What happened
On 10 June 2004, a Boeing 777-236, registration G-YMME, was performing a scheduled flight from London Heathrow Airport. During the takeoff and initial climb phase, the flight crew observed a continuous loss of fuel. The aircraft was carrying a heavy fuel load of approximately 101,000 kg for a service to Harare.
Following the detection of the leak, the crew and air traffic control managed the situation safely, ensuring the aircraft returned to the airport. A subsequent inspection of the aircraft revealed that the centre wing fuel tank purge door had not been reinstalled. The leak was only apparent during this specific flight because the heavy fuel load provided the necessary pressure and volume to expose the opening, whereas previous flights had utilized much lower fuel levels in the centre tank.
The investigation
The AAIB investigation focused on the maintenance history of the aircraft, specifically a 2C maintenance check conducted at British Airways Maintenance Cardiff (BAMC) between 2 May and 10 May 2004. Investigators examined the procedures for draining and purging the centre wing fuel tank, as well as the installation of various panels and doors.
Technical examinations revealed several deficiencies in the Aircraft Maintenance Manual (AMM). Specifically, the diagrams used for inspecting the rear spar were inaccurate, and the instructions for the purge process contained errors. The investigation also looked into the maintenance organisation's internal processes, including how work was recorded, how staff were trained on specific aircraft zones, and the effectiveness of their technical query systems.
Findings
- The fuel leak was caused by the absence of the centre wing tank purge door.
- The door was likely removed during the recent maintenance visit to facilitate access or as part of a routine purge process but was not refitted or recorded.
- Maintenance staff involved in the subsequent inspection of the tank were unfamiliar with that specific aircraft zone and were unaware the door had been removed.
- Deficiencies in the AMM, including incorrect diagrams and flawed procedures, contributed to the lack of clarity during maintenance tasks.
- The maintenance organisation's internal reporting and technical query systems failed to ensure that known documentation errors were corrected before they impacted live maintenance tasks.
- A lack of effective control over removed components and a failure to consistently record routine work contributed to the error.