On August 24, 2001, at 1820 hours Pacific daylight time, a Ryan ST3KR, N48742, was substantially damaged during an off-airport emergency landing near Camarillo, California, following loss of engine power in cruise flight. The airline transport certificated pilot and one passenger were not injured. The personal flight was operated by the American Airpower Heritage Flying Museum under 14 CFR Part 91. The local area flight departed from Camarillo at 1800. Visual meteorological conditions prevailed and no flight plan was filed. The pilot reported he was giving rides in the antique aircraft to thank museum volunteers of the Confederate Air Force squadron at Camarillo. Before takeoff, the aircraft was fueled to capacity, which he reported was sufficient for 2 hours endurance. About 20 minutes after takeoff, while in normal cruise flight and without warning, the engine lost power. During the ensuing forced landing in an open field, the landing gear struck a culvert and a wing was damaged. Post-flight inspection revealed that a clevis on the throttle linkage rod separated from the rod at the cockpit control quadrant. A rivet, intended to lock the clevis to the rod shaft, was never installed during fabrication/assembly of the linkage and absence of the rivet had not been detected during subsequent annual inspections. Museum personnel told the Safety Board investigator that it was their belief that the throttle linkage had, most likely, been field fabricated or disassembled, cleaned and reassembled, and then reinstalled in the airplane during the last restoration of the World War II-era aircraft, 358 flight hours prior.