On August 21, 1997, about 1705 hours Pacific daylight time, a Beech H35, N4689D, collided with terrain after a loss of engine power in the airport traffic pattern at the Nut Tree Airport, Vacaville, California. The airplane was substantially damaged. The certificated private pilot and passenger were not injured. The airplane was being operated as a business flight by the pilot/owner under 14 CFR Part 91 when the accident occurred. The flight originated in Ukiah, California, at 1600. Visual meteorological conditions prevailed at the time and no flight plan was filed. The pilot reported that he took off with 38 gallons of fuel, with the fuel selector on the left tank. He stated that the fuel gauges in the aircraft always read "full," so he checked his fuel visually and timed each tank. He switched the fuel selector to the right tank about 18 nautical miles from Nut Tree Airport. While entering right traffic for runway 20, he put the landing gear and 10 degrees of flaps down and heard a "funny noise." The pilot reported that he put the throttle forward but the engine didn't seem to respond. He retracted the flaps and turned for the runway. The aircraft crashed in a field approximately 1/4 mile from the end of runway 20. The propeller was bent and the landing gear sheared off. The pilot reported to the police officer that responded to the site that he "blew it and ran out of gas." A Federal Aviation Administration inspector from the Sacramento Flight Standards District Office responded to the accident site. He reported that preliminary inspection of the aircraft revealed that the fuel selector was in the "off" position and fuel was present at the carburetor inlet when the line was removed. The inspector further reported that the fuel was drained from the aircraft. The right tip tank was empty, but had been damaged in the accident, the right auxiliary tank held about 9 gallons, and the right main tank held about 14 gallons. The left tip tank held about 2 gallons; the left auxiliary tank held 6.5 gallons, and the left main tank held about 3/4 gallon. The engine rotated normally and thumb compression was verified in all six cylinders. The inspector reported that he did not notice any restriction of the induction air path to the engine. He stated that he inspected the top spark plugs from all six cylinders and found that they displayed normal wear patterns. The engine oil was full. The hand operated fuel pump and fuel selector operated normally. Both magnetos sparked electrodes when rotated by hand. The engine driven fuel pump pumped liquid normally when rotated by hand. There was no water contamination present in the fuel that was drained from the aircraft. The Pilot's Operating Handbook for aircraft serial no. D4874 was reviewed and relevant portions are appended to this file. The handbook states that the carburetor returns about 3 gallons per hour of excess fuel. Fuel return lines are routed through the selector valve to the left main cell. The auxiliary cells and right main cell return fuel to the left main cell only.