U.S. Department Advisory of Transportation Federal Aviation Administration Circular Subject: Pilot Guide: Flight in Icing Conditions Date:10/8/15 AC No: 91-74B Initiated by: AFS-800 Change: This advisory circular (AC) contains updated and additional information for the pilots of airplanes under Title 14 of the Code of Federal Regulations (14 CFR) parts 91, 121, 125, and 135. The purpose of this AC is to provide pilots with a convenient reference guide on the principal factors related to flight in icing conditions and the location of additional information in related publications. As a result of these updates and consolidating of information, AC 91-74A, Pilot Guide: Flight in Icing Conditions, dated December 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. This AC does not authorize deviations from established company procedures or regulatory requirements. John Barbagallo Deputy Director, Flight Standards Service 10/8/15 AC 91-74B CONTENTS Paragraph Page CHAPTER 1. INTRODUCTION 1-1. Purpose ..............................................................................................................................1 1-2. Cancellation ......................................................................................................................1 1-3. Definitions.........................................................................................................................1 1-4. Discussion .........................................................................................................................6 CHAPTER 2. ATMOSPHERIC CONDITIONS ASSOCIATED WITH ICING 2-1. Aircraft Icing Conditions ..................................................................................................9 2-2. Cloud Types and Aircraft Icing ......................................................................................10 2-3. Fronts ..............................................................................................................................12 2-4. Convective Weather and Ice Crystals .............................................................................14 CHAPTER 3. ICING EFFECTS, PROTECTION, AND DETECTION 3-1. Forms of Icing .................................................................................................................15 3-2. General Effects of Icing on Airfoils ................................................................................17 3-3. Effects of Icing on Unprotected Wings ..........................................................................19 3-4. Deicing Systems..............................................................................................................19 3-5. Anti-Icing Systems..........................................................................................................21 3-6. Effects of Icing on Roll Control......................................................................................22 3-7. Tailplane Icing ................................................................................................................22 3-8. Propeller Icing .................................................................................................................23 3-9. Antenna Icing ..................................................................................................................24 3-10. Cooling Inlet Icing ..........................................................................................................24 3-11. Effects of Icing on Critical Systems ...............................................................................24 3-12. Certification for Flight in Icing Conditions ....................................................................26 3-13. Airplanes Not Certificated for Icing ...............................................................................28 3-14. Maintenance Considerations ...........................................................................................28 3-15. Ice Detection ...................................................................................................................29 3-16. Visual Cues of SLD Conditions ......................................................................................30 CHAPTER 4. FLIGHT PLANNING 4-1. Preflight Planning Information .......................................................................................33 4-2. Icing Intensity .................................................................................................................35 4-3. PIREP Cautions ..............................................................................................................36 CHAPTER 5. ICING OPERATIONS 5-1. General ............................................................................................................................39 5-2. Regulations for Icing Operations ....................................................................................39 5-3. Available In-Flight Information ......................................................................................40 5-4. Preflight...........................................................................................................................41 Page iii 10/8/15 AC 91-74B 5-5. Taxi .................................................................................................................................43 5-6. Takeoff and Climbout .....................................................................................................43 5-7. Cruise ..............................................................................................................................44 5-8. Descent ............................................................................................................................46 5-9. Holding ...........................................................................................................................46 5-10. Approach and Landing ....................................................................................................46 5-11. Wing Stall .......................................................................................................................48 5-12. ICTS ................................................................................................................................48 5-13. Roll Upsets ......................................................................................................................49 CHAPTER 6. SUMMARY 6-1. General ............................................................................................................................51 6-2. Avoidance .......................................................................................................................51 6-3. Vigilance .........................................................................................................................51 6-4. Guidance .........................................................................................................................51 APPENDIX 1. RECOMMENDED READING (2 pages) ...........................................................1 APPENDIX 2. ICING CHECKLISTS (6 pages) .........................................................................1 LIST OF FIGURES Figure 2-1. Warm Front ...............................................................................................................13 Figure 2-2. Cold Front .................................................................................................................13 Figure 3-1. Clear Ice ....................................................................................................................15 Figure 3-2. Clear Ice Buildup with Horns ...................................................................................15 Figure 3-3. Rime Ice ....................................................................................................................16 Figure 3-4. Mixed Ice ..................................................................................................................16 Figure 3-5. Lift Curve ..................................................................................................................18 Figure 3-6. Drag Curve ................................................................................................................18 Figure 3-7. Wing Boot .................................................................................................................19 Figure 3-8. Tail Down Moment ...................................................................................................23 Figure 3-9. Pitchover Due to Tail Stall .......................................................................................23 Figure 3-10. Propellor Ice Accretion During an SLD Encounter ..................................................24 Page iv 10/8/15 AC 91-74B CHAPTER 1. INTRODUCTION 1-1. PURPOSE. This advisory circular (AC) updates the previous version and contains essential information concerning safe flight in icing conditions, what conditions a pilot should avoid, and how to avoid or exit those conditions if encountered. The information provided is relevant to fixed-wing aircraft, including those operating under Title 14 of the Code of Federal Regulations (14 CFR) parts 91, 121, 125, and 135. The general guidance provided here in no way substitutes for aircraft-type-specific information in a particular Airplane