Flying during the winter season can be one of the most spectacular experiences there is. Especially in the mountains. But winter time means that we have to take special preparations to safeguard ourselves and the aircraft, so that flying remains fun even in the cold season and does not become a life threatening situation.
Winter equals freezing weather, snow and ice. Ice can really ruin the aerodynamics of an aircraft if present on a wing surface. Engines can also experience ice depending on humidity.
Two types can develop here: fuel / throttle and induction ice. Evaporation of fuel causes a drop in temperature, when enough moisture and the temperature drops below freezing (in the carb throat) ice will form on the throat of the carb, causing a restriction. It is imperative to understand that this can happen in summer too! It all depends on temperature drop and moisture content. Throttle ice forms on the valve. Apply full carb heat when an unexpected RPM drop or MAP change (constant speed prop) sets in.
Induction ice forms when flying in circumstances where ice will form on the induction system restricting the flow of air to the carb. Applying carb heat doesn't work here, the use of alternate air is the only solution.
To prevent the build up of ice, use carb heat periodically. Like every 15 minutes or so and apply it for 30 seconds so that any ice can melt. Try to make a habit of this procedure by doing this year round, it will save the day some day. If you have a carb temperature indicator then apply enough carb heat to keep the carb temp above 5 Celsius to avoid icing.
If ice was present in the carburettor it will melt due to applying carb heat and the engine will momentarily run rough as it tries to run on water, which it wasn't designed to do. When the ice is removed RPM will rise and MAP too.
For engines with a fuel injection system the selection of alternate air is the solution when icing is suspected. Keep it on until entering an area with warmer air. Make sure you are aware of the freezing level, descent below that if necessary.
Precipitation in winter time is frozen above the freezing level and usually just plain wet/rain below that. Only aircraft allowed to fly in known icing conditions can legally do so, it may not be smartest thing to do, however. Rain can turn to snow real quick and hide important navigation details on the ground. Whiteout occurs when the snow covered terrain blends into the overcast sky. Any horizon is very difficult, if not impossible to see. If this happen (like inadvertently flying into clouds) go to instruments, make a 180 turn at rate one and fly back.
Descending for landing through a thin cloud or fog layer can result in a reduced forward visibility to several hundred feet or less. While above that layer the horizontal and vertical visibility are quite good. This could be even worse when the landing runway heading is directly into the setting sun.
Landing on wet, snow covered surfaces should be done at the minimum speed possible for the situation, not downhill, keeping the aircraft straight with the rudder. Do not use the brakes, locked wheels will result in loss of directional control. With a taildragger, keep out of heavy snow patches or shallow depths. It could nose over unexpectedly.
Refuel the aircraft to minimize the change for moisture formation in the tanks during the night. Have it parked in a hanger, if possible. If left outside, use the control locks and tie it down to the ground. Use control locks on the steering column or external between the flaps and ailerons, do remember to lock the rudder and elevator too. If you have wing covers, use them to keep the wings clear. Any snow on the aircraft changes its weight and if too much gets on the tail, the result could be an aircraft sitting on its tail feathers.
If your aircraft needs to cover any inlet, use the bright orange types. They are highly visible and the change of forgetting them the next day is minimized, it could be a surprise to notice on take off that your airspeed indicator isn't working (always check airspeed alive on the take-off roll).
If heavy snow is expected during the night and the aircraft sits outside, be prepared to regularly clean the wings. This will avoid too much weight on the structure.