Paul Lewis/Washington DC

A series of technical problems and suspected component failures has conspired to ground temporarily half the US Marine Corps' fixed and rotary-wing fleet.

As of last week, the USMC had ordered all of its 198 Bell AH-1W SuperCobra attack helicopters, 165 Sikorsky CH-53E Super Stallion heavylift machines and 11 new Bell Boeing MV-22 Osprey tiltrotors to suspend flying pending inspections. In addition, more than 70 Boeing/BAE Systems AV-8B Harriers have been grounded since late July.

According to the USMC, the CH-53Es will remain grounded until it has completed an inspection of the helicopter's swash-plate duplex bearing. This follows the 10 August crash of a US Navy MH-53E mine-sweeping version of the helicopter off Corpus Christi, Texas, which killed four crewmen.

The wreckage has been recovered and is being transported to Cherry Point Marine Corps air station (MCAS) for inspection. The USN in the meantime has grounded its 43 MH-53Es.

Bell, meanwhile, is dispatching inspection teams to MCAS New River and MCAS Camp Pendelton to look for a batch of 20 rotor blades, the spars of which are believed to be susceptible to fatigue cracking.

The blades were among 30 produced prior to 1982 that are equipped with two-piece balance weights. Stress fractures have been discovered in the gap between the weights. Each blade will be electromagnetically inspected to isolate the suspect components from the unaffected single-weight blades.

The USMC's embryonicMV-22 fleet has been grounded for a second time after a precautionary landing and subsequent inspection revealed the failure of a coupling on the driveshaft which interconnects the power from the two engines. The other 10 Ospreys will also be inspected less than three months after an earlier grounding, following a fatal crash in April, was lifted.

Marine officials hope to restore the remainder of its Rolls-Royce F402-408-powered AV-8B fleet to flying status once vibration and oil analysis testing is completed. Some 30 of the 106 AV-8Bs grounded since July have been cleared.

Source: Flight International