Both aircraft came in "hot and high" with the wind at their backs - a recipe for disaster in any landing but particularly for ships heavy with troops.
Trying to salvage the botched approach, the pilots sharply slowed their "tilt-rotor" V-22 Ospreys and dropped them like runaway elevators into the darkness outside of Marana, Ariz.
What the pilots didn't know was that the craft were caught in the helicopter equivalent of a "graveyard spiral," descending so fast that they were drowning in their own swirling downwash.
One V-22 rolled over and crashed in flames, killing 19 Marines on board. The other skidded the length of a football field.
Within seconds, a realistic training mission had become a disaster that is now fueling doubts about the safety - and future - of one of the military's hottest and most controversial new aircraft.
That accident last April, the third and by far the worst in 11 years of V-22 testing, was attributed to "human factors." But when a fourth crash 10 months later in North Carolina killed four more Marines, including a top Osprey pilot, suspicion shifted.
Now the machine itself and the radical technology that lets it take off and land as a helicopter and fly as an airplane are on trial.
A General Accounting Office report released yesterday said the Osprey may not be as safe or reliable as conventional helicopters and that the Navy and Marine Corps bypassed "significant testing that would have provided additional knowledge on V-22 flying qualities and susceptibility" to the aeronautics phenomenon that killed the 19 Marines in the April crash.
This finding comes as the Marines are trying to persuade Congress to spend $38 billion for full production.
Once hailed as revolutionary, the craft is being criticized as an example of engineering excess: Oversold by devotees, pushed into production too fast, tricky to fly and a nightmare to maintain.
Whether that's true - and indeed, whether the program will ultimately survive - won't be determined soon. However, its fate is being decided on several fronts.
- A Defense Department panel is evaluating the entire project, and the Bush administration has signaled that the Osprey is one Pentagon program it might cut. Indeed, Vice President Dick Cheney tried to kill it because of its cost when he was secretary of defense in the first Bush administration.
- Last month, the V-22's first squadron commander was relieved of duty after acknowledging that he ordered Marines to falsify maintenance records. The Pentagon is investigating.
- Meanwhile, the Marines grounded their eight remaining Ospreys in December, and the Pentagon's decision to order 458 Ospreys by 2013 is on hold.
Military officials and the manufacturers - Bell Helicopter Textron of Fort Worth, Texas, and Boeing's helicopter division - stress that no one has yet found the tilt-rotor concept to be flawed, and they say they regularly redesign parts as problems emerge.
Support also remains strong in Congress. Many civil-aviation planners continue to predict that commercial versions will someday ease airport congestion.
But several official reports on the V-22 and interviews with people intimately acquainted with it - including some long-time fans - reveal technical, mechanical and operational problems that help explain the current outcry for more development and testing.
A litany of issues
Among other things, the difficulties include:
- A maze of complicated controls that, when working, smoothly assist with important flight functions but have left pilots helpless when they've gone out of kilter.
- A history of high maintenance demands and breakdowns, especially chronic leaks in vital hydraulic systems.
- A tendency to roll over during rapid descents, which investigators say played a role in last year's Arizona crash.
"I think there is a lot of learning left to do in this airplane," says Gregory McAdams, a retired Boeing V-22 program manager who, as a Marine lieutenant colonel in 1982, helped launch the project.
"My personal opinion is that we could be rushing it."
The big question for some people is whether the aircraft will perform as required under violent battlefield conditions, since it has already challenged some expert pilots on training missions.
The Marines, traditionally the first into war, want 360 Ospreys to replace their Vietnam-era transport helicopters. The Air Force Special Operations Command hopes to buy 50 and the Navy 48. They'd cost around $60 million each.
"If you have to fly this thing with kid gloves, I don't see how it can be a combat aircraft," says James Furman, a former military helicopter pilot and an attorney retained by the family of the pilot killed in the Arizona crash.
Even Gen. James Jones, the commandant of the Marines, supports the re-examination of the V-22. He sees "some legitimate questions that have to be answered."
If experts conclude tilt-rotor technology is "too fragile," the Marines will drop it, he adds.
They won't have to make that choice, predicts Carl Harris, Bell Helicopter Textron spokesman. "We will get through this difficult time and we will have an aircraft that will certainly meet our customers' needs."
'Buck Rogers' technology
The Marines chose the V-22 as their war horse of the future because on paper there is little it cannot do.
It lands, takes off and hovers like a helicopter. Once the craft is under way, the 38-foot rotors on each wingtip can be rotated until they face forward, allowing the aircraft to cruise at more than 300 mph. It has twice the range of traditional helicopters.
"It took some Buck Rogers kinds of advances in technology to even make the V-22 fly," says aviation author and historian Jay Miller. "It's not a helicopter, but it's not an airplane in the traditional sense, either."
The aircraft has three independent flight-control systems, two computers, three navigation systems and three hydraulic systems. With its bank of colored computer displays, the cockpit looks more like the flight deck of a modern jetliner than a Spartan warbird.
Boeing provides those sophisticated digital avionics and fly-by-wire flight controls, and also the fuselage and some subsystems. Bell provides the wing, transmissions, rotors and engines.
Military officials and Bell and Boeing declined requests for interviews with current pilots, citing concerns about interfering with the ongoing Pentagon investigations.
But former tilt-rotor test pilots and others who have flown the V-22 say that pilots love it - when it is working right.
"It's amazingly simple, but you've got to know what you are doing," says one former pilot who spoke on condition of anonymity.
The computerized controls are smart enough to know when the aircraft is supposed to be a helicopter and when it is expected to fly like an airplane.
During takeoff, the conventional stick, rudder pedals and thrust lever automatically function like helicopter controls.
Once the aircraft gains enough forward speed - 45 to 90 miles an hour - the wings begin to produce lift. At that point, the controls start behaving as they would on an ordinary airplane.
The pilot has the choice of letting the computer tilt the engines and rotors forward for airplane flight or taking over with a button on the control stick. Some who have worked on the V-22 program call the plane an engineering masterpiece. But they also blame its complexity for many of its nagging problems.
"It's a technical wonder, but it has never been very reliable," says the former V-22 pilot. "If you sit any of the pilots down with a beer, they'll tell you the same thing."
Hundreds of malfunctions
Ever since its development, the V-22 has been what aviators call a maintenance monster.
Pilots say it is rare for any V-22 flight to end without some kind of maintenance squawk, ranging from hydraulic leaks to mysterious computer glitches that have been known to shut down critical flight instruments without warning.
During an eight-month operational evaluation last year - when Pentagon officials put the V-22 through its paces aboard ships and in the desert - the aircraft required 70 percent more maintenance than the CH-46 helicopters that it would replace.
Philip Coyle, the Pentagon official who supervised those tests, identified 723 malfunctions in critical components. Of those, 177 were in "flight-critical subsystems," such as a door that wouldn't open after landing.
"Failures related to the hydraulic system deserve special mention," Coyle wrote.
The aircraft has three separate hydraulic systems. Small titanium lines carry high-pressure fluid needed to move components such as wing flaps or to tilt the craft's heavy engines and rotors up and down as flight modes change.
The narrow lines are less vulnerable to being pierced by enemy bullets. But pressures that are 66 percent higher than those in most aircraft cause chronic leaks.
The latest Osprey crash apparently was triggered by a hydraulic failure, according to Gen. Jones, the Marine commandant.
Fasteners 'were falling off'
"Reliability, maintainability, availability, human factors and interoperability issues" led Pentagon evaluators to conclude that the V-22 was not yet "operationally suitable."
Interoperability refers to whether the aircraft's sophisticated electronics and radio systems could communicate well with other combat participants. They couldn't, according to the report.
In an interview, Lt. Gen. Fred McCorkle, deputy Marine commandant for aviation, recalls program briefings at which mechanics poured out plastic bags of broken parts "right here on the table."
"Seventy percent of the problems were with fasteners that were falling off," he says.
Bell says the Pentagon's operational evaluation last year was based on four early V-22s. It says that 118 reliability and maintenance improvements have been developed for later models. The company says "more robust" fasteners are also being installed.
There's no evidence that the V-22's maintenance problems have caused any of the crashes, McCorkle and other government officials say.
What did cause the crashes
There's an old aviation saying that the more tombstones there are after an accident, the greater the pressure to fix the problem.
Engineers don't wait for fatalities, of course. They try to imagine every possible disaster and design it out from the start.
Suppose, for example, that a V-22 were forced to land with its huge rotors facing forward - which would guarantee that they'd strike the ground. The graphite composite blades are designed to "broomstraw" into harmless fibers, reducing the risk of flying pieces.
Fuel tanks automatically fill with nonflammable nitrogen gas as they empty, so bullets or shrapnel won't ignite vapors.
But sometimes, engineers and designers can't imagine problems that appear when the aircraft enters service. Those unpleasant discoveries are called "unk-unks" - short for unknown unknowns.
"It is the unk-unks that will jump up and bite you," says McAdams, the former Boeing manager.
The Osprey that crashed in North Carolina was piloted by Lt. Col. Keith Sweaney, 42, one of the Corps' most talented and experienced tilt-rotor pilots.
That crash was especially alarming because the computerized, redundant systems apparently failed in a way that left the crew unable to save their ship. A ruptured hydraulic line contributed, McCorkle says.
Sweaney "followed everything by the book," says McCorkle.
In the Arizona crash, investigators believe both aircraft were essentially swallowed by their own downdraft - a phenomenon called "vortex ring state."
The ships were descending at more than 2,000 feet a minute - well beyond the limits in the V-22 operating manual.
A helicopter descending too quickly without sufficient forward airspeed can go into the vortex ring state. When that happens, instead of riding above the turbulence generated by its whirling rotors, the aircraft drops into the churning air, losing lift.
Why it's a problem for the V-22
The pilot's instinctive response is to add power to slow the descent. But that actually accelerates the descent by drawing even more turbulent air through the rotors.
In most helicopters, the easiest way to escape is to tilt the nose of the machine forward and fly into more stable air.
But some critics - as well as crash investigators and Pentagon inspectors - say that the phenomenon in a V-22 may be more serious because one rotor can be affected before the other.
"Such a situation can easily be envisioned in flight conditions" when pilots are busy, Coyle wrote in the Pentagon's field evaluation of the V-22. The first sign is "when the aircraft initiates an uncommanded, uncontrollable roll."
McCorkle and other military officials dispute the suggestion that a V-22 is harder to handle in such conditions. The pilot's ability to tilt the rotors should make it easier to fly into stable air than in a helicopter, he says.
Nevertheless, the V-22 handbook now prohibits descents faster than 800 feet per minute whenever the craft is in helicopter mode.
Such limits might prevent crashes but could make a V-22 trying to land troops in hostile territory a sitting duck, critics say. Helicopter pilots in Vietnam devised techniques to swoop in at more than twice that rate.
"At that rate, a guy could pull out his black-powder musket and take all day to draw a bead on you," says Furman, the lawyer and former helicopter pilot.
Thirty lives lost
Over the program's lifetime, four V-22s have crashed, with a loss of 30 lives.
Furman and other critics say such losses are unacceptable. Defense officials readily agree.
But they note that enlisted personnel are also dying in the 35-year-old helicopters that the V-22 would replace. Those aircraft are so old that the Marines call them "legacy airplanes."
Six Sea Knights have crashed during training accidents in the past five years, killing 26 Marines and sailors, tragedies that drew a fraction of the attention the Osprey crashes received. Fourteen died when two helicopters collided in midair and another seven were killed when their helicopter approached a ship too low --however, those factors had nothing to do with the CH-46's age. Several previous aircraft programs also suffered heavy losses in their early years, according to the Naval Safety Center, which maintains military accident records.
The F-14 Tomcat, now the Navy's muscle plane, suffered 27 fatal accidents in its first five years - and it carries only two people, unlike the Osprey's capacity of two crew members and 24 troops.
From the 1940s to the 1960s - when high-speed fighters were being developed - experimental jets littered the high desert outside Edwards Air Force Base in California like giant lawn darts.
The difference now, military aviation officials say, is that every crash is taken as a sign a program is a flop. But part of the uproar over the V-22 is that for the first time in years, a planeload of Marines died along with the pilots.
"In a transport, you can ill afford even a random pattern of losses, because you have all those people in the back," says David Chu, who opposed the V-22 in the early '90s as an assistant defense secretary.
Top Marine brass now agree that before the V-22 program moves forward, its problems must be identified and fixed.
"If it takes six more months of testing, then I want to take six more months of testing," says McCorkle.
"But I don't want to look up four years from now and see 10 more legacy airplanes that have killed 40 of my Marines because we were so nearsighted that we didn't work this technology."
Information from Bloomberg News and the Fort Worth Star-Telegram was used in this report.