# Icing Conditions & De-icing

> Hazards of ice accretion and procedures for de-icing and anti-icing.

- **Subject:** 070 — Operational Procedures
- **Section:** 071-02 — Special Operational Procedures and Hazards (General Aspects)
- **Topic code:** 071-02-02
- **Last reviewed:** 2026-04-01
- **Author:** Pablo Asensio Martínez
- **HTML version:** https://pilotsyllabus.com/en/operational-procedures/special-operational-procedures-and-hazards-general-aspects/icing-conditions/

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## Hazards of Icing
*   **Aerodynamics**: Increases drag (up to 40%), decreases lift (up to 30%), increases stall speed, changes pitching moment.
*   **Weight**: Adds weight to the aircraft.
*   **Instrumentation**: Blockage of pitot/static ports can lead to erroneous airspeed and altitude readings.
*   **Engine**: Ice ingestion can cause flameout or damage fan blades.

## De-icing vs Anti-icing

![Aeroflot Airbus A330-200 de-icing](https://upload.wikimedia.org/wikipedia/commons/4/48/Aeroflot_Airbus_A330-200_de-icing_Pereslavtsev.jpg)

*   **De-icing**: Removal of existing contaminants (ice, snow, slush) from the aircraft surfaces. Usually done with heated fluid (Type I) or mechanical methods.
*   **Anti-icing**: Application of a fluid that prevents the accumulation of contaminants for a limited time.

## De-icing/Anti-icing Fluids
*   **Type I**: Orange. Low viscosity. Used for de-icing. Short holdover time.
*   **Type II**: Light yellow. Pseudoplastic (thickens when static, shears off during takeoff). Used for anti-icing.
*   **Type III**: Yellow. For slower aircraft (lower rotation speed).
*   **Type IV**: Green. Thickest fluid. Longest holdover time. Used for anti-icing.

## Holdover Time (HOT)
The estimated time the anti-icing fluid will prevent the formation of frost or ice and the accumulation of snow on the protected surfaces of an aircraft.
*   Begins at the **start** of the anti-icing application.
*   Influenced by fluid type, concentration, OAT, and precipitation type/intensity.
*   **Clean Aircraft Concept**: No aircraft may take off if frost, ice, or snow is adhering to any critical surface (wings, control surfaces, etc.).

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