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When frost adheres to the airplane or it is snowing, you need to make sure the airplane is clean when you depart. You've probably seen the trucks spraying aircraft in the winter before departure, but what are the spraying it with?

I know of at least 4 types of de-/anti-ice fluids but perhaps there are others. What does each fluid consist of and what is its function? How do I know if these fluids are available at an airport I plan to operate from? Are there limits in how soon I must depart once fluid is applied?

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Fluid Types

Wikipedia contains a good summary of the different types of fluid:

Types

  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. Typically the fluid film will remain in place until the aircraft attains 100 knots or so (almost 200 km/h), 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 light yellow 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 light yellow in color.

  4. Type IV fluids meet 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.

Chemical Composition

The main component of deicing fluid is usually propylene glycol or ethylene glycol. Other ingredients vary depending on the manufacturer, but the exact composition of a particular brand of fluid is generally held as confidential proprietary information.

Call ahead to the airport to see what kind of deice/anti-ice fluid that they have because each one is different.

Time Limits

Every year, the FAA publishes tables which include information about how long the various deice fluids will provide protection under various weather conditions. Here is an example table:

Holdover Table

For this particular fluid (ABAX ECOWING AD-49 Type IV) we can lookup a specific example such as:

  • -10 Degrees Celcius
  • 75% fluid and 25% water
  • Light Snow

This shows that the fluid will provide protection for 1:40 to 2:05. If you are delayed longer than that, you will need to deice again. Since every part of the aircraft needs to be protected, the timing starts when they first start spraying the aircraft. Note that other types of fluid (particularly Type I fluids) have much shorter holdover times than this, so be careful and make sure that you check!


Resources

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