HISTORY OF FLIGHT: On October 10, 1993, at 1537 central daylight time, a Piper PA-36-285, N57577, was destroyed near Estelline, Texas, when it impacted vehicles during an aerial application maneuver. The private pilot sustained fatal injuries. Visual meteorological conditions prevailed throughout the area for the local aerial application flight. According to the cotton gin manager, the pilot ground surveyed the field that morning. They had discussed utilizing 175 gallons of paraquat dichloride for defoliation of cotton. The operator stated the cotton field was owned by a "CO-OP," of which the pilot was a member. Witnesses reported the following information during personnel interviews. One swath run was completed and during the turn around maneuver, the airplane was observed approaching the cotton field from the southeast. Witnesses reported the winds from the south/southeast at 5 to 10 mph and a Farenheit temperature of 70 degrees. They further said that numerous downdrafts occurred in the vicinity of the cotton gin obstructions. The airplane was observed descending and banking to the left and right when the wing struck a cotton trailer and two trucks parked at the gin. The airplane came to rest on the second truck. A post impact fire occurred. As the pilot released the emergency exit door, he fell to the ground; however, the chemical poured from the hopper and saturated his body prior to being rescued. WRECKAGE AND IMPACT INFORMATION: The airplane came to rest on a measured magnetic heading of 135 degrees (see enclosed diagram for details) on the bed of the cotton truck. The fuselage and left wing was in an inverted position. The engine was on the ground. An outboard section of the left wing and the leading edge showed crushing and buckling. The right wing flap came to rest beyond the truck. The remainder of the airframe was destroyed by the fire. Flight control continuity was shown by an examination of the flight control cables. One propeller blade was twisted and curled with gouges near the tip. The second propeller blade was curled forward with the blade tip bent aft. MEDICAL AND PATHOLOGICAL INFORMATION: An autopsy was performed at the University Medical Center, Lubbock, Texas. Chemical burns and paraquat dichloride toxicity were reported as the cause of death. According to the enclosed Regional Flight Surgeon's report, there were no traumatic injuries suffered during the impact sequence. TEST AND RESEARCH On December 12, 1993, the engine was disassembled and examined (see enclosed report) at Mobile, Alabama. Inspected components exhibited operational signatures and fire damage. There were no anomalies that would have contributed to a power loss. ADDITIONAL INFORMATION: The airplane was released to the owner's estate following the investigation.