Carb Ice Forms Even on Warm Days
Carb icing is a year-round threat because the carburettor is much colder than outside air; use carb heat below the green arc and check for icing in SCADIE checks.
1 min readKapiti Aero Club safety team
It's easy to be lulled into a false sense of security in the warmer months, but the threat of carburettor icing is constant. Carb icing is a build-up of ice in the carburettor that causes a restriction. This results in an overly rich mixture going into the cylinders, causing rough running and loss of power.
Carb icing can form in conditions from -10°C up to +25°C. It's much colder inside the carburettor than outside because of the venturi effect (accelerating air drops in temperature) and fuel evaporation (which absorbs latent heat). So even if it's warm outside, it may not be so warm in the carburettor!
Symptoms: rough running and loss of RPM. Treatment: apply carb heat, which takes warm air from around the exhaust instead of cool outside air. This melts the ice, which will temporarily make the symptoms worse as water runs through the engine.
Take steps to avoid carb icing where possible, and be aware of the conditions that favour it:
- Use carb heat outside the green range (below 1900 RPM in the C152).
- Check carb heat on the ground before departure.
- Check for carb icing frequently during SCADIE checks.
It is most likely to form between 10°C and 15°C with relative humidity above 40%.