14 C.F.R. § 33 app D to Part 33
The ice crystal icing envelope is depicted in Figure D1 of this Appendix.
Within the envelope, total water content (TWC) in g/m3 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.
Ice crystal size median mass dimension (MMD) range is 50-200 microns (equivalent spherical size) based upon measurements near convective storm cores.
The TWC can be treated as completely glaciated (ice crystal) except as noted in the Table 1 of this Appendix.
Table 1-Supercooled Liquid Portion of TWC
| Temperature range-deg C | Horizontal cloud length-nautical miles | LWC- g/m3 |
| 0 to -20 | [LESS THAN EQUAL TO]50 | [LESS THAN EQUAL TO]1.0 |
| 0 to -20 | Indefinite | [LESS THAN EQUAL TO]0.5 |
| [LESS THAN] -20 | 0 |
The 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.
14 C.F.R. § 33 app D to Part 33