The problems are described in the latest annual report from the Defense Department’s operational testing directorate, led by Charles McQueary.

The V-22 is a helicopter-plane hybrid developed by Bell Helicopter Textron and Boeing. During an “operational utility evaluation” conducted last summer in the desert at Kirtland Air Force Base, NM, the effectiveness of the Osprey for training missions and potential combat missions was “degraded by poor aircraft availability,” says the report, issued Jan. 18.

“Frequent part and system failures, limited supply support, and high false alarm rates in the built-in diagnostic systems caused frequent flight delays and an excessive maintenance workload,” the report says.

Some of the reliability problems “may be attributable to the extended exposure to the desert operating environment” where the assessment occurred, says the report.

The Osprey provided only “marginal operational availability” during the 41 flights (74 flight hours), the report says.

The Air Force Operational Test and Evaluation Center conducted the assessment using four of the service’s CV-22 aircraft. The testing started June 6, 2006, and wrapped up July 10, said Katherine Gandara, a spokeswoman for the center. The final test flight for the assessment was conducted June 30, she said. All of the testing took place in the desert, she said.

The Marine Corps version of the V-22 would likely suffer the same kinds of problems in desert conditions, a Pentagon source said.

Both versions of the aircraft are very similar except the CV-22 has some extra equipment for special operations missions. The Air Force plans to buy 50 Ospreys for its special operations troops, while the Marine Corps plans to buy 360.

The report urges the V-22 program to correct the deficiencies noted in the “operational utility evaluation” before the CV-22 begins its initial operational testing and evaluation in FY-08.

The report also calls on the program to monitor the operational suitability of the Marine Corps’ Block B version of the Osprey, which is due to deploy this year, to determine the “discrepancy” between the solid performance reported in the operational evaluation of the Marine Corps version and the problems now coming to light.

James Darcy, the Navy’s spokesman for the V-22 program, said the problems encountered in last summer’s testing involved both known and previously unknown issues.

Program officials do not believe these issues will delay fielding plans for the Marine Corps or Air Force versions of the Osprey, he said.

Darcy said the testing in New Mexico was originally intended to test the Air Force’s rigorous training curriculum. This was a “much more stressful evaluation” compared to the conditions and types of flights that the V-22 program anticipates on an actual deployment, he said.

But Philip Coyle, a former director of operational testing and evaluation at the Pentagon, and now a senior adviser with the Center for Defense Information, said it is amazing how many reliability problems continue to affect the V-22.

“This produces a maintenance and support burden that the Marines really can’t afford,” he said. “All of the reliability problems that they continue to have here in the [United] States -- it’s going to drive them crazy overseas.”