TOKYO — Japanese investigators studying the potentially flammable batteries that have grounded Boeing’s 787 fleet wrapped up an on-site inspection at the batteries’ manufacturer Monday and said they would continue their inquiry at a maker of a device that monitors the batteries.
Japan’s Ministry of Transport said that for now, investigators had found no quality control problems during an eight-day inquiry at GS Yuasa, the maker of the lithium-ion batteries at the center of the inquiry. But officials stressed that the cause of recent battery malfunctions was still unknown, and that GS Yuasa remained under investigation.
GS Yuasa made the batteries that overheated during an All Nippon Airways flight this month, prompting an emergency landing. That event came just days after another GS Yuasa battery aboard a parked Japan Airlines plane caught fire at Boston’s Logan Airport. The events have prompted regulators worldwide to ground all 787s, and for Boeing to halt deliveries.
It is still unclear whether problems lie with the batteries or with another part of the plane’s complex electronics. On Monday, the Ministry of Transport said inspectors would start checks at Kanto Aircraft Instrument, which makes a monitoring unit that detects a battery’s voltage, current, temperature, and other vital parameters.
“We do not know where the problems lie, so we are simply doing checks in order,’’ said an official at the ministry’s Civil Aviation Bureau who declined to be quoted by name, citing protocol.
It was too early to say that GS Yuasa was off the hook or that inspectors would not be back at the battery maker for more checks, he said.
“We have seen what we needed to see for now, and are moving on, but that does not mean that there was definitely no problem with the battery,’’ the official said.
He said that at Kanto Aircraft, officials would check manufacturing processes to make sure there were no quality control breaches. Kanto Aircraft officials could not immediately be reached for comment. GS Yuasa said it could not comment on ongoing investigations. The National Transportation Safety Board, which is also investigating the batteries, has completed an examination of the monitoring unit at Kanto Aircraft Instrument, in Fujisawa, near Tokyo.
The US-led team examined circuit boards that monitor the batteries, and found the boards damaged, which limited the information the team could obtain. The team ‘‘found no significant discoveries,’’ the board said in a news release.
Plagued by production delays, the 787 Dreamliner finally went into service last year as Boeing’s next-generation, state-of-the-art aircraft made from lightweight composite materials that has greatly improved the jet’s fuel efficiency. The 787 also relies on electronic systems far more than previous aircraft, including lithium-ion batteries, which are lighter but are more prone to overheating.
Japan’s government stepped in to give the plane and its made-in-Japan technology a boost in 2008 by easing safety regulations, fast-tracking the rollout of the groundbreaking jet for Japan’s biggest airlines, according to records and participants in the process, Reuters reported.
“I believe the request for the changes came initially from the airlines. Ultimately, it was a discussion of measures to lower operating costs for the airlines,’’ Masatoshi Harigae, head of aviation at Japan’s Aerospace Exploration Agency, told the news service.
There is no suggestion that easing regulatory standards contributed to the problems facing the Dreamliner, and the looser regulations did not specifically address the risk of the plane’s batteries catching fire.