Some pilots have the need, while others have the desire, to fly during cold weather. Whether you do it or not is something that you have to sort out for yourself. Cold weather flight operations require preparation of the pilot and the airplane.
Not many pilots are comfortable when they need to "expand their comfort zone" through trial and error. They find it reassuring to be exposed to the "unknowns" before venturing outside their circle of comfort.
Loaded with the knowledge that you can perform cold weather flight without suffering dire consequences will make winter flying enjoyable, but it requires preparation. You might do some research using the internet and talk with a knowledgeable instructor. Perhaps the best source of information is the forums of many pilot associations. They can provide practical advice about the operating procedures and precautions for the particular model airplane you fly.
The pilot must be equipped, in addition to knowledge, with the proper attire for the flight operation. This includes cold-weather clothing and a survival kit. The importance of a survival kit cannot be over-stressed. It must be located where it is accessible. I would rather off-load fuel, baggage or passengers than to leave my survival kit at home.
All mechanical equipment, including airplanes and their components, are designed for operation within certain temperature ranges. Exceeding the temperature range of the airplane or equipment may create premature failures.
The temperature ranges for operating your airplane comes from the manufacturer who can make predictions of their product’s performance.
Without specific information about your airplane, seek the advice of competent operators (remember those pilot forums) and mechanics permanently situated in the location where you wish to operate. They can judge the requirements and limitations for the peculiarities of their area.
For operating in very cold environments, insulation, called lagging, may need to be installed on all oil lines, oil pressure lines, and oil tanks to eliminate congealing of the oil.
Some manufacturers provide baffles, winter front covers, and oil cooler covers, as optional equipment items for winter operations.
You’ve probably seen duct tape or silver tape on airplanes in cold climates. It is not legal to cover a portion of the oil cooler with tape.
Oil is important. It must lubricate, cool, seal, and clean the engine. For that you will want a multi-viscosity rather than straight-weight oil. Phillips Petroleum and Shell multi-viscosity oils are approved by the FAA and they meet the requirements of Avco Lycoming Specification No. 301F and Teledyne Continental Motors specification MHS-24B.
The viscosity of the oil is important in cold weather operations. If the oil is too thick, it will not lubricate the engine when cold. If too thin, it will break down at high temperatures. Multi-viscosity oil is good for the engine.
Disregard any claim that multi-viscosity oils will permit longer intervals between oil changes. There are many by-products an oil must clean, such as rust, corrosion, acids, and varnishes, so stick to your regular oil change schedule.
OIL BREATHER LINE
Moisture forms whenever combustion occurs. Most of the moisture is scavenged out the exhaust. Some moisture, however, finds its way into the crankcase. When these crankcase vapors cool, they condense in the crankcase breather line. If the ambient temperature is at freezing or below, the breather line may freeze closed. When this occurs, pressure builds up in the crankcase that might cause the oil filler cap to blow off or an oil seal to rupture, causing oil to pump "overboard."
Some pilots have their mechanics drill a small hole in the breather line where it comes out of the crankcase, or cut a slit, if the line is a hose, to relieve the pressure if it freezes. This hole may result in a dirty engine compartment; whereas, if a punch is used to indent an area above the hole or concave the hole surface, the pipe will breathe without leaking oil from the hole. The hole or slit should be located where its pressure relief effect will not direct oil toward an exhaust pipe.
An operating cabin heater is essential for winter flights. Without adequate cabin heat, sub-zero air along with the pilot’s breath can fog or ice windows in a matter of minutes. If this occurs, the only recourse may be to open an air vent. Unpleasant as exposure to sub-zero air may be, it does not compare to the discomfort of trying to land with zero visibility.
Lack of heat can be pilot incapacitating to the extent that one cannot change radio frequencies or perform a simple task like picking up a pencil. It also results in the pilot exhibiting impaired judgment.
Although the likelihood of a cabin heater failure occurring in flight is small, it does happen.
I can vividly recall one night flying a Cessna turbo 310 from Jackson, Wyo. to Minneapolis when the gas heater failed. We diverted to Billings, Mont. It was a chilly –10ºF. By the time we tracked down a mechanic to have the heater checked out, it began working again.
Because of icing at lower altitudes, we selected flight level 190, and continued toward Minneapolis. Murphy visited again and the darn heater quit. This time we diverted to Bismarck, N.D. It was –40 at 19,000 feet and the same on the ground at Bismarck.
You cannot imagine and I cannot find the words to describe how cold we were. I’ve been goose hunting and have fallen into the Snake River at –30ºF. Struggling back to the car, my clothing froze solid. That was not cold compared to the cold in an airplane. We were prepared with cold-weather gear (winter hats, coats and gloves), but all of us neglected to have cold-weather footwear.
It’s near impossible to find a mechanic late at night in Bismarck, especially when the temperature is –40.
We finally found an unheated hangar that was unlocked. To avoid the wind and cold we ventured in. Our feet hadn’t quite reached the numb stage so we removed our shoes and walked around with bare feet on the frozen cement floor. Why? Because it was warmer than our feet.
We determined the gas heater failure was not a mechanical failure, but rather, a frozen fuel supply line. After adding an anti-ice additive we continued to Minneapolis basking in heat that would melt a candle.
When the airplane is kept outside during freezing temperatures, the battery should be kept fully charged to prevent loss of power. Once it is "dead" it will freeze, often breaking the casing. If you can’t connect a trickle charger, remove the battery and store it in temperatures of 60º to 75ºF.
Do not jump start a dead battery and go flying. When subjected to a high charge rate, it may explode. The battery will have to be removed, warmed, and charged slowly.
At near-freezing temperatures, mud and slush may be splashed into the wheel covers of fixed-gear airplanes or thrown into the wheel wells of retractable-landing gear airplanes during taxi and takeoff. It then freezes during flight, creating landing problems.
During cold weather, remove the wheel pants from fixed-gear aircraft. About all you can do with a retractable-gear airplane, is to let the wheels spin down to sling off excess moisture after takeoff, then recycle the gear as a preventive procedure.
Because of multi-viscosity oils it is possible to start an airplane engine without preheating, even in temperatures as low as -25ºF. Be warned that this will decrease the life of the engine.
Generally,+20ºF or lower is considered a mandatory "preheat" temperature. Below the pour point, oil quickly turns to a molasses-type liquid and any colder temperature results in the oil rapidly approaching a solid.
In a sheltered area, the engine may be kept warm with the use of a mechanic’s drop cord with a 60- to 100-watt bulb installed. Place this light near the bottom of the engine, inside the cowling. It will keep the engine toasty. If the airplane is outside the use of an insulated engine blanket (old quilt) will be required.
When using a forced-air engine heater, it is possible to direct the hot air blast at the cylinders. When the engine appears heated and ready to go, the oil is still in a near-frozen state. Direct the hot air blast at the bottom of the oil pan (through the cowl flaps if there isn’t an opening).
When the engine is shutdown after a flight, moisture condenses on the inside and outside of the case. Preheating causes these tiny, frozen droplets to melt and disappear. If the preheating continues until the moisture disappears entirely on the outside of the engine and the propeller turns easily, the preheating process is complete.
Above 20ºF the engine maybe started without preheat, but the oil may be partially congealed. Some manufacturers recommend that the propeller be turned over by hand at least four times to relieve some of the stress on the starter and battery. If the Pilots Operating Handbook does not recommend pulling the propeller through, don’t do it. You may be "rubbing" metal against metal and the engine won’t like it.
Never operate a starter motor for more than 90 seconds continuously. If the engine does not start, allow a full minute before attempting another start. This allows the starter motor to cool down. After the initial attempt, do not operate the starter for more than 30 seconds continuously.
Some pilots have a tendency to over prime during cold starts. This washes the oil from the cylinder walls when raw fuel is directed into the cylinders without passing through the carburetor and intake manifold.
After starting the lack of lubrication causes scoring of the cylinder walls. This in turn causes a lack of compression and causes hard starting.
Over priming can also cause induction fires. If a fire occurs, continue operating the starter in an attempt to suck the fire back into the engine where it belongs.
The most common problem that plagues engines that have not been preheated is that of "frosted" spark plug electrodes. The pilot tries to start the engine. The engine fires a couple of times and then quits. Any further attempt at starting is futile since there has been sufficient combustion to cause some moisture in the cylinders, but insufficient combustion to heat them up. As a consequence, the water condenses on the spark plug electrodes, freezes to ice, and shorts them out.
Give it up. The engine is not going to start. The only remedy is heat. If an engine heater is not available, remove the plugs and heat them until all moisture disappears.
For prolonged cold-weather operations, switching to fine-wire spark plugs helps eliminate the frosted-plug problem and improves cold starts. They cost a bit more (about 4 times more) than the massive-electrode plugs, but they save money on fuel and they last longer, making them cheaper in the long run.
When the temperature is extremely cold, fuel vaporization becomes a problem. Immediately after starting, apply carburetor heat to help vaporize the fuel. As soon as the engine will run smoothly without carburetor heat, turn it off.
Engines have a habit of quitting during prolonged idling because insufficient heat is produced to keep the plugs from fouling. Avoid prolonged idling and you’ll avoid iced-over or fouled spark plugs.
OIL PRESSURE INDICATION
You should look for an oil pressure indication within 30 seconds after starting in warm temperatures. There should be an indication within 60 seconds during cold temperatures.
If there is no indication turn off the mags, rather than the mixture, to stop the engine faster, and investigate the problem.
If the airplane requires changing the position of the fuel selector valve to select a different tank as the flight progresses, it is wise, in the winter, to change to the other tank while leaving a 30-minute reserve in the original tank.
It is possible to have condensation or contamination in the tank you are switching to, and the engine just won’t run. You then have the option of going back to the original tank and having a 30-minute reserve to find a landing place.
Use isopropyl alcohol or anti-icing fluid in the fuel, as recommended by the manufacturer, during cold-weather operations.
Taxiing will present a challenge when the surface is snow covered or icy. Often there is no place where you can stop the airplane and perform a run-up without "slip sliding away." Do the run-up during taxi.
PROCEDURE FOR LEANING—TAKEOFF
The mixture must be leaned in accordance with the manufacturer’s recommendation. We know that maximum performance at high altitude airports is obtained only after the mixture is adjusted to obtain maximum engine efficiency.
It is equally important to lean the mixture for the landing as well as for the takeoff in the event a go-around maneuver must be performed.
Leaning the mixture at high altitude airports to obtain maximum power available for takeoff is based on the DENSITY ALTITUDE, not the physical altitude.
You may be operating from a high elevation strip during the winter when no leaning of the mixture is required.
During the let-down for landing, if the engine is cooled too fast, thermal stresses occur in the engine. The valves may become warped and certain parts may crack or become distorted.
This occurs because the engine uses different types of metals in its various components. Metals with different rates of contraction and expansion can raise havoc when cooled too fast. For example, a turbocharger may experience temperatures of up to 1,600-degrees Fahrenheit in normal cruise flight. If the throttle is reduced to idle while descending, the internal turbocharger components’ temperature may cool below freezing in a very short time. The situation is aggravated during the winter.
During descent in an airplane with a constant-speed propeller, maintain the manifold pressure no lower than the bottom of the green arc, around 15 inches.
For an aircraft equipped with a fixed-pitch propeller, keep 1,500 rpm as a minimum.
This technique not only keeps the engine "ready for action" if a go-around maneuver becomes necessary, it will also prevent thermal shock.
Sometimes losing altitude is difficult while carrying power. Slow to the flaps extended speed and add flaps to create drag. Then the "extra" power required to pull the airplane through the air during the descent will keep the engine warm.
If the airplane has retractable gear, lower the gear (observe the maximum gear operating and extended speeds) to create additional drag.
One may get away with thermally shocking the engine and making a go-around with full power, but the cumulative effects of the induced stress may be such that the engine will quit some day during normal operations.
Mountainous terrain is inhospitable to downed flyers, but the winter exacerbates all problems. The pilot must be aware of the terrain and have some contingency plan established beforehand for what would happen if a forced landing occurred.
When the weather turns bad en route, having the ability to fly IFR is not always an out. Aircraft icing requires not only the instrument ticket, but also an airplane equipped to handle the weather.
The possibility of a forced landing, especially a survivable forced landing, during the winter requires the pilot to plan the flight more conservatively than during any other time of the year.
Blue skies, tail winds and safe flying!