Incident Overview
The pilot reported that the aircraft was in level flight at 800 feet above ground level when severe yaws occurred in rapid succession. Simultaneously, torque readings fluctuated between 30 and 100 pounds. The pilot immediately entered autorotation and selected a landing spot heading into the wind.
Collision with Powerlines
As the pilot began the flare, a passenger sighted powerlines directly ahead. The pilot made evasive corrections, but the aircraft struck the wires and subsequently impacted the ground left side first.
Engine Examination
A teardown of the engine revealed an accumulation of foreign material in the compressor and diffuser sections of the engine.
Probable Cause
No probable cause was stated in the source.