Two cells in a battery for the auxiliary power unit used in the All Nippon Airways 787 that made an emergency landing last month were found to be swollen, the Japan Transport Safety Board said Tuesday.
The board had initially said the battery for the auxiliary power unit was undamaged but later found the slight swelling following detailed scrutiny through a tomography scan.
Even so, "the priority of our probe is on the main battery" that was severely damaged and charred, a board official said. Investigations have so far found that all eight cells of the main battery experienced heat-caused damage and signs of unusual heat generation called "thermal runaway."
In another incident in Boston involving a Boeing Dreamliner operated by Japan Airlines Co., a cell in the lithium-ion battery for the APU was identified as the source of the battery fire, according to the U.S. National Transport Safety Board.
Dreamliners worldwide have been grounded since the ANA 787 emergency landing Jan. 16 at Takamatsu Airport in Kagawa Prefecture due to smoke in the cockpit.