Definition
A form of induction system icing that occurs when fuel vaporizes in the intake airstream and absorbs heat from the surrounding air, causing the air temperature to drop below freezing and water vapor to deposit as ice on the throttle plate, venturi walls, and nearby surfaces. It can form at outside air temperatures well above freezing, typically up to about 70 °F, when humidity is high.
Plain English
Ice that forms inside the engine's air intake because fuel turning from liquid to vapor cools the air sharply, and any moisture in that air freezes onto the metal parts. It can happen on warm, humid days, not just cold ones.
Context Anchor
Seen in induction system and carburetor ice discussions, especially when learning why carburetor ice can form even when the outside air is above freezing.
Derivation
From 'evaporate,' Latin 'evaporare' meaning 'to turn into vapor.' The name points to the cause: the cooling effect of fuel evaporating is what triggers the icing.
Why Pilots Care
Uncorrected, it restricts airflow and can cause engine roughness or total power loss.
Grounding Statement
Picture fuel mist entering the carburetor, changing into vapor, and chilling the surrounding air enough that moisture freezes on the inside walls.
Intuition Check
Do not assume icing only happens when the outside air is below freezing. Evaporative icing can form because the air inside the carburetor becomes colder than the outside air.
Example Sentence 1
On a warm, muggy afternoon, the pilot pulled on carburetor heat during descent to prevent evaporative icing from forming in the throttle area.
Example Sentence 2
High humidity and temperatures between twenty and seventy degrees Fahrenheit increase the risk of evaporative icing in carbureted engines.