THE PILOT'S FAILURE TO PROPERLY USE CARBURETOR HEAT, THE FORMATION OF CARBURETOR ICE, AND FAILURE OF THE PILOT TO MAINTAIN ROTOR RPM AFTER LOSS OF ENGINE POWER, WHICH RESULTED IN A LOSS OF CONTROL AND COLLISION WITH TERRAIN. A FACTOR RELATED TO THE ACCIDENT WAS: THE WEATHER CONDITION, WHICH WAS CONDUCIVE TO CARBURETOR ICING.