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NTSB yet to reach conclusion on cause of 787 lithium-ion battery fire

8-Mar-2013 11:14 AM

US National Transportation Safety Board stated (07-Mar-2013) it continues to focus on the design, certification and manufacturing processes of the lithium-ion battery system used on the grounded Boeing 787, noting it has yet to reach a conclusion about what caused a lithium-ion battery fire aboard a Japan Airlines 787 at Boston Logan International Airport in Jan-2013. The lithium-ion battery used to start the aircraft’s APU, manufactured by GS Yuasa, remains central to the investigation. The APU battery consists of eight lithium-ion cells, assembled in two rows of four cells each. Each cell contains a flammable electrolyte liquid, and has a nominal voltage of 3.7 volts. When the JAL incident battery was disassembled, cells 5 through 8 on the right side of the battery showed the most thermal and mechanical damage, according to the NTSB. “Thermal damage was the most severe near cell 6,” the interim report explains, noting: “Continuity measurements using a digital volt meter indicated that all of the cells were found to be electrically short circuited except for cell 8". The means all except one of the battery cells were electrically short-circuited. Vent discs were found to be opened slightly on cells 1 through 3, intact on cell 4 and “opened more completely, leaving a ruptured appearance” on cells 5 through 8, the NTSB said. The aircraft’s flight data recorder (FDR) showed the APU was started while the 787 was being taxied to the gate after arriving in Boston. Smoke was later detected in the aft cabin by cleaning personnel. At around the same time, a maintenance manager in the cockpit observed that the APU had shut down automatically. “The FDR data also showed that, about 36 seconds before the APU shut down…the voltage of the APU battery began fluctuating, dropping from a full charge of 32 volts to 28 volts about seven seconds before the (APU) shutdown,” the NTSB said. [more - original PR] [more - original PR - Interim Factual Report] [more - original PR - Presentation] [more - original PR - Oct-2007 FAA special condition for 787 lithium ion battery installation]