A Japanese V-22 Osprey lands at Camp Kisarazu, Japan, June 16, 2022.

A Japanese V-22 Osprey lands at Camp Kisarazu, Japan, June 16, 2022. (Akifumi Ishikawa/Stars and Stripes)

TOKYO — Japan’s army grounded its fleet of V-22 Osprey aircraft after the U.S. Marines identified a mechanical problem that caused a crash that killed five service members in June 2022.

The 14 Ospreys of the Japan Ground Self-Defense Force — all based at Camp Kisarazu in Chiba prefecture — were grounded July 22, a day after the Marine Corps released its report on a June 8, 2022, crash east of San Diego, Calif., a spokesman for the Japan Ground Self-Defense Force said by email Friday.

"It is to check to make sure that measures, which were mentioned in the accident investigation report released by the U.S. side, are applied in the best possible way to the Japanese Ospreys," the spokesman said.

Some Japanese government officials are required to speak to the media only on condition of anonymity.

The twin-engine tiltrotor aircraft takes off and lands like a helicopter, but in flight it can rotate its propellers, or proprotors, and cruise like an airplane. Versions of the aircraft are flown by the Marine Corps, Navy and Air Force.

In a report of 400-plus pages, the Marines said the fatal crash occurred due to “a dual hard clutch engagement,” which caused a drive system to fail, resulting in “catastrophic loss of thrust” on the right proprotor.

This caused “unrecoverable departure from controlled flight,” according to the Marines.

The hard clutch problem has plagued the U.S. military for some time. The Air Force temporarily grounded its Ospreys in August 2022 because of it. The Marines at the time said they were aware of the problem since 2010 but had developed a procedure for addressing it in flight.

In February, the Air Force, Marines and Navy imposed maximum flight hours because of the problem that temporarily grounded some of their tiltrotors, according to USNI News.

Japan’s Ospreys use parts confirmed safe and pilots are trained to respond to the situation detailed in the U.S. report, the Japanese spokesman said.

The Ground Self-Defense Force will resume Osprey flights once officials confirm that measures mentioned in the U.S. report have been addressed and all possible safety measures have been taken, the spokesman said.

Stars and Stripes reporter Seth Robson contributed to this report.

author picture
Hana Kusumoto is a reporter/translator who has been covering local authorities in Japan since 2002. She was born in Nagoya, Japan, and lived in Australia and Illinois growing up. She holds a journalism degree from Boston University and previously worked for the Christian Science Monitor’s Tokyo bureau.

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