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Carburetor ice is most likely to form in
Choices
high-temperature, very dry conditions only.
Dry air doesn't ice up.
✓ any conditions with visible moisture and ambient temperatures from 20°F to 70°F.correct
especially 50-70°F at high humidity). even on warm summer days, evaporative cooling in the venturi can drop fuel-air mixture temp 50°F+ and freeze water vapor. Carb ice forms when humid air passes through the venturi and the temperature drops sharply (evaporative cooling + pressure drop). Most likely range: ambient 20-70°F with visible moisture or high humidity. The 50-70°F warm-but-humid range is the worst — pilots assume 'too warm to ice' and don't apply carb heat. Symptoms: gradual RPM loss (fixed-pitch) or MP loss (constant-speed). Apply carb heat IMMEDIATELY when suspected; expect rough running as ice melts.
only at altitudes above 10,000 ft.
Carb ice can form at any altitude.
only at night.
Carb ice doesn't care about time of day.
Why
especially 50-70°F at high humidity). even on warm summer days, evaporative cooling in the venturi can drop fuel-air mixture temp 50°F+ and freeze water vapor. Carb ice forms when humid air passes through the venturi and the temperature drops sharply (evaporative cooling + pressure drop). Most likely range: ambient 20-70°F with visible moisture or high humidity. The 50-70°F warm-but-humid range is the worst — pilots assume 'too warm to ice' and don't apply carb heat. Symptoms: gradual RPM loss (fixed-pitch) or MP loss (constant-speed). Apply carb heat IMMEDIATELY when suspected; expect rough running as ice melts.
FAA source: FAA-H-8083-25C, PHAK Ch. 7, carburetor icingbrowse the reference library →
Original study question written for this course — representative of FAA knowledge-test topics, not an actual current FAA exam question.