FAA Sport Pilot Airplane (SPA)WeatherHard
A pilot flying a carbureted trainer at cruise power in hazy conditions with an OAT of 68°F and visible moisture in the air should be most concerned about which hazard, even though the temperature is well above freezing?
- ACarburetor icing caused by the temperature drop from fuel vaporization and the venturi effect
- BPitot-static system icing blocking airspeed indications
- CFrost accumulation on the windscreen
- DStructural icing forming on the wings and tail
Show answer & explanationAnswer & explanation
Correct answer: A. Carburetor icing caused by the temperature drop from fuel vaporization and the venturi effect
Carburetor icing can occur at outside air temperatures as high as 100°F (38°C) with high relative humidity because fuel vaporization and the venturi effect in the carburetor can drop the internal temperature by 60-70°F. This can cause icing even in seemingly warm, moist conditions.
Why the other options are wrong
- B. Pitot icing typically requires freezing or near-freezing conditions and moisture, not 68°F ambient.
- C. Frost requires surface temperatures at or below freezing, not applicable at 68°F.
- D. Structural icing requires visible moisture at or below freezing temperatures, which does not apply here.
Carburetor Icing
Ice that forms inside a carburetor's venturi and throttle plate due to the temperature drop from fuel vaporization and reduced pressure, even in above-freezing outside air temperatures.
- Can occur with OAT as high as 100°F given high relative humidity
- Caused by evaporative cooling and venturi effect, dropping internal temp 60-70°F
- Most likely near cruise/low power settings with high humidity
- Carburetor heat is the standard remedy; check carb icing probability charts
Memory trick: Carb Ice hides even in Warm skies — venturi steals the heat.