With a crew of 15 (1 captain, 2 first officers and 12 cabin crew ) and 151 passengers, a Boeing 777-236 was scheduled to operate a flight from London Heathrow Airport to Harare Airport in Zimbabwe. According to the flight plan, the total fuel load was 101.017 kg, including nearly 19.000 kg of tankered fuel for the return flight to Heathrow.
The fuel vapour trail is clearly visible (source; AAIB © Steve Flint)
During the external preflight inspection, performed by the supernumerary first officer, refuelling was still in progress. Of the fuel load, 43.400 kg was in the centre tank.
After all preparations were completed and clearance was received the aircraft was pushed back and both engines were started. According to the clearance and in accordance with ATC taxi instructions, the aircraft was taxied to Runway 27L by the pilot flying, the first officer. At 19.03 local time the aircraft the aircraft took off and followed the SID (Standard Instrument Departure). Once the aircraft was airborne an aircraft lining up behind the Boeing 777, contacted ATC, reporting "smoke" (later determined to fuel) was visible from the center section of the aircraft and the smell of vuel vapour was noticed. This was acknowledged by ATC and the Boeing 777 crew was informed accordingly while they continued the SID and climbed to 6000 feet ASML. After receiving the information the crew checked systems and indications on the cockpit displays, but did not see anything abnormal. This make them drawthe conclusion they had a fuel leak from the center tank. This conclusion was reinforced by reports from the ground and other ground observers who observed a 2 mile (3 kilometer) vapor trail from the aircraft.
A return to Heathrow was initiated, the crew decided to dump fuel to reduce the aircraft weight to the maximum landing weight. Brake use was also discussed, and it was decided to use the Autobrake at the "Autobrake 1" setting (the lowest possible setting) to minimise wheel and brake temperatures. An emergency was declared and 24 minutes of fuel dumping was started over the sea. With ~4000 kg fuel remaining in the center tank the aircraft was set up for an approach and landing on Runway 27L once fuel dumping was completed. During the approach no vapour trail was visible and a successful landing was carried out at 20.05 local time. The open purge door
The aircraft was inspected by the (source AAIB © Unknown)
Fire Brigade and they reported no apparent
fuel leaks were visible. The aircraft taxied to its parking position under its own power. A post flight inspection revealed thathe fuel tank purge door was not in place, it was hanging on a lanyard inside the center tank. A plastic bag was attached to the aircraft structure adjacent to the purge door, containing the screws to secure the purge door in place.
The purge door, according to the Aircraft Maintenance Manual (AMM), is used during fuel tank maintenance;
"The center purge door is used to remove fuel fumes form the center section"
The (open) purge door visibility from the ground (Source: AAIB © Unknown)
The incident was investigated by the Air Accidents Investigation Branch, on the 16th of March 2007 they published their final report. (available by clicking here)
The following causal factors were listed in the report;
The center wing tank was closed, without ensuring the purge door was installed
A job card should have been raised for removal and refitting of the purge door.
The missing purge door was not discovered with the center wing tank leak check because; - They AMM did not mention the purge door for leak checking the center wing tank - With no record the purge door was removed, there was no check carried out of the purge door - The AMM fuel quantity required to leak check the purge door was incorrectly stated in the AMM
Awareness of the purge door's existence was low among the staff that had worked on the aircraft, partly caused by lack of information in the AMM.
Safety action was taken by the operator and the manufacturer to avoid reoccurance.