Results of 787 Fire Probe Relieve Boeing; Challenging Repairs Loom
July 19--The initial report from British investigators into the 787 Dreamliner fire at Heathrow Airport delivered good news for Boeing's trouble-plagued jet.
Though how the July 12 fire started and why it was so severe remain mysterious, the investigators definitively fingered a small electronic device that's found on lots of other airplanes as the source of the fire.
"It doesn't look like this fire had anything to do with the unique attributes of the 787," said Hans Weber, a respected technical expert in the aviation world and president of consulting firm Tecops International.
The incident, not long after two battery fires grounded the 787 for three months, appears to be "incredible bad luck" for the Dreamliner program, he said.
The report from the U.K.'s Air Accidents Investigation Branch (AAIB) also revealed that, despite how it looked on TV footage, the fire did not burn through the roof of the Dreamliner.
Still, repairing the damaged Ethiopian Airlines jet will clearly be a major challenge for Boeing's engineers.
The AAIB interim report, released Thursday, confirmed the fire centered on an electronic device weighing less than 7 pounds, an Emergency Locator Transmitter (ELT), which transmits location data to satellites in the event of a crash.
Investigators recommended the Federal Aviation Administration (FAA) order the devices disabled on all 787s pending further investigation and recommended the U.S. agency also review the devices' performance in other planes.
Boeing said it supports those recommendations, calling them "reasonable precautionary measures to take as the investigation proceeds."
The focus on a rare malfunction of this electronic beacon damped fears that the fire was the result of some broader problem with the 787's electrical systems.
The report points to the ELT, which sits in the fuselage ceiling just in front of the tail fin, as the sole source of the fire, either due to the lithium batteries inside it or from a short in a connecting wire.
It did not explain how such a relatively small energy source -- an inactive battery with five 3-volt cells carrying just 55 amp-hours of charge -- could severely damage a substantial area of the jet's carbon-fiber-reinforced plastic skin.
For comparison, the 787's main batteries that proved so problematic earlier this year each weighed 63 pounds and had eight 32-volt cells. Each of those two batteries generates 150 amps on power-up; the total charge isn't clear.
In addition, the emergency beacon's batteries use a lithium-manganese chemistry that is relatively stable compared with the more volatile lithium-cobalt chemistry of the main batteries.
The AAIB report says Honeywell, which supplies the ELT, has produced some 6,000 units of the same design. They are on a wide range of aircraft, and the 787 fire has been "the only significant thermal event" to date.
Yet firefighters initially struggled to put out the fire, according to the report.
After the control tower noticed smoke from the plane, firefighters rushed to the jet, entering through a passenger door, and "encountered thick smoke" that became denser as they moved to the rear, where they saw signs of fire "above the ceiling panels."
They initially tried to extinguish the fire with a handheld halon fire extinguisher. When this proved ineffective, they ripped out a ceiling panel and doused the fire with water from hoses.
Because airliners have neither fire detection or suppression systems above the cabin ceilings, the report says, "had this event occurred in flight it could pose a significant safety concern and raise challenges for the cabin crew in tackling the resulting fire."
Source: Aviationpros.com
No comments:
Post a Comment