Air Force Special Ops Command Grounds CV-22 Fleet Due to Safety Issue

The stand down is the latest safety concern related to Osprey flight operations this year. [Courtesy: U.S. Air Force / Yasuo Osakabe)

Air Force Special Operations Command (AFSOC) has grounded its fleet of CV-22 Osprey aircraft in order to conduct safety investigations following a string of incidents involving the aircraft's clutch, according to officials.

The stand down order issued August 16 applies to all 52 CV-22 tiltrotor aircraft in AFSOC's fleet, command spokesperson Lt. Col. Rebecca Heyse told FLYING.

AFSOC first began using the CV-22, which is the Special Operations variant of the Marine Corps MV-22 aircraft, for long-range infiltration and exfiltration missions in 2007.

AFSOC officials made the stand down call Tuesday following two recent incidents involving a "hard clutch engagement" issue inside the gearbox that connects the propeller rotor to one of the aircraft's two Rolls-Royce Liberty AE1107C engines, Breaking Defense reported. If the clutch slips, the power load transfers to the other engine as designed, but then rapidly transfers back when the clutch re-engages. The scenario forces an immediate landing and could potentially lead to loss of control of the aircraft or an uncontrolled landing, Heyse told the news outlet.

Four such incidents have occurred in the last five years, two in the last six weeks, according to Air Force Magazine.

READ MORE: Tower Controller Credited With Save of CV-22 at Kirtland AFB

A safety investigation is now underway.

"In coordination with the Joint Program Office, AFSOC has been unable to gather enough engineering data analysis to accurately identify [the] root cause of the hard clutch engagement so it’s unknown if it's mechanical, design, software or some combination of any of those," Heyse said in an email.

"Right now we are not releasing any additional details of these incidents as safety investigation boards are still ongoing," she said, adding that, as of Thursday, there was no projected timeline for how long the stand down could last.

The stand down is the latest safety concern related to Osprey flight operations this year. In March, four Marines were killed when a Marine Corps MV-22B crashed during a training exercise in Norway.

In early June, five Marines were killed when the MV-22B they were traveling in went down in Southern California. That incident, in part, led the U.S. Navy to order a "safety pause" at the time for all non-deployed aircraft.