Flight restrictions on the Bell-Boeing V-22 Osprey tiltrotor will likely remain in place for at least another year.

That was the prediction from the admiral in charge of US Naval Air Systems Command (NAVAIR), which acts as the airworthiness authority for all three Osprey variants operated by the US military.

Speaking to congressional lawmakers in Washington on 12 June, Vice Admiral Carl Chebi said he would not certify the V-22 type for a return to unrestricted flight operations until outstanding safety issues have been addressed.

“We are methodically looking at material and non-material changes that we can make to allow for a full mission set without controls in place,” Chebi says. “Based on the data that I have today, I’m expecting that this will not occur until mid-2025.”

The Pentagon grounded its entire fleet of Ospreys in December 2023 after a US Air Force CV-22 crash killed eight personnel off the coast of Japan. Three months later in March 2024, NAVAIR cleared the tiltrotor aircraft for a return to limited flight operations, pending the development of crew recertification procedures by each service.

However, significant questions about the deadly 2023 crash remain unanswered.

While authorities in March said they had identified which aircraft component failed, the exact reason for the fatal breakdown was not understood when the Osprey fleet was cleared to resume flights.

“We have high confidence that we understand what component failed and how it failed,” Colonel Brian Taylor, NAVAIR’s V-22 programme manager, said in March.

The Pentagon has still not revealed which component failed or how the failure occurred, describing it only as a “catastrophic aircraft mechanical failure that had never been seen before in the V-22 fleet”.

A military investigation board “was able to determine the sequence of events that occurred and the root cause of the mishap”, according to Chebi, with NAVAIR then developing new safety procedures to reduce the risk of similar incidents.

Written testimony submitted to Congress by Chebi states those mitigation measures include aircraft logbook reviews and serial number verification of “safety-critical life-limited components”, aircraft ground turns to verify proper operation of the V-22 drivetrain, planning constraints limiting the flight time required to land at a divert airfield and modified emergency procedures.

According to NAVAIR, the Osprey is currently approved only for flights within a restricted envelope. That includes remaining within 30 minutes flying time of a divert airfield, according to draft budget documents being considered by lawmakers.

Despite the uncertainty surrounding the V-22, the type’s largest operator of the tiltrotors has aggressively pushed forward with recertification.

The US Marine Corps (USMC), which is the largest V-22 operator with 348 examples in service, began Osprey flights within weeks of the grounding bulletin being lifted.

USMC V-22s were seen landing on naval flight decks as soon as 6 April ? under what the service described as its “deliberate and methodical approach to returning their MV-22s to full operational capacity”.

Chebi’s latest comments seem to call into question both the likely prospects and the safety of that programme.

Since 2022 the have been four fatal Osprey crashes within the US fleet, which resulted in the loss of four aircraft and deaths of 20 personnel.

A separate issue with the tiltrotor’s clutch also remains unresolved, although NAVAIR has developed safety mitigation procedures for so-called “hard clutch engagement” .

A senior navy procurement official who testified alongside Chebi on 12 June revealed the service is preparing to test a re-designed Osprey clutch system, with the goal of delivering it to the fleet in 2025.