(Bloomberg) -- The US military is grounding its entire fleet of Osprey aircraft to investigate a possible equipment problem that may have caused a deadly crash in Japan, where officials have raised concern about the safety of the tilt-rotor aircraft.

The Air Force, Navy and Marine Corps said in separate statements they are standing down on operations of the aircraft after “preliminary investigation information indicates a potential materiel failure caused the mishap,” Naval Air Systems Command, which is responsible for the Marine and Navy variants, said on its X social media page.

The grounding applies to the Pentagon’s 431 V-22 models that include 360 for the Marines, 54 for the Air Force 29 for the Navy, which flies a version that transports people and cargo on to aircraft carriers, according Naval Air Systems statistics.

The Air Force released a statement saying it directed a standdown of its version of the aircraft, the CV-22 Osprey, after the crash off the southwestern Japan island of Yakushima that killed eight US airmen. It used similar wording as the statement from Naval Air Systems to justify the grounding.  

Both branches said “the underlying cause of the failure is unknown at this time.”

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The US Air Force said in a separate statement on Wednesday the bodies of three US airmen found among the submerged wreckage of the Osprey in Japan have been recovered. Two other bodies were removed from the wreckage earlier this week; one body was found soon after the crash last week, while two others are missing and presumed dead.

All the families of the people involved have been notified, Pentagon spokesman Brigadier General Pat Ryder said in a briefing this week. The Air Force also released a list of those killed that included pilots and flight engineers in their 20s and 30s. 

The Japanese government had called for US military forces in the country to suspend use of the Osprey, which was made by a unit of Boeing Co. and the Bell Helicopter unit of Textron Inc., so that checks can be made.

The accident in Japan a week ago is one of the deadliest for the tilt-rotor aircraft that has been in use for more than 20 years. These have included an Osprey accident in 2000 that killed 19 Marines in Arizona. In August, three Marines were killed and five others critically injured after their aircraft went down while performing drills off Darwin, Australia.

The US Air Force Special Operations Command has 51 Ospreys, the Marine Corps flies as many as 400 and the Navy operates 27, the Associated Press reported.

The plane has two propeller engines on its wings that can be tilted to make it fly like a helicopter, so it can land in tight spaces. The propellers can also be moved in flight to a position horizontal with the wings to fly like a traditional airplane. 

--With assistance from Tony Capaccio.

(Updates in third graph with number of V-22 grounded)

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