Now the new military aircraft that's causing a stir, not just in the air.

NewsHour Correspondent Betty Ann Bowser reports.

The Marines have been putting in long hours, flying from early afternoon until late at night because they're getting ready to take a new aircraft to war in Iraq.

It's called the V 22, the Osprey.

With temperatures hovering in the one hundreds at a remote location in the Arizona desert, the conditions were miserable.

Similar to what they'll find when they get to the Iraqi desert.

We're flying multiple aircraft every day, complex missions.

We're operating the aircraft in a harsh environment.

The dust, the heat.

And we're doing it every day.

Got it.

And the best, too.

Lieutenant Colonel Buddy Bianca has spent the last eight years of his life training and flying the Osprey, and he loves it.

All right, thanks, guy.

It's not evolution.

It's revolution.

It's different.

The Osprey is different, alright.

It can take off and land like a helicopter.

But when the engines are in a horizontal position, it can fly like a conventional airplane.

General James Conway, commandant of the Marine Corps, made the decision to send Osprey to Iraq.

It's not the next generation aircraft.

It is a technological leap.

It is it is pushing the envelope of science to be able to do with this airplane what no other airplane or no other nation has developed the capability to do.

The Marines say the Osprey can fly higher, faster and further than the Vietnam era Conventional helicopters it's replacing.

And they say it will save lives.

If you look at the profile of the aircraft that we have lost, it's almost exclusively from ground fire.

But if you compare that against the profile that the Osprey offers, the ability to get above small arms fire or RPG rockets that in some cases have knocked out aircraft.

All of those things point towards greater levels of survivability and just much more effectiveness on the battlefield.

The Osprey is the most expensive vertical lift system in the history of the Pentagon.

In 25 years of development.

It's cost $20 billion as far back as the 1980s.

Questions about the price tag were being raised.

Then Defense Secretary Dick Cheney told the NewsHour in 1989 that he wanted to kill the program.

It's an expensive system.

Over the course of the next five years, if we go with a V 22 Osprey, I'd have to spend $10 billion.

Manufacturers Bell Helicopter and Boeing Aerospace mounted a huge public relations campaign.

This is the lift America needs.

In the end, Cheney's decision didn't stick.

Congress reinstated funding.

So today, the Osprey is in full blown production at a cost of $110 million a piece.

But it's not just cost that has disturbed some people.

Even the Pentagon's own former chief weapons tester Philip Coyle, now a senior adviser at the Center for Defense Information, says the Osprey won't stand up to insurgent ground fire.

It's not armored.

It's not a tank.

It's an aircraft.

And so you have a very complex piece of equipment where bullets or other kinds of projectiles can strike that is cannot practically be protected.

Ospreys, critics also point, to the aircraft's troubled safety record in 1991.

A test pilot survived this crash of a prototype.

But over the years there have been three other crashes that killed 26 Marines and four civilians after a crash in the year 2000.

The Corps went back to the drawing board, redesigned much of the aircraft and conducted extensive flight tests.

But Coyle says not all the bugs have been worked out and the Marines know it.

It's turned out to be a relatively unreliable aircraft.

The Osprey has had any number of different kinds of mechanical failures over its history electrical failures, electronic failures, hydraulic failures.

And so even in the most recent testing, its reliability and availability has not been up to the standards that the Marines require.

General Conway bristles at suggestions that he is sending an unsafe aircraft into a war zone.

Do you think this aircraft is reliable?

Well, I do, or we wouldn't be deploying and putting Marines in the back of it.

Okay.

I've flown in aircraft now three times.

I am really impressed with its with its characteristics and what it's going to bring to the battlefield.

And I will assure you that if we did not feel that way, we would not be putting America's great young warriors into the back of the aircraft.

What a marine Corps internal document obtained by the NewsHour dated June 7th shows the Osprey is still having serious maintenance problems.

Just a few months away from deployment to Iraq.

Identified were fuel system leaks and nose landing gear failures.

Either one of those could cause an accident.

Also cited were failures with the flight control computer and the deicing system.

Its problems are difficult to troubleshoot or identify, and air conditioning breakdowns were said to negatively impact the Ospreys ability to fly in hot climates.

Because of these and other problems for the past nine months.

The newest aircraft have been fully mission capable only 62% of the time.

When asked for an explanation, the Marines said these problems were old news that mitigation and improvement plans are in place for all these issues and that Osprey is on schedule to deploy.

Still, just a few weeks ago, when the NewsHour was taping training in Yuma, there were two problems on two different Ospreys in one day.

The first was when Lieutenant Colonel Bianca got a failed light in the cockpit and had to switch to another Osprey.

The second was in the desert where the NewsHour went to take a picture of several Ospreys landing.

When they didn't show up, we were told one had an electrical issue.

But Osprey maintenance crews argue it's not any more challenging than any other aircraft.

I think the maintenance is just where it should be.

It's a it's a newer aircraft.

So it has it's it's growing pains along the way, and we're working through them quite fast.

Former weapons tester Coyle disagrees.

Hardly a week goes by.

Maybe it's two or three weeks before I read and one of the defense trade journals or in a newspaper article or someplace that there's been another Osprey failure.

Those things happen.

We readily admit them.

They reach a level of public visibility that we're not ashamed of because it's a natural sequence of events.

When you're building a new airplane and putting it into operation Osprey.

Critics also say the aircraft still has design flaws.

Austin, Texas attorney Jim Firman, an experienced Vietnam War combat helicopter pilot, represented the families of Marines killed in an Osprey crash.

The case was settled out of court, he says, when the Osprey flies in helicopter mode.

It is susceptible to something called vortex ring state.

That's when air that a helicopters rotors push down, recirculating up, causing the aircraft to lose lift and crash.

With the Osprey because you have two engines there side by side.

It reacts to vortex ring state.

And in a very unusual way, it results in a very rapid roll that's unrecoverable if you're at a low altitude and that that was never resolved.

It's a aerodynamic issue with that aircraft that really cannot be designed out.

Osprey flight manuals tell pilots to avoid vortex ring state by not descending too quickly.

But Furman says that puts pilots in a dilemma when confronted with insurgent ground fire.

Either fly by the book and take enemy fire or get out of harm's way fast and risk vortex ring state.

When you're getting shot at, you're going to do anything that you can do to try to save yourself and the people on board.

And if you have some flight restrictions, that's going to be very restrictive on your survival.

How concerned are you about vortex ring state?

Not at all.

That was something that that I think we had to discover and understand the impacts.

So we've learned how to deal with it.

And it's not something that we're concerned about.

Lieutenant Colonel Paul Roark is the commander of the first Osprey Squadron that will be deployed to Iraq.

He says he and his pilots are trying to avoid vortex ring state.

Vortex ring state as an aerodynamic phenomenon only occurs at very low forward air speeds and very high rates of descent.

The last thing that I would do if I were being engaged is get slower and drop.

So I fly in formation and it won't give me an idea of why we fly information we just work harder to support.

Rox Pilots have undergone special training in flight tactics.

You think all the bugs have been worked out?

I feel completely comfortable flying the aircraft.

And I tell you, my wife wouldn't let me off if she didn't do so.

Yeah, I'm very comfortable.

Furman says confidence is not enough to overcome another potentially dangerous problem.

The Osprey cannot auto rotate when the helicopters engines fail.

Pilots use the lift created by the spinning rotors to auto rotate and land safely.

One of the requirements for any helicopter is that it be able to order rotate auto rotation to a helicopter pilot.

It's like an injection seat.

And so it would be like manufacturing fighter jets and not putting ejection seats on the back of the Osprey without auto rotational capability.

Osprey pilot Captain Mike Parrott says he's trained to handle that kind of crisis.

If we have any type of dual engine failure as an airplane, it still handles in an amazing way.

But if we're down low to the ground, I'm very confident we've practiced it in the simulator over and over and over.

And it's something that we have trained to and learned to do.

Conway says critics like Furman and Coyle should give the aircraft a chance.

If you look at the history of any new aircraft, any aircraft, period, aircraft do crash.

And it's it's a fact of life.

My concern is that there is a body of critics out there that will once again insist they be heard from when the next Osprey crashes to say, I told you so.

I just want to see Osprey given the opportunity to prove itself.

The first Ospreys will go to Iraq in September.