On June 19, 2000, about 1215 hours Pacific daylight time, a Beech G35, N5801, collided with the ground while maneuvering in the traffic pattern at the Byron, California, airport. The airplane was owned and operated by the pilot and was destroyed in the ground collision sequence. The commercial pilot/owner succumbed to his injuries at 1600 the day of the accident while in the hospital. The commercial pilot/flight instructor received serious injuries. Visual meteorological conditions prevailed for the instructional flight operating under 14 CFR Part 91, and no flight plan was filed. A preflight weather briefing had been obtained from Reno AFSS. The instructional flight originated at Hayward, California, about 1200, and was destined for Modesto, California, with practice instrument approaches at Hayward, Modesto, Livermore and Tracy airports. The airplane was observed by witnesses to overfly the Byron airport about 1,200 feet above ground level (agl). Their attention was drawn to the airplane when they heard the engine either shutdown or power back to idle. They observed the airplane glide around and make a low pass down runway 05 at an altitude of 200-300 feet agl. The airplane then made a steep left turn toward runway 30. During this turn, the nose pitched down and the aircraft impacted the ground with its nose and left wing tip, approximately 150 feet to the right of runway 30 centerline. The uncontrolled airport has a common traffic advisory frequency of 123.05 mHz. One communication radio was found at 123.3 mHz. The airport was unattended the day of the accident. Postaccident examination of the fuel system revealed fuel quantities estimated to be about 24 gallons between the four fuel tanks. The right main tank (20 gallons) was selected and had 18 gallons. The other three tanks were estimated at 2 gallons each. Wing flaps were estimated at 10 to 15 degrees of extension. The landing gear was found in the retracted position. A dual control yoke was installed. The recording tachometer indicated 1990.34 hours. An engine examination was conducted at the airplane recovery facility in the presence of the Federal Aviation Administration (FAA). All engine systems and functions were examined for operational ability and conditions. Fuel was found in the gascolator housing and the fuel flow divider screen was clean. All three propeller blades displayed tortional twisting, leading edge damage, and chordwise striations. The instructor pilot told the FAA coordinator that he does not recall the accident. He did not file an accident report.