On August 16, 2001, about 1615 central daylight time, a Grumman-Schweizer G-164A, piloted by a commercial pilot, sustained substantial damage during a forced landing following a loss of engine power during an aerial-application flight near Petersburg, Nebraska. The 14 CFR Part 137 flight was operating in visual meteorological conditions and was not on a flight plan. The pilot, who was the sole occupant, was not injured. The local flight originated from the Antelope County Airport, Neligh, Nebraska, about 1515. The pilot reported, "While spraying at 6 [feet] AGL the engine began running rough and quit. I made an emergency landing in a muddy soybean field, sliding to a stop damaging the right lower wing and right landing gear." A postaccident examination of the airplane revealed that the number 8 cylinder head had separated from the cylinder barrel between the second and third cooling fins. This condition is identified in Pratt and Whitney Airworthiness Directive (AD) 78-08-07. The AD requires a recurring visual inspection of the cylinder at 150 hour or 100 hour intervals. Cylinders that had been ultrasonically tested prior to installation on the engine were to be inspected at 150 hour intervals. Cylinders that had not been ultrasonically tested prior to installation on the engine were to be inspected at 100 hour intervals . According to the aircraft maintenance records, the airplane had accumulated 99.8 hours time in service since the inspection was last performed. It is not known if the failed cylinder had been ultrasonically inspected.