Monday, May 12, 2008

AAIB: Latest Bulletin on British Airways crash investigation

AAIBThe U.K.'s Air Accidents Investigation Branch (AAIB) issued a new special bulletin earlier today, with updated information about the Board's investigation of the crash landing of a British Airways Boeing 777 aircraft at London's Heathrow Airport (LHR). The accident occurred on January 17, 2008, when BA Flight 038, arriving at LHR from Beijing, landed short of runway 27L after losing power in the final stages of its approach. The newest report, AAIB Bulletin S3/2008, cites evidence of low fuel pressure in both engines of the accident aircraft, a Boeing 777-236ER (registration number G-YMMM), as leading to an uncommanded loss of power.

The report says the "reduction in thrust on both engines was the result of a reduced fuel flow" and notes that "the engine control system detected the reduced fuel flow and commanded the fuel metering valve to open fully. The fuel metering valve responded to this command and opened fully but with no appreciable change in the fuel flow to either engine."
The evidence to date indicates that both engines had low fuel pressure at the inlet to the HP pump. Restrictions in the fuel system between the aircraft fuel tanks and each of the engine HP pumps, resulting in reduced fuel flows, is suspected.
The AAIB's latest Special Bulletin on the crash of BA Flight 038 addressed several alternative explanations for the crash, ruling them out as causes. Specifically mentioned:
  • no evidence of an aircraft or engine control system malfunction
  • no evidence of a wake vortex encounter, a bird strike or core engine icing
  • no evidence of any anomalous behaviour of any of the aircraft or engine systems that suggests electromagnetic interference
  • fuel was of good quality, with no evidence of contamination or excessive water
  • no unusual deterioration or physical blockages of the fuel system and pipe work
  • spar valves and the aircraft fuel boost pumps were serviceable and operated correctly during the flight
The report did find that "the high pressure (HP) fuel pumps from both engines have unusual and fresh cavitation damage to the outlet ports consistent with operation at low inlet pressure."

The AAIB investigation is continuing, with a focus on trying to determine why neither engine responded to the demanded increase in power when all of the engine control functions operated normally. No single parameter from the flight data has been identified as abnormal. The ongoing investigation centers on identifying "abnormal combinations of parameters."

Click here to download AAIB Bulletin S3/2008. (3-page 'pdf' file)

Related: Click here to view all posts about British Airways Flt 038 on Aircrew Buzz.