WASHINGTON — The Air Force cleared its CV-22 Ospreys tiltrotor aircraft to resume flying, some two-and-a-half weeks after grounding them due to a clutch problem that remains unresolved.

Lt. Gen. Jim Slife, head of Air Force Special Operations Command, on Friday authorized the command’s fleet of 52 Ospreys to resume flying, with measures to limit the risk from “hard clutch engagement” incidents. AFSOC Spokeswoman Lt. Col. Rebecca Heyse said the aircraft are expected to start operating again this weekend.

Slife grounded AFSOC’s tiltrotor Ospreys Aug. 16 after two hard clutch engagement incidents in the preceding six weeks, saying he was concerned about airmen’s safety. AFSOC said it wanted to find the cause of the malfunctions and ways to mitigate them. AFSOC Ospreys, many of which are deployed to Europe and Asia, had experienced two other clutch issues since 2017, making four clutch incidents in all for the command.

The U.S. Marine Corps, which has had 10 hard clutch engagement incidents in its MV-22 Osprey since 2010, did not follow suit, telling reporters that it believes the clutch problem can be managed with training.

Hard clutch engagement happens when the clutch that connects the Osprey’s rotor gear box to its engine slips. This causes the Ospreys to immediately transfer the power load from that engine to the other engine, to ensure the aircraft can keep running in the event of an engine failure.

When the clutch on the original gear box re-engages and the power load transfers back, this creates a large transfer of torque within milliseconds and the Osprey lurches. Air crews are taught to immediately land in these emergencies.

The Air Force and Marine Corps said no one has been injured in their hard clutch engagement incidents, although some gear boxes or engines have had to be replaced, making them Class A mishaps due to their cost.

Heyse said AFSOC is still not sure why the Osprey clutches are slipping, but that the command has put steps in place to try to manage them for the near term. AFSOC studied the data from all 15 recorded hard clutch engagement incidents across the Osprey enterprise to figure out what was a common factor there.

One key risk mitigation step: AFSOC has instructed its Osprey pilots to take a two-second pause immediately after taking off to keep the clutch from slipping, instead of going to full power immediately, Heyse said.

Marine Corps officials told reporters last month that its Osprey pilots are instructed to hover after taking off to check instruments and ensure the clutch isn’t slipping.

AFSOC is also bringing squadron leadership into discussions on ways to mitigate clutch problems, before missions where the Ospreys might have a higher risk of such an incident happening because of their operational requirements.

And AFSOC is modifying its Osprey training simulators to better reflect clutch slipping scenarios, and is increasing training for Osprey pilots on flying under marginal power and aborted takeoffs. Heyse said this is important because the clutch issues usually happen in the takeoff process.

“Until a root cause is identified, and solution implemented, the focus is on mitigating operations in flight regimes where [hard clutch engagements] are more prevalent and ensuring our aircrews are trained as best as possible to handle [them] when they do occur,” Heyse said in an email.

Since the stand-down, all of AFSOC’s Osprey crews have also taken part in briefings from the Osprey joint program office, along with the command’s experts, to help them understand these clutch incidents and how to handle them.

Aircrews also took surveys that allowed them to suggest ways to handle or solve the clutch problem.

CV-22 maintainers are conducting inspections of the aircraft to make sure the systems are tracking the correct information on drivetrain components. AFSOC said that it is reviewing data from the aircraft, and is considering replacing drivetrain components after a certain number of flight hours.

And AFSOC said it hopes to find the root cause of these clutch slippages in the long term, and putting a permanent solution in place.

Heyse said AFSOC’s maintainers used the stand-down period to conduct a great deal of maintenance on the Ospreys.

Stephen Losey is the air warfare reporter for Defense News. He previously covered leadership and personnel issues at Air Force Times, and the Pentagon, special operations and air warfare at Military.com. He has traveled to the Middle East to cover U.S. Air Force operations.

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