On May 21, 1998, about 2200 eastern daylight time, a North American T-28B, N944RJ, registered to Tyler Aviation, Inc., was substantially damaged during landing at the Spartanburg Downtown Memorial Airport, Spartanburg, South Carolina. Visual meteorological conditions prevailed at the time and no flight plan was filed for the 14 CFR Part 91 positioning flight. The commercial-rated pilot, the sole occupant, was not injured. The flight originated from the Greenville Downtown Airport, Greenville, South Carolina, about 2145. The pilot stated that the purpose of the flight was for his night currency. Before departure, he was advised by the Anderson Flight Service Station that the only thunderstorm activity was located east of Spartanburg, his planned destination; the thunderstorm was dissipating. While taxiing to takeoff, the controller advised him that the thunderstorm appeared to be over the destination airport, but it was beyond the radar coverage area. The pilot elected to depart and while in contact with Greer Approach Control, he was advised that the thunderstorm was over the airport. He changed to the UNICOM frequency for verification and was advised of the wind direction and velocity and, "...there was just light rain [sic] coming down [sic] altho there was much [sic] lightening and thunder in the [sic] vacinity." He activated the runway lights using the UNICOM frequency, had good visibility, then switched back to Greer Approach Control. He advised the controller that based on the information given to him by the person monitoring the UNICOM, and with the airport in sight, he was inbound to land. As he switched back to the UNICOM frequency, "...it started raining much harder..."; however, he had the airport in sight and elected to continue. The airplane was landed in the first 1/4 of the runway that was covered with water and, "I let the aircraft coast for a little so as to slow down before [sic] breaking action was initiated however the aircraft would not slow down as usual. I commenced [sic] breaking action at about the half way point but I could feel the tires slipping [sic] haveing very little effect on speed reduction." He also reported deploying the speed brake with little effect. The airplane traveled off the end of the runway, down an embankment, and collided with a guard rail. Postcrash examination of the runway and accident site by a FAA airworthiness inspector revealed that white deposits were noted on the runway beginning about 1,000 feet before the departure end, and continued to the end. The airplane rolled onto a grass overrun traveling 158 feet, descended, impacted onto a road, then a guard rail, coming to rest about 196 feet from the departure end of the runway. The brakes were examined and found to operative with no evidence of preimpact failure or malfunction. Braking action was evident in the grass beyond the departure end of the runway. Review of the landing distances chart for the airplane revealed that based on the temperature and airplane weight, the ground roll distance was calculated to be about 1,420 feet. The chart is for predicated on full flaps extended, and a hard surface runway. A correction for wet runway surface is not included. According to the Executive Director of the South Carolina Organ Procurement Agency, Inc., (S.C.O.P.A.), her agency had arranged with Tyler Aviation, Inc., to fly tissue on the evening of the accident from Spartanburg, to Charleston, South Carolina. Review of a certified re-recording of the weather briefing revealed that about 2011 local, on the day of the accident, a person who identified himself as Toby Tyler with the accident airplane registration, contacted the Anderson Automated Flight Service Station (AFSS). He stated that the airplane was at the Greenville Downtown Airport, flying to Charleston in a couple of hours. The pilot was advised of a severe thunderstorm watch covering the whole state of South Carolina, and, "the only thing I see so far is one thunderstorm east of Greer, moving east, and looks like uh its deteriorating...." Review of a South Carolina Aeronautical Chart revealed that the eastern edge of the city of Greer as depicted, is located about 12 nautical miles west of the center of the Spartanburg Downtown Memorial Airport. According to an employee from a fixed base operator who was working on the night of the accident, he received a phone call about 2100 hours from Lifeguard Flights advising him that an airplane would be landing about 2200 to pick up tissue from an ambulance. At about 2140, the pilot called on the UNICOM frequency for an airport advisory and he advised the pilot that it was raining and the wind was from 035-042 degrees at 10 knots. At about 2150, he observed the lights from the airplane approaching runway 5 and noted that the rainfall had increased considerably as the approach was being made. He did not see the airplane land, but he went outside to wait for the airplane to taxi to the ramp. He was then advised by phone that the airplane had crashed and drove to the crashsite where he was advised that the pilot was alright. He then drove back to the office and when he arrived, the ambulance was already there. He advised the ambulance personnel that the airplane had crashed and noted that they were concerned about the status of the tissue.