NTSB Recommends Improvements for Certifying Lithium-ion Batteries

The agency determined that shortcomings in design and certification led to the fire in a battery being installed on a Boeing 787.

According to a report from the National Transportation Safety Board, shortcomings in design and certification led to the fire in a lithium-ion battery installed on a Boeing 787 jetliner that had just completed intercontinental flight to Boston.

Early in the investigation, the NTSB said that the fire began after one of the battery's eight cells experienced an internal short circuit leading to thermal runaway of the cell, which propagated to the remaining cells, causing full battery thermal runaway. This condition caused smoke and flammable materials to be ejected outside the battery's case and resulted in excessive heat and a small fire.

"The investigation identified deficiencies in the design and certification processes that should have prevented an outcome like this," said NTSB Acting Chairman Christopher A. Hart. "Fortunately, this incident occurred while the airplane was on the ground and with firefighters immediately available."

Investigators said that Boeing's safety assessment of the battery, which was part of the data used to demonstrate compliance with these special conditions, was insufficient because Boeing had considered, but ruled out, cell-to-cell propagation of thermal runaway but did not provide the corresponding analysis and justification in the safety assessment.

As a result of its findings, the NTSB is recommending that the FAA improve the guidance and training provided to industry and FAA certification engineers on safety assessments and methods of compliance for designs involving new technology.

"Through comprehensive incident investigations like this one, safety deficiencies can be uncovered and addressed before they lead to more serious consequences in less benign circumstances," said Hart.

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