Japan probe finds signs of thermal runaway, short-circuit in ANA 787 battery

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Japanese safety investigators have released new data showing signs of thermal runaway and a short-circuit in the main battery failure on an All Nippon Airways Boeing 787 in January.

The findings, released in a 12-slide presentation, appear similar to the evidence released last week by the US National Transportation Safety Board, which also reported evidence of a short circuit and thermal runaway that led to a fire on a parked Japan Airlines 787 in Boston earlier the same month.

But there also appear to be certain differences in the heat damage caused in the two incidents.

Whereas the most damage on the JAL auxiliary power unit (APU) battery was located in the fifth of eight cells, the ANA battery showed the most extensive thermal damage in the third and sixth cells, including a hole in the side of the sixth cell and a meltdown of the anode - or the positive electrode - in the third cell, according to the briefing by the Japan Transport Safety Board (JTSB).

The Japanese investigators also are investigating why a grounding wire inside the battery enclosure was severed. A root cause for the thermal runaway effect and the short circuit in the ANA battery is also being pursued by the JTSB, as well as by the NTSB for the JAL battery.

The global 787 fleet has been grounded for nearly three weeks due to the battery malfunctions. Boeing on 5 February asked the US Federal Aviation Administration to resume flight tests with the 787, but the agency's response, if any, was not immediately available.

The 787 is the first commercial airliner to use lithium-ion batteries as an emergency power source and as the starter for the APU.

Lithium-ion batteries can generate about twice the amount of power as a comparable nickel-cadmium battery, which was introduced in aircraft in the late 1970s.

Boeing selected a particularly powerful type of lithium-ion battery, featuring a lithium-cobalt-dioxide chemistry. The JTSB, for example, shows that each of the eight cells of the GS Yuasa-designed battery can store up to 72Ah of electricity.

Tesla is the only electric car maker to rely on lithium-cobalt-dioxide as a power source, but does it an different way. Rather than rely on a single unit containing eight large cells with 72Ah of storage capacity, the Tesla Roadster is powered by more than 6,000 tiny, single-cell batteries with a storage capacity of about 3Ah.