ANA B788 near Takamatsu on Jan 16th 2013, battery problem and burning smell on board (including JAL Boston, Ethiopian London and

On Sep 24th 2014 the JTSB released their final report concluding the probable causes of the serious incident of JA804A were:

The emergency evacuation was executed on Takamatsu Airport taxiway in the serious incident, which was a consequence of emergency landing deriving from the main battery thermal runaway during the airplane’s takeoff climb.

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. 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.

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 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 JTSB stated in the findings: "We cannot disregard the fact that all battery incidents (the serious incident inclusive) occurred in winter. Therefore, at present low temperature environment was the possible contributing factor to the battery failure.

The JTSB annotated in the findings that the ground wire "fused" when 1,010 Amperes were running across the wire while cell 7 was venting.

The JTSB listed a number of possible scenarios leading to the thermal runaway stating that observations on the flight data recorder permits to identify the cause of the thermal runaway was an internal short circuit. The JTSB stated: "From the analyses of internal short circuit, three possible candidates for interior short circuit remain: lithium metal deposition in the cell, metal piece contamination, and damaged separator. Given the fact that all similar battery incidents occurred in the cold season, lithium metal deposition deriving from charging under cold conditions could have existed. However, it is unlikely that lithium metal deposition was the sole causal factor of the internal short circuit leading to venting. It is possible that electric transient or other factors combined may have affected the lithium metal deposition leading to an internal short circuit. As no mechanism of internal short circuit was conclusively identified, we are unable to exclude the possible involvement of other factors associated with design and manufacturing."

The JTSB found that tests performed replicated thermal runaways with the actual on-board configuration however did not include internal short circuit simulation. During development of the batteries simulations of internal short circuits had been performed, however did not simulate the on-board configuration. These tests did not develop into thermal runaways. The JTSB therefore stated: "RTCA/DO-311, which is referred to by the latest version of LIB airworthiness standard TSO-179a, does not stipulate test procedures to properly simulate internal short circuit. It should be amended to mandate internal short circuit tests simulating proper on-board environment."