What happened
On 17 January 2008, a Boeing 777-236 ER, registration G-YMMM, was performing a commercial passenger flight from Beijing to London Heathrow. The flight proceeded normally through a region of extremely cold air between the Urals and Eastern Scandinavia, where ambient temperatures reached -76ºC.
During the final approach to Runway 2FR, the aircraft was configured for landing with the autopilot and autothrottle engaged. While the autothrottle commanded an increase in thrust, the right engine's thrust dropped to approximately 1.03 EPR at a height of 720 ft. Seven seconds later, the left engine's thrust similarly decreased to 1.02 EPR. This reduction in power was caused by a drop in fuel flow. The aircraft subsequently sustained damage beyond economical repair, resulting in 1 serious injury and 4 minor injuries among the crew, while all 136 passengers remained uninjured.
The investigation
Investigators examined the aircraft's engine control systems, fuel systems, and environmental conditions. Analysis of the Flight Data Recorder and the Electronic Engine Controller indicated that the engine control system detected the reduced fuel flow and commanded the fuel metering valve to open fully. However, this command did not result in any measurable change in fuel flow to the engines.
Engine examinations revealed that the high pressure (HP) fuel pumps on both engines exhibited fresh cavitation damage at the outlet ports, which is consistent with operating under low inlet pressure. While the aircraft's fuel was found to be of high quality and met all specifications, the investigation focused on the fuel system components between the tanks and the HP pumps.
Findings
- The reduction in thrust on both engines was driven by a reduction in fuel flow.
- Both engines experienced low fuel pressure at the inlet to the high pressure fuel pumps.
- The high pressure fuel pumps showed evidence of cavitation damage consistent with low inlet pressure.
- The aircraft's fuel met all required specifications and showed no signs of contamination or water.
- There was no evidence of engine control system malfunction, bird strikes, or external interference.