Heathrow Boeing 777 Crash Update

The January 17, 2008 crash landing of a British Airways Boeing 777 at London Heathrow remains a mystery with release of an interim report by the UK Air Accidents Investigation Branch (AAIB). But accident investigators are now concentrating on possible issues with the twinjet's high pressure fuel pumps. No...

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The January 17, 2008 crash landing of a British Airways Boeing 777 at London Heathrow remains a mystery with release of an interim report by the UK Air Accidents Investigation Branch (AAIB). But accident investigators are now concentrating on possible issues with the twinjet's high pressure fuel pumps.

No evidence of a mechanical fault has been found with the Boeing 777, which crashed just short of the runway after the pilots reported losing power at the end of a flight from China. All 139 passengers and six crewmembers on board escaped safely.

The AAIB interim report said "the autopilot and the auto-throttle behaved correctly and the engine control systems were providing the correct commands prior to, during and after the reduction in thrust. Examination of the engines indicated no evidence of a mechanical defect or ingestion of birds or ice."

Initial speculation into the cause of the accident centered around possible bird ingestion, fuel flow problems or an auto-throttle glitch that caused the engines to cut off. But the AAIB quickly determined that the "engines did not shut down and both engines continued to produce thrust at an engine speed above flight idle, but less than the commanded thrust."

Both Rolls-Royce Trent 895-17 turbofans on BA's Boeing 777-236 (G-YMMM) failed to respond to demands for more power moments before the first-ever crash of a Boeing 777.

The British AAIB's initial statement on the BA38 accident said: "Initially the approach progressed normally, with the autopilot and auto-throttle engaged. The aircraft then descended rapidly and struck the ground, some 1,000 ft short of the paved runway surface, just inside the airfield boundary fence. The aircraft stopped on the very beginning of the paved surface of Runway 27L. During the short ground roll the right main landing gear separated from the wing and the left main landing gear was pushed up through the wing root. A significant amount of fuel leaked from the aircraft but there was no fire.

"Interviews and Flight Data Recorder analyses show the flight and approach to have progressed normally until the aircraft was established on late finals. At approximately 600 ft and two miles from touchdown, the auto-throttle demanded an increase in thrust from the two engines, but the engines did not respond. Following further demands for increased thrust from the auto-throttle, and subsequently the flight crew moving the throttle levers, the engines similarly failed to respond. The aircraft speed reduced and the aircraft descended onto the grass short of the paved runway surface," the initial AAIB report added.

While analysis of the FDR and Cockpit Voice Recorder ruled out engine failure, mechanical defects and ingestion of birds, the AAIB did identify " some small items of debris" in the aircraft fuel tanks with "the relevance of this debris still being considered."

Tests on the fuel showed no signs of contamination or unusual levels of water content, but "detailed examination of both the left and right engine high pressure fuel pumps revealed signs of abnormal cavitation on the pressure-side bearings and the outlet ports. This could be indicative of either a restriction in the fuel supply to the pumps or excessive aeration of the fuel. The manufacturer assessed both pumps as still being capable of delivering full fuel flow," the AAIB added.

"Investigations are now underway in an attempt to replicate the damage seen to the engine high pressure fuel pumps, and to match this to the data recorded on the accident flight. In addition, comprehensive examination and analysis is to be conducted on the entire aircraft and engine fuel systems, including the modeling of fuel flows taking account of the environmental and aerodynamic effects," the AAIB report stated.

Meanwhile, Boeing has accepted a safety recommendation from the AAIB as regards procedures to cut off the fuel supply in the event of a crash.

The advisement states: "Boeing should notify all Boeing 777 operators of the necessity to operate the fuel control switch to cut-off prior to operation of the fire handle, for both the fire drill and the evacuation drill, and ensure that all versions of its checklists, including electronic and placarded versions of the drill, are consistent with this procedure."