The Defense Ministry will resume flights of F-35A stealth fighter jets that have been suspended since an April crash off Aomori Prefecture, with pilots to undergo training for spatial disorientation to prevent similar accidents.

“We will carefully provide an explanation to related local governments,” Defense Minister Takeshi Iwaya said on June 10, when the ministry released the results of its investigation into the crash.

Investigators concluded that the pilot likely suffered from spatial disorientation.

Ministry officials on the same day visited the Aomori prefectural office and Misawa, a city that hosts the Air Self-Defense Force’s air base where the crashed fighter jet was stationed, to explain the results of the investigation and plans for preventive measures.

They asked local officials for understanding of the resumption of flight operations.

The F-35A crashed about 135 kilometers off the coast of Aomori Prefecture after taking off from the Misawa base for a combat exercise involving three other F-35As on the night of April 9.

Major Akinori Hosomi, 41, the flight leader, died in the crash.

According to investigators, the F-35A was flying horizontally at an altitude of about 9,600 meters when the ground controller ordered Hosomi to descend to prevent him from drawing close to a U.S. military aircraft.

Hosomi replied on his radio, “Yes, roger." The F-35A then started descending almost vertically at a steep angle and plummeted about 4,900 meters in only 20 seconds.

Hosomi was then ordered by the controller to veer to the left.

“Yes,” he replied in affirmation and said, “Knock it off (abort the exercise).”

He sounded calm, according to the ministry. But the fighter jet continued its abnormal vertical nosedive.

Within a little more than 10 seconds after the exchange, the F-35A crashed into the Pacific Ocean at an estimated speed exceeding 1,100 kph.

There was little evidence that the pilot attempted to eject or take action to pull out of the dive, according to the ministry.

Based on these circumstances, the ministry concluded that the pilot was in a state of spatial disorientation and lost a sense of equilibrium. He was unaware that his fighter was nosediving toward the ocean.

To prevent similar accidents, the ministry will conduct flight simulator training for pilots to experience spatial disorientation.

It was the first-ever crash of an F-35A, prompting the ministry to ground 12 others of the aircraft.

(This article was written by Yoshitaka Ito and Ryuichi Yamashita.)