NTSB Identification: SEA98LA091.
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Accident occurred Tuesday, June 09, 1998 in CHINOOK, MT
Probable Cause Approval Date: 02/11/2000
Aircraft: STEPHENS VORTEX, registration: N9261N
Injuries: 1 Fatal.

NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.

The private pilot, who was the builder of the gyroplane, had logged about 21 hours of flight time in gyroplanes, but did not have a gyroplane rating. A witness observed the gyroplane's departure and climb-out from the airport. When the gyroplane was approximately 400-500 feet AGL, the witness observed the nose pitch down slightly, then rapidly upward about 40 degrees, then down rapidly about 40 degrees below horizontal then back up as before. The witness said the gyroplane then seemed to fall nearly vertically downward to the ground, and speculated that there was some sort of catastrophic failure to the aircraft. FAA inspectors, however, found no evidence of inflight breakup, or a main rotor blade strike of the empennage.

The National Transportation Safety Board determines the probable cause(s) of this accident to be:

The pilot's failure to maintain aircraft control for an undetermined reason.

Full narrative available

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