Japanese regulators have joined their US counterparts in all but ruling out overcharged batteries as the cause of recent fires on the Boeing Co 787 Dreamliner, which has been grounded for a week with no end in sight.
Solving the battery issue has become the primary focus of the investigation, though the head of the US Federal Aviation Administration said on Wednesday there are still no firm answers as to the cause and no clear timetable yet for returning the plane to flight.
Meanwhile, as deliveries of the cutting-edge passenger jet back up, a key Chinese customer lamented the delays and said its growth plans were being hampered by its inability to get the planes on time.
Regulators grounded the Dreamliner on Jan. 16 after a series of safety incidents, including battery fires on planes in the United States and Japan. The Japanese incident forced a plane to make an emergency landing.
Last weekend the US National Transportation Safety Board said the fire on a Japan Airlines Co Ltd 787 in Boston was not due to excess voltage, and on Wednesday, Japanese officials all but ruled it out for the incident on an All Nippon Airways Co Ltd plane there.
"On the surface, it appears there was no overcharging," said Norihiro Goto, chairman of the Japan Transport Safety Board, at a media briefing.
"The fact that such electrical system-related incidents would occur consecutively, purely from my perspective, could not have been expected. We are finding it difficult trying to figure out what kind of investigative stance we should take."
Late Wednesday, the NTSB said more tests are underway on the battery damaged in the Boston fire, including CT scans of the individual cells. The board's chairman, Deborah Hersman, is due to provide a fuller update Thursday.
The investigation has also renewed scrutiny on the FAA's 2007 decision to let Boeing use a highly flammable battery technology on the 787. A US Senate committee will hold a hearing in coming weeks to examine aviation safety oversight and the FAA's decision, a congressional aide said on Tuesday.
While the NTSB and JTSB hunt for a solution to the battery question,