Impact icing
Impact icing: ice forms on the OUTSIDE of the aircraft and plugs an opening, e.g. engine air intake (PHAK ch.7).
| Icing type | Where / how |
|---|---|
| Impact | Outside; plugs an opening |
| Carburettor | Inside carb throat; moisture freezes as fuel vaporises |
| Airframe | Ice builds on wings and tail |
- Fuel injection not immune: avoids evaporative (carburettor) icing, less icing-prone overall, but air intake impact icing possible in EITHER engine type (PHAK ch.7).
Alternate air (backup path drawing air from inside the engine cowling if normal intake blocks; PHAK ch.7):
| Engine | Opens with |
|---|---|
| Carburettor | Carb heat |
| Fuel-injected | Dedicated alternate air source |
- Alternate air source normally automatic; manual backup if it malfunctions (PHAK ch.7).
- Engine power loss in flight: open alternate air source (fuel injection) or apply carb heat (carburettor) while setting up the glide. Cause may be blocked intake air, not fuel (TP 1102).
Trap: thinking a fuel-injected engine cannot ice up. Less prone than carburettor, but air intake can still ice over on either type.
References
- PHAK ch.7 (Fuel Injection Systems)
- TP 1102 (Flight Training Manual)