Flaws in manufacturing, insufficient testing and a poor understanding of an innovative battery all contributed to the grounding of Boeing’s 787 fleet last year after a fire in a jet at Boston’s airport and another incident in Japan, according to a report released Monday by regulators.
The report, by the National Transportation Safety Board, assigned in the starkest terms yet the blame for the 787’s battery problems. The safety board investigating the Boston episode suggested for the first time that manufacturing flaws introduced defects that led a battery cell to fail, though the board stopped short of drawing a firm conclusion. The failure of that cell rippled to other cells, causing the battery to consume itself in fire and smoke.
The episode occurred after a Japan Airlines flight from Tokyo landed at Boston’s Logan International Airport on 7 January, 2013, and after all passengers had left the plane. Ground workers detected smoke from the plane’s electrical bay, which was eventually traced to one of its two lithium-ion batteries. The following week, a second episode involving a 787 Dreamliner in Japan – in which a smoking battery forced an emergency landing – prompted regulators to ban the jets’ flights until the problem could be resolved.
The board found a wide range of failings among manufacturers and regulators. The battery’s maker, GS Yuasa of Japan, used manufacturing methods that could introduce potential defects but whose inspection methods failed to detect the problem, the board found.
Boeing’s engineers failed to consider and test the worst-case assumptions linked to possible battery failures, it said. And the Federal Aviation Administration failed to recognise the potential hazard and did not require proper tests as part of its certification process, the report said.
The battery problems underscored concerns about the use of a new and potentially hazardous technology aboard commercial airliners – powerful lithium-ion batteries – and what steps plane makers and regulators should take to make sure they are safe.
The planes were allowed to fly again after Boeing instituted new safety features. It kept the battery’s basic design but added internal components to reduce the chance of overheating and combustion. To persuade regulators to allow the planes back in the air, Boeing also encased each of the two batteries in new steel boxes meant to contain any fire and prevent it from spreading.
Doug Alder, a spokesman for Boeing, said the company remained confident in the improvements it had made to the battery system, and in its safety. Boeing, he said, agrees “with the report’s probable cause finding – a short circuit within one battery cell led to venting and cell-to-cell propagation that caused the battery failure.”
This was the first time large lithium-ion batteries were used aboard a commercial jet. The 787 has two of them, one for its auxiliary power unit, or A.P.U., and a second to turn on its flight deck computers. Boeing had initially determined that a battery cell might fail in one out of 10 million flight hours. Instead, by the time the two episodes happened, the 787 fleet in service had logged fewer than 52,000 hours, according to the safety board.
“The incident resulted from Boeing’s failure to incorporate design requirements to mitigate the most severe effects of an internal short circuit within an A.P.U. battery cell,” the report said. It also faulted the F.A.A. for failing to identify the design problem.
The NTSB had already concluded that the battery failure came from an internal short circuit in cell 5 or cell 6 and led to a fire that propagated to other cells – known as a thermal runaway. But the battery was too damaged for specialists to figure out what had caused the internal short in the first place.
But its investigation found that the manufacturing process allowed defects that could lead to internal short circuiting. GS Yuasa, it said, “did not test the battery under the most severe conditions possible in service, and the test battery was different than the final battery design certified for installation on the airplane.”
Shortly after the report was made public, GS Yuasa issued a statement through a United States-based public relations firm and defended its manufacturing methods. “We appreciate and respect the NTSB.’s final report, although the root cause of this internal short circuit remains elusive,” GS Yuasa said in a statement. “We remain fully confident, however, in the quality and safety of our batteries, our state of-the-art manufacturing processes and our highly skilled and trained employees.”
Industry research on lithium-ion hazards has found that cell failures in other industries had been caused by internal faults from the manufacturing process, according to the safety board. But GS Yuasa did not have a formal inspection process that could reliably identify any defects, the board said in its report.
Both Boeing and GS Yuasa also underestimated the risks of a catastrophic failure, the board said. They relied on a single test, known as a nail penetration test, to simulate a short circuit to find out under what circumstances the battery might ignite.
This test took place in November 2006, and Boeing concluded that a short circuit inside one of the battery cells would be limited to the release of smoke from the battery and an increase in temperature, but “no propagation of thermal runaway to adjacent cells, damage to the battery case, fire or explosion,” according to the NTSB.
In a series of recommendations, the safety board said the F.A.A. should work with lithium-battery experts to research battery technology and identify conditions that could lead to another such fire.
In a statement, the F.A.A. said that the Boston fire had helped it better understand lithium-ion batteries. “The F.A.A. has implemented many of the N.T.S.B.’s recommendations about modifications in testing, safety standards and design,” the agency said.
©2014 The New York Times News Service