NTSB: Reassess safety of 787 battery

WASHINGTON -- The government should reassess its safety approval of the Boeing 787's lithium ion batteries, the nation's top accident investigator said yesterday, casting doubt on whether the airliner's troubles can be remedied quickly.

If Boeing is forced to switch to a different type of battery, it would add weight to the plane -- and fuel efficiency is one of the 787's main selling points.

The aircraft maker did get some good news yesterday: It received permission from the Federal Aviation Administration to conduct test flights under limited circumstances with special safeguards. The tests are a critical step toward resolving the plane's troubles. The airliners have been grounded for three weeks. Boeing needs to test the batteries under flight conditions before a solution can be approved.

The flights will be conducted over unpopulated areas, and extensive preflight testing and inspections and in-flight monitoring are required, the FAA said in a statement.

But there also was new trouble for the plane Boeing has dubbed the "Dreamliner." The National Transportation Safety Board said the results so far of an investigation into last month's battery fire in a Japan Airlines 787 while it was parked at a Boston airport raise new questions about the safety certification of its batteries. An analysis of the origin of the fire contradicts some of the assumptions that were made about the battery's safety at the time the system won government approval, the board's chairwoman, Deborah Hersman, said.

The NTSB investigation shows the fire started with multiple short-circuits in one of the battery's eight cells, she said. 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, she said.