Accident Investigation Board Report On Osprey Crash in Japan

Air Force investigators have determined the fatal CV-22B crash that occurred off the coast of Japan in November was caused by a “catastrophic failure” of a proprotor gearbox — a mechanical failure that the service said was made more likely due to the crew’s in-flight decisions and the Osprey program office’s prior failure to effectively communicate relevant data to the military services.

Those findings were made public today after an Accident Investigation Board, led by Lt. Gen. Michael Conley, who is now the commander of Air Force Special Operations Command, concluded its work.

“This has been a hard eight months. We lost eight air commandos that were valued members of this command,” Conley told reporters on Wednesday. “And the small, elite group of crew members that fly CV-22s. They were out there doing the mission we ask them to do that day and it’s important we don’t lose sight of that.”

The November crash killed eight airmen from the 21st Special Operations Squadron, 353rd Special Operations Wing, the remains of one of whom the service was not able to recover despite a search that lasted until early January.

In an executive summary outlining the crash’s timeline, investigators wrote the crew were participating in a joint exercise on Nov. 29 and had just taken off from Marine Corps Air Station Iwakuni when they received the first of five “left-hand proprotor gearbox (PRGB) chip burn” advisories.

Per Air Force guidance, crews are directed to land as soon as possible if they receive that warning three times during a flight, but service regulations also provide commanders some discretion based on their circumstances and mission. And within that discretion is where the AIB said the crew’s actions were “causal” to the crash.

“The MC [mishap crew] continued their planned mission with limited discussion of divert considerations or the changing dynamics of the situation. …The MC never discussed or considered landing to rendezvous with G23,” according to the report. G23 refers to a separate aircraft crew that was flying the same mission and tasked to help with maintenance issues

More than an hour after leaving the Marine Corps Air Station and having by that time received five aircraft warnings about the gearbox, the crew diverted towards Yakushima, which was roughly 60 miles away, without discussing alternative landing options or what conditions would require the crew ditch the aircraft, according to investigators.

“While on final approach to Yakushima Airport, at approximately 800 feet above ground, the left-hand PRGB catastrophically failed,” the report says. “When the gearbox failure occurred, the aircraft became unrecoverable. At that point no pilot actions could have saved” the aircraft or crew. Investigators also determined the PRGB at some point caught fire but said it was not a factor in the mishap.

The report goes on to state the aircraft’s mechanical failure “most likely” began as fatigue cracking in one of the gearbox’s components. When the cracking was exacerbated, other components within the gearbox began to malfunction, which led to the crew receiving the multiple cockpit warnings.

As the gearbox deteriorated, investigators say, the pilot contributed to the aircraft’s destruction and crew’s deaths by continuing the mission despite the warnings and not communicating with the crew about what options were available.

Conley told reporters the gearbox breaking down and the pilot’s decision-making were “causal findings” in the final report. “It doesn’t mean blame. It doesn’t mean liability. It simply means that these were the circumstances that led and caused the incident,” he said.

Investigators also wrote that the V-22 program office was culpable as well because they “inadequately communicated to the military services” data on the strength and reliability of the PRGB’s internal components, which are “critically important” to the aircraft’s functions. That poor communication “substantially contributed to the mishap,” according to the summary.

Conley said as a result of the investigation, the Air Force has changed its policies surrounding how urgently crews are advised to land when presented with multiple “chip burn” advisories, which he compared to the “check engine” light that appears in most cars — it’s a warning that appears on occasion, but not frequently.

He also said that while there have been changes to training and emergency procedures related to the gearbox, the service has not pulled back the discretion pilots are given while flying.

“We need our aircraft commanders to be trusted up there,” he said. “We can’t get in the cockpit with them from afar so we have to trust them to do what they think is in the best interest of the crew that day.”

Conley said the crew had spent “weeks and months planning” to do the mission and that “internal pressure” may have contributed to their choices to press on in the moment. That same type of pressure was at the center of public discussions in 2017 when investigations found two Navy destroyers separately collided with other vessels due in part to the crews being overworked and sleep deprived. Lawmakers pressed Navy brass at that time to answer for whether or not the service had developed a culture that was pushing sailors to the brink.

Asked if that was a concern for AFSOC, Conley said investigators did consider the issue but weren’t convinced it was a major factor. Still he acknowledged, “It’s always important that our leadership teams try to find the right balance between mission focus and not pushing the mission too far to past a situation where we’re assuming too much risk.”

The AIB’s findings come as the Pentagon has found itself in an increasingly difficult position in managing the V-22 Osprey fleets, of which variants are used by the Navy, Air Force, Marine Corps as well as the Japanese military.

In the wake of a separate incident, the Marine Corps in 2022 revealed it had known about a phenomenon involving a clutch failure since 2010 and insisted it had procedures in place to prevent disaster. But the Pentagon only recently implemented repair plans to more definitively prevent “hard clutch engagements” following a string of incidents, all of which immediately prompted outside speculation about what role the clutch may have played.

The incidents have also led to Pentagon-wide groundings of the V-22 fleets, which in turn has infuriated lawmakers who both represent the servicemembers hurt or killed in the accidents and must foot the costly bill of having hundreds of military aircraft effectively paralyzed.

Meanwhile, families of servicemembers killed in a previous V-22 crash are pursuing litigation against industry contractors associated with the aircraft.

“We seek accountability, answers, and change. Our goal isn’t to see this platform removed; it’s to know that someday we will be able to say, ‘their lives enabled others to live,’ knowing what happened to them won’t ever be repeated,” Amber Sax, widow of Cpt. John Sax, a Marine killed in a 2022 incident, said in a May statement.

“Finding the root cause of these mechanical failures and pressing for full transparency for our military, service members, and their families is only part of our advocacy,” she continued.