What happened
On 27 March 2014, a Qantas Airways Limited Airbus A380-842, registered VH-OQL, departed Dubai International Airport for London. Shortly after takeoff, while the aircraft was climbing through approximately 2,000 feet, the flight crew received an ECAM warning indicating a failure of the number 3 engine. The engine had undergone an uncommanded in-flight shutdown (IFSD) despite all prior indications appearing normal.
The crew declared a PAN and leveled the aircraft at 6,000 feet. An attempt to restart the engine using the starter assist was unsuccessful, as the crew noted no rotation in the engine's high-pressure stage. Following the decision to return to Dubai, the commander initiated fuel jettisoning. The aircraft landed safely at Dubai International Airport after approximately one hour of flight time. There were no injuries among the 4/84 passengers or 19 crewmembers on board.
The investigation
The GCAA AAIS investigation focused on the mechanical integrity of the Rolls-Royce Trent 900 engine. Post-flight inspections by maintenance staff revealed metal contamination in the engine's master chip detector. Further examination of the engine's internal components, specifically the external gear box (EGB) and the step aside gearbox (SAGB), showed that while the EGB could be rotated manually, the high-pressure spool remained stationary, indicating a mechanical disconnection.
Investigators examined the angled drive shaft (ADS) and found that while it was within manufacturing limits, a subsequent balance test revealed an unbalance condition outside of acceptable limits. Detailed borescope inspections of the internal gearboxes revealed significant debris in the oil pump inlet screen and damage to the driven bevel gear.
Findings
- The primary cause of the engine shutdown was mechanical damage within the SAGB, which severed the drive to the EGB.
- This disconnection caused a loss of drive to the fuel pumps, oil pumps, and generators, triggering the shutdown.
- Insufficient clamping load at the bolted joint between the bearing support and the housing allowed for relative movement during operation.
- The unbalance of the angled drive shaft acted as a contributory factor by increasing the rate of wear through vibration.
- Prior to the incident, the aircraft had been released to service despite a deferred maintenance item regarding metal debris detected in the oil chip detector during the previous flight.