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Mon, Feb 04, 2008

Focus Shifts To Fuel Contamination In BA 777 Accident

Low Temps May Have Resulted In Ice Formation

Investigators into the January 17 downing of a British Airways Boeing 777-236ER on approach to London's Heathrow Airport reportedly suspect fuel-system contamination to be the cause... in particular, the possibility ice formed in the fuel during the airliner's flight from Beijing, resulting in fuel flow blockage.

As ANN reported, the 777 landed short of runway 27L at Heathrow, after its two Rolls-Royce Trent 895 turbofans failed to spool up in time to arrest the airliner's descent. While 13 persons onboard the plane were injured in the hard landing,  there were no fatalities among the 152 persons onboard.

According to an update issued January 23 by the UK's Air Accident Investigation Board, the 777's autothrust system commanded an increase in thrust from both engines. Both engines initially responded.. but after about three seconds the thrust of the right engine reduced to just above flight-idle, with the left engine following about eight seconds later.

The Wall Street Journal reports other factors for the aberration remain under consideration... but FAA officials are increasingly pointing towards some form of fuel contamination as the cause of the accident -- specifically, "small-sized contamination building up in the engine fuel systems" or "ice in the fuel somehow limiting the fuel flow to the engines," according to a memo sent to high-level FAA regulators last week.

So far, investigators have found no evidence of malfunctions to the 777's computer systems, or the engines themselves... which should come as something of a relief to Boeing, and operators of the popular widebody airliner. Less comforting, though, is the prospect of similar problems cropping up during other long-distance flights -- especially on increasingly common polar routes, like the accident flight.

According to the FAA memo, the 777 encountered a "high humidity, cold environment, conducive to ice formation" on its flight to Heathrow. Onboard sensors recorded a fuel temperature at minus 34 degrees Celsius, or minus 29 degrees Fahrenheit -- leading some investigators to theorize ice particles formed in the fuel, and in turn impeded flow to the engines at the critical time. Investigators also reportedly found internal damage to at least one fuel pump on the 777, suggesting the pumps weren't receiving adequate fuel flows, according to an anonymous source close to the investigation.

The memo also revealed possible hints of problems to come -- saying the pilots received "a maintenance message indicating excessive water in the center tank" while taxiing for takeoff on two flights prior to the accident flight. In each case, however, the warnings disappeared before action was taken to address the problem. The 777's center tank would have fed both engines on descent and approach, according to experts cited by the WSJ.

Subsequent testing of fuel recovered onboard the accident aircraft, as well as from other planes that refueled in Beijing around the same time, showed the fuel met specifications.

A safety bulletin will be released by Boeing and UK aviation officials in the coming days, updating 777 operators on the investigation. Both US and British investigators say it's too soon to issue specific recommendations to address potential center tank icing, however.



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