Search crews have located the wreckage of a US Air Force Bell Boeing CV-22 Osprey that crashed off the coast of Japan on 29 November.

The Air Force Special Operations Command (AFSOC) tiltrotor aircraft crashed near Japan’s Yakushima Island, some 50 miles (80km) south of the island of Kyushu. All eight crew aboard are believed to have been killed.

CV-22 adn MC-130J air-to-air refuelling

Source: US Air Force

The US Air Force has not disclosed why the Osprey crashed, though the Pentagon had grounded the type earlier this year due to a clutch-engagement issue

Dive teams and surface ships on 4 December discovered parts of the wrecked Osprey, including its fuselage, according to AFSOC. Remains of six deceased crew have also been located.

“Currently there is a combined effort in recovering the remains,” AFSOC says, noting the recovery effort is the command’s top priority.

Only one crew member has been identified, as of 4 December – 24-year-old Staff Sergeant Jacob Galliher, an airborne linguist.

The Pentagon lists the status of the unidentified personnel as missing.

“As search and rescue operations continue, our joint force and Japanese allies stand united in our determination to bring our air commandos home,” says AFSOC commander Lieutenant General Tony Bauernfeind.

The US Navy and Japanese armed forces are assisting the air force’s search and recovery effort.

The CV-22 was assigned to the US Air Force’s 353rd Special Operations Wing, based at Yokota Air Base west of Tokyo.

AFSOC has not said why the Osprey crashed. The Pentagon had grounded the type in February due to a hard-clutch-engagement issue – a persistent problem for both AFSOC and the US Marine Corps, which operates the MV-22 variant of the tiltrotor.

Hard clutch engagement refers to incidents in which the Osprey’s clutch releases from the rotor system and suddenly re-engages, according to the V-22 joint programme office (JPO). The hard engagement sends an impulse through the drive train, which can damage the system.

The JPO said at the time that a technical solution for the problem had been identified and retrofits were being rolled out.