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| Winter Flying |
| Enjoy the Season Safely |
By Fletcher Anderson
 As this is being written we have had our first few frosts of the winter, which means that we are entering that happy period here in Telluride, Colorado when all the bugs have died so we have clean windshields, but we don’t have to dig the planes out of the snow yet. About this time of year you begin to hear lots of talk about winter storage at the airport. I am here to tell you that you can ignore this discussion. I am going to let you in on a very poorly kept secret: winter in this part of the world is the best time of year for flying there is!
True enough, winter will bring more than its share of blizzards which can last for days on end. You aren’t going to be flying on those days, and neither is anyone else. Give up the notion of flying a small aircraft during a snowstorm right now. But in between the storms the flying is near perfect. The air is much colder and therefore much more dense. Your engine will develop more than summer horsepower. It will cool better. Your wing will develop more lift. You will take off shorter, climb steeper, and cruise faster. Perhaps you know that winter winds blow stronger than summer, but have you considered that cold winter air is typically more stabile than hot summer air? Despite the sometimes higher winds, turbulence is generally less than summer. Morning temperature inversions are the norm and can persist well into mid day, so morning air is more stabile still.
The mountains are jaw-droppingly scenic at any time of year, but certainly no less so under a mantle of snow. A dusting of snow transforms the desert, and you can enjoy it without head banging midday convective turbulence, or a river of sweat gluing you to your vinyl seat. An occasional sprinkling of desert rain can even firm-up a powdery dirt strip.
I could run on in this vein for several pages, but if you are already convinced, let’s move on to a few precautions.
The basic trouble with flying in the winter is that it is cold. It would be great if your plane spent the winter in a heated hangar. One of the planes I fly does. We preflight indoors, open the hangar door, and off we go just like summer. But the other planes I fly all live outdoors.
It can be necessary to arrive at work over an hour early to fly those planes.
If your engine is using a straight weight oil, it is time to see about an oil change. At about 20 degrees straight 50 weight oil is about as thick as old honey. Around zero degrees it resembles very bad tasting Jello, and below zero it gradually congeals into something like candle wax. Even the thick honey has very poor engine lubricating qualities and flows very poorly through oil lines. Your best guess about how well something as dense as candle wax flows through your oil cooler is exactly correct -- it doesn’t flow at all. Assuming that you managed to get the engine started, you could quickly destroy it when first there was no lubrication anywhere from the cold oil, and then as things warmed up the big chunk of solidified oil in the oil cooler blocked the return flow. There is a special drill for flying with this kind of oil in the interior of Alaska where temperatures drop into the –50’s. As soon as you shut down the engine, you drain all the still warm oil into a bucket and take it indoors. The next morning before starting the engine, you heat the bucket of oil on a stove and then pour it back into the engine. You need a pretty good reason to fly to go through that every day.
Extreme measures to pre-heat the engine are always necessary when the temperature is deeply sub zero, but not too demanding on a normal January morning. If you are using straight weight oil (for example if you just replaced a cylinder), then you will have to preheat the engine before starting whenever the temperature is below freezing. There are two ways to do this. The easy way to preheat is to have an electric heating element installed on the bottom of the crankcase. Two hours before you fly (no more is necessary) plug the heater into an extension cord. Otherwise, either the FBO has or you will acquire a propane space heater with a duct to direct hot air under the cowling. Fire up the space heater and wait. When the engine feels warm to the touch it can safely be started. Seldom is this longer than a fifteen-minute process, and you can do the rest of the preflight during that time. (Don’t throw the fuel from the fuel tester near the heater, though -- bad things will happen.)
Despite the obvious hassle factor, I prefer the propane heater method because it preheats everything under the cowling, not just the engine block.
In some parts of the world there is a real concern about moisture condensing inside the engine when it cools after being run. That is not too much of a concern in the dry Southwest. Nevertheless, if you start the engine, you should be sure to warm it up all the way to normal operating temperatures to get rid of any moisture which might be in there.
Multigrade oil is a boon during the winter months because it provides good lubrication at both hot and very cold temperatures. While warmer is certainly better, we have never had a problem starting unheated Lycoming O-320 and O-360 engines with Aeroshell 15-50 oil at temperatures down to 20 degrees. If you elect to do so, first pull the propeller through three revolutions to circulate a little oil and limber things up. Then be diligent about warming the engine up fully before taking off. Remember the oil in the oil cooler has to warm up too. Certain engines, notably Continental O-460s, run much more smoothly and warm up better with carb heat on. The operator’s manual is the definitive guide here.
By the way, in sub zero temperatures, nothing works that well in an aircraft. That includes the radios and all the instruments. They will begin to do much better as the cabin warms up.
At least in the mountains, airframe icing in flight is sometimes less of a problem in winter than it is in spring and fall. Moisture in the air is often frozen below the point where it accumulates on the wings. However, ice and snow accumulation on the airframe while on the ground can be a serious problem. On a clear night, a thick layer of frost can form. During a storm both ice and snow can build up to thickness of several inches. It is not the weight of the ice and snow that is the problem, rather it is the change in shape of the airfoil and the increased roughness. Ice on the fuselage is not a big problem. Ice on the flying surfaces and propeller is. Just how rough is too rough to fly? It is very difficult to give a definitive answer to that question. One technique is to find out by just trying to takeoff with however much accumulation you find, hoping that if you are flying in clear sunny air, it will eventually sublimate off. Before you try this technique, consider the experience of a charter pilot in Glenwood Springs, Colorado on his way to sunny Lake Powell some years ago: Despite considerable frost accumulation, his aircraft lifted off about where it normally did. What it could not do was climb out of ground effect. The runway in Glenwood drops off over a small cliff down into the river, and so did the aircraft, which came to rest upright in mid stream. Fortunately, water levels are lower in the winter, so the water was just lapping up over the doorsills. This was all very funny for everyone except the pilot and his passengers, but it could have been tragic -- the aircraft could have climbed out poorly, then stalled because the rough frost disrupted the airflow.
The less adventurous pilot will elect to get rid of ice on all the flying surfaces before takeoff. This usually means vigorous application of a push broom. Light frost may be polished smooth with a towel. Again, there is an easy way: Cloth wing covers and windshield covers accumulate all the frost, ice, and snow. Just peel them off and you are ready to go. No wing covers? Wrapping a piece of black trash bag plastic over the wing will help melt ice off even in below freezing temperatures.
Winter or summer, condensation of moisture in the fuel tank can contaminate the fuel. In winter that moisture might be in the form of floating ice crystals rather than droplets at the bottom of the tank. Even in the arid southwest, filling the tanks after each flight reduces that possibility.
Carburetor ice can form when the temperatures are between freezing and about 60 degrees and you have moisture in the air (and, of course, when you have a carburetor.) These conditions can occur at any time of year. Often in winter carb ice is no problem because it is so cold that the moisture in the air has already frozen. Carb ice can form during taxiing, so checking the carb heat to clear it before take off is imperative. Carb ice is a bigger problem when you throttle back to descend to land. Moist air goes through the carburetor and then expands as it goes by the closed throttle. Expanding cools the air and frost forms inside the carburetor. Rather than try to calculate whether carb ice might form, just use carb heat for every approach.
Slush or even just water on the runway can be a problem for retractable landing gear. The slush can freeze on climb-out and lock the gear in the up position. Cycling the gear a few times on the climb breaks up this ice as it is forming.
Most people realize that metal, (and indeed everything else) is much more brittle in extreme cold. In terms of hazards to flight, extreme temperatures here means way down in the minus 60 or 70 degree range. At those temperatures, the metal of the airframe might not be exactly brittle, but is certainly less ductile or elastic than it normally is. Radical aerobatics might be discouraged. Around zero degrees, your Plexiglas windows are more brittle than usual, as is your plastic cabin trim, but in practice there is no real cause for alarm.
You may not have used your cabin heater since last March. This might be a good time to have a mechanic take a look at it. Most small aircraft heaters consist of a cuff surrounding an exhaust pipe. An exhaust leak fills the cabin with carbon monoxide. A simple monoxide detector is a cheap piece of protection. Gas powered heaters can also produce monoxide, and some of them have a nasty reputation for catching on fire.
Taxiing on ice or snow can be more exciting than you want. Just like driving your car, the way to taxi on an icy ramp is very slowly with very low power settings. Taxiing in deep snow risks getting stuck. In a nose wheel aircraft, keep the yoke way back to keep the nose wheel light and never let the aircraft come to a full stop.
A takeoff from an ice runway is very straightforward because you almost instantly have rudder effectiveness, so you never notice that the tires have no traction. In deep powder snow, the same soft field takeoff technique used for dirt or sand works just fine. Hold the yoke back to lift the nose wheel out of the snow and the aircraft will fly off in ground effect at very low speed, then fly in ground effect until you reach normal climb speed.
A long descent to land in extremely cold temperatures runs the risk of cooling the engine below the temperatures needed to get full power for a go around. A descent at a lower rate with more power can help alleviate this trouble.
Landing on a snow-packed or icy surface can mean poor traction. Last winter I was following local charter pilot Todd Wilson home from maintenance. He touched down right on the numbers will full flaps right at the slowest possible airspeed. His next radio call was to Unicom “braking reported nil at the first taxiway by a 206,” followed shortly by “nil at the second taxiway,” and so on for the next 3000 feet of runway. There being little else of equal entertainment value going on that afternoon, the line crew all came out to watch my landing. Sure enough, despite the heads up, I too slid all the way to mid field. Neither of us had any problems other than the long distance used because the rudder remains effective until you are going very slowly. The obvious problem could be running out of runway. On pure smooth ice, one option would be to deliberately ground loop and add power when you were going backwards. Alternately, it might be safer to run off into the snow in the over run area.
Landing in deep snow requires normal soft field landing technique. The trouble is that you cannot really tell from the air how deep the snow on the ground actually is. In 1996 I made a low pass at Sand Wash, Utah, and deduced that the snow cover was only about two inches deep. When I touched down, powder snow plumed up over the cowling and at full power the best I could do was a very slow taxi at less than walking speed. Not daring to stop, I ran back and forth up and down the runway six times until I had packed out a trench two feet deep from which I took off.
What I might have done was deliberately made a couple of touch and goes to test the snow surface. What I narrowly avoided having to do was foot pack the whole runway in order to get out of there.
No one likes to think much about crashing, and indeed most of us go to great lengths not to do it. Regarding winter crashes, there is some good news and some bad news. The good news is that winter crashes tend to be a little more survivable. That is because you are sometimes crashing, (or does making a forced landing sound more appealing?) in snow, which both cushions the impact and helps prevent fire. The bad news is that once having survived the crash, you are in a survival situation in the depths of winter in an area even more remote at this time of year than in summer.
Most pilots flying over remote areas in winter pack sleeping bags, a little food, and something to use to make a fire. Snowshoes and more elaborate survival gear than that would certainly not be out of place. Yet it is amazing how many people you see getting into a small plane in winter without such basic gear as gloves, a warm coat, or snow boots. While the standard advice is to stay with the plane and wait to be found, the reality is that you should not expect to be found very soon. Properly equipped, you have the option of a downhill walk to the nearest road. Unequipped, you have a choice between freezing to death in the plane or getting stuck walking out and freezing elsewhere. Remember that the weight of this survival gear is minimal and your aircraft will be flying better.
Winter flying requires certain precautions, but then so does summer, spring, and fall flying. When those precautions are taken, winter flying can be at least as safe if not safer than flying at any other time of year. Because of the smoother, denser air, it can be the most pleasant time of year to fly. The argument over the most scenic time of year to fly is unwinnable. Drop in to Telluride and we can debate it.
Fletcher Anderson is a flight school operator and sometimes corporate pilot based in Telluride Colorado. He can be found wandering around on the ramp in the predawn hours in a pair of Sorells with a snow shovel on his shoulder. |
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