On May 7, 1998, at 0706 central daylight time, an Air Tractor AT-402, agricultural airplane, N91660, was substantially damaged after impacting the ground while maneuvering near Forrest City, Arkansas. The non-instrument rated commercial pilot, sole occupant of the airplane, was not injured. The airplane was owned and operated by Hutcherson Flying Service Inc., of Forrest City, Arkansas, under Title 14 CFR Part 137. Visual meteorological conditions prevailed for the aerial application flight for which a flight plan was not filed. The flight originated from the Forrest City Municipal Airport, approximately 22 minutes prior to the accident. The flight departed with 140 gallons of fuel and a full load of liquid herbicide to be dispensed over rice fields in the area. According to the pilot, after completing 6 passes over the field, the drifting chemicals covered the windshield. The pilot stated that he used the airplane's window washer; however, the washer was ineffective in clearing the chemicals from the windshield. On the next pass, while travelling from west to east into the rising sun, the main landing gear of the airplane collided with a rice levee. The pilot added that the propeller was damaged and the landing gear was torn off by the initial impact. The pilot further stated that subsequent to the propeller impact with the levee, the engine lost power and the airplane landed on a vacant field across the road from the field being sprayed, coming to rest in the upright position. During a telephone interview conducted by the NTSB investigator-in-charge, the pilot confirmed that at the time of the accident, the airplane was flying eastbound into the rising sun, and his forward visibility was impaired by the spray on the windshield.