Illustrating Japan's commitment to the 787, its two main carriers, Japan Airlines and All Nippon Airways, have been Boeing's biggest buyers for the jet, taking 24 of the 50 delivered so far.
The troubles they have seen include leaked fuel and a cracked cockpit windshield. But the most alarming were the incidents involving batteries, including a fire centered in an auxiliary power unit of a Japan Airlines 787 that took firefighters 40 minutes to extinguish.
GS Yuasa's Yamamoto said he was unsure how long the investigation into the problems with the 787 would take. Each day will likely hurt. The company's share price sank another 5 percent on Thursday and is approaching a 52-week low.
"This will not be decided by us. The Transport Ministry is in charge," Yamamoto said.
"But I don't think this is going to be a matter of just a few days. Not quite so soon."
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