The US National Transportation Safety Board has ruled out excess voltage as the cause of a battery fire on the Boeing 787 Dreamliner jet operated by Japan Airlines at Boston airport this month, the agency said on Sunday.
Last week, governments across the world grounded the Dreamliner jet after a problem with a lithium-ion battery on a second 787 plane, flown by All Nippon Airways, forced the jet to make an emergency landing in western Japan.
"Examination of the flight recorder data from the JAL B-787 airplane indicates that the APU (auxiliary power unit) battery did not exceed its designed voltage of 32 volts," NTSB said in a statement forwarded by a Boeing Japan representative.
On Friday, a Japanese safety official told reporters that excessive electricity may have overheated the battery in the ANA-owned Dreamliner which was forced to make an emergency landing at Japan's Takamatsu airport last week.
US investigators have examined the lithium-ion battery that powered the APU, where the battery fire started in the JAL plane, as well as several other components removed from the airplane, including wire bundles and battery management circuit boards, the NTSB statement said.
On Tuesday, the investigating group will convene in Arizona to test and examine the battery charger and download non-volatile memory from the APU controller, it added.
Japan's GS Yuasa Corp makes batteries for the Dreamliner, while France's Thales makes the control systems for the battery.