On May 9, 1996, at 1625 central standard time, a Cessna 172G, N202EX, registered to and operated by a private owner under Title 14 CFR Part 91, impacted terrain during a forced landing near Okmulgee, Oklahoma. Visual meteorological conditions prevailed at the site and a flight plan was not filed. The private/instrument rated pilot received minor injuries and the airplane sustained substantial damage. A review of the air traffic control data revealed that the airplane originally departed Tulsa, Oklahoma, with a planned destination of Corsicana, Texas. While en route at 6,000 feet MSL, a loss of engine power occurred. The pilot requested vectors to Okmulgee. Realizing that he could not make the airport, the pilot requested vectors to the nearest airport, Foster Field. During the emergency decent, the pilot restarted the engine at 2,500 feet and elected to land at Okmulgee to inspect the airplane. The pilot reported the airport in sight and at 1355 canceled his IFR flight plan. The airplane landed at Okmulgee without further incident. The following information was obtained from interviews conducted by the FAA inspector and the investigator-in-charge, and information gleaned from the witnesses and the pilot. The pilot tried to get the airport manager to inspect the airplane. The airport manager is an A & P; however, his contract with the city prohibits him from working on aircraft. The airport manager gave the pilot some suggestions for troubleshooting and a mechanic located at the field checked the airplane. The mechanic did not find any obvious problems and suggested that the problem could be in the carburetor. The mechanic further said that the next day he could check the carburetor and order any required parts; however, he could not guarantee that the carburetor would be the problem. The pilot insisted that he was going home and stated that he would climb the airplane over the airport and check the engine prior to departing for Corsicana. After 2 full power ground run-ups, the airplane departed on runway 17 and climbed to 4,000 feet MSL. The pilot flew the airplane in various attitudes, configurations, and power settings without engine discrepancies. During the on course turn, a total loss of engine power occurred. A forced landing for runway 17 was initiated; however, during the final approach, the airspeed showed 55 mph and the pilot realized that the airplane would not make the runway. During the landing flare/touchdown the left wing struck a tree and the airplane came to rest nose down. Structural damage occurred to the wings. A review of the aircraft maintenance records and FAA records by the investigator-in-charge revealed the following information. On January 12, 1968, the ignition switch was replaced. On April 14, 1976, Airworthiness Directive (AD) 76-07-12 was issued concerning checking the ignition switch during ground run-ups. The AD states that if the engine continues to run with the switch in the "OFF" position (indicating a malfunctioning switch) repair or replacement of the switch or use of an alternate FAA approved method must be accomplished. This AD must be complied with at each 100 hour inspection by the mechanic performing the inspection or by the pilot. The airplane was purchased by the current owner on December 19, 1988. On August 11, 1990, a logbook entry by a mechanic stated "checked AD's." The last annual inspection was logged on March 5, 1996, and the mechanic stated "AD's current" and the airplane and engine were found to be "airworthy and approved for return to service." On May 30, 1996, at Air Salvage of Dallas, Lancaster, Texas, an engine test run was conducted under the direction of the FAA inspector. The engine would operate intermittently through the ignition switch positions. The FAA inspector found that the switch could be "jiggled" and the engine would stop and that the ignition key could be removed with the switch in any of its positions. On the pilot/operator report, the pilot listed the carburetor as the malfunction. During the engine run no mechanical discrepancies were found with the carburetor that would have contributed to the loss of engine power. The ignition switch was further examined by the FAA inspector at J & G Aero Carburetors (FAA Approved Repair Station) of Dallas, Texas. Internal contact points of the switch were worn through and the contact plate on the back of the switch was worn and exhibited evidence of arcing.