Boeing Co. officials insist that a smoking 787 Dreamliner battery worked the way it was designed to work. However, battery experts aren't heaping praise on the aircraft manufacturer.
"At least it didn't go into thermal runaway," Ralph Brodd, founder of the lithium battery consultancy Broddarp of Nevada, told us. "It didn't cause a fire or cause other cells to catch fire. But it also shows they havenít really fixed the problem yet."
The 787 Dreamliner's latest battery dustup occurred this week during pre-departure maintenance on a Boeing 787 parked at Tokyo's Narita International Airport. Japan Airlines mechanics noticed white smoke spewing from the bottom of the fuselage and found a possible failure of the main battery on cockpit instrumentation, according to a memo distributed by the airline (and sent to us via email by Boeing). "The safety pressure relief valve connecting to one battery cell out of eight was found to have opened, and it was found that liquid had dispersed in the main battery enclosure."
Boeing officials told us via email: "The issue occurred during scheduled maintenance activities with no passengers on board. The improvements made to the 787 battery system last year appear to have worked as designed."
During a press conference in March, Boeing officials had said that, with the latest modifications, "a fire could not begin, develop, or be sustained." The key was the addition of an enclosure that would eliminate the possibility of fire by venting gases through a dedicated line. "If a [battery] cell were to vent, it would vent into this enclosure," Mike Sinnett, vice president and chief engineer of the 787 program, said at the press conference. "It ruptures a burst disc in the enclosure, which allows all those gases to go immediately overboard."
Concerns were raised after last year's incidents because Boeing employed a lithium-ion battery with a cobalt oxide cathode, which can generate a lot of energy but is also prone to overheating. However, Boeing told us this week that its 787 fleet now stands at 115 delivered airplanes, which have flown more than 38,000 flights for a total of 72 million miles without incident since returning to service in April.
The National Transportation Safety Board said it will participate in an investigation of the latest incident. Japan's Civil Aviation Bureau will lead the investigation.
Battery experts who spoke to Design News called the new battery design's success level a matter of interpretation.
"If you had your car in for an oil change and the battery started smoking, would this be OK?" Donald Sadoway, John F. Elliott Professor of Materials Chemistry at MIT, told us in an email. "It's clear to me that the battery is unstable and that they have taken steps to contain its failures."
Brodd said that, even though the latest incident is worrying, "it's much better than having the battery catch fire."