On October 10, 1996, about 0845 Pacific daylight time, a Piper PA-36-300, N2331Y, crashed in hills south of Prosser, Washington. The airplane was being operated under visual flight rules (VFR) as a local area aerial application flight when the accident occurred. The airplane, operated by Aircraft Applications Inc., sustained substantial damage. The certificated commercial pilot, the sole occupant, was fatally injured. Visual meteorological conditions prevailed. The accident occurred on the second flight of the day. The first flight had departed the airport at 0730. After the first flight, the pilot reported that he had encountered a lot of turbulence between the departure runway and the hill where the accident eventually took place. However, he said that the wind was calm at the orchard site where the spraying was taking place, so 150 gallons of "Stop Drop", a hormone type product for control of preharvest drop of apples, was loaded onto the airplane. The pilot also added twenty gallons of fuel to give a total of 75 gallons of fuel on board. The airplane departed the Prosser airport at 0835 in a westerly direction for several miles before turning south towards the hills which were between the airport and the orchard. Three witnesses who saw the airplane and heard the engine running, varied in their description of the engine noise from "popping" to "...running strong and all at once the sound stopped...". FAA inspectors responded to the scene of the accident and documented the wreckage. A copy of this documentation is attached to this report. On October 25, 1996, an engine examination was accomplished at the Prosser airport under FAA supervision. No evidence of pre-impact failure was found. A copy of the engine examination is attached to this report. An autopsy was performed on the pilot by Benton County. Cause of death was listed as "massive trauma to the head, neck and chest." Toxicological testing performed by the Civil Aero Medical Institute in Oklahoma City, Oklahoma resulted in negative findings for alcohol and drugs except for acetaminophen.