The Japanese panel investigating the Dec. 16 mishap involving an All Nippon Airways 787 Dreamliner said Tuesday signs of an uncontrolled chemical reaction at high temperature, known as a "thermal runaway," were found in the jet's main battery.
Signs of such a chemical reaction were also seen in some cells of a Japan Airlines Co. Dreamliner battery that caught fire in Boston nine days earlier. The ANA jet had to make an emergency landing in Kagawa Prefecture due to smoke in the cockpit.
All of the cells of the battery installed in the ANA 787 showed thermal damage, Transport Safety Board Chairman Norihiro Goto said at a news conference. "Cells 3 and 6 were severely damaged and cells 1, 2, 7 and 8 were swollen or deformed," he said.
The positive electrode of cell 3 was found to have experienced particularly severe damage, while any relationship between these phenomena and the mishap still remains unknown, Goto said.
"We only know that there seems to have been a thermal runaway and (cells) experienced high temperature, but we don't know how that happened," he said.
The panel said it will widen the scope of its investigation into the electrical system and other components of the ANA plane.