An investigation into another fatal crash of a U.S. military Osprey plane in late November is looking at a possible failure of the plane’s propeller rotor gearbox, U.S. officials briefed on the preliminary findings say.
event, A US Air Force V-22 Osprey crashed into the ocean off the coast of JapanThe deaths of eight servicemen were the fourth fatal crash of the unique tiltrotor aircraft in less than two years. 20 US servicemen were killed in the incidents. This led to the rare grounding of all Osprey aircraft by all branches of the US military in December.
The cause of the accident has been ruled out Japan The investigation is still ongoing and has not been determined, according to people familiar with the investigation.
A spokesman for the Air Force Special Operations Command told NBC News that the command had no new information to provide at this time.
Ospreys can take off vertically like helicopters, but then tilt their two rotors to fly like twin-prop planes. The military has about 400 Ospreys in use by the Navy, Marines and Air Force, although most are flown by the Marine Corps.
In the past, Ospreys have sometimes had a problem called “hard clutch engagement,” which led to an accident in June 2022 that killed five Marines. In February 2023, the military said that while they had yet to determine the root cause of the severe clutch incidents, officials said they were 99% confident that the clutch problem had been resolved. The last of the 19 hard clutch incidents reported by all three service branches occurred in January 2023, the Army’s joint program office for the aircraft told NBC News.
The Pentagon’s joint program office said in a statement that military leaders are committed to providing the military with “the safest, most reliable aircraft possible. … The safety and well-being of our personnel, as well as the reliability of the V-22, continue to be a priority in our discussions as we determine our return to our flight plan.”
While it was initially believed that the Osprey could take up to a year to land, it is now expected that the aircraft could return to flight soon, possibly within weeks, according to multiple military officials.
Metal chips in gearboxes
However, NBC News’ review of the Osprey crash and threat data from the Navy and Marine Corps shows other incidents involving propeller rotor gearboxes. Since July 2022, at least seven metal chips have been found in gearboxes, although no fatalities have been reported.
“One would hope it would be investigated really seriously,” said Tom Farrier, a retired military accident investigator. “It makes me wonder if there is a connection between the chip detection and the clutch problems. I would expect the Marines and Navy to spend a lot of resources on education.
Each of the twin rotors has its own gearbox. The gearbox is as big as a motorcycle and performs a function similar to the gearbox of a car. Inside the box are magnets that detect small loose metal chips like nails. According to aviation experts, after they are detected, a warning signal is sent to the pilot.
Marine pilots are instructed that if a metal chip is detected in the gearbox, they should land as quickly as possible out of pocket. checklist for pilots. If there is a secondary indication of a metal chip, then pilots are instructed to land immediately, regardless of where they are based on the checklist and incident reports.
A hazard report dated Oct. 5, 2022, in Hawaii, where chips were found in the Marine Osprey gearbox, noted: “This incident is further evidence that [Osprey] gearboxes are not meeting service life expectations and more work needs to be done to understand why [Osprey] proprotor gearboxes encounter chips.”
In another hazard report from Hawaii in June 2023, marine records show that a warning light for chips in the mast rotor gearbox came on twice in the Osprey cockpit “rapidly”. According to the report, the plane was shut down and chips were found in the gearbox. The report states, “There is no clear reason for the chip formation other than old gearboxes.”
Five months later, another Marine report from Hawaii indicated that the chip warning light came on while the plane was between the islands of Maui and Lanai. There was no secondary sign of the metal chip, so the Osprey continued to Maui and landed. After some maintenance, the plane was “sent back for a reliability flight” and the metal chip light came back on. After that, according to the Navy, the entire gearbox was “deemed bad” and required replacement.
The report states that “V-22 [prop rotor gear boxes] chip is known to occur, but there is no standard reason for why or how often. By submitting these reports, we can track the frequency of incidents.”
As of November 2022, an incident involving a single-prop rotor gearbox chip on a seaplane is reportedly still under investigation.
Detailed Air Force data on the crash was not available in time for publication.