An Australian Transport Safety Bureau (ATSB) investigation into a depressurisation incident involving a Cessna 441 Conquest has resulted in a new ultrasonic bond inspection procedure for the aircraft’s emergency exit door.   

During a 22 July 2020 charter flight from Broome to Browns Range, Western Australia, with two pilots and six passengers on board, a Skippers Aviation operated Cessna 441 experienced a rapid depressurisation shortly after reaching its planned cruising altitude of flight level 270 (approximately 27,000 ft). In response the pilots and passengers donned their oxygen masks and the pilots performed an emergency descent.

When at 10,000 feet, the pilots removed their oxygen masks, instructed the passengers to do the same and confirmed they were all responsive and uninjured. After communications with the operator’s senior base pilot, the pilots continued their flight with the aircraft depressurised to Browns Range, where the aircraft landed without further incident.

During their walk-around of the aircraft both pilots noticed the lower aft section of the emergency exit door skin had disbonded.

“A structural fatigue investigation concluded that the emergency exit door progressively disbonded between the inner and outer skin, likely due to the age of the aircraft, facilitated by a combination of corrosion, moisture, and flight cycles,” said ATSB Director Transport Safety Dr Stuart Godley.

“This weakened the structure, which resulted in an accelerated failure of the bondline and rapid depressurisation of the cabin when the aircraft reached flight level 270.”

The incident aircraft was manufactured in 1978 and had accumulated over 27,000 flight hours and was operating under a supplementary type certificate (STC) life extension program developed by West Star Aviation. As a result of this incident and the subsequent discovery of two further disbonded doors in two other Cessna 441s operating under the life extension STC, it was concluded that the STC’s existing visual inspection procedures for the emergency exit door bondline were inadequate.

In January 2021 Textron Aviation (the type certificate holder for Cessna aircraft) released a service letter for the Model 441 Conquest/Conquest II introducing an ultrasonic bond inspection of the the aircraft’s emergency exit door to verify the integrity of the emergency exit door bondline.

Separately, the operator is seeking a design advice response from the Civil Aviation Safey Authority for the modification of its Conquest aircraft with the installation of rivets through the bondline and subjecting the door to additional inspection requirements.

The investigation also notes that the incident aircraft returned to Broome with the pilots applying the minimum equipment list for the pressurisation system.

As a result, the special flight permit process to recover the aircraft for repair was not followed, which removed the opportunity for an independent assessment that the flight could be conducted in a safe manner.

“After landing at Browns Range and discovering the disbonded door skin, the pilots elected to continue with the return flight to Broome with the pressurisation system inoperative, which was consistent with the initial advice they received from their company,” said Dr Godley.

“However, whenever new information about an abnormal situation becomes available, decisions may need to be re-evaluated, as the initial reasoning may no longer be valid. In addition, for the scenario of a structural failure, the special flight permit process should be followed to manage the potential risks associated with a damaged aircraft.”

Read the final report: Door failure and depressurisation involving a Cessna 441, VH-LBY, near Broome, Western Australia, on 22 July 2020

The Australian Transport Safety Bureau Commission acknowledges the retirement of Greg Hood as Chief Commissioner and Chief Executive Officer, and sincerely thanks him for his leadership, professionalism, guidance and compassion in leading the ATSB from 1 July 2016 to 30 June 2021.

Mr Hood retires from the Bureau at the completion of his five-year term, in which time he drove an innovation and transformation agenda at the ATSB, which saw the introduction of world-leading practices like a multi-modal teams approach to investigations, new recruitment practices, a tertiary partnership with RMIT University, and new technologies to support investigations such as remotely piloted aircraft and 3D modelling. All have helped to further establish the ATSB as a global leader in transport safety investigation.

During his tenure Mr Hood, with the other members of the ATSB Commission, approved more than 530 aviation, rail and maritime investigation reports for public release to improve transport safety for all Australians.

In addition, under Mr Hood’s leadership, the ATSB developed a strategic property plan that included the establishment of a Melbourne office and increases in staffing in the agency’s Brisbane and Perth offices, and introduced a replacement program for all enterprise IT systems, including the procurement of a new investigation information management system.

Mr Hood also served a two-year term as Chair of the International Transportation Safety Association (ITSA), the network of the heads of 18 independent transport safety investigation authorities, at a time when the world was navigating the COVID-19 pandemic, and when safe and efficient transport networks were needed like never before.

He also oversaw a partnership agreement with the Defence Flight Safety Bureau (DFSB) to align accident investigator skillsets and to participate in each other’s investigation activities, and further strengthened the ATSB’s close working relationships with New South Wales’ Office of Transport Safety Investigations (OTSI) and Victoria’s Chief Investigator, Transport Safety (CITS).

The Commission thanks Greg Hood for his service, and wishes him the very best for his well-earned retirement.  

ATSB Chief Operating Officer Colin McNamara will act as Chief Commissioner and Chief Executive Officer pending the appointment of Mr Hood’s successor.

Key points

• Pilot incorrectly believed they had been provided a landing clearance;
• Runway incursions remain one of the most significant risks to safe aviation;
• Pilots are strongly encouraged to identify potential conflicts or runway incursions that may develop during circuits early;
• Flight training schools reinforce training regarding occupied runways and go‑arounds to students.

The student pilot of a Sling 2 aircraft which conducted a touch and go landing at Moorabbin Airport above a PA-28 aircraft that was lined up at the displaced threshold of the same runway incorrectly believed they had been provided a landing clearance, an ATSB investigation into the July 2020 incident has found.   

The PA-28 was lined up on the displaced threshold for Moorabbin Airport’s runway 17 Left awaiting take-off clearance while the Sling 2 was conducting a circuit for a touch and go landing on the same runway. Although the Sling 2’s pilot saw the PA-28 lined-up, they continued their approach, believing that air traffic control had provided a clearance for a touch and go. The Sling subsequently passed above the PA-28 and conducted the touch and go.

The pilot of the Sling, not believing any incident had occurred, continued conducting circuits, while the instructor pilot in the PA-28 reported the incident after completing their training flight.

“The runway incursion by the Sling aircraft removed the required runway separation between their aircraft and the PA-28,” said ATSB Director Transport Safety Stuart Macleod.

“Runway incursions remain one of the most significant risks to safe aviation operations and a key global safety priority.”

The investigation found the student pilot of the Sling had sighted the PA-28 but decided to conduct the touch and go landing due to an incorrect belief that the controller had provided a landing clearance.

Further, the ATSB identified that the student pilot’s training had not been effective in conveying that a go‑around must be initiated if the runway is occupied.

Subsequent to the incident, the student’s flying training organisation introduced changes to its training program and updated student and instructor educational materials, procedural guidance and exam content.

“Pilots are strongly encouraged to identify potential conflicts or runway incursions that may develop during circuits early and to attend carefully to air traffic control communications,” said Mr Macleod.

“It is important that flight training schools reinforce training regarding occupied runways and go‑arounds to students.”

The investigation also found that the Moorabbin air traffic controller did not identify the developing conflict or recall the Sling passing above the PA-28 and conducting a touch and go landing.

“This investigation also serves to remind air traffic controllers of the importance of monitoring all aircraft and providing clear and unambiguous instructions to pilots to avoid runway incursions and related occurrences.”

Read the final report: Runway incursion involving Sling 2, VH-ZSD, Moorabbin Airport, Victoria, on 23 July 2020

The structural failure of a wagon during the operation of a rail freight service was due to an existing fatigue crack at a weld in the wagon’s underframe, which was likely detectable during routine inspections, a transport safety investigation has found.

The incident shows the importance of properly managing ageing assets to ensure continued safe operation, the investigation notes.

On the morning of 6 January 2021, a contractor working near the rail line near Kiacatoo, in central New South Wales, noticed one of the wagons of passing Pacific National freight train 3YN2 was broken and dragging along the track.

This was promptly referred to the train controller at Junee, who in turn notified the train’s crew. Upon stopping, the crew inspected the 977-metre long train and found the broken wagon with its air tank resting on the rail.

It was loaded with two containers carrying zinc concentrate, which remained secured.

The investigation into the incident, undertaken by the Office of Transport Safety Investigations (OTSI), which conducts rail safety investigations in NSW on behalf of the ATSB, found the wagon had dragged along the track for at least 11 kilometres, with superficial scrape marks identified on the rail and at three level crossings.

Outside of the damage to the track and wagon, no further damage and no injuries were reported.

The investigation concluded it likely an existing crack in the wagon’s underframe had worsened between the train’s departure earlier that morning from Broken Hill, causing the centre of the wagon to sag and make contact with the track.

Oxidation (rust) on the bottom portion of the fracture suggested the existing crack had been there for some time, while the remaining fracture face was fresh, and likely progressed quickly during operation.

Given the oxidation, the investigation concluded the crack was likely detectable during numerous general examinations and roll-by inspections, including those undertaken in the hours prior to the incident.

The wagon was an ICX class wagon with a butt weld at the midpoint of its load-bearing centre sill, a location of known risk. ICX class wagons were manufactured from around 1968 onwards.

“This incident highlights the importance of managing ageing assets to ensure continued safe operation through the lifecycle of the asset,” said OTSI Chief Investigator and CEO Dr Natalie Pelham.

“Rolling stock operators should ensure that their maintenance and inspection regimes effectively monitor and detect conditions that might escalate and contribute to accidents.”

Following the incident, Pacific National released a rolling stock safety notice detailing the failure and requiring an inspection of all affected wagons within the class.

The operator has also said it plans to develop a lifecycle asset management strategy for the affected class of wagons with a butt weld, and complete a risk assessment to assess the limitations of those wagons for ongoing use.

Pacific National has committed to review its wagon maintenance manual to include all necessary details for ICX wagons, and to review and adjust its current non-destructive inspection strategy across its full fleet of wagons.

Read the final report: Rolling stock irregularity on train 3YN2, near Kiacatoo, New South Wales, on 6 January 2021

Key points

• During approach to the airport in darkness, the aircraft was not maintained within the required navigational tolerance;
• Adherence to procedures and careful monitoring of aircraft and approach parameters provides assurance that an instrument approach can be safely completed;
• If the criteria for safe continuation of an approach are not met, pilots should conduct a missed approach. 

A Fairchild SA227 Metro aircraft was not maintained within the required navigational tolerances while conducting an ILS approach to land at night at Melbourne Airport, an ATSB investigation has found.

The aircraft, conducting a night freight flight from Launceston on the evening of 18 January 2021 with a single pilot on board, was being positioned to commence a night-time Instrument Landing System approach to runway 27 at Melbourne. While joining the approach, a turn was not commenced until after the aircraft crossed the localiser track.

After crossing the localiser track and while descending along the approach glideslope, the aircraft descended clear of cloud and the pilot sighted the runway, the investigation notes. At that time, the aircraft was positioned slightly less than full-scale on the course deviation indicator (CDI) to the right of, and tracking away from, the localiser track. From this position, the pilot elected to continue the approach visually.

However, exacerbated by a prevailing southerly wind, the aircraft continued tracking away from the localiser and, shortly after, proceeded beyond the full scale of the CDI, requiring that a missed approach be initiated. However, the pilot assessed that the visual approach could be continued.

The aircraft continued to deviate from the localiser track and at 2135, reached a maximum lateral deviation of 0.55 nautical miles. The pilot then turned the aircraft further to track toward the localiser while continuing to descend. At about the same time, the Melbourne Tower air traffic controller noticed the deviation and contacted the pilot.

At 2136, at about 980 ft above mean sea level (about 583 ft above ground level), the aircraft was re‑established within full-scale CDI deflection and landed shortly after.

“The ATSB found that during approach to the airport in darkness, the aircraft was not maintained within the required navigational tolerance,” said ATSB Director Transport Safety Stuart Macleod.

“While that should have resulted in the conduct of a missed approach, the approach was continued with the aircraft manoeuvring significantly below the minimum safe altitude.”

Mr Macleod noted that operational procedures are designed to ensure consistency of pilot action and aircraft operation during the approach and landing phases of flight.

“Adherence to procedures and careful monitoring of aircraft and approach parameters provides assurance that an instrument approach can be safely completed,” he said.

“Most importantly, if the criteria for safe continuation of an approach are not met, pilots should conduct a missed approach to negate the risk of colliding with obstacles or terrain.”

Read the final report: Flight below the minimum safe altitude involving Fairchild SA227, VH-OZV, 9 km east of Melbourne Airport, Victoria, on 18 January 2021

A Boeing 737 freighter aircraft developed multiple technical issues that the flight crew could not resolve using the approved non-normal checklist procedures, resulting in the crew conducting an emergency descent and diversion during which they experienced separate incapacitation events, an ATSB investigation details.

The 737-376SF aircraft, operated by Express Freighters Australia, was conducting a scheduled freight flight from Brisbane to Melbourne on the evening of 15 August 2018 with two flight crew on board. During cruise the crew observed the master caution warning light flickering, and then identified that the right wing-body overheat annunciator was illuminating.

In response the flight crew actioned the non-normal checklist. When this did not resolve the overheat indication, the crew then conducted further troubleshooting in consultation with line maintenance operations personnel in Sydney.

As the flight progressed towards Narrandera, the crew identified that the cabin pressure was reducing, commenting to each other that they both felt slightly unwell. As the cabin altitude continued to climb and anticipating that it would exceed 10,000 feet, the crew elected to don the emergency oxygen masks and advised air traffic control that they had commenced a descent.

During the initial phases of that descent, the captain became temporarily incapacitated due to ingesting an increased supply of oxygen. This was due to the captain selecting the emergency flow setting while manipulating the oxygen mask settings. The first officer then declared a MAYDAY, advising of issues with the aircraft and that they had commenced an emergency decent. The flight was subsequently diverted to Canberra Airport.

After the captain had recovered, the first officer experienced incapacitating symptoms consistent with hyperventilation. The captain then declared a PAN PAN radio call to air traffic control, informing of the first officer’s incapacitation and requesting the attendance of emergency services on arrival at Canberra. The aircraft was landed without further incident.

The ATSB’s investigation identified that the intermittent flickering of the master caution light and overheat annunciator was likely due to an electrical fault in the right wing-body overheat detection system.

A fault with a valve in the aircraft air conditioning system prevented isolation of the right wing-body duct, which led the crew to conduct further troubleshooting during which the cabin air supply was reduced. In conjunction with a higher than normal cabin leak rate, the reduced airflow also lessened the cabin pressure.

“The flight crew responded to the cabin pressure reduction by donning their oxygen masks and descending the aircraft,” said ATSB Director Transport Safety Stuart Macleod.

“During the descent, the captain selected emergency flow on the oxygen mask resulting in an ingestion of gaseous oxygen, causing their temporary incapacitation.

“After the flight was diverted to Canberra, the first officer then experienced symptoms consistent with hyperventilation, leading the captain to declare the first officer incapacitated.”

After landing, both the captain and first officer were transported to hospital via ambulance for medical assessment. Post‑occurrence medical testing and assessments did not identify lasting effects from the flight.

Separately, the aircraft was inspected by maintenance personnel.

“Maintenance engineers identified a range of serviceability issues with the aircraft fuselage cabin drain valves, fuselage door seal, and the auxiliary power unit duct bellow seal that affected the capacity for the aircraft to hold cabin pressure,” Mr Macleod said.

Subsequent to the occurrence the operator implemented a range of changes to its maintenance program, including incorporating a functional check of the cabin drain valves; specifically verifying the integrity of the auxiliary power unit duct bellows seal; and introducing an enhanced aircraft cabin pressurisation system check.

“This occurrence is a reminder to flight crews of the hazards of dealing with system malfunctions that are not resolved using the approved non-normal checklist procedures,” said Mr Macleod.

“Configuration changes to an aircraft system may induce other effects due to underlying unserviceable components that may not be immediately apparent.”

The investigation also reminds flight crews to be aware that non‑normal situations can lead to a misapplication of emergency equipment in the moment that it is actually needed. In this case the selection of the emergency flow setting on the fixed oxygen system resulted in a temporary incapacitation of the captain.

“A series of non‑normal events, in conjunction with the use of emergency equipment, can add pressure and workload to the flight crew.”

Read the final report: Depressurisation and crew incapacitation Boeing 737-376SF, VH-XMO, 19 km north of Narrandera Airport, New South Wales, on 15 August 2018

Key Points

• While flying after last light in moderate to severe turbulence, the Visual Flight Rules rated pilot likely became spatially disorientated and lost control of the helicopter;
• Research shows that pilots not proficient in instrument flying will become spatially disorientated and lose control within minutes after visual cues are lost;
• A diversion or precautionary landing is almost certainly the safest option if day VFR rated pilots find themselves in a situation where last light is likely to occur before the planned destination is reached.

The collision with water of a Bell UH-1H helicopter near Anna Bay, NSW, resulting in the loss of all five people on board, highlights the significant risk of visual pilots attempting to fly in instrument conditions, the Australian Transport Safety Bureau (ATSB) investigation into the 6 September 2019 accident notes.

The pilot of the UH-1H likely became spatially disorientated and lost control of the helicopter while flying in dark night conditions, the investigation found. Published last light for Anna Bay was 6:01pm, with recorded data showing that the helicopter made a rapidly descending left turn and collided with water at about 6.13pm.

Wreckage of the helicopter was subsequently located in about 30 metres of water, approximately 5 kilometres south-west of Anna Bay, almost three weeks after the accident.

The pilot was only qualified to fly by day under the Visual Flight Rules – VFR – and so was not trained or experienced in maintaining control of the helicopter with sole reference to the flight instruments, the investigation notes.

“The ATSB found that the pilot continued to fly after last light without the appropriate training and qualifications, and then into dark night conditions that provided no visual cues. That significantly reduced the pilot's ability to maintain control of the helicopter, which was not equipped for night flight,” said ATSB Chief Commissioner Greg Hood.

“Once visual references were lost, the pilot likely became spatially disorientated and lost control of the helicopter, resulting in a collision with water.”

The helicopter had departed from Brisbane’s Archerfield Airport on a repositioning flight to Bankstown Airport, in Sydney. After refuelling at Coffs Harbour Airport, the helicopter then departed for Bankstown at 4.48pm, which the investigation determined would have left insufficient time for the helicopter to safely reach its destination before the published last light.

As the flight passed the halfway point and progressed closer to the destination, the pilot may have become increasingly committed to continuing with the original plan.

Consequently, deciding to turn back or divert may have been perceived as increasingly difficult, the investigation notes.

“A pilot’s decision to continue their flight when faced with reducing visual cues may be influenced by self-induced pressure to complete their flight,” Mr Hood said.

Air traffic control (ATC) from the nearby Williamtown Royal Australian Air Force Base had made several radio calls with the helicopter prior to the accident, assisting the pilot with requested altitude changes. During one exchange, the pilot commented to ATC about the turbulent conditions they were experiencing. The controller acknowledged the conditions and made a further offer of assistance should it be required.

Visual cues may have been available to the pilot from ground‑based lighting close to the aircraft’s track as the flight progressed after last light. However, at 6.11pm the helicopter commenced a left turn and departed the VFR coastal route and tracked offshore on what appeared to be a direct track to Bankstown.

As the helicopter flew over a featureless sea with overcast conditions blocking out celestial lighting, the pilot likely lost any remaining visual cues and encountered dark night conditions. Williamtown ATC radar contact with the helicopter was lost about two minutes later.

“Research has shown that pilots not proficient in maintaining control of a helicopter with sole reference to flight instruments will become spatially disorientated and lose control within one to three minutes after visual cues are lost,” Mr Hood said.

“A VFR flight in dark night conditions should only be conducted by a pilot with instrument flying proficiency as there is a significant risk of losing control if attempting to fly visually in such conditions.

"If day VFR‑rated pilots find themselves in a situation where last light is likely to occur before the planned destination is reached, a diversion or precautionary landing is almost certainly the safest option, or ATC may be able to provide assistance with available landing options.”

The investigation also found that the pilot, who was under the care of a non-aviation medical specialist, did not disclose on-going medical treatment for significant health issues to the Civil Aviation Safety Authority (CASA). While not considered to be a contributing factor to the accident, this non-disclosure prevented specialist consideration and management of the ongoing flight safety risk the medical conditions and prescribed medications posed.

“This tragic accident also highlights the importance of aviation medical certificate holders reporting relevant conditions and medications to their Designated Aviation Medical Examiner,” Mr Hood said.

“Pathways exist for managing certain medical conditions that do not preclude a pilot from maintaining an aviation medical certificate.”

Read the final report: Loss of control and collision with water involving Bell UH-1H, VH-UVC, 5 km south-west of Anna Bay, New South Wales, on 6 September 2019

Key points:

• After an unsuccessful action to recover from an unanticipated rapid left yaw during a go-around, the pilot did not have sufficient time to deploy the floats nor conduct a controlled ditching;
• Investigation highlights the importance of applying sustained full opposite pedal if an unanticipated yaw occurs;
• Passengers (particularly in overwater flights in helicopters) need a specific briefing on the location and operation of exit doors.

The Australian Transport Safety Bureau (ATSB) is reminding helicopter operators about the importance of considering skill consolidation processes when transitioning pilots to a new and technically different helicopter type, and to build safety margins into their operations to give pilots the best opportunity to succeed. 

The reminders come following the ATSB’s completion of a systemic investigation into an accident involving a Eurocopter (Airbus Helicopters) EC120B helicopter which collided with the water after the pilot experienced a significant loss of directional (yaw) control during a go-around. The EC120B, registered VH-WII and operated by Whitsunday Air Services, had departed Hamilton Island Airport, Queensland on 21 March 2018 on a charter flight to a pontoon at Hardy Reef, on the Great Barrier Reef, with a pilot and four passengers onboard.

While on a slow approach—to allow several birds to disperse—the pilot yawed the helicopter to the left with the intent to land on one of two positions on the pontoon. This subjected the helicopter to about a 20-knot crosswind from the right. When approximately 7 feet above the pontoon, the pilot noticed a message illuminate on the helicopter’s vehicle engine multifunction display (VEMD) and elected to conduct a go-around.

During the go-around and when about 30–40 feet above the water, the helicopter suddenly and rapidly yawed to the left. After unsuccessful control inputs to recover from the rapid left yaw, and with limited time, the pilot was unable to conduct a controlled ditching and the helicopter collided with water. The helicopter’s emergency pop-out floats were not deployed, and the helicopter almost immediately rolled inverted and rapidly filled with water.

The pilot and two of the three rear-seat passengers evacuated from the helicopter with minor injuries. Although the impact forces were survivable, the other two passengers (seated in the front left and middle rear seats) were unconscious following the impact and did not survive the accident. The helicopter later sank and was unable to be recovered.

“The ATSB’s investigation determined it was likely the pilot experienced a high workload during the final approach to the pontoon and a very high workload during the subsequent go-around,” said ATSB Director Transport Safety Dr Mike Walker.

The investigation found that although none of the possible VEMD messages required immediate action, the pilot considered a go-around to be the best option given the circumstances at the time. During the go-around, after the helicopter started rapidly yawing to the left, it is very likely the pilot did not immediately apply full and sustained right pedal input to counter the rapid left yaw.

In the two weeks prior to the accident, the pilot (with a total of about 1,300 flying hours) had obtained a new type rating to fly the EC120B. While accumulating 11 hours experience in command on the EC120B, the pilot had also flown about 16 hours in another and technically different helicopter type (a Bell 206L3).

“The operator had complied with the regulatory requirements for training and experience for pilots on new helicopter types but had limited processes in place to ensure pilots with minimal time and experience on a new and technically different helicopter type had the opportunity to effectively consolidate their skills required for conducting operations to pontoons,” Dr Walker said.

The EC120B has a clockwise-rotating main rotor and a ‘Fenestron’ shrouded tail rotor system. In 2005, the helicopter’s manufacturer released a service letter to remind pilots that Fenestron tail rotors require significantly more pedal travel than conventional tail rotors when transitioning from forward flight to a hover. A section of that letter stated that pilots needed to be prepared for a significant forward movement of the right foot and that insufficient application of [right] pedal would result in a leftward rotation of the helicopter during the transition to hover.

The ATSB found that the safety margin associated with landing on the pontoon at Hardy Reef was reduced due to a combination of factors, each of which individually was within relevant requirements or limits. These factors included the helicopter being close to the maximum all-up weight; the helicopter’s engine power output being close to the lowest allowable limit; the need to use high power to make a slow approach in order to disperse birds from the pontoon; and the routine approach and landing position on the pontoon requiring the pilot to yaw left into a right crosswind (in a helicopter with a clockwise-rotating main rotor system).

In addition, the investigation also identified safety factors associated with the operator’s use of passenger-volunteered weights for weight and balance calculations, the operator’s system for identifying and briefing passengers with reduced mobility, bird hazard management at the pontoons, and passenger control at pontoons.

“Since this accident, the operator has implemented several additional processes for pilots transferring to new helicopter types and for operations at pontoons,” Dr Walker said.

“This includes pilots conducting only into-wind operations at pontoons until they have obtained 20 hours on type. The operator has also introduced a safety management system, and revised processes for obtaining accurate passenger weights, in addition to several other proactive safety enhancements to its operations.”

In the year following the accident, the helicopter manufacturer released a safety information notice about unanticipated left yaw in helicopters with a clockwise-rotating main rotor system. The notice provided detailed advice regarding the circumstances where unanticipated yaw can occur and the importance of applying full opposite right pedal if it occurs.

The notice also stated that for helicopters with a clockwise-rotating main rotor system, that pilots prefer (as much as possible) yaw manoeuvres to the right, especially in performance-limited conditions.

Dr Walker said this accident, along with many other previous accidents, demonstrates the importance of pilots having helicopter type experience when faced with unfamiliar situations in performance-limited conditions, and to follow the immediate actions specified by the helicopter manufacturer, which typically includes immediately applying full opposite pedal input in the event of a loss of yaw control at low height and airspeed.

“Operators, as part of their safety management processes, should consider skill consolidation during and following the in command under supervision phase and provide as much consolidation as possible to reduce the risk of transitioning to a new aircraft type,” he said.

“This is particularly relevant for types with significant differences to those a pilot has previously flown and for operations with reduced safety margins. Pilots and operators should identify and avoid situations that present potential for loss of yaw control in their helicopter type.

“This could include planning approaches that can be rejected by turning with the torque of the helicopter. For example, if crosswind turns are required when landing, conduct turns to the right in a helicopter with a clockwise-rotating main rotor system.”

The investigation also identified that the passengers were not provided with sufficient instructions on how to operate the emergency exits. The passenger seated next to the rear left sliding door was unable to locate the exit operating handle during the emergency, and as a result the evacuation of passengers was delayed until another passenger was able to open the exit. The nature of the door handle’s design was such that its purpose was not readily apparent, and the placard providing instructions for opening the sliding door did not specify all the actions required to successfully open the door.

“Our investigation emphasises that for helicopter flights over water, given the risk of inversion, capsize and disorientation following a ditching, it is imperative that passenger safety briefings include how to operate the passenger’s seatbelt and the location and operation of the emergency exits,” Dr Walker said.

“Operators and pilots of EC120Bs should ensure that passengers in the rear of the helicopter are specifically briefed about the location of the operating handle and the three actions required to open the rear left sliding exit—which is to pull the handle up, push the door out, and slide the door back.”

Read the final report: Loss of control and collision with water involving Eurocopter EC120B, VH-WII, Hardy Reef, 72 km north-north-east of Hamilton Island Airport, Queensland, on 21 March 2018

Key points:

• An undetected error in the fuel quantity gauges (overreading) resulted in the aircraft departing with insufficient fuel;
• Although the fuel level low annunciators were illuminated, the pilot believed the overreading fuel gauges which indicated sufficient fuel to continue to Broome;
• Fuel exhaustion in both tanks led to both engines losing power, resulting in a forced landing on a highway;
• Reliable fuel quantity cross-checking is essential. 

The forced landing on a highway of a Cessna Conquest aircraft with a pilot and nine passengers on board due to fuel exhaustion highlights the importance of accurate fuel management, an ATSB investigation details. 

The Cessna 441 Conquest had departed Fitzroy Crossing for Broome in Western Australia during the afternoon of 2 March 2018 on the last sector of a four-sector scheduled passenger flight.

During descent, the FUEL LEVEL LOW annunciators illuminated, and the pilot observed that both fuel quantity gauges indicated sufficient fuel remaining and continued flying towards Broome.

Subsequently the right engine began surging, followed by similar surging from the left engine. The right engine then lost power and the pilot conducted the engine failure checklist. 

The pilot declared a MAYDAY and advised air traffic control that, as the left engine was still operating, the aircraft would be able to reach Broome. However, the left engine also lost power and both engines were unable to be restarted.

With both engines not providing power, the pilot assessed that the aircraft would not reach Broome and they tracked to the south towards the Great Northern Highway in the vicinity of Roebuck Plains. The pilot landed the aircraft safely on the highway approximately 21 NM east-south-east of Broome.

ATSB Director Transport Safety Dr Mike Walker said undetected water contamination in the fuel tanks, possibly due to condensation forming in the close-to-empty fuel tanks while the aircraft was sitting in humid conditions following maintenance, resulted in the aircraft’s fuel quantity gauges significantly overreading the level of fuel on board. 

The ATSB investigation was unable to determine how the water contamination was not detected despite different pilots conducting fuel quality checks.

“Accurate fuel management is a critical aspect of safe flight operations and it is important to utilise all available means in order to gain the highest assurance that fuel quantity measurement is accurate,” said Dr Walker. 

“It is essential that a reliable fuel quantity cross-check is adopted, utilising at least two independent methods and a conservative approach.”

The investigation report notes that although the pilot routinely compared indicated versus calculated fuel quantities, and indicated versus flight-planned fuel quantities, the pilot did not routinely conduct two other methods stated in the operator’s procedures for cross-checking fuel quantity gauge indications (the use of the fuel totaliser, and prior to engine shutdown after a flight, switching the fuel boost pumps off and checking whether either of the X-FER PUMP FAIL annunciators would illuminate).

“Although the operator had specified multiple methods of cross-checking fuel quantity gauge indications for its Cessna Conquest fleet, there were limitations in the design, definition and/or application of these methods,” Dr Walker said.

The primary method used (indicated versus calculated fuel) was self-referencing in nature, and not able to detect gradual changes in the reliability of fuel quantity gauge indications.

The operator’s pilots also did not record (and were not required to record) sufficient information on flight logs to enable trends or patterns in fuel quantity gauge indications to be effectively identified, and pilots did not routinely cross-check information from fuel quantity gauge indications with information from the independent fuel totaliser.

The FUEL LEVEL LOW annunciators likely illuminated approximately 30 minutes before the fuel was exhausted in each tank, and when the aircraft was still within range of suitable alternative airports, the investigation notes.

“Pilots are required to fully understand the functionality of the low fuel warning system on their aircraft and treat any warning annunciations as being accurate unless there is overwhelming evidence otherwise,” said Dr Walker.

Following the incident, the operator increased the frequency of fuel quantity comparison checks to a known quantity, specified clearer requirements for determining discrepancies when using fuel totaliser figures, implemented additional fuel management record keeping, and increased the focus on fuel management procedures during training.

Read the final report: Fuel exhaustion and forced landing involving Cessna 441, VH-LBY, 39 km east of Broome Airport, Western Australia, on 2 March 2018