TOKYO -- An investigation into a lithium ion battery that overheated on a Boeing 787 flight in Japan last month found evidence of the same type of "thermal runaway" seen in a similar incident in Boston, officials said Tuesday.
The Japan Transportation Safety Board said that CT scans and other analysis found damage to all eight cells in the battery that overheated on the All Nippon Airways 787 on Jan. 16, which prompted an emergency landing and probes by both U.S. and Japanese aviation safety regulators.
They also found signs of short-circuiting and "thermal runaway," a chemical reaction in which rising temperature causes progressively hotter temperatures. U.S. investigators found similar evidence in the battery that caught fire last month on a Japan Airlines 787 parked in Boston.
Photos distributed by the Japanese investigators show severe charring of six of the eight cells in the ANA 787's battery and a frayed and broken earthing wire -- meant to minimize the risk of electric shock.
All 50 Boeing 787s in operation are grounded as regulators and Boeing investigate the problem. The Japanese probe is focusing on flight data records and on the charger and other electrical systems connected to the damaged battery.
Lithium ion batteries are susceptible to short-circuiting or catching fire when they overheat. Boeing built in safeguards to gain safety certification for use of the relatively light and powerful batteries to power various electrical systems on the 787, the world's first airliner made mostly from lightweight composite materials.
Investigators earlier said they found no evidence of quality problems with production of the 787's batteries by Kyoto-based GS Yuasa whose own aerospace ambitions are on the line.