Aircraft De-Icing and Anti-Icing Fluids

Guidance for Aircraft and Aerodrome Operators around winter operations

It is the operator's responsibility to ensure that de-icing/anti-icing fluids used are acceptable to the aircraft manufacturer, by type and proprietary brand names.

The temperature of the fluid at the nozzle of the de-icing equipment is an important factor in satisfactorily achieving the de-icing process.

A number of de-icing fluids only have a two-year shelf-life, yet shelf-life expiry dates are not in all cases marked on fluid containers. Should the dates not be found on fluid containers, they may be recorded on the fluid delivery notes. Clearly, fluids that have exceeded their shelf-life cannot be used.

Fluids must meet the requirements of the applicable Society of Automotive Engineers (SAE) or International Organization for Standardization (ISO) performance specification including the derivation of holdover time. A number of different types of de-icing/anti-icing fluids are available, which fall into the following type classifications:

Type I Fluid (Unthickened) (SAE AMS 1424 or ISO 11075)

This fluid has a high glycol content and low viscosity in its concentrated form. De-icing performance of the fluid is good. However, due to low viscosity, it provides only limited anti-icing protection during freezing precipitation. It is used predominantly for removing frozen deposits from aircraft surfaces, either as the first step in a two-step operation or where precipitation has stopped. With this type of fluid, no additional protection is provided by increasing the concentration of the fluid in the fluid/water mix.

Type II Fluid (Thickened) (SAE AMS 1428 or ISO 11078)
 

This fluid generally has a lower glycol content in its concentrated form than Type I fluid due to the inclusion of a pseudo plastic thickening agent. This effectively means that when applied to the surface of an aircraft the viscosity is high, thus allowing the fluid to remain on and protect against freezing precipitation for a period of time. However, the increasing effect of the airflow over the wing during the take-off roll will effectively 'shear' the fluid, reducing its viscosity and allowing it to readily flow off the critical surfaces. With this type of fluid the holdover time can be extended by increasing the concentration of fluid in the fluid/water mix. Type II fluids are usually straw coloured.

Type III (Thickened) (SAE AMS 1428)

Type III fluid is designed primarily for aircraft with low rotation/take-off speeds, and it may not require specialised low shear application and transfer equipment, but fluid manufacturers’ guidance should be followed in this respect. When used for anti-icing, Type III fluids have holdover time guidelines typically less than those of a Type II fluid but significantly longer than those of Type I fluids.

Type IV Fluid (Thickened) (SAE AMS 1428)

This fluid is similar in both composition and operation to Type II fluids. However, through the use of advanced thickening systems, it is able to provide longer holdover time than Type II fluids when used in concentrated form. As with Type II fluids the holdover time can be extended by increasing the concentration of fluid in the fluid/water mix. Type IV fluids are usually coloured green.

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FOP.Admin@caa.co.uk
 

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