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Don't Let Carburetor Ice Happen To You

Aleksander Markin

Between 1998 and 2007, there were 212 accidents due to carb icing - resulting in 13 fatalities.

But before you keep reading, think about the weather outside today. It's September, but the temps are still pretty warm. If you were flying, could you pick up carb ice? The answer may surprise you...

The Conditions For Carb Ice

You know carb ice happens - but when do the conditions present the most risk? Obviously, when the humidity is high, the risk increases, but according to the NTSB, carb ice can happen when relative humidity is as low as 35%, when you're operating at low power settings.

The temperature range where carb ice can occur is equally surprising. According to the FAA, carb ice is possible from 10F to over 100F, with serious icing possible from 20F to over 90F (-7C to 32C).

What Causes Carb Ice?

There are three types of induction icing:

  • Throttle ice
  • Fuel vaporization ice
  • Impact Ice

Throttle Ice

Throttle ice forms when your throttle is partially closed, typically between cruise power and idle. As air moves through the the Venturi in your carburetor, it decreases in temperature, condensing water vapor from the air. The water then starts freezing to the carburetor parts, restricting airflow. Eventually, you'll start losing RPM or manifold pressure, your engine may start running rough, and if the ice gets bad enough, your engine will quit.

So how do you fix carb ice? Turn on your carb heat, and prepare for some nasty sounds. Carb heat directs warm air into your carburetor, which starts melting the ice. Where does the ice go? Through your engine, making it cough, wheeze and shake until the ice is gone. It's not fun to hear, but stick with it, because it will eventually get better. There are countless NTSB report where pilots turned off carb heat because they thought they were making the situation worse, only to totally lose the engine shortly after. You don't want to be one of those statistics.

The video below is a great example of what it sounds like when you turn your carb heat on, when you have carb ice. Listen to the engine as the carburetor starts melting the ice starting at 4:02.

Video courtesy Cubonaut875

Fuel Vaporization Ice

Next up is fuel vaporization ice, which is a result of the cooling effect when your fuel mixes with air and vaporizes in the carburetor. The temperature drop yields the same results as throttle ice - moisture condenses out of the air and water starts freezing to the carburetor.

The fix is the same as throttle ice too: turn on your carb heat and prepare for ugly sounds.

Impact Ice

The third type is impact ice, which doesn't necessarily happen in your carburetor. This type of icing is most common in visible moisture - clouds, snow, sleet, rain, etc. As cold, moisture-laden air contacts anything solid, ice can start to form. This can happen on your air intake, filter, or carburetor.

So what's the fix for impact ice? Again, carb heat, for a couple reasons. Pushing warm air into your carburetor will melt any ice that might be there, but on most planes, carb heat also pulls air from a different source (typically within your cowling), which means if your air filter is packed with ice, carb heat will solve the problem. If you're flying a fuel-injected airplane, using alternate air accomplishes the same task.

jzawodn

Preventing Carb Ice Is Better Than Getting It

The best way to avoid carb ice is to follow your airplane flight manual and use carb heat whenever icing is probable. But in the event that you do pick up carb ice, remember to always use full carb heat, prepare for a very rough running engine, and know that eventually your carburetor will be clear.

Colin Cutler

Colin is a Boldmethod co-founder, pilot and graphic artist. He's been a flight instructor at the University of North Dakota, an airline pilot on the CRJ-200, and has directed development of numerous commercial and military training systems. You can reach him at colin@boldmethod.com.

Images Courtesy:

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