Cause of Icing

Two conditions are necessary for accumulation of ice on your aircraft: First, the aircraft must be flying through visible moisture. Second, the temperature of water or the aircraft must be freezing or colder. 

There are two general types of icing which directly effect aircraft:

	Induction Icing:	This includes carburetor icing as well as air intake icing. Carburetor icing forms in the carburetor venturi. It occurs when the OAT is between -7°C and 21°C and relative humidity is above 80%. Air intake icing usually requires the aircraft surface temperature to be 0°C or colder with visible moisture present. It can also form in clear air if the relative humidity is high and the temperature is close to freezing.
	Structural Icing:	This builds up on any exposed surface of an aircraft. There are two general types of Structural Icing:
	Rime Ice:		Is normally encountered in Stratus Clouds. It results from instantaneous freezing of tiny water droplets striking the aircraft surface. It has an opaque appearance.
	Clear Ice:		This may develop in areas of large water droplets which are found in Cumulus Clouds or in freezing rain beneath a warm front inversion. When the droplets flow over the aircraft structure, they glaze the aircraft's surfaces. Clear ice is the most serious form of ice because it has the fastest rate of accumulation, adheres tenaciously to the aircraft, and is more difficult to remove.

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