US air safety investigators have identified how a battery fire on a Boeing 787 Dreamliner occurred last month but have not discovered the cause, the head of the NTSB said Thursday.
National Transportation Safety Board chairwoman Deborah Hersman said evidence pointed to a single cell on the eight-cell lithium-ion battery on a parked Japanese Airlines 787 at Boston's Logan airport.
There were multiple signs of short-circuiting in the cell, which led to an uncontrollable rise in temperatures, or thermal runaway, to adjacent cells, Hersman said.
"We are now working to identify the cause of the short circuit on cell six," she said at a news conference to update her agency's probe of the January 7 incident.
The battery fire, and a burned battery that forced an All Nippon Airways 787 flight into an emergency landing on January 16, resulted in the global grounding of all 50 787s in service until the problem is fixed.