Update: Some US Air Force, marine corps V-22s grounded over hard clutch engagements

An MV-22B from the 31st Marine Expeditionary Unit takes off in the Philippine Sea on 2 June 2021. (US Navy)

The US Air Force (USAF) and US Marine Corps (USMC) grounded an undisclosed number of Bell-Boeing MV-22 and CV-22 Ospreys on 3 February, citing hard clutch engagements because of worn input quill assemblies, a gearbox part that transmits power between the Rolls-Royce AE 1107C engines and the aircraft's proprotors. Hard clutch engagements occur when the engine's clutch disengages uncommanded and then rapidly re-engages, sending an impulse through the assembly, and causing the aircraft to lurch. The Osprey automatically transfers all power to the second engine when the clutch slips. In most cases, it quickly transfers it back to both engines when the clutch re-engages, according to Janes analysis.

The grounded aircraft have high-time input quill assemblies, according to a 5 February announcement by the V-22 Joint Program Office (JPO). However, neither the input quill assembly hour threshold nor the number of grounded aircraft was released by the JPO, citing operational security concerns. The input quill assemblies in the grounded aircraft will be replaced, with the tiltrotor returning to flight status once the repairs are complete.

“To date, there have been 15 confirmed [hard clutch engagement] events,” the US Navy (USN), which runs the V-22 JPO, told Janes in an email. “The relevant [input quill assembly] time limit, applicable to a select number of V-22 aircraft, was initiated based on recent data analysis and an uptick in hard clutch engagement events over the last year.”