Marine Corps Osprey in June 2023 preparing to embark the USS New York, a San Antonio-class amphibious transportation dock ship. (William Bennett IV/U.S. Navy)

WASHINGTON — The Navy, Marine Corps and Air Force on Friday lifted the flight ban on grounded V-22 Ospreys following a deadly crash in November, the services announced.

“We have high confidence that we understand what component failed and how it failed,” said Marine Corps Col. Brian Taylor, the V-22 program manager at Naval Air Systems Command.

The aircraft has been grounded since Dec. 6 after an Osprey operated by Air Force Special Operations Command crashed in Japan on Nov. 29 killing eight service members. The U.S. military grounded about four hundred Air Force, Navy and Marine Corps Ospreys. Japan also grounded its fleet of 14 Ospreys.

The Japan incident and an Osprey crash in Australia in August that killed three Marines are under investigation.

Investigators probing the latest crash are looking at a possible problem involving the aircraft’s propeller rotor gearbox, NBC News reported. Military officials, when speaking to reporters this week, could not provide further information about why the crash occurred or what the material failure was.

Lt. Gen. Tony Bauernfeind, who leads Air Force Special Operations Command, said it was a “catastrophic material failure.”

“Given that we have been sharing information with our [Naval Air Systems Command] teammates, I have the highest confidence that the safety protocols that they are considering once we return to fly will ensure that we’re addressing what we found out from that catastrophic material failure as we move forward,” he said.

Taylor said there are no plans to make hardware changes to the aircraft but focused more on maintenance and procedural changes to address this issue.

Defense Secretary Lloyd Austin met with top service leaders on March 1 where he endorsed the military service’s plans for a safe and measured return to the operation, The Associated Press reported. The decision to end the flight ban is up to Naval Air Systems Command, but Austin had asked for an informational briefing on the matter because of the significant safety concerns and the fact that three of the services and a critical ally are involved in the program.

The Marines will take a three-phased approach, training Osprey pilots and crew members before moving to squadrons and training them in basic and advanced missions on the MV-22 Osprey, and eventually going into pre-deployment training for their next assigned mission. The second and third phases will vary in length with some units not returning to operational capacity until late spring or early summer, the service said in a statement.

Vice Adm. Daniel Cheever, commander of Naval Air Forces, said “return to flight is not the same as return to mission.”

The most experienced Navy pilots will begin training immediately. But moving the training to squadron- and mission-based goals, which includes getting CMV-22B Ospreys back on ships, could take several months or more.

“It’s serious business. So we’re just going to make sure we’re safe as we step back into that,” Cheever said.

Bauernfeind said Air Force crews have been conducting simulator training since the stand-down to retain some capabilities. But due to being off for three months, he anticipates it will take the Air Force more than three months to get back to pre-grounding proficiency levels.

The Osprey is a fast-moving aircraft that can take off like a helicopter and then tilt its engines and propellers to fly like an airplane.

The stand-down is one of the largest military aircraft groundings, affecting flight operations for three services. But it’s not the longest. When the Osprey was still in development, two crashes in 2000 killed 23 Marines and led the Corps to ground the program for nearly 18 months.