The US Marine Corps is mounting a rearguard action to defend the Bell Boeing V-22 Osprey, as a combination of alleged maintenance irregularities, the recent fatal crash of a second tiltrotor and the inauguration of a new vice-president historically hostile to the programme and intent on reviewing defence priorities throws the future of the programme into doubt.

The Osprey is now the subject of three investigations, which have pushed back full production approval indefinitely. At stake is a $40 billion programme with the USMC planning to buy 360 MV-22Bs and the US Air Force 50 special operations CV-22As.

Past V-22 opponents include former defence secretary and now vice president Richard Cheney. The USMC, fearful that the Osprey again faces the political axe, has been making the case for theV-22's range, payload and speed advantages over conventional helicopters and that there is no suitable alternative.

Tiltrotor operations remain suspended pending the outcome of the investigation into December's crash of a MV-22 belonging to VMMT-204 squadron at New River, North Carolina. The loss of a second Osprey in nine months prompted the out-going Secretary of Defence William Cohen to launch a programme review.

Further damage has been inflicted on the Osprey and USMC's credibility by revelations that the commander of VMMT-204, the lead MV-22 squadron, instructed subordinates to falsify maintenance records. Readiness and reliability rates have been subject to criticism, but the USMC denies that the alleged irregularities are linked to the latest crash.

"We're 99% complete with the December mishap investigation, and everything indicates that the aircraft experienced a hydraulic system failure followed by an error in software inputs to the flight control systems," says Lt Gen Fred McCorkle, USMC deputy commandant aviation. He goes on to say that the marines can see "no relationship" between the accident and the maintenance allegations.

McCorkle says the tiltrotor was 10% into a transition to helicopter mode when a problem was detected. Transition was aborted and the V-22 returned to 100% fixed-wing mode seconds before impacting the ground.

A No1 hydraulic system failure has been attributed to a line wearing through, but no explanation has been given as to why the two back-up systems did not take over, other than a software glitch resulting in loss of control.

The Department of Defense Inspector General has launched an investigation into the alleged falsification of maintenance records. The commander of VMMT-204 has been relieved of his duties pending the investigation's conclusion.

Source: Flight International