The incident was notified to the Air Accidents Investigation Branch (AAIB) on 11 June 2004. The AAIB investigation team comprised:
Mr J J Barnett - (Investigator-in-Charge)
Mr K Conradi - (Operations)
Mr S J Hawkins - (Engineering)
Mr C Pollard - (Engineering)
Mr A Foot - (Flight Recorders)
After takeoff from London Heathrow Airport a vapour trail was seen streaming aft of the aircraft. The flight crew diagnosed that the aircraft was probably leaking fuel from the centre wing fuel tank. They declared an emergency and decided to jettison fuel to reduce to maximum landing weight before returning to Heathrow. Their intention was to minimise heating of the brake units during the landing roll in order to reduce the risk of fire if fuel was to leak onto the wheelbrakes. After landing, the aircraft was met by the Airfield Fire and Rescue Service who reported some vapour emanating from the left landing gear but no apparent fuel leaks.
The fuel leak was caused by fuel escaping through an open purge door inside the left main landing gear bay, on the rear spar of the centre wing tank. The purge door had been removed during base maintenance at the operator’s maintenence organisation in Cardiff, between 2 May and 10 May 2004, and had not been refitted prior to the aircraft’s return to service.
The investigation identified the following causal factors:
1. The centre wing tank was closed without ensuring that the purge door was in place.
2. When the purge door was removed, defect job cards should have been raised for removal and refitting of the door, but no such cards were raised.
3. The centre wing tank leak check did not reveal the open purge door because:
i. The purge door was not mentioned within the Aircraft Maintenance Manual (AMM) procedures for purging and leak-checking the centre wing fuel tank.
ii. With no record of the purge door removal, the visual inspection for leaks did not include the purge door.
iii. The fuel quantity required to leak check the purge door was incorrectly stated in the AMM.
4. Awareness of the existence of a purge door on the Boeing 777 was low among the production staff working on G-YMME, due in part to an absence of cross references within the AMM.
Following the incident, significant safety action was taken by both the maintenance organisation and the aircraft manufacturer to address issues discovered during the investigation. The AAIB made five Safety Recommendations.
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Published 10 December 2014