On April 21, 1997, at 1200 central daylight time (cdt), a Cessna 421C, N283PT, registered to Prostrollo Leasing Company, of Madison, South Dakota, received substantially damaged after impacting a chain link fence and a parked vehicle at Pierre Municipal Airport, Pierre, South Dakota. The pilot's left foot struck and advanced the number one engine throttle of the running engines, while the pilot went aft to close the cabin door after discharging a passenger. The airline transport pilot reported no injuries. The 14 CFR Part 91 flight was operating in visual meteorological conditions. An IFR flight plan was on file. The flight departed Madison, South Dakota, at 1055 cdt. According to the pilot's written statement, he was discharging a passenger with the engines running on the wet ramp area at Pierre Municipal Airport. The pilot set the brakes and then needed to go aft and shut the cabin door. The pilot said "In turning to egress the cockpit, I believe my left foot hit the left throttle #1 eng [engine] went to takeoff power. I was thrown between the two forward passenger seats on my back stunned the aircraft lunged forward struck a fence turning to the right, the right eng [engine] struck a vehicle parked on the ramp side of the fence."