Flying In the Deep Freeze

Since it’s January, and I happen to be in northern New Jersey where evening temperatures have been dropping into the single digits this week, I’m feeling particularly motivated to bring up the subject of winter flying. If you’re feeling a bit cramped and compromised by cold weather though, take heart, because it could be worse: you could live up in Frostbite Falls.

These folks could teach us a thing or two (besides being thankful that if we do have single digit temperatures, at least they’re probably not preceded by a minus sign). I think it might be especially apropos to accentuate the subject of winter flying with a real-life introduction to what to most of us would consider to be the penultimate caricature of winter, which is what flying in northern Minnesota makes abundantly clear. (And no, there isn’t really a Frostbite Falls in Minnesota—or Maine, either. But it was probably the inspiration for the supposed home turf of that now-famous genre cartoon featuring a certain moose and flying squirrel.)

Seriously, the point is that there are some very illuminating things regarding pre-flights, piloting techniques, and caring for aircraft that we can learn from the pilots who regularly brave wind-chills that effectively bring Antarctic air to the middle of America. And there’s no dishonor in learning by extrapolation, if it brings the point across. So what’s it like in a place like International Falls, where pilots regularly experience temperatures of 30 degrees below zero, and wind-chills that can approach one hundred degrees below zero?!

For one thing, there’s no shortage of snow up there. They get somewhere around eight feet of the stuff each year. But snow or even ice is not the principal problem. The most confounding enemy is simply the cold itself. When it’s 15 below, you probably want a snowsuit or mukluks (and don’t even think about starting your engine without a preheat). But your plane needs a few things, too. Here are a few other things to think about:

* In such extremely cold temperatures, the engine breather tubes for piston aircraft (especially the end portion) can freeze over completely. When blocked, the crankcase can become pressurized, and engine oil is literally blown overboard. Operators in these northern climes use insulating material around the breather tubes and also drill holes in the side, which permits continued venting, if the ends of the tubes still freeze up. The message here, for the rest of us: when it’s really cold, check that the breather tubes are still able to (breathe, that is).

* Pilots flying in extremely cold air have also learned to use a couple of different techniques when it comes to the mixture control and carburetor heat. First, they have learned to leave the carburetor heat on during taxi, and during at least part of takeoff, as well. It isn’t because of carburetor ice, though; the air is usually quite dry. It’s simply because the induction air can be so cold (having a greater density) that introducing this unheated heavy air can result in a mixture that is actually too lean for the engine to operate properly. (Think about that: We lean out the mixture when the air gets thin, but we don’t often stop to think that since we can’t enrich the mixture beyond the default “full rich” of sea level, that the only recourse might be to artificially thin out the air, when it gets too thick!)

* Also, once an airplane is shut down, it has sometimes proven helpful to immediately return the mixture to the full rich position, as well as leaving the carburetor heat on full, because when they come back again to start the engine another day, the controls might be frozen and simply be too stiff to move.

* Another related aspect of mixture control in very cold air is to remember you can have a higher than normal fuel consumption, simply because the mixture is richer than needed.

* It is often advised for pilots to leave the power on during the entire descent, to prevent the blasting cold from chilling an idling engine into quitting altogether.

* Another reason for pilots to learn to fly by sound and feel rather than always relying upon gauges is that in extremely cold air, tachometers can fail or give erroneously high indications.

* When they leave an airplane out in the cold, they often tie it down with the tail of the airplane pointed into the wind to help shield the engine from flash freezer winds, and help postpone its otherwise inevitable return to frozen dormancy. (I myself would feel comfortable doing this only if there were a guaranteed means for preventing any buffeting of the more exposed empennage, however.)

* Airplane owners up there have also found that replacing any flush-mounted sump drains with a type that allows them to be pulled shut by hand is very useful, should they get frozen in the open position.

* Continental polar air such as that in the central United States below the Canadian border can reach temperatures low enough where crystals will actually begin forming in fuel (although 100LL is less likely to have this problem than 80-octane fuel or automotive fuel), and some pilots keep a handy supply of an isopropyl alcohol based fuel drying agent, as well as antifreeze additives.

* Above all else, the most important measure is still a proper engine preheat. Surprising to some, it happens that limbering up and heating the engine oil from its sluggish molasses-like state is actually less critical than what can happen to the engine cylinders and the crankshaft themselves, in a sub-zero environment. The reason is that aluminum shrinks and expands at twice the rate that steel does. When an engine is manufactured, the tolerances used between its various internal moving parts are calibrated in reference to much warmer temperatures. Now imagine an aluminum crankcase, cooling and contracting around a steel crankshaft; or aluminum pistons, heated and expanding inside their cooler surrounding steel cylinders…and you might wince, merely at the thought. Many owners fly aircraft having internally installed pre-heating systems such as the ones manufactured by Tanis, which only require the user to have a spare electrical outlet to provide the necessary trickle of heat to keep hibernation at bay. Interestingly, this imperative isn’t just confined to aircraft, but applies to the everyday automotive world as well; many offices, motels, and public buildings in these locales provide outdoor outlets for the installed pre-heating systems of their customers’ cars.

* Living and flying where it is extremely cold, pilots routinely carry extra cold weather clothing such as snowmobile suits and insulated footwear. (Most aircraft heaters apparently work quite well, but when the temperature drops below zero, that isn’t the case.) This should apply to all of us, though, always. Wherever you fly, you should always dress (or bring the proper clothing along) so that you could, in effect, “walk home”.

* And as you might guess, these pilots check their ELTs before every cross-country flight. The reasons are probably obvious, of course.

Just as many of these pointers were probably no great surprise, a few of them were, to me, when I had first heard of them. Being that pilots usually prefer to err on the side of caution, some of these things might be handy to remember, one frigid day. May your flights all be warm ones.