ANA Boeing 787 Japan Transport Safety Board investigating the January 16 2013, battery smoke incident onboard All Nippon Airways Boeing 7...
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| ANA Boeing 787 |
The investigation could not conclusively identify the mechanism of the internal short circuit, which is presumed to cause the heat generation in the battery cell.
The main battery thermal runaway during the airplane’s takeoff climb was due to the internal heat generation in cell 6, which very likely developed into venting, making it the initiating cell, resulting in cell-to-cell propagation and subsequent failure of the main battery. It is very likely that cell 6 internal heat generation and increased internal pressure caused it to swell, melt the surrounding insulation material and contact the brace bar creating a grounding path that allowed high currents to flow through the battery box. The currents generated arcing internal to the battery that contributed to cell-to-cell propagation consequently destroying the battery.
The low temperature during overnight stay possibly contributed to the internal short circuit as the three battery incidents (this serious incident inclusive) occurred in the midst of cold January and low temperature is said to be favorable for lithium metal deposition. In addition, there are reports of cell contamination deriving from manufacturing, which may be related to the cause of the battery event.
JTSB also stated the 787 manufacturer- Boeing's Lithium ion battery testings were insufficient to simulate realistic flight conditions.
"The internal short circuit test by nail penetration method under the simulated on-board configuration with the battery ground wire demonstrated a thermal runaway, while the test without the ground wire did not".
The possible contributing factors to the thermal propagation are that the test conducted during the developmental phase did not appropriately simulate the on-board configuration, and the effects of internal short circuit were underestimated, the report says.
On January 16, 2013, the ANA Boeing 787-8, took off from Yamaguchi-Ube Airport for Tokyo International Airport. When it was climbing through 32,000 ft, an instrument indication of battery failure came on, accompanied by unusual smell in the cockpit. The airplane diverted to Takamatsu Airport and landed there.
Commercial airliners traditionally have used Ni-cd batteries as the main battery and for starting an APU; 787s use light weight, high capacity lithium ion batteries (LIBs). The main battery is identical to the APU battery. The main battery is installed in the forward EE bay, while the APU battery is in the aft EE bay. The 787 uses LIBs of significantly different design and capacity for applications such as flight control electronics (FCE), recorder independent power supply (RIPS) and emergency lights.
