THE PILOT'S FAILURE TO ENSURE THAT ICE WAS PROPERLY REMOVED FROM THE AIRPLANE BEFORE FLIGHT, POSSIBLY DUE TO IMPAIRMENT OF JUDGMENT CAUSED BY A PRESCRIPTION DRUG (VALIUM) THAT WAS NOT APPROVED FOR USE WHILE FLYING. FACTORS RELATED TO THE ACCIDENT WERE: THE PILOT'S FAILURE TO PROPERLY REPORT HIS MEDICAL HISTORY ON HIS FAA MEDICAL APPLICATION, AND FAILURE OF THE DESIGNATED MEDICAL EXAMINER TO REPORT THE PILOT'S KNOWN MEDICAL HISTORY.