At 1256 Pacific time, the pilot reported loss of engine power. The airplane subsequently impacted terrain during the forced landing. The private pilot, who had rented the airplane, and his two passengers were fatally injured; the airplane was substantially damaged. Visual conditions prevailed.
A U.S. Army helicopter pilot observed the airplane at about 500 feet agl approaching power lines. The airplane pitched up 15 degrees, yawed to the right and made two 360-degree rotations while in a vertical descent before impacting terrain.
Examination revealed a two-inch hole in the top of the crankcase.