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NTSB Cites Deficient Safety Assessment by Boeing in 787 Fire

by Gregory Polek

 - December 1, 2014, 3:05 PM

The FAA issued an airworthiness directive in April 2013 that mandated modifications to Boeing 787 batteries and resulted in a lengthy grounding of the world's fleet. (Photo: Flickr: Creative Commons (BY-SA) by valentin hintikka)

Boeing’s incorrect assumptions about the effects of a short circuit in the main ship battery of the 787 and insufficient guidance for manufacturers to use in determining and justifying such “key” assumptions in safety assessments contributed to the January 7, 2013 battery fire aboard a parked Japan Airlines Dreamliner at Boston Logan Airport, according to an aircraft incident report issued by the U.S. National Transportation Safety Board on Monday.

Specifically, the report said Boeing’s safety assessment for the airplane’s main and APUbatteries assumed that a short circuit within a cell would result in venting of only that cell and not cause a fire. Furthermore, Boeing did not provide engineering rationale and justification to support the incorrect assumption. Finally, the assessment did not consider the consequences of an incorrect assumption or incorporate mitigations in the design to limit their effects, said the NTSB report.

Investigators found that the fire began after one of the battery’s eight cells experienced an internal short circuit, leading to thermal runaway of the cell. Propagation to the remaining cells led to full battery thermal runaway, which resulted in a small fire and caused smoke and flammable materials to exit the battery case.

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

Because the APU and main lithium-ion batteries installled on the 787 represented new technology not adequately addressed by existing regulations, the Federal Aviation Administration required that Boeing demonstrate compliance with special conditions to ensure the safety of the battery on a transport category aircraft. Investigators said that Boeing’s safety assessment of the battery proved insufficient because the company 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, Boeing andFAA engineers did not fully scrutinize the potential for cell-to-cell propagation of thermal runaway, ultimately allowing the hazard to go undetected by the certification process.

As a result of its findings, the NTSB made 15 safety recommendations to the FAA, two to Boeing and one to the battery maker, GS Yuasa of Japan. In the case of the FAA, it recommended that the agency improve the guidance and training provided to industry and certification engineers on safety assessments and methods of compliance for designs involving new technology.

“The aviation industry is continually benefitting from technological advances, and we are hopeful that the lessons learned in this investigation will further enhance the industry’s ability to safely bring those innovative technologies to market,” concluded Hart.