Boeing 787 Battery Was Not Overcharged, Japanese Investigators Say

Regulators around the world have grounded the advanced 787, called the Dreamliner, after a battery malfunction and smoke caused pilots aboard an All Nippon Airways flight to make an emergency landing last week, and a similar battery aboard a parked 787 operated by Japan Airlines ignited at Logan Airport in Boston on Jan. 7.

Japanese investigators who retrieved the charred and disfigured battery pack from the All Nippon plane initially suspected overcharging, a dangerous condition where a battery is charged beyond its electrical capacity and becomes susceptible to overheating and fire. Experts in lithium-ion batteries — the type under investigation on the Dreamliner — have suggested that the batteries may have been charged too quickly, pointing to charging issues rather than problems with the batteries themselves.

But data retrieved from the All Nippon jet suggested that the battery had not been charged beyond its maximum design voltage, 32 volts, Norihiro Goto, chairman of the Japanese Transport Safety Board, told reporters Wednesday. The U.S. Federal Aviation Administration announced similar findings Sunday from its investigation into the lithium-ion battery that caught fire in Boston.

Mr. Goto said that readings aboard the All Nippon flight showed the battery’s voltage stayed relatively stable at 31 volts, just under the maximum voltage, until pilots detected a strange smell in the cockpit about 15 minutes after takeoff. The data showed a sudden, unexplained drop in the battery’s voltage after that, Mr. Goto said.

“There is no direct evidence of overcharging,” Mr. Goto said, though he stressed it was too early to reach a firm conclusion, given the complexity of the electrical systems aboard the 787. “There is a possibility that something went wrong within the battery itself.”

The damaged battery is now being inspected by the Japanese Aerospace Exploration Agency, which will take CT scans to examine its interior.

The authorities will then send the battery to its Japanese manufacturer, GS Yuasa, which will help investigators take the unit apart for further scrutiny, Mr. Goto said.

The unit that overheated aboard the All Nippon Dreamliner was the jet’s main battery, while the fire on the Japan Airlines jet was blamed on its auxiliary battery. Both batteries have similar structures and are made by GS Yuasa, which has pioneered the development of large lithium-ion batteries for use in trains and planes. Smaller lithium-ion batteries are used widely in cellphones and laptops.

GS Yuasa has said it is cooperating fully with investigators from both the United States and Japan.

Article source: http://www.nytimes.com/2013/01/24/business/global/boeing-787-battery-was-not-overcharged-japanese-investigators-say.html?partner=rss&emc=rss