At the start of a two-day hearing held by the National Safety Transportation Board, Boeing’s chief engineer on the 787, Mike Sinnett, said the calculation that a battery would fail only once every 10 million flight-hours applied to the design of the battery and did not include possible manufacturing flaws. The testimony seemed to point to GS Yuasa, the Japanese manufacturer of the battery.
The purpose of the safety board’s hearing was to figure out how Boeing and the Federal Aviation Administration — despite years of careful work — could have missed the potential for catastrophic failure when the battery was initially certified in 2007. But the broader focus was how the plane’s manufacturers and regulators can cope with rapid changes in technology that may outstrip their ability to predict problems. The 787 is the first major commercial airplane to make extensive use of lithium-ion batteries.
The safety board is investigating the fire on Jan. 7 in a Japan Airlines 787 parked at a gate at Boston’s Logan Airport. A second incident, involving a similar battery on an All Nippon Airways plane on a Japanese domestic flight, led to the grounding of all 50 of the planes Boeing has so far delivered.
“We are here to understand why the 787 experienced unexpected battery failures following a design program led by one of the world’s leading manufacturers and a certification process that is well-respected throughout the international aviation community,” said the board’s chairwoman, Deborah A. P. Hersman.
Mr. Sinnett said the failure calculation was based on data provided by GS Yuasa. “That value essentially is reached by experience with similar type cells,” he said. “GS Yuasa had experience with over 14,000 cells of similar makeup. They had millions upon millions of those cells without any cell venting.”
One of the tests consisted of driving a nail into a battery cell to provoke a short circuit. While the cell failed, the test did not result in a fire. But under repeated questioning, Mr. Sinnett acknowledged that the nail test had been inadequate and was not “conservative enough.” Boeing, he said, found that the batteries could catch fire only if they were overcharged.
The Boeing executive was pressed to say whether the company stood by its original risk estimate. He declined to do until investigators determined the cause of the two battery failures. Ms. Hersman did not seem satisfied with the answer. At one point she complained, “There is some obfuscation here.”
During questioning, Mr. Sinnett gave a narrower definition of Boeing’s risk estimate than the company had in the past. “That once in 10 million flight hours doesn’t apply to things like abuse of the battery,” he said. “It doesn’t necessarily apply to a nonconforming battery, meaning a battery that was not built for the type design. So there are other things that can cause the failure of a battery that don’t contribute to that one in 10 million hours.”
The F.A.A. last week approved Boeing’s plans to fix the plane’s lithium-ion batteries, an important step in lifting the grounding of the 787s in the United States. Boeing’s fixes include better insulation for the batteries’ eight cells and a stainless steel box that will encase the batteries and contain any fire and vent possible smoke or hazardous gases out of the planes.
“There is still more work to be done in the investigation,” Ms. Hersman said.
Boeing told the F.A.A. it planned to use lithium-ion batteries on its 787 in 2003. Because airplane regulations at the time did not cover such batteries, the F.A.A. in 2007 approved Boeing’s use under nine special conditions that covered the need to contain or vent any hazardous materials.
Article source: http://www.nytimes.com/2013/04/24/business/safety-board-examines-787-battery-approval.html?partner=rss&emc=rss
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