Aeronautics and space. Part25:Airworthiness standards: transport category airplanes. SubpartF:Equipment. Section25.1420:Supercooled large drop icing conditions.
(a) If certification for flight in icing conditions is sought, in addition to the requirements of § 25.1419, an airplane with a maximum takeoff weight less than 60,000 pounds or with reversible flight controls must be capable of operating in accordance with paragraphs (a)(1), (2), or (3), of this section.