ATSB investigation report
On 20 May 2017, in-flight engine shutdown on a Qantas Airbus A380-842 aircraft, regVH-OQG, flight QF 94, from Los Angeles International Airport (LAX), United States, to Melbourne, Australia.
The flight departed LAX at 0542 at the maximum take-off weight of 569 tonnes. About two hours after departing LAX, the flight crew requested and received ATC clearance to climb to FL 340. The flight crew commenced the climb and increased the thrust on all four engines to 93 per cent ‘N1’.
As the aircraft passed FL 325, the crew on the flight deck heard a loud bang and felt a sudden and unusual vibration of the aircraft, which reduced significantly after about 2 seconds. The first officer noticed No. 4 engine’s N1 was much lower than the other three engines – at about 49 per cent (although the flight data showed about 71 per cent N1). The captain, who was in the crew rest area, heard the bang and felt the vibration so he returned to the flight deck.
Shortly after, an advisory message (ADV) appeared on the engine warning display and 6 seconds later the message ‘ENG 4 NORM MODE FAULT’ appeared on the ECAM, along with the associated checklist, a single chime and illumination of the master caution. The ECAM message indicated that there was a problem with the full authority digital engine control (FADEC) of that engine. That fault was triggered by the automatic reversion of the FADEC of engine 4 to alternate mode, caused by the loss of air data or engine sensing parameters.
At 0726:44, the engine fire warning ‘ENG 4 FIRE’ ECAM message displayed.
At 0727:02, the flight crew selected the No. 4 engine master switch off, then pushed the engine No. 4 fire button and discharged one fire retardant agent. The engine fire ECAM cleared.
With the No. 4 engine shut down, the crew decided to return to Los Angeles.
At 0944, the fuel jettison was completed over water prior to crossing the coast, about 140 NM from LAX.
The flight crew conducted a normal approach and autoland landing onto runway 25L at about 0956.
The first officer indicated that unlike his experience of Boeing aircraft, where there was a hard limit for engine vibration, they did not get an ECAM generated for the high vibration.
According to the captain, flight crew are trained to strictly adhere to ECAM protocols. The high engine vibration procedure was part of the abnormal procedures menu and not presented as an ECAM. Therefore, the FADEC ECAM had higher priority than the high vibration advisory, and the crew did not shut down the engine until the engine fire warning ECAM required this action.
Initial engineering inspection of the No. 4 engine following the incident found damage to the low‑pressure turbine blades. There was no visible indication of fire and the event was contained, such that there was no breach of the engine casing. There was minor damage to the right flap and flap fairing from debris exiting the rear of the engine.
Engine manufacturer investigation
Rolls-Royce, the manufacturer of the aircraft’s Trent 900 engine, conducted an investigation into the engine failure that caused the shutdown.
A teardown of the engine found internally-corroded low-pressure turbine stage 2 (LPT2) blades. The corrosion led to fatigue cracking and subsequent release of blade shroud debris, resulting in significant downstream engine damage.
The corrosion resulted from chemical residue in the hollow blades from cleaning operations at the last service (July 2015). Consequently, Rolls-Royce conducted a thorough audit of cleaning operations and took additional safety action (see Safety action section).