Carburetor ice

Ice that forms inside the throat of a carburetor installed on an aircraft reciprocating engine. When air flows through the carburetor venturi, it speeds up, and both its pressure and temperature drop. When liquid fuel is discharged into the throat of the venturi, it vaporizes, and this change of state drops its temperature. When the temperature of the air is low enough, moisture in the air condenses out and freezes. It is possible for carburetor ice to build up inside the venturi and restrict the air flowing into the engine enough to cause the engine to stop. Carburetor ice is normally prevented by heating the air before it enters the carburetor.