Burned 787 battery not overcharged
An examination of the flight data recorder indicated that the battery did not exceed its designed voltage of 32 volts, the National Transportation Safety Board said.
NTSB investigators are continuing to look at the battery system and plan to meet officials from Securaplane Technologies, manufacturer of the charger for the 787s lithium ion batteries, at the company's headquarters in Tucson, Arizona, said board spokeswoman Kelly Nantel.
"Potentially there could be some other charging issue," Ms Nantel said. "We're not prepared to say there was no charging issue."
Even though it appears the voltage limit was not exceeded in the case of the Japan Airlines 787 battery that caught fire on January 7 in Boston, Massachusetts, it is possible that the battery failures in that plane and in an All Nippon Airways plane that made an emergency landing in Japan last week may be due to a charging problem, said John Goglia, a former NTSB board member and aviation safety expert.
Too much current flowing too fast into a battery can overwhelm the battery, causing it to short-circuit and overheat even if the battery's voltage remains within its design limit, he said. "The battery is like a big sponge," Mr Goglia said. "You can feed it with an eye dropper or you can feed it with a garden hose. If allowed, it will soak up everything it can from the garden hose until it destroys itself."
There are so many redundancies and safeguards in aviation that when an accident or mishap occurs, it is almost always the result of a chain of events rather than a single failure, he said.
The Japan Airlines plane caught fire while it was sitting on the tarmac at Boston's Logan Airport. In a separate incident on January 16, an ANA flight made an emergency landing in western Japan after a cockpit message warned of battery problems and a burning smell was detected in the cockpit and cabin.
An investigator in Japan said on Friday that the burned insides of the plane's lithium ion battery showed the battery received voltage in excess of its design limits. Since then, all 50 787s that Boeing has delivered to airlines' fleets have been grounded and the manufacturer has halted deliveries of new planes until it can address the electrical problems.
The batteries in two incidents "had a thermal overrun because they short-circuited," Mr Goglia said. "The question is whether it was a manufacturing flaw in the battery or whether it was induced by battery charging."