The National Transportation Safety Board (NTSB) said on Thursday that the Federal Aviation Administration (FAA) which accepted test results from Boeing in 2007, failed to properly assess the risks of smoke or fire leaking from the batteries on Boeing’s new 787 jets.
Investigators probing the January 7 incident on a Japan Airlines 787 Dreamliner found evidence pointing to a single cell on the battery that caught fire. They have ruled out two possible reasons for the short circuit — an outside impact to the battery and an external short-circuit.
There were multiple signs of short-circuiting in the cell, one of eight on the lithium-ion battery, which led to a thermal runaway, overheating up to 500 degrees, which in turn spread to the rest of the cells.
Boeing had picked the new lithium-ion technology since it would provide more power than traditional batteries of the same size. But battery experts had questioned their use because, under certain conditions, they can overheat and ignite.
Boeing had estimated that a battery smoke event would occur less than once in 10 million flight hours, while it has instead happened twice in less than 100,000 flight hours, according to reports.
“We have left a lot of issues on the table,” said Deborah Hersman NTSB chairwoman. “We have not yet identified what the cause of the short-circuit is. We are looking at the design of the battery, at the manufacturing, and we are also looking at the cell charging. There are a lot of things we are still looking at.”
The FAA’s decision to certify the batteries has come under scrutiny. While the federal regulator is stretched thin and typically relies on testing data from Boeing, lithium batteries are an area where the agency has some expertise. The safety board said it would issue an interim report in the next 30 days.