What happened
On 8 February 2005, an Airbus A340-642, registration G-VATL, was operating a flight from Hong Kong to London Heathrow. While cruising at Flight Level 380 in Dutch airspace, the number 1 engine lost power and ran down. Shortly thereafter, the number 4 engine also began to lose power.
The flight crew initially suspected a fuel leak; however, they soon identified a fuel management issue. Although the crew manually opened all fuel crossfeed valves, the transfer of fuel from the centre, trim, and outer wing tanks to the inner wing tanks was only partially successful. Due to the lack of clear indications regarding the fuel transfer progress, the commander elected to divert the aircraft to Amsterdam Schipol Airport. The aircraft landed safely on three engines.
The investigation
The AAIB investigation focused on why the engines experienced fuel starvation despite having sufficient total fuel on board for the remainder of the flight. Investigators examined the functionality of the Fuel Control and Monitoring Computer (FCMC) and the Flight Warning Computer (FWC).
Technical analysis revealed that the automatic fuel transfer process had ceased approximately eight hours prior to the engine power loss. The investigation also looked into why the crew did not receive timely warnings regarding the dwindling fuel levels in the engine feed tanks. While bench tests of the FCMC, FWC, and Fuel Data Concentrator (FDC) did not reveal specific hardware faults, the investigation identified critical failures in the data output and warning logic.
Findings
- The primary cause of the engine power loss was fuel starvation resulting from the failure of the automatic fuel transfer system.
- The automatic transfer process stopped because of a failure in the discrete outputs from the master FCMC.
- The flight crew was not provided with timely warnings because the Flight Warning Computer disregarded low fuel level data from the FDC, as the system logic determined at least one FCMC was still providing an output.
- The crew did not notice the impending fuel starvation because the fuel system display page showed total fuel quantity rather than the specific levels in the engine feed tanks.
- The crew attempted to relight the number 1 engine at Flight Level 380, which exceeded the maximum guaranteed altitude for a relight specified in the Quick Reference Handbook (QRH).
- There was no evidence of a fuel leak; the engine rundown was strictly due to the tanks running dry.