NTSB Identification: FTW98LA327.
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Accident occurred Wednesday, July 22, 1998 in ENGLEWOOD, CO
Probable Cause Approval Date: 02/16/2001
Aircraft: Robinson R22 BETA, registration: N8350N
Injuries: 2 Minor.

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 instructor and his student were practicing 180 degree autorotations, preparing for the student's commercial and flight instructor checkrides. The maneuvers were begun between 610 and 660 feet above the ground. They completed several autorotations without incident. The instructor said the helicopter dipped slightly as airspeed increased by 5 knots to 65-70 knots indicated. Main rotor rpm decreased slightly, so he made an aft cyclic input and lowered collective slightly. Rate of descent suddenly increased rapidly and the instructor decreased bank angle with cyclic, increased power, and raised the collective. He flared to arrest the rate of descent as much as possible and pulled collective to cushion the landing. The instructor said he thought wind shear or a strong downdraft caused the accident.

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

An encounter with unanticipated windshear or a downdraft.

Full narrative available

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