The service has known about the issue with hard clutch engagement since 2010, and has trained its pilots how to respond when such emergencies happen, Marine Corps spokesman Maj. Jim Stenger said in a statement to reporters.
Air Force Special Operations Command grounded its fleet of 52 CV-22 Ospreys on Tuesday after two clutch issues occurred in the past six weeks. That followed two other incidents that occurred since 2017.
This problem occurs when the clutch, which connects the propeller’s rotor gear box to its engine, slips. That causes the Osprey to transfer the power load to the other engine almost instantaneously so the aircraft can keep from crashing.
The original gear box’s clutch then reengages, the power load transfers back in a span of milliseconds and the large transfer of torque causes the Osprey to lurch, the Air Force said.
Aircrews then land immediately for safety reasons. The Air Force said the problems in the past have led to the replacement of Ospreys’ gear boxes and engines, which makes them Class A mishaps, or issues that cause damage totaling at least $2.5 million.
Air Force Special Operations Command said that because it’s unsure what is behind these clutch issues, commander Lt. Gen. Jim Slife did not feel comfortable flying them, and therefore grounded them to figure out the root cause and how to stop the problem.
But the Marine Corps feels this is an issue that can be managed by training aircrews on how to respond, and that the potential for an occurrence is common knowledge among its fleet personnel. Officials said there were no injuries associated with the Corps’ hard clutch engagement incidents, although some gear boxes or engines were replaced as a result.
The Corps is distributing guidance on the hard clutch engagement issue and plans to conduct briefings with Osprey aircrew and maintainers, said a defense official, who spoke with reporters on the condition of anonymity.
The Marines have a fleet of about 296 Ospreys, and have flown them for 533,000 flight hours.
The V-22 program has experienced a total of 15 instances of hard clutch engagement, including 10 in Marine Corps Ospreys, since 2010, the defense official said. The Navy confirmed Thursday it has not experienced this problem with its CMV-22 variant, which is the newest in the Osprey fleet and began its first deployment last August.
More than two-thirds of these problems have occurred seconds after takeoff, when power is quickly applied, the defense official said, so the Corps plans to reinforce its takeoff maneuvers to remind aircrews of the importance of checking gauges. Those instruments will often alert the aircrew that such a problem is about to occur so the pilots can quickly and safely land them.
The Marine Corps also plans to work with the V-22 program office and industry partners to develop additional alert indicators in the cockpit over the long term so pilots can better know when a clutch problem is emerging. The defense official said these longer-range fixes might take one to three years to implement.
Marines also fly the MV-22 differently than the Air Force flies its CV-22s, which contributed to its decision to continue flying the Osprey, the Corps said in a document distributed Thursday. That includes the fact that Marines typically fly MV-22s over water after launching from amphibious ships.
For example, a Marine official said in the briefing call, the Marines will instruct Osprey pilots who take off over water to hover while checking instruments and making sure the clutch isn’t slipping. After conducting those checks, the Osprey will then move on to conduct maneuvers.
Because Marine MV-22s are usually launched from amphibious platforms over water, the Marine official said, they are better able to hover for a period without encountering dust storms or enemy threats, which Air Force Ospreys might encounter over land. Air Force Ospreys might need to more quickly leave the takeoff area for tactical reasons, he added.
The Marine official also said the Corps is talking with the Air Force, V-22 Joint Program Office and other organizations about the clutch issue.
Stephen Losey is the air warfare reporter for Defense News. He previously covered leadership and personnel issues at Air Force Times, and the Pentagon, special operations and air warfare at Military.com. He has traveled to the Middle East to cover U.S. Air Force operations.