US and Japanese aviation safety officials have finished their initial investigation of a badly damaged battery from a Boeing 787 Dreamliner plane.
Officials from the Federal Aviation Administration, US National Transportation Safety Board and Boeing joined Japanese authorities in the probe.
They were looking into what caused warning lights to go off on an All Nippon Airways domestic flight earlier this week, prompting the aircraft to make an emergency landing at Takamatsu airport.
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The incident prompted regulators in the United States and around the world to ground the 50 Dreamliners in service.
The lightweight, carbon-composite 787 has been plagued by a number of mishaps.