{"data":{"id":"us/14-cfr-appendix-d-to-part-33","jurisdiction":"us","citation":"14 CFR Appendix D to Part 33","heading":"Appendix D to Part 33—Mixed Phase and Ice Crystal Icing Envelope (Deep Convective Clouds)","body":"The ice crystal icing envelope is depicted in Figure D1 of this Appendix.\nWithin the envelope, total water content (TWC) in g/m 3 has been determined based upon the adiabatic lapse defined by the convective rise of 90% relative humidity air from sea level to higher altitudes and scaled by a factor of 0.65 to a standard cloud length of 17.4 nautical miles. Figure D2 of this Appendix displays TWC for this distance over a range of ambient temperature within the boundaries of the ice crystal envelope specified in Figure D1 of this Appendix.\nIce crystal size median mass dimension (MMD) range is 50-200 microns (equivalent spherical size) based upon measurements near convective storm cores.\nThe TWC can be treated as completely glaciated (ice crystal) except as noted in the Table 1 of this Appendix.\nTable 1—Supercooled Liquid Portion of TWC\nTemperature range—deg C Horizontal cloud length—nautical miles LWC— g/m3\n0 to −20 ≤50 ≤1.0\n0 to −20 Indefinite ≤0.5\n\u003c −20 0\nThe TWC levels displayed in Figure D2 of this Appendix represent TWC values for a standard exposure distance (horizontal cloud length) of 17.4 nautical miles that must be adjusted with length of icing exposure.","path":["Title 14—Aeronautics and Space","CHAPTER I—FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION","SUBCHAPTER C—AIRCRAFT","PART 33—AIRWORTHINESS STANDARDS: AIRCRAFT ENGINES"],"source_url":"https://www.ecfr.gov/api/versioner/v1/full/2026-08-25/title-14.xml","current_through":"2026-08-25","vintage":"","retrieved_at":"2026-08-27T02:24:20Z","sha256":"b6c3ddb62ef753728c39b18ed9ab429d7fe61dedb56fe209a7fd1b1c1d578ebd","source_id":"us-cfr","stale":true,"prev":"us/14-cfr-appendix-c-to-part-33","next":"us/14-cfr-34.1"},"notice":"GroundRules: Original legal text. Not legal advice."}