Incident Summary
On 10 June 2004, a serious incident occurred involving a Boeing 777-236, registration G-YMME, during departure from London Heathrow Airport. The aircraft experienced a fuel leak from the centre wing tank (CWT). The flight crew became aware of the leak and returned to Heathrow, where the aircraft landed safely without further incident.
Flight History
The aircraft departed on a scheduled flight. Shortly after takeoff, the flight crew observed indications of a fuel leak. They declared an emergency and returned to Heathrow, where a safe landing was made. No injuries were reported among the passengers or crew.
Post-Flight Inspection
A post-flight inspection revealed that the centre wing tank purge door was missing. This door, located on the lower surface of the centre wing tank, provides access for maintenance and is normally closed and fastened. Its absence allowed fuel to escape from the tank during flight.
Maintenance Background
The purge door had been removed during a 2C maintenance check performed on G-YMME in the days leading up to the incident. The check included a centre tank drain and purge procedure. After the maintenance tasks were completed, the purge door was not reinstalled. The failure to close the door was not detected during subsequent inspections or leak checks.
Several job cards were used during the maintenance, including those for the centre tank drain and purge, and fuel leak checks. However, the open purge door was missed by maintenance personnel and inspectors.
Aircraft Maintenance Manual Issues
The investigation identified deficiencies in the Aircraft Maintenance Manual (AMM) provided by the manufacturer. Specifically, diagrams for the rear spar inspection did not depict the baffle doors in the centre wing tank, which may have contributed to confusion during maintenance. Additionally, procedures for removal and installation of the purge door were not sufficiently clear.
Organisational Factors
The maintenance organisation's quality assurance procedures were reviewed. The investigation found that the quality oversight did not ensure that the purge door was reinstalled and checked. The occurrence reporting system within the organisation was also examined, and while it existed, it was not effectively used to capture this type of error.
Conclusion
The serious incident was caused by the centre wing tank purge door being left open after maintenance, resulting in a fuel leak. The investigation highlighted gaps in maintenance procedures, manual clarity, and quality assurance that failed to detect the open door.