Japan’s safety body fails to determine cause of overheating Dreamliner battery

The Japan Transport Safety Board (JTSB) has failed to identify the cause behind the overheating of a lithium-ion battery on-board ANA Holdings’ Boeing 787 Dreamliner last year, suggesting simulation testing to avoid similar incidents.

The overheating problem in the battery led to the three-month grounding of the Dreamliner fleet worldwide.

Lack of appropriate testing during the developmental phase may have contributed to the lithium-ion battery overheating, the agency observed.

JTSB said: "Internal heat generation in cell 6 very likely developed into venting, making it the initiating cell, resulting in cell-to-cell propagation and subsequent failure of the main battery.

"Cell 6 heat generation was probably caused by internal short circuit; however, the conclusive mechanism thereof was not identified.

"In the serious incident, the internal short circuit of a cell developed into cell heat generation, thermal propagation to other cells, and consequently damaged the whole battery."

The agency also pointed to cold winter air as a possible factor for the damage of battery cells and electrical wiring.

JTSB has recommended the US Federal Aviation Authority (FAA) to mandate aircraft and equipment manufacturers to carry out tests simulating actual flight operations.

The 787 was plagued by several problems last year, including battery fire, crack in the window of a cockpit, an oil leak from a generator inside an engine, a brake problem and fuel spillage.

Boeing has redesigned the battery system with improved insulation of the cells, and resumed commercial flights in May 2013 after the FAA approval.

Last week, the FAA issued a safety directive which requires replacement of certain foam-like plugs near the lithium battery on some of the 787s, to ensure availability of proper fire-suppression systems.

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Image: Boeing 787 Dreamliner from ANA Holdings’ fleet. Photo: courtesy of Boeing.