The NTSB has cast doubt on Japan's Transport Safety Board's speculation that a charging overload was behind battery fires that led to the grounding of Boeing 787 fleet. In an update Sunday, the NTSB said the flight data recorder aboard the Japan Airlines aircraft whose APU battery burned on the ground at Boston's Logan Airport Jan. 7 showed the battery never exceeded its design limit of 32 volts. On Friday, Japanese officials said they believed overcharging caused that fire and the one in an ANA 787 that was involved in an emergency landing and evacuation last Wednesday. Japan released photos of the battery that burned virtually under the feet of the pilots as they dove for the ground while on a domestic flight to Kaneda. The photo shows a mass of charred wires and cells within a thin case that shows signs of distortion but apparently wasn't breached. For comparison the agency put a good battery beside it.
The Japanese investigators said the ANA battery looks like the battery that fried in the APU bay of a Japan Airlines 787 a week before and they believe both batteries caught fire because they were being overcharged. "If we compare data from the latest case here and that in the U.S., we can pretty much figure out what happened," investigator Hideyo Kosugi told The Associated Press. He said the evidence suggests "voltage exceeding the design limit was applied." The NTSB says it will share the conflicting data from its investigation with the Japanese.