AI.III.C.K3kFAA-S-ACS-25 · Nov 2023Knowledge
k. Frost
Meteorology applicable to the departure, en route, alternate, and destination under visual flight rules (VFR) in Visual Meteorological Conditions (VMC), including expected climate and hazardous conditions such as: k. Frost
Bottom line
Frost is a crystallized deposit formed from water vapor on surfaces at or below 0 degrees C (32 degrees F). Frost disrupts the flow of air over the wing and can drastically reduce lift production while increasing drag. An aircraft must be thoroughly cleaned and free of frost prior to beginning a flight.
Key numbers
| Number | What it means |
|---|---|
| 30 percent lift reduction from frost, snow, or ice no thicker or rougher than coarse sandpaper on the leading edge or upper wing surface | Lift loss |
| up to 40 percent drag increase from the same thin accumulation | Drag increase |
| 80 percent or more drag increase from larger accretions | Heavy accretions |
| 110 knots rotation speed for Type II and IV fluids | Fluid speed limit |
| within five minutes prior to beginning takeoff | Contamination check |
FAA references
- AC 135-17 — AC 135-17
- PHAK ch. 12 (p. 12-15) — FAA-H-8083-25C (2023)
- AWH ch. 20 (p. 20-7) — FAA-H-8083-28A
- AC 91-74, para. 7-1 — AC No: 91-74A
- AWH ch. 21 (p. 21-5) — FAA-H-8083-28A
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