Investigators Still Have Not Determined Cause

One would think the January 2008 landing crash of a British Airways Boeing 777-200 would present something close to the ideal scenario for an aviation accident investigator: a largely-intact airframe, 152 survivors to give their accounts of the mishap (which resulted in no fatalities,) and even additional information from a dedicated crash recorder installed by the airline, on top of the data recorders mandated by federal authorities.

Well, one would think. Five months after an accident that caught the world's attention -- and sent shivers down the spines of operators of the erstwhile widebody, which prior to the January 17 mishap had never suffered a catastrophic accident -- investigators still have no solid leads why the aircraft's twin turbofans spooled down on approach to Heathrow, causing the jet to pancake about 1,000 feet short of the runway.

The Washington Post reports British authorities aren't saying much about the accident, despite initial speculation -- fueled in part by the Air Accident Investigation Board's own reports -- the problem was caused by ice or some other obstruction in the airliner's fuel system. That scenario remains the odds-on favorite, though no one is 100 percent certain.

"This is a great mystery, and I never expected this accident to be this difficult to solve, given the state-of-art tools on the plane and the fact that the aircraft was largely intact," said Bill Voss, president of the Flight Safety Foundation. "This has potentially broad implications that go beyond this one airplane, depending on what they find."

With a lack of new details -- and no one from British Airways, Boeing, or enginemaker Rolls-Royce inclined to give additional information -- the industry has questioned whether the jetliner's extended time flying over a desolate part of Siberia, through temperatures as low as -49 degrees Fahrenheit, caused ice particles to form in the fuel.

Authorities reply that shouldn't have been of particular concern, however. The fuel's freezing point was -70 degrees, and after the crash investigators determined the fuel the plane received in Beijing was within specifications in regards to foreign particles, or matter that may have raised the freezing point. Many point out ice particles also would have melted as the jet descended -- and besides, both engines should have been drawing fuel from separate tanks.

One initial concern -- that the 777 suffered a failure of its engine-control or flight computers -- was also quickly proven false, as investigators found the aircraft's autopilot properly commanded both engines to increase power, but the engines were starved of fuel.

The question "what if" has also cropped up in some circles -- what if the plane's engines had failed not so close to Heathrow... but somewhere over Siberia, near the Arctic Circle and far from emergency airports. Like most widebody twin-engine airliners, the 777 is certified under Extended-range Twin-engine Operational Performance Standards, or ETOPS -- a set of standards governing the maximum distance it may operate away from alternate landing sites, in the event of engine failure.

The 777 has been certified to the longest ETOPS range allowable... but the standards are based on the failure of one engine, not both, which before January 17 many believed to be near-impossible.

FMI: www.aaib.dft.gov.uk/home/index.cfm, www.faa.gov, www.britishairways.com