De-icing

De-icing is defined as removal of snow, ice or frost from a surface. Anti-icing is understood to be the application of chemicals that not only de-ice, but also remain on a surface and continue to delay the reformation of ice for a certain period of time, or prevent adhesion of ice to make mechanical removal easier.

De-icing can be accomplished by mechanical methods (scraping, pushing); through the application of heat; by use of dry or liquid chemicals designed to lower the freezing point of water (various salts or brines, alcohols, glycols); or by a combination of these different techniques.

On the ground, when there are freezing conditions and precipitation, de-icing an aircraft is crucial. Frozen contaminants cause critical control surfaces to be rough and uneven, disrupting smooth air flow and greatly degrading the ability of the wing to generate lift, and increasing drag. This situation can cause a crash. If large pieces of ice separate when the aircraft is in motion, they can be ingested in engines or hit propellers and cause catastrophic failure. Frozen contaminants can jam control surfaces, preventing them from moving properly. Because of this potentially severe consequence, de-icing is performed at airports where temperatures are likely to be around 0 °C (32 °F).

In flight, droplets of supercooled water often exist in stratiform and cumulus clouds. They form into ice when they are struck by the wings of passing airplanes and abruptly crystallize. This disrupts airflow over the wing, reducing lift, so aircraft that are expected to fly in such conditions are equipped with a de-icing system.

De-icing techniques are also employed to ensure that engine inlets and various sensors on the outside of the aircraft are clear of ice or snow.

Deicing fluids consisting of propylene glycol (PG) and additives are widely used by airlines for deicing aircraft.Ethylene glycol (EG) fluids are still in use for aircraft de-icing in some parts of the world because it has a lower operational use temperature (LOUT) than PG. However, PG is more common because it is less toxic than ethylene glycol.

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