WASHINGTON — The government should reassess its safety approval of the Boeing 787 lithium ion batteries, the nation's top accident investigator said Thursday, casting doubt on whether the airliner's troubles can be quickly remedied.
The National Transportation Safety Board is investigating last month's battery fire in a Japan Airlines 787 "Dreamliner" while it was parked in Boston. The results so far contradict some of the assumptions that were made about the battery's safety at the time the system won government approval, said the board's chairman, Deborah Hersman.
The probe 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.
The findings are at odds with what Boeing told the Federal Aviation Administration when that agency was working to certify the company's newest and most technologically advanced plane for flight, Hersman said. Boeing said its testing showed that even when trying to induce short-circuiting, the condition and any fire were contained within a single cell, preventing thermal runaway and fire from spreading, she told reporters at a news conference.
Boeing's testing also showed the batteries were likely to cause smoke in only 1 in 10 million flight hours, she said. But the Boston fire was followed nine days later by a smoking battery in an All Nippon Airways plane that made an emergency landing in Japan. The 787 fleet has recorded less than 100,000 flight hours, Hersman noted.