US Marine Corps MV-22 crash traced to hard clutch engagement

Bell Boeing MV-22B Osprey. (Janes/Lindsay Peacock)

A fatal 8 June 2022 US Marine Corps (USMC) MV-22 crash in Glamis, California, was traced to dual hard clutch engagement (HCE) in the right engine assembly, according to a report released on 21 July. The accident report found no fault in either aircraft maintenance or the crew's conduct.

The crash killed five marines. The aircraft and crew were assigned to the 3rd Marine Aircraft Wing, based at Marine Corps Air Station Miramar, California, and were conducting low-altitude runs over a gunnery range when the incident happened.

The accident occurred when the right engine clutch, which connects the engine to the proprotor, disengaged and rapidly re-engaged, an occurrence called a hard clutch engagement. The strain from the HCE caused a shaft to shear in the tiltrotor's Single Engine and Interconnect Drive System (Single Engine/ICDS), which connects the two engines together such that one engine can power both proprotors. The Single Engine/ICDS failure resulted in a loss of thrust from the right proprotor, which sent the MV-22 into an unrecoverable turning descent, according to the accident report.

“The degraded drivetrain caused by the dual [hard clutch engagement] event and subsequent Single Engine/ICDS failure created an unrecoverable departure from controlled flight,” the report said.

The V-22 Joint Program Office (JPO) released a statement referring to the dual engagement as a “catastrophic, unpreventable, and unanticipated mechanical failure”.

HCEs occur when the engine clutch disengages from the proprotor and suddenly re-engages, sending an impulse through the engine assembly and causing the aircraft to lurch.

At least 15 HCEs have occurred in V-22s since 2010, according to the USMC accident report.