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Investigators believe pilot error caused Osprey crash

crash scene
The MV-22 Osprey crashed April 8, killing 19 Marines  

Top brass plan to be onboard when training flights resume

May 10, 2000
Web posted at: 6:30 p.m. EDT (2230 GMT)


In this story:

'Vortex ring state'

Almost $16 billion at stake

RELATED STORIES, SITES icon



WASHINGTON -- Investigators believe the crash of a Marine Corps V-22 Osprey last month in Arizona was caused by pilot error, CNN has learned. At least one more test is being planned to verify that preliminary finding.

Marine officials Tuesday confirmed that the accident, which took the lives of all 19 Marines on board, was not the result of mechanical malfunction.

Pentagon sources said the Marine V-22 pilot brought the tilt-rotor aircraft down too fast without enough forward motion, resulting in a loss of lift under the right rotor.

Sources say the pilot's rate of descent was between 1,700 and 2,000 feet per minute, more than double the recommended limit for hovering with little forward motion, according to data recovered from the V-22's flight data recorder.

The recommended "flight envelope" for the V-22 Osprey is not to descend faster than 800 feet per minute when flying slower than 40 knots (46 mph).

The V-22 is a hybrid aircraft that can take off, land and hover like a helicopter, and then, by rotating its engines, fly like an airplane.

'Vortex ring state'

At the time of the crash, the V-22 was in the hover mode at 280 feet with an air speed of 37 knots, (42 mph) slowing down to get into position to land.

At a Pentagon briefing Tuesday, the head of Marine Corps Aviation, Lt. Gen. Fred McCorkle, told reporters that the rapid rate of descent combined with the slow air speed caused a condition familiar to helicopter pilots called "vortex ring state" or "power settling."

McCorkle said, "Power settling is the incapability to stop a rate of descent when the aircraft begins to settle into a vortex ring state. The vortex ring state occurs when the velocity of the downwash from the rotor is approximately equal to the rate of descent of the aircraft, causing the air to recirculate up and around and back down through the rotor system."

Sources tell CNN investigators now believe this was caused not by any design flaw, or improper guidelines, but instead by a mistake by the pilot.

Pentagon officials said the conclusion was not announced at the Tuesday briefing because the investigators are still planning to conduct a simulation to verify their preliminary findings, and because, by law, McCorkle is prohibited from making any public statements as to the cause until the investigation has officially ended.

Osprey image
The Osprey can fly like a plane and hover like a helicopter  

Almost $16 billion at stake

McCorkle said the corps would resume flying test models of the aircraft this week and is expected to resume training flights of production models with troops in a week or two.

The V-22 is built by Boeing Co. and Bell Helicopter Textron. A full-scale production decision is scheduled for October, and the Marine Corps plans to buy 360 at a cost of $44 million each.

The aircraft have been grounded since the night training crash at a small airfield near Tucson, Arizona.

McCorkle said Marine Corps Commandant Gen. James Jones had so much confidence in the V-22 that he and Air Force Chief-of-Staff Gen. Michael Ryan would fly on the initial troop training flight later this month.

Military Affairs Correspondent Jamie McIntyre and Reuters contributed to this report.



RELATED STORIES:
Marines postpone announcement on fate of Osprey aircraft
May 3, 2000
Bodies to be recovered from Osprey wreckage
April 11, 2000
Possibility of pilot error considered in probe of Marine crash
April 10, 2000
Members of presidential helicopter squadron among Marine crash victims
April 9, 2000
A Crash and a Collusion?
September 20, 1999
Marine Crash Statistics
May 10, 1996

RELATED SITES:
MV-22 Osprey
Osprey On-Line
U.S. Marine Corps
Marine Corps News

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