Icing Conditions - Icing Prevention and Removal

Icing Prevention and Removal

Several methods exist to reduce the dangers of icing. The first, and simplest, is to avoid icing conditions altogether, but for many flights this is not practical.

If ice (or other contaminants) are present on an aircraft prior to takeoff, they must be removed from critical surfaces. Removal can take many forms:

• Mechanical means, which may be as simple as using a broom or brush to remove snow
• Application of deicing fluid or even hot water to remove ice, snow, etc.
• Use of infrared heating to melt and remove contaminants
• Put the aircraft into a heated hangar until snow and ice have melted
• Position aircraft towards the sun to maximize heating up of snow and ice covered surfaces. In practice this method is limited to thin contamination, by the time and weather conditions.

All of these methods remove existing contamination, but provide no practical protection in icing conditions. If icing conditions exist, or are expected before takeoff, then anti-icing fluids are used. These are thicker than deicing fluids and resist the effects of snow and rain for some time. They are intended to shear off the aircraft during takeoff and provide no inflight protection.

To protect an aircraft against icing in-flight, various forms of anti-icing or deicing are used:

• A common approach is to route engine "bleed air" into ducting along the leading edges of wings and tailplanes. The air heats the leading edge of the surface and this melts or evaporates ice on contact. On a turbine powered aircraft air is extracted from the compressor section of the engine. If the aircraft is turbocharged piston powered, bleed air can be scavenged from the turbocharger.
• Some aircraft are equipped with pneumatic deicing boots that disperse ice build-up on the surface. These systems require less engine bleed air but are usually less effective than a heated surface.
• A few aircraft use a weeping wing system, which has hundreds of small holes in the leading edges and releases anti-icing fluid on demand to prevent the buildup of ice.
• Electrical heating is also used to protect aircraft and components (including propellors) against icing. The heating may be applied continuously (usually on small, critical, components, such as pitot static sensors and angle of attack vanes) or intermittently, giving an effect similar to the use of deicing boots.

In all these cases usually only critical aircraft surfaces and components are protected. In particular only the leading edge of a wing is usually protected.

Carburetor heat is applied to carbureted engines to prevent and clear icing. Fuel-injected engines are not susceptible to carburetor icing but can suffer from blocked inlets. In these engines an alternate air source is often available.

Note there is a difference between deicing and anti-icing. Deicing refers to the removal of ice from the airframe; anti-icing refers to the prevention of ice accumulating on the airframe.