Japan’s Air Self-Defense Force concludes F-35A crash off northern Japan caused by human error

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

The conclusion is in line with an interim investigative report in June that pointed to human error. The report’s findings were based on the ASDF’s probe as well as expert analyses of radar data and communication records involving other F-35As that were training with the plane in question at the time of the crash on April 9.

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 concluded the pilot crashed without realizing his plane was barreling toward the sea.

According to the ASDF’s analysis, the jet, based at Misawa Air Base in Aomori Prefecture, started to descend after ground control told the pilot, Maj. Akinori Hosomi, to do so at around 7:26 p.m. to maintain its distance with a U.S. military aircraft some 36 km away. But the jet kept descending and disappeared from the radar.

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

Japan plans to procure a total of 147 F-35 jets, 105 of which are expected to be F-35As. The state-of-the-art fighters cost more than ¥10 billion each.

The jet involved in the accident was one of nine F-35As that were assembled and checked by Mitsubishi Heavy Industries Ltd. prior to their delivery. The remaining four were assembled and checked in the U.S.