The U.S. Air Force said Wednesday it has grounded its fleet of its Ospreys due to safety concerns, and the move will also affect the tilt-rotor aircraft stationed in Japan.

The Air Force Special Operations Command directed a "safety standdown" of its CV-22 fleet on Tuesday due to "an increased number of safety incidents," the command's public affairs director Rebecca Heyse said in a statement.

According to defense-focused U.S. media outlets, the safety issues are linked to a malfunctioning clutch inside a gearbox that impacts the transfer of drive from the engine to the propeller rotor.

In the coming days, the command will work with industry partners and others to fully understand the issue and develop risk control measures to mitigate the likelihood of catastrophic outcomes.

The move "does impact those CV-22 stationed in Japan," a U.S. Air Force official said.

Since 2017, there have been four incidents involving the clutch problem during flight with two occurring in the past six weeks, it said. No one was injured in the incidents.

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

U.S. forces in Japan have deployed 24 MV-22s at U.S. Marine Corps Air Station Futenma in the southern prefecture of Okinawa, and more than five CV-22s at Yokota Air Base in the suburbs of Tokyo. MV-22 is a variant used by the Marines and CV-22 is one used by the Air Force.

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