On January 26, 2001, at 1555 central standard time, a Cessna 152 single-engine airplane, N5295Q, was substantially damaged during a forced landing following a loss of engine power near Lancaster, Texas. The flight instructor and student pilot were not injured. The airplane was registered to Airline Training Academy Inc., (ATA) of Orlando, Florida, and operated by ATA Inc., of Arlington, Texas. Visual meteorological conditions prevailed and a visual flight rules flight plan was filed for the 14 Code of Federal Regulations Part 91 instructional flight. The airplane departed Fort Worth Spinks Airport at 1545, and was destined for Tyler, Texas. The flight instructor stated that approximately five minutes into the cross-county instructional flight, a "slight" drop in engine RPM occurred. The engine gauges were indicating "nominal" engine operation; however, the engine RPM continued to decrease. Subsequently, a "positive indication of power loss [was] noted." The flight instructor executed the engine restart procedures according to the manufacturer's pilot operating handbook, but the engine failed to restart. The flight was unable to reach an alternate airport, and the instructor executed a forced landing to a field. During the touchdown, the nose wheel contacted soft ground, and the airplane nosed over and came to rest inverted. The FAA inspector, who responded to the accident site, stated that the left wing's rear spar was bent, and both wing tanks contained fuel. According to the maintenance logbooks, the airplane received an annual inspection on January 20, 2001, at a tachometer time of 1,413.3 hours. During the annual inspection, the carburetor was removed for additional maintenance. At the time of the accident, the airplane had accumulated 2 hours total time since the annual inspection. On February 22, 2001, NTSB investigators and a Textron Lycoming representative examined the Lycoming O-235-L2C (serial number L-2715-15) engine at Air Salvage of Dallas, Lancaster, Texas. The engine cowling and spark plugs were removed. The bottom spark plug on the #3 cylinder contained a piece of lead, and the plug was unable to produce a spark. Ignition spark was obtained through both magnetos and all ignition leads and spark plugs, excluding the aforementioned bottom #3 spark plug. The ignition timing was tested using an electronic timing indicator, and the engine was timed to 21.5 degrees before top dead center. The propeller was rotated, and continuity was established to the valves and the vacuum pump. Inside the cockpit, the fuel selector, carburetor heat and mixture controls were moved and found operational. When the throttle control was actuated from inside the cockpit, the throttle cable and lever did not actuate the throttle shaft and throttle valve. The castellated lock nut securing the throttle lever to the throttle shaft was found not to be saftied, via a required cotter pin. The lock nut had loosened, allowing the throttle cable and lever to move without movement of the throttle shaft and throttle valve..