)
• Although required by the harness instrument commonly issued by the Civil Aviation Safety Authority, the operator did not appraise shooting crews of the risks of using only a harness for restraint during low-level flight. (Safety issue)
• A harness instrument, commonly issued by the Civil Aviation Safety Authority (CASA), stated that a harness could be used instead of a seatbelt for take-off and landing. Although not intended by CASA, this instrument was easily able to be misinterpreted as indicating that a seatbelt was not required to be used during take-off and landing. (Safety issue)

Other findings

• To conduct the shooting task, the helicopter was periodically required to operate at a height of around 50 ft over a lightly wooded area. This reduced opportunity to prepare for and make a successful forced landing.

Safety issues and actions

Helmet provision and use

Safety Issue number: AO-2019-025-SI-01

Safety issue description: Although the Director of National Parks’ safe operating procedures required shooters and spotters to wear helmets during aerial culling tasks, helmets were not provided or used on a routine basis.

The Director of National Parks' risk management

Safety issue Number: AO-2019-025-SI-02

Safety issue description: The Director of National Parks did not actively manage the risk of the aerial culling task being conducted in the Kakadu National Park, or effectively supervise the operation. As a result, an increase in the number of crew, a change in helicopter type and change of helicopter operator all progressed without requisite risk management. This exposed crew to avoidable harm during low-level aerial shooting operations.

Aerial platform shooter emergency training

Safety issue number: AO-2019-025-SI-03

Safety issue description: Recurrency training and drills in aircraft emergencies were not required for reissue of an aerial platform shooting permission. Some shooters last conducted training about 20 years prior, during initial issue of their permissions.

Harness instrument clarity

Safety issue number: AO-2019-025-SI-04

Safety issue description: A harness instrument, commonly issued by the Civil Aviation Safety Authority (CASA), stated that a harness could be used instead of a seatbelt for take-off and landing. Although not intended by CASA, this instrument was easily able to be misinterpreted as indicating that a seatbelt was not required to be used during take-off and landing.

Crew risk awareness

Safety issue number: AO-2019-025-SI-05

Safety issue description: Although required by the harness instrument commonly issued by the Civil Aviation Safety Authority, the operator did not appraise shooting crews of the risks of using only a harness for restraint during low-level flight.

Safety action not associated with an identified safety issue

Additional safety action by Jayrow Helicopters

Following inspection of VH-FHW on site, the helicopter operator:

• immediately actioned a fleet wide check and retorque of engine flexible and rigid oil, air and fuel lines/hoses/pipes attachments
• improved procedures for use of third party harnesses aboard company aircraft
• outsourced human factors training for engineers which expanded quality and content of the training.

Additional safety action by Director of National Parks

Following the accident, the Director of National Parks immediately suspended aerial culling activity.

In January 2021, the DNP advised of the following safety actions:

• upgraded handheld radios with higher wattage, providing improved communications channels through broader broadcast range for staff undertaking aviation activities. The use of these radios is prioritised for staff undertaking remote work…

As part of their broader commitment to ensuring safety in aviation activities, the DNP and department have also established a program of work relating to aviation activity risk management and mitigation. This includes:

• establishing an updated enterprise WHS Information System (WHSIS), with the planned implementation of incident reporting and hazard modules to occur in early 2021. The WHSIS will assist with recording and managing risks and hazards in relation to high-risk operational activities including aviation activity risks
• infrastructure investment in the KNP radio and telecommunications network. For example, a total of $7 million has been committed to a new tower network within KNP and planning for those infrastructure upgrades is underway; and procurement of additional handheld radios and personal tracking/emergency call devices for staff working on the park
• establishment of a Departmental Focus Group, being a group comprised of operational staff/business areas undertaking aviation activities (including aerial culling operations) and WHS/risk and business continuity specialists to take a collaborative approach to addressing WHS critical risks and controls across the portfolio. The group is planned to commence operating in February 2021.

Sources and submissions

Sources of information

The sources of information during the investigation included the:

• pilot of the accident flight
• pilots and Head of Flight Operations of the aircraft operator
• engineers of the approved maintenance organisation
• aerial culling crew on board the helicopter and other Parks Australia personnel
• Civil Aviation Safety Authority
• engine manufacturer
• crew restraint harness manufacturer
• aerial platform shooting subject matter experts
• Northern Territory Police
• recorded data from the GPS unit on the aircraft.

References

Civil Aviation Safety Authority 2013, Safety Behaviours: Human Factors Resource Guide for Engineers, Canberra, ACT.

Hart T & Sander A 2016, Memory and Moderate to Severe Traumatic Brain Injury, Model Systems Knowledge Translation Center, VA, USA.

Hobbs A, 2008, An Overview of Human Factors in Aviation Maintenance, Australian Transport Safety Bureau, Canberra, ACT

Jawahar M & McLaughlin GL 2001, Toward a descriptive stakeholder theory: An organizational life cycle approach, Academy of Management Review, 26(3): 397–414.

Motley EB 2006, Aircraft Accident Survivability: Rotary Wing Aircraft, Naval Air Warfare Center, MD, USA.

Nadine B. Sarter & Heather M. Alexander (2000) Error Types and Related Error Detection Mechanisms in the Aviation Domain: An Analysis of Aviation Safety Reporting System Incident Reports, The International Journal of Aviation Psychology, 10:2, 189-206, DOI: 10.1207/S15327108IJAP1002_5

North Atlantic Treaty Organization 1989, The Human Factors Relating to Escape and Survival from Helicopters Ditching in Water, AGARD-AG-305E, Canada.

Reason J & Hobbs A, 2003, Managing Maintenance Error: A practical guide, CRC Press, Boca Raton, USA.

Transport Canada 2016, Advisory circular: Brace for Impact Positions for all Aircraft Occupants, AC 700-036, Ottawa, Canada.

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 aircraft
• aerial culling crew on board the helicopter
• helicopter operator
• approved maintenance organisation
• engine manufacturer
• Director of National Parks
• Civil Aviation Safety Authority.

Submissions were received from the:

• helicopter operator
• Director of National Parks
• Civil Aviation Safety Authority.

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

Purpose of safety investigations & publishing information

Purpose of safety investigations The objective of a safety investigation is to enhance transport safety. This is done through: identifying safety issues and facilitating safety action to address those issues providing information about occurrences and their associated safety factors to facilitate learning within the transport industry. It is not a function of the ATSB to apportion blame or provide a means for determining liability. At the same time, an investigation report must include factual material of sufficient weight to support the analysis and findings. At all times the ATSB endeavours to balance the use of material that could imply adverse comment with the need to properly explain what happened, and why, in a fair and unbiased manner. The ATSB does not investigate for the purpose of taking administrative, regulatory or criminal action. Terminology An explanation of terminology used in ATSB investigation reports is available here. This includes terms such as occurrence, contributing factor, other factor that increased risk, and safety issue. Publishing information  Released in accordance with section 25 of the Transport Safety Investigation Act 2003 Published by: Australian Transport Safety Bureau © Commonwealth of Australia 2021 Ownership of intellectual property rights in this publication Unless otherwise noted, copyright (and any other intellectual property rights, if any) in this report publication is owned by the Commonwealth of Australia. Creative Commons licence With the exception of the Coat of Arms, ATSB logo, and photos and graphics in which a third party holds copyright, this publication is licensed under a Creative Commons Attribution 3.0 Australia licence. Creative Commons Attribution 3.0 Australia Licence is a standard form licence agreement that allows you to copy, distribute, transmit and adapt this publication provided that you attribute the work. The ATSB’s preference is that you attribute this publication (and any material sourced from it) using the following wording: Source: Australian Transport Safety Bureau Copyright in material obtained from other agencies, private individuals or organisations, belongs to those agencies, individuals or organisations. Where you wish to use their material, you will need to contact them directly.

The ATSB has assisted the Myanmar Accident Investigation Bureau’s investigation of a collision with terrain involving Biman Bangladesh Airlines – DHC-8-402Q, registered S2-AGQ, Yangon-Mingaladon Airport, Myanmar on 8 May 2019.

The aircraft was operating on a flight from Shahjalal International Airport, Bangladesh to Mingaladon Airport, Myanmar. On board were six crew and 28 passengers. Weather at Yangon was reported as poor, due to the presence of a thunderstorm in the area. The aircraft collided with Runway 21 at Yangon-Mingaladon Airport, Myanmar during the landing phase. The aircraft was destroyed and twenty occupants were reportedly injured.

The aircraft cockpit voice recorder (CVR) and flight data recorder (FDR) from S2-AGQ were brought to Australia by two senior Myanmar investigators on 10 June 2019. In the presence of the Myanmar investigators, both recorders were successfully downloaded on the 11 and 12 June 2019 at the ATSB data recovery facility in Canberra, Australian Capital Territory. In addition, the ATSB assisted the Myanmar investigation team with preliminary factual analysis of the recorded data. All data recovered from the CVR and FDR was provided to the Myanmar investigators to assist with their Annex 13 investigation.

The ATSB also assisted the Bangladesh Accredited Representative on 27 June 2019 with a replay of the CVR and review of the FDR data.

There are no ongoing actions for the ATSB at this stage. Any enquiries regarding the investigation should be addressed to the Myanmar Accident Investigation Bureau at the contact details listed below:

Myanmar Accident Investigation Bureau
First Floor, DCA HQ Building (B)
Yangon 11021, Myanmar
Tel: 951 533162
Fax: 951 533016
Email: aungmaw23@gmail.com

On 14 April 2019, an Aeroprakt A22LS Foxbat collided with terrain while conducting mustering operations on Aldville Station approximately 120 km north-west of Cunnamulla, Queensland. The aircraft sustained substantial damage and the pilot was fatally injured.

Recreational Aviation Australia (RAAus) is investigating the accident and has requested assistance from the Australian Transport Safety Bureau (ATSB) in:

• recovering data from an on-board GPS unit
• conducting metallurgical and failure analysis on components of the aircrafts control system
• conducting failure analysis on the aircraft’s damaged wing covering.

To facilitate this work the ATSB has initiated an external investigation under the Transport Safety Investigation Act 2003.

Any enquiries relating to the accident investigation should be directed to RAAus at: www.raa.asn.au.

Safety summary

What happened

On 20 March 2019, the pilot of an Airbus Helicopters AS350B3e, registered VH-SZS (SZS) was performing aerial work on Pernatty Station, South Australia, approximately 60 km east of Woomera Airfield. The task involved helicopter powerline stringing from the Mount Gunson South substation to the Carrapateena mine site, a total distance of 51 km. The stage being conducted on the morning of 20 March was from pole 159 to pole 179, a distance of 4.8 km. Stringing operations continued normally for poles 161, 162 and 163. However, while approaching pole 164, at about 1017, witnesses reported seeing the helicopter collide with the pole and impact terrain near the base of the pole. The pilot, who was the sole occupant, received fatal injuries.

What the ATSB found

The ATSB found that shortly after the pilot was trained in powerline stringing, for unknown reasons they modified the taught stringing methodology. The new methodology placed the helicopter at low level in the vicinity of the powerline poles, increasing the risk of a collision. It also exacerbated the uptake of dust which, in combination with the position of the sun and the rearward attitude of the aircraft likely reduced the pilots’ visibility of pole 164 and their situational awareness of it.

These factors, combined with the short distance and large elevation gain between pole 163 and 164, led to the pilot inadvertently colliding with pole 164. It was also found that the indirect supervision provided to the newly trained pilot was ineffective in identifying that a modified stringing method was being used.

What has been done as a result

The helicopter operator has advised the ATSB that they have made the following changes to their operations manual. The changes relate specifically to the supervision and review of newly authorised pilots in specialist tasks, and includes:

• Mandated and expanded In Command Under Supervision time requirements for pilots as part of initial task training for relevant specialist tasks.
• The introduction of consolidation flight checks at key points for pilots newly authorised in relevant specialist tasks.
• The mandated extension of time that pilots newly authorised in relevant specialist

tasks are mentored by an experienced pilot.

Safety message

This investigation shows that experience alone will not always prevent a pilot from having an accident. In this case the pilot was a very experienced deputy chief pilot with nearly 6,500 flight hours. The ATSB research publication AR-2012-035 provides some insight as to why experience does not always provide a safeguard:

• Experience alone can never compensate for high risk activity.
• Sound decision-making and experience do not necessarily go together.
• Using pilot experience as mitigation for potential operational risks is inadvisable. If the risks are unacceptable for a qualified and competent pilot, there should be no reason for an experienced pilot to accept them.

The investigation also highlights the value of direct supervision of pilots who have recently been trained in a new task.

The occurrence

On 20 March 2019, the pilot of an Airbus Helicopters AS350B3e, registered VH-SZS (SZS) was performing aerial work on Pernatty Station, South Australia, approximately 60 km east of Woomera Airfield (Figure 1).

Figure 1: Accident location

Source: Google Earth, annotated by ATSB.

The helicopter operator (Aeropower) had been contracted to conduct powerline stringing operations (see the section titled Power line stringing methodology) for a new 132 kV electrical transmission line from the Mount Gunson South substation to the Carrapateena mine site (operated by OZ Minerals). The task involved stringing draw wire^[1] and optical ground wire. The total length of the stringing operations, 51 km, was divided into twelve stages that were identified with reference to numbered transmission poles. The stage being conducted on the morning of 20 March was from pole 159 to pole 179, a distance of 4.8 km.

On the morning of the accident the Aeropower pilot and refueller rose at about 0430 Central Daylight‑saving Time.^[2] After breakfast, at about 0630 they attended the first of three morning briefings. The first briefing was run by Ventia, the primary contractor for the powerline operation (see the section titled Operational information). All workers were breath-tested for alcohol during this briefing. After the Ventia briefing, the Aeropower duo then attended the Powerlines Plus (PLP) briefing at about 0700. After the PLP briefing, at about 0730, the refueller drove the pilot to the nearby Carrapateena Airport.

At 0842 the pilot took-off from Carrapateena Airport. After about two minutes of flight, the pilot returned the aircraft to the airport due to what was later described as a warning light in the cockpit. After about seven minutes on the ground, the pilot took-off again and flew to pole 179 (the last pole of the stage) for a radio check with the stringing team ground-crew. The pilot then flew the length of the stage to the start point (pole 159) for a fly-by inspection of the job site. The pilot then flew to the refuelling point, nick-named the ‘Turkey’s nest’, landing at about 0858 (Figure 2). Here the pilot rendezvoused with the refueler and the stringing team for the last pre-start briefing for those workers directly involved with the helicopter operations.

During this meeting the pilot briefed one of the ground crew, supplied by the powerline company, on how to hook-up the draw wire to the helicopter as they had not performed this task previously. The aircraft was also refuelled. Afterward, the stringing team proceeded to their assigned work positions and at about 1000 the pilot took off and proceeded to pole 159 to commence stringing operations.

Figure 2: ADS-B^[3] derived flight data for VH-SZS on 20 March 2019.

Figure 2 Shows the ADS-B flight data for VH-SZS on the day of the accident.

Source: FlightRadar24 and Google Earth, annotated by ATSB.

In preparation for helicopter stringing operations, the draw wire had previously been strung to a pulley on pole 159 using an elevated work platform. Just after 1000, when SZS reached pole 159, ground crew attached the draw wire to a remote hook fitted to the helicopter at the end of a 30 ft longline. SZS then pulled the draw wire out from a Tesmec S.p.A.^[4] (Tesmec) stringing machine and proceeded to pole 160 to clip the draw wire into the pulley. Stringing operations continued normally for poles 161, 162 and 163.

While approaching pole 164 at about 1017, witnesses reported seeing the helicopter collide with the pole and impact terrain near the base of the pole. Several ground crew from the stringing team that were near the helicopter came to assist. They extinguished a small post-impact fire and removed the pilot from the aircraft to a safe distance. A short time later emergency services and paramedics from the mine site attended the scene and confirmed that the pilot, who was the sole occupant, had received fatal injuries.

________

1. The draw wire is thinner (13 mm) and lighter (0.55 kg/m) than the conductor wire (31.5 mm, 1.96 kg/m). After the helicopter strings the draw wire, a ground-based winch is used to pull the conductor wire through.
2. Central Daylight‑saving Time (CDT): Coordinated Universal Time (UTC) +10.5 hours.
3. ADS-B: Automatic Dependent Surveillance–Broadcast is a surveillance technology in which an aircraft determines its position via satellite navigation and periodically broadcasts it, enabling it to be tracked.
4. Tesmec S.p.A. are an Italian manufacturer of stringing machines. In this case, a diesel-powered hydraulic winch/brake, provides tension while the helicopter is drawing wire out and then acts as a winch to pull the final conductor wire back though.

Context

Pilot information

General information

The pilot held commercial pilot licences for both aeroplanes and helicopters, issued on 17 November 2000 and 20 November 2009 respectively. The pilot was rated for both single‑ and multi-engine fixed wing aircraft, as well as single‑engine helicopters. Design feature endorsements that the pilot held included manual propeller pitch control, tail wheel, gas turbine and retractable undercarriage endorsements. Additionally, the pilot had a low-level endorsement for helicopter sling operations issued on 17 November 2009 and an aeroplane aerobatic endorsement, issued on 8 January 1998. The pilot was also a licenced aircraft maintenance engineer.

A review of the pilot’s Air Maestro^[5] logbook showed that at the time of the accident the pilot had accumulated a total flying experience of approximately 6,370 hours. About 45 of those hours were in the previous 30 days and about 77 hours were in the last 3 months. Most the pilot’s flying experience (5,280 hours) was in helicopters, and the majority of that (4,537 hours) was in the MD500, a single‑engine light utility helicopter. The pilot had 240 hours on the AS350, the same type flown on the day of the accident, with about 49 hours in the last 3 months on that type. The pilot’s licence book indicated that the pilot had last completed a single-engine helicopter flight review on 24 Jan 2019 that was valid for 12 months.

Powerline stringing training

The pilot, who was the deputy chief pilot (DCP) for Aeropower Pty. Ltd., had been with the company since the late 1990s. In that time, the pilot had accrued about 2,400 hours in powerline operations. This included about 1,343 hours in powerline patrol and inspection, 643 hours insulator washing and nearly 400 hours in platform work.

The DCP had observed powerline stringing operations in December 2018, on a job in Wollongong, New South Wales. However, all the DCPs formal powerline stringing training was conducted during the three days of the first tour at Carrapateena.

The training involved the:

• DCP observing the chief pilot (CP) from the ground
• DCP observing in the aircraft
• CP observing the DCP while flying dual
• DCP stringing solo with the CP observing from the ground.

The DCP was deemed satisfactory in all requirements and on 7 February 2019 the CP signed-off the DCP for powerline stringing operations. The training comprised a total 7.2 hours with 1.4 hours of those with the DCP in command. At the time of the accident the pilot had a total of 25 hours experience in powerline stringing.

Medical information

The pilot held a Class 1 Aviation Medical Certificate that was valid until 2 Oct 2019 with no restrictions. The pilot was reported to be very fit and active and displayed normal behaviour on the morning of the flight and was well-rested. He was not reported to be taking any prescription medications and had no reported medical condition that could have affected his ability to operate an aircraft that day.

A post-mortem examination identified no significant background natural disease, which could have contributed to the accident. Toxicological analysis concluded that the toxicology was also non‑contributory to either the accident or cause of death.

Aircraft information

Overview

VH-SZS (SZS) (Figure 3) was an Airbus Helicopters^[6] AS350B3e Écureuil (Squirrel) light utility helicopter manufactured in 2012. The aircraft was a single-engine helicopter with six seats in the basic configuration. The primary structure of the aircraft was constructed of sheet metal, while the canopy, underside access cowling, transmission and engine cowlings were made of composite materials. The cabin area was accessible through four doors, two hinged pilot doors and two sliding rear doors.

Figure 3: Image showing VH-SZS

Figure 3 shows VH-SZS, a single turboshaft‑powered Airbus Helicopters AS350B3e Squirrel.

Source: Supplied

Engine and rotors

The main rotor system comprised of three composite main rotor blades constructed of a fiberglass spar with a composite skin over a foam core. The blades were attached to a composite semi-rigid, bearingless starflex hub. The two-blade tail rotor was also manufactured of composite materials moulded onto a fibreglass spar. The tail rotor was mounted to a lightweight sheet metal tail boom. All flight controls were hydraulically boosted, with hydraulic power supplied by a single hydraulic pump which was belt driven by the engine-to-transmission driveshaft. SZS was powered by a Turbomeca Arriel 2D engine, which was a free turbine^[7] turboshaft engine. The engine was controlled by a dual-channel, full authority digital engine control (FADEC) system.

Engine Data recorder

The aircraft was fitted with a Sensorex Engine Data Recorder (EDR). The EDR was a light recorder that exclusively records data sent by the FADEC system for maintenance purposes. For both FADEC channels, engine parameters and failure flags were recorded. Engine parameters were recorded continuously at a sample rate of 1 second and at a sample rate of 20 ms for a limited duration when a failure occurs.

Maintenance

The helicopter was built in 2012 and operated in New Zealand before being imported to Australia in 2016. A Certificate of Airworthiness inspection was completed 11 March 2016, and the certificate of registration was transferred to the current owner on 13 December 2018. SZS had a current maintenance release, issued on 19 October 2018 which was valid for a period of 150 hours or 12 months, whichever was sooner. At the time of the accident the aircraft had accrued 100.4 hours since the maintenance release. The maintenance release was not in the helicopter, as required, it was located in the pilot’s belongings in the accommodation area.

The helicopter was maintained in accordance with the manufacturer’s documentation. At the time of the accident, there were no known maintenance deficiencies with the helicopter.

Aircraft weight and Balance

A weight and balance was performed on 16 January 2019 with an expiry date of 15 January 2022. Additionally, weight and balance calculations indicated that the aircraft was below maximum take‑off weight and within the centre of gravity limits for the duration of the flight

Mack Pull

To facilitate stringing operations, the helicopter was fitted with a Mack Innovations (Australia) Pty Ltd (Mack Pull) bidirectional line stringing system. The Mack Pull provides a hard point located under the belly and to the side of the aircraft that is designed to carry a standard cargo hook. It assists with aerial work applications that require sideways flight and was specifically designed for power cable stringing work as it helps to keep the cable within the pilots’ field of vision.

A 30 ft longline was attached to the cargo hook on the Mack Pull and a Mechanical Specialties 301 remote hook was attached to the other end of the 30 ft longline. A cockpit mounted load meter gave a visual indication to the pilot of the load placed on the system. The load rating on both the remote hook and the 30 ft longline was 3,000 lbs (1,360 kg).

Flight recorders

The aircraft was not fitted with a flight data recorder or a cockpit voice recorder, nor was either required by regulations.

Meteorological information

Graphical Area Forecasts (GAF)^[8] for the area of operations, as well as aerodrome forecasts (TAF), meteorological aerodrome report (METAR)^[9] and Automatic Weather Station (AWS) reports from Woomera Airfield were obtained from the Bureau of Meteorology. The forecasts (GAF and TAF) predicted no significant weather in the area of operations for the duration of the accident flight.

The METARs for Woomera Airfield (about 60 km west of the accident site) at 0930 indicated that the surface wind was 160° (True) at 9 kt. At 1000 the wind was 170° at 10 kt and at 1030 the wind was 160° at 9 kt. For all times the QNH^[10] was 1015 hPa and the conditions were CAVOK.^[11]

At the time of the accident the Woomera AWS recorded the temperature at 24.4 °C, 8 knots of wind (with maximum gusts of 10 kt) from 166°, and a QNH of 1015.8.

Weather data measured at the Carrapateena mine showed that at 1010 (about 7 minutes before the accident) the temperature was 27.5 °C and the wind was 1.7 kt from 128°. There were no significant changes in those conditions on the morning leading up to the accident.

On-site observations

Observations of the conditions on the day were consistent with the meteorological reports. It was reported that during the last pre-flight briefing the pilot commented that the conditions were good for flying. Other witnesses described the conditions as sunny and a little bit windy. Several witnesses noted both the strength and position of the sun, which was reported to be in the direction that the aircraft was travelling. Geoscience Australia data showed that at the time of the accident the azimuth^[12] of the sun was 65° and its altitude was 35°. The bearing from pole 163 to pole 164 was 49°.

Additionally, the presence of a large amount of dust in the vicinity of the aircraft was noted by several witnesses. This can be seen in Figure 4, which shows a sequence of images of the aircraft traversing from pole 163 to pole 164.

Figure 4: VH-SZS traversing between pole 163 and 164.

Figure 4 shows VH-SZS traversing between pole 163 and 164. Pole 163 is visible in the image, while pole 164 is out of the frame to the right. The direction of travel is from left to right in this image.

Source: Witness

Wreckage and accident site information

Accident site

The accident site was located about 60 km east of Woomera South Australia, on the OZ Minerals Carrapateena mine site (Figure 1). The mine is located on Pernatty Station, a 2,147 km² livestock station about 136 km north of Port Augusta. The start of the stringing stage (pole 159) was about 5 km south-west of Carrapateena Airport and the aircraft had traversed about 1 km to pole 164.

Wreckage examination

Site and wreckage examination did not identify any aircraft defects or anomalies that might have contributed to the accident. Markings on pole 164 (Figure 5) indicated that the helicopter collided with the pole about 17 m above the ground. The main rotor blade (MRB) contacted the pulley mounted on the insulator, the ladder and pole during the accident sequence. The pulley fractured from its mounting bracket and came to rest on the access road, 15 m from the pole. The ladder was struck and bent toward the direction of the pulley, consistent with the direction of rotation of the MRBs. The pole had a number of MRB strikes, which progressed in a downward direction as the helicopter descended (inset in Figure 5).

Figure 5: Impact marks and damage to pole 164.

Source: ATSB

After impacting the pole, the helicopter came to rest on its right side approximately 2 m from the base of the pole (Figure 6). The aircraft had rotated approximately 90° to the left of its direction of travel.

Figure 6: The accident site near pole 164. The direction of travel of the helicopter was from pole 163 to pole 164.

Source: ATSB

The cockpit and fuselage roof were substantially disrupted from impact forces. The tail boom had almost entirely detached at the fuselage junction and fractured forward of the horizontal stabiliser, due to ground impact. Two of the MRBs had separated from the rotor head and came to rest side‑by‑side next to the fuselage. The third blade remained attached and had become entangled around the main rotor gearbox.

The longline, which had separated from the Mack Pull, was found a short distance away toward Pole 163. The draw wire was also found to have separated from the remote hook on the longline. The ATSB recovered a number of components from the accident site for further examination.

Engine

The engine assembly was examined and found to be complete with no evidence of pre-accident defects. All engine plumbing and wiring looms were connected to their respective components. The chip detector and magnetic plugs were examined and found to be clear of particles. The engine fuel and oil filters were examined and found to be clear of contaminants.

Recorded engine data

The engine data recorder (EDR) was shipped to France and downloaded by the of Bureau d’Enquêtes et d’Analyses (BEA). The BEA analysed the data in consultation with the aircraft manufacturer (Airbus Helicopters) and the engine manufacturer (Safran Helicopters Engines). The analysis showed that the engine was performing in a satisfactory manner until contact with the pole, when the EDR recorded a torque overlimit. The BEA report concluded that;

No anomaly was found prior the impact with the ground/pylon.

Fuel

SZS was fully fuelled on the morning of the flight from an intermediate bulk container (IBC), which was owned and maintained by the operator. The amount of Jet A1 taken aboard was 315 litres, which was sufficient to carry out the planned work for that morning.

A fuel sample was taken from the aircraft post-accident and from the IBC. Both series of testing indicated that the fuel was clean and clear of any contaminants.

Instruments and Avionics

The instrument panel fitted to SZS was the basic panel with added turn and slip and glideslope indicators. An air conditioning control panel and hour meter was also installed.

Emergency Locator Transmitter (ELT)

SZS was fitted with a KANNARD 406 AF-H ELT. The ELT, with part number S1822502-02 and serial number LX1100019317, had an expiry date of November 2024. The ELT activated automatically during the accident sequence and was deactivated by an attending police officer.

Flight controls

All flight controls were examined, and control continuity was established for both main and tail rotor systems. A number of control tubes displayed bending damage due to contacting the surrounding structure during the accident sequence.

Mack Pull and longline

An examination of the Mack Pull and cargo hook did not reveal any defects. Company standard practice was to install the longline with a shackle at both ends however, the draw wire did not have a shackle fitted for the connection to the remote hook. The upper end connected to the helicopter hook did have the shackle installed as required.

The remote hook and longline detached from the aircraft cargo hook during the accident and were located a short distance from SZS, drawn backwards by the retracting load of the draw wire. It could not be determined how it unhooked from the Mack Pull cargo hook. After detaching from the Mack Pull, the remote hook struck a large rock, indicated by orange paint transfer from the hooks’ outer cage. The hook then bounced to another location, shown by a ground scar. The draw wire was found detached from the remote hook. On-site testing indicated it was likely the uncoupling of the draw wire occurred during the impact with the rock.

Post impact fire

A small post impact fire occurred at the engine exhaust. Responders used hand-held fire extinguishers to prevent the spread of fire to the airframe. The resulting damage was minimal and did not show evidence of a fire outside of the engine exhaust.

Additional information

Operational information

The pilot, who was the deputy chief pilot (DCP) for Aeropower and the chief pilot (CP) mobilised to Adelaide on 31 January 2019 in preparation for operations at Carrapateena. The intention was that the CP would use this job as an opportunity to train the DCP in powerline stringing operations, then once signed-off, the DCP would complete the rest of the job solo. On 3 February both pilots mobilised to Port August and arrived at Carrapateena on 4 February for an all-stakeholder briefing for the stringing operation. The key stakeholders present were:

• OZ Minerals – the mine site operator
• Ventia – Principal contractor
• ElectraNet – Contracted to build, own, operate and maintain the powerline infrastructure
• Powerlines Plus (PLP) – sub-contracted by Ventia to build the powerline
• Aeropower – contracted by PLP for the helicopter stringing operations.

Later that day the Aeropower pilots were audited by an independent safety auditor contracted by ElectraNet to assess their capability to safely undertake the job. At this point Aeropower were already contracted to do the work. The next day, 5 February, flying operations began.

Summary of stringing operations

Tour 1 of the helicopter powerline stringing operations started on 5 February and continued until 7 February. During these 3 days, stages 5 and 6 were completed. Stage 5 comprised 22 poles while stage 6 comprised 21 poles. Each stage was completed thrice, once for each of the three wires suspended by the poles. At the end of tour 1, on 7 February, the DCP was signed-off on powerline stringing and the CP departed the site.

Stringing for tour 2 started on 18 February and was conducted by the DCP solo, without the CP on-site. Stage 7 (15 poles), was completed on 18 February and stage 8 was completed on 19 February (19 poles). Again, all stages were conducted three times.

Tour 3 stringing operations commenced on 10 March with the 20 poles of stage 4. This was followed the next day with stage 9 (21 poles). Again, all stages were completed three times by the DCP flying solo. Tour 4 started 9 days later, on 20 March. Including the 4 poles strung on the morning of the accident, the pilot had strung 122 poles, all but the last 4 were strung 3 times.

Accident span gradient

The span width between poles 163 and 164 (the accident span) was 174 m, one of the shortest the pilot had undertaken at Carrapateena. Indeed, of the 122 spans that the pilot had strung at Carrapateena, only 4 were shorter than the accident span. In addition, the elevation gain between pole 163 and 164 was 12.86 m. This was the largest elevation gain of any span the pilot had undertaken at Carrapateena. As a result of the span length and elevation gain, the accident span between pole 163 and 164 had the greatest gradient of any span the pilot had conducted at Carrapateena.

Use of load rings

In response to an ATSB investigation (ATSB report 200300011), the Civil Aviation Safety Authority (CASA) airworthiness bulletin AWB 25-006 was issued (and has since been revised). The bulletin applies to all rotorcraft engaged in underslung load / non-human external cargo. It highlights the importance of using a primary load ring and shackle on cargo hooks to prevent both an inadvertent release or a jammed hook.

The Aeropower operations manual was consistent with this regulatory guidance, with sections 9.1.3 and 9.1.4 stating;

9.1.3. DO NOT put a rope of any kind directly onto the cargo hook. It can twist and hang up preventing release if required.

9.1.4. DO use a shackle or primary load ring to attach directly to the hook to ensure smooth release. Make sure it is large enough to fall free without becoming trapped by the dropping tongue of the hook.

On the day of the accident a Powerlines Plus ground staff was assigned to hook up the draw wire to the helicopter. As they had not performed the task before, during the pre-flight briefing, the pilot instructed the ground staff on the procedure. It was reported that the use of a load ring or shackle was not mentioned, and that the instruction given was to connect the draw wire directly to the remote hook. Other ground staff reported never seeing a load ring or shackle between the draw wire and the remote hook at any time during the Carrapateena operations.

Power line stringing methodology

The purpose of powerline stringing is to attach electrical conductor wire to pulleys that are suspended on towers (or poles). Light-weight conductor wire on smaller poles can be strung using an elevated work platform (‘cherry-picker’) and pulled through with a small winch. While heavier gauge wires, such as that used at Carrapateena, necessitates the use of heavy machinery to pull the conductor between towers. Helicopters can also be used for powerline stringing. The advantage of using helicopters are;

• Much faster than pulling a conductor wire with a bulldozer.
• Minimised disruption to ecologically or culturally sensitive land (the Carrapateena site had cultural sensitivities).
• The ability to traverse rugged terrain that would be inaccessible to ground-based heavy machinery.

One of the limitations of using a helicopter is the weight carrying capacity of the aircraft. For jobs that require a heavy conductor wire, a lighter weight draw wire is strung by the helicopter. Then, a fixed position ground-based winch uses the draw wire to pull the heavier conductor wire back through the pulleys.

Taught methodology

Between 5 and 7 February 2019, the DCP received instruction in helicopter powerline stringing methodology. The stringing method taught by the CP had several key features, these included:

• A straight-line flight path is maintained between each pole.
• The helicopter hovers and traverses at an angle of about 90° (sideways) to the path of the wire. This ensures that visibility of both poles in maintained. The strung pole should be visible through the right cockpit door/window and the target pole should be visible through either the left cockpit door/window or the open rear left door (Figure 7).

Figure 7: Orientation of helicopter relative to path of travel during stringing operations.

 Source: Aeropower work instruction AS350 – Mack Pull

• After clipping in the draw wire to the pulley, height is maintained for a short distance to ensure there is enough weight in the line to hold it down on the pulley.
• As the helicopter traverses to the next pole, altitude is gained to a height greater than that of the next pole.
• The helicopter traverses directly over the top of the target pole. Visibility of the pole is maintained by use of aircraft mounted mirrors.
• Once clear on the other side of the pole, the helicopter descends to the height of the target pulley to clip the wire in.
• The process continues until the stage is complete.

Observed methodology

The DCP was deemed competent in the stringing method and signed-off by the CP at the end of tour 1 on 7 February 2019. All subsequent stringing operations were conducted by the DCP solo.

Nothing unusual or untoward was observed regarding the stringing methodology during the two days of flight operations of the second tour. However, the Aeropower refueller, who was experienced in stringing operations, never observed the stringing operations due to the location of the refuelling site. During the third tour a different Aeropower refueller was on-site and took photographs and video of the stringing operations. Some of the key points observed were;

• After clipping in the draw wire to the pulley the helicopter traversed out to the side (left side relative to direction of travel) en-route to the target pole.
• The aircraft did not gain altitude while traversing in-between poles.
• The helicopter pulled the draw wire in a pronounced tail-back attitude, with respect to the direction of the pull (Figure 4).
• Rather than traversing directly over the target pole, the helicopter came back in from the left side and came over and around the pole.

This modified technique continued into tour 4 and was observed by a number of witnesses on the day of the accident. Witnesses stated that the helicopter never came above the height of pole 164 before colliding with it.

ADS-B data (Figure 8) from the day of the accident shows a flight path consistent with what was described by witnesses. The data shows that the aircraft maintained a low altitude between poles. Only once in close proximity to the next pole did the aircraft rise above the height of the pole. The data also shows the aircraft tracking to the left of the direct path and traversing around the pole rather than directly over it.

Figure 8: ADS-B data of the flight path from pole 159 to 164

Source: FlightRadar24 and Google Earth, annotated by ATSB.

Regulatory oversight

Other than the low level and sling operations endorsements, there are no other specific Civil Aviation Safety Authority (CASA) requirements for undertaking powerline stringing operations. Additionally, there are no recommendations or requirements from CASA regarding the training requirements for operators training pilots in powerline stringing. Nor are there any requirements for any supervision post-training. It is up to the individual operators to provide what they determine to be an appropriate syllabus of training and supervision.

The pilot was provided the training required by Aeropower procedures and satisfied all CASA and Aeropower requirements to conduct powerline stringing. Although there was no requirement in Aeropower procedures for post-training supervision, the CP did try to provide indirect supervision after they had left Carrapateena. The CP stated they were in regular contact with the DCP during tours 2 and 3 to check up on how the DCP was going. It was reported that the DCP did not raise any concerns regarding the job or the stringing methodology.

Related occurrences

A review of the ATSB’s national aviation occurrence database revealed only one other occurrence reported to the ATSB in the 20 years between 2000 and 2019 involving helicopter powerline stringing operations. That accident, also involving an Aeropower aircraft, was investigated by the ATSB (Investigation report AO-2008-025). A summary is below.

On 9 April 2008, the crew of a McDonnell Douglas Helicopter Company MD369ER helicopter registered VH-PLU, experienced a substantial loss of engine power while conducting low-level powerline stringing operations. The helicopter impacted the ground and was seriously damaged. The two occupants were seriously injured.

The investigation determined that the pilot in command was operating the helicopter with a fuel tank quantity that did not guarantee continuous operation of the engine at the flight attitudes experienced during the powerline stringing operation.

As a result of the accident, the operator revised its fuel management procedures for powerline stringing operations.

In the same 20-year period Aeropower was involved in the following five accidents that were investigated by the ATSB (this includes AO-2008-025, previously mentioned):

• 200505332: Loss of tail rotor authority – 9 km north of Warwick Queensland, VH-SUV
• AO-2008-025: (Summarised above) Fuel-related event 16 km south-east of Townsville Airport, Queensland 9 April 2008
• AO-2008-078: Wirestrike - McDonnell Douglas 369D, VH-PLJ, 13 km north of Murray Bridge, South Australia, 19 November 2008
• AO-2012-082: Collision with terrain - Schweizer 269C-1 helicopter, VH-LTO, Redcliffe Aerodrome, Queensland, 18 June12
• AO-2016-078: Fuel exhaustion and collision with terrain involving McDonnell Douglas Corporation 369, VH-PLY, 36 km north‑west of Hawker, South Australia, on 17 July 2016

Of note, the wirestrike fatal accident in 2008 (AO-2008-078) involved a pilot that was recently instructed in a new task (platform work – joint-testing). The accident occurred the day after training had completed on the pilot’s first unsupervised joint-testing job. Although experienced, with 3,744.2 total flight hours, at the time of the accident the pilot had a total of about 27 hours on platform work.

The report stated:

Had the chief pilot been able to supervise the task on the day of the occurrence as planned, it was possible that he may have detected one or more of the earlier mid-span transpositions and alerted the crew to the hazard. That would probably have forewarned the crew to anticipate other mid-span transpositions along the line, and increased the likelihood that they would detect the transposition between towers STR0031 and STR0032.

One of the safety factors identified by the investigation was;

There was no direct supervision of the joint-testing operations [Minor Safety issue].

_______

5. Air Maestro is a cloud-based Pilot Management Software which includes an electronic pilot’s logbook.
6. Since the helicopter was manufactured, the type certificate of the helicopter was changed from Eurocopter to Airbus Helicopters.
7. A free-turbine turboshaft is a form of turboshaft or turboprop gas turbine engine where the power is extracted from the exhaust stream of a gas turbine by an independent turbine, downstream of the gas turbine and is not connected to the gas turbine.
8. Bureau of Meteorology.">Following requests from the aviation industry, the Bureau of Meteorology changed the format of Area Forecasts (ARFORs) from text based to graphical on 9 November 2017. The new format is known as a Graphical Area Forecast (GAF). More information regarding GAFs is available from the Bureau of Meteorology.
9. A METAR is a routine report of meteorological conditions at an aerodrome.
10. QNH: the altimeter barometric pressure subscale setting used to indicate the height above mean seal level.
11. Ceiling and visibility okay (CAVOK): visibility, cloud and present weather are better than prescribed conditions. For an aerodrome weather report, those conditions are visibility 10 km or more, no significant cloud below 5,000 ft, no cumulonimbus cloud and no other significant weather.
12. Bearing of celestial body measured clockwise from true north.

Safety analysis

Introduction

While stringing powerlines to the Carrapateena mine about 60km east of Woomera Airfield, South Australia, Airbus Helicopters AS350B3e Écureuil (Squirrel) registered VH-SZS, pulled draw wire towards pole 164. Witnesses observed the aircraft traverse slowly up the gradient of rising terrain towards the pole in a near backwards attitude toward the morning sun and in the presence of substantial dust. As the aircraft approached the pole it was observed to continue to fly in a controlled manner until it collided with the pole and fell to the ground.

Site and wreckage examination did not identify any aircraft defects or anomalies that might have contributed to the accident. The recorded engine data also showed no anomalies with the engine prior the impact with the pole. Additionally, no evidence was found to suggest any medical, fatigue related or physiological issues that would have affected the pilot’s performance on the day of the flight. Therefore, this analysis will focus on the operational and environmental factors that led to an experienced helicopter pilot inadvertently colliding with a known obstacle.

Development of the accident

Altered methodology

The pilot received 7.2 hours of training in helicopter powerline stringing in the 3 days of the first tour between 5 February and 7 February 2019. By the third tour (March 10-11) video and photographs taken of the stringing operations showed that the pilot had altered the methodology from that which was taught. Witnesses on the day of the accident also described the same modified method being used. The new method placed the helicopter at a lower operating height above the ground, in a tail-rear attitude, while tracking out to one side before climbing around the pole.

It is not known when exactly the pilot began altering the stringing method, only that it was in use during the third tour and on the accident day. It is therefore likely that the pilot had successfully strung dozens of poles using the new method before the accident, possibly re-enforcing the validity of the method to the pilot.

Span length

By 20 March, the pilot had strung 122 poles (almost all of which were strung 3 times). The length of these spans varied from 156 m to 351 m. The vast majority (85 per cent) of the spans were between 200‑300 m in length, with the average being about 250 m. The accident span was
174 m, one of the shortest of the 122 the pilot had done. Only 4 spans were shorter, and they were all strung on March 10, 10 days prior to the accident. Additionally, the span immediately prior to the accident was 253 m. The accident span was nearly 80 m shorter than the average span, and 79 m shorter than the penultimate span. Based on the pilot’s previous experience, it is possible the pilot’s expectation was that pole 164 was still some distance away at the time on the collision. Compounding this risk was the gradient of the accident span. With an elevation gain of 12.86 m, the span between poles 163 and 164 had the greatest gradient of any the pilot had flown at Carrapateena.

Visibility of pole 164

A feature of the taught stringing method was that both the recently strung pole and the next target pole are both visible at all times. Maintaining a straight-line path between the poles with the aircraft at 90° (sideways) to the relative track ensures visibility of both poles is maintained. The method also places the aircraft at an altitude higher than the target pole, therefore safeguarding against collision. The pilot’s altered methodology placed the helicopter both at lower altitude and in a pronounced tail-rear attitude.

The low altitude exacerbated the amount of dust in the air around the helicopter. Witnesses described a plume of dust higher than the nearby poles. Although the perspective of observers on the ground may not accurately represent that of the pilot, it is clear from observations and photographs taken on the day (Figure 4), that there was significant dust in the vicinity of the helicopter as it approached pole 164.

Analysis of the sun position and observations made on site indicated that the sun would have been in the general direction of the pilot’s vision of pole 164. Although the pilot was wearing a helmet mounted visor at the time of the accident, sun glare, particularly in combination with dust, may have reduced visibility of the pole.

Additionally, several witnesses, as well as photographs, show that the helicopter was being flown in a near backwards attitude as it traversed towards pole 164. Although it is difficult to determine the exact proportional effect of each element in isolation, it is likely that in combination, the near backwards attitude of the aircraft, significant dust and the position of the sun would have led to a reduction of the pilot’s visibility of pole 164 and the ground. In the absence of visual cues of the pole it is likely that the pilot’s situational awareness of pole 164 was degraded leading to the pilot inadvertently colliding with it.

Supervision

The operator did not have any documented requirements for supervision after the pilot was signed-off for powerline stringing, nor were they required to by regulations. Despite this, after the chief pilot left Carrapateena on 7 February 2019, they were in contact with the deputy chief pilot by telephone several times to check-in and see how the job, and the pilot, were going. Unfortunately, this indirect supervision relied either on the pilot being aware there was a problem with their methodology, or the pilot disclosing that they had intentionally altered the methodology.

The investigation could not determine why the pilot modified the stringing methodology. It is possible it was a result of an unperceived degradation of a newly taught skill, or the intentional modification of the technique. In either case, it is highly likely that ongoing supervision by an experienced powerline stringing operator would have identified the modified methodology and the associated risks.

Findings

From the evidence available, the following findings are made with respect to the Collision with terrain involving Airbus Helicopters AS350B3e, VH-SZS 60 km east of Woomera Airfield, South Australia, on 20 March 2019.

Contributing factors

• The pilot was using a stringing technique that was different to that instructed by the chief pilot. The modified method resulted in the aircraft operating at a lower height above the ground, which led to the pilot colliding with pole 164.
• Due to a combination of the attitude of the aircraft, dust and the position of the sun, it is likely that the pilot lost situational awareness of pole 164, leading to the collision with it.

Other factors that increased risk

• There were no requirements in Aeropower procedures to provide any post-training supervision for powerline operations. What supervision was provided was ineffective in identifying that a modified stringing method was being used by the pilot. [Safety issue]

Safety issues and actions

Safety issue: Aeropower post-training supervision

Safety issue number: AO-2019-015-SI-01

Safety issue description: There were no requirements in Aeropower procedures to provide any post-training supervision for powerline operations. What supervision was provided was ineffective in identifying that a modified stringing method was being used by the pilot.

Sources and submissions

Sources of information

The sources of information during the investigation included the:

• Aeropower Pty. Ltd.
• OZ Minerals
• ElectraNet
• Civil Aviation Safety Authority
• South Australian Police Service
• Bureau of Meteorology.
• Airservices Australia
• accident witnesses
• video footage and photographs of the accident flight and other photographs and videos taken on the day of the accident and prior to the accident.
• recorded data from the Engine Data Recorder unit on the aircraft.

References

Aeropower work instruction AP-WI 2653 – Cable Stringing – AS350 – Mack Pull

Aeropower operations manual AP-OM 0610 – Powerline stringing (Electrical pylon cable laying)

ATSB investigation report (200300011)

Civil Aviation Safety Authority (CASA) airworthiness bulletin AWB 25-006

ATSB research publication AR-2012-035

Submissions

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

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

• Civil Aviation Safety Authority
• Aeropower Pty. Ltd.
• The chief pilot
• OZ Minerals
• Ventia
• Powerlines Plus
• ElectraNet
• BEA

Submissions were received from the Civil Aviation Safety Authority, Aeropower, the chief pilot and OZ Minerals. The submissions were reviewed and where considered appropriate, the text of the report was amended accordingly.

Purpose of safety investigations & publishing information

Purpose of safety investigations The objective of a safety investigation is to enhance transport safety. This is done through: identifying safety issues and facilitating safety action to address those issues providing information about occurrences and their associated safety factors to facilitate learning within the transport industry. It is not a function of the ATSB to apportion blame or provide a means for determining liability. At the same time, an investigation report must include factual material of sufficient weight to support the analysis and findings. At all times the ATSB endeavours to balance the use of material that could imply adverse comment with the need to properly explain what happened, and why, in a fair and unbiased manner. The ATSB does not investigate for the purpose of taking administrative, regulatory or criminal action. Terminology An explanation of terminology used in ATSB investigation reports is available here. This includes terms such as occurrence, contributing factor, other factor that increased risk, and safety issue. Publishing information  Released in accordance with section 25 of the Transport Safety Investigation Act 2003 Published by: Australian Transport Safety Bureau © Commonwealth of Australia 2021 Ownership of intellectual property rights in this publication Unless otherwise noted, copyright (and any other intellectual property rights, if any) in this report publication is owned by the Commonwealth of Australia. Creative Commons licence With the exception of the Coat of Arms, ATSB logo, and photos and graphics in which a third party holds copyright, this publication is licensed under a Creative Commons Attribution 3.0 Australia licence. Creative Commons Attribution 3.0 Australia Licence is a standard form licence agreement that allows you to copy, distribute, transmit and adapt this publication provided that you attribute the work. The ATSB’s preference is that you attribute this publication (and any material sourced from it) using the following wording: Source: Australian Transport Safety Bureau Copyright in material obtained from other agencies, private individuals or organisations, belongs to those agencies, individuals or organisations. Where you wish to use their material, you will need to contact them directly.

Safety summary

What happened

On 28 January 2019, at 1908 Eastern Daylight-saving Time,^[1] a Sikorsky S-64E Skycrane, registered N173AC and operated by Erickson Inc., collided with water at Wood Creek Dam, Victoria. The collision occurred following an approach to the dam to fill an external tank with water for firebombing operations. All the crew exited the aircraft and swam to shore. One crewmember was seriously injured and two were uninjured. The aircraft was substantially damaged.

What the ATSB found

The ATSB found that the approach path to the dam was incrementally shortened over the course of the days’ operation. It is likely that the final tight approach path was at the upper margins of allowable speed and angle of bank, requiring a steep flare that contributed to the aircraft entering vortex ring state on approach.

Furthermore, the shape of the dam and surrounds of the site reduced the opportunity for recovery, and the aircraft impacted the water. The carriage of additional crew increased the risk of injury, while training for emergencies directly supported the crew’s survival.

What's been done as a result

Erickson Inc. advised that the following safety action was taken in response to this occurrence:

• vortex ring state avoidance and recovery was to be emphasised in future training and checking
• a policy preventing non-essential personnel from being aboard during firefighting operations had been introduced.

In addition, the organisation that facilitated operation of the United States‑registered Skycrane during Australian firebombing operations, Kestrel Aviation, advised that the following safety action was also undertaken:

• It was reiterated to pilots that, though aircrew work in close partnership and cooperation with aerial attack supervisors (AAS), AAS instructions are advisory. The pilot in command retains full authority to make decisions to ensure the safety of the aircraft and management support was available if escalation was required.
• Kestrel Aviation increased the frequency of contact with Erickson Inc. crews to provide safety management support, and reduce operational pressure.

Safety message

When performing aerial work it is easy to accept incremental changes that gradually reduce margins. While these changes often increase efficiency, it is worth checking how much an operation has deviated from earlier versions and re-evaluating elements if they appear less stable.

Helicopters excel in confined areas, yet are vulnerable when operating within them. Periodic reassessment of confined areas, and approach and departure profiles, should be done throughout the duration of an operation. Both supervising parties and operating crews are well-positioned to do this.

The ATSB has previously emphasised the importance of Helicopter Underwater Escape Training (HUET) for all over-water helicopter operators. This accident demonstrates the value of HUET in saving lives.

Following an accident, it is common to overlook the need to unplug one’s helmet. Using a good quality extension cable that will maintain the integrity of communications and release under tension in the event of an emergency can also save lives.

__________

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

The occurrence

What happened

On 28 January 2019, a Sikorsky S-64E Skycrane, registered N173AC, operated by Erickson Inc., was prepared for firebombing flying activities at Essendon Airport, Melbourne, Victoria. The Crew Chief, a licenced aircraft maintenance engineer, confirmed the aircraft’s serviceability and readied it for flight.

The crew of N173AC comprised three specialists:

• Pilot in Command (PIC), handling the aircraft and managing the task
• Second in Command (SIC), supporting the PIC with operational calculations and monitoring
• Crew Chief, voluntarily supporting the crew in flight with systems knowledge, and keeping a lookout for obstacles behind the aircraft, from a rearward‑facing seat.

The crew were highly experienced in S‑64 firebombing operations. The PIC had eighteen years’ helicopter experience and had operated the S-64 for four years. The SIC had forty-four years’ helicopter experience, twenty years flying S-64, and had been firefighting in Australia for twenty years. The Crew Chief had thirty-four years’ experience in helicopter engineering, including twenty-six years maintaining and developing the S-64.

All the crew reported that they were acclimatised and well-rested. Both pilots acted as alternating PIC and SIC in two-hour cycles throughout the day. The PIC sat in the left seat, and the SIC in the right. The pilots exchanged positions and roles prior to the beginning of each cycle. The accident occurred on the third cycle of the day.

Figure 1: Sikorsky S-64E Skycrane helicopter, N173AC

Source: Uniform Photography

History of the flight

At about 1000 Eastern Daylight‑saving Time,^[2] the crew repositioned the aircraft to Latrobe Valley Airport, 125 km east of Melbourne. There, they rested and prepared the aircraft while awaiting further instructions. After lunch, the crew was tasked with firebombing activities to the west of Thomson Dam, Aberfeldy, Victoria (Figure 2).

An aerial attack supervisor (AAS) coordinated the aerial assets for the firefighting mission. The AAS identified a dip site.^[3] The considerations for selection of the dip site included:

• no obstacles or wires
• that the site would remain clear of smoke
• the distance from the flame front allowing efficient delivery of suppressant
• aircraft working in concert could fill and drop their load while maintaining safe separation from each other.

Once the AAS identified the dip site, they showed the firebombing crew its location. The firebombing crew then had the final say on the dip site’s suitability for the operation.

Figure 2: Dip site location (Fire boundary as of 31 January 2019)

Source: Country Fire Authority

The dip site was Wood Creek Dam, 7 km west of the fire front. It sat at 3,480 ft above mean sea level, at the eastern base of Mount Gregory, in the Yarra Ranges National Park, Victoria (Figure 3). It had a narrow body and steep sides surrounded by tall trees. The crew assessed the dip site as confined, but not outside acceptable limits of operation.

The flight crew used the Aircraft Weight Reference Guide to calculate how much water the aircraft could carry, and then reduced the calculated figure by 91 kg to optimise performance for departure from the dip site.

Figure 3: The steep sides and narrow body of the dip site pictured from the west

Source: Department of Environment, Land, Water and Planning, Victoria, annotated by the ATSB

The crew used the aircraft’s pond snorkel^[4] to fill the tank. The snorkel required the aircraft to be stationary for up to 45 seconds, and a dedicated pump provided the pressure to fill the tank. While there were operating instructions and a checklist, there were no specific procedures around approaching waterways with a pond snorkel.

The operator classified firebombing as an external load operation, since the suppressant can be jettisoned. Procedures for control of the aircraft during external load operations required:

• descent with any combination of airspeed and rate of descent as long as rate of descent was below 800 ft/min when below 200 ft above ground/water level
• landing with a nose-up attitude of less than 10° in order to avoid tail skid strike
• limiting angle of bank to 30° for safe operation when the Automatic Flight Control System (AFCS) was engaged
• AFCS to be engaged in normal operations in order to smooth pilot inputs
• minimum clearance to obstacles of half a main rotor diameter (11 m for the S‑64).

During filling, the helicopter was positioned one main rotor diameter from the left-hand side of the dam for the PIC to keep visual hover references. This left no more than two rotor diameters to the right.

On each fill, the crew flew a descending right turn, stopped in a high hover, then descended vertically into the dam. Satellite data showed early approaches had a final approach length of 300 m to 400 m. As the aircraft crossed the southern tree line of the dip site, airspeed averaged 30 kt, and the rate of descent averaged 630 ft/min.

After a number of water drops, the AAS re-tasked the crew to fight a flame front further north, which was east-northeast from the dip site. Each drop was also incrementally further north. This resulted in the crew gradually tightening the approach to the dip site (Figure 4).

Figure 4: Change in working location over time

Source: Google Earth, Kestrel Aviation, annotated by the ATSB

During the occurrence approach, the tighter approach resulted in a greater than normal flare^[5] to arrest the aircraft at the aiming point in the dip site. The higher nose pitch up prompted the SIC to advise the PIC to move forward of the trees before descending any further to ensure tail rotor clearance. Clear of the trees, the flare was increased.

While descending with a nose-high attitude, the aircraft struck the water tail-first, submerging and removing the tail rotor, causing rapid rotation to the right through one and half turns. While rotating, the main rotor blades separated as they contacted water. The right cockpit door separated from the fuselage, and the aircraft came to rest on its left side, submerging the cockpit.

Each crewmember recalled the rehearsed drills from their helicopter underwater escape training (HUET). They identified their seat belt and nearest exit to orientate themselves in the aircraft. They all waited until the last moment to draw a breath, and did not unbuckle and exit the helicopter until motion had ceased. The crew reported that it was not possible to see anything underwater, and that jet fuel contamination was present.

The SIC in the right seat exited through his doorway, from which the door was already missing. The PIC could not open his door so he swam across the cabin (up) and was assisted by the SIC to exit through the right hand door. As the rear door was jammed, the crew chief in the aft seat pushed out a window from the rear of the cabin, and exited through it.

Neither pilot unplugged their helmet. However, the extension cords from the aircraft to the helmet plug allowed the plug to release, preventing the helmets from snaring the pilots. All three crew escaped, and inflated their life jackets. Two crew were uninjured, and one crewmember sustained a knee injury.

At the time of the accident, crews aboard S-76 and S-61N helicopters were assessing the potential of the dip site for later use in night operations. An AAS aboard the S-76 relayed details of the accident to an incident controller who enacted the emergency response plan. Neither the S-76 nor the S-61N was equipped or able to provide direct assistance, other than monitoring, and relaying information.

Following exit from the helicopter, the only form of communication available to the Skycrane crew was hand signals. They gave thumbs-up indications to the crew of the overhead S-61N to advise that they were okay. The Skycrane crew then swam to shore and trekked through dense bush to a road where they were met by rescuers.

Meteorological information

The crew received a situation report, including weather and a common barometric pressure^[6] as they began the firefighting activity. Following the failure of a 4G-equipped iPad earlier in the day, beyond this report, the crew did not have access to up-to-the-minute weather data.

The weather on the day saw temperatures over 25°C, a significant reduction from recent heatwave conditions. Winds aloft were northerly and pushed plumes of smoke to the south. The crew and witnesses to the event all assessed the wind to have been a northerly. The crew of the Skycrane advised that the wind had dropped off from around 16 kt and remained a light northerly.

Turbulence was reported to be mild. Outside of smoke, visibility was greater than 10 km. At the time of the accident, the sun was at 258°, and 15° above the horizon.

Locations on the ground showed significant local variation in wind direction and strength throughout the day (Figure 5).

Figure 5: Local variation in wind speed and direction. (15-minute average 1900 to 1915)

Source: Google Earth, Wunderground, Bureau of Meteorology, annotated by the ATSB

Flight recorders

It was a contractual requirement that all firefighting aircraft were equipped with satellite tracking devices. That data was stored remotely from the aircraft and was available shortly after the accident. The system recorded the location, altitude, heading, and groundspeed of the aircraft at 15‑second intervals for the duration of operation.

The Skycrane was also fitted with a Universal Avionics CVR-120 cockpit voice recorder (CVR). Divers recovered the CVR 45 days after the event, once the complex task of recovering the helicopter allowed access to the device. The CVR, submerged for the duration, showed little outward damage, yet voice data could not be recovered from the unit.

Vortex ring state

Vortex ring state (VRS) is a condition of powered helicopter flight that causes a loss of lift in the rotor system. During normal operation, the rotor system pushes large amounts of air down while it produces lift. If the helicopter descends into this downwash, the air can recirculate back up and over the rotors instead of it flowing down and away. This causes the same parcel of air to circulate around the rotor. As a result, the rotor system no longer has the steady stream of air required to produce lift and the helicopter will descend despite the application of additional power.

The United States Federal Aviation Administration Helicopter Flying Handbook details the methods of VRS recovery as follows:

The traditional recovery is accomplished by increasing airspeed, and/or partially lowering collective to exit the vortex. In most helicopters, lateral cyclic thrust combined with an increase in power and lateral antitorque thrust will produce the quickest exit from the hazard. This technique, known as the Vuichard Recovery (named after the Swiss examiner from the Federal Office of Civil Aviation who developed it) recovers by eliminating the descent rate as opposed to exiting the vortex.

The crew were trained to use the Vuichard recovery technique for recovery from vortex-ring state. In the Skycrane, it requires the pilot to apply full power, right cyclic^[7] and left pedal to side slip the helicopter out of its own downwash and into the ascending air just outside of the rotor system.

Safety analysis

Shortening of approach and vortex ring state

The sun progressed to a point low in the west, opposing the crew’s turn onto final approach, and casting long shadows from the steep sides, across the tree line and the surface of the dam. The crew reported that from their angle of approach the surface looked glassy, supporting their assessment of the wind becoming lighter. Video recorded shortly after the event showed that the shape of the dip site and shadows disguised a light tail wind. Wind was only visible on the surface through a 10-degree arc from the south-southwest.

A witness to the event reported that the aircraft had an apparent high rate of descent and a nose‑high attitude. The crew reported that they did not feel that any of the parameters were excessive, though speed and angle of bank were felt to be at the higher end of their normal range.

The satellite data showed the accident approach was a right-hand turn, with about a 30° angle of bank, and a radius of 150 m. The rate of descent developed from 650 ft/min to 780 ft/min. All flight parameters were within operational limits, however the length of the final approach was considerably shorter than earlier approaches (Figure 6).

The shorter approach at the upper end of the acceptable envelope of operation required a steeper than normal flare to stop the helicopter. The crew reported that once they descended below the tree line, the aircraft generated no lift and fell into the dip site, colliding with water. The crew stated that they had very likely encountered vortex ring state (VRS). The topography, high rate of powered descent, and steep flare that reduced the airspeed, created conditions conducive to the onset of VRS. The crew reported that the rapidity of onset and dimensions of the dip site did not provide enough time or space to manoeuvre sideways to effect a recovery.

Figure 6: Shortening of final approach path

Source: Google Earth, Kestrel Aviation, annotated by the ATSB

Carriage of additional crew

The operator’s operations manual stated that only flight crew and crew essential to the operation could be carried aboard the aircraft during firefighting operations. The operation could be conducted without the Crew Chief and not all company Crew Chiefs were on board their aircraft during firefighting operations.

While the Crew Chief had significant system and task knowledge, he was not required to be on board the helicopter. On this occasion, his presence exposed him to the significant hazards associated with underwater egress. More generally, the carriage of additional personnel during specialised operations like firefighting exposes them to unnecessary risk.

Egress from the submerged helicopter

Although two other helicopters were overhead, and their crews had activated the emergency response, no immediate assistance was available to the Skycrane crew. The crew had to rely on their own resources and equipment to survive.

The crew reported that Helicopter Underwater Escape Training (HUET) was fundamental to their survival. HUET enabled the crew to act rationally and decisively when submerged in the cockpit and to use the regularly‑practiced drills to escape the aircraft.

Additionally, the helmet cord release mechanism (Figure 7) prevented snaring and potential drowning after the pilots exited the submerged aircraft without unplugging their helmets.

Figure 7: Helmet cord release mechanism

Source: ATSB

Findings

These findings should not be read as apportioning blame or liability to any particular organisation or individual.

• The crew conducted a tight descending right hand turn into the dam, inside the upper margins of the flight envelope. This approach required a steep flare on arrival and likely resulted in the rapid onset of vortex ring state.
• The dam’s steep sides and narrow tapered body provided limited opportunity for vortex ring state recovery actions, contributing to collision with water.
• The Crew Chief's presence aboard the aircraft during firebombing operations exposed him to unnecessary risk.
• All crewmembers credited their survival to skills learned and practiced in Helicopter Underwater Escape Training. In addition, the helmet cord extension cables detached easily from the aircraft, contributing directly to the crew's egress from the flooded cockpit.

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 2020 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.

__________

2. Eastern Daylightsaving Time (EDT): Coordinated Universal Time (UTC) + 11 hours.
3. Dip site: A body of water at which firebombing aircraft draw water for firefighting operations.
4. Pond snorkel: A flexible hose which hangs below the helicopter to allow the tank to be filled from a variety of water sources.
5. Flare: the nose-up pitch of a helicopter used to reduce airspeed and rate of descent.
6. Common barometric pressure: All aircraft in the vicinity set the same pressure on the subscale of the altimeter. This allows aircraft to more accurately maintain vertical separation from each other.
7. Cyclic: a primary helicopter flight control that is similar to an aircraft control column. Cyclic input tilts the main rotor disc, varying the attitude of the helicopter and hence the fore, aft, and lateral direction.

Safety summary

What happened

On the morning of 19 January 2019, a Eurocopter EC130 helicopter, registered VH-YHS, conducted a private flight from Moorabbin Airport to an authorised landing area (ALA) near Mansfield, Victoria with the pilot and two passengers on board. A return flight to Moorabbin was planned for later that afternoon.

At about 1500 (Australian Eastern Daylight Time - AEDT), the pilot and passengers boarded the helicopter at the ALA for the return flight. The pilot prepared for take-off and lifted off the helicopter more rapidly than he normally did. As the helicopter became airborne, it began to rotate counter-clockwise (yaw to the left). The pilot tried to control the yaw but the helicopter quickly turned through 360° and, unable to control it, he made a decision to land the helicopter.

The left skid of the descending helicopter subsequently contacted the ground, resulting in a rolling movement that led to the main rotor blades striking the ground. The collision destroyed the aircraft, the pilot sustained minor injuries however the passengers were uninjured.

What the ATSB found

The investigation did not identify any airworthiness issues with the helicopter and it was considered that the loss of control was not attributable to a mechanical issue. It was also determined that the prevailing light winds did not contribute to the loss of control.

The pilot reported that he did not lift the helicopter into a balanced hover, and tried controlling its yaw mainly with the cyclic control instead of through the full application of opposing right, tail rotor pedal. Management of unanticipated yaw in helicopters with shrouded tail rotors (Fenestron) is the subject of the manufacturer’s guidance and learnings from similar accidents.

Safety message

This accident demonstrates the criticality of helicopter pilots understanding the aircraft’s characteristics so that they can anticipate its response when becoming airborne, and are not surprised by events. Controlling yaw in helicopters with a Fenestron tail rotor, as in this case, is an important consideration. Airbus Helicopters and the European Union Aviation Safety Agency (EASA) provide specific guidance relating to this issue to assist pilots.

The occurrence

What happened

At 1033 Eastern Daylight‑saving Time^[1] on 19 January 2019, a Eurocopter EC130 helicopter, registered VH-YHS (YHS), departed Moorabbin Airport for a private authorised landing area (ALA), 19 km south-south‑east of Mansfield, Victoria. The pilot and two passengers were on board for the private flight to a rural property and intended to conduct a return flight that afternoon. The pilot’s pre-flight inspection had not identified any defects or outstanding maintenance issues for the helicopter.

At 1115, after an uneventful flight, YHS landed at the rural property. Over the next few hours, the pilot attended to various matters there as planned, and had lunch with the passengers.

Shortly before 1500, the pilot and passengers returned to the helicopter. The helicopter was parked in an open area, facing south with a 0.5 m-high earth mound to its left (Figure 1). The mound prevented water entering the nearby shed and ran the length of the area, which had clusters of trees around it in different directions. The pilot had undertaken five previous flights to the property in the helicopter in the previous 5 months.

After assisting the passengers to board the helicopter, the pilot conducted a walk-around and did not identify anything unusual. He then boarded and, following a normal engine start, carried out his take-off checks. As was his usual practice, he set the friction settings for both the cyclic^[2] and collective^[3] controls to minimum resistance.^[4] The wind was about 10 kt from the south-west (about 45° to the right of the helicopter), the sky was clear and it was approximately 30º C.

As the pilot increased to full power for take-off, he observed that the front right passenger had not put on her headset and signalled for her to do so. While he waited for her to put the headset on, keeping YHS on the ground, he noticed the cabin temperature was 32 ºC and turned on the air‑conditioning.

Shortly after 1500, the pilot was again ready to take-off. He raised the helicopter off the ground, more rapidly than he normally did without getting the usual ‘fine balance’^[5]. At a height of about 3 m above the ground, the helicopter began to yaw to the left (turning counter-clockwise), seemingly pivoting about the tail and its attitude became progressively unstable (Figure 1, Top).

The pilot applied inputs, mainly cyclic, to control the helicopter’s movement but the yaw increased. The aircraft now seemed to be pivoting about the main rotor, moving closer to the trees and shed (Figure 1, Middle). The pilot recalled that the helicopter felt ‘unstable’ and moved the cyclic but did not get the response he expected. In seconds, the helicopter had turned through 360° (Figure 1, Bottom). Unable to control the helicopter, the pilot decided to land and lowered the collective.

As the helicopter descended, its left skid contacted the mound, resulting in the helicopter pivoting around that skid and the main rotor blades striking the ground. The helicopter came to rest on its left side, facing the shed (Figure 2). The sequence, from lift-off to ground contact, occurred over about 5 seconds.

The pilot turned off the engine and battery, exited through the shattered left windscreen and assisted the passengers from the helicopter. The pilot sustained minor injuries while the passengers were uninjured.

Figure 1: Accident sequence

Source: ATSB analysis of information from pilot and witness video (partial) superimposed on Google Earth image

Figure 2: Accident site

Source: Seven News Melbourne, annotated by ATSB

Pilot

The pilot completed his helicopter flight training in a Hughes 300 helicopter in 2010. He completed EC130 type training in November 2011 and had accumulated 227 flight hours in that aircraft (from a total of 315 flight hours). Since his last flight review in November 2017, he had flown YHS for 13.5 hours of which 4 hours had been in the 90 days preceding the accident – the last flight being 46 days prior.

The pilot commented that he had:

• not heard or seen anything unusual with the helicopter before the accident
• tried controlling the yaw mainly with the cyclic, did not know how much right pedal he had used and assessed that he should have used more pedal to control yaw
• not flown regularly since his last flight review and noted that during his EC130 type training he had needed more pedal input than in the Hughes 300.

Aircraft information

The EC130 is a single-turbine engine helicopter with a clockwise-turning main rotor and a shrouded Fenestron tail rotor (Figure 2). The helicopter has a maximum take-off weight of about 2,427 kg and can carry seven occupants. The EC130 is a high-performance helicopter compared to the Hughes 300 (in which the pilot first trained). The Hughes 300 has a counterclockwise turning main rotor and a conventional unshrouded tail rotor.

The EC130 with its Fenestron anti‑torque system^[6] requires greater right pedal^[7] input to overcome torque from the main rotor during lift off than a helicopter with a conventional tail rotor. The pedal control inputs are also not linear with respect to the effect on helicopter yaw.

The helicopter’s manufacturer (Airbus Helicopters) published service letter 1673-67-04 in February 2005 with guidance for managing yaw. The letter reminded pilots that the Fenestron anti‑torque system requires more right pedal travel than a conventional tail rotor to counter left rotation (yaw). The letter stated that if sufficient pedal is not applied quickly to correct yaw, its rate will increase. Further, insufficient pedal input to stop yaw combined with pilot input to decrease altitude could result in the helicopter rolling to the side and contacting the ground.

Post-accident activities

There was no recorded data to determine the flight control inputs and their effect on the motion of YHS during the accident. The pilot’s account, a partially obscured witness video, and photographs of the wreckage were the main sources of evidence.

The maintenance organisation for YHS carried out an examination at the accident site before moving the wreckage to its maintenance facility. This examination found no evidence of airworthiness issues that could have resulted in the accident. It was also determined that the helicopter was within its performance envelope and had sufficient fuel for the planned flight.

The ATSB sought the manufacturer’s input for this accident and was advised that as no technical (mechanical or control) issues with YHS had been identified by the maintenance organisation, the accident was probably the result of a handling error.

In July 2019, about 6 months after the accident, Airbus Helicopters published safety information notice 3297-S-00 to highlight unanticipated yaw. The notice warned that an unanticipated yaw can be rapid and is most often toward the left (where the main rotor rotates clockwise). It further noted that even if the pilot’s response was prompt, the yaw might not immediately subside and lead to the pilot thinking that the input was ineffective.

Similar accident

In October 2015, an EC130 helicopter was departing Megève altiport, France, for a sightseeing flight when the pilot lost control of the aircraft, which collided with the ground (BEA2015-0647 report). The helicopter was destroyed, and the seven occupants were injured.

The pilot had 300 flight hours in helicopters, including 9.5 hours in an EC130 and 74 in the similar AS350 helicopter. The investigation found that while stabilised in the hover, the pilot initiated a left turn to face the climb out direction. However, the pilot was unable to stop or slow the yaw and decided to land, lowering the collective. The helicopter yawed through several more revolutions before colliding with the ground. No technical issues to explain the accident were identified.

As part of the investigation, a flight in a helicopter of the same type in similar conditions was undertaken, and it was found that pushing the right pedal to 70 per cent of its travel stopped a yaw rate of 100° per second to the left in 3 seconds.

Safety analysis

The earlier flight made by VH-YHS (YHS) that day indicated the helicopter was operating normally with no defects. The high-performance helicopter was also operating well below its maximum capacity with only three occupants.

In preparing to take-off, the pilot lifted YHS more rapidly than he normally did without first letting it rest lightly on the skids and applying control inputs to lift it gently into a balanced, controlled hover for the climb out. The higher-than-normal application of control inputs resulted in the torque from the main rotor not being balanced by the anti-torque from the Fenestron tail rotor. Consequently, once the helicopter was off the ground it yawed significantly to the left. The wind from the right may also have initially increased the yaw rate.

The pilot’s pre-take-off checks did not confirm that everyone and everything was ready for the flight. As a result, he had to delay the take-off while a passenger put on her headset. He then noticed the elevated temperature and turned on the air-conditioning. These interruptions may have influenced his actions in lifting off more rapidly than he normally did.

The rate of left yaw offered limited time to regain control. The pilot reported that he principally applied cyclic control rather than the required full application and maintenance of opposing right, tail rotor pedal input. When his applied inputs did not arrest the yaw rate, the pilot assessed that the best option was to land the helicopter.

Similar accidents in the same or comparable helicopters, together with manufacturer’s guidance, provide information for pilots to manage unanticipated yaw and avoid accidents. These show that the outcome of YHS’s attempted landing with a significant yaw rate was somewhat predictable - a skid contacting the ground, the helicopter rolling over and the main rotor blades striking the ground. The rapid development of the accident sequence (about 5 seconds) also illustrates the limited time for pilot actions/decisions in such hazardous situations, which fortunately did not result in serious injury in this case.

The maintenance organisation’s examination found no evidence of airworthiness issues with YHS to explain the accident. The pilot’s account and the manufacturer’s comments also support a conclusion that a mechanical issue and the light wind did not contribute to the accident.

Findings

These findings should not be read as apportioning blame or liability to any particular organisation or individual.

• The pilot was unable to control VH-YHS yawing to the left after lifting off and decided to land. When the left skid of the descending helicopter contacted the ground, it rolled over and the main rotor blades struck the ground, destroying the aircraft with the pilot sustaining minor injury.
• No mechanical issue with the helicopter was identified and the prevailing light wind did not contribute to the loss of control and subsequent collision.

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 2020 Ownership of intellectual property rights in this publication Unless otherwise noted, copyright (and any other intellectual property rights, if any) in this report publication is owned by the Commonwealth of Australia. Creative Commons licence With the exception of the Coat of Arms, ATSB logo, and photos and graphics in which a third party holds copyright, this publication is licensed under a Creative Commons Attribution 3.0 Australia licence. Creative Commons Attribution 3.0 Australia Licence is a standard form licence agreement that allows you to copy, distribute, transmit and adapt this publication provided that you attribute the work. The ATSB’s preference is that you attribute this publication (and any material sourced from it) using the following wording: Source: Australian Transport Safety Bureau Copyright in material obtained from other agencies, private individuals or organisations, belongs to those agencies, individuals or organisations. Where you wish to use their material, you will need to contact them directly.

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1. Eastern Daylightsaving Time (EDT): Coordinated Universal Time (UTC) + 11 hours.
2. Cyclic: a primary helicopter flight control that is similar to an aircraft control column. Cyclic input tilts the main rotor disc, varying the attitude of the helicopter and hence the lateral direction.
3. Collective: a primary helicopter flight control that simultaneously affects the pitch of all blades of a lifting rotor. Collective input is the main control for vertical velocity.
4. The helicopter flight manual suggests adjusting flight control friction settings to the preferred resistance.
5. The fine balance is a two-step lift-off where the pilot lifts the helicopter slightly to be light on the skids, while making control inputs to balance the helicopter, before gently lifting into the hover.
6. The function of the helicopter tail rotor/Fenestron is to counteract the torque produced by the main rotor to maintain directional control.
7. Pedals: a primary helicopter flight control. Left and right pedal input moves the helicopter in the corresponding direction to maintain control for directional flight (yaw).