May 4, 2000
Web posted at: 6:35 p.m. EDT (2235 GMT)
WASHINGTON (CNN) -- The U.S. Marines on Thursday delayed making an announcement on plans for the fate of the V-22 Osprey aircraft in the wake of a crash last month in Arizona that killed 19 Marines.
The Marines had been expected to announce on Thursday that flights of two test aircraft would resume this week. But sources say Marine Corps Commandant Gen. James Jones ordered a delay in the announcement.
MESSAGE BOARDThe sources also said investigators are focusing on "human factors" concerning the April 8 crash, but have still not reached any conclusion about whether pilot error was to blame.
The tilt-rotor aircraft is unique in its ability to take off and land like a helicopter, then rotate its propellers 95 degrees and fly like an airplane.
At the time of the crash, the Osprey was hovering in helicopter mode while attempting a night landing with another V-22 at a desert airstrip in Marana, Arizona, about 30 miles northwest of Tucson.
According to Pentagon sources, the pilot was maneuvering behind the lead aircraft when the V-22 lost lift under its right rotor, tilted dangerously to the right and then plunged nose-first into the runway, bursting into flames.
Theories on what went wrongInvestigators are now looking at whether an aerodynamic phenomenon known as "vortex ring state" could have caused the aircraft to suddenly drop to the ground.
Aviation experts say the phenomenon is something that can happen when a helicopter is hovering without any forward or lateral motion. In that instance, it is possible for the aircraft to get caught in its own prop wash, lose lift and drop to the ground rapidly, something also known in helicopter parlance as "settling with power."
Investigators looked at whether the prop wash from the other V-22 could have caused the phenomenon, but have determined from radar data that the two aircraft were too far apart for that to have been a major factor.
The preliminary finding suggests that the Marines may have to make changes in how V-22 pilots are trained or may have to make modifications to the aircraft.
Marine officials will say only that the investigation is continuing, and that there has been no finding of pilot error.
Pilots had extensive flight experienceThe Osprey that crashed came off the production line in January and had 135 hours of flight time.
Both the Osprey's co-pilots had extensive flying experience. Maj. John A. Brow had logged 97 hours in the Osprey, Maj. Brooks S. Gruber 86 hours. Brow had 3,777 total flight hours in various aircraft; Gruber had 2,117 hours.
The Marines aboard the April 8 flight were participating in a test of how the aircraft would perform in a simulated "noncombatant evacuation," a carefully choreographed rescue of civilians from a hostile environment.
The Osprey, named for a diving bird of prey, is manufactured by Boeing Co. and Bell Helicopter Textron.
The current phase of "operational evaluation," or field testing, in which Marines fly four production-model Ospreys in realistic training missions, began last October and will be finished in June.
Military Affairs Correspondent Jamie McIntyre contributed to this report.
Bodies to be recovered from Osprey wreckageRELATED SITES:
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