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Anti-icing = Precautionary measure (before ice has been accumulated on the surfaces)
De-icing = process that removes ice, snow, etc. from the critical surfaces of an aeroplane
Combined de-icing/anti-icing = 2 Basic procedures have been established;
1: (One-step de-icing/anti-icing) - Applying a heated fluid under pressure to remove the existing layer of ice while anti-icing agent is applied
2: (Two-step de-icing/anti-icing) - Firs the actual de-icing is carried out and only then is an anti-icing agent applied
Holdover time = Estimated time during which the anti-icing becomes effective
Weather Conditions
- Drizzle
Uniform precipitation consisting of tine, fine and densely distributed rain droplets (diameter between 0,1 - 0,5 mm)
- Fog
Visible collection of water droplets, which can restrict visibility. Occurs when temperature and dew point are the same thus saturating the air
Fog = visibility drops below 1km
Wet Haze = visibility up to 5km
- Freezing fog
Supercooled water droplets. This haze freezes on contact with surfaces
- Freezing rain or drizzle
Rain or drizzle in the form of supercooled water droplets freezing on contact with surfaces
- Frost
Caused by deposition, when water vapour (gas) turns into solid (ice) when in contact with frozen surfaces
- Rain
Liquid precipitation consisting of droplets with a diameter of more than 0,5 mm
- Rime
Is a white or milky deposit of ice formed by the rapid freezing of supercooled water droplets as they hit the surfaces
- Slush
Snow supersaturated with water. Usually occurs when snow gradually begins to melt and temperatures are still slightly positive or at 0°C
- Snow
Precipitation in the form of ice crystals
Dry snow = at ambient temperatures of just below freezing point
Wet snow = at ambient temperatures of just above freezing point
The clean aircraft concept
States that a take off may not be conducted if the surfaces of an aircraft are affected by icing, snow, slush or frost unless otherwise specified in the flight manual.
These do not only cause aerodynamic problems but can also block moveable parts.
The procedure of de-icing and anti-icing must be followed up by a visual inspection of all critical surfaces, usually carried out be the de-icing personnel.
Type of de-icing and anti-icing fluids
The basic principle of these fluids is to lower the freezing point in order to prevent or delay the formation or built-up of ice, snow, etc. on the aeroplane. There are 4 types;
Type 1
- Sticky
- Available in diluted or concentrated form
- Contains high proportion of glycol (80%), rest is water, rust inhibitor, etc.
- Must be heated before applying
- Can be orange coloured
- Usually only for de-icing
- Very short hold-over time
Type 2
- Viscous
- Available in diluted or concentrated form
- Adheres better but separates during take off
- Consists of more than 50% glycol
- Used for de-icing and anti-icing in freezing temperatures
- Can be white coloured
Type 3
- Viscous
- Available in diluted or concentrated form
- Adheres better but separates during take off
- Effectively obsolete
- Used for de-icing and anti-icing
- Similar properties to type 2 but are only suitable for temperatures below -25°C
- Can be yellow coloured
Type 4
- Viscous
- Available in diluted or concentrated form
- Adheres better but separates during take off
- Using for de-icing and anti-icing
- Similar properties to type 2 but only suitable for temperatures below -30°C
- Can be green coloured
Important: An anti-icing fluid must never be applied to an existing layer, that layer must first be removed by de-icing again
Hold-over Time
The specified times (from the tables) apply from the commencement of the completion of the final de-icing/anti-icing procedure. When de-icing is conducted in 2 stages, the hold-over time commences from the start of the 2nd stage.
Adverse effects of icing;
- Can change the geometry of the wings leading to lift decrease
- Increase in drag
- Restrict or block moving parts
- Add weight which reduces performance
- Parts of ice can fly off during take off
- Blockage of pitot tubes, static ports and AOA sensors
Entry into known icing conditions;
The type-related procedures specified in section B of the operations manual must be observed and applied
- Engine anti-ice selected ON when RAT is 10°C or below, and visible moisture in any form is present
- WING/TAB de-ice should be selected as soon as ice is observed
- Maximum flap extension is limited to Take off and approach when ice remains during approach and landing
- Minimum sustained airspeed in icing conditions is 106KIAS
- Flaps 30° is prohibited when any ice is observed on the outside surfaces
De-icing = process that removes ice, snow, etc. from the critical surfaces of an aeroplane
Combined de-icing/anti-icing = 2 Basic procedures have been established;
1: (One-step de-icing/anti-icing) - Applying a heated fluid under pressure to remove the existing layer of ice while anti-icing agent is applied
2: (Two-step de-icing/anti-icing) - Firs the actual de-icing is carried out and only then is an anti-icing agent applied
Holdover time = Estimated time during which the anti-icing becomes effective
Weather Conditions
- Drizzle
Uniform precipitation consisting of tine, fine and densely distributed rain droplets (diameter between 0,1 - 0,5 mm)
- Fog
Visible collection of water droplets, which can restrict visibility. Occurs when temperature and dew point are the same thus saturating the air
Fog = visibility drops below 1km
Wet Haze = visibility up to 5km
- Freezing fog
Supercooled water droplets. This haze freezes on contact with surfaces
- Freezing rain or drizzle
Rain or drizzle in the form of supercooled water droplets freezing on contact with surfaces
- Frost
Caused by deposition, when water vapour (gas) turns into solid (ice) when in contact with frozen surfaces
- Rain
Liquid precipitation consisting of droplets with a diameter of more than 0,5 mm
- Rime
Is a white or milky deposit of ice formed by the rapid freezing of supercooled water droplets as they hit the surfaces
- Slush
Snow supersaturated with water. Usually occurs when snow gradually begins to melt and temperatures are still slightly positive or at 0°C
- Snow
Precipitation in the form of ice crystals
Dry snow = at ambient temperatures of just below freezing point
Wet snow = at ambient temperatures of just above freezing point
The clean aircraft concept
States that a take off may not be conducted if the surfaces of an aircraft are affected by icing, snow, slush or frost unless otherwise specified in the flight manual.
These do not only cause aerodynamic problems but can also block moveable parts.
The procedure of de-icing and anti-icing must be followed up by a visual inspection of all critical surfaces, usually carried out be the de-icing personnel.
Type of de-icing and anti-icing fluids
The basic principle of these fluids is to lower the freezing point in order to prevent or delay the formation or built-up of ice, snow, etc. on the aeroplane. There are 4 types;
Type 1
- Sticky
- Available in diluted or concentrated form
- Contains high proportion of glycol (80%), rest is water, rust inhibitor, etc.
- Must be heated before applying
- Can be orange coloured
- Usually only for de-icing
- Very short hold-over time
Type 2
- Viscous
- Available in diluted or concentrated form
- Adheres better but separates during take off
- Consists of more than 50% glycol
- Used for de-icing and anti-icing in freezing temperatures
- Can be white coloured
Type 3
- Viscous
- Available in diluted or concentrated form
- Adheres better but separates during take off
- Effectively obsolete
- Used for de-icing and anti-icing
- Similar properties to type 2 but are only suitable for temperatures below -25°C
- Can be yellow coloured
Type 4
- Viscous
- Available in diluted or concentrated form
- Adheres better but separates during take off
- Using for de-icing and anti-icing
- Similar properties to type 2 but only suitable for temperatures below -30°C
- Can be green coloured
Important: An anti-icing fluid must never be applied to an existing layer, that layer must first be removed by de-icing again
Hold-over Time
The specified times (from the tables) apply from the commencement of the completion of the final de-icing/anti-icing procedure. When de-icing is conducted in 2 stages, the hold-over time commences from the start of the 2nd stage.
Adverse effects of icing;
- Can change the geometry of the wings leading to lift decrease
- Increase in drag
- Restrict or block moving parts
- Add weight which reduces performance
- Parts of ice can fly off during take off
- Blockage of pitot tubes, static ports and AOA sensors
Entry into known icing conditions;
The type-related procedures specified in section B of the operations manual must be observed and applied
- Engine anti-ice selected ON when RAT is 10°C or below, and visible moisture in any form is present
- WING/TAB de-ice should be selected as soon as ice is observed
- Maximum flap extension is limited to Take off and approach when ice remains during approach and landing
- Minimum sustained airspeed in icing conditions is 106KIAS
- Flaps 30° is prohibited when any ice is observed on the outside surfaces
