The US National Transportation Safety Board (NTSB) has announced the origin of the fire on the Japan AirLines Boeing Dreamliner, January 7th. The battery was believed to have had an “initiating event” in one of its eight cells; this was assessed using the flight data recorder and evidence form the thermal and mechanical damage.
The cell identified as the starting point “showed multiple signs of short-circuiting, leading to thermal runaway condition, which then cascaded to other cells.” The evidence suggests the cells reached 260oC.
Chairman of NTSB, Deborah Hersman, said potential causes of the initiating short circuit being evaluated include battery charging, the design and construction of the battery, and the possibility of defects introduced during the manufacturing process.
The cause of the short circuit remains unknown and further investigations will focus upon design and certification requirements of the battery system.
During its certification process Boeing considered the types of failures that might affect the battery, following tests it found no evidence that cell-to-cell spread or fire would be a problem and that smoke emitting from the cell would not occur during more than one in ten million flight hours.