The crash of an Air Force MV-22 Osprey last year off Japan that killed eight Airmen was caused by a “catastrophic failure” in one aircraft’s gearboxes that led to an “unrecoverable” loss of control just as the crew was about to conduct an emergency landing, a service investigation released Aug. 1 found.
The mishap and multiple other fatal crashes over the last several years led to a monthslong grounding of the military’s entire Osprey fleet. The Osprey’s long-running issues with the gearbox have led to questions surrounding the aircraft’s future. The November crash, which shook the Air Force Special Operations Command (AFSOC) community, has led the command to rethink and limit the service’s use of the Osprey for now and reevaluate the number of CV-22 pilots and aircrews it needs.
The CV-22 has two prop-rotor gearboxes mounted in each rotating engine nacelle, which allow the tilt-rotor aircraft to take off like a helicopter and fly like an airplane. While officials involved in the Osprey program said soon after the crash the problem in the November crash was not a so-called “hard-clutch engagement,” a transmission issue, which has been faulted in previous mishaps, the ultimate problem that doomed the Nov. 8 flight Osprey involved the troublesome gearbox.
A metal gear failed, causing small chips to lodge in the gearbox. This ultimately caused the left-hand gearbox and drivetrain to fail completely, pitching the aircraft into a roll and nosedive into the ocean.
“That resulted in a complete roll,” Lt. Gen. Michael E. Conley, the head of AFSOC, told reporters ahead of the announcement. “The aircraft did two full rolls and ended up impacting the water.”
An Osprey pilot, Conley, previously a one-star general, led the Accident Investigation Board. Conley jumped two stars when he was confirmed to lead AFSOC.
The crash was the deadliest CV-22 in Air Force history. 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 were killed. There have been 11 crashes involving the Osprey since 1992, in which 61 people have died. There are some 400 V-22 variants across the Air Force, Navy, and Marine Corps.
In a rare move, his report put some of the blame on Pentagon leadership.
“[S]afety assessments and their findings were given insufficient treatment at the program level and have been inadequately communicated to the military services, creating lack of comprehensive awareness of PRGB [prop-rotor gearbox] risks, and limiting opportunities to impose risk mitigation measures at the service or unit level,” Conley wrote. “I find, by the preponderance of the evidence, that inadequate action at the program level and inadequate coordination between the program office and the services prevented comprehensive awareness of PRGB risks, and substantially contributed to the mishap.”
The transmission complexity in the Osprey has been a known issue since the aircraft debuted in the 1990s. The engine, weight, and vibration have to rotate, which puts enormous stress on the gears and driveshaft. Conley’s report underscores that.
The report also found that the crew’s actions contributed to the crash. The report found they should have diverted earlier in the flight but delayed an attempted emergency landing despite repeated and escalating warnings in the cockpit.
But the gear chipping phenomenon is not new, and the report ultimately blamed the aircraft, rather than the aircrew, as the primary cause of the crash. The chipping issue is common enough that the aircraft has a system designed to detect and clear the chips.
Conley compared the chip warnings to “a check engine light in your car.”
“The chips are a byproduct of just the gearboxes themselves,” he added. “It’s not unique to a V-22.”
The crew received six so-called “chip burn” warnings. When the aircrew decided to divert, they did not choose the closest airfield, and after the third chip burn warning, the aircraft was just 10 miles from the nearest airfield. The report said there was “an insufficient sense of urgency throughout the entire mishap sequence.” The pilot, Hoernemann, was also the mission commander for the exercise the aircraft, callsign GUNDAM 22, was participating in and may have felt the need to complete the mission, the report found. The crew received a sixth chip burn warning that indicated the aircraft was no longer burning off the stray metal pieces.
Conley said the crew likely faced “internal pressure” to complete the mission. “We ask crew members to make a million decisions, and sometimes seemingly mundane decisions or easy ones end up being consequential, and in this case, a series of decisions resulted in them extending the flight longer than they should have,” he said.
In the minutes before the accident, the crew was hovering and waiting for clearance to land from Japanese air traffic control at an airfield in Yakushima.
The pieces degraded the prop-rotor gearbox to the point where it no longer turned the Osprey’s left prop-rotor mast. Within six seconds of the prop-rotor gearbox failure, the drive system failed and the aircraft was unrecoverable. It crashed into the water, killing all eight Airmen abroad. The aircraft was assigned to 21st Special Operations Squadron at Yokota Air Base, Japan.
The accident investigation board was convened by then-AFSOC boss Lt. Gen. Tony Bauernfeind, with the investigation spanning from Dec. 6, 2023 to May 30, 2024, AFSOC said in a press release. The probe collated maintenance logs, interviews, flight recorder data, wreckage inspection, engineering and human factors analysis, and other evidence to assemble “a detailed sequence of events” surrounding the mishap, the command said.
Naval Air Systems Command (NAVAIR) boss Navy Vice Adm. Carl P. Chebi, who heads the office that oversees the Osprey program, said in June that he did not expect the Osprey to return to full, unrestricted flight operations until mid-2025.
But Conley said while the Air Force is not using the CV-22 in combat operations, he indicated the service may soon return the Ospreys to full non-combat operations. AFSOC returned Ospreys to limited operations in March but recently pulled them from an exercise in Japan to focus on “internal training.”
“We’re getting back in the ballpark where I think we will be supporting combatant commanders this year, this calendar year,” Conley said.
The crew of the mishap flight was comprised of Airmen from the 21st Special Operations Squadron, 1st Special Operations Squadron, and 43rd Intelligence Squadron.
“This has been a hard eight months,” Conley said. “We lost eight air commandos that were valued members of this command.”