What happened
On 8 February 2005, an Airbus A340-642, registration G-VATL, was operating a long-haul flight from Hong Kong to London Heathrow. During the flight, the crew encountered a situation involving the aircraft's fuel system that necessitated a diversion. The incident involved an undetected imbalance in fuel quantities between tanks, which was complicated by technical malfunctions within the aircraft's monitoring and control systems.
The investigation
The AAIB investigation focused on the technical integrity of the fuel management systems, specifically examining the Fuel Control and Management Computers (FCMC), Fuel Data Concentrators (FDC), and the Flight Warning Computers (FWC). Investigators analyzed the flight data recorder and cockpit voice recorder to reconstruct the timeline of the fuel imbalance and the crew's response. The examination included a detailed review of the Display Management System (DMS) and how data from the fuel quantity sensors was processed and presented to the flight crew via the Engine and Warning Display (EWD) and System Display (SD).
Findings
- The investigation identified a failure in the automatic fuel transfer process.
- There were significant issues regarding the accuracy of fuel warnings and the display of fuel status on the cockpit screens.
- The investigation established that a failure in the fuel control and management computers contributed to the crew's inability to accurately monitor the fuel levels in certain tanks.
- The complexity of the fuel system and the way data was processed through the master/slave relationship of the FCMCs created a situation where critical fuel information was not correctly communicated to the crew.