On January 9, 2003, about 1715 mountain standard time, a Davis Yak-3 UR-2000, N498SD, collided with terrain during an off airport forced landing at Parker, Arizona. The pilot/owner was operating the airplane under the provisions of 14 CFR Part 91. The private pilot, the sole occupant, sustained serious injuries; the airplane sustained substantial damage. The personal cross-country flight departed Chino, California, at 1600, en route to Parker. Visual meteorological conditions prevailed, and no flight plan had been filed. A witness stated that the airplane attempted to land, but appeared to land long. The airplane was near the end of the runway before the pilot aborted the landing. The witness said that the engine did not sound like it was running smoothly. The airframe sustained substantial damage during a collision with terrain about 1.5 miles from the airport. According to the pilot, after landing long on runway 19, he attempted a go-around. The propeller blades remained in the high-pitch, low-rpm setting, and the engine did not develop sufficient power to sustain flight. He felt that the propeller shaft extension mechanism failed prior to his landing approach, resulting in the loss of propeller control. He felt that this loss of control resulted in the longer than normal landing, and the failure of the engine to deliver sufficient power to maintain flight during the aborted landing. The Airport/Facility Directory, Southwest U. S., indicated that runway 19 was 4,780 feet long and 75 feet wide. The runway surface was asphalt, and the field elevation was 452 feet.