Boeing 787 probe widens. Overcharged battery ruled out.

Boeing 787 battery that caught fire on a Japan Airways jetliner was not overcharged, government officials say. The Boeing 787 battery didn't exceed its 32 volt limit, and the NSTB is looking into other possible causes. 

The battery that caught fire in a Japan Airlines Boeing 787 in Boston earlier this month was not overcharged, but government investigators said there could still be problems with wiring or other charging components.

An examination of the flight data recorder indicated that the battery didn't exceed its designed voltage of 32 volts, the National Transportation Safety Board said in a statement.

NTSB investigators are continuing to look at the battery system. They plan to meet Tuesday with officials from Securaplane Technologies Inc., manufacturer of the charger for the 787s lithium ion batteries, at the company's headquarters in Tucson, Arizona, said Kelly Nantel, a spokeswoman for the board.

"Potentially there could be some other charging issue," Nantel said. "We're not prepared to say there was no charging issue."

Even though it appears the voltage limit wasn't exceeded in the case of the Japan Airlines 787 battery that caught fire on Jan. 7 in Boston, it's 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, according to 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," 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 almost always is the result of a chain of events rather than a single failure, he said.

The Japan Airlines plane caught fire Jan. 7 while it was sitting on the tarmac at Boston's Logan Airport. In a separate incident on Jan. 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 Friday that the burned insides of the plane's lithium ion battery show 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," Goglia said. "The question is whether it was a manufacturing flaw in the battery or whether it was induced by battery charging."