AAIB Special Bulletin: Boeing 777 Heathrow Crash Update

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British investigators are now trying to come up with a combination of "normal" conditions that could have led to the abnormal absence of fuel available to the engines of a British Airways Boeing 777-236 ER on approach to London's Heathrow airport in January. "The evidence to date indicates that both engines had low fuel pressure at the inlet to the (high pressure) pump," according to a special bulletin released by the Air Accidents Investigation Branch (AAIB). But why? The 777 fell short of Runway 27L at London's Heathrow airport, Jan. 17, collapsing the gear structure and damaging the aircraft beyond economical repair, but injuring only 13 of the 152 aboard. The report indicates causal suspects as yet unidentified "restrictions in the fuel system" somewhere between the aircraft's fuel tanks and its high-pressure fuel pumps.

There is no evidence of wake encounter, bird strike, core engine icing, or any anomalous behavior of any of the aircraft's systems suggesting electromagnetic interference. There is no evidence of fuel contamination or "excessive" water in the fuel. In fact, the AAIB's report states that "no individual parameter from the flight of G]YMMM has been identified to be outside previous operating experience." The aircraft was operated within its certified flight envelope throughout the entire flight and recorded data has revealed "no evidence of an aircraft or engine control system malfunction." Investigators are now working to identify abnormal combinations of the normal parameters recorded by the accident aircraft, and some attention has already been paid to the particularly cold weather the jet encountered that day,

Ambient air temperatures in the area were as low as minus 76 degrees centigrade on Jan. 17, but the lowest air temperature recorded during the flight was minus 45 degrees centigrade with a minimum recorded fuel temperature of minus 34 degrees centigrade. Testing of fuel samples collected from the airliner show it to best Jet A-1 specifications for freezing (not above minus 47); it froze at minus 57 degrees centigrade. Nonetheless, at an altitude of 720 feet on short final, after initially responding to an increase in thrust commanded by the autothrottles, both engines reduced thrust to about 1.03 EPR. Flight data recorder information and memory from the electronic engine controller indicate that the engine control system detected the reduced fuel flow and commanded the fuel metering valve to open fully, which it did. However, no appreciable change in the fuel flow was recorded and the aircraft, G-YMMM, fell to the ground short of the runway.