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As I'm writing this, it's 87 degrees outside my office. Less than 90 miles from me, there's a PIREP for moderate icing. And, there's no AIRMET for ice. How can that possibly be?
Ok, so this PIREP was at FL250, but it can happen a lot lower. And it can happen at an altitude you're planning to fly on your next IFR flight. And the worst part? Since it's summer, you may not have givin icing a lot of thought, or thought about it at all.
When you're flying around the freezing level, which is possible even in the middle of summer, you're sitting right in the band of highest ice potential.
Icing typically happens when the temperature is between 0C and -23C. And clear ice, the less fun type of ice (not that any ice is fun), happens in the relatively warm temperature band between 2C and -10C.
Most of the time when you see icing PIREPs in the summer, it has to do with building cumulus clouds. Cumulus clouds typically form due to strong convection, and on top of that, they usually have a lot of water in them.
And, the more aggressive the lifting action in the cloud you're about to fly through, the larger the water drops (and possible supercooled large drops, or SLD) can be. Which means if you're flying near the freezing level or colder, your chances of getting significant icing goes up, a lot.
Simply put, cumulus clouds that are near or below freezing are a perfect opportunity for you to turn your plane into a summertime ice cube.
There is some good news. Cumulus clouds tend to not extend very far horizontally, which means you can usually navigate around them with a little coordination with ATC. And, if you end up in one, chances are you'll fly out the other side an a relatively short amount of time.
But, on the other hand, cumulus clouds usually have a lot of vertical development. And because of their lifting action and high water content, icing can exist across thousands of vertical feet within the cloud. Which means that it can be hard (or impossible) to climb or descend to an altitude in the cloud where you're not picking up ice.
So what's the best way to keep yourself from turning into a flying ice cube on your next flight?
If you're within a few degrees of the freezing level, make sure you're ready to use your anti-ice or de-ice system, and get ready to work with ATC to deviate around the weather.
And if you don't have de-ice or anti-ice system on board, start coordinating a diversion with ATC as early as possible. After all, it's best to stay out of a cumulous cloud and wonder if it has ice, rather than being in the middle of it watching your airplane turn into a flying snow globe.
Colin is a Boldmethod co-founder and lifelong pilot. He's been a flight instructor at the University of North Dakota, an airline pilot on the CRJ-200, and has directed the development of numerous commercial and military training systems. You can reach him at colin@boldmethod.com.