News Column

NTSB Questions Boeing 787 Battery Design, Certification

Feb. 7, 2013

Dominic Gates

Boeing 787. (Eric Prado, Creative Commons)
Boeing 787. (Eric Prado, Creative Commons)

The National Transportation Safety Board has pinpointed the start of the 787 Dreamliner battery fire on a parked Japan Airlines jet a month ago as a short circuit inside a single cell.

The agency still hasn't identified the cause of the initial short circuit but has narrowed down the suspects.

Details provided by the NTSB make clear that Boeing will have to redesign the battery for a long-term fix.

In addition, the NTSB pointed to failures in the airplane certification process conducted by Boeing and the Federal Aviation Administration, which failed to identify the hazards revealed by this incident.

"The assumptions used to certify the battery must be reconsidered," NTSB chief Deborah Hersman said in a detailed media briefing. "Our task now is to see if appropriate layers of defense and checks were built into the design, certification and manufacturing process."

The overheating that started in cell 6 of the eight-cell battery spread to all the others and caused the fire, Hersman said.

She said Boeing assessed the chances of a single cell short circuit and the impact that such an event might have on the battery in various tests conducted during the certification process.

Boeing concluded that these tests "showed no evidence of cell-to-cell propagation or fire in the battery."

But in the fire on the Japan Airlines jet, that's exactly what happened.

In another certification test, Hersman said, Boeing studied the possibility that a failure in a single cell would result in smoke emission from the battery and estimated that this would happen "less than once in every 10 million flight hours."

"The 787 fleet has accumulated less than 100,000 flight hours," Hersman said. "Yet there have now been two battery events resulting in smoke less than two weeks apart on two different aircraft."

The second event, several days after the fire on the Japan Airlines plane, forced an All Nippon Airways 787 flight in Japan to make an emergency landing.

Hersman identified three potential root causes for the short circuit:

-Some malfunction in the battery charging system;

-Contamination within the battery as a result of the manufacturing process; and

-An inadequate battery design.

But whichever of these is found to have started the overheating, it's clear from Hersman's remarks that the battery safety features failed to cope with the initial failure and Boeing will have to revisit the design.

"We're looking at the total design of the battery, including the physical separation of cells, their electrical interconnections and their thermal isolation from each other," Hersman said.

Source: (c)2013 The Seattle Times Distributed by Mclatchy-Tribune News Service.

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