When an aircraft is to be exposed to extreme cold for any length of time, extra care should be taken to see that the aircraft is prepared for winter. All covers for engines, air conditioning system intakes, pitot and static system openings, and ram air inlets should be installed to prevent snow and ice accumulations. Small covers should be conspicuously marked or tagged so that they are not likely to be overlooked before flight.
If the aircraft is to be parked in snow or ice conditions, it sometimes saves time and man-hours to paint around doors and frequently opened access panels with one of the inhibited glycol antifreeze compounds. The glycol may be painted on surfaces under snow covers to prevent the cover freezing to the surface. It can also be used full strength on wing or tail surfaces themselves to prevent frost. However, if snow is expected, painting exposed surfaces is rarely useful, since the slush that forms will be more troublesome than dry snow.
Another timesaver can be parking the wheels on planking rather than on ice or packed snow, or when sleet or slush may be expected to freeze tires to the ground. Sand can be used for such a purpose but should be confined to wheel areas and not distributed where it may be drawn into the engines on starting.
Flaps and spoilers should be retracted. Aircraft with movable horizontal stabilizers should have them set at approximately zero. All water and waste systems should be drained or serviced with an antifreeze solution when applicable.
If an aircraft is to be parked for a long period of time, leaving a window partially open will permit circulation of the air inside and help prevent frosting of the windows. The best way to remove snow is to sweep off as much as possible. One method is to throw a line over the fuselage and drag the snow off. A brush or broom can be used on wing and tail surfaces. Do not damage vortex generators on aircraft that have them.
A certain amount of snow may freeze to the aircraft surfaces which cannot be brushed off. It is important that all surfaces are entirely free of ice, snow, or frost before takeoff.
Most commercial facilities have spray equipment for applying deicing fluids, which are usually diluted with water and sometimes heated. Glycol antifreeze compounds, often identified by military specification numbers, have been materially improved. The compound recommended for commercial use is MIL-A-8243A. This is ethylene glycol and propylene glycol in approximately 3:1 ratio, with added corrosion inhibitor and a wetting agent. It has low toxicity, causes no damage to aircraft metals, and has no effect on most plastics, paint, or rubber.
If hot air is used for deicing, particularly from a ground starter unit, skin areas should not be overheated. A large flow of warm air is more effective than a blast of hot air. Any temperature under the boiling point of water is safe.
Should the last layer of ice or snow be melted from the fuselage, or from the leading edges of the wing, by internal heating from ground sources, the water will probably run down and refreeze in unheated areas, and must be removed again. Whatever the deicing method, inspect the trailing edge mechanism areas of the wing and tail to be sure that water or slush has not run down inside to refreeze.
When conditions warrant, preheating is used on the following sections or parts of the aircraft: accessory section, nose section, Y-drain valve, all oil lines, oil tank sump, starters, instruments, tires, cockpits, and elevator trim tabs.
Check all drain valves, oil tank sumps, oil drains, fuel strainers, vent lines, and all main and auxiliary control hinges and surfaces, for the existence of ice or hard snow. Thoroughly check all deicing equipment to ensure proper operation. Alcohol tanks must be checked for proper level of deicing alcohol.
The use of an external heater is permissible at temperatures below 0° C for heating oil and engine(s). If a heater is not available for heating the oil, the oil can be drained, heated, and put back into the system.
When starting a reciprocating engine in cold weather, try to catch the engine on the first starting attempt to prevent ice forming on the spark plugs. If ice should form, remove the spark plugs, bake, and reinstall.
In freezing weather, ice may form on the propellers while the engine is warming up. Using the propeller deicer (if available) during warmup eliminates this condition. The turbine engine should be easier to start in very bad weather than the average piston engine. Turbine engines do not require oil dilution, priming, or lengthy warmup.
Turbine engine compressor rotors should be checked to see that ice has not formed inside. This is particularly necessary when an engine has shut down in driving rain or snow. Be very careful when running engines if icy conditions exist. With icy pavement, chocks slide very easily, and once the aircraft is in motion it is difficult to stop. After a flight, the oil is diluted prior to shutdown of reciprocating engines equipped with an oil dilution system, if temperatures near or below freezing are expected before or at the time of the next start. When it is necessary to dilute the oil, consult the manufacturer's instructions for the applicable aircraft. These instructions should be strictly followed; otherwise the engine can be damaged.
When fueling aircraft, the fuel tanks should be left about 3 to 5 percent below maximum capacity. This allows for expansion in the event the aircraft is brought into the hangar prior to the next flight. Fuel expands approximately 1 percent for each 10° C increase in temperature. If fuel tanks are filled to the normal levels, at a temperature of approximately 0° C to 10° C, and later brought into a warm hangar (20° C), the ensuing expansion will overflow the tanks, causing a fire hazard.
Tires should be inflated to load standards, regardless of possible rise in pressure under warmer conditions. Underinflation quickly causes overheat that would result in more tire damage and more possibility of blowout than a slight amount of overinflation. If a tire is frozen to the ground, it should be thawed with warm air or water and moved before it refreezes.
It is easy to exceed nose gear towing load limits in snow or slush. If the airplane must be towed in deep snow, it should be pulled by cables attached to the main landing gear lugs. The aircraft battery should require no special attention other than the normal routine servicing.