Definition
The formation of ice inside the carburetor of a piston aircraft engine, caused by the rapid temperature drop that occurs when fuel vaporizes and air accelerates through the carburetor venturi. The cooling effect can lower the internal temperature well below the outside air temperature, causing moisture in the air to freeze on the throttle valve and venturi walls. The accumulating ice restricts airflow, reducing engine power and, if untreated, can cause the engine to run rough or stop completely.
Plain English
Ice forming inside the engine's carburetor because the air cools sharply as it passes through. The ice blocks airflow, the engine loses power, and if it gets bad enough the engine can quit.
Context Anchor
Encountered during piston-engine operations, especially during low power, descent, or humid conditions, and when using carburetor heat in response to engine roughness or power loss.
Derivation
‘Carburetor’ comes from the French ‘carburer’, meaning to combine with carbon — the device mixes fuel with air. ‘Icing’ simply means ice forming. Together, the term describes ice forming inside the fuel-air mixing device, which is exactly what happens.
Why Pilots Care
Uncorrected carburetor icing can cause partial or total loss of engine power in flight.
Analogy
It is like frost building up inside a drinking straw: the straw may still be open, but less air can pass through it. In an engine, that reduced airflow can mean reduced power.
Grounding Statement
Think of how a cold drink can sweats on a humid day — the air around it cools and moisture condenses. In a carburetor, that cooling is severe enough to freeze the moisture solid inside the engine's air passage.
Intuition Check
Carburetor icing does not mean the whole airplane is covered in ice. It also does not require freezing outside air; it can happen in moist air well above freezing.
Example Sentence 1
During a long descent with the throttle pulled back, the pilot noticed a slow drop in engine RPM and applied carburetor heat to clear the carburetor icing.
Example Sentence 2
Carburetor icing formed during descent through visible moisture, requiring immediate use of heat to restore power.