The U.S. Air Force has grounded its entire fleet of CV-22 Osprey tiltrotor aircraft on Wednesday after discovering a problem with its engine clutch.
Air Force Special Operations Command (AFSOC) public affairs director Lt. Col. Rebecca Heyse told American Military News that the command had grounded all of its CV-22 Osprey aircraft on Tuesday after recent “hard clutch engagement” incidents.
All Air Force CV-22s are assigned to AFSOC. Defense News reported the command operates 52 of the aircraft.
AFSOC Commander Lt. Gen. Jim Slife ordered the stand down.
The problem impacted the clutch connecting the Osprey’s rotor gearbox to the engine. A “hard clutch engagement” would occur when the clutch would slip and then catch hard, causing the aircraft to lurch.
Heyse told Breaking Defense that CV-22 air crews have had to land their aircraft immediately when these clutch problems have occurred.
AFSOC has encountered four “hard clutch engagement” incidents since 2017, including two incidents in the past six weeks.
None of these four reported hard clutch incidents on AFSOC CV-22s have resulted in any injuries but the command is already taking precautions.
“We absolutely owe the air crew information about why this is happening and how we’re going to mitigate it,” Heyse told Defense News.
Heyse said it’s not clear if the problem has to do with the aircraft’s mechanics or the software controlling the engines.
“In coordination with the Joint Program Office, AFSOC has been unable to gather enough engineering data analysis to accurately identify root cause, so it’s unknown if it’s mechanical, design, software or some combination of any of those,” Heyse said.
“The safety of our Airmen is of the utmost importance, therefore no AFSOC CV-22s will fly until we will determine the cause of the hard clutch engagements and risk control measures are put in place,” she said.
AFSOC does not yet know how long their CV-22s could stay grounded.
“In the coming days, the AFSOC staff will work with the Joint Program Office and industry partners to fully understand this issue and develop risk control measures to mitigate the likelihood of catastrophic outcomes,” Heyse said. “Ultimately, the goal is to determine a viable long term materiel solution.”
The U.S. Navy and U.S. Marine Corps also both operate their own V-22 Osprey variants, the CMV-22B and MV-22B variants.
AFSOC’s grounding decision came on the same week the U.S. Marine Corps released the results of an investigation into a March MV-22 Osprey crash in Norway. Four Marines were killed in that crash incident, which the service attributed to the pilot’s exceeding the aircraft’s angle-of-bank limits in flight.
Another Marine MV-22 Osprey crashed in Imperial County, Calif. in June, though the cause of that crash is under investigation. Five Marines were killed in that crash.
The Navy and Marine Corps did not immediately respond to a Breaking Defense request for comment. The Marine Corps later told the publication it has been aware of the hard clutch engagement problem for years but is not grounding its aircraft over the issue.
“The hard clutch issue has been known to the Marine Corps since 2010, and as such, we have trained our pilots to react with the appropriate emergency control measures should the issue arise during flight,” the service said in a Thursday statement.
The Marine Corps said the V-22 program — which covers the Navy, Marine Corps and Air Force Osprey variants — have only recorded 15 hard clutch engagement incidents. The Marine Corps has recorded 10 of these 15 incidents, while the Navy has seen none on its CMV-22s.
AFSOC’s grounding decision also comes after the Air Force grounded most of its F-35A Lighting II fighter jets over a potential problem with the aircraft’s ejection seats.