Data from the flight recorder retrieved from the Japan Air Lines Boeing 787 that caught fire on January 7 while parked at Boston Logan International Airport shows that the airplane’s APU battery did not charge beyond its design limit of 32 volts, according to the U.S. National Transportation Safety Board. Investigators have disassembled the lithium-ion battery in question, an eight-cell unit made by Japan’s GS Yuasa, in an effort to help determine the cause of the first of two separate battery failures that led to the grounding of all 50 Dreamliners Boeing has delivered to seven airlines around the world. Japanese authorities have yet to determine whether or not the battery failure that forced an emergency landing of an All Nippon Airways 787 in western Japan last Wednesday had overcharged as widely reported. That incident prompted both ANA and JAL to ground their 787s, and preceded a mandated suspension of Dreamliner service in the U.S. and around the globe.
NTSB investigators have also examined several other components removed from the JAL airplane, including wire bundles and battery management circuit boards. The team has developed test plans for the various components removed from the aircraft, including the APU battery management unit, the APU controller, the battery charger and the start power unit. The group plans to convene on Tuesday in Arizona to test and examine the battery charger and download nonvolatile memory from the APU controller. The board has also sent several other components for download or examination to Boeing in Seattle and Yuasa facilities in Japan.
Meanwhile, U.S. aviation authorities continue to work with Boeing engineers “around the clock” to devise an inspection regime for the now grounded fleet of Boeing 787s. In its emergency airworthiness directive issued on January 16, the Federal Aviation Administration specifically mandated a modification to the battery system or “other actions” to comply with whatever method the FAA’s Seattle Aircraft Certification Office deems appropriate. Contacted for comment, Boeing would offer only a statement indicating that “discussions are ongoing.”
That engineers would first consider virtually all other options before a complete change in battery type would seem natural, however, given the extent to which the use of the particular 32-volt units influenced the design of the electrical system as a whole.
A week before the FAA action, Boeing 787 program manager Mike Sinnett tried to allay any concerns about the use of lithium-ion batteries in the Dreamliner, calling the decision to use the Yuasa units “not the only choice, but the right choice” to meet the power requirements of the so-called “more electric” airplane. Still, it didn’t take long after the groundings last Wednesday for observers to begin questioning Boeing’s selection.
An assessment by international consultancy Lux Research notes that even among lithium-ion batteries types, Boeing could have picked a safer alternative with little loss of performance. The 787’s batteries use lithium cobalt oxide (LCO), a material that imparts “excellent” energy density but does not resist overheating well. Once started, lithium-ion fires typically generate oxygen, making them difficult to extinguish. In the first case of battery failure, aboard a Japan Air Lines 787 parked at Boston Logan Airport, firefighters needed 40 minutes to put out the resulting fire.
In choosing LCO, Boeing eschewed safer alternatives such as lithium-iron phosphate (LFP), according to Lux. Even when overcharged, LFP changes only slightly in structure, it noted, preventing oxygen release and resisting the repeating cycle of heat generation known as thermal runaway. “This decision is all the more shocking considering major automakers early on refused to entertain the possibility of using LCO in passenger vehicles due to safety concerns,” said the Lux report.
All 50 Boeing 787s delivered to customers remain grounded while the FAA and Boeing try to devise at least an interim fix to return the fleet to the air. Until then, Boeing will not deliver any more of the airplanes, even while it maintains its production rate of five airplanes a month.