Far from solving the mystery of what caused a Boeing 787's battery to burst into flames in Boston earlier this month, a recent visit to Tucson by aviation safety investigators catalyzed even more questions.
National Transportation Safety Board investigators tested a lithium-ion battery charger unit and start-power unit manufactured by Oro Valley-based Securaplane Technologies Inc., NTSB Chairman Deborah A.P. Hersman said during a news conference Thursday in Washington, D.C.
There was "one minor finding with each unit," she said. "We're still trying to determine the significance of those findings."
No further details on the Tucson tests were available, and no overall cause has yet been identified by investigators.
"We know the lithium-ion battery experienced a thermal runaway, we know there were short circuits, and we know there was a fire," Hersman said.
Investigators don't yet know the sequence of events, and they don't know what other systems failed leading to or relating to the fire.
Everything from the design of the battery and its components, manufacturing records and supplier audits, to the ins and outs of the certification process will be reviewed, Hersman said.
"We have to understand why this battery resulted in a fire when there were so many protections that were designed into the systems," she said.
That could take awhile. Investigators plan to continue doing tests on the damaged batteries as well as on so-called "exemplar batteries," which have not been damaged.
At least one test on the docket takes a week to complete.
Two shifts of investigators are working in the United States and in Japan, Hersman said.
Americans are leading the inquiry into what caused the 787 battery fire in Boston Jan. 7, and they are working closely with the Japanese-led team investigating the smoking battery that led to a 787's emergency landing in Japan about a week later.
Investigators have done CT scans of the eight-cell battery, and follow-up tests have been performed on the most-damaged cells, Hersman said.
Meanwhile, Boeing's flagship 787 Dreamliner planes remain grounded while a separate Federal Aviation Administration review continues.
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