June 10 (UPI) -- A pilot's spatial disorientation likely caused the crash of a Japanese F-35 fighter jet this spring, Japan's defense minister said after the release of a preliminary report.
Minister Takeshi Iwaya told reporters the pilot, Maj. Akinori Hosomi, 41, is thought to have lost his bearings during an exercise in April with Japan's Air Self-Defense Force and showed no signs of ejecting before the crash. Japan had grounded its fleet of 13 F-35As after the crash.
The ministry said the pilot, who had accumulated 3,200 flight hours, appeared to fly the fighter directly into the ocean during the night training exercise.
The ministry said the pilot, whose body was found a week ago, appeared to lose his bearings during a high-speed descent but was not aware of it. He had been communicating with the control tower before the accident without any indication of trouble, investigators said.
Spatial disorientation can account for as many as 10 percent of all aviation accidents, most of which are fatal.
"We will fully enforce training to avoid spatial disorientation and will fully explain to local residents before deciding to resume flights," Iwaya said.
The Japanese air force said it will begin flying the F-35 again soon.