[Avionics Today 12-3-2014] The National Transportation Safety Board (NTSB) concluded its investigation into a lithium-ion battery that caught fire onboard a parked Boeing 787 in 2013. According to the agency's accident investigators, the battery had design flaws and should not have been certified by the FAA.
NTSB officials say that an internal short circuit on the battery, manufactured by GS Yuasa Corp, led to a thermal runway of the cell. When this occurred, the condition caused flammable materials to be ejected outside the battery case and produced a fire, which took place on a Japan Airlines (JAL) Dreamliner in January 2013. Following that incident, a second similar occurrence with an overheating battery on an All Nippon Airways (ANA) 787 led to a global grounding of all in-service Boeing 787s last year. Boeing then redesigned the lithium-ion battery system and was able to get it returned to service by April 2013.
To satisfy operators and FAA, Boeing re-designed the battery internals
(but did not change battery chemistry), increased internal cell spacings and insulation, hardened the internal electronics within the battery housing, had their subcontractors modify the charge control system, enclosed the entire battery in a massive sealed stainless-steel container and added an outboard titanium exhaust port. Testing showed the new system to be far more robust, and technicians were unable to re-create any fire scenario within the new pack and its associated system.
"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."
Initially, Boeing had determined that the lithium ion battery cell was prone to failure in one out of 10 million flight hours. However, the JAL and ANA incidents occurred while the 787 fleet had logged fewer than 52,000 hours, NTSB said in its report.
While the board did not state any one specific cause of the fire, its 97-page report into the battery condition indicates that the battery contained a design flaw that should have been identified during the regulatory certification process.
As a result of its findings, NTSB has recommended that the FAA improve guidance and truing provided to FAA and industry certification engineers on safety assessments and methods of compliance for designs involving new aircraft technology, such as the lithium-ion battery system on the 787.
"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.