NTSB Identification: SEA01LA003.
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Accident occurred Tuesday, October 10, 2000 in TWIN FALLS, ID
Probable Cause Approval Date: 05/18/2001
Aircraft: Enstrom F-28F, registration: N223RS
Injuries: 2 Uninjured.

NTSB investigators may have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.

The pilot reported that during a maintenance test flight to check controls, collective pitch position, throttle positioning, and rpm correlation control entering an autorotation, he entered the autorotation with low rpm. When the pilot corrected with collective pitch, the correlator over responded, resulting in an rpm overspeed. The pilot closed the throttle and increased the collective, however, the rpm dropped and the pilot had to complete the autorotation to touch down on rough terrain. So as not to have any forward speed at touch down, and fearing that the helicopter might roll over, the pilot anticipated a hard flare to stop the forward speed. Just prior to touch down, the tailrotor contacted the ground, and the tailrotor gearbox separated from the tail boom. The helicopter yawed to the right about 150 degrees before the pilot was able to level the helicopter, arrest the yaw and land without further incident.

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

The pilot's failure to maintain adequate rotor rpm. Unsuitable terrain was selected for the maintenance test flight operation.

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