NTSB Identification: CHI05CA120.
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Accident occurred Friday, May 20, 2005 in Lakeview, MI
Probable Cause Approval Date: 09/13/2005
Aircraft: Brantly Helicopter B-2B, registration: N2274U
Injuries: 2 Uninjured.

NTSB investigators used data provided by various entities, including, but not limited to, the Federal Aviation Administration and/or the operator and did not travel in support of this investigation to prepare this aircraft accident report.

The helicopter rolled over during a practice autorotation. The purpose of the flight was for the dual student to practice autorotations in preparation for a rotorcraft rating. He stated the accident occurred during the third autorotation of the flight. The student reported that during the autorotation the airspeed decreased below 40 miles per hour and the rotor rpm decayed. He stated the CFI took control of the throttle, rolling it on and off about three times, but they were too slow and low. He stated the helicopter impacted the ground "hard." The student reported that he did not notice a mechanical failure/malfunction with the helicopter, reporting that they just got too slow and the rotor rpm decayed. He continued to report, "I learned later that when practicing autorotations, I should not roll the throttle to idle, because there is a governor that keeps it at about 2,000 rpm when the collective is lowered." He stated his CFI never said anything to him about not rolling the throttle to idle. The CFI stated the engine quit during the simulated engine failure. He stated they made a full touchdown autorotation into a soft field and the left skid dug into the terrain causing the helicopter roll over.

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

The dual student failed to maintain adequate rotor rpm during the practice autorotation and the instructor's delay in attempting remedial action. A factor associated with the accident was the soft terrain that was encountered.

Full narrative available

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