WASHINGTON — An undisclosed number of V-22 Ospreys across three services will halt operations until a component tied to the engine is replaced, a defense official said Saturday, as part of an ongoing effort to address a hard clutch engagement issue that first alarmed the Air Force in summer 2022.

At issue is the input quill assembly, which attaches the Osprey’s engine to its prop-rotor gear box. The V-22 Joint Program Office on Saturday announced a time limit for these parts’ use, after a recent data analytics effort showed a clear connection between the age of the input quill assemblies and the aircraft’s likelihood of experiencing a hard clutch engagement.

The Defense Department is not disclosing the flight hour limit at which the input quill assembly must be replaced, nor how many of about 400 total aircraft across all the services will require this immediate maintenance work.

Still, a defense official, who spoke to a small group of reporters on condition of not being named, said Marine Corps, Navy and Air Force Special Operations Command squadrons will continue training and operations with aircraft that have not met that time threshold as the others are replaced.

There are no further operational restrictions, the official told Defense News during the call, saying that “the aircraft that have input quills under this time limit are ready to go and ready to train and ready to fight tonight.”

The Marine Corps has an inventory of 296 MV-22s, according to its spring 2022 aviation plan. Air Force Special Operations Command has 52 CV-22 aircraft, and the Navy is in the midst of receiving the 44 CMV-22s it purchased to support carrier strike groups.

The decision, which was made over the course of the past week, followed the recent completion of an analysis by the V-22 Joint Program Office’s engineers into the hard clutch engagement problem, of which the services have seen an uptick in occurrence.

“This recommendation was based on the progressive increase in these hard clutch engagement events,” the official said. “From that, and looking at the totality of the data, we in recent weeks have been able to determine that this time limit was an appropriate step for us to take.”

Osprey aircrews are required to land immediately after such a hard clutch engagement. In the past, they have led to the replacement of Ospreys’ gear boxes and engines, meaning such an incident would qualify as a Class A mishap, costing millions of dollars each. These incidents, though, have not caused any deaths or injuries to personnel.

Another hard clutch engagement incident involving an Osprey occurred in the last weekend of January, a separate source familiar with the matter, who was not authorized to talk on the record and asked not to be named, told Defense News.

That incident underscored how important it was to address this problem, the source said, reinforcing the joint program office’s data showing hard clutch engagements were happening more frequently.

These engagement happens in Ospreys when the clutch connecting the propeller’s rotor gear box to its engine slips. Ospreys are designed to transfer the power load from that engine to the other engine immediately when this happens, which would allow it to keep operating on a single engine if one failed.

But these events cause a large transfer of torque as the original gear box’s clutch reengages and the power load transfers back, within milliseconds. That torque transfer causes the Osprey to lurch in ways that greatly alarmed Air Force Special Operations Command leadership when they saw a string of these incidents in summer 2022.

But, the Air Force and Marine Corps had different responses.

In August 2022, AFSOC commander Lt. Gen. Jim Slife ordered the grounding of the command’s 52 CV-22 Ospreys after two hard clutch engagement problems in the preceding six weeks and two other incidents that had occurred since 2017. Nobody was injured in those four incidents, the Air Force said, but Slife felt it was necessary to ensure airmen’s safety.

That Air Force fleetwide Osprey grounding was lifted two and a half weeks later, after putting steps into place for aircrews to manage the clutch problems and updating training to address these incidents.

But, at the time of the Air Force grounding, the Marine Corps said it had known about the problem since 2010 and already had trained its pilots how to respond when such emergencies happen. It opted not to ground its Ospreys at that time.

The Navy had not experienced the problem with its new CMV-22 variants.

The Marine Corps flies its MV-22s differently than the Air Force. Marines typically fly MV-22s over water after launching them from amphibious ships. The service instructs pilots to hover shortly after takeoff and check instruments to make sure the clutch isn’t slipping before going on to conduct maneuvers.

The defense official said the joint program office has been studying the problem since 2010, but that effort ramped up significantly after 2022′s Air Force grounding.

The joint program office had 24 lines of effort related to the clutch, the official said ― including lab and flight tests of the component ― to better understand the hard clutch phenomenon, work on a “complete redesign of this clutch assembly” for potential future installation, and a data-mining effort looking at clutch performance across the V-22′s 700,000 total flight hours throughout three decades.

Squadrons for the time being will replace the input quill assembly on affected aircraft with the parts already in the supply system. They already have the tools, manuals and expertise to do the repair work themselves, the official said.

Once an input quills is replaced, the part will last for “years” before needing to be replaced again, the official said, based on the overall flight hours of the aircraft.

If the effort between the joint program office and the Bell-Boeing-led industry team develops a better system, that would be considered for implementation in the longer-term, the official said.

Megan Eckstein is the naval warfare reporter at Defense News. She has covered military news since 2009, with a focus on U.S. Navy and Marine Corps operations, acquisition programs and budgets. She has reported from four geographic fleets and is happiest when she’s filing stories from a ship. Megan is a University of Maryland alumna.

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.

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