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Deicing Fluids

Deicing fluid,

Ground deicing of aircraft is commonly performed in both commercial and general aviation. The fluids used in this operation are called deicing or anti-icing fluids. The initials ADF (Aircraft Deicing Fluid), ADAF (Aircraft Deicer and Anti-icer Fluid) or AAF (Aircraft Anti-icing Fluid) are commonly used.-

Deicing fluids come in a variety of types, and are typically composed of ethylene glycol (EG) or propylene glycol (PG), along with other ingredients such as thickening agents, surfactants (wetting agents), corrosion inhibitors, colors, and UV-sensitive dye. Propylene glycol-based fluid is more common because it is less toxic than ethylene glycol.

SAE International (formerly known as the Society of Automotive Engineers) publishes standards (SAE AMS 1428 and AMS 1424) for four different types of aviation deicing fluids:

  1. Type I fluids have a low viscosity, and are considered "unthickened". They provide only short term protection because they quickly flow off surfaces after use. They are typically sprayed on hot (130–180 °F, 55–80 °C) at high pressure to remove snow, ice, and frost. Usually they are dyed orange to aid in identification and application.
  2. Type II fluids are pseudoplastic, which means they contain a polymeric thickening agent to prevent their immediate flow off aircraft surfaces. Type II prevents snow, ice or frost contamination from adhering to the aircraft from the apron to takeoff. Typically the fluid film will remain in place until the aircraft attains 100 knots (190 km/h) or so, at which point the viscosity breaks down due to shear stress. The high speeds required for viscosity breakdown means that this type of fluid is useful only for larger aircraft. The use of Type II fluids is diminishing in favour of Type IV. Type II fluids are generally clear in color.
  3. Type III fluids can be thought of as a compromise between Type I and Type II fluids. They are intended for use on slower aircraft, with a rotation speed of less than 100 knots. Type III fluids are generally bright yellow in color.
  4. Type IV has the same purpose and meets the same AMS standards as Type II fluids, but they provide a longer holdover time. They are typically dyed green to aid in the application of a consistent layer of fluid.

The International Organization for Standardization publishes equivalent standards (ISO 11075 and ISO 11078), defining the same four types.

Deicing fluids containing thickeners (Types II, III, and IV) are also known as anti-icing fluids, because they are used primarily to prevent icing from re-occurring after an initial deicing with a Type I fluid.