Editor’s note: This story was updated at 7:52 p.m. EST with additional information.
WASHINGTON — The military announced late Wednesday it was grounding all of its Osprey V-22 helicopters, one week after eight Air Force Special Operations Command service members died in a crash off the coast of Japan.
The Air Force, Navy and Marine Corps took the extraordinary step of grounding tons of of aircraft after a preliminary investigation of last week’s crash indicated that a materiel failure — that something went improper with the aircraft — and never a mistake by the crew led to the deaths.
The crash raised recent questions on the security of the Osprey, which has been involved in multiple fatal accidents over its relatively short time in service. Japan grounded its fleet of 14 Ospreys after the crash.
Lt. Gen. Tony Bauernfeind, head of Air Force Special Operations Command, directed the standdown “to mitigate risk while the investigation continues,” the command said in a press release. “Preliminary investigation information indicates a possible materiel failure caused the mishap, however the underlying reason behind the failure is unknown right now.”
In a separate notice, Naval Air Systems Command said it was grounding all Ospreys. The command is chargeable for the Marine Corps and Navy variants of the aircraft.
The Air Force said it was unknown how long the aircraft could be grounded. It said the standdown was expected to stay in place until the investigation has determined the reason behind the Japan crash and made recommendations to permit the fleet to return to operations.
The U.S.-made Osprey is a hybrid aircraft that takes off and lands like a helicopter but can rotate its propellers forward and cruise much faster, like an airplane, during flight.
Its unique design has been a think about multiple incidents. While the investigation into last week’s crash has only just begun, it renewed attention on the aircraft’s safety record, particularly on a mechanical problem with the clutch that has troubled this system for greater than a decade. There even have been questions as as to whether all parts of the Osprey have been manufactured in line with safety specifications.
In August, the Marines found that a fatal 2022 Osprey crash was brought on by a clutch failure, but the foundation cause was still unknown. In its report on the crash, the Marines forewarned that future incidents “are unattainable to stop” without improvements to flight control system software, drivetrain component material strength, and robust inspection requirements.”
Air Force Special Operations Command has 51 Ospreys, the U.S. Marine Corps flies as many as 400 and U.S. Navy operates 27.
The Osprey remains to be a comparatively young aircraft within the military’s fleet — the primary Ospreys only became operational in 2007 after a long time of testing. But greater than 50 troops have died either flight testing the Osprey or conducting training flights within the aircraft, including 20 deaths in 4 crashes over the past 20 months.
An Osprey accident in August in Australia killed three Marines. That accident also remains to be under investigation.
Tara Copp is a Pentagon correspondent for the Associated Press. She was previously Pentagon bureau chief for Sightline Media Group.