Federal safety investigators remain perplexed by what caused a battery on a Boeing 787 to burst into flames earlier this month in Boston. All of the 787s are grounded worldwide after problems with the new airliner also surfaced in Japan.
At a briefing Thursday, the head of the National Transportation Safety Board said it could be a long time before the plane dubbed the Dreamliner is cleared to fly.
So far, NTSB investigators have examined the charred remains of the battery and the electrical system with CT scans, taken component pieces apart and used sophisticated technology to test them, and have pored over documents. Yet they still don't know much about the sequence of events that produced such an intense fire that took firefighters more than 1 1/2 hours to extinguish.
"We do not expect to see fire events onboard aircrafts," NTSB Chairman Deborah Hersman said. "This is a very serious air safety concern and we are all responding to try to address what happened, why it happened and to make sure the aircraft that fly are safe."
The battery involved was a 63-pound lithium-ion battery; these kinds of batteries are known to catch fire. The Federal Aviation Administration imposed special conditions on Boeing's use of the battery, and extra safety measures were required.
Nevertheless, investigators say there was a "thermal runaway" inside the battery, which is an uncontrolled chemical reaction between electrolytes and electrodes. They also found evidence of high current damage from a short circuit inside the battery.
Aviation safety expert Hans Weber says the trouble could have started from the battery owing to a manufacturing defect.
"It could have been the circuitry that protects the battery against overcharging or excessive discharging and things of that nature," he says. "It could have been something else in the electronics control circuitry."
The NTSB will be probing other areas, too, and is questioning the FAA's procedure for approving or certifying this new and highly innovative airplane.
"Were those certification standards adhered to, and then the question of 'Were they appropriate?' " Hersman says. "We will be working very closely with a number of groups, including the FAA and Boeing, as we collect that information and evaluate the analysis and the risk assessments that were done."
The NTSB says it will also be exploring safety concerns raised by more than one whistle-blower. In addition, investigators are working with a team in Japan probing the cause of a severe battery failure on another Boeing 787.
With no clear answers or insightful clues, the safety board's Boston-plane investigation is likely to take some time. Once the cause is known Boeing will have to come up with a fix and the FAA will have to test and approve it.
Aviation analyst Scott Hamilton says the Boeing 787 could remain grounded for quite some time.
"Indefinite is indefinite, whether that's two months, three months, six months — we don't know. But it's not going to be back in the air anytime soon," he says.
Boeing said on Thursday it is working tirelessly on the problem and is assisting investigators in the U.S. and Japan. The airplane maker added that it deeply regrets the impact it is having on its airline customers. What the company didn't say was that it deeply regrets what all this has done to its reputation and that of its flagship airplane.