A Japanese airway reported problems months before battery failures grounded Boeing Dreamliner jets, according to the New York Times.
All Nippon Airways said 10 lithium-ion batteries were replaced months before multiple problems questioned their reliability. All the events occurred from May to December of last year. The airline reported the problems to Boeing, but was not required to tell safety regulators.
The National Transportation Safety Board is now focusing their investigation on the battery problems.
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The investigation comes after an unexpected drop in the 787's main battery forced an emergency landing Jan. 16. A 787 also caught fire while parked at Logan Airport in Boston Jan. 7.
Boeing has claimed that any problems with the batteries do not threaten planes or passengers.
The planes use lithium cobalt batteries manufactured by GS Yuasa. They are the most powerful of their kind, but also most flammable.
The F.A.A. investigated a similar case in 2011 where a lithium-ion battery on a Cessna CJ4 business jet started smoking while it was being charged.
The incident forced Cessna to replace the battery on its planes with nickel cadmium batteries.
The 787 incidents remain under investigation.
