FLT WAS CLRD FOR ILS APCH. ABOUT 10 MI FROM RWY PLT REPORTED HIS GLIDESLOPE WAS NOT WORKING. FLT WAS THEN CLEARED FOR ASR RADAR APCH. AT 1.5 MILES FROM RWY FLT WAS LOST FROM RADAR. WITNESSES REPORTED ACFT FLEW OVERHEAD AT TREE TOP LEVEL WITHOUT THE ENG RUNNING. ACFT HIT TREES AND THEN CRASHED INTO GND INVERTED. PROPELLER HAD NO ROTATION DAMAGE. NO EVIDENCE TO INDICATE PRECRASH MALFUNCTION OF ENGINE WAS NOTED. THE MIXTURE CONTROL WAS IN THE CRUISE LEAN POSITION AND THE CARBURETOR HEAT WAS IN THE COLD POSITION. NO INST APCH PLATES WERE FOUND OPEN IN THE COCKPIT. THE FLT WAS OPERATING IN CONDITIONS WHICH WOULD CAUSE VISIBLE CARB ICE AT CRUISE POWER AND SERIOUS CARB ICE AT GLIDE POWER. POST MORTEM EXAMINATION OF THE PLT INDICATED HE SUFFERED FROM MILD CEREBRAL ATROPHY AND HYPERTENSIVE ARTERIOSCLEROTIC HEART DISEASE. THE PLT WAS PRESCRIBED HYPERTENSIVE MEDICATION BUT WAS NOT TAKING IT AT THE TIME OF THE ACCIDENT.