On May 14, 1996, at 0945 eastern daylight time, a Grumman-Schweizer G164A-600, N6620Q, operated by Downtown Airport Inc., was substantially damaged during a forced landing after takeoff from the Vineland-Downtown Airport, Vineland, New Jersey. The commercial pilot was not injured. Visual meteorological conditions prevailed for the agriculture application flight that originated at the Vineland-Downtown Airport (28N). No flight plan had been filed for the flight conducted under 14 CFR Part 137. The pilot and airplane had flown 3 to 4 hours of application flights prior to the accident takeoff. The airplane was loaded with a chemical pesticide, and departed runway 20. In the NTSB Form 6120.1/2, the pilot stated that he departed 28N for an application flight. He further stated: "...Immediately after liftoff the engine began missing, smoking and backfiring violently. Not...able to maintain sufficient airspeed, I dropped the load (207 gallons of pesticide) and landed straight ahead in a freshly plowed field. The main gear sunk into the topsoil, and the aircraft nosed over..." Examination of the engine by a Federal Aviation Administration Inspector revealed: "...The #8 cylinder head was cracked open from the forward spark plug boss over the top of the head to the rear spark plug boss, and progressed down to the steel cylinder barrel. No other contributing causes could be substantiated during this investigation..."