What happened
On 10 June 2004, a Boeing 777-236, registration G-YMME, operated by British Airways, departed from London Heathrow Airport. During the climb, a vapour trail was observed streaming from the rear of the aircraft. The flight crew identified a potential fuel leak originating from the centre wing tank and declared an emergency. To mitigate the risk of a wheel brake fire upon landing, the crew decided to jettison fuel to reach the maximum landing weight, thereby reducing the energy required during the landing roll.
Upon landing, airfield rescue services noted vapour emanating from the left landing gear, though no active fuel leaks were visible at the time. The investigation later determined that fuel had been escaping through an open purge door located on the rear spar of the centre wing tank.
The investigation
Investigators established that the purge door had been removed during base maintenance at the operator's Cardiff facility between 2 May and 10 May 2004. Crucially, the door had not been reinstalled before the aircraft returned to service. The removal was not recorded on any defect job cards, and no personnel came forward to claim responsibility for the omission.
Several factors prevented the error from being detected. The maintenance organisation had been aware of an error in the Aircraft Maintenance Manual (AMM) diagram for two years, but this information had not been communicated to production staff. Furthermore, the fuel quantity specified in the AMM for performing a leak check was insufficient to reveal a leak through the open door. The inspection was also hampered because the purge door was not visible from the ground with the gear doors closed, and the specific area was not inspected during a subsequent rear spar check due to an error in the maintenance manual's location instructions.
Findings
- The fuel leak was caused by fuel escaping through an unsecured purge door inside the left main landing gear bay.
- The purge door was removed during maintenance and not refitted prior to flight.
- There was a lack of awareness regarding the purge door's existence due to poor cross-referencing in the AMM.
- Maintenance procedures failed to include a requirement to check or tether the purge door.
- A shortage of planning resources and a lack of formal tracking for unresolved technical queries contributed to the oversight.
- The maintenance organisation's culture regarding error reporting was potentially hindered by concerns over disciplinary boundaries.
Safety action
The AAIB issued several safety recommendations to British Airways Maintenance Cardiff, focusing on improving the Maintenance Error Management System (MEMS), ensuring better dissemination of technical information from team leaders to mechanics, and establishing clearer disciplinary policies to encourage the reporting of maintenance errors.