The airplane was substantially damaged after impacting Lake Russell at about 2223 Eastern time. The non-instrument-rated private pilot and three passengers were fatally injured. Instrument conditions prevailed. After the flight took off and at about 2222, ATC issued an on-course clearance. This clearance was acknowledged by the pilot, and was the last transmission received from the airplane. Radar tracking data indicate the airplane made a slight left turn for an on-course heading then made a right turn of approximately 100 degrees. Radar data showed the airplane at an altitude of 2400 feet msl at 2223. Approximately 12 seconds after the 2400-foot radar return, another radar return showed an altitude of 0 feet. The wreckage was located in Lake Russell in about six-foot-deep water. Recovery divers estimated the engine was embedded approximately four feet into the floor of the lake.