On July 27, 1996, at 0800 central daylight time, a Pezetel M-18A airplane, N7643J, was substantially damaged following a loss of control while landing near McGehee, Arkansas. The airplane, owned and operated by Evans Flying Service of McGehee, Arkansas, was being operated under Title 14 CFR part 137. The commercial pilot was not injured. Visual meteorological conditions prevailed for the local aerial application flight for which a flight plan was not filed. The flight originated at the McGehee Municipal Airport at 0730. The pilot reported to the FAA inspector that he experienced a complete brake system failure as he applied the brakes during the landing roll. In telephone interviews with the investigator-in- charge, the pilot stated that "after touchdown on runway 36, he applied brake pressure which momentarily worked and managed to slow down the airplane." The pilot added that as "he reapplied the brakes a second time, he noticed the complete loss of wheel brakes." The pilot further stated that he checked the hydraulic fluid reservoir and the brake system prior to the flight. The flap system, which is also powered by the hydraulic system, was operational prior to the brake failure and subsequent loss of control. The pilot added that after losing the brakes, the "torque took over and [the airplane] ran off the runway." The pilot was not able to maintain directional control and the airplane overran the right side of the runway and came to a stop in a 5 foot ditch. Both wings and the empennage sustained structural damage. The right main landing gear collapsed. According to the operator, the brake failure was the result of the failure of the hydraulic brake system for undetermined reason. At the time of the accident, the airplane had accumulated a total of 748 flight hours since new.