On December 21, 1999, at 1545 central standard time, a Cessna 210, single-engine airplane, N6561X, impacted trees and terrain following a total loss of engine power near Bulverde, Texas. The airplane was owned by a private individual dba Lonesome Dove Aviation, Inc, of Carson City, Nevada, and operated under 14 Code of Federal Regulations Part 91. The private pilot and the pilot rated passenger received serious injuries, and the airplane sustained substantial damage. Visual meteorological conditions prevailed, and a flight plan was not filed for the local maintenance test flight. The time of departure was approximately 1500. During a telephone interview, conducted by the NTSB investigator-in-charge (IIC), and on the Pilot/Operator Aircraft Accident Report (NTSB Form 6120.1/2), the pilot reported that the airplane had undergone an annual inspection with an overhaul of the engine cylinders. During final approach at "approximately 500 feet agl and 1/4 mile from the intended runway, the engine suddenly and totally lost power." The pilot reported that the aircraft "cleared a ridge, a dry creek bed, and after the right wing contacted a tree, [the airplane] came to rest inverted." Local authorities reported to the FAA inspector responding to the site that the airplane landed approximately 1000 yards south of the pilot's private airstrip. The FAA inspector found the right wing approximately 20 feet agl in a tree. The cockpit came to rest inverted. The tail section was found separated aft of the baggage compartment and resting upright on the bottom of the fuselage. The aircraft was released for recovery to Air Salvage of Dallas (ASOD), Lancaster, Texas, for further examination. On January 11, 2000, under the surveillance of the IIC, the Continental IO-470-E engine, serial number 7759-0-F, was started and run for 15 minutes with maximum power of 2500 rpm at 28 inches manifold pressure observed. Magneto drops were 110 rpm's (left) and 75 rpm's (right). Following the engine run, a differential cylinder compression check confirmed compression for all cylinders. The cockpit ignition switch was examined. Continuity was confirmed at each switch position (OFF, LEFT, RIGHT, BOTH). The fuel selector valve was found selected on the right tank and was jammed in that position. Air pressure was applied to the right fuel line at the right wing root and a stream of blue colored fuel was observed as it was ejected from the engine pump inlet line. Each wing was equipped with a Monarch Auxillary fuel tank. When electrical power was applied to the auxillary tank transfer pumps, both pumps activated. Maintenance records were reviewed by the IIC. No open discrepancies were found. The aircraft and all records were released to the owner's representative on January 11, 2000.