December 9, 2003
Osprey aircraft logs 1,000 accident-free hours since deaths
Marine Corps says vertical-takeoff V-22 is safe to fly
By OTTO KREISHER
COPLEY NEWS SERVICE
WASHINGTON – The Marine Corps' vertical-takeoff V-22 Osprey has flown 1,000 accident-free hours since test flights were resumed 18 months ago and has proven it can function safely in potentially deadly rapid descent conditions, the government's top test pilot said.
The tilt-rotor aircraft also has demonstrated that it can be operated safely on amphibious assault ships with other rotary wing aircraft, Marine Lt. Col. Kevin Gross said.
But a former Pentagon test-and-evaluation expert, Phillip Coyle, questioned whether the Marines had completed all the planned tests to prove that the Osprey can be operated aggressively while losing altitude quickly, a maneuver that caused one of the three fatal accidents that have dogged the V-22 program.
Coyle, former director of the Operational Test and Evaluation Office, also expressed concern yesterday that the Marines have yet to show that a number of the large troop-carrying aircraft can operate together effectively in the tight conditions on amphibious ships.
Gross said they have completed the tests necessary to document the tilt-rotor's response to vortex ring state – a dangerous condition similar to a fixed-wing aircraft stall – that rotary wing aircraft encounter when descending too quickly at low airspeed.
The condition, which causes a rotor to lose lift, was blamed for the crash that killed 19 Marines in April 2000 at Marana, Ariz.
"We believe we understand where that (vortex ring state) boundary lies . . . and understand how the aircraft responds," Gross said. "We believe we have explored this enough."
Coyle, however, said the government decided not to finish a second phase of vortex ring state testing. "They didn't want to take the time and money to do it," he said.
The former test director said he believed the Osprey testers had shortened planned tests on aggressive maneuvers of the type a crew could encounter on a combat mission.
But Gross said they had conducted tests involving "operational type" maneuvers during rapid descent and discovered that hard maneuvers actually delay vortex ring state.
The V-22 also recently completed tests on the amphibious assault ship Bataan to determine if changes in the flight control computer software can stop an Osprey from rolling excessively when hit by the downwash of a helicopter while sitting on the flight deck with its rotors turning.
In the trials last month, when buffeted by the rotor wash from hovering CH-46s and CH-53s, the roll was less than half of what was expected, Gross said.
However, because a second Osprey was late reaching the ship due to mechanical problems, the testers were not able to determine whether the tilt-rotor's downwash would cause a worse roll than the heavier CH-53s. While Gross said they do not believe it would, Coyle said it was possible that the Osprey's smaller rotors could produce a stronger downwash.
A final series of tests next fall by a newly created V-22 squadron will determine whether the Osprey is ready for operational duties after more than 20 years in development and testing.
Copyright 2003 Union-Tribune Publishing Co.