What happened
On November 7, 2012, an Emirates Boeing 777-300ER, registration A6-EBO, was performing a scheduled passenger flight from Bangkok to Dubai. During the climb and transition to cruise, the flight crew noticed significant deviations in the right engine's performance, including elevated Exhaust Gas Temperature (EGT) and high N2 vibrations. As the flight progressed, the crew observed a substantial increase in EGT, N2, and fuel flow on the right engine compared to the left.
Following a period of monitoring, the aircraft experienced several engine surges and loud bangs. This was immediately followed by an engine fire warning for the right engine. The crew executed emergency procedures, which included discharging a fire extinguisher bottle, and successfully shut down the affected engine. The aircraft then diverted to Mumbai International Airport, performing a single-engine descent and landing without further incident. There were no injuries among the 190 passengers or 16 crew members on board.
The investigation
An investigation by the AAIB India, involving technical experts from the NTSB, GCAA, and Boeing, examined the engine and the aircraft's systems. Ground inspections in Mumbai revealed soot deposits and paint blistering on the right engine's thrust reverser cowls. Investigators identified that the fuel line supplying the right Variable Bleed Valve (VBV) actuator had separated at the weld.
Technical analysis of the engine revealed that the sequence of events began with high N2 vibrations caused by damage to the High Pressure Turbine (HPT). This vibration led to the physical separation of the VBV actuator fuel supply line. The resulting fuel leak, combined with a flame front from an engine stall passing through the VBE cavity, ignited the fuel-air mixture in the under-cowl area, creating a rich, sooty fire.
Findings
- The primary cause of the incident was high N2 vibrations resulting from damage to the High Pressure Turbine (HPT), which caused the VBV actuator fuel supply line to fracture at the weld.
- The separation of the fuel line allowed fuel to leak into the under-cowl area.
- An engine stall allowed a flame front to travel through the VBV cavity and the core cooling compartment valve, igniting the leaking fuel.
- The flight crew followed all appropriate non-normal checklists and emergency procedures effectively.
- The aircraft was properly maintained and the weather conditions were favorable.