On July 18, 2015, at 2125 eastern daylight time, a Grumman American AA-1B, N8969L, was substantially damaged during a forced landing after a partial loss of engine power in Lititz, Pennsylvania. The flight instructor and a passenger, who was a student pilot were not injured. Night visual meteorological conditions prevailed and no flight plan was filed. The local personal flight was operating in the traffic pattern at Lancaster Airport (LNS), Lancaster, Pennsylvania, and was conducted under the provisions of 14 Code of Federal Regulations Part 91.According to the flight instructor, the airplane had not been flown in a while, and the purpose of the flight was to "take it around the airport pattern for a few landings." He and the student pilot had just completed a flying lesson in another airplane, and he invited the student to fly with him on the accident flight. Prior to the flight, the airplane's battery required a jump-start to start the engine, after which the flight instructor ran the engine for 20 minutes to charge the battery. He shut down the engine, restarted it successfully, and then repositioned the airplane to add 13 gallons of non-ethanol automotive fuel, and estimated the total fuel quantity on board was 16 gallons. Prior to takeoff, he performed a preflight inspection and engine run-up with no issues noted. The flight departed runway 31, remained in the traffic pattern, and performed two touch-and-go landings. On the third and final circuit in the traffic pattern, while on the downwind leg, the pilot reduced the engine power and selected 15° of flaps to initiate a descent to the runway. When the airplane was on the base leg of the traffic pattern, the engine experienced a partial loss of power. The pilot raised the flaps, increased the mixture to rich, and switched the fuel selector in an attempt to restart the engine. He then elected to perform a forced landing and turned toward a cornfield. After landing in the cornfield, during the landing roll, the airplane nosed over and came to rest inverted. Examination of the wreckage by a Federal Aviation Administration (FAA) inspector revealed that the outboard section of the right wing leading edge, fuselage nose section, and rudder were substantially damaged. Flight control continuity was confirmed from the cockpit controls to the control surfaces. The throttle, mixture, and carburetor heat controls were found in the full forward position, and remained connected to their respective locations on the engine. The inspector was unable to examine the fuel tanks for fuel quantity due to the airplane's inverted orientation. Crop damage leading up to the wreckage was about 90 feet long and oriented east-northeast. A subsequent examination of the engine by an FAA inspector revealed that all four cylinders exhibited thumb compression and both magnetos produced spark on all towers. Crankshaft and valvetrain continuity were established by manual rotation of the propeller. The top spark plugs were removed, the electrodes were intact, grey in color, and a small amount of oil was present on the No. 1 electrode. The wings had previously been removed, which precluded inspection of the fuel tanks. According to the airplane maintenance records, it had accrued about 2 hours of operation between November 2012 and March 2014, 1 hour of operation between March 2014 and March 2015, and 0.6 hour between March 2015 and the time of the accident, including the accident flight. The most recent annual inspection was performed on March 20, 2015. At that time, the engine had accrued a total of 3,011 hours, with 1,079 hours since overhaul. The pilot held commercial and flight instructor certificates with ratings for airplane single-engine land and instrument airplane. According to his logbook, he had accrued a total of 320 flight hours, and he reported 2 hours of flight experience in the same make and model as the accident airplane. His most recent first class medical certificate was issued on July 16, 2015. The recorded weather at LNS, at 2153, reported wind from 050° at 5 knots; visibility 10 statute miles; few clouds at 11,000 ft above ground level; temperature 23° C; dew point 22° C; and an altimeter setting of 29.92 inches of mercury. The carburetor icing probability chart from Federal Aviation Administration (FAA) Special Airworthiness Information Bulletin (SAIB): CE-09-35 Carburetor Icing Prevention, June 30, 2009, indicated a probability of serious icing at glide power at the temperature and dew point reported at the time of the accident. The pilot did not mention if he utilized the application of carburetor heat during the accident sequence.