Inadequate design and testing caused last year's battery fire that led to the grounding of Boeing Co.'s Dreamliner jets for more than three months, investigators concluded.
Boeing had certified that overheating in one cell of the lithium-ion battery couldn't spread to others and the Federal Aviation Administration approved the design and testing. The National Transportation Safety Board faulted both in a final report for not anticipating how the power packs might fail, and cited battery maker GS Yuasa Corp. for poor manufacturing.
Monday's findings bring to a close an almost two-year probe into events that triggered the longest grounding of a large commercial aircraft by U.S. regulators since jets were introduced in the 1950s. It also prompted a re-examination of the dangers of lithium-ion power packs that have helped drive advances in personal electronic devices and electric cars.