The National Transportation Safety Board has attributed a lithium-ion battery fire in a Boeing 787 Dreamliner to shortcomings in design and certification. The fire occurred January 7, 2013, in a 787 that had just completed an intercontinental flight from Narita and was parked at a gate at Boston Logan. The fire occurred in an auxiliary power unit in a battery manufactured by Kyoto-based GS Yuasa. There were no injuries.
The NTSB had earlier concluded the fire began after one of the battery’s eight cells experienced an internal short circuit leading to thermal runaway, which propagated to the remaining cells causing full battery thermal runaway.
“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.”
The NTSB said that because the APU and main Li-ion batteries installed 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 that the battery was safe for use on a transport category aircraft.
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, the potential for cell-to-cell propagation of thermal runaway was not thoroughly scrutinized by Boeing and FAA engineers, ultimately allowing this safety hazard to go undetected by the certification process.
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.
NTSB investigators also identified a number of design and manufacturing concerns that could have led to internal short circuiting within a cell.
As a result of the investigation, the NTSB made 15 safety recommendations to the FAA, two to Boeing, and one to GS Yuasa.
“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,” said Hart.
The complete report is available at http://go.usa.gov/HJtJ.
Earlier, Japan’s transportation safety authority reported that it could not identify the cause of Li-ion battery fires, including one in a plane forced to land in Japan. The fires led to a three-month grounding of the Dreamliner fleet while the battery was redesigned.
See related article, “Fire Protection Engineers Address Li-ion Safety.”