The NTSB says a short circuit in one of eight cells in the APU battery of a Japan Airlines Boeing 787 led to the fire in the aircraft at Boston Logan Airport Jan. 7. At a news conference on Thursday, NTSB Chairman Debra Hersman said evidence from the flight data recorder and damage to the battery itself indicates the battery and not the aircraft systems were at fault. "That cell showed multiple signs of short circuiting, leading to a thermal runaway condition, which then cascaded to other cells," said an NTSB news release. "Charred battery components indicated that the temperature inside the battery case exceeded 500 degrees Fahrenheit." That was a factor. While the finding shines most of the spotlight on battery manufacturer Yuasa, the NTSB does not leave the FAA and Boeing off the hook.
Hersman said the high level of safety enjoyed by the airline industry has come by building layers of redundant defenses against disaster. "Our task now is to see if enough and appropriate layers of defense and adequate checks were built into the design, certification and manufacturing of this battery." But she said Boeing's estimate (accepted by the FAA) that a battery failure leading to the release of smoke into the aircraft would occur once in 10 million flight hours was obviously incorrect since there were two such events (including the in-flight battery fire aboard an ANA 787 two weeks after the JAL incident) in the first 100,000 hours. "The failure rate was higher than predicted as part of the certification process and the possibility that a short circuit in a single cell could propagate to adjacent cells and result in smoke and fire must be reconsidered," she said. The FAA allowed Boeing to ferry a 787 to its manufacturing facility in Everett on Thursday but only after the crew extensively inspected the batteries. It's still not clear when the Dreamliner will be returned to regular service.