On the evening of 6 August 2016, Jetstar Airways flight JQ12, a Boeing 787 aircraft, registered VH‑VKK, departed from Tokyo, Japan on a scheduled passenger transport flight to the Gold Coast, Queensland. On board the aircraft were two flight crew, nine cabin crew and 309 passengers.
The aircraft was pushed back from the gate at Narita Airport, Tokyo, at 1133 UTC. About two and a half hours into the flight, cruising at FL 400, the flight crew were alerted to low engine oil pressure in the right engine. The flight crew performed the checklist actions, which led to shutting down the right engine. The captain identified Guam Airport as the nearest suitable airport, about 370 km to the south of their position. They descended the aircraft to FL 220 due to single engine performance limitations and diverted around some weather as they tracked towards Guam Airport. The captain reported that they made an uneventful one engine landing on runway 24 at about 1520 UTC.
On inspection, the right engine transfer gearbox was found to be fractured, which was the source of the loss of oil from the engine.
This incident highlights the importance of flight crew complying with checklist actions when dealing with a fault condition. Inflight, the crew did not have knowledge of the extent of the damage to the engine transfer gearbox. However, by following their training and checklist procedures, they reduced the risk of a potential escalation of the fault.
On the evening of 6 August 2016, Jetstar Airways flight JQ12, a Boeing 787 aircraft, registered VH-VKK, departed from Tokyo, Japan on a scheduled passenger transport flight to the Gold Coast, Queensland. On board the aircraft were two flight crew, nine cabin crew and 309 passengers.
The aircraft was pushed back from the gate at Narita Airport, Tokyo, at 1133 UTC. About two hours into the flight, the flight crew received an engine indication and crew alerting system (EICAS) message ELEC GEN DRIVE R2, which indicated a fault with the number 2 generator in the right engine. The flight crew performed the checklist actions for that fault, which included disconnecting the number 2 generator drive from the engine driven accessory gearbox (AGB) and starting the auxiliary power unit to supplement the aircraft electrical power with the auxiliary power unit driven generators.
About 30 minutes later, cruising at FL 400, the secondary engine instruments appeared on the flight crews' multi-function displays and the flight crew detected there was a low oil quantity indication for the right engine. While the flight crew investigated the engine indications, another EICAS message annunciated, ENG OIL PRESS R, which indicated low oil pressure in the right engine. The flight crew performed the checklist actions for low oil pressure in the right engine. The right engine auto-throttle was switched off and the right engine thrust lever retarded to idle. The low oil pressure EICAS message momentarily cleared before it returned again, and the flight crew shut down the right engine in accordance with the checklist procedures.
The captain identified Guam Airport as the nearest suitable airport, about 370 km to the south of their position. They made a PAN call to Guam air traffic control, who provided them with a clearance to manoeuvre as required for a landing at Guam Airport. The flight crew sent a message using the aircraft communications addressing and reporting system to their operations control that they were diverting the aircraft to Guam. They descended the aircraft to FL 220 due to single engine performance limitations and diverted around some weather as they tracked towards Guam Airport. The captain reported that they made an uneventful one engine landing on runway 24 at about 1520 UTC.
After the aircraft vacated the runway, the captain held the aircraft on the taxiway to allow the airport emergency services to inspect the engine before they taxied the aircraft to the arrival gate. The aircraft was shut down at the arrival gate without further incident.
When the engine cowls were opened for the initial inspection there was a large quantity of oil found throughout the engine and a considerable amount of metallic debris found within the engine oil system. A data download of the engine was performed and the results were sent to GE Aviation, the engine manufacturer, for review. GE Aviation provided options for returning the aircraft to service, of which Jetstar determined an engine change was the most expeditious.
GE Aviation found there was no history or shift in oil system parameters except for the chip count on this flight. Chips are detected and recorded by the engine debris monitoring system (DMS), within the engine oil system.
On the incident flight, the right engine oil system started to detect chips from about one hour into the flight. The chip count reached seven when the crew were alerted to disconnect the number 2 generator. At 1415 a status message was generated for ENG OIL DMS R, which indicated the chip count for the right engine had reached eight.
Between 1415 and 1419 the chip count reached 11, there was a rapid loss of engine oil, a momentary spike in vibration from the engine number 1 bearing, and the EICAS message to the flight crew reporting low engine oil pressure. The engine was shut down and the aircraft landed about 52 minutes later.
Engine rotation is transmitted to an inlet gearbox (IGB) with a radial driveshaft, which connects to a transfer gearbox (TGB). The TGB transmits the engine speed to the AGB via a horizontal driveshaft (Figure 1). The AGB drives the accessories necessary for engine operation and other aircraft services, such as the generators for the aircraft electrical system. The engine oil system provides lubrication, cooling and removes debris from the gearboxes.
On inspection, the TGB housing was found to be fractured (Figure 2). The TGB oil screen was found with metallic debris and the engine oil DMS sensor was found with metallic debris (Figure 3). The manufacturer's inspection of the TGB failure indicated it was consistent with a known failure mode of the TGB described in their service bulletin (SB) 72-0298.
Pre-modified TGBs have a radial bevel gear with potential resonance modes (see Resonance) in the engine operating range. Excitation of resonance modes may lead to a gear fracture, which can result in engine oil loss and an in-flight shut down. The SB modification introduces a new damper ring groove to the radial bevel gear and a damper ring to mitigate the excitation of the resonance modes.
GE Aviation recommended the compliance periods for the SB in Table 1 below, which are based upon the number of cycles since new (CSN) for the TGB as of 31 March 2016.
The SB related modifications for the Jetstar 787 fleet was managed with a risk profile developed by GE Aviation. The risk profile had four levels of risk for TGB failures, which depended on a number of engine operating factors in addition to the TGB CSN. Jetstar responded to the SB terminating action by immediately sourcing additional post-modification units from the manufacturer and prioritised the TGB modification in accordance with the order of highest to lowest TGB risk until the incident flight. The incident engine TGB was identified as the lowest risk (based on lowest CSN, limited in-service operational data and GE Aviation recommendations) for the Jetstar fleet at the time of the incident.
The incident engine TGB had 181 CSN at the time of the incident and therefore the compliance date to complete the SB for this engine was 31 March 2017. The engine modification to comply with the SB for the incident engine was scheduled for 31 December 2016.
All machinery have a natural frequency of vibration. If a particular abnormality in the machinery generates a forced vibration, which vibrates in-phase and at the same frequency as the natural frequency of vibration, then the energy will magnify. The frequency at which this occurs is known as the resonant frequency (Figure 4). If there is insufficient damping present at the resonant frequency, then the amplitude of the vibrations will increase with each cycle. Excessive movement of components with high energy can cause a catastrophic failure of the machinery.
Twin engine turbine aeroplanes are normally restricted to operating on routes where if an engine fails or is shut down in-flight, the aircraft is within 60 minutes flight time, at the cruise speed for one engine inoperative, to a suitable airport. Extended diversion time operations (EDTO) permit the Boeing 787 to operate on routes which are further than the 60 minutes flight time in the event of an engine in-flight shut down (IFSD). EDTO approval for an operator is subject to the continuous monitoring of the engine IFSD rate.
For the Jetstar Boeing 787 fleet the EDTO approval at the time of the incident was for up to 180 minutes, which required a target IFSD rate of not greater than 0.02 per 1,000 flight hours. Prior to the incident flight, Jetstar were operating at a rolling 12 month IFSD rate of 0 per 1,000 flight hours, which increased to 0.0096 post-incident. Jetstar have performed several unscheduled engine changes on their 787 fleet since introduction into service, but no changes prior to the incident flight related to the fault condition identified in SB 72-0298.
The ATSB notes that the failure of the TGB and loss of oil is a potential failure mode known to the engine manufacturer and operator. This condition is under risk management through the service bulletin process and the operator was within the compliance period at the time of the incident. Prior to the incident flight, the incident TGB was assessed as being in the lowest risk profile for the operator's fleet.
In light of the incident, Jetstar amended their TGB modification schedule in order to prioritise at least one engine TGB on each aircraft airframe in their fleet at the earliest opportunity (known as depairing or decoupling). The fleet was completely depaired from 26 August 2016. Jetstar completed the modification programme for their fleet in November 2016.
This incident highlights the importance of flight crew complying with checklist actions when dealing with a fault condition. Inflight, the crew did not have knowledge of the extent of the damage to the engine TGB. However, by following their training and checklist procedures, they reduced the risk of a potential escalation of the fault.
At altitudes above 10,000 ft in Australia, an aircraft's height above mean sea level is referred to as a flight level (FL). FL 400 equates to 40,000 ft.
The secondary engine instruments are only displayed when an abnormal condition is detected.
Chip count refers to metallic debris detected within the engine oil system, which may be a leading indicator of machinery failure. Chip count indicates the number of metal chips detected by the debris monitoring system.