Federal accident investigators say a short-circuit and an uncontrolled chemical reaction apparently took place in a Boeing 787 battery before the battery caught fire earlier this month in Boston.
National Transportation Safety Board Chairman Deborah Hersman says investigators have not yet determined the root cause of the lithium ion battery fire.
Hersman briefed the media Thursday on the board's investigation into the Jan. 7 incident. She says the significance of the fire "cannot be understated" since the expectation is there will not be fires on airliners. She says Boeing is supposed to have built safeguards into the aircraft to prevent that.
The Federal Aviation Administration grounded all 787s operated by U.S. carriers after another 787 battery failure in Japan. There are just six 787s domestically, all owned by United Airlines.