47-51-12 DOUGLAS: Applies to All converted C-47 Series Aircraft With Ram Non-ram (Hydraulic) Type Carburetor Airscoop. \n\nTo be accomplished not later than March 1, 1948. \n\nCompliance with the following items is necessary to preclude carburetor icing: \n\n1.\tThe carburetor alcohol system must be used. \n\n2.\tThe accessory cowling and engine fire seal must maintain not more than 1/4-inch clearance of the collector ring. \n\n3.\tThe cable system for operation of the hot air door must be rigged to 30 pounds tension. \n\n(Part B of Douglas Service Bulletin DC-3 No. 251 dated April 15, 1947, covers this same subject. Part A of the same Bulletin is not mandatory, but optional compliance may be accomplished when parts are available.)