Inspections of lithium-ion battery maker GS Yuasa have found no defects in the process that manufactured the batteries that failed aboard two Boeing 787s earlier this month, according to Japanese government officials quoted in media reports.
US investigators, meanwhile, say they found nothing wrong at sites in Tucson and Phoenix where suppliers make the battery control and monitoring units.
The two updates likely eliminate the possibility of manufacturing error as a cause for the battery failures that have grounded the 787 fleet for nearly three weeks, and focus the search for a root cause more narrowly on the design of the battery and how it is installed in the aircraft.
The Japan Transport Safety Board and the National Transportation Safety Board are continuing to investigate the battery malfunctions, while the Federal Aviation Administration and Boeing also search for the root cause and how the safety hazard slipped through the certification process.
The 787 was grounded on 16 January after a main battery over-heated and failed on an All Nippon Airways flight over Japan. That incident occurred nine days after an auxiliary power unit battery failed and caught fire on board a parked Japan Airlines 787 in Boston.
The NTSB's analysis has found a short-circuit in the JAL battery, which likely triggered the fire. It remains unclear why the battery short-circuited, and why the battery compartment was unable to contain the fire within the battery box.