Surface contamination effects
Aircraft critical surface contamination (ACSC): frost, ice, or snow on a critical surface that can adversely affect aircraft performance (TC AIM GEN 5.1).
Frost on upper wing (TC AIM AIR 2.12.2):
- Roughens smooth surface: cuts lift, raises drag and stall speed, even when thin enough to see through.
- Medium or coarse sandpaper roughness on leading edge and upper surface: lift down up to 30%, drag up 40%. Much of lift loss traces to leading edge.
- Thicker or rougher contamination: stall speed, controllability, drag all worse.
- Affects large aircraft, small aircraft, helicopters alike. Performance and handling change is wide-ranging, unpredictable.
- Roughness as thin as 0.40 mm (1/64 in.) disrupts airflow over lift and control surfaces. Hurts manoeuvrability most on takeoff and initial climb (TP 10643).
- Weight of ice or snow raises lift needed to get airborne (TP 10643).
Where contamination hurts:
| Where | Effect | Cite |
|---|---|---|
| Wing lower surface (frost) | No significant lift effect; can raise drag and cut climb-gradient capability | TC AIM AIR 2.12.2 |
| Clear ice | Can break loose at rotation or in flight; rear-mounted engines can ingest it: engine damage | TC AIM AIR 2.12.2 |
| Slush | Do not assume it flows off on takeoff; remove it; can hide dangerous sheet of ice beneath | TC AIM AIR 2.12.2 / TP 10643 |
| Any other part of aircraft | Adds load; chunks dislodging or refreezing melted precipitation can jam controls | TP 1102 |
Other sources:
- Taxiing: wheels, propellers, other aircraft can throw water, snow, mud onto wings and tail (TP 1102).
- Ice, insects, or fluid residue on sensitive wing designs: stall-risk factor (AC 700-031 s.7.2).
Trap: frost thin enough to see through still cuts lift; 0.40 mm of roughness is enough.
References
- TP 1102 (Flight Training Manual)
- TC AIM AIR 2.12.2
- TP 10643 (When in Doubt... Small and Large Aircraft)
- AC 700-031 s.7.2
- TC AIM GEN 5.1 (ACSC definition)