HISTORY OF FLIGHT On March 24, 2010, about 1115 eastern daylight time, a Cessna 152, N93441, was substantially damaged during a forced landing in a field following partial loss of engine power, near Moore, South Carolina. The certificated flight instructor (CFI) and student pilot were not injured. Visual meteorological conditions prevailed, and no flight plan was filed for the local instructional flight which departed from Spartanburg Downtown Memorial Airport (SPA), Spartanburg, South Carolina, about 1045. The flight was conducted under the provisions of Title 14 Code of Federal Regulations Part 91. The pilots had been performing maneuvers at 3,000 feet above mean sea level (msl) and had began a descent to 2,500 feet msl utilizing carburetor heat for the engine. In a written statement the student pilot reported that after performing several maneuvers including slow flight and three approach to landing stalls the engine began making unusual noises and minor vibrations. The engine began running "rough" and the CFI elected to perform a forced landing in an open farm field. On final approach to the field the CFI had shut off the fuel valve; however, did not shut off the engine in case a little "extra" power was needed at touchdown. During the landing roll the nose wheel encountered soft soil and the airplane nosed over and came to rest inverted. The airplane incurred substantial damage to both wings and the empennage. PERSONNEL INFORMATION According to the pilot and Federal Aviation Administration (FAA) and records, the CFI held a commercial pilot certificate with ratings for airplane single-engine land, multi-engine land, and instrument airplane, and a flight instructor certificate with ratings for single-engine and instrument airplane. Her most recent FAA second-class medical certificate was issued on April 1, 2008, at which time the pilot reported 25,000 total hours of flight experience. According to the student pilot and FAA records, the student pilot was issued her third-class medical certificate on October 12, 2009 which also served as her student pilot certificate. She had accumulated 35 total hours of flight experience all of which were in the accident aircraft make and model. AIRCRAFT INFORMATION The airplane was a Cessna 152, manufactured in 1982. It was equipped with a Lycoming O-235-L2C engine. It was two-place, all-metal, high-wing, single-engine, cantilever monoplane with fixed tricycle landing gear. The airplane's most recent 100-hour inspection was accomplished on January 21, 2010 and at that time had 6,337.4 total hours time in service. An entry in the maintenance logbook dated March 20, 2010 revealed a sparkplug in the No. 4 cylinder bottom position was "fouled out" and the "helicoil in sparkplug hole bad." The helicoil was replaced, a sparkplug was installed and torqued, and the engine was run and flight tested, and were reported as "Ok." METEOROLOGICAL INFORMATION The 1115 recorded weather observation at SPA, located approximately 5 miles northeast of the accident site, included winds from 030 degrees at 6 knots, clear skies, 10 miles visibility, temperature 18 degrees C, dew point 11 degrees C, and an altimeter setting of 30.10 inches of mercury. WRECKAGE AND IMPACT INFORMATION The airplane was located in an open plowed field, inverted, and approximately 5 miles from the intended destination airport. The wings, fuselage, and tail section were impact damaged. According the FAA investigator that arrived on-scene the airplane was up righted and a considerable amount of fuel was drained from the wing tanks and no contaminants were found. The engine cowling was removed and the No. 4 cylinder bottom sparkplug and helicoil had become unthreaded from the cylinder and was found hanging next to the engine suspended from the sparkplug wire. On March 25, 2010 the FAA inspector reported to the Safety Board that a new sparkplug was inserted into the cylinder and the engine started and "ran normally." ADDITIONAL INFORMATION In a written statement the mechanic reported that he had replaced the helicoil on the No. 4 Cylinder since it "came out with the plug." He stated that "it [helicoil] had been cross threaded and the plug was completely fouled." He further reported that the CFI had stated that the engine began to run rough after the student pilot "jammed the throttle" to the full power setting. In a telephone interview with the NTSB investigator the mechanic stated that they use "a standard size heli-coil." In a follow-up telephone interview with the CFI it was confirmed that the student pilot was told several times to apply power slowly. However, the student pilot "got nervous after practicing power off stalls" and did apply power very quickly. Immediately after that, the engine began to run rough. According to Textron-Lycoming Service Instruction 1043A dated September 19, 1969, "Spark Plug Heli-Coil Insert Replacement" states in part "…standard size inserts have been found in holes with badly damaged threads that had not been repaired by retapping…does not recommend standard size Heli-Coil Inserts for replacement in the spark plug holes…repair facilities are urged to stock only .010 oversize Heli-Coil spark plug inserts…"