I'll go out on a limb and say a problem with the drive train is a solid reason to ground the aircraft. It will be interesting to see what the Navy and Marines do in response.
AFSOC Grounds CV-22 Osprey Fleet Over Safety Issue - Air Force Magazine
AFSOC Grounds CV-22 Osprey Fleet Over Safety Issue - Air Force Magazine
Air Force Special Operations Command grounded its CV-22 Osprey fleet Aug. 16 as part of a safety stand down, with no timeline set for the aircraft to begin flying again, the command confirmed to Air Force Magazine.
The stand down, ordered by AFSOC commander Lt. Gen. James C. “Jim” Slife, comes after two incidents of “hard clutch engagement” in the past six weeks, AFSOC spokesperson Lt. Col. Rebecca Heyse said in an emailed statement.
Hard clutch engagement involves the clutch connecting the rotor gear box to the engine slipping, then catching hard, causing the aircraft to lurch.