The Pentagon is ordering fleet-wide inspections of the Bell-Boeing V-22 Osprey after a so-called “near-crash” in November almost brought down another of the safety challenged tiltrotors.
A 20 December flight bulletin issued by Naval Air Systems Command (NAVAIR), which serves as the airworthiness authority for the V-22, directing the inspection of each tiltrotor to “verify the flight hours on each proprotor gearbox prior to an aircraft’s next flight”.
Ospreys under an unspecified flight hour threshold will be issued a new interim flight clearance, containing “additional risk mitigation controls”, NAVAIR says.
The US Marine Corps and Air Force Special Operations Command collaborated with the navy to implement the safety bulletin and new flight clearance, according to NAVAIR. Combined, the three services operate more than 400 V-22s, with the USMC’s 348 examples comprising the vast majority of the global fleet.
The Japanese Ground Self-Defense Force also operates 14 of the MV-22 variant.
While the specific nature of the new flight procedures was not revealed, NAVAIR says they will remain in place until the proprotor gearboxes (PRGBs) receive a mechanical upgrade or the flight hour threshold is exceeded.
The metallurgical weakness within the V-22 transmission is thought to manifest itself relatively early in the component’s lifespan, meaning PRGBs with flight hours above the threshold have been deemed safe.
“Due to operational security concerns, the specifics of the V-22 flight-hour threshold, number of aircraft affected and additional flight controls will not be released,” NAVAIR says.
Physically replacing each transmission with a stronger version is projected to take several years across the entire fleet.
The PRGB issue has been attributed as the cause of a 2023 crash off the coast of Japan that killed eight US Air Force personnel, whose CV-22 experienced engine failure as a result of metal chip fragments generated by the gearbox weakness.
That incident has become known as the Gundam-22 crash, so named for the aircraft’s call sign.
A similar proprotor gearbox issue almost brought down another USAF CV-22 I in November over the US state of New Mexico, in what the Pentagon earlier this month described as a “near-crash”.
Changes to flight procedures instituted in the wake of Gundam-22 allowed the crew in New Mexico to safely land the aircraft when onboard sensors triggered a chip fragment warning.
Earlier guidelines allowed for multiple such alerts before triggering emergency procedures. Safety guidelines now specify a “land as soon as practical” directive for a single chip fragment warning and a “land as soon as possible” mandate in the event of a second warning.
The Pentagon had grounded the entire Osprey fleet in December 2023 while an investigation was conducted, ultimately clearing the troubled tiltrotor for limited flight operations three months later – notably without a mechanical remedy for the problem in place.
USMC Ospreys have been flying non-combat missions since at least April, while air force CV-22s returned to full combat operations in the autumn. That was despite the head of NAVAIR saying in June that he did not expect to fully lift flight restrictions on the Osprey until mid-2025.
Those restrictions include limiting the flight time required to land at a divert airfield and modified emergency procedures. It was those modified emergency procedures that apparently prevented a more serious incident over New Mexico in November.
