Deicing and anti-icing fluid types
Two jobs:
- De-ice: remove contamination already on the surface.
- Anti-ice: stop new contamination forming before takeoff.
FPD (freezing point depressant) fluid lowers the freezing point of water in liquid or crystal (ice) phase (TP 10643 para 23).
Four SAE/ISO types (TC AIM AIR 2.12.2):
| Type | Thickness | Glycol / freeze point | Job | Holdover | Colour | Built for |
|---|---|---|---|---|---|---|
| I | Unthickened (thin, low viscosity) | Min 80% glycol as concentrate; applied heated | De-ices (melts existing); very limited anti-icing | Shortest of four | Orange | - |
| II | Thickened | Min 50% glycol; min freeze point -32 C | Anti-ices (stays on wing); also de-ices when heated | Longer than I | Clear or pale straw | Vr above 100 KIAS |
| III | Thickened, properties between I and II | - | - | Longer than I, shorter than II | - | Vr below 100 KIAS |
| IV | Same spec as II | Same as II | - | Significantly longer than II | Emerald green | Vr above 100 KIAS |
Vr = rotation speed.
- Type II: needs shear of a fast takeoff run to thin out and flow off.
- Type IV:
- Green: layer consistent, not mistaken for ice.
- Flows less readily than Type II: use enough for uniform coverage.
- Effectiveness can be seriously diminished if Type I overlay procedure not followed.
Type II handling (TC AIM AIR 2.12.2):
- Applied with improper equipment: loses 20% to 60% of anti-icing performance.
- Not every Type II is compatible with every Type I.
- Type II over badly contaminated Type I: weakened.
Trap: thickened not better on every aircraft. Type II and IV suit Vr above 100 KIAS only; below, degradation can be significant (TC AIM AIR 2.12.2).
References
- TC AIM AIR 2.12.2
- TP 10643 (When in Doubt... Small and Large Aircraft)