AA.I.C.K3kFAA-S-ACS-11A · Nov 2023Knowledge
k. Frost
Meteorology applicable to the departure, en route, alternate, and destination for flights conducted under Instrument Flight Rules (IFR) to include expected climate and hazardous conditions such as: k. Frost
Bottom line
Frost, including hoar frost, is a crystallized deposit formed from water vapor on surfaces at or below 0 degrees C (32 degrees F). Frost, snow, or ice accumulations on the leading edge or upper wing surface no thicker or rougher than coarse sandpaper can reduce lift by 30 percent and increase drag up to 40 percent. Underwing frost formations generally do not influence aircraft performance and flight characteristics as severely as leading edge and upper wing frost.
Key numbers
| Number | What it means |
|---|---|
| 30 percent lift reduction from frost, snow, or ice on the leading edge or upper wing surface no thicker or rougher than coarse sandpaper | Lift loss |
| 80 percent or more drag increase from larger accretions | Large accretions |
| 110 knots minimum rotation speed for Type II and IV anti-icing fluids | Fluid rotation speed |
| within five minutes prior to beginning takeoff | Contamination check |
FAA references
- PHAK ch. 12 (p. 12-15) — FAA-H-8083-25C (2023)
- AC 91-74, para. 7-1 — AC No: 91-74A
- AWH ch. 20 (p. 20-7) — FAA-H-8083-28A
- AC 135-17 — AC 135-17
- AWH ch. 21 (p. 21-5) — FAA-H-8083-28A
- AC 91-74 Appendix 2 — AC No: 91-74A
Build understanding you can use
Unlock the full lesson and continue studying this element.
- Full teaching sections: What it is; Key points; Rules and numbers; How it is done
- Check your understanding with answers you can reveal
- Common mistakes paired with the FAA facts that correct them