The NTSB has released its report from this investigation:
The NTSB determines that the probable cause of this incident was an internal short circuit within a cell of the APU lithium-ion battery, which led to thermal runaway that cascaded to adjacent cells, resulting in the release of smoke and fire. The incident resulted from Boeing’s failure to incorporate design requirements to mitigate the most severe effects of an internal short circuit within an APU battery cell and the FAA’s failure to identify this design deficiency during the type design certification process.
As a result of this investigation, the NTSB makes safety recommendations to the FAA, Boeing, and GS Yuasa. The NTSB previously issued safety recommendations to the FAA regarding (1) insufficient testing methods and guidance for addressing the safety risks of internal short circuits and thermal runaway and (2) the need for outside technical knowledge and expertise to help the FAA ensure the safe introduction of new technology into aircraft designs.
The NTSB determines that the probable cause of this incident was an internal short circuit within a cell of the APU lithium-ion battery, which led to thermal runaway that cascaded to adjacent cells, resulting in the release of smoke and fire. The incident resulted from Boeing’s failure to incorporate design requirements to mitigate the most severe effects of an internal short circuit within an APU battery cell and the FAA’s failure to identify this design deficiency during the type design certification process.
As a result of this investigation, the NTSB makes safety recommendations to the FAA, Boeing, and GS Yuasa. The NTSB previously issued safety recommendations to the FAA regarding (1) insufficient testing methods and guidance for addressing the safety risks of internal short circuits and thermal runaway and (2) the need for outside technical knowledge and expertise to help the FAA ensure the safe introduction of new technology into aircraft designs.
