Five Marines who took off on training flight on June 8, 2022, died when their Osprey suffered a catastrophic clutch issue, the Marine Corps revealed in an investigation report Friday.

Despite the findings — and earlier concerns over the possibility of a deadly crash caused by the clutch — the military continues to fly the V-22 with no firm understanding of the cause or any definitive mechanical fix for the problem in sight.

The five Marines are the first known casualties of a persistent mechanical issue — a hard clutch engagement, referred to as HCE — that shredded the components responsible for powering the aircraft’s propellers. The issue has plagued the Osprey platform for years, but it was not acknowledged publicly until a month after their aircraft crashed in southern California.

Amber Sax, the wife of John Sax, one of the pilots who died on that Osprey, told Military.com on Friday after the new revelation from the Marine Corps that a tragedy like her husband’s death is not something she wants others to experience.

“The aviation community is our family. John loved being a Marine; John loved flying the Osprey,” she said. “This is a difficult day for so many. We just want to make sure this doesn’t happen to anyone else.”

The report and accompanying letters from Marine Corps leaders lay bare the scope of the problem. Despite a history of at least 15 such incidents between March 2010 and August 2022, “the root cause of HCE remains unknown,” Maj. Gen. Bradford Gering wrote in a March letter accepting the investigation results.

Gering wrote that the fix the Pentagon touted in February — replacing a part of the drivetrain called an input quill assembly — serves only to reduce the chance of this costly, and now deadly, issue from happening again.

“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,” Gering wrote.

Despite no clear understanding of what causes the problem, the office that runs the Osprey program for the Pentagon claimed in a statement released Friday 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%.”

The office’s statement added that the results of this investigation “have further driven efforts to mitigate the HCE phenomenon, identify root cause and prevent it from occurring.”

The massive, 400-page report released by the Marine Corps on Friday reveals that the Marines of Swift 11 — the call sign of the doomed Osprey — had little indication that anything was wrong in the moments leading up to their crash.

The Osprey left Camp Pendleton that morning with a wingman headed for an aerial gun range near the California and Arizona border. The training flight was going normally until 12:12 p.m., when the Osprey told its wingman that its gearboxes were getting too hot.

However, one of the enlisted crew in the accompanying Osprey later told investigators “that’s pretty normal” for the maneuvers they were doing because of the heat in the summer of southern California. “Nothing seemed strange about that,” he added.

The procedure was for the Osprey to climb to a higher altitude to help cool the oil in the gearboxes.

Investigators say Swift 11 began its climb at 12:14 p.m. Seconds later, it would slam into the ground from a height of around 500 feet.

The crash was so sudden that the crew of the accompanying Osprey — Swift 12 — didn’t realize what happened at first. Investigators said that the doomed Osprey made no radio calls and no one witnessed the crash. When Marines in the wingman Osprey spotted the smoke from the crash, the same enlisted crew member told investigators he thought it was an oil or tire fire.

“I did not think for a second that it was our wingman,” he said in written testimony.

After they weren’t able to raise Swift 11 on the radio, they flew in for a closer look, and reality dawned on them. Despite the thick, black smoke, one of the pilots on Swift 12 told investigators that “you could tell it was an Osprey.”

Investigators determined that Swift 11 crashed so violently that its fuel cells ruptured and caught fire. The ensuing fire was so fierce that it destroyed the Osprey’s black box. When the crew from a nearby Navy helicopter landed nearby and tried to put out the flames, they found that their fire extinguishers did nothing.

The remains of all five Marines — Capt. Nicholas Losapio, Capt. John Sax, Cpl. Nathan Carlson, Cpl. Seth Rasmuson, and Lance Cpl. Evan Strickland — were found at their stations, the report said.

The oldest Marine, Sax, was 33. The youngest, Strickland, was only 19.

Two months later, on Aug. 18, the Marine Corps, responding to the Air Force’s grounding of its own Osprey fleet over HCE concerns, would tell reporters that its pilots could handle the issue.

“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,” Maj. Jim Stenger, a spokesman for the Marines, said at the time.

According to the documents included in the report on the crash, the crew of Swift 11 were some of the best the Corps had to offer.

The squadron that the Osprey belonged to — Marine Medium Tiltrotor Squadron 364, known as the Purple Foxes — had recently been named the Marine medium tiltrotor squadron of the year. The citation specifically noted the squadron surpassed 10,000 mishap-free hours and “managed risk across a wide spectrum of desert and littoral combat operations.”

Furthermore, the lead pilot of Swift 11, Losapio, was widely regarded as an excellent aviator.

His commanding officer told investigators that he was a “phenomenal” officer and pilot who was “leaps and bounds ahead of his peers in terms of capability and stick control.”

Friday, however, the office that manages the Osprey program for all the services called the incident “unpreventable and unanticipated.”

While the Air Force was more cautious and grounded its aircraft in August as the Marines continued to take to the skies, the pause was short-lived.

That same month of August would see one of the Air Force’s CV-22 Ospreys get stuck on a remote nature reserve in Norway after the crew experienced a hard clutch engagement, forcing an emergency landing. There were no fatalities, but retrieving the aircraft began an intense ordeal involving international cooperation.

By September, just two weeks after grounding its Ospreys, the Air Force announced it had cleared them to fly once more, saying that, despite not having a mechanical fix for the issue, “the focus is on mitigating operations in flight regimes where HCEs are more prevalent and ensuring our aircrews are trained as best as possible to handle HCEs when they do occur,” a spokesperson said at the time.

–Hoan–