Gearbox, Crew Blamed for Deadly Japan Osprey Crash in Results of Air Force Investigation

The deadly crash of an CV-22B Osprey off the coast of Japan that claimed the lives of eight airmen in November was caused by a catastrophic failure in the gearbox of its left proprotor and how it was handled by crew members, according to the Air Force investigation into the crash.

A copy of the investigation obtained by Military.com says investigators found that components inside the gearbox began cracking and releasing debris, which then wedged between other components and eventually caused the left proprotor to stop turning, putting the aircraft into an unrecoverable spin.

The incident was the last of three deadly crashes that struck the Osprey community in recent years and triggered a monthslong grounding of the aircraft. While Ospreys resumed flight in March, they were cleared to fly without a full understanding of what brought down the Air Force flight in Japan and adhered to a restriction that bars flying more than 30 minutes from an airfield.

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The investigation reveals that throughout the flight of Gundam 22 -- the call sign of the aircraft that crashed -- the pilots received warnings that there were tiny metal chips in their gearbox but that they were being addressed by an internal system of sensors and magnets.

However, after a third warning, Air Force policies say that the crew needed to "land as soon as practical" -- a formal condition that means "extended flight is not recommended" but leaves the landing site and length of flight up to the pilot in command.

The crew decided to continue with the mission before two more warnings and a more serious alert of a persistent chip in the gearbox meant the crew had to land "as soon as possible." They diverted to Yakushima Island in Japan, which has a small airport.

The chips were actually part of a gear that was slowly disintegrating inside the gearbox. Eventually, a large enough piece of the gear sheared off and severely damaged other parts of the gearbox, stopping the left proprotor from spinning.

"That resulted in a complete roll. … The aircraft did two full rolls and ended up impacting the water," Lt. Gen. Michael Conley, the head of Air Force Special Operations Command, told reporters at a briefing Wednesday.

Gundam 22 crashed into the water off the coast of Yakushima as the crew was waiting to land.

Given this series of decisions, the report said that the pilots "inadequately prioritized continuing the mission over considerations related to the risk of extended flight without redundancy."

However, the phenomenon of chipping in the aircraft gearboxes is not new and, while the report faults the crew, Conley also told reporters that the airmen didn't actually violate any policy and broadly acted in accordance with their training.

In February 2024, NBC reported that "since July 2022, there have been at least seven instances of metal chips found in the [Osprey] gearboxes, though no fatalities have resulted."

The crash report also notes that the chipping problem was known to the military office that oversees the Osprey and that there was "inadequate action" on its part in dealing with the issue, which "prevented comprehensive awareness of [proprotor gearbox] risks, and substantially contributed to the mishap."

Despite that, the report also found fault with the crew -- whom the Air Force previously called "the best of us" and "naturally talented" pilots -- saying that they had "an insufficient sense of urgency throughout the entire mishap sequence" and, once a fifth warning cropped up and the pilots finally decided to land, they did not choose the closest airfield.

It's not immediately clear from the report that the crew had any other indications that something was seriously wrong with their aircraft, and Conley said that "this is the first time that this specific part has failed on a V-22 of any any type in almost 800,000 flight hours."

The three-star general and V-22 pilot also described the warnings the crew was seeing as "kind of like a check engine light in your car -- you could drive your car for 10 years and not get any or you could drive next week and get three different ones for multiple reasons."

Conley told reporters that "the chips are a byproduct of just the gearboxes themselves. … It's not unique to a V22" and that the first five alarms meant "that the detector had detected the chip and successfully burned it off."

He also confirmed that the pilots "followed their training to read the checklists and to look for secondary indications," undercutting the report's conclusion that the pilots took unnecessary risks with "a potentially serious mechanical problem."

Although he said the crew's actions contributed to the mishap, Conley told reporters that 
"there's nothing to indicate that they did anything deliberately to violate any policy."

Since the crash, AFSOC protocol has changed, and crews are advised to land as soon as practical after a single chip burn and "as soon as possible" after a second chip burn, he said.

The crash off the coast of Yakushima Island, Japan, on Nov. 29 marked the deadliest CV-22 incident in the Air Force's history.

Killed in the crash were Maj. Jeffrey T. Hoernemann; Maj. Eric V. Spendlove; Maj. Luke A. Unrath; Capt. Terrell K. Brayman; Tech. Sgt. Zachary E. Lavoy; Staff Sgt. Jake M. Turnage; Senior Airman Brian K. Johnson; and Staff Sgt. Jake Galliher.

Following more than 40 days of a massive search effort, the remains of the airmen -- with the exception of Spendlove -- were recovered.

The Air Force, alongside the other military services that fly the Osprey, grounded their V-22s shortly after the crash. Within roughly four months, the Pentagon cleared the services to fly again.

While the other branches quickly resumed flight, the Air Force was more cautious. The service said last month that only a handful of its aircraft were flying at Cannon Air Force Base in New Mexico. The Air Force also said it planned to examine the number of pilots and aircrews for the Osprey as part of a reevaluation.

Vice Adm. Carl Chebi, head of Naval Air Systems Command, which oversees the V-22 program, said during a House hearing testimony last month that he does not expect V-22s to return to full unrestricted flight operations until "mid-2025."

However, Conley, the AFSOC commander, told reporters Wednesday that, while the service is not using the CV-22 in combat operations, the timeline explained by Chebi may now be bumped up.

"We're not providing any combat capability, but I'll tell you we're getting close," Conley said. "I don't want to discuss the specifics of operational deployments, but we're getting back in the ballpark where I think we will be supporting combatant commanders this year, this calendar year."

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