Ask My Sky Mom. Aviation wit and wisdom.

Hey Mom,

I have been a student pilot for about the last 6 months, so this will be my first winter flying. What is shock cooling, how do I know if it’s happening, and what am I supposed to do about it if it does happen, or to prevent it?

Thanks,

A Shockingly Cool Almost-Pilot

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Hey there, Coolio,

First, a  misnomer I’d like to correct. Hon, if you’re a student pilot, you ARE a pilot. That is an FAA pilot certificate you hold in your hot little hand, even if it IS preceded by the word student.

Now that we have that straightened out, the shocking news about shock cooling is that it may be a myth after all. A hotly contested, long held myth to be sure, but there is great debate about whether shock cooling poses an actual threat. So what are we talking about? The idea that, when you make a sudden power reduction, particularly on a very cold day, that air cooled engine you’ve developed a habit of depending on will suddenly lose temperature. So? Well, when things get colder, they contract. Air, fuel, METAL…yes, metal! The idea is that with a sudden reduction in power and the continuing rush of cooling air through your cowling, the rapid contraction of metal may be enough to crack a cylinder head, or at least cause the potential for stuck valves. Either one can ruin your day by shortening your flight and causing you to get creative about a potential unplanned, off airport landing…but I digress.

Shock cooling sounds plausible enough to me, but there are those who argue that the cooling that engines undergo after a normal shutdown is more rapid than what you could possibly induce by power reduction and descent in most cases, or that properly managed engine temps never get high enough that the differential experienced would be damaging anyway. Hmm. They insist that the incidence of engine problems is no higher for those who operate frequently in environments that would provide conditions ripe for shock cooling if the pilot were unwary.

Whether you subscribe to the oft repeated warnings to beware the potential for shock cooling or you think it’s a pile of hooey, a few best practices will help you prevent it if it does exist, and help you extend the life of your engine even if it doesn’t.

*Make power changes smoothly rather than abruptly regardless of the outside air temperature.

*Plan your descents early so that you never have to make drastic power reductions. (Ahem. This one will do more than keep your engine happy. This will keep your passengers happy. Which is nearly as important, if frequently ignored;)

*Install (and remove!) winter kits as specified in the POH for your airplane. They may include air restrictors, oil cooler covers, or other innovations to prevent as much cooling airflow through the cowl of your airplane as you’d otherwise see.

*If you are very concerned, get a CHT gauge or an EGT gauge and learn how to use ‘em.

Shocked? I hope not. Cool. Safe winter flying, my Midwestern friend, and enjoy the endless hanger flying and debate this one will inspire on those murky winter days we know are coming,

Mom

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You’ve got questions? I’ll find you an answer. Email your aviation related question to mom@myskymom.com and check out myskymom.com to read the answers to questions previously posted. An educated pilot is a safe pilot is a happy pilot!  Read on, fly safe, and remember: the only stupid question is the one you didn’t ask!

~ by myskymom on October 20, 2009.