Airplanes seem to like cold weather. They pick up speed more rapidly on the takeoff roll and lift off with little or no effort. The controls have a crisp, quick feel thats lacking during the summer months. The engine(s) sound at the peak of strength.
Cold air and airplanes do well together. Well, most of the time. There are a few drawbacks.
One of the biggest problems for cross-country fliers is that reliable icing forecasts are as rare as honest crooks. Icing sometimes shows up where none was supposed to be and is frequently absent from where its supposed to be.
The inaccuracy of the weather predictions leads many people to ignore icing forecasts in favor of going and taking a look, but that strategy is charged with danger. Anyone flying an airplane that is not equipped for flight into known icing conditions should consider a forecast for ice as being accurate. If the forecast calls for the possibility of ice, however, there are more options at hand.
If you plan to fly into an area where there is a possibility of icing, get the briefer to tell you where the moisture is. Then study the temperature aloft conditions. If there appears to be moisture at the right temperatures along your route of flight, find out what might lift and cool that air.
Winds from the Pacific Ocean and northwest winds from Lake Erie and Lake Ontario can create some of the worst icing conditions in the United States. The Great Lakes provide the moisture that the passing winds pick up. In eastern Ohio, western Pennsylvania and New York, rising terrain forces the moisture upward and a vast icing potential exists.
In the Midwest, its difficult to forecast icing with any kind of accuracy because of the powerful winter inversions. Between the ground and 3,000 feet, the temperature may climb 10 degrees C. If moisture is coming up from the Gulf of Mexico and there is a strong southerly flow aloft, the Midwest can develop some heavy icing.
Obviously, the key to understanding the risk of icing is to know where the source of possible moisture is and how close you are to that source.
Over most of the country east of the Rockies, the moisture comes from the south or the east. A low pressure center will carry moisture counterclockwise and northward, ahead of the lows center.
If you are northeast or east of the center of the low, the moisture will be new and usually in liquid droplet form – and that spells icing. If you are north or west of the center of the low, the moisture has been swirled up and around the top of the lows center. The moisture is most likely frozen into snow or ice already.
The forecast you get from the briefer will tell you that both sides of the low are the same – with icing the same on either side. But if you are flying northwest or west of the low, the icing chances are dramatically reduced, if not eliminated.
Can You Make It?
If there is any secret for dealing with ice, its to always have an out. Because of the serious trouble that may await you at altitude, youll need to keep an escape route in mind. It could be a 180-degree turn, a landing at the closest airport, or a climb or descent.
It will depend on whether there is a suitable airport available, the traffic, the cloud conditions and the terrain. Let ATC know that you are in ice and need to get out immediately. Ask for a lower or higher altitude, or a vector out of the stuff.
Because ATC will ask you how you plan to solve your problem, an important preflight step is to develop a thorough understanding of the vertical cross-section of the air mass in which you will be flying. From November through March, you can expect snow squalls, icing, mountains obscured, and severe turbulence from the southerly jet stream.
Developing the specific strategies for getting out of ice requires that you get the answers to some important questions from the weather briefer.
• Find out where the fronts are. Most ice is in the low pressure centers and in the fronts.
• Find out what direction the fronts are moving. Where will the fronts be located when you takeoff and where will they be when you reach your destination?
• Ask about the cloud bases. If you can stay below the clouds and out of freezing rain, there is little chance of structural icing.
• Find out how high the cloud tops are. If you are flying a light, non-turbocharged aircraft, you probably cant make it through an ice-laden front with tops over 8,000 feet. If you do get on top, you may not be able to stay in the clear. Remember that the clouds balloon up much higher over mountainous terrain.
• Consider several alternative routes. Flying over terrain with a low MEA is a good idea. The weather is usually much better, with less ice than if you decide to go over even a small mountain range.
• Get pireps. These reports deserve a lot of attention, both when planning the flight and while en route. Remember that one pirep isnt enough to base your strategy on.
Preflight planning is the time to review your potential escape routes. If temperatures are above freezing below you, descend if you pick up ice – but only if you can still maintain enough altitude for safe flight. You may be able to climb into cold, clear air on top where the ice will sublimate, but that strategy may backfire if you have to descend into ice in order to land at your destination. Check to see if alternate airports will be in the clear.
If you cant develop sound escape routes, you should seriously consider canceling the flight.
Getting Ready to Go
Once you start the cold-weather preflight of the airplane, it is soon clear that there are a number of things to add to the standard checklist.
Carry extra fuel. Icing conditions may mean increased aerodynamic drag and, in some airplanes, the necessity to use carb heat extensively. In either case youll fly slower unless you use higher power settings. No matter which way you go, fuel consumption will be higher.
Even after adding the extra fuel, keep the airplane as light as possible. A heavier airplane will take longer to climb through clouds, increasing its exposure to potential icing situations.
Beware of ice and snow in and on the airplane. Any time moisture meets freezing temperatures ice forms somewhere. After flying in cold weather, the crankcase vapors may freeze in the engine breather tube – spelling trouble on the next flight.
If the ice isnt removed and doesnt melt, the next time the engine is run the crankcase will pressurize, pushing oil through the seals and overboard. Pilots in the far north use insulated breather tubes and drill a few holes in the sides. Even if the end freezes, the crankcase vapors still vent out the holes in the sides.
Visible snow, frost or ice on the airframe must be removed before flight, of course. Keeping the airplane in a hangar can prevent airframe ice, but hangaring is not always possible on a cross-country flight.
There are a couple of ways to remove snow and ice. De-icing fluid or hot water can be applied with a garden sprayer. The pilot (or ideally the pilots teenage children) can break ice up and brush it off. The aircraft can be towed into a heated hangar until the ice melts.
Keep in mind that melting the snow or ice can lead to problems if the water remains on the airplane and refreezes. Control surfaces can jam or become dangerously unbalanced.
Frost is a little more insidious. It may not appear to amount to much, but it can have some serious effects in reducing aircraft takeoff and climb performance. A sandpaper-thin layer of rough frost has been shown to destroy as much as 30 percent of normal lift. If the aircraft does lift off, it is so close to stall that any turbulence or maneuvering could cause loss of control.
The accidents blamed on frost on the wings tend to support the notion that the airplane will lift off and fly in ground effect, then stall when the pilot tries to climb further. The top surface of the wing is simply not smooth enough to develop a lower pressure differential.
While you are doing this exterior de-icing, remember to cover the pitot tube and the static sources to prevent any liquid being blown into the systems and causing erratic readings. But make absolutely sure that you uncover the ports after the de-icing treatment is over.
While examining the airframe, make certain that the landing gear is free of accumulated slush. Slush can freeze the gear into the gear wells of a retractable and cause the wheels of a fixed gear airplane to lock, especially if the airplane is fitted with wheel fairings.
The Price of Carelessness
The responsibility for ensuring that the airplane is ready to fly is firmly with the pilot. Some pilots have come to grief after assuming that the snow would blow off during takeoff. Others have found that melting the snow does no good if the water refreezes during the climb to altitude.
If ice or snow collects inside the control surfaces or freezes to the outside of them, aerodynamic flutter or vibration can result.
The airplanes tail surfaces and ailerons have been carefully balanced to operate without any unusual characteristics. A very small amount of ice can change all that careful design work and maintenance, and can be very hard to stop. Immediately reducing airspeed far below where the vibration began will sometimes stop it. Delaying a corrective measure can spell disaster. Vibration and flutter can quickly cause the control surfaces to deform or depart the aircraft.
There are places where frozen water can hide in an airplane that can cause some major worries. The fuel system is probably the worst of the hazards. Condensation moisture in the tanks can freeze and block the fuel lines. This is particularly a problem in airplanes with rubber fuel bladders. Water that collects in the wrinkles can be difficult to sump, making a buildup of water to dangerous levels relatively easy.
Remember also that preflight extends into the cockpit.
The cold may affect your nav/comms and flight instruments as well. Consider the case of the pilot making an early-morning air taxi flight in IFR conditions in January. He made sure that all frost was removed from his wings and tail surfaces before he called for his IFR clearance. The departure airport was an uncontrolled field, so the pilot received his clearance and void time by telephone. The clearance void time was tight and didnt allow the pilot much time to warm up the airplane.
After entering IFR conditions following takeoff, the aircraft turned off course and crashed into rising terrain. Investigators determined that the gyro instruments were not operating at proper speed due to the cold and were presenting unreliable information.
Dont Forget the Contents
Once youve preflighted the trip and the plane, dont forget to give some thought to the occupants. Dont start a winter flight if you arent physically fit. Cold weather can sap a lot of energy. Just doing a thorough winter preflight inspection takes more time and effort than in warm weather.
Flying safely and being physically fit are directly connected. No pilot is alert when his body is below par. Flying requires quick thinking plus excellent coordination. If you fly when you are under the weather, fatigued or under the influence of alcohol, you are inviting trouble.
Prepare for a cold weather flight before you get to the airport by putting some thought into the clothes that you are going to wear. February weather in the Dakotas will call for considerably more than a sweater, some loafers and a light jacket. Think about long underwear, a parka with a hood, fur-lined boots and gloves and a scarf around your face. Sub-zero wind chills and North winds can be fierce.
If you have ever had a heater fail in flight, or one that barely puts out any warmth at all, you know that you will want your warm clothes or a blanket close to you in the cabin. Warm clothing wont help you much if its stored in an inaccessible baggage compartment.
Start Your Engines
Once the plane and occupants are ready to go, the temptation is to fire up the engine and proceed as if it were a fine May day. Beware that temptation.
When oil is very cold it will congeal and cut down on the starters ability to crank the engine. And if it does start, the oil is so thick that it cant be pumped through the engine very well. The internal engine parts start a metal-to-metal grinding that produces lots of wear. In general, preheat the engine any time the ambient temperature drops below 20 degrees F.
Preheating should do more than just warm the engine oil. Warm oil is necessary, but preheating also protects the cylinders and crankshaft from damage. Engine tolerances are not calculated at sub-zero temperatures, and different metals react to heat changes differently. For example, aluminum shrinks and expands at twice the rate of steel, boding ill for crankcase-to-crankshaft and piston-to-piston sleeve clearances.
Another thing to remember is that cold starts lead some pilots into over-priming the engine in an attempt to get started before the battery gives up. Excessive throttle pumping and electric boost pump priming can lead to an engine fire.
What can really be annoying is when a cold-soaked engine gives a couple of snorts and bangs, and starts for a second or two, then quits. It probably wont start again for a while. The cylinders have been flash-heated by the partial combustion, and the moisture in the air will condense and form ice on the spark plug electrodes. The plugs will be short-circuited by the ice and external heat will be necessary to get a start now.
FBOs at airports where cold weather is a fact of life are usually well-equipped to apply heat to balky engines. Some of them use electrical power to heat the crankcase or oil dipstick. Others use 12-volt electric motors to circulate air warmed by LP gas heaters into the engine compartments. Adding heat blankets to the mix will make the preheat more thorough and effective.
When taxiing, remember that snow and ice on the ground and the runways are more than a challenge. They can ruin your day.
The most common problem results from taxiing at a speed so slow that the airplane bogs down in drifts and layers that are no more than a couple of inches high. But dont taxi so fast that the nose gear is damaged by running against chunks of ice and dont slide out of control.
Most pilots generally ignore crosswind taxi technique and get by most of the year. But crosswind taxi technique becomes very important on ice. Think about what positions the elevator and ailerons should be in to offset the crosswind before you start taxiing over the slippery icy surface.
Tuck em In and Freeze em
In airplanes with retractable gear, avoid areas of slush or standing water. A couple of minutes after takeoff, recycle the landing gear to make sure it doesnt freeze into place inside the wells. If they do freeze in the wells, even the emergency extension system may not free them.
Finally, a runup location should be carefully selected. It may be a difficult choice. If you end up on icy surfaces, point the airplane in a safe direction. Make sure you are ready to back off on the throttle if the airplane starts to slide forward.
If takeoff distance is a factor, think about how conditions will change the airplanes performance. If you are located where the snow and ice are removed, the cold air is likely to make performance very good. If you are facing a crosswind and a snow-covered surface, the normal takeoff limits arent very valuable.
Alaskan pilots learn to increase normal hard-surface runway requirements by 10 percent in light snow, 20 percent in hard-packed snow on a cold day and 30 percent on a warm-day snowpack. Limit crosswinds to half of the demonstrated limit unless the runway is ice-slicked – then limit it to a quarter of the demonstrated component.
Ive used those limitations for years, in and out of snow-covered fields in Gallup and Sante Fe, N.M., and Bishop and Tahoe City, Calif. If your POH offers other guidance, take it. But most are mute on the point.
These limits may seem excessively conservative. True, you wont make some takeoffs and landings you might otherwise attempt, but you wont bang up airplanes, either.
Takeoff should be accomplished along the lines of the soft or rough field takeoff. You want a rolling takeoff. Dont stop on the runway unless directed by ATC; you dont want frozen brakes.
Apply power smoothly and be prepared for some swerving on the takeoff roll as you hit patches of drifting snow. Take immediate action with the rudder to keep rolling straight. Dont forget the aileron correction for crosswind, if you need it.
Cruise is pretty straightforward. Keep the engine temps up and stay out of icing conditions.
Icing layers in stratus clouds are usually thin and changing altitude may be the best plan. The icing layers in cumulus clouds are a different matter. They are usually several thousand feet thick. You may need to circumnavigate the area.
If you encounter freezing rain, reverse course and land if youre flying VFR. If you are IFR, get clearance to climb into the warmer air above or on top of the cloud layer.
Descending can create a major dilemma, particularly if you are IFR. Come down too soon and you may be faced with an extended trip through icing conditions. Wait too long and youll get a slam-dunk at the end. Whether you believe in shock cooling or not, a high rate of descent at low power will cool the cabin off as well as make ears pop.
Tell the controller what you want to do, based on weather conditions and the distance from your destination. Ive been doing it for years in light planes and have always had full ATC cooperation.
Certainly, you may get some wide vectoring at a busy terminal if you ask for a gradual descent. Its the price you pay if you arent flying a Citation.
Coping With Ice on Approach
If you have picked up a little ice and are approaching to land, keep in mind that the handling characteristics and the stall speed may be much different than on a clean airplane.
Once you are carrying the ice, you have qualified as your own test pilot. There arent any numbers in the POH for this one. The thicker the ice accumulation on the airfoil surfaces, the higher the approach speed should be.
You may have a windshield that you cant see through. The ice may block your vision straight ahead. Most of the accidents happen when the pilot loses control of the airplane during the approach or landing. Turn the defroster to high, carry a little extra power and turn off the cabin heat to send as much heat to the defroster as possible. If thats not enough, you may need to open a window and attempt to scrape some of the ice away with a credit card, putty knife, or whatever you have handy.
Dont make any large or abrupt changes in flap setting or power during the approach and landing. Fly the airplane onto the runway. Dont forget that the higher landing speed will increase the distance you will need to get stopped, especially if the runway is covered by ice or snow.
Keep the crosswind aileron correction in and stay straight on the runway. Wait until youre clear or the runway before you mess with cleaning up the flaps, cowl flaps or lights. Taxi carefully to parking, remembering that the snow can hide many evils.
With some reasonable planning and careful preparation, you should be able to enjoy safe, comfortable flying throughout the winter months.
Winter flight carries with it some remarkable beauty and also makes light planes more useful to those who want to travel. Although the elements may be a bit more hostile when temperatures are low, winter flying doesnt have to be extraordinarily risky – as long as both pilot and plane are prepared for the challenges ahead.
-by Raymond Leis
Raymond Leis is a CFII and ATP with more than 23,000 hours.