The Ground Self-Defense Force has temporarily grounded its V-22 Osprey fleet based at a camp east of Tokyo after the U.S. Air Force halted flights of its fleet over safety concerns, the Defense Ministry said Saturday.

The suspension of flights for the tilt-rotor aircraft stationed at Camp Kisarazu in Chiba Prefecture came after the Air Force directed a "safety standdown" of its CV-22 fleet on Tuesday due to a clutch malfunction inside the plane's gearboxes.

File photo shows a Japanese Self Defense Forces V-22 Osprey in flight over Kisarazu, Chiba Prefecture, in November 2020. (Kyodo)

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U.S. Air Force grounds Ospreys over safety concern, including in Japan

The ministry's Kyushu Defense Bureau said it is confirming the details of the safety issues and doing additional inspections of the V-22 aircraft in Japan. No timeline has been given for when operations will restart.

Ospreys, which take off and land like a helicopter but cruise like a plane, have a record of accidents and mishaps in Japan and abroad.

The Japanese government has been acquiring the aircraft as part of the nation's efforts to improve its ability to defend its remote islands amid increasing instability in the Asia-Pacific region.

Nine V-22s have arrived at Camp Kisarazu since 2020. Compatibility tests for radio and other Japan-specific equipment were completed at the end of last year. In January, then Defense Minister Nobuo Kishi boarded one of the planes.

The ministry plans to acquire a total of 17 V-22s for the GSDF and preparations are going ahead with a view to permanently deploying them at Saga airport in the southwestern prefecture of Saga by 2025.

In Japan, the U.S. Air Force has idled CV-22s at Yokota Air Base in the west of Tokyo.

The U.S. Marine Corps has deployed a fleet of MV-22s, the Marine variant of the Ospreys, at Air Station Futenma in the southern prefecture of Okinawa, and appears to be continuing to operate them even after the Air Force move.

Okinawa Gov. Denny Tamaki has called for the fleet to also be grounded for safety checks if the aircraft are afflicted with the same issue.