Read the owner’s manuals for several aircraft, and you’ll discover cold-weather starts are different for each engine, but there are some fairly universal rules to follow during cold start attempts. Some pilots refuse to move prop blades under any circumstances, but I always pull them through several times to break any possible hydraulic lock. Fuel is reluctant to vaporize in cold weather, and you’ll need to prime the engine(s) more than normal if you expect to start on the first or second try, an important consideration when two tries may be all you’ll get.
Don’t be overly enthusiastic about priming in cold weather, however. Limit engine cranking to no more than 15 seconds at a time. Remember, too, that constant speed prop mechanisms are oil-operated. Oil in the prop hub may have congealed, and you may need to let it warm up before you can expect the prop control to function.
Managing engine power after start can require you to split the difference between idling too slowly (which can ice the plugs) and too fast (which, as mentioned above, can score cylinders and cause ring damage). Keep power high enough so the engine runs smoothly, but not so high that you compromise lubrication with the cold oil. Most bush pilots recommend leaving cowl flaps closed in bitterly cold weather, especially during the warmup. The last thing you need during a start at -20 degrees F is a higher volume of cold air sucked through the cowling.
Avoid fast taxiing to keep from coating the wheels and brakes with snow and ice. If conditions are truly slick, you might consider doing the run-up and much of the power-up phase of pretakeoff checks on the roll to avoid losing control of the airplane in the run-up area. Just make certain you don’t lose control on the taxiway.
It’s axiomatic that directional control on a snow-covered runway can be trickier than on dry asphalt. Accordingly, avoid using braking for directional control, especially on patchy snow and ice. Let a locked wheel slide off glare ice onto dry pavement, and you may be sideways faster than you can think about it. During the takeoff run, use pure nosewheel/tailwheel steering until the rudder gathers enough aerodynamic authority. If there’s a crosswind that normally would demand differential braking for directional control, consider offsetting the nose an appropriate amount left or right of centerline before initial power-up.
Anything that increases rolling friction extends takeoff run, and snow can be a particular problem because it also affects directional control. Even if the runway is smooth and level, but covered with a flat layer of snow with no ice underneath and the wind is calm, expect the takeoff run to be at least 20 percent longer. Soft-field technique should be used just as you would on a grass strip, i.e., lift the nose or tailwheel off early to reduce rolling friction. You’ll want to get the airplane into the air as quickly as possible so you can accelerate quicker and climb away.
If you’re departing from a slushy runway in a retractable, you also should consider leaving the wheels down for a few seconds after liftoff to blow accumulated snow off the gear legs and out of the wells so it won’t freeze into ice in the cold temperatures aloft.
Engine temperature management in extremely cold weather can be daunting. Just as it’s often difficult in hot weather to keep engines from overheating, it may be a challenge to keep the cylinder heads warm in winter. Quite often, you can leave cowl flaps closed for the entire flight, and experienced-cold country aviators suggest using Vy for climb rather than cruise climb speed to reduce airflow through the cowling.
As mentioned last month, I nearly always flight-plan for higher altitude in winter for a number of reasons. Navigational radio range is extended at taller heights, and that may be important when a blanket of snow obscures VFR ground reference points. For the same reason, higher provides a better pad of altitude in case you need to look for a place to park it in an emergency. Much winter weather is low-lying, so flying tall also gives you a better chance of clearing the clouds.
In-flight icing is a hazard all its own, one that has generated a plethora of articles, so we can hardly hope to fully cover the subject here. Icing is perhaps the most publicized hazard of winter flight, but it’s less common than you might imagine. Temperature, pressure, humidity and ionization all have to be right to produce airframe ice. When they are, though, the result isn’t fun.
Snow may look nasty to fly in, and it does reduce visibility, but it’s generally not much of a problem in flight, as it rarely adheres to aircraft surfaces enough to distort an airfoil. Conversely, true icing may occur over a much wider range of temperatures than you might imagine. While most icing happens between about zero and -10 degrees C, I’ve seen it at -20 degrees C. Colder temperatures generally don’t allow icing since there’s little humidity present and, therefore, poor adhesion.
There are two types of ice—clear and rime. The first normally is associated with vertical clouds such as cumulus. It’s a denser form of ice, so it’s tougher to break loose, and its temperature is most likely between about zero and -5 degrees C. Rime is the more common, garden-variety form—a chalky, more aerated, less cohesive collection of frozen water that’s found in flatter, stratus clouds over a wider range of temperature. Because of its airy composition, rime is easier to sublimate or break away.
Freezing rain is a phenomenon you’d better hope you never encounter, as it can accrete at an amazing rate. As the name implies, freezing rain results from an inversion when rain falls through sub-zero air below. Freezing rain isn’t limited to winter. I’ve seen it in all seasons, including in August over Libreville, Gabon, hard by the equator.
Remember that your primary instrument in predicting icing, the ever-popular, refrigerator-style outside air temperature (OAT) gauge, is probably the second least accurate instrument in the cockpit, right behind the airspeed indicator. Even if OAT is correct, the temperature inside a cloud may be dramatically different from that in the clear.
If you challenge the clouds in winter and encounter airframe icing, the best escape route may be up rather than down, as climbing may take you above the clouds completely. Also, remember that if you climb and things only get worse, you can always come back down. If you descend first and pick up more ice, you may lose the option of climbing out the top.
Keep in mind, however, that the tops of cumulus clouds are where the ice gods hold their parties. Some of the highest rates of ice accretion are found in cloud tops. I once had an Aerostar turn into an instant popsicle over the Gulf of Mexico at -20 degrees C and 19,000 feet when I was too stupid/lazy to circumnavigate a cumulus top. Unless you just naturally enjoy having the windshield become totally opaque in about five seconds, always elect to deviate around cloud tops rather than flying bravely straight through them.
Assuming the weather between departure and destination is less dramatic (usually the case), your biggest challenge in winter may come when it’s time to put the airplane back on the ground. The temperature at typical cruising altitudes may be well below -10 degrees C, so you’re liable to increase your risk of icing as you descend into warmer air below. If you fly a fairly fast airplane, aerodynamic heating at high cruise speeds may help offset some airframe icing. Slow the airplane to approach speed, and you’ll lose that heating effect. Be especially wary if you’re assigned an altitude in the middle of the ice or a holding pattern that flies you through an area of icing. Don’t be shy about telling the controller you prefer ice in your Gatorade rather than on your airplane.
Letdowns through a layer of ice can present problems, too. In those instances when I have considerable altitude to lose and must descend through a possibly ice-laden overcast, I’ll often stay higher longer, then drop through at a relatively high descent rate. To avoid shock-cooling the engine, I leave power at a tolerable level, but configure the airplane for the approach early. That way, I can penetrate the ice at maximum vertical velocity (1,000 fpm or more), but minimize forward speed to reduce ice buildup. I like to arrest that high descent rate well above my target altitude, but I always keep in mind that, at this stage of the flight, any ice I accumulate probably will stay with me through the landing.
Speaking of landings, you may need to be more attentive during winter than in summer. Winds sometimes are stronger, snow and ice on the runway can be significant considerations, and falling snow during the approach can render landing lights worse than useless. Stay off the brakes after touchdown if there’s any question of ice, and beware of “black ice,” a phenomenon of icing on asphalt that may be nearly invisible. If you must use the brakes because of a short runway, do so very warily, applying them gently and evenly to avoid asymmetric braking across patches of bare asphalt. To paraphrase one of Mother’s old sayings, Take all the runway you want, but don’t use more than you have.
Just as with landing on a dry runway, do your braking in a straight line. Bring the airplane practically to a full stop pointed straight ahead before even considering a turn off the active. Don’t try to make a high-speed turnoff to accommodate the controller if you sense even a hint of directional problems. An icy runway isn’t the place to practice short-field approaches, but don’t wait too long to apply the binders. Braking action at the opposite end of the runway may be especially poor where aircraft residues such as tire rubber, fuel and hydraulic fluid accumulate.
Finally, rethink your summertime attitude regarding alternates in winter. Weather moves faster in the late months. What was clear and 20 two hours ago at your destination may be down to 200 and a half in another hour when you arrive. It’s a mistake to assume early-morning fog at your destination will dissipate as quickly as it might in summer, too. The sun is farther south, arcs lower on the horizon and has to shine diagonally through more atmosphere, so less heat and light reach the ground to burn off the clouds. Shorter hours of daylight also contribute less heating.
If these warnings lead you to believe winter flying isn’t worth it, you might want to reconsider. Winter can be a spectacular time to fly. True, you need to exercise more cautious weather judgment, and there are some different operational considerations to flying when the thermometer is low, but with a little care, winter can be one of the most rewarding times of year to fly.