FAA Aviation Mechanic Powerplant (AMP)Fuel, Induction and LubricationEasy
During preflight inspection on a cool, humid morning, a mechanic explains to a student why a float-type carburetor is prone to icing even when the outside air temperature is well above freezing. What is the primary cause of this icing?
- AFuel vaporization and pressure drop in the venturi cause a temperature drop that can be 60-70°F below ambient
- BCold fuel entering the carburetor from an underground storage tank
- CThe throttle plate conducting heat away from the intake manifold
- DStatic electricity buildup in the fuel bowl attracting moisture
Show answer & explanationAnswer & explanation
Correct answer: A. Fuel vaporization and pressure drop in the venturi cause a temperature drop that can be 60-70°F below ambient
Fuel vaporization combined with the pressure drop as air passes through the venturi causes a significant temperature drop, which can freeze moisture in the incoming air even when ambient temperatures are relatively warm and humidity is high.
Why the other options are wrong
- B. Fuel temperature from storage has negligible effect compared to the venturi cooling effect.
- C. The throttle plate does not cause the temperature drop responsible for icing.
- D. Static electricity is not a recognized cause of carburetor icing.
Carburetor Icing
Ice forms in the carburetor venturi due to temperature drop from fuel vaporization and pressure reduction, even in warm, humid conditions.
- Temperature drop can be 60-70°F
- Most likely with high humidity and temps 20-90°F
- Symptoms include rough running and loss of RPM/manifold pressure
- Carburetor heat melts ice by routing unfiltered warm air
Memory trick: Venturi vaporizes fuel, vaporizing chills the air—ice follows even on warm days