The pilot of an AW139 emergency medical service helicopter received a TCAS ‘resolution advisory’ collision alert while transiting airspace above Mangalore Airport en route to Royal Melbourne Hospital when a Piper Seminole aircraft conducted an unanticipated missed approach to the airport, an ATSB investigation report details.

The report details that on the afternoon of 6 June 2021, as the Seminole aircraft tracked north along the RNAV-Z runway 36 approach to Mangalore, the AW139 helicopter was about 10 NM north of Mangalore and tracking south to overfly the airport at 3,100 ft. At about 1555, the Seminole commenced a missed approach resulting in the helicopter’s TCAS (traffic alerting and collision avoidance system) displaying a traffic advisory, followed by a resolution advisory.

Six seconds later, the aircraft passed in cloud 451 m (in a straight line) from each other with a minimum vertical separation of 543 ft and a minimum horizontal separation of 333 m. Both aircraft were in cloud throughout the occurrence.

"The ATSB’s investigation into this occurrence found that while the helicopter pilot was aware of the Seminole, they did not consider the possibility of the Seminole conducting a missed approach, which might conflict with the helicopter’s flight path,” said ATSB Director Transport Safety Stuart Macleod.

“The Seminole’s pilot, meanwhile, reported not hearing broadcasts from the helicopter and misinterpreted traffic advice from air traffic control, and consequently was not aware of the helicopter nearby and that an incident had occurred.”

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

“As such, this incident highlights the importance of effective flight crew TCAS training,” Mr Macleod said.

“TCAS is a complex system which serves as a ‘last line of defence’ in airborne collision avoidance. Thorough knowledge of the system is critical in ensuring that crews respond appropriately to TCAS resolution advisories.”

The Seminole was not equipped with with TCAS or Automatic Dependent Surveillance Broadcast (ADS-B) IN (nor was it required to be), the report notes.

“The ATSB stresses that in non-controlled airspace the effective use of radio remains a primary defence in avoiding mid‑air collisions, achieved by maintaining an effective listening watch and proactive communication,” Mr Macleod said.

“In addition, the ATSB strongly encourages equipping all aircraft with ADS‑B transmitting, receiving and display devices as they can significantly assist pilots in identifying and avoiding conflicting traffic.

“The continuous positional information ADS‑B provides can predict a developing situation many minutes before it becomes hazardous – a significant improvement on both point‑in‑time radio traffic advice and ‘see‑and‑avoid’.”

Read the final report: Airborne collision alert involving AgustaWestland AW139, VH-YXH and Piper PA-44-180, VH-HMQ, Mangalore Airport, Victoria, on 6 June 2021

The Australian Transport Safety Bureau has released a preliminary report from the ongoing investigation into an accident involving a geophysical survey aircraft west of Norseman, Western Australia on 3 March 2022.

The report details factual information established in the investigation’s early evidence collection phase, and contains no analysis or findings, which will be detailed in the investigation’s final report.

The aircraft, a Cessna U206G modified for low-level geophysical survey, had departed Kalgoorlie to a survey site about 120 km west of Norseman with the pilot the sole occupant on board.

The aircraft began its survey pattern at about 1252, tracking back and forth over the area at about 25 m (82 ft) above ground level. At 1343, the aircraft’s final GPS position showed it heading west at 116 kt, at about the intended survey height.

The alarm was raised when the aircraft did not return to Kalgoorlie by the expected time.

During subsequent search operations, the accident site was located in dense bushland 124 km west of Norseman, with the pilot confirmed to have been fatally injured.

On deploying to the accident site, ATSB transport safety investigators determined that the point of impact indicated the aircraft initially struck trees in an upright, but relatively steep nose-down attitude. The aircraft then impacted the ground on its left side and continued through the bush in a southerly direction, coming to rest about 45 m from the initial point of impact.

“ATSB investigators found no indications of pre-impact structural failures, and were able to establish continuity of the aircraft’s flight controls, while propeller damage and strike marks observed in the trees indicated the engine was producing power at the time of impact,” said ATSB Director Transport Safety Dr Mike Walker

“There was no indication of fire in the wreckage trail, either in the bushland or aircraft components, however the remainder of the aircraft was almost entirely destroyed by a post-impact fire.”

Along with its survey of the accident site and recovery of key components for further analysis, the ATSB has conducted interviews, and collected aircraft, operator and pilot records and documentation.

“As we progress, the ATSB will further review documentation and records, and the retrieved aircraft components,” Dr Walker continued.

The investigation will also further analyse the flight path information from the aircraft’s GPS tracking device, and review the risk controls in place for low-level survey work.

“A final report will be released at the conclusion of the investigation,” Dr Walker concluded.

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

Read the preliminary report: Collision with terrain involving a Cessna U206G, VH-JVR, 124 km west of Norseman, Western Australia, on 3 March 2022

The Australian Transport Safety Bureau has released a preliminary report from its on-going investigation into the breakaway and grounding of a product tanker in the Port of Brisbane during flooding on 27 February 2022.

The preliminary report outlines factual information established through the transport safety investigation’s early evidence collection phase. It does not include analysis or findings, which will be detailed in the ATSB’s final report.

The Hong Kong-flagged product tanker CSC Friendship was alongside the Ampol Products Wharf in Brisbane, loaded with 25,000 tonnes of diesel oil and 7,000 tonnes of gasoline for a voyage to Adelaide, on the evening of 27 February.

A low-pressure system and associated rain and wind was impacting the greater Brisbane area, resulting in significant flooding of the Brisbane River.

At about 2250, during an increased ebb tidal flow in the river, one of the ship’s stern lines parted suddenly. This increased the load on the 13 remaining mooring lines which, over the following 90 minutes, also failed.

During this time, the ship’s crew used the main engine and an anchor in an attempt to arrest the ship’s movement, and a number of harbour tugs attended to assist.

Despite these efforts, the ship broke away from the berth at about 0028 on 28 February, was swept downstream, and grounded to the east of Clara Rock beacon at Lytton Rocks Reach.

About half an hour later, a harbour pilot arrived by launch and boarded the grounded ship via the ship’s pilot ladder.

The pilot quickly established the ship was aground with the port quarter on the bank, bow slightly in the channel, and head down river.

Over the next four hours, the pilot attended the ship and, working with the ship’s crew and tugs, re-floated it at 0530. During the re-floating efforts, the ship grounded a second and third time.

After re-floating, CSC Friendship was moved downriver and anchored at Brisbane’s ship-to-ship transfer anchorage at about 0645. Subsequent inspections confirmed some shell plate damage, including buckling and medium to heavy abrasion of the hull, but no hull penetration or cracking of plate or welds.

The ship then travelled to Port Botany to discharge its cargo, before sailing to China for dry dock and repair.

The ATSB’s continuing investigation will examine weather and flood conditions prior to and during the breakaway and grounding, the effectiveness of the port procedures, operational guidance and inter-agency communications during a flood event, and the mooring arrangements relevant to this incident.

Investigators will also review internal and external shipboard communication systems, analyse relevant human factors, and verify, interpret, and analyse recorded data.

Read the preliminary report: Breakaway and grounding involving CSC Friendship, Port of Brisbane, Queensland, on 27 February 2022

After changing their flight plan in-flight without reviewing NOTAMs, the pilot of a Citation business jet landed on a closed runway which did not have the required number of unserviceability cones and crosses in place, an Australian Transport Safety Bureau investigation finds.

During pre-flight planning on 21 October 2021, the pilot of a Cessna 510 Citation Mustang checked the NOTAMs for Temora Airport, a planned refuelling stop for flight from the Sunshine Coast to Essendon Airport with four passengers on board.

“When checking the NOTAMs for Temora, the pilot dismissed notices that were deemed irrelevant to the planned flight, which was intended to land on runway 05 due to forecast weather conditions,” ATSB Director Transport Safety Dr Stuart Godley said.

“This included dismissing a NOTAM detailing that runway 18 at Temora was closed due to works in progress.”

During cruise, the pilot reviewed more up-to-date weather information and made the decision to land on runway 18, rather than 05, due to changes in wind direction and apron accessibility.

“Not hearing any broadcasts on the aerodrome’s Common Traffic Advisory Frequency (CTAF), the pilot elected to land straight-in with a 5-mile final approach to save on time and fuel,” Dr Godley continued.

On touchdown, the pilot noticed cones across the runway a long distance ahead of the threshold, but judged there was sufficient distance to stop safely before reaching them, and so elected to continue with the landing.

The pilot reported not seeing any other markings to indicate the closure of the runway.

During its investigation, the ATSB found while white crosses had been placed on the runway, they were not in locations visible to aircraft conducting a straight-in approach on runway 18. Further, the size and number of unserviceability marking cones along the runway were insufficient to fulfil the requirements of the Civil Aviation Safety Regulations Part 139 Manual of Standards (MOS) for closed runways.

“An essential component of pre-flight planning is to check all NOTAMs relevant to the planned flight, and potential changes to the plan. This includes all NOTAMs regarding all aviation facilities that a pilot plans to use,” Dr Godley said.

“Additionally, aerodrome operators must ensure all markings displayed for works are in accordance with the current MOS for aerodromes to ensure clear communication of changes that may affect the safety of aircraft operations.”

Read the final report: Landing on closed runway involving Cessna 510, VH-MSU, Temora Aerodrome, New South Wales, on 21 October 2021

Key points:

• Boeing 787 being used for freight operations flew from Melbourne to Los Angeles with tape covering its engine cowl fan static ports;
• While the flight was uneventful, the covered ports meant redundancy for the engine electronic control system was reduced;
• Job instruction card for restoring a 787 to service did not link to Boeing’s recommended procedures;
• Qantas has amended its engineering instructions to properly reference Boeing’s recommended procedures.

A Boeing 787 being used for a freight flight flew from Melbourne to Los Angeles with tape over four of its static ports, a new ATSB investigation report details.

After the Qantas 787-9 aircraft, registered VH-ZNJ, landed in Los Angeles on the morning of 22 September 2021, a Qantas engineer found tape covering the four static ports on the aircraft’s engine fan cowls.

Static ports provide important air pressure data to aircraft systems. Boeing recommends they be covered, to avoid contamination, when the aircraft is parked for periods up to 7 days, and Qantas incorporated this instruction into its ‘normal’ parking procedure.

The ATSB investigation details that on the day before the incident flight, an engineer undertook the parking procedure on the aircraft, which included covering the engine cowl static ports with ‘remove before flight’ barricade streamer tape.

“Later that day, another engineer was tasked to conduct the ‘restore’ procedure to return the aircraft to flight status,” ATSB Director Transport Safety Stuart Macleod explained.

“The tape on the engine fan cowls was not removed by that engineer, as per the manufacturer’s procedures, and this wasn’t identified by flight crew or dispatch during pre-departure checks.”

VH-ZNJ subsequently took off with the tape still on its engine fan cowl static ports.

“While the flight was uneventful, the covered ports meant redundancy for the engine electronic control system was reduced,” Mr Macleod noted.

The ATSB found that while the job instruction card (JIC) developed by Qantas for parking a 787 did link to Boeing’s recommended procedures, the JIC for restoring it back to service did not.

“This was a missed opportunity to assist engineers to readily access the current procedures and determine which ports were covered, and also allowed for different interpretations of which ports could be covered,” Mr Macleod said.

“When performing safety‑critical tasks like aircraft maintenance, it is very important that procedures are clear and unambiguous to avoid misinterpretation and error such as occurred in this incident.”

At interview, the flight crew’s second officer, who conducted an exterior inspection of VH-ZNJ before the flight, reported they were aware of the fan cowl ports, but not that they could be covered by tape.

The second officer also reported they were somewhat distracted during the inspection, as they had found a pitot tube cover on the ground, and were trying to hand it off to an engineering staff member at that time.

“The second officer also believed Qantas engineering had conducted a pre-flight inspection prior to the flight crew arriving at the aircraft,” Mr Macleod added.

Following the occurrence, Qantas distributed memos to engineering, and flight and ramp crew, highlighting the location of the fan cowl static ports and that they may be covered.

In addition, the airline amended its ‘park’ and ‘restore’ engineering instructions to both reference Boeing’s procedures.

The investigation report also notes the metre-long tail of the ‘remove before flight’ tape covering the static ports was stuck down, to prevent it being torn from the fuselage in strong winds, as per Boeing’s recommended procedure.

“This likely reduced the visibility of it covering the fan cowl static port covers,” Mr Macleod said.

“Targeted inspection of locations and components, rather than relying on streamers, which can detach, can help to identify when these covers or devices have not been removed.”

Read the final report: Aircraft flight preparation occurrence involving Boeing 787-9, VH‑ZNJ, Melbourne Airport, Victoria, on 22 September 2021

An Airvan aircraft overran the runway on landing after the pilot continued the approach despite being unable to fully extend the flaps and did not apply maximum braking in time after the aircraft landed long.

An ATSB investigation report into the accident details that on 26 December 2021, the Geraldton Air Charter operated GA-8 Airvan was conducting an air-transport flight from Geraldton to East Wallabi Island, off the Mid West coast of WA.

While initially planning for six passengers, the pilot decided to add a seventh from another flight shortly before departure, and later reported this rearrangement resulted in preparations for the flight being rushed.

Earlier in the day, the pilot had flown a Cessna 172 with a personal emergency position indicating radio beacon (EPIRB) device positioned on their right hip.

The pilot knew the EPIRB’s positioning on their right hip could prevent the full extension of the Airvan’s flap lever – which sits to the right of the pilot’s seat – but they forgot to move the EPIRB to their left hip during the rushed flight preparations.

Approaching East Wallabi Island about 30 minutes into the flight, the pilot positioned the aircraft to join the right base leg of the circuit for runway 36, and extended the first stage of flap by moving the flap lever.

“When the pilot turned onto the final leg of the circuit and attempted to select full flap for the landing, the EPIRB obstructed the lever’s movement and prevented it from locking into the full flap position,” ATSB Director Transport Safety Stuart Macleod explained.

Further attempts to select full flap were unsuccessful.

“The investigation notes the pilot did not consider a go around to allow for trouble shooting or repositioning of the EPIRB and continued the approach with just the first stage of flap extended,” said Mr Macleod.

During the landing flare, the aircraft floated more than the pilot expected, and touched down about midway along the runway – almost 300 m beyond the original landing aim point, and about 350 m from the runway’s end.

Mr Macleod noted the reduced drag of the first stage flap setting, possibly combined with a higher than normal approach speed, led to the longer float.

“While a go around should again have been considered at this stage, from the touchdown point it was still possible to stop the aircraft in the remaining runway using maximum braking,” Mr Macleod said.

“However, possibly due to prioritising retracting the flaps after landing, and the pilot not immediately recognising the risk of an overrun, maximum braking was not applied until there was insufficient runway remaining.”

The Airvan overran the runway by about 15 m, resulting in substantial damage to the aircraft, with a main landing gear leg detaching. However, the pilot and passengers were uninjured.

“This accident emphasises the need for careful flight preparation,” Mr Macleod reflected.

“Taking time to confirm that all required actions have been completed prior to departure minimises the chance of in-flight complications.”

Mr Macleod noted the accident also underlines the importance of commencing a missed approach early when an approach and landing deviate from the plan, and a safe landing cannot be assured.

“Pilots should always have a clearly-defined decision point where they can go-around if they’re not confident that a safe landing is achievable,” he said.

“This is especially relevant when landing on shorter runways.”

Read the final report: Runway overrun involving Gippsland Aeronautics GA-8, VH-WSB, East Wallabi Island, Western Australia, on 26 December 2021

Key points:

• Preliminary report details factual information established in the investigation’s early evidence collection phase;
• On-going investigation to consider flight profile, helicopter components, witness accounts, and imagery and video footage;
• Analysis and findings will be outlined in the investigation’s final report.

The ATSB has released a preliminary report from its on-going investigation into a fatal accident involving a UH-1H helicopter during firebombing operations north of Launceston, Tasmania on 14 February 2022.

The crew of an air attack helicopter that was monitoring the Labrina fireground had tasked the UH-1H, registered VH-UHX (UHX), to conduct a water drop on a small hot-spot, the report details. After UHX filled its underslung water bucket at a nearby dam, the air attack crew subsequently observed it conduct a water drop that missed the target, before commencing a gradual left turn and track away from the staging area.

Suspecting UHX’s pilot was encountering an in-flight difficulty, and wanting to avoid any potential conflict with the approaching helicopter, the air attack pilot initiated a climbing 360° turn. After completing the turn the air attack pilot trailed UHX and observed the helicopter descend toward an open paddock where it impacted the ground.

A witness at the staging area, meanwhile, also observed UHX miss the hot-spot when releasing its water load, before it commenced a descending profile, entered a hover and then rapidly yawed twice, before descending from view below the tree line.

The pilot sustained fatal injuries in the accident, and the helicopter was destroyed from impact forces and a fuel-fed fire.

Analysis of the accident site by ATSB transport safety investigators established that the helicopter had impacted the ground along a westerly flight track. Ground scars at the site showed that the tail section made first contact with the ground, followed by the skids, main rotor blades and the cabin.

The helicopter’s tail section, including the tail rotor gearbox, had separated from the fuselage, and had come to rest a short distance from the main wreckage. The bucket and line, meanwhile, had been released from the helicopter prior to the ground impact and were positioned approximately 300 m from the wreckage.

“It is important to note that this preliminary report details factual information established in the investigation’s early evidence collection phase, but it does not detail analysis or findings, which will be outlined in the investigation’s final report,’ ATSB Director Transport Safety Stuart Macleod said.

“As the investigation progresses, the ATSB will continue to analyse the flight profile, further examine helicopter components including the engine, transmission and tail rotor gearbox, consider witness accounts, and analyse accident imagery and video footage.”

The investigation will also give consideration to the helicopter’s performance, maintenance and operational history, emergency procedures, and pilot qualifications, medical history and experience.

Mr Macleod noted a final report will be published at the conclusion of the investigation.

“However, should a critical safety issue be identified at any time during the investigation, the ATSB will immediately notify relevant parties so they can take appropriate and timely safety action.”

Read the preliminary report: Collision with terrain involving Garlick Helicopters UH-1H, VH-UHX, 36 km north of Launceston, Tasmania, on 14 February 2022

A review of search data from the original Australian Transport Safety Bureau-led search for the missing MH370 aircraft has concluded that it is highly unlikely there is an aircraft debris field within the reviewed search area. 

In late January 2022, the ATSB asked Geoscience Australia to undertake a review of some of the sonar imagery collected during the original search for MH370, conducted between October 2014 and January 2017.    

The ATSB made the request after British aerospace engineer Richard Godfrey proposed an impact location for MH370 within an area surveyed during the original ATSB-led search, after his analysis of Weak Signal Propagation Reporter (WSPR) data.    

“The Geoscience Australia report notes that it is highly unlikely that there is an aircraft debris field within the area reviewed,” said ATSB Chief Commissioner Angus Mitchell. 

The review identified 11 objects not analysed during the original search. However, none were assessed to be from an aircraft wreckage debris field.    

Eight of the objects were assessed as most likely geological features, and while three were identified as anthropogenic (ie not naturally occurring), none were determined to be associated with an aircraft. 

Geoscience Australia Chief Executive Officer Dr James Johnson said over a two-month period, a team of experts had reviewed a band of high-resolution sonar imagery spanning 4,900 square kilometres.    

“This data allowed us to detect objects as small as 30 centimetres by 30 centimetres. If the aircraft was within the area we have reviewed, the sonar data would have shown a scatter field of highly reflective debris,” Dr Johnson said.   

“I want to thank my team for the skill and heart they brought to this work and the Australian Transport Safety Bureau for their leadership and partnership throughout this process.”   

Said Mr Mitchell: “The ATSB concluded its formal involvement the search for MH370 in 2017, but we acknowledge the importance of locating the aircraft to provide answers and closure to the families of those who lost loved ones and in the interests of aviation safety. 

“Can I thank Geoscience Australia for their work in applying their expertise and knowledge in reviewing the original search data.” 

Stated Dr Johnson, “We all understand the emotion that will come with this news, and those at the centre of this tragedy remain in our thoughts.”   

The data review report is available for download here.

Media inquiries: media@atsb.gov.au

Key points:

• AW139 rescue helicopter entered an uncommanded descent and lateral drift, coming within an estimated 20 ft of terrain before being recovered by pilot;
• Even for experienced air crews, operations in low-light conditions are challenging;
• Operator is in the process of installing new search lights across their fleet of AW139s, and taken other steps, with the aim of preventing a reoccurrence.

An AW139 rescue helicopter came within an estimated 20 ft of terrain as a result of an uncommanded descent and lateral drift during a 24 July 2020 night-time mission to retrieve bushwalkers from a national park.

The Toll Helicopters-operated AW139 had departed Shellharbour Airport, near Wollongong, NSW, with four crew onboard, comprising a pilot, aircrew officer, paramedic and doctor, tasked to recover two lost bushwalkers from the Bungonia National Park, east of Goulburn.

The flight was conducted under the night visual flight rules with the pilot, aircrew officer and paramedic using night vision goggles.

“On arrival at the search and rescue location, the helicopter tracked over high ground past the edge of an escarpment, where the terrain drops away to a valley floor,” ATSB Director Transport Safety Stuart Macleod explained.

“During the subsequent visual search phase an uncommanded, and increasing, rate of descent and lateral drift developed.”

The aircrew officer, who was in the main cabin by the right door, identified the increasing rate of descent and lateral drift towards a ridgeline and provided corrective instructions to the pilot.

It was estimated that the helicopter came within 20 ft of the ridgeline before the descent and drift were arrested.

Mr Macleod said the ATSB investigation found the pilot’s likely fixation on locating the bushwalkers resulted in them not maintaining an effective scan on the cockpit instruments and outside visual references.

“This resulted in the loss of hover reference and development of an unintended descent and lateral drift.”

In response to the loss of reference the pilot unsuccessfully attempted to engage the helicopter’s auto hover rather than commence an overshoot.

“A subsequent focus on selecting the automated mode further delayed the resumption of the scan and recognition of the increasing descent rate.”

Mr Macleod said radio communications between the paramedic and the ground party hindered communications between the pilot and aircrew officer.

“This inhibited the aircrew officer's ability to verify with the pilot whether the observed initial movement was intentional, preventing recovery from the initial drift and descent.”

In addition, the pilot subsequently did not announce losing hover reference, delaying the aircrew officer’s awareness of the developing situation and support to the pilot.

The ATSB also found the helicopter’s external white lighting (two pilot-steerable landing lights, and a steerable winch and handheld light operated by the aircrew officer) was inadequate.

“At the operating height the external white lighting was inadequate to illuminate the terrain below the helicopter, resulting in the pilot not identifying the developing rate of descent while searching for the bushwalkers.”

As a result of the incident, Toll Helicopters made several changes to their procedures and equipment aiming to prevent a reoccurrence.

These include fitting its AW139s with with a dedicated high-powered search light, amending sterile cockpit procedures, and changes to the operations manual.

The operator has also introduced additional human factors training with a focus on spatial disorientation, confirmation bias and communication techniques for all flight and medical crew.

“Operations at night in low light conditions can be challenging to even the most experienced crews,” Mr Macleod said.

“Low light conditions reduce available visual cues for maintaining aircraft position and undesired aircraft states can develop rapidly.

“To mitigate these risks, crews conducting night operations in such conditions should maintain adequate references, taking into account equipment limitations such as external lighting, and maintain an effective scan to ensure continual awareness of the position and movement of the helicopter.”

Read the final report: Loss of control and near collision with terrain, Leonardo Helicopters AW139, VH-TJO, 25 km east of Goulburn Airport, New South Wales, on 24 July 2020

Key points:

• While flying in the vicinity of a valley, R44 helicopter entered a low-G condition;
• Subsequent extreme teetering and mast bump resulted in the in-flight break-up of the helicopter;
• Investigation highlights that pilots of helicopters with semi-rigid rotor heads must avoid low-G situations.

A Robinson R44 helicopter broke up in flight as a result of extreme teetering, either due to turbulence or inappropriate control inputs, an Australian Transport Safety Bureau investigation has concluded.

A search was launched after the helicopter, flown by a student and instructor pilot, failed to return from a training flight from Goulburn Airport, in the Southern Tablelands region of New South Wales, on the afternoon of 2 December 2020.

Wreckage of the helicopter was found later that evening in the Bungonia State Conservation Area, approximately 31 km east of Goulburn. The accident site was also 4 km north-west of the helicopter’s last recorded ADS-B transmission, which indicated it was descending into a valley.

The helicopter’s engine and fuselage had been exposed to fire, which had self-extinguished before emergency services arrived. Both pilots were fatally injured.

ATSB investigators surveyed the wreckage trail and main wreckage site and, despite fire damage, recovered and examined several components of the helicopter’s main rotor.

Examinations confirmed a mast bump had occurred, and that the helicopter had subsequently broken up in flight.

“Mast bumping is where the inboard end of the main rotor blade contacts the helicopter’s main rotor shaft,” ATSB Director Transport Safety Stuart Macleod explained.  

In R44 helicopters, this can generally be identified by extensive damage to the teeter stops and varying degrees of damage to the main rotor shaft.

“The semi-rigid – or teetering – main rotor design of the R44 and several other popular helicopters relies on rotational force to lift the blades off the droop stops on the rotor hub during flight,” Mr Macleod said.

“During normal operation, the rotor is free to teeter and flap around its designed flight axis via the teeter hinge, while polyurethane teeter stops limit the degree of teetering.”

A mast bump can occur when extreme teetering causes the rotor blades to exceed this allowance, and contact the rotor hub at a high speed.

“The ATSB investigation found that, while flying in the vicinity of the valley, the helicopter entered a low-G condition due to turbulence, inappropriate control inputs, or a combination of both,” Mr Macleod said.

“Low-G conditions can be catastrophic for helicopters with semi-rigid rotor heads. A pilot’s ability to recover from low-G remains uncertain, and would be dependent on airspeed and time available. Pilots must therefore avoid low-G situations.”

Mr Macleod noted pilots should make a careful study of terrain, forecasts and observations applicable to a proposed flight, to identify in advance any significant weather or mechanical turbulence, and avoid flying in these conditions.

“Pilots should avoid flying downwind of hills, ridges or other potential sources of turbulence, particularly during changing or unpredictable weather conditions, and should use slow and small control inputs when encountering turbulence,” Mr Macleod said.

The investigation report also urges operators to consider the benefits of installing recording devices on their helicopters.

“While the fire would likely have prevented data recovery in this case, the inclusion of readily-available cockpit video recorders on helicopters with semi-rigid rotor heads would provide valuable insights into low-G mast bumping events, which could help prevent future occurrences,” Mr Macleod concluded.

Since the occurrence, Robinson has introduced cockpit video/audio recorders as standard equipment on new R44s, having previously been available on the larger R66 models. The recorders are currently optional on the smaller R22s, but will also become standard on these models in 2023, with retrofit kits made available.

Read the final report: In-flight break-up involving Robinson R44 Raven I, VH-HGU, 31 km east of Goulburn Airport, New South Wales, on 2 December 2020