Study on Airworthiness Problems of Operating in Supercooled Large Drops Icing Conditions for Transport Category Airplanes

FAA has issued a Notice of Proposed Rulemaking (NPRM) on supercooled large drops (SLD) icing conditions[1]. Based on following up and studying of the newest SLD icing materials, the paper gives a detailed analysis of SLD icing conditions for transport category airplanes airworthiness problems. The proposed Part 25, Appendix O about SLD icing conditions are analyzed and compared with Part 25, Appendix C, including icing clouds extend or range, altitude-temperature envelop, liquid water content (LWC) and drop diameter distribution. The changes of icing envelopes used by IPS design and certification are detailed analyzed. The proposed SLD amendment related regulations are summarized, and the proposed new §25.1420 are deeply analyzed, including the requirements of each subsection, and the requirements of the three SLD icing certification options. Moreover, the certification and compliance of the proposed §25.1420(a) directly referring to the three certification options are discussed, respectively.