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Source: Boeing to propose 787 battery fix to FAA

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Japan's Transport Ministry said Wednesday its investigation has uncovered a new problem: The aircraft's auxiliary power unit, which contains a lithium ion battery, was improperly connected to the main battery that overheated.

NTSB investigators found the Boston fire started with multiple short-circuits in one of the battery's eight cells. That created an uncontrolled chemical reaction known as "thermal runaway," which is characterized by progressively hotter temperatures. That spread the short-circuiting to the rest of the cells and caused the fire.

The board's findings are at odds with Boeing's initial battery testing before FAA's safety certification of the plane, which concluded that any short-circuiting could be contained within a single cell, preventing thermal runaway and fire from spreading.

Among the measures being discussed to make the batteries safe enough to return the 787 to the skies are adding more ceramic spacers between battery cells to contain any short-circuiting and fire within that cell. That would be in line with Boeing's initial test results.

More ceramic spacers would make the battery larger, which would require a bigger box to contain the battery cells. A more robust box lined with material to prevent any fire from spreading is also under discussion.

"What Boeing is trying to do is fix the battery so that (its initial testing) assumption is now valid," said Jon Hansman, a Massachusetts Institute of Technology aeronautics professor and a member of the FAA's Research and Development Advisory Committee.

"So if you can fix this part, the rest should be ok," he said.

Boeing hasn't said how much the 787 grounding will cost it. Imperial Capital analyst Ken Herbert estimated last week that it could cost Boeing $25 million a month in direct costs, with the total price tag climbing past $1 billion, including spending to fix the problem and expenses for delayed deliveries.

Boeing is still building five 787s each month, and has said it still wants to speed up to 10 a month by the end of the year. The company had orders for 800 of the planes at the time they were grounded.

It would take a delay of more than a couple of months for Boeing to back away from its speed-up plan, UBS analyst David Strauss wrote in a note on Wednesday.

Copyright 2013 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

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