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SESK: Stuff Everyone Should Know · sesk.info/pilot-carb-ice-first-sign

With a fixed-pitch propeller, what is usually the first sign of carburetor ice?

A drop in engine RPM, sometimes followed by roughness.

  1. A drop in engine RPM ✔
  2. Engine roughness
  3. Lower oil temperature

Why: Ice in the carburetor chokes off the fuel and air, so RPM falls. Engine roughness may follow later. With a constant-speed propeller you would see a drop in manifold pressure instead.

Huh, didn't know that: With a constant-speed propeller, carburetor ice shows as lower manifold pressure but no RPM loss, because the prop adjusts pitch.

The dad joke
Why was the tachometer so gloomy? Its numbers kept dropping.
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Sources

  1. FAA Pilot's Handbook of Aeronautical Knowledge (FAA-H-8083-25C), Chapter 7 https://www.faa.gov/regulations_policies/handbooks_manuals/aviation/faa-h-8083-25c.pdf
  2. FAA Private Pilot Airplane (PAR) sample questions https://www.faa.gov/sites/faa.gov/files/training_testing/testing/test_questions/par_questions.pdf

Test yourself in the game

Flying & DronesPer the FAA, carburetor icing can occur at outside air temperatures as high as about what?Flying & DronesWith carburetor ice present, what happens to RPM when full carburetor heat is applied?Flying & DronesAs an airplane climbs with the mixture left at full rich, the fuel-air mixture becomes what?

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