US Air Force grounds Osprey fleet after dangerous clutch problem

Image: U.S. Air Force

A problem with the clutch on Air Force Special Operations Command’s CV-22 Osprey aircraft has prompted the command to ground its fleet while it tries to find the cause.

In an email to Defense News, AFSOC public affairs director Lt. Col. Becky Heyse said that the command’s 52 tiltrotor Ospreys were grounded on Tuesday due to recent “hard clutch engagement” incidents. Two such problems have happened in the last six weeks, and there were previously two others that occurred since 2017.

AFSOC Commander Lt. Gen. Jim Slife ordered the stand-down to ensure airmen’s safety, Heyse said.

No one was injured as a result of the four clutch problems.

“We absolutely owe the air crew information about why this is happening and how we’re going to mitigate it,” Heyse said. “Because we don’t have that now, Gen. Slife didn’t feel comfortable flying them.”

The stand-down and clutch problem was first reported by Breaking Defense.

Hard clutch engagement occurs when the clutch connecting the propeller’s rotor gear box to its engine slips. When this happens, Ospreys are designed to transfer the power load from that engine to the other engine immediately, which would allow it to keep operating if an engine failed.

In these incidents, the clutch on the original gear box has engaged and the power load transferred back, within a span of milliseconds. The large transfer of torque causes the Osprey to lurch, and the air crews land immediately. These problems in the past have led to the replacement of Ospreys’ gear boxes and engines, which qualified them as Class A mishaps.

Heyse said AFSOC is not sure whether it is a mechanical, design or software problem causing these hard clutch engagements, and as a result can’t put solutions in place to stop it from happening again until the command knows more. It is not yet known how long the Ospreys will be grounded.

AFSOC staff will work with the V-22 Joint Program Office and industry partners — the CV-22 is made by Bell Boeing, and its engines are built by Rolls-Royce — to study the data, figure out what is causing it and develop ways “to mitigate the likelihood of catastrophic outcomes.”

Nine Marines have died in two of that service’s MV-22B Osprey crashes earlier this year. A crash in Norway in March killed four Marines, and investigators concluded pilot error was the primary cause. In June, five Marines died in another MV-22B Osprey crash, this one in California. Those two crashes, as well as four other Class A mishaps this year, prompted the Marine Corps to order a one-day safety standdown for aviation units this summer.