IMPROPER PLANNING/DECISION BY THE PILOT, WHICH RESULTED IN EXCESSIVE ACCUMMULATION OF STRUCTURAL ICING (ON THE AIRCRAFT'S WINGS, STABILIZERS, FUSELAGE, AND/OR ENGINE INLETS), AND HIS FAILURE TO MAINTAIN ADEQUATE AIRSPEED AND AIRCRAFT CONTROL. FACTORS RELATED TO THE ACCIDENT WERE: THE PILOT'S INADEQUATE WEATHER EVALUATION DUE TO LACK OF AVAILABLE INFORMATION AT THE AUTOMATED FLIGHT SERVICE STATION (AFSS), HIS FAILURE TO OBTAIN ADDITIONAL INFORMATION FROM OTHER WEATHER STATIONS (EITHER BEFORE TAKEOFF OR DURING THE FLIGHT), HIS LACK OF EXPERIENCE IN THIS MAKE AND MODEL OF AIRCRAFT, AND ICING CONDITIONS AT CRUISE ALTITUDE.