FAILURE OF THE PILOT TO MAINTAIN ADEQUATE AIRSPEED ON FINAL APPROACH, WHICH RESULTED IN AN INADVERTENT STALL/SPIN. FACTORS RELATED TO THE ACCIDENT WERE: THE ADVERSE WEATHER (ICING) CONDITIONS, THE ACCUMULATION OF AIRFRAME/WING ICE, THE PILOT'S IMPROPER USE OF THE ANTI-ICE/DEICE EQUIPMENT, INADEQUATE TRAINING OF THE PILOT CONCERNING FLIGHT IN ICING CONDITIONS, AND INADEQUATE SURVEILLANCE OF THE OPERATION BY THE CHIEF PILOT (COMPANY/OPERATOR MANAGEMENT).