QUANTICO, Va. - After years of delays and setbacks, the Marine Corps said yesterday that it plans to deploy its unconventional V-22 Osprey aircraft in military operations in Anbar province in Iraq in September.

The decision virtually assures that production of the aircraft, a hybrid of airplane and helicopter technology, will continue at Boeing's sprawling Ridley Township plant in Delaware County well into the future.

The Marines said that despite fatal crashes and ongoing design and production problems going back more than 20 years, the flaws had been worked out. The Marines said intensive testing of the aircraft established that it was superior to the two helicopters it was intended to replace, the CH-46 Sea Knight and the CH-53 Sea Stallion, the Marines' main transport helicopters.

"We have gone through a deliberative process, and we believe this is the most capable system," said Lt. Gen. John Castellaw, the Marines' deputy commandant for aviation.

The aircraft is a joint venture of Textron Inc. and Boeing Co., which assembles the Osprey fuselage at its Ridley plant. The Osprey can take off vertically like a helicopter, but can also fly like an airplane at high speeds by tilting its engines forward.

The military plans to purchase 458 Ospreys, the bulk of them destined for the Marines. Deployment of the aircraft to a war zone suggests a high level of confidence among the Marines about its capabilities.

If it performs well there, its chances of continued funding by Congress likely would be enhanced.

As part of yesterday's announcement, the Marines took reporters on a 25-minute demonstration flight at the Marine base here, a trip designed to showcase the aircraft's speed and maneuverability advantages over helicopters.

Only a few years ago, continued production of the aircraft seemed uncertain.

A crash in Arizona in April 2000 claimed the lives of 19 Marines. A crash in December of that year in North Carolina killed four more, and prompted the Pentagon to halt all flights to determine whether the Osprey concept was flawed.

Concern focused largely on aerodynamic features unique to the Osprey, and its tendency on some descents to become enveloped in its own rotor downwash - a condition known as vortex ring state - and then crash.

While helicopters are subject to similar difficulties, little was known at the time of the Arizona crash, which was attributed to vortex ring state, about steps pilots could take to reverse that condition.

Since then, the military and Boeing officials say they have developed flight tactics that make it relatively simple to avoid the condition, or to reverse it if it arises.

Castellaw said that, with that and other problems having been solved, the aircraft clearly was superior to helicopters as a means of transporting Marines into war zones.

Because it is able to fly like an airplane, it is twice as fast and much quieter than a helicopter, and capable of withdrawing under enemy fire far more rapidly.

Moreover, the Osprey also can fly at a much higher altitude, up to 10,000 feet with passengers, putting it out of the range of shoulder-fired missiles and machine-gun fire.

Some critics of the aircraft - which, according to the Government Accountability Office, costs about $100 million apiece - maintain that it is less maneuverable than a helicopter as it descends.

But the Marines said yesterday that the Osprey's ability to withdraw under enemy fire at speeds far greater than a helicopter's makes it a safer aircraft.

"If you have ever gone rabbit hunting, you know that the rabbit is a lot harder to hit if it is running than if it is sitting still," Castellaw said.

About the Osprey   

Purpose: Military combat aircraft.

Key features: Takes off and lands like a helicopter, flies like a turboprop airplane.

Capacity: 24 combat troops or up to 20,000 pounds of cargo.

Fuselage length: 57.3 feet

Rotor diameter: 38 feet

Speed: 288 to 345 m.p.h.

Range: 734 miles

Manufacturers:

Boeing makes the fuselage and flight-control systems.

Bell Helicopter Textron makes the wing, transmission and rotor systems, and handles engine installation.

SOURCE: Boeing Co.EndText

Contact staff writer Chris Mondics at 215-854-5957, or cmondics@phillynews.com.