CFI Brief: Icing Systems

Temperatures have started dropping up here in the Northwest and the leaves have all but fallen off the trees. With the official start to winter a little more than a month away, what better time than to have a quick Brief on ice, particularly those systems which prevent us from falling to earth looking like a giant ice cube.

There are two main systems to discuss in terms of equipment, anti-ice and deicing systems. It says it all in the name; anti-ice equipment is used to PREVENT the formation of ice while deicing equipment is designed to REMOVE the buildup of ice once it has accumulated. The majority of light training aircraft in which you will be flying as a student pilot have a very limited amount of equipment to deal with icing, typically just pitot heat. Usually part of your pre-flight inspection includes turning the pitot heat on and feeling the pitot tube to make sure the heating element is functioning (careful it can get hot!).

Once you get into flying some higher performance aircraft and or light twins, you will start to see different types of icing equipment installed on the various aircraft. As a pilot it’s important to familiarize yourself with this equipment and the operation of it as well as the limitations. Some commonplace anti-ice/deice equipment include inflatable deicing boots. These are leading edge devices made of rubber that with the help of an engine driven pneumatic pump can inflate, cracking the ice causing it to fall free. The inflation of the boots is controlled from the cockpit by the pilot. An alternative to boots is a thermal anti-ice system which uses hot bleed-air from the engine to heat the leading edges of the aircraft and provide icing protecting. This type of system is usually found on larger commercial passenger aircraft and corporate jets. Another system you may encounter is the weeping-wing; an anti-freeze solution known as TKS is pumped out of (or “weeps”) from little holes in the leading edges of the aircraft. The solution in a sense “unsticks” the ice from the leading edges allowing aerodynamic forces to remove the ice.

Cross section of a deicing boot. Uninflated (top) Inflated (bottom).
Cross section of a deicing boot. Uninflated (top) Inflated (bottom).

Some other areas in which icing can occur include the windscreen and propeller. There are two main anti-ice systems to protect these areas: an alcohol system and a heating system.

Just like your pitot tube there are several other important external elements on an aircraft that need to be protected from ice including static ports, stall-warning sensors, and even fuel vents. These devices are also protected like the pitot tube by an electrically heated anti-icing systems.

Even with all these protecting systems available aircraft are still not intended to be flown in icing conditions for sustained periods of time. Some aircraft are not authorized or certified to be flown into known icing conditions at all.

NASA has a really good comprehensive course on in-flight icing that’s worth checking out:

Get out there and have fun in the sky this winter, but use good judgement and save the ice for your lemonade this summer.

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