In the January 2008 crash, the flight from Beijing to London was routine until the the aircraft was on final approach, when both engines had an uncommanded power reduction, or engine rollback, which caused the plane to land short of the runway. Although the aircraft was seriously damaged, only one of the 136 passengers was seriously injured, and there were no serious injuries among the 16 crew members.
The Air Accidents Investigation Branch (AAIB) of the UK is heading the investigation, and has released several interim reports, most recently in March 2009. In that report, a buildup of ice in the fuel system was identified as a likely cause of the uncommanded power reduction.
The most revealing insights provided by Boeing was that this kind of fuel icing problem was identified in the 1960s with the B-52, and the lessons learned from that experience led to changes in fuel system design that largely eliminated the problem. The January 2008 British Airways event, and a subsequent November 2008 rollback event involving a single engine on a Delta 777, led to a very thorough review of both the 777 fuel system and to the dynamics of fuel icing.
Among the more surprising findings from fuel system tests (which included system components from the accident airplane) was that in some situations, 777s flying with Rolls Royce engines can have ice form in the fuel system, and that ice could in turn block fuel flow at the fuel oil heat exchanger.
It was a difficult problem to study because ice formation was somewhat unpredictable in that tests similar environmental and fuel flow conditions may have produced significant amounts of ice in one test, and very little or no ice in another test.
In spite of the difficulty Boeing had in recreating the conditions that could cause icing, solving the problem was relatively easy. Changes in the fuel oil heat exchanger, plus changes in flight crew procedures, will be enough to prevent these kids of icing events in the future.
AAIB is still investigating this accident, and when the final report is released, AirSafe.com will review the report and summarize the findings in the AirSafe.com News.
For more details on this investigation, including videos summarizing previous Interim reports from the AAIB, visit 777.airsafe.org.
Report on March 2009 AAIB and NTSB Updates
Watch or listen to the report below, or read the transcript
Audio: MP3 | Video: iPod/MP4 | WMV | Google Video | YouTube
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