Key power panel extensively damaged in Dreamliner fire
A Boeing engineering document says "extensive smoke, fire and structural damage" occurred to a key electrical panel during the in-flight fire on Tuesday's Dreamliner test flight.
Times aerospace reporter
The fire on board a 787 Dreamliner test plane Tuesday caused substantial damage to one of two main power-distribution panels inside the rear electrical-equipment bay, Boeing said Thursday.
An engineering document obtained by The Seattle Times says "extensive smoke, fire and structural damage exist to the P100" electrical panel.
That panel is a key component that takes power from the left engine's generator and distributes it through the airplane to power vital systems.
Photos accompanying the document showed several charred electrical boxes and a burned insulation blanket that is meant to keep heat and flames away from the carbon-fiber plastic-composite fuselage.
Senior Boeing executives told The Times that the photos reveal specific innovations in the electrical panel's design that could benefit competitors. At their request, the Times decided not to publish the photos, but only to describe what they show.
Dreamliner No. 2's backup-electrical systems covered for the failure of the power panel, and the pilots were able to land the plane safely in Laredo, Texas.
Boeing is still looking for the cause of the fire and studying its impact, which may include structural damage behind the panel. It has yet to determine when the 787 test fleet can fly again.
The P100 panel, about 3.5 feet tall, is a foot below the passenger floor just behind the airplane's wing. Inside the panel is a collection of separate electrical boxes, including control units, circuit breakers and relays.
The official engineering photos show the fire damage centered at two boxes called contactors low down on the panel. The contactors open circuits or close them as the power needs of airplane systems fluctuate.
Two contactors in the panel were severely damaged by the fire. One "caught fire and melted," according to the engineering document. The other had "extensive fire and smoke damage to backside."
"The rear (of the P100) panel has melted," the engineering document states. "The molten aluminum has dripped down causing potential damage to wire bundles, fuselage and stringers."
A close-up photo of the contactor box where the fire started shows it blackened and with a mass of molten material that has oozed out the bottom. A hole was burned right through the back of the panel.
The contactor box below it appears to have been damaged by the fire in the first box. Its blackened top is covered in soot and molten material.
Soot and smoke residue extends up to the top of the panel and to the wire bundles threaded in the space between the panel and the passenger floor.
One of the photos shows a hole about 12 to 15 inches long in the back of the panel, and alongside it a charred fuselage-insulation blanket.
Behind that blanket, placed there for fire protection, is the carbon-fiber fuselage skin.
The photos, taken during initial inspection of the damage, do not show the condition of the fuselage skin behind the blanket. The document says that "due to limited access," the engineers were "unable to inspect area to determine the amount of damage."
The airplane has two parallel main electrical panels in the same bay. Each draws a half megawatt of AC power at 235 volts, P100 from the left engine and P200 from the right.
While the photos clearly show the extensive damage to P100, the assumption is that P200 was untouched.
Late Thursday, Boeing issued a media update confirming the fire's location and the ignition of the insulation blanket.
It said "the insulation self-extinguished" but provided no details.
The P100 panel on Dreamliner 2 has been removed along with the insulation material near the unit and a replacement panel is being shipped to Laredo, Boeing said.
The engineering document states that before flying again, mechanics must disassemble the P100 and document the damage "to each component ... (and) to composite fuselage where there were contacts with molten aluminum, burn marks and potential heat damage."
Boeing insists that the airplane's backup power sources can — and in this case did — cover the loss of a major power-distribution panel.
Boeing touts the 787 as an "all-electric airplane," meaning it uses electricity rather than "bleed air" diverted from the jet engines to power systems on the plane.
Hans Weber, president of Tecop International and an aviation-technical consultant, said that doesn't mean it's more vulnerable to electrical failure.
The plane's redundant electrical generators combine to deliver 1.45 megawatts of power in a network that can work around any single failure, he said.
And the jet's rudders, flaps and other flight-control surfaces are moved by three parallel hydraulics systems: two that run directly off the engines, each with a backup electrical pump, and a third that is wholly electrically driven. The pilot needs only one of those three systems to land the airplane safely.
"All of this provides a high level of redundancy," Weber said. "Parts of the system can fail while the aircraft can still be maintained under controlled flight conditions."
Boeing said inspection of the site of the fire "will take several days and is ongoing."
"It is too early to determine if there is significant damage to any structure or adjacent systems," Boeing said. "We are working through a repair plan. In addition, we are determining the appropriate steps required to return the rest of the flight-test fleet to flying status."
The head of the 787 program, Scott Fancher, said Wednesday that his team will take as long as it takes "to do it right."
Dominic Gates: 206-464-2963 or firstname.lastname@example.org
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