What Is Carburetor Ice In Aircraft Systems?

When operating a system that utilizes a float-type carburetor in its engine, the system is at risk of carburetor icing, a harmful phenomenon that can shut down an engine entirely. A properly functioning carburetor directs a fuel and air mixture directly into the engine; however, if the fuel vaporizes within the venturi and the air pressure decreases, the temperature will drop and ice will form on the internal surfaces of the carburetor. As this can have a detrimental effect on the functions of an engine, the blog will cover the causes of carburetor icing and the measures you can take to prevent it.

Carburetor icing occurs in very specific conditions, as it is a result of combined relative humidity and outside air temperature causing vapor to condense directly into ice along the internal surfaces of the carburetor. This interferes with the combustion process as well as the working properties of certain parts of the carburetor like the throttle valve or the venturi throat. When ice covers the surfaces, the flow of the air and fuel mixture to the engine may be reduced or halted entirely. Typically, icing occurs when the temperature averages less than 70 degrees Fahrenheit and the relative humidity is above 80 percent because this creates a drastic change in environment due to the sudden cooling that takes place within the carburetor, causing quick temperature drops of up to 70 degrees.

Depending on the type of engine with which your system operates, signs of carburetor icing will show differently in the malfunctions that manifest themselves in your aircraft. For example, if your aircraft relies on a fixed-pitch propeller, you may notice a decrease in rotations per minute (rpm), followed by engine roughness. Meanwhile, if you operate an aircraft with a constant-speed propellor, carburetor icing will not be evident in the speed of the propellor, but instead it is usually indicated by a decrease in manifold pressure, as propellor pitch in this type of engine is automatically adjusted to compensate for any reduction in power.

While carburetor icing can occur at any point in flight, it is particularly dangerous when an aircraft is using reduced power during descent. This is because the ice within the carburetor could build continuously for a while and go unnoticed if the pilot is not employing additional power. A popular method for combating carburetor icing in aircraft is for those that employ float-type carburetors to also employ a carburetor heat system. These systems work specifically to reduce the drastic temperature changes that occur and create a more stable environment for combustion to occur. Regardless of propeller type, the addition of a heat system could help prevent your aircraft from avoidable system malfunctions.

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