Definition
Ice that forms inside an aircraft's carburetor when the rapid pressure drop and fuel vaporization in the venturi cool the incoming air below freezing, causing moisture in the air to condense and freeze on internal surfaces such as the throttle plate and venturi walls. The accumulated ice restricts airflow to the engine, causing a loss of power and, if uncorrected, complete engine stoppage.
Plain English
Ice that builds up inside the engine's carburetor and blocks air from getting through. The engine starts losing power and can quit if the ice is not melted out.
Context Anchor
You may encounter this during low-power operations such as descents, steep spirals, traffic pattern work, or any situation where engine power is reduced for an extended time.
Derivation
Carburetor comes from the French carburer, meaning to combine with carbon — a reference to mixing fuel with air. The ice forms inside this device, hence the name. Knowing this reminds pilots that the problem lives inside the fuel-air mixing system, not on the airframe.
Why Pilots Care
Carburetor ice can cause engine roughness, power loss, or complete stoppage, leading to an immediate need for corrective action to maintain thrust.
Grounding Statement
Even on a cool or humid day that does not feel freezing, the air inside the carburetor can cool enough for moisture to freeze on the inside surfaces.
Intuition Check
Do not assume carburetor ice only happens in freezing weather. It can form when outside air is above freezing if the air is moist and the carburetor cools it enough inside the engine.
Example Sentence 1
During the prolonged descent in the steep spiral, the pilot applied carburetor heat to prevent carburetor ice from forming at the reduced power setting.
Example Sentence 2
Turning on carburetor heat cleared the ice and restored smooth engine operation.