On October 21, 2000, approximately 1345 Pacific daylight time, an experimental Hallett-1 gyroplane, N8331H, collided with a power line during takeoff from Flying "B" Airport, Yelm, Washington. The private pilot, who was the sole occupant, was not injured, but the aircraft, which was owned and operated by the pilot, sustained substantial damage. The 14 CFR Part 91 local personal pleasure flight, was being operated in visual meteorological conditions. No flight plan had been filed. The aircraft did not carry an ELT. A video of the takeoff shows that after liftoff, the aircraft climbed at a very shallow angle. When asked about this in a post-accident telephone interview, the pilot stated that for a number of hours prior to the attempted takeoff, the gyroplane's engine had been running lean and hot, and had therefore not been producing the expected maximum power. As it reached a point where the aircraft was approximately 90 percent of the way down the runway, it still had not reached an altitude equal to the height of the marked power line off the departure end. Instead of aborting the takeoff at that point, the pilot continued the takeoff sequence and attempted to increase the gyroplanes angle of climb. According to the pilot, as he neared the departure end of the runway, it seemed to him that the engine's power output began to decay. Believing that he would not be able to clear the power line, he attempted to fly underneath it. Although he missed the marked main transmission wire, he did not see that there was a smaller unmarked wire strung further down the pole. As he maneuvered to miss the main wire, the rotor mast of the gyroplane contacted the lower wire, stopping the rotation of the main rotor. Immediately after the main rotor hit the wire, the aircraft dropped about 10 feet onto the surface of an adjacent road.