The late November crash during a military exercise prompted a multi-month grounding of the aircraft -- which can take off and land vertically like a helicopter and also fly like an airplane -- and a more than five-month investigation into the incident.

The crash "was caused by a catastrophic failure of the left-hand prop rotor gearbox that created a rapidly cascading failure of the aircraft's drive system, resulting in an instantaneous asymmetric lift condition that was unrecoverable" by the crew, the Air Force Special Operations Command said in a statement.

Contributing factors to the crash "include inadequate risk management and ineffective crew resource management," it said.

Ospreys have suffered a string of fatal accidents, including a crash in northern Australia that killed three US Marines in August, and another in Norway during NATO training exercises in 2022 that left four dead.

Three Marines were killed in 2017 when another Osprey crashed off Australia's north coast and 19 Marines died when their Osprey crashed during drills in Arizona in 2000.

The United States also temporarily grounded the aircraft in Japan in 2016 after an Osprey crash-landed off Okinawa.