Although some recreational fliers ground themselves during the dingy winter months, most pilots continue to rely on their airplanes even when the mercury dips and the gray skies move in. And theres no reason not to, as long as you take into account the icy grip winter weather can have on everything it touches.
Planning for defensive flying in winter conditions begins on the ground. For VFR flight, youll need to plan to stay clear of clouds by a reasonable distance and be alert for signs of carb ice. For the pilots who are going to go IFR, things get more complicated. Watching The Weather Channel just isnt enough.
Preflight planning has to be thorough and thoughtful. Consider the route you plan to fly, and ask yourself if there are any alternates available. A trip over the mountains might mean turbulence, massive downdrafts on the lee side, and moderate to severe icing. A safer alternative might be a series of detours to terrain with lower MEAs, usually much better weather and less ice.
Some pilots depend on pilot reports to identify where the hazards are. Pireps need to be studied with care. What do they tell you about the areas that you are planning to fly through? How do the conditions and times match up with what your forecast says you can expect? Do you have a way out if unfavorable conditions develop?
You are better informed if you have more than one pirep from an area. If you depend on just one and dont relate it with the time and your forecast, you may be surprised when you get there.
Above all, plan an escape route for each part of your flight, just in case icing shows up. You may have to descend, climb, make a 180-degree or even land immediately at a nearby airport. Youll need to look carefully at your charts to determine what the terrain factors are, and if suitable airports are near your route of flight. If you fly in congested areas like the northeast, consider also the preferred routing of ATC and what will happen if all the light planes call in asking for diversions.
Remove all the ice or snow from the wings. The wing was designed to be flown perfectly clean. Thats the only way it will produce maximum lift. Every winter there are pilots who think that the takeoff roll will blow the collected snow from the wings. It doesnt work. There is almost always a lift-reducing, airfoil-modifying sticky snow underneath. Brush or sweep it off and be sure. If there is an ice layer below, youll need deicing/anti-icing fluids to ensure best wing performance.
Its best to polish frost to as smooth a condition as possible. It may take a lot out of you, but the price of airplanes is high, and hospital expenses keep rising all the time.
If you cant store the airplane in a heated hangar when ground icing is a threat, you may need to have your aircraft sprayed with deicing fluid before flight. The mixtures are similar to automobile antifreeze – ethylene and propylene glycol mixtures. Glycol mixtures are 20 percent water and about 80 percent glycol and are heated before they are sprayed on. The water melts the ice and the glycol brings the freezing point down at least 11 percent, which prevents ice from reforming for about 45 minutes. However if its very cold, with heavy precipitation, the ice can come back much more quickly. Places you dont want sprayed include the windows, pitot tubes, static ports and air intakes.
Special care is also needed around brakes and wheel wells. The high pressure from the sprayers can damage the hoses and fittings. Getting deicing fluid in the brakes can cause them to glaze or cake when the brakes heat up from use, diminishing braking action.
You need to be extra careful with a winter preflight. In a case in Illinois, a pilot flying a Cessna 182 drained water from the fuel tanks during preflight. During a local VFR flight the engine failed and the pilot made a forced landing in a wooded area. Investigation revealed ice in the gascolator.
Another frosted area that gets forgotten on preflights, causing needless accidents, is the horizontal tail surfaces. These surfaces continually carry an aerodynamic down load. The stabilizer has a negative angle-of-attack to compensate for the fact that the airplane is designed with the center of gravity in front of the center of lift.
If the streamlined flow of air across the surfaces of the stabilizer and elevator is spoiled by frost, ice or damage, the distorted airflow will have a serious effect on elevator control. The airplane may become unbalanced and exhibit a dangerous nose-heavy condition. Moderate to serious buffeting can be expected. Make sure the frost and ice is off the top and bottom of those horizontal tail surfaces before flight.
Cold weather requires thinned oil. Be sure that the oil in the engine is the correct viscosity for the temperatures of the season.
Engine (and sometimes cabin) preheat is a good idea, if available, when the temperature approaches freezing. The POH is the authority for preheat advice.
Make certain that the anti-ice and deicing equipment is in working order. Include the pitot heat; it seldom gets a functional check on the ground.
Clean off all of the accumulated slush from the landing gear, especially on retractables. Youll need to check wheel wells for ice accumulation. If you have taxied through wet snow, mud or slush, youll need to confirm that the wheel wells arent packed up. Landing gear can freeze in the wells, preventing extension. The really big slush collectors on fixed gear airplanes are the wheel fairings. They need to be removed in winter.
Youll want to be sure that there is control freedom of movement in all directions. Often, water that has been used to remove ice on the airframe will refreeze, blocking the control movements.
Make every effort to keep the aircraft as light as possible. Eliminate all of the items that you dont need. The more weight you need to carry, the more time you will spend in the ice, due to a slower climb rate.
Plan to carry extra fuel. There is always a possibility that there will be a performance penalty caused by ice accumulation. The power required to maintain altitude may be increased to a much higher amount than normal cruise. You can expect the fuel consumption to rise.
Airplanes tied down in very cold weather can pick up ice in a number of places you hadnt thought of before. Sometimes the hangars arent warm enough to guarantee everything is unfrozen.
Heres a case from New Hampshire where the pilot noted that the temperature was -4 degrees F. The airplane was kept in an unheated hangar and was equipped with an E-Z Heater airplane engine heater system. About 5 minutes after takeoff the pilot noticed a high oil pressure indication. Oil started to spray on the windshield and some smoke came into the cockpit. The pilot later said: Not knowing the extent of the damage, and thinking that I might have an engine fire, I chose to make an off airport landing.
An investigation showed that the oil had come out through the nose seal and the crankcase breather line was plugged with ice. There is an FAA Advisory Circular, 91-13C, that states: … special care is recommended during the preflight to assure that the breather system is free of ice.
Finally, in case there are still hard-nosed pilots who believe that snow, ice or frost on the wings will work for takeoff, heres one from Juneau, Alaska. The pilot of a PA-18 Super Cub did not remove ice from the wings during preflight. Following takeoff, the pilot ran into control difficulties. He circled the field for a landing but stalled during the approach and crashed in a field, short of the runway. The Cub was totaled, but the pilot got out with minor injuries. The pilot had 22,000 hours total time, and 8,000 of those hours were in the Super Cub. Ice is a great leveler of pilot egos.
A pilot needs to be aware that braking action on ice or snow is generally poor. Certainly to be avoided during taxi are short turns or quick stops. Dont taxi through snow banks or small snowdrifts along the edge of the runway. You might be unpleasantly surprised to experience solid ice under the snow.
Keep the taxi speed slow on icy taxiways. Counteracting the tendency of the airplane to weathervane in crosswinds may be a limiting factor. When using the brakes, tap them lightly and briefly. Youll have a skid develop if you lock up the wheels with hard braking pressure. Runups are a problem. Find a dry patch of pavement on the taxi strip or leave some space ahead to slide a little as you run up.
Snow piled up along the edge of the taxiways snags wingtips every winter. The wingtips and the tail structures take a beating, and the flight stops there. Extreme caution is necessary to avoid the aircraft repair bills.
If your airplane is so equipped, check the ice-protection equipment as required by the airplanes POH. If there are deicer boots, these need to be coated with approved anti-icing fluid to slow down ice accumulation.
Before takeoff, check the wing and tail surfaces for any accumulation of snow or freezing precipitation. Make absolutely certain that the wing and tail surfaces are clean. I have shut down and gone outside to do that final check after taxiing through free-standing water and slush. In a couple of cases, I had more fluid deicing to do on the underside.
Although it may seem excessively cautious, realize that even light frost on top of a wing – a rough sandpaper finish – is enough to cut lift by up to a third. Ice on the bottom sides of the wing and horizontal stabilizer surfaces could result in major lateral control problems at liftoff.
If you have several pilot reports of the tops of the clouds, planning to climb through a possible layer of icing to on-top is a relatively safe way of coping with an icing forecast. If, for some reason, your climb is delayed by ATC and the ice starts to accumulate, advise the controller immediately.
If you cant get clearance to a higher altitude, request a vector away from traffic so you can continue your climb and get out of the icing. If you cant get any cooperation, use your emergency authority under FAR 91.3.
You need to take immediate action once ice plastering begins. If you wait too long, its possible in some conditions for the load of ice to be so great that about all you have left is the option to descend. Its important that you understand where the ice forms first in your range of view on the aircraft. It usually is the OAT gauge probe.
The faster you can detect ice formation, the more promptly you can start some action – operating the boots or moving out of the icing zone.
Of course there is still the old enemy of carbureted engines – carb ice. Here is the case of a Cessna 152H pilot who had inadvertently entered a cloud at about 3,000 feet while descending at night. He then started a climb and obtained an IFR clearance to Corvallis, Ore. Shortly afterward he was cleared to descend to 4,000 feet and broke out of IMC over Albany, Ore. He canceled IFR, reduced power from 2,600 rpm to about 2,200 rpm, and quickly descended to 2,000 feet for the remainder of his flight.
Shortly after reaching 2,000 feet, the engine quit and the prop stopped without warning. The pilot then executed a dark night forced landing. Carb ice was to blame.
Ice Man Cometh
When you first see ice forming and the accumulation rate is very small, this is what is known as a trace of ice. This is the way it should be reported. Unless your airplane has certified ice protection equipment, you need to plan to get out of it as soon as possible. If you continue along in trace icing for more than an hour, you are asking for trouble.
Light icing means you occasionally need to use the deicing equipment to remove it, or the anti-icing systems to prevent its buildup. You can expect serious problems if you spend even an hour in light icing. Its another situation where you should take immediate action to get out of these conditions.
Icing accumulation can cause some airframe vibrations that are hard to locate. There is usually noise that accompanies the vibrations. Now and then an antenna mast will ice up, vibrate and snap off the airplane. The trick here is drive off panic and take immediate action. The old phrase: aviate, navigate and communicate fits here.
Moderate icing is the next stage. Its serious. Even short encounters will build up large accumulations of structural icing. With this type of hazardous icing you need to use whatever ice protection equipment you have and divert immediately. No ifs.
If your airspeed drops 10 knots using your normal cruise power setting, its a strong clue as to how much ice is accumulating on your airframe. Its time to get out. Where to go?
Well, youll need to have an idea of what conditions are above and below you, including the estimated temperature and moisture content. If you cant descend or climb, the only choice left is a 180-degree turn.
Dont wait until the situation is beyond salvaging. Work with ATC early. Start working with them as soon as the first ice begins to build on the airframe. Be sure that the controller understands that you need a priority clearance to change altitude or direction as soon as possible. You need to get to warmer air or a cloud-free altitude.
If you need to declare an emergency to get out of trouble, do it. Losing control, with an ultimate crash, may be the other answer. When on-top, and well before getting into clouds that contain freezing moisture, ask ATC for a climb, providing your aircraft can keep you on top.
If the temperature is close to freezing and youre in the clouds, ask for a tops report up ahead. You should be able to decide from this report whether climbing is better than descending. If you have a thick icing layer to get through, your airplane performance might not be able to get you up that high.
Using the autopilot is not a good idea in icing conditions. The autopilot covers up the effects of the ice on the control system and can result in an unexpected violent stall/spin situation.
The worst-on-worst case is severe icing. The buildup of ice is so fast that even the best ice protection equipment cant reduce the accumulation. Options? Climb, divert, descend or land. Now.
Make pireps as you fly your route and ask for them as well. Talk to ATC and flight service about any forecast changes or new weather developments.
Consider the case of a 2,800-hour pilot flying a Beech Sierra on a cold, dark night in March. The pilot held a commercial certificate and CFI, SEL, MEL, and glider ratings. His destination of Teterboro, N.J., showed a ceiling of 800 feet and visibility 1.5 miles in light freezing rain.
The pilot received a preflight weather briefing and was advised of precautions for occasional moderate mixed and rime icing, as well as severe mixed and clear icing along the route of his flight. He launched anyway. Enroute he encountered icing conditions and ice accretion on the aircraft. Manifold pressure began decreasing and the pilot was unable to maintain altitude. Subsequently, he made a forced landing and the airplane struck a house and a car.
The pilot said, At 5,000 feet, I expected to be above the freezing level, due to a temperature inversion. This was the case until I reached the Philadelphia area, where I then encountered light rime icing on the leading edges. Afterward my manifold pressure dropped to 21 inches, and I began to lose altitude. Although I expected to receive an increase in manifold pressure on my descent, none occurred.
At about 2,000 feet, I felt that I could not make (a nearby airport) and declared a mayday. I was maintaining 95 knots. Post accident examination of the airplane included a functional test of the engine in a test cell. The engine operated rich below 1,800 rpm, and takeoff power was achieved. No mechanical problems were noted with the airplane.
Ending It All
You might be able to climb on top of the clouds and cruise to your destination ice-free, but you are still not parked there yet. There may be a freezing level at or near the surface. That can ice up your airplane and produce a windshield that you cant see through for landing. Planning ahead can help.
Most of the icing accidents occur when the pilot loses control during approach or landing. Remember that structural icing gives the airfoils new and untested shapes that dont always respond to the pilots actions. Even a thin layer of ice will call for a 20 percent increase in speed on final. Be cautious in traffic pattern turns. The stall potential is high.
The extra speed will increase your stopping distance on the runway, too. Adequate runway lengths are part of preflight airport selection. You might be used to a 3,000 foot runway under VFR conditions, but it wont work well if youre carrying a load of ice. Increased speed and zero flaps will make the landing distance much longer than usual. There also could be ice and snow on the runway, which will certainly increase stopping distance.
A Cessna 340 pilot was flying an ILS into Westhampton, N.Y. Controllers had cleared the airplane for the ILS approach to runway 24, circle to land on runway 06. The airplane broke off the approach to runway 24 and was observed on the left downwind for runway 06, flying in and out of clouds. When the airplane made the left base-to-final turn, the left wing struck the ground. Just before the crash the engines were reported by witnesses to be at full power.
Several pilots from the Air National Guard at the airport went to the crash site, arriving only minutes after the crash. They observed layered ice on the aircrafts wings and empennage. One ANG pilot said the ice appeared to be approximately 1/8th inch in thickness throughout the left and the right wing surfaces, and the rear empennage sections.
Another ANG pilot described the weather at the time of the accident as approximately a 500-foot ceiling, visibility less than 1 mile, with freezing rain and sleet.
The NTSB blamed the accident on the pilots poor decision, which resulted in ice accretion on the aircraft, degradation of aircraft performance, an aerodynamic loss of control and inflight collision with the ground.
On any IFR approach that may contain icing on final, be cautious with the use of flaps. Lowering them while experiencing moderate to severe icing may disrupt the airflow over the tail, causing it to stall. Changes in flap or power settings should be made in small increments and only after the landing gear is extended.
What to do with an iced-over windshield that wont respond to the defroster? I have, in slow airplanes – and with a well-gloved hand – opened the side window and scraped off enough ice with a plastic checklist or credit card for a keyhole approach to landing. Youll need to take rapid glances through the side windows, to correct for crosswinds, as well. Of course the best solution is to turn the windshield defroster on high before you let down through icing conditions. In some cases you may need to turn off the cabin heater to get more heat to the windshield. You may also want to place approach chart books or sectionals to deflect heat directly on the windshield.
At many small airports and a few large ones, airplane owners have moved their airplanes into hangars for the winter. Flying for them is done for the year. Maybe they will visit at each others hangars and sit around the heater on the worn-out sofas, talking about the possibilities for next spring and summer flights.
Most of the airplanes arent well-equipped for winter flight and the pilots have, in many cases, let their IFR proficiency slip. The daylight hours are shorter, too. So, the use of instrument skills and equipment are a requirement for many winter cross-country flights.
But winter can be one of the best times of year to fly. The colder air is usually crisper, cleaner and readily accepted by the engine. Power seems to gain. The visibility is unusually good.
There are cold weather problems, but once you are aware of them, planning a safe flight is not difficult. Pilots will need to be up to the challenge of winter flights. It will require a review of basic pilot skills, possibly a renewal flight or two for some of them. But thats why most of us came to fly in the first place, accepting the challenges and still being successful and safe pilots.
-by Raymond Leis
Raymond Leis is a CFII and ATP with more than 23,000 hours.