Japan’s Transport Safety Board said an investigation into a lithium ion battery aboard a Boeing 787 flight in Japan last month found evidence of the same type of ‘‘thermal runaway’’ seen in a similar incident in Boston.
The board said in a report Tuesday that CAT scans and other analysis found damage to all eight cells in the battery that overheated on an All Nippon Airways 787 on Jan. 16, prompting an emergency landing.
They also found signs of thermal runaway, a chemical reaction in which rising temperature causes progressively hotter temperatures. US investigators found similar evidence in the battery that caught fire last month on a Japan Airlines 787 parked in Boston.
Photos distributed by 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 inquiry is focusing on flight data records and on the charger and other electrical systems connected to the damaged battery.
Lithium ion batteries are more susceptible to catching fire when they overheat or to short-circuit than other types of batteries. 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.
Meanwhile, US regulators said Tuesday that they are evaluating a Boeing request to conduct test flights of its 787 Dreamliners.
The Federal Aviation Administration confirmed the request, but officials declined to elaborate.
Boeing officials didn’t immediately reply to a request for comment. Boeing’s request to the FAA was first reported by The Seattle Times.
Investigators earlier said they found no evidence of quality problems with production of the 787’s batteries by Kyoto, Japan-based GS Yuasa, whose own aerospace ambitions are on the line.
Yuasa said Tuesday that its April-December net profit fell 3.6 percent to $59.6 million from a year earlier, as demand for batteries lagged due to sluggish demand in Japan and overseas.