The Japanese Air Self-Defense Force concluded Friday that the crash in April of an F-35A stealth fighter into the Pacific Ocean was caused by the pilot experiencing "spatial disorientation" and not by any mechanical problem.

The conclusion is in line with an interim investigative report in June which pointed to human error. The report's findings were based on the ASDF's probe as well as experts' analyses of radar data and records of communication with other F-35As that were flying with it at the time during training.

(File photo taken in June 2017 shows the Japanese Air Self-Defense Force's F-35A stealth jet that crashed into the Pacific off the coast of northeastern Japan)

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In compiling the final report, investigators found that the pilot did not have enough time to stabilize the aircraft after a warning alarm went off, the ASDF said. The interim report had concluded the pilot crashed without realizing his plane was barreling toward the sea.

According to the ASDF analyses, the jet, from Misawa Air Base in Aomori Prefecture, started to descend after ground control told the pilot, Maj. Akinori Hosomi, to decrease altitude at around 7:26 p.m. on April 9, to maintain distance with a U.S. military aircraft flying some 36 kilometers away. But the jet kept descending before disappearing from the radar.

Japan recovered fragments of the jet and some of Hosomi's remains. All other F-35As based in Misawa were grounded after the crash but resumed flights earlier this month.