Inviting comments, the FAA has published a draft of its proposed revision and consolidation of two previous pilot guides to flight in icing conditions. The draft, in the form of Advisory Circular 91.74B, contains essential information concerning safe flight in icing conditions, what conditions should be avoided and information about how to avoid or exit those conditions.
As a result of these updates, AC 91-74A, "Pilot Guide: Flight in Icing Conditions," dated Dec. 31, 2007, and AC 91-51A, "Effect of Icing on Aircraft Control and Airplane Deice and Anti-Ice Systems," dated July 19, 1996, are cancelled. Although intended as a guide, the FAA notes the term “must” used in AC 91.47B means regulatory requirements and the term “should” reflects FAA recommendations.
Virtually every section of the 60-page document contains new or revised material, including an appendix entitled "Icing Checklist," changes to the list of definitions, an explanation of supercooled liquid droplets and additional illustrations. The circular is directed to pilots operating under Parts 91, 121, 125 and 135. Comments are due July 23.