A precautionary order that temporarily grounded all 84 BellBoeing V-22 Ospreys currently in service marred a celebration for the US Air Force CV-22 programme’s latest milestone event.

The CV-22 fleet passed the initial operational capability (IOC) milestone on 19 March. The IOC event officially ushers the new aircraft type into combat service, although the USAF has already deployed CV-22s.

Two days later, however, a US Marine Corps MV-22 crew in Iraq heard unusual noises after landing, and discovered four bolts had shaken loose inside one of the engine nacelles, said a spokesman for the US Naval Air Systems Command.

The missing bolts are supposed to hold in place a fixed swashplate that transmits flight control inputs governing the V-22’s blade pitch during helicopter mode, according to NAVAIR.

As a safety precaution, NAVAIR grounded all 73 MV-22s and 11 CV-22s in the inventory. Loose bolts, although still in place, have been found in three more of the 76 aircraft inspected through Wednesday morning. All four affected aircraft were based in Iraq, the NAVAIR spokesman said.

Two of the four aircraft with loose bolts have been repaired and return to service, along with the 72 other aircraft that cleared inspection, the spokesman added. Eight more aircraft remain grounded until they can clear inspection, which is expected by end-week.

NAVAIR is investigating whether defects in either the maintenance, manufacturing or design of the aircraft are to blame for the bolts coming loose, the spokesman said.

Source: FlightGlobal.com