Key points:

• Unsecured flat rack end wall extended upwards, dewiring high voltage overhead line equipment
• During emergency response, risk of close proximity of high voltage overhead line equipment to the flat rack end wall was not identified or controlled.
• Occurrence highlights the importance of ready access to checklists for rarely completed and emergency response tasks, and effective coordination during an emergency response.

Over a kilometre of overhead powerlines were pulled down when the collapsible end wall of a flat rack container being transported on a freight train extended in transit, contacting an overpass and pulling down the high voltage lines, a new ATSB report details.

The incident occurred on 18 August 2018 when Aurizon-operated intermodal freight train YC77, consisting of a single 2800 class diesel-electric locomotive and 32 flat wagons and crewed by a single driver, was approaching Cooroy, in the Sunshine Coast hinterland, en route from the Acacia Ridge Intermodal Terminal in Brisbane.

Examination of CCTV footage showed that as the train passed through Cooroy, the rear end wall of the top of a stack of three empty flat racks was in the extended position, with overhead line equipment (OHLE), including copper wires, entangled on the wagon and dragging along the station platform. No-one was on the Cooroy station platform at the time of the dewirement, although a southbound passenger train was scheduled to arrive about 30 minutes later.

“The ATSB investigation found that securing of the collapsible end walls of the flat racks was not checked on arrival at the freight terminal or after they were loaded on the train,” said ATSB Director Transport Safety Dr Mike Walker.

“In addition, there was not an effective system in place to ensure personnel required to check the securing of unusual loads, such as empty flat racks, had sufficient knowledge of their responsibilities, or ready access to relevant procedures, guidance and checklists.”

Although the OHLE was de-energised due to the tripping of a circuit breaker during the dewirement, it was not considered electrically safe until it had been isolated, tested and earthed. The ATSB found that on multiple occasions following the dewirement, train crew accessed a three metre exclusion zone associated with the OHLE, prior to the wires being isolated and earthed on site.

Further, network control centre personnel did not advise train crew of the status of the OHLE during the emergency response period, and the infrastructure operator, Queensland Rail (QR), did not have an effective process in place to ensure that safety-critical actions were co-ordinated and completed when multiple network control officers were involved in responding to an OHLE emergency, the investigation notes.

“This occurrence has highlighted the importance of having checklists for rarely conducted tasks and emergency response tasks in the rail environment, and ensuring these checklists are readily available and used by operational personnel,” Dr Walker said.

“This includes checklists for loading and securing personnel, rail traffic crew and network controllers.”

In response to the incident, Aurizon has updated its processes and checklists for the loading of flat racks, provided further training on flat rack securing requirements, and is undertaking a program to improve access to its safety management system, including relevant procedures and checklists. In addition, Aurizon is in the process of drafting procedures related to driver only operations (DOO) on its network.

QR has also mandated the use of a network control officer checklist for OHLE emergencies and is reviewing related aspects of its emergency response procedures. In addition, QR has provided additional training to both network control officers and train crew in relation to identifying objects in close proximity to OHLE and applicable exclusion zones. QR has also taken proactive safety action in the form of further training for NCOs when dealing with emergencies involving a DOO crewing arrangement.

Read the final report: Dewirement involving freight train YC77, Cooroy, Queensland, on 18 August 2018

Key points:

• Wheel rim fractured and tyre deflated due to undetected fatigue cracking, a known issue
• Non-detection likely due to inadequate guidance on inspection requirements for wheels operated with a flat tyre

A Saab 340 main landing gear wheel rim fracture and tyre deflation was likely due to insufficient guidance in the operator’s maintenance procedures for component maintenance inspections, a new ATSB reports says.

On 20 August 2019, a Regional Express Saab 340B, registered VH-ZLX, departed Adelaide, for a scheduled passenger flight to Port Lincoln. During the post flight walk around after landing, the first officer discovered that the left main outboard landing gear tyre was deflated and that a piece of the wheel was missing. The missing section of the wheel was recovered from the runway strip at Adelaide.

The wheel had been fitted to VH-ZLX on the day of the incident, after its removal from another aircraft in July 2019, due to the detection of an audible leak. It was returned to the operator’s maintenance facility with an ‘unserviceable’ tag and ‘repair’ noted on the standard tyre change form. The operation of the wheel with a deflated tyre was not noted.

ATSB examination of the wheel found an area of fatigue cracking had developed in the bead seat region and progressed 86 mm around the circumference before the rim section separated due to overstress, a known issue with this wheel type previously resolved with updated maintenance schedules and practices.  

The large size of the fatigue area along with the relatively low number of flight cycles since its last non-destructive testing indicate the cracking could have been detected following its removal in July 2019.

The ATSB determined that the opportunity to detect the fatigue cracking was limited as the operator’s wheel maintenance forms did not adequately convey the inspection requirements for wheels operated with flat tyres. As a result, inspections that may have detected the crack were not carried out.

The ATSB safety message from this investigation highlights that when situations or issues arise that do not fit into standard operating procedures, maintenance personnel should always be prepared to consult or request further guidance. This guidance can come from internal support materials, such as procedures, or external materials such as maintenance manuals or the manufacturer.

In response to the incident, Regional Express have updated their wheel maintenance procedures to ensure that non-normal inspections are identified and carried out. The airline has also reinforced to maintenance personnel the need to fully complete unserviceable tags to ensure subsequent maintenance personnel fully understand the nature of reported defects.

Read the final report: Landing gear wheel failure involving Saab 340, VH-ZLX, Adelaide Airport, South Australia, on 20 August 2019

Key points:

• Worn bushings led to fretting damage on a lever arm in the fourth-stage variable stator vanes within a General Electric CF6-80E1 engine’s high-pressure compressor
• Non-mandatory variable stator vane lever arm inspections were not effective in detecting the bushing wear
• When maintenance organisations carry out additional activities to what is required, they should consider checking with the manufacturer to avoid unintended consequences

An operator’s proactive replacement of worn bushings inadvertently contributed to an Airbus A330’s engine experiencing excessive vibration, an ATSB investigation found.

Shortly after departure from Brisbane Airport on a scheduled flight to Auckland on 15 April 2018, the flight crew of a Qantas Airbus A330-200 received an advisory notification indicating excessive vibration from the left engine. The crew reduced thrust on the left engine to idle, and the noise and vibrations ceased.

The crew elected to return to Brisbane, where the aircraft landed uneventfully. The thrust on the left engine remained at idle during the air turn back.

The ATSB investigation found that worn bushings had led to fretting damage on a lever arm in the fourth-stage variable stator vanes within the General Electric CF6‑80E1 engine’s high-pressure compressor. The lever arm fractured, allowing the variable stator vanes to become off schedule (misaligned), affecting the airflow entering the stage four high-pressure compressor.

The airflow disturbance resulted in abnormal aerodynamic loading and ultimately, fatigue failure of a fourth stage compressor blade. The downstream turbomachinery was then damaged due to the progression of blade debris through the engine.

The ATSB found that three non-mandatory variable stator vane lever arm inspections were carried out prior to the occurrence but were not effective in detecting the bushing wear.

General Electric intended that replacement of the complete set of bushings was required when more than half of the accessible bushings were worn. However, the operator had proactively replaced worn bushings individually when found during maintenance. As a result, the threshold to replace the complete set would not be reached and inaccessible bushings would not be replaced.

As a result of this occurrence, Qantas inspected all CF6-80E1 engines in its A330 fleet for similar defects, with none identified. Additionally, Qantas issued a maintenance memo to service personnel, highlighting the maintenance actions for the variable stator vane system and precautions to be aware of when carrying out work in this area.

The investigation report’s safety message warns that when maintenance organisations carry out additional activities to what is required, they should consider checking with the manufacturer to confirm that no unintended consequences could be introduced.

Read the final report: Engine surge and high vibration involving Airbus A330, VH-EBR, 44 km north-east of Gold Coast Airport, Queensland, on 15 April 2018

Key points:

• Engine failed as a result of an internal oil fire, weakening a turbine disk and resulting in turbine blades being released
• Fire occurred when oil leaked from an oil sump due to carbon deposits (coking)
• Maintainers had followed the correct troubleshooting procedure but were unable to determine the reason for the high oil consumption

Coking in an oil sump led to a Saab 340 regional airliner’s right engine failing, a new ATSB investigation has established.

The Regional Express Saab 340B was operating a scheduled passenger service from Moruya to Merimbula on the New South Wales South Coast on 29 August 2019, with the aircraft’s right engine (a GE CT7) being monitored for high oil consumption. About eight minutes into the flight and shortly after levelling off at an altitude of 9,000 feet, the flight crew observed a right engine fire indication. As they conducted the engine fire checklist, the crew heard the engine surge and a loud bang, and the cabin crew member reported seeing a brief flash of light from the aircraft’s right side.

The flight crew continued the engine shutdown checklist and subsequently shut the engine down and elected to continue to Merimbula, based on their proximity to the destination and with the aircraft already having been set up for the approach.

The crew entered a holding pattern to complete all the required checklists and to ensure the availability of emergency services at the Merimbula Airport, where the aircraft landed without further incident.

An ATSB investigation found that the engine failed as a result of an internal oil fire, which weakened a turbine disk and resulted in turbine blades being released. The fire occurred when oil leaked from an oil sump (known as the B-sump) due to carbon deposits, or coking, within that sump. The coking was most likely due to either the sump not being completely clean when installed at the last major overhaul and/or accelerated coking.

As a result of the incident, GE has enhanced the troubleshooting procedures to identify internal engine oil leaks more effectively. They have also developed enhancements to the overhaul facility cleaning procedure for the affected oil sump.

This incident highlights the importance, when piloting multi-engine aircraft, of maintaining the ability to operate with one engine inoperative. Aircraft turbine engines are complex, and can fail for reasons that are rare and difficult to identify prior to the failure, the investigation notes.

In this occurrence, the maintainers had followed the correct troubleshooting procedure but were unable to determine the reason for the high oil consumption. The flight crew’s skill and knowledge, however, along with built-in system redundancies, ensured the overall safety of the flight.

The report notes that there have been only two known occurrences of CT7 engine failures or in-flight shutdowns due to significant coking in the B-sump.

Read the final report: Engine failure involving Saab 340B, VH-RXX, near Merimbula, New South Wales, on 29 August 2019

Key points:

• Pilots took off with fog forecast and fog developing in the area
• The descent in low visibility resulted in the pilot having insufficient time to manoeuvre the balloon to climb above the trees after sighting them
• The ATSB has issued a safety recommendation to CASA to undertake a risk assessment of the reduced visibility exemption to the visual flight rules for balloons

Sixteen passengers sustained injuries, three of them serious, when their hot air balloon collided with trees and landed heavily after their pilot aborted the flight due to fog and poor visibility, an ATSB investigation report details.

The Kavanagh G-525 balloon, with a pilot and 24 passengers on board, was one of three balloons operated by the International Balloon Flight Company that launched from Peppers Creek near Pokolbin, New South Wales for a planned one-hour scenic flight on 30 March 2018.

The ATSB’s investigation found that the three pilots decided to launch despite forecast fog and developing fog at the launch site, without an awareness of the fog’s extent.

“This resulted in the balloons being above a layer of fog through which they had to descend,” said ATSB Director Transport Safety Stuart Macleod.

The descent in low-visibility conditions diminished the accident balloon pilot’s ability to see trees in the approach path, the investigation notes. This, combined with a 12 knot wind at the landing site, resulted in the pilot having insufficient time to manoeuvre the balloon to climb above the trees after sighting them.

“Adequate weather planning is essential for safe ballooning operations, including to ensure that the pilot is able to see and avoid obstacles during landing,” Mr Macleod said.

“Balloon pilots must ensure weather conditions are compatible with the limitations of balloon manoeuvrability.”

The investigation noted that the pilots’ decision to take off was permitted under a Civil Aviation Safety Authority (CASA) exemption to visual flight rules for balloons allowing them to operate in visual meteorological conditions with a minimum of 100 metres visibility below 500 feet above ground level.

“This visual flight rules exemption permits balloons to arrive and depart in foggy conditions without assurance that sufficient visibility existed to see and avoid obstacles," Mr Macleod said.

“The rule permitted the pilots to launch the balloons in the conditions experienced prior to the accident flight.”

As a consequence, the ATSB has issued a safety recommendation to CASA to undertake a risk assessment of the reduced visibility exemption to the visual flight rules for balloons, to determine whether it assures an adequate level of safety.

“The ATSB remains concerned that, given the climb performance/profile of balloons, the current visual meteorological criteria for operation below 500 feet above ground level do not provide assurance that sufficient visibility exists to see and avoid obstacles.”

However, the ATSB acknowledges and welcomes CASA’s planned publication of an advisory circular (AC) to provide guidance for balloon operators and pilots regarding weather assessment and low-visibility operations.

Mr Macleod noted that this investigation highlights that is it is vital that pilots obtain a full appreciation of the weather for the duration of the planned flight from the Bureau of Meteorology, which is the approved source of aviation meteorology products.

“Fog is fickle, and the ultimate responsibility for a pilot’s decision on whether to launch or not rests with the pilot,” he said.

“This decision needs to address factors and limitations related to the pilot, balloon, environment and operation.”

Separately, the investigation found the pilot and ground crew did not follow the operator’s emergency procedures to not move injured passengers after the accident, increasing the risk of exacerbating their injuries.

Read the final report: Controlled flight into terrain involving Kavanagh Balloons G-525, VH-HVW, Pokolbin, New South Wales, on 30 March 2018

Key points:

• Flight crew elected to return to Perth after detecting a popping or banging sound from the left engine
• Managing partial power loss a more complex scenario than a complete engine failure
• Both engines found to have erosion damage to the high pressure turbines

The flight crew of a Dash 8 turboprop airliner elected to return to Perth Airport soon after take-off after detecting a popping or banging sound from the vicinity of the left engine, an ATSB investigation report details.

The Skippers Aviation DHC-8-315 (Dash 8-300) had departed Perth Airport for the Duketon Gold Mine on 23 April 2019. Climbing through approximately 250 feet above ground level, as the landing gear was being retracted, the flight crew heard a popping or banging sound from the vicinity of the number one (left) engine and detected a reduction in power from that engine. At about the same time, the pilot flying experienced a yaw through the aircraft controls. The crew also noted a gradual reduction in right engine power.

The flight crew decided not to shut down the malfunctioning engine immediately, allowing them to concentrate on continuing the climb during a period of increased workload. Both engines responded to an increase in power, however the crew elected to return to Perth Airport, where an uneventful landing was conducted.

A subsequent inspection of both engines found erosion damage to both high pressure turbines, with the damage to the left engine more pronounced. This erosion damage likely disrupted the airflow through the left engine, inducing the symptoms reported by the crew.

The ATSB investigation report stresses that a partial power loss presents a more complex scenario to flight crew than a complete engine failure. In these circumstances the engine is still providing some power but the power may be unreliable, and that reliability may be difficult to assess.

In this case, while the affected engine appeared to return to normal operation, the flight crew remained committed to returning to the airport. Abnormal engine operation, even if only transient, can be an indication of a developing fault and therefore the safest course of action is to discontinue the flight as soon as possible.

The investigation’s safety messages note that this occurrence highlights the benefits of timely and appropriate flight crew action in response to a power loss on take-off.

Read the final report: Engine malfunction and return involving Bombardier DHC-8-315, VH-XKJ, Perth Airport, Western Australia, on 23 April 2019

Key points:

• Helicopter came into a high hover in a crosswind during a hydraulics-off training exercise
• Hovering the AS350 without hydraulics can lead to a rapid loss of control
• A detailed preflight briefing was not conducted before the flight

Hovering the AS350 Squirrel helicopter with hydraulics assistance disabled can lead to a rapid loss of control with catastrophic consequences even for highly experienced pilots, an ATSB investigation highlights.

AS350BA Squirrel helicopter registration VH-BAA was conducting an emergency procedures training flight from Hobart Airport on 7 November 2017 with a pilot under instruction (undergoing type rating endorsement training on the type) with the helicopter operator’s chief flying instructor (CFI), when it collided with the ground during a simulated hydraulic system failure exercise. The CFI, who was seated on the left, was fatally injured in the accident, while the pilot under instruction sustained serious injuries.

The helicopter was not fitted with, nor was it required to be, cockpit voice and flight data recorders, however analysis of airport CCTV footage, photographs and air traffic control data allowed the ATSB to determine the accident’s sequence of events.

That analysis showed that the helicopter entered a high hover without hydraulics with a crosswind, however, the AS350 flight manual stipulates that in order to ensure control following a hydraulic system failure (or simulated failure), a shallow approach should be made into wind and the helicopter should not enter a hover.

Entering a high hover with a crosswind rendered the helicopter uncontrollable, ATSB Director Transport Safety Mr Stuart Macleod said, with a number of elements having the potential to cause a delay in restoring hydraulics and preventing the pilots from regaining control.

”The AS350 flight manual notes that without hydraulics the helicopter is subject to rapid changes in control direction and force,” Mr Macleod said.

As detailed in the flight manual, the safe practice of a hydraulic failure sequence in the AS350 requires a flat final approach into wind and a no-hover or slow run‑on landing at a speed of around 10 knots. This is a compromise to minimise the speed of the run-on landing and avoid hovering.

“Compliance with the AS350 flight manual requirements following a real or simulated hydraulic failure ensures that the helicopter remains controllable during all phases of flight.”

The report notes that flight test evaluation of the AS350 by the Royal Australian Air Force’s Aircraft Research and Development Unit in 1997 – all three arms of the Australian Defence Force have operated the AS350 for helicopter pilot training – found that while hovering without hydraulics that the AS350 is subject to random perturbations and a reduction in control authority, Mr Macleod noted.

“This and many other similar accidents illustrate that hovering an AS350 without hydraulic assistance can lead to a rapid, catastrophic loss of control even for highly experienced pilots,” he said.

The ATSB reviewed 34 investigations of accidents involving AS350 helicopters’ hydraulic systems worldwide, Mr Macleod noted, with data indicating that loss of control accidents during simulated hydraulic failure training do occur to even highly experienced pilots.

“The average recorded experience of flight instructors involved in these events was over 9,000 hours total time, with over 1,000 hours of those on the AS350. These are very experienced helicopter pilots,” Mr Macleod said

The investigation also details that a preflight briefing was not conducted before the flight, which may have led to confusion over roles in controlling the helicopter as the emergency progressed.

“This accident’s rapid development reinforces the need for a clear understanding and coordination between instructor and student when conducting hazardous activities such as simulated system failures,” Mr Macleod said.

Subsequent to the accident the operator has undertaken a number of safety actions, including updating the training school’s operations manual with stricter controls on performing AS350 sequences in line with the flight manual requirements.

Separately, the ATSB notes that in 2019 the AS350’s manufacturer, Airbus Helicopters, released a Safety Information Notice (No. 3246-S-29) and accompanying educational video covering hydraulic failure training in the AS350. The video can be viewed on the Airbus website here(Opens in a new tab/window).

Read the final report: Loss of control and collision with terrain involving Eurocopter AS350BA, VH-BAA, Hobart Airport, Tasmania, on 7 November 2017

Key points:

• Missing nut allowed bolt to separate from bellcrank in cyclic control assembly
• Self-locking nut was likely either not reinstalled or inadequately torqued after recent overhaul
• Verbal communications are not a reliable means for capturing essential tasks over extended time periods

A self-locking nut that was likely either not reinstalled or inadequately torqued during maintenance, allowing a bolt to separate from a bellcrank in a Robinson R22’s cyclic control in-flight, resulted in the helicopter’s unrecoverable loss of control and collision with terrain, fatally injuring the pilot.

The R22 had departed Cloncurry Airport, north-west Queensland, on 2 August 2017, on a ferry flight to reposition for aerial mustering after having undergone a major overhaul. About fourteen minutes after take-off witnesses observed a plume of smoke in the general direction of the helicopter’s path. The wreckage of the R22 was subsequently located about 7 km to the north-north-west of the airport.

The ATSB’s investigation subsequently identified that a fastener – a bolt and self-locking nut – which connected the helicopter’s cyclic assembly’s horizontal push-pull tube to a bellcrank, was missing. After re-examining the helicopter wreckage, the bellcrank and a bolt, later confirmed to be from the missing fastener, were recovered from the wreckage site and examined by the ATSB.

ATSB Director Transport Safety Dr Stuart Godley said the separation of the bolt would have resulted in the main rotor disc tilting back beyond its normal operating limits and striking the tailcone.

“Different scenarios were examined for the cause of the bolt separation; however, as it was not possible for the helicopter to operate for any length of time without a nut attached to the bolt, it was likely that the nut was not reinstalled or inadequately torqued during the helicopter’s recent 2,200-hour overhaul,” Dr Godley said.

The investigation also found that the maintenance organisation had not recorded and tracked all maintenance activities for the overhaul as the work progressed over a period of almost four months.

Instead, it had adopted a number of work practices that increased the risk of memory-related errors and omissions, including using abbreviated inspection checklists, not recording all flight control disturbances, and not progressively certifying for every inspection item as the work was completed.

“This investigation highlights the limitations of verbal communication as a method of explaining and understanding problems and their unreliability as a means for capturing essential tasks over an extended time period,” Dr Godley said.

“Maintenance organisations are urged to consider the human factors elements associated with their practices, capture them in their documented quality control procedures, and ensure they are complied with.”

The investigation noted that in the weeks prior to the accident the maintenance company was experiencing a period of very high workload that likely exceeded the workforce’s capability and reduced the chief engineer's capacity to oversight maintenance activities. In addition, in the years leading up to the accident, staff changes reduced the maintenance provider’s levels of qualifications and experience.

The investigation also found the maintenance organisation had limited internal independent oversight and increased reliance on audits for the evaluation of its quality performance.

“Audits are essential for independently verifying the effectiveness of an organisation's processes and procedures. This accident reinforces the importance of auditors inspecting the evidence collected during an audit to ascertain whether the requirements are being met, specifically conformance with the relevant standards,” Dr Godley said.

“Audits may also be used to identify potential underlying human factors issues, which may be raised as an observation or opportunity for improvement to inform the auditee of best industry practices.”

Read the final report: Loss of cyclic control and in-flight break-up involving Robinson R22 helicopter, VH-HGU, 7 km north-north-west of Cloncurry Airport, Queensland, on 2 August 2017

An incident in which a rail safety worker was nearly struck by two trains within the airport tunnel near the Sydney suburb of Redfern highlights the importance of planning and controlling rail corridor worksites, an investigation details.

The rail safety worker had left the worksite in the Eastern Suburbs Railway tunnel to find a toilet. After entering an adjacent worksite at Redfern Station, the worker used the public toilets at the station but was prevented from returning to the worksite by the barricades for another worksite. The worker entered the entrance to the airport tunnel, mistakenly believing it would take them safely back to their worksite.

While in the tunnel, the worker heard a train approaching. Moving clear of the track, the worker clung to the wall of the tunnel, three seconds before train 89-K passed by at about 45km/h. Train 89-K came to an emergency stop and reported a near-miss to the area controller. The worker, meanwhile, moved past the now-stationary train, only to cross into the path of a second train, 88-C, near the mouth of the Up side of the tunnel.

The driver of 88-C also made an emergency brake application, and reported a near-miss to the area controller. The area controller began warning trains of a possible trespasser in the area, as the identity of the person was unknown.

Following the two near-misses, after finding a path to the worksite, the worker completed the shift without advising anyone of the incident until the afternoon. 

The transport safety investigation into the occurrence, undertaken by the NSW Office of Transport Safety Investigation (OTSI), on behalf of the ATSB, found that the rail safety worker had not been briefed about the other worksite, or the requirements on how to access the station. As a result, the worker entered a worksite without receiving or seeking a project site induction, left the protected area, and entered a live tunnel.

Additionally, the worker signed the project site induction record sheet, despite not being present for an induction.

In response to this incident, Sydney Trains removed the worker from safe working duties, and conducted a number of briefings following the occurrence in order to communicate lessons learned with the workgroup.

The investigation’s safety message highlights the importance of planning and controlling worksite within the rail corridor. This is particularly important when staff are working within tunnels and at platforms where access can be from multiple directions

Workers must ensure that they receive safety briefings prior to undertaking work or entering a new work area, and seek further information if required prior to starting work, the investigation notes. Workers are also advised to stop and find a safe place if they become lost or are separated from their work group.

Additionally, workers should report all safety incidents in a timely manner.

Read the final report: Near miss with rail safety worker by trains 89-K and 88-C, near Redfern, New South Wales, on 8 September 2018

A fan blade failure in an Airbus A330’s Rolls-Royce Trent 700 engine due to a fatigue crack has led to enhanced inspection processes and technical solutions that reduce the likelihood of future similar occurrences, a new ATSB investigation report details.

In June 2017, an AirAsia X Airbus A330-300 sustained an engine failure while operating a scheduled passenger flight from Perth to Kuala Lumpur. About one hour into the flight, during a step change in altitude, the flight crew heard a metallic bang, significant vibrations could be felt through the airframe, and an ‘ENG 1 STALL’ warning was triggered.

The flight crew executed the relevant engine malfunction procedure and commenced a single-engine return to Perth. While the airframe vibrations continued during the return to Perth, the aircraft landed there without further incident.

On the ground an inspection found about three quarters of one fan blade was missing from the failed left engine.

Subsequent detailed structural analysis determined that the failure of the fan blade was due to a fatigue crack which had initiated from within the blade’s internal structure where an internal reinforcing membrane joins to the blade’s convex skin panel.

Detailed structural analysis determined that the failure of the fan blade was due to a fatigue crack.

The report notes the blade manufacturing process produced a variation in the internal membrane-to-panel acute corner geometry that, in combination with the inherent high level of blade panel stress, could lead to increased localised stresses in those corner areas and the initiation and propagation of fatigue cracking.

The investigation also determined that the scheduled inspections recommended by Rolls-Royce to detect cracking in Trent 700 fan blades were insufficient to detect early onset fatigue cracks in the membrane to panel bond before those cracks could progress to failure.

Rolls-Royce have taken a number of proactive safety actions to mitigate future blade failures. These include reviewing the design and manufacturing of the Trent 700 fan blade and releasing service bulletins covering engine inspections (one of which was supported by a European Aviation Safety Agency (EASA) issued Airworthiness Directive).  

The engine manufacturer also introduced new a control system modification, designed to shut the engine down quickly when fan blade failure event occurs to reduce damage to the fan shaft. 

During the complex manufacturing process of Trent 700 fan blades, a latent issue developed that was not realised for a number of years, the investigation notes. This demonstrates the importance for manufacturers of critical components, and regulators monitoring the manufacturers, to have systems in place to quickly identify core issues and put in place measures to mitigate risk.

The report also notes that this incident represents a good example of how manufacturers, through quick and positive actions, can communicate engineering solutions and technical information to operators and maintenance providers through messages, service bulletins and service letters.

It also demonstrates how regulatory authorities can work with manufacturers and incorporate mandatory safety solutions through communications, including Airworthiness Directives.

Read the final report: Engine failure involving Airbus A330, 9M-XXE, near Carnarvon, Western Australia, on 25 June 2017