WASHINGTON -- Marine Corps investigators believe last month's MV-22 Osprey crash that killed 19 Marines probably was caused by a loss of aerodynamic lift that forced the aircraft into a fatal nose dive.
The investigators are close to ruling out mechanical failure as a cause and do not believe the investigation will find a need to redesign the aircraft, a unique hybrid of airplane and helicopter, officials said Monday.
Investigators also have found no indication of recklessness by the pilot, Maj. John A. Brow, 39, of California, Md.
One Pentagon official said investigators are about 90 percent certain that the crash at a small airport north of Tucson, Ariz., was caused by an aerodynamic phenomenon known as ''settling with power.''
This condition, also known as ''vortex ring state,'' occurs when a helicopter settles into the wash produced by its own rotor system. This can happen in circumstances combining a rapid rate of descent, low forward airspeed and a nearly vertical descent. The aircraft's descent is so rapid that the flow of air at the inner portion of the rotor blades is upward rather than downward. The upward flow of air caused by the aircraft's descent can reach a level that is greater than the downward flow produced by blade rotation. At this point the aircraft can sink uncontrollably.
It is not clear what caused the Osprey to get into the ''settling with power'' problem.
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