Deadly Osprey Incidents Mount as Air Force Investigates Potential Mechanical Issue in Japan Crash

Four CV-22 Osprey tiltrotor aircraft taxi for takeoff
Four CV-22 Osprey tiltrotor aircraft taxi for takeoff from Yokohama North Dock, Japan, April 5, 2018. (U.S. Air Force photo by Senior Airman Joseph Pick)

The Air Force said Thursday its Osprey aircraft are still crucial to operations but will remain grounded until they're deemed safe to fly following the service's most deadly crash that killed eight airmen, as well as a long-standing mechanical issue and recent deadly Marine Corps mishaps.

The most recent crash off the coast of Japan Nov. 29 killed all crew members aboard and triggered a grounding Wednesday of all Air Force, Marine Corps and Navy V-22 Ospreys. An initial investigation after debris was fished from the ocean indicated a mechanical failure in the Air Force special operations Osprey, raising new questions about the safety of the aircraft and a mysterious clutch issue that has plagued it for over a decade.

"We remain confident that the CV-22B Osprey offers a solution to the joint force that no other capability can answer in the special operations community right now," Capt. Amy Rasmussen, an Air Force Special Operations Command spokeswoman, told "The CV-22 enables U.S. Special Operations Command to conduct nighttime, long-range, infiltration and exfiltration missions. Its versatility, speed and vertical-lift capabilities are not met by any other existing fixed- or rotary-wing platform."

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The investigation into the crash in Japan is still ongoing, but the revelation that it could be a mechanical issue with the Osprey raises concerns amid a recent history of mishaps and deadly incidents.

Three Marines were killed in August when their MV-22 Osprey crashed during training in Australia -- the cause has yet to be publicly confirmed by the service -- and five Marines died in 2022 when their Osprey suffered a catastrophic clutch failure during training in California.

In August 2022, Air Force Special Operations Command announced it was grounding its Osprey fleet and working to train and brief pilots on the issue. Just a day after that announcement, the Marine Corps revealed to reporters that not only has the service known about the clutch issue since 2010 but it was "common knowledge" among the community but said its pilots could handle the issue without grounding their fleet.

In February, the military announced it would again ground some of its Ospreys because they suspected that a single part that connects the aircraft engines to its gearbox -- the input quill assembly -- wears out more quickly than previously thought, leading to the clutch issue. They stressed that the move was a "mitigation" and not a fix.

Then came the deadly crashes in August and November.

"As you can understand, there will always be an inherent risk in military aviation," Pentagon spokeswoman Sabrina Singh said Thursday when asked about the latest militarywide grounding. "The Osprey is one of the premier assault aviation systems that we have. ... It's an incredibly useful platform for all of our services to use."

The Marine Corps echoed the Air Force's statement on Thursday, saying it remains confident in the Osprey.

"The MV-22B Osprey is a highly capable military aircraft and the Marine Corps has confidence in this platform. Flying an aircraft is an inherently dangerous mission to execute, but we train to reduce risk and to reinforce the safety of all service members," Capt Alyssa J. Myers, a spokesperson for the Corps, told on Thursday.

Two months prior to the Nov. 29 Osprey crash, two Marine V-22 Ospreys in Japan diverted on Sept. 14 within just two hours of each other due to "cockpit caution indications" in the aircraft while flying near where the Air Force Osprey crashed last week.

As mishaps mount, questions over the airframe have also increased. For over a decade, the elusive mechanical issue, called a "hard clutch engagement," has plagued the Air Force and Marine Corps aircraft.

Its true cause is still unknown, and the issue seemingly went unaddressed until August 2022 when the Air Force announced its surprise stand-down and publicly revealed the mechanical issue.

An Air Force Special Operations Command official told that preliminary findings into the Nov. 29 mishap show that the flight hours on the input quill assembly were likely below the 800 flight-hours threshold for replacement that was announced in February.

Known Problem, Mysterious Cause

Unbeknownst to the public, the Osprey had been suffering from hard clutch engagements, or HCEs, for over a decade -- at least 15 happened between 2010 and 2022.

The issue occurs within the Osprey's complex web of clutches and linkages that are designed to allow one engine to power both propellers in case of failure. When it is encountered, it typically shreds the components responsible for powering the aircraft's propellers.

In August 2022, when the Marine Corps revealed to reporters that it had known about the issue, spokesman Maj. James Stenger stressed that there wasn't "a single catastrophic event" attributed to the hazard.

However, even the nonlethal incidents of clutch problems that have become publicly known are far from minor.

That same month, an Air Force Osprey experienced a hard clutch engagement that forced it to make an emergency landing on a remote Norwegian nature preserve. There were no fatalities, but retrieving the aircraft required an intense international effort. reported that another hard clutch engagement with an Air Force Osprey also happened in 2017 while the aircraft was midflight over Arizona. The crew managed to make a quick emergency landing at a nearby airport.

One of the airmen on that flight said, "If this would have happened overseas ... this could have spelled ... death."

In contrast to the Marine Corps, which operates the vast majority of the military's Osprey fleet, Air Force officials have publicly acknowledged that the incidents, however rare, are a problem.

Lt. Gen. Jim Slife, then the head of Air Force Special Operations Command, told reporters at an Air Force conference in September 2022 that "each one of them results in a kind of a Christmas tree of lights, caution lights in the cockpit."

"I'm really, really proud of our crews and the way they've been able to safely land these airplanes, but I'd rather they not have to demonstrate their superior skill because we put superior controls in place to prevent them from having to do that," Slife added.

In July, the Marines released their investigation into the crash of an Osprey more than a year prior that killed five Marines in southern California.

That investigation revealed that the aircraft -- callsign Swift 11 -- was brought down by an unforeseen and previously undocumented "dual hard clutch engagement."

The report on the crash found that not only was there no way for the pilots of Swift 11 to see the problem coming, once it happened there was nothing they could have done to prevent it and nothing they could do to save themselves after it occurred.

Furthermore, the investigation also revealed that the military had no idea what actually causes the clutch issues.

"Once the root cause of HCE is understood, then and only then, can improvements to flight control system software, drivetrain component material strength, and robust inspection requirements be developed where applicable," Maj. Gen. Bradford Gering wrote in a letter that accompanied that investigation.

That did not stop the office that runs the Osprey program for the military from claiming that "through a combination of efforts, including the recent input quill assembly replacement bulletin in February 2023, the risk of a HCE event occurring was reduced by greater than 99%."

It's a claim that has raised skepticism.

The program manager of the V-22 program, Col. Brian Taylor, told in an interview shortly after the investigation's release that the Pentagon has "a good understanding of what happens and where it happens, and it happens inside of the input quill."

"The piece that we're missing, really, is just the initiating events ... that's the part that we're continuing to look for," he added.

A Unique Aircraft

The Osprey's defenders often point to a Marine Corps statistic that for every 100,000 hours of flight, the aircraft has fewer mishaps than other aircraft in the Corps' inventory, like the F/A-18 Super Hornet, the F-35B fighter jet and the CH-53E Super Stallion.

However, while true, that statistic is based off of the most serious type of mishap -- Class A -- that results in $2.5 million or more in damage, destruction of the aircraft or deaths. It does not capture other HCE incidents that can be costly and harrowing but nonfatal mishaps that fall short of that top classification.

Furthermore, the aircraft that the Osprey is being compared to carry far fewer service members. An F/A-18 or F-35 jet typically has just a single pilot while the Osprey has pilots, crew and potentially passengers. As a result, while the aircraft has only had four crashes over the past 20 months, it has also killed 20 people.

The aircraft, by its nature, is also less able to recover from an issue should one occur. Unlike fixed-wing aircraft, it is not able to be equipped with ejection seats or glide to a landing.

It also isn't able to make use of "autorotation" -- a safety maneuver helicopters use where the engine is disengaged and the rotors spin as air moves past them while descending.

While the specific circumstances and cause of the Nov. 29 Osprey crash remain unknown, the incident marks the deadliest CV-22 crash in the Air Force's history and the largest loss of life on the service's airframe, according to Air Force Safety Center data.

Prior to the training crash in Japan, three service members and a civilian contractor died when an Air Force Osprey crashed in April 2010 in Afghanistan, according to Air Force Safety Center Data. The cause could not be determined by an investigative board.

Families, Communities Left to Grieve

Since the Osprey's first flight in 1992, it has been involved in numerous crashes, accidents and mishaps, leading to more than 60 deaths.

Following the Marine Corps Osprey crash in Australia, communities across the country memorialized the three Marines -- two pilots and a crew chief -- who died: Cpl. Spencer R. Collart, 21; Capt. Eleanor V. LeBeau, 29; and Maj. Tobin J. Lewis, 37.

Out of the 20 others that were treated after the wreck, one remained in critical condition as of November.

For Collart, hundreds of well-wishers, family and friends attended a vigil in his honor in northern Virginia.

"He loved aviation," his mother, Alexia Collart, who wore a gold pin from his squadron, told in September. "We actually got to go into a hangar and see the Ospreys in Hawaii. He gave us a tour and he was so proud ... he knew everything."

All but two of the remains had been recovered from the Nov. 29 Air Force wreckage as of Thursday afternoon. Once their names were revealed, tributes began pouring in from public officials almost immediately.

California Gov. Gavin Newsom said Tuesday that he had ordered flags to be flown at half-staff to honor a local airman who was killed, as well as the other crew members.

"Jennifer and I are heartbroken by the loss of eight airmen, including Maj. Luke Unrath of Riverside, and we send our deepest condolences to their family, friends and colleagues during this painful time," he wrote in a statement Tuesday. "California joins the nation in mourning this devastating loss and honoring their service to our country."

Jess Boozer, the wife of Maj. Jeffrey Hoernemann, who was killed in the Japan crash, wrote on Facebook that she did not expect last week would be the last time she would see her husband.

"If I knew Wednesday morning when you left for work would be the last time I saw you, I would have hugged you tighter and never let you go," she wrote on Facebook. "You will always be my best friend and the greatest love of my life."

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