Investigators in 777 crash looking at fuel systems
Investigators studying last week's crash landing of a British Airways Boeing 777 said Wednesday they are looking closely at the possibility...
Seattle Times aerospace reporter
Investigators studying last week's crash landing of a British Airways Boeing 777 said Wednesday they are looking closely at the possibility that the accident was caused by an interruption in the flow of jet fuel to the engines.
The cause of the Jan. 17 crash at London's Heathrow airport has not been established. Even if it is a fuel-flow interruption, that doesn't necessarily exonerate Boeing.
But this focus of the investigation seems to increase the possibility of an external cause such as contamination of jet fuel loaded before the 777 took off from Beijing.
Alternative scenarios, such as a software control-system failure, clearly would be the manufacturer's responsibility and could bring into question the safety of the airplane.
"All possible scenarios that could explain the thrust reduction and continued lack of response of the engines" are being examined, the U.K.'s Air Accidents Investigation Branch said Wednesday. "This work includes a detailed analysis and examination of the complete fuel-flow path from the aircraft tanks to the engine-fuel nozzles."
The plane, carrying 136 passengers and a crew of 16, lost power about 2 miles from touchdown at a height of 600 feet. It was the first crash in the more than a dozen years that airlines have flown the 777.
The U.K. agency leading the investigation made clear that, contrary to some initial reports, the jet's two Rolls-Royce engines did not fail at precisely the same moment, and neither failed completely.
The aircraft was approaching with the autopilot engaged when the autothrust system commanded the pilot to increase thrust from both engines.
"The engines both initially responded but after about 3 seconds the thrust of the right engine reduced," the report said. "Some eight seconds later the thrust reduced on the left engine to a similar level. ... Both engines continued to produce thrust at an engine speed above flight idle, but less than the commanded thrust."
The accident resulted in few injuries. The co-pilot was credited with heroic skill in keeping the plane aloft over nearby houses and putting it down onto the grass 1,000 feet short of the runway.
The report said that "the autothrottle and engine-control commands were performing as expected prior to, and after, the reduction in thrust," suggesting that the primary software controlling the system functioned as it should.
Singling out fuel flow suggests investigators are zeroing in either on fuel contamination — perhaps from an external fuel source or maybe from some internal leakage of other fluid into the fuel tanks — or on some leakage in a fuel line serving both engines.
After fueling in Beijing, the plane flew nonstop to London. The fuel tanks would have been low as the jet came in to land at Heathrow. A contaminant at the bottom of the tanks potentially could have blocked the fuel flow to both engines.
If that was the cause, Boeing executives, engineers and mechanics will let out a sigh of relief.
As a large, twin-engine airplane, the 777's ability to serve airlines on ultra-long-haul routes depends upon the reliability of its engines.
Engines occasionally have failed in flight for various reasons, and the affected 777s have continued flying safely on the remaining engine. No 777 has previously had two engines fail together.
Unlike a typical uncontrolled plane crash into the ground, the jet survived the crash landing largely intact, providing investigators a great deal of information on its condition. Boeing is providing technical assistance to the investigation, company spokesman Jim Proulx said.
Dominic Gates: 206-464-2963 or firstname.lastname@example.org
Copyright © 2008 The Seattle Times Company
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