WASHINGTON — Boeing acknowledged on Tuesday that its original tests of lithium-ion batteries on its 787 Dreamliner planes underestimated the risks of fire, though it defended its previous assessment that such a hazard was unlikely.
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 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 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 certified in 2007. But the broader focus was how manufacturers and regulators can cope with rapid changes in technology that may outstrip their ability to predict problems.
The board is investigating the fire on Jan. 7 in a Japan Airlines 787 parked at a gate at Logan Airport in Boston. 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.
Sinnett said the failure calculation was based on data provided by GS Yuasa, which “had experience with over 14,000 cells of similar makeup.”
The Boeing executive was pressed to say whether the company stood by its original risk estimate. He declined to do so until investigators determine the cause of the two battery failures.
The FAA last week approved Boeing’s plans to fix the plane’s lithium-ion batteries, an important step in lifting the grounding of the 787s. Boeing’s fixes include better insulation for the batteries’ cells and a steel box that will and contain any fire and vent smoke or gases out of the planes.