NTSB Finds Source of Boeing 787 Battery Fire: Announces Review of Battery System
The high profile investigation, which contributed to an eventual worldwide grounding of the airplane since January 16th, has focused on the incident in Boston. NTSB Chairman Deborah Hersman reported that investigators on the case isolated the problem to a short circuit that began in an individual lithium ion battery cell. The initial cell then suffered multiple short circuits resulting in a chain reaction called thermal runaway, which then spread to other cells in the battery case.
While investigators have managed to figure out the ‘what’ and ‘where’, the all important ‘why’ remains elusive. External short circuiting and mechanical impact damage to the battery have been ruled out, Hersman said. But other than those pretty much every other possibility is still fair game. Hersman noted that several possible suspects include the charging of the battery, “design and construction…, and the possibility of defects introduced during the manufacturing process”.
What makes the incident particularly concerning, along with another related Dreamliner incident in Japan two weeks later, is that something like this should not have happened according to Boeing. Testing by the company indicated that smoking batteries were given one in ten-million flight hours odds, and yet exactly that has happened twice before the entire fleet reached even one hundred thousand flight hours. What’s more, on board safeguards in place to prevent the oft-volatile lithium-ion batteries from spreading to one another in the event of an incident failed.
“Obviously what we saw in the 787 battery fire in Boston shows us there were some risks that were not mitigated, that were not addressed…We need to understand what happened. There have now been two battery events resulting in smoke, less than two weeks apart, on two different aircraft. This investigation has demonstrated that a short-circuit in a single cell can propagate to adjacent cells and result in smoke and fire. The assumptions used to certify the battery must be reconsidered.” said Hersman.
She noted that the safety board is likely weeks away from determining the cause of the fire, and that they would release a report within the next thirty days. While the FAA has final authority on whether or not to allow the airplane to fly again in the US, today’s announcements are unlikely to hasten a thumbs up decision.