The U.S. NTSB has issued 18 recommendations to the FAA, Boeing and lithium-ion battery manufacturer GS Yuasa Corporation following its 23 month investigation into a 787 auxiliary power unit (APU) battery fire on a Japan Airlines Boeing 787 on the ground in Boston on Jan. 7, 2013.
A second battery failure nine days later, on an All Nippon Airways 787 in flight over Japan, led to an FAA airworthiness directive on the main and APU batteries (which have identical designs) and grounding of the nascent fleet of 50 aircraft.
While the bulk of recommendations focus on battery manufacturing, engineering and certification flaws that led to a short circuit and “thermal runaway” within one of the eight cells, followed by failure of adjacent cells and the resulting smoke and fire, investigators also found issues with FAA certification processes in general, and the 787’s flight data and cockpit voice recorders in particular.
“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,” the NTSB says in the probable cause statement. The NTSB did not identify a specific reason why the first cell failed, but says GS Yuasa’s cell manufacturing process “allowed defects that could lead to internal short circuiting, including wrinkles and (foreign object debris).”
Boeing is responsible for the integration and certification of batteries and chargers in the 787’s electrical power conversion subsystem but contracts the 787 electrical power conversion subsystem design to Thales Avionics Electrical Systems. Thales then subcontracts the main and APU battery system components to suppliers, including GS Yuasa for the design and manufacturing of the main and APU batteries.
Fifteen recommendations are directed at the FAA, including a request for new or upgraded processes for improved oversight of production approval holders (Boeing) and their suppliers; revisiting design standards for large li-ion batteries in relation to internal heating and monitoring, and requiring manufacturers to demonstrate the worst-case conditions during type certification. The FAA performed its first audit of GS Yuasa shortly after the fleet grounding, finding several “non-compliance” items, including assembly and installation instructions for battery components, issues that have since been corrected.
Boeing, which relied on Thales to verify its subcontractors’ compliance with quality control and other standards, audited Thales, GS Yuasa and a circuit board supplier after the incident and found 17 “items of non-compliance,” mostly dealing with following written procedures and gaining authorization for procedural and testing changes for the battery. The NTSB issued two recommendations to Boeing—establishing “more effective” oversight of suppliers and making more robust safety assessments for new technologies, and one recommendation to GS Yuasa to enhance its cell manufacturing processes to minimize or prevent defects. The NTSB has previously issued five recommendations to the FAA related to battery testing while the investigation was ongoing. All five are listed as “Open – Acceptable Response.”
Unrelated to the battery, investigators discovered several issues with the 787’s new GE-built enhanced airborne flight recorder (EAFR), a combined flight data and cockpit voice recorder found only in the 787. The NTSB says the two EAFRs on board recorded “stale flight data” for some parameters (data that appeared to be valid and continued to be recorded after a parameter source stopped providing valid data), delaying investigators’ “complete understanding of the recorded data during the initial stages of the investigation.”
Investigators also found that almost all cockpit voice recordings while the aircraft was airborne on the previous flight were “completely obscured by the ambient cockpit noise”, an issue that did not affect this investigation but could be problematic in the future. The NTSB notes that the EAFR was certified under a FAA Technical Standard Order in which the agency took exception to installation and performance requirements called out by European specifications. “As a result, the (cockpit voice recorder) certifier and installer can determine what constitutes an acceptable recording without use of any industry-approved standard regarding specific installation guidance,” the NTSB says. The NTSB has asked the FAA to remove the exception or to provide specific guidance.
Boeing says that while the performance of the flight data recorder and cockpit voice recorder did not play a part in the incidents, the company is “examining the recommendations and will take any appropriate actions following our review of the report.”