AAIB: Restriction to the fuel flow appears to have caused the uncommanded power reduction that led a British Airways Boeing 777-200 to crash-land at Heathrow
Restriction to the fuel flow between the fuel tanks and the engine fuel pumps appears to have caused the uncommanded power reduction that led a British Airways Boeing 777-200 to crash-land 300m short of the runway at London Heathrow airport on 17 January, according to a just-released Air Accident Investigation Branch interim statement.
But the AAIB makes it clear it has, so far, found no evidence of a physical obstruction in the fuel lines, although there are signs that the fuel pressure at the inlet to the engine high pressure (HP) fuel pumps had dropped because the pumps showed signs of “unusual and fresh cavitation damage”.
The agency explains: “The evidence to date indicates that both engines had low fuel pressure at the inlet to the high pressure [HP] fuel pumps. Restrictions in the fuel system between the aircraft tanks and each of the engine HP pumps, resulting in reduced fuel flows, is suspected.”
The investigator says it has been working – and is continuing to work - with Boeing, to try to reproduce the circumstances of the flight, which involved particularly cold upper air on the long journey from Beijing, to see whether the low temperatures could have affected the behaviour of the fuel system.
The fuel on board, says the AAIB, “is of good quality, in many respects exceeding the appropriate specification, and shows no sign of contamination or excessive water.”
The interim report rules out suggestions that electronic jamming signals, associated with either terrorism or with security arrangements surrounding the delivery of the British prime minister to the airport at that time, might have affected the engines’ digital fuel control units, commenting: “There is no evidence of any anomalous behaviour of any of the aircraft or engine systems that suggests electromagnetic interference.” It also rules out birdstrike, wake vortex encounter, and says there was no evidence of core engine icing.
The fuel control system acted as it should, says the AAIB report, providing details of the action of each component as recorded by the aircraft’s quick access recorder, adding that the entire flight was flown “within its certified flight envelope”.
Aircraft profile: Boeing 777