The U.S. 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 hundreds of aircraft after a preliminary investigation of last week’s crash indicated that a materiel failure — that something went wrong with the aircraft — and not a mistake by the crew led to the deaths.
The crash raised new questions about the safety 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 stand-down “to mitigate risk while the investigation continues,” the command said in a statement. “Preliminary investigation information indicates a potential materiel failure caused the mishap, but the underlying cause of the failure is unknown at this time.”
In a separate notice, Naval Air Systems Command said it was grounding all Ospreys. The command is responsible for the Marine Corps and Navy variants of the aircraft.
The Air Force said it was unknown how long the aircraft would be grounded. It said the stand-down was expected to remain in place until the investigation determined the cause of the Japan crash and made recommendations to allow the fleet to return to operations.
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In Japan, where U.S. military Ospreys had a non-fatal crash once and a number of incidents, the latest accident — which killed American service members between the ages of 24 and 36 — has rekindled safety concerns just as the Japanese government builds a new base for its fleet of Ospreys.
Chief Cabinet Secretary Hirokazu Matsuno told reporters in Tokyo the government has already formally requested that the U.S. military ensure the safety of Ospreys before their flights, but that Tokyo will seek further information from the U.S. side because it also affects the safety of Japan’s own Osprey fleet.
“Needless to say, ensuring flight safety is the top priority of aircraft operation,” Matsuno said. “Japanese Self-Defence Force also operate Ospreys, and in order to ensure their flight safety, we will continue to ask the U.S. side to share information with us.”
U.S. military has hundreds in its fleet
The U.S.-made Osprey, manufactured by Boeing and Bell Textron, 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 factor in 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 the program for more than a decade. There have also been questions as to whether all parts of the Osprey have been manufactured according to safety specifications.
In August, the Marines found that a fatal 2022 Osprey crash was caused by a clutch failure, but the root cause was still unknown. In its report on the crash, the Marines forewarned that future incidents “are impossible to prevent” 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 the U.S. Navy operates 27.
The Osprey is still a relatively young aircraft in the military’s fleet — the first Ospreys only became operational in 2007, after decades of testing. But more than 50 troops have died either flight-testing the Osprey or conducting training flights in the aircraft, including 20 deaths in four crashes over the past 20 months.
An Osprey accident in August in Australia killed three U.S. Marines. That accident is also still under investigation.
In 2022, four U.S. personnel were killed when an Osprey crashed in a remote part of northern Norway during a NATO training exercise.