An Air Force investigation into a deadly November CV-22 Osprey crash in Japan found that worn parts inside the plane’s transmission sheared apart in a split-second failure that doomed the plane and killed all eight crew members aboard . Though the failure came inside the gearbox that powered the plane’s giant left rotor and gave the crew no hope for survival, it was not the type of malfunction that has been blamed for a string of similar Osprey crashes in recent years.
As the plane approached Yakushima Airport at approximately 800 feet, the report found, the transmission “catastrophically failed, causing sudden asymmetric lift, and forcing the [Osprey] into an immediate left roll, resulting in the aircraft abruptly rolling twice before impacting the water. When the gearbox failure occurred, the aircraft became unrecoverable. At that point no pilot actions could have saved the [plane].”.
The investigation, released on Thursday by Air Force Special Operations Command, also laid blame on the Osprey’s pilot and, to a lesser extent, its crew for not appreciating the severity of the danger the plane was in and choosing to fly 60 miles before landing after a series of warnings inside the plane’s cockpit. As the parts inside the gearbox began to fail, sensor gave the crew a series of six warnings. Though none clearly indicated that a failure was imminent, “the dialogue amongst the [crew] did not indicate a sense of urgency commensurate with the increasing seriousness of the condition.”
“The [pilot] did not adequately assess the risk of extended overwater flight with a potentially serious mechanical problem and did not direct anyone in the [crew] to research other landing options that would get the [aircraft] on the ground sooner,” the investigation found.
But an attorney who represents two crew members from the crash told Task & Purpose that blaming the crew only deflects from the underlying mechanical failure that destroyed the plane, which the crew had no role in.
“I think the Osprey aircraft has some issues that the pilots run into all the time,” Timothy Loranger said Thursday. “And so, what that might tend to do is put the crew into this mindset of: Well, this isn’t really serious.; we can reset a computer; we can do something that will make that go away and then it won’t be a problem. That’s what happens when you have a platform that has within it some flaws and some issues that they have to deal with on a daily basis.”
The two pilots onboard were both experienced Air Force majors, the report said. The aircraft commander was an Osprey instructor pilot who had just graduated from the Air Force’s elite Weapons School in June. He had 953 hours of flight time in CV-22s, and over 1,300 total flying hours. The co-pilot was an even more seasoned pilot, with over 1,800 flight hours, but had spent about half of those in secretive special operations U-28s, a traditional prop airplane. He had transferred to flying Ospreys in 2021, and had over 300 hours in the tilt-rotor planes on the day of the flight.
Regardless of blame, the report made clear that the crew could not have saved themselves once a critical component failed.
Gearbox issues, but not a clutch failure
The crash was the third deadly Osprey incident in under two years, and led to a multi-month grounding of the aircraft, of which about 50 are flown by the Air Force and close to 350 by the Marines. All were grounded for months, but have since returned to the air.
An accident investigation board that looked into the Gundam 22 crash determined that the Osprey became “unrecoverable” after the failure of a key component called the Left-Hand Proprotor Gearbox, or PRGB, according to a copy of the investigation.
“Failure of the left-hand PRGB high-speed planetary section was most likely initiated by a crack in one of the high-speed pinion gears and fatigue cracking of the associated pinion gear’s bearing cage, which eventually fractured through the high-speed planetary carrier assembly,” the investigation found.
Significantly, the investigation did not find any evidence that Gundam 22 experienced a type of engine failure known as a hard clutch engagement, which has caused more than dozen other Osprey mishaps, including a June 2022 MV-22B crash that killed five Marines.
None of the clutch components aboard Gundam 22 were damaged, according to the investigation.
Instead, the investigation concluded that the U.S. military’s joint program office that oversees the Osprey fleet has not fully recognized possible safety issues associated with the PRGB.
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“Safety 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 risks, and limiting opportunities to impose risk mitigation measures at the service or unit level,” the investigation found. “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.”
Pilot decisions were “causal” to the crash
The crash came at the end of a long day of flying. Gundam 22 departed Yokota Air Base, where it was assigned to the 21st Special Operations Squadron, four hours before the crash to participate in a joint exercise. The crew had dealt with a series of mechanical issues, including failed computers. At roughly 49 minutes before the crash, the plane’s sensors gave the first of six warnings that tiny metal particles were beginning to appear in the fluid that runs through the plane’s gearbox. Air Force guidance requires that aircrews “Land as Soon as Practical” after the third such warning, a less severe direction than the Air Force’s other warnings to “Land as Soon as Possible” and the worst-case “Land Immediately.”
Though just 10 miles from the nearest airfield when the first warning appeared, the pilot decided to continue the mission.
The fifth warning, the report said, was more severe and, per Air Force rules, triggered a “Land as Soon as Possible” emergency. At that point, the pilot diverted to Yakushima, though it was not the closest place to land, the investigation found. The pilot also did not descend below the clouds to look for other places to touch down or ditch if necessary. The investigation also faulted the pilot for not declaring an emergency until he was asked by airfield operations at Yakushima Airport and for adding several minutes to the flight by approaching the airport in a normal box pattern and telling the co-pilot to put the Osprey in a holding pattern to allow a civilian aircraft to take off.
The report did not make a definitive determination on if the plane might have safely landed without any of the pilot’s delays. The rules for reacting to warnings have since been tightened, the Air Force said, with a first warning triggering a “Land as Soon as Practical” instruction and a second moving to “Land as Soon as Possible.”
An Air Force Special Operations Command spokesperson said that while the investigation determines facts and findings, it “does not assign blame.”
But Loranger said that it is difficult for the families of the crew members killed in the Gundam 22 crash to read the questions raised in the investigation about whether the pilot could have prevented the crash.
“It’s a lot to process,” Loranger said. “It can be very painful. So, I think it’s really important to understand what happened is there was a flaw in the aircraft. That’s what caused the crash. And so that needs to be emphasized – and perhaps maybe not given equal weight to pilot considerations under the circumstances.”
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