A document dump by the US NTSB this week revealed extensive details on the safety regulator’s investigation into the battery fires that have grounded Boeing’s 787 Dreamliner. But the report also showed that investigators remain far from determining what caused the batteries to catch fire.
According to a 39-page interim factual report, released this week as part of 499 pages of studies, NTSB investigators have determined that a system designed to vent smoke outside the aircraft during a battery fire failed to function due to a lack of power after the battery caught fire as a Japan Air Lines 787 sat on the tarmac following a flight to Boston’s Logan Airport on January 7.
A second battery incident occurred in Japan nine days later, leading safety regulators around the world to ban the 787 from commercial flight.
Boeing had said the venting system failed because the plane was on the ground and therefore lacked cabin pressure to expel the smoke.
The NTSB report also showed abnormal battery function shortly before the fire, with the flight data recorder showing sharp voltage fluctuations. About 21 minutes after the aircraft landed, the battery dropped to zero and then spiked to 28 volts three times in three minutes. A crew member reported smoke in the cabin three minutes later.
Still, the voltage fluctuations never exceeded 32 volts, the battery’s rated level, and neither the NTSB nor Boeing has yet been able to determined what sparked the fires.