A thorough preflight inspection is important in temperature extremes. It is natural to hurry
over the preflight of the aircraft and equipment, particularly when the aircraft is outside
in the cold. However, this is the time you should do your best preflight
inspection.
Fuel Contamination
Fuel contamination is always a possibility
in cold climates. Modern fuel pumping facilities are generally equipped with good filtration
equipment, and the oil companies attempt to deliver pure fuel to your aircraft. However,
even with the best of fuel and precautions, if your aircraft has been warm and then is parked
with half empty tanks in the cold, the possibility of condensation of water in the tanks
exists.
Fueling Facilities
Another hazard in cold climates is the
danger of fueling from makeshift fueling facilities. Fuel drums or "case gas,"
even if refinery sealed, can contain rust and somehow contaminants can find their way into
the fuel. Cases are on record of fuel being delivered from unidentified containers which was
not aviation fuel. As a precaution, we suggest:
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Where possible, fuel from modern fueling facilities; fill your tanks as soon as possible
after landing, and drain fuel sumps to remove any water which may have been introduced.
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Be sure the fuel being delivered is, in fact, aviation fuel and is the correct grade (octane)
for your engine.
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If you are not using modern fueling facilities, be sure to filter the fuel as it goes into
your tanks. NOTE: A funnel with a dirty worn out chamois skin is not a filter, nor
will a new, clean chamois filter out water after the chamois is saturated with water. Many
filters are available which are more effective than the old chamois. Most imitation chamois
will not filter water.
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Special precautions and filtering are necessary with kerosene and other turbine fuels.
Manufacturers can supply full details on handling these fuels.
Fuel Filters and Sumps
Fuel filters and sumps
(including each tank sump) should be equipped with quick drains. Sufficient fuel should be
drawn off into a transparent container to see if the fuel is free of contaminants.
Experienced operators place the aircraft in level flight position, and the fuel is allowed to
settle before sumps and filters are drained. All fuel sumps on the aircraft are drained
including individual tank sumps. Extra care should be taken during changes in temperature,
particularly when it nears the freezing level. Ice may be in the tanks which may turn to
water when the temperature rises, and may filter down into the carburetor causing engine
failure. During freeze-up in the fall, water can freeze in lines and filters causing
stoppage. If fuel does not drain freely from sumps, this would indicate a line or sump is
obstructed by sediment or ice. There are approved anti-ice additives that may be used.
Where aircraft fuel tanks do not have quick drains installed, it is advisable to drain a
substantial amount (1 quart or more) of fuel from the gascolator; then change the selector
valve and allow the fuel to drain from the other tank.
Advisory Circular (AC) 2O-43C, Aircraft Fuel Control,,
(http://www.airweb.faa.gov/Regulatory_and. . .89790036862569C3004BA88B?OpenDocument) contains excellent information on fuel
contamination. Paragraphs 10 and 11 are especially pertinent to many light aircraft and
include a recommendation for periodic flushing of the carburetor bowl.
Aircraft Preheat
Low temperatures can change the viscosity of
engine oil, batteries can lose a high percentage of their effectiveness, instruments can
stick, and warning lights, when "pushed to test," can stick in the pushed position. Because
of the above, preheat of engines as well as cockpit before starting is considered advisable
in low temperatures. Use extreme caution in the preheat process to avoid fire. The
following precautions are recommended:
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Preheat the aircraft by storing in a heated hangar, if possible.
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Use only heaters that are in good condition and do not fuel the heater while it is running.
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During the heating process, do not leave the aircraft unattended. Keep a fire extinguisher
handy for the attendant.
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Do not place heat ducting so it will blow hot air directly on parts of the aircraft; such as,
upholstery, canvas engine covers, flexible fuel, oil and hydraulic lines or other items that
may cause fires.
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Be sure to follow the manufacturer's procedures.
Engine Starts
In moderately cold weather, engines are sometimes
started without preheat. Particular care is recommended during this type of start. Oil is
partially congealed and turning the engines is difficult for the starter or by hand.
There is a tendency to overprime, which results in washed-down cylinder walls and possible
scouring of the walls. This also results in poor compression and, consequently, harder
starting. Sometimes aircraft fires have been started by overprime, when the engine fires and
the exhaust system contains raw fuel. Other fires are caused by backfires through the
carburetor. It is good practice to have a fireguard handy during these starts.
Another cold start problem that plagues an unpreheated engine is icing over the spark plug
electrodes. This happens when an engine only fires a few revolutions and then quits. There
has been sufficient combustion to cause some water in the cylinders but insufficient
combustion to heat them up. This little bit of water condenses on the spark plug electrodes,
freezes to ice, and shorts them out. The only remedy is heat. When no large heat source is
available, the plugs are removed from the engine and heated to the point where no more
moisture is present.
Engines can quit during prolonged idling because sufficient heat is not produced to keep the
plugs from fouling out. Engines which quit under these circumstances are frequently found to
have iced-over plugs.
After the engine starts, use of carburetor heat may assist in fuel vaporization until the
engine obtains sufficient heat.
Radios
Radios should not be tuned prior to starting. Radios should be turned on after the aircraft
electrical power is stabilized, be allowed to warm up for a few minutes, and then be tuned
to the desired frequency.
Ice, Snow, and Frost
A common winter accident is trying to take off with frost on the wing surface. It is
recommended that all frost, snow, and ice be removed before attempting flight. It is best to
place the aircraft in a heated hangar. If so, make sure the water does not run into the
control surface hinges or crevices and freeze when the aircraft is taken outside. Don't
count on the snow blowing off on the takeoff roll. There is often frost adhering to the wing
surface below the snow. Alcohol or one of the ice removal compounds can be used. Caution
should be used if an aircraft is taken from a heated hangar and allowed to sit outside for an
extended length of time when it is snowing. The falling snow may melt on contact with the
aircraft surfaces and then refreeze. It may look like freshly fallen snow but it usually
will not blow away when the aircraft takes off.
If an aircraft is parked in an area of blowing snow, special attention should be given to
openings in the aircraft where snow can enter, freeze solid, and obstruct operation.
These openings should be free of snow and ice before flight. Some of these areas are as
follows:
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Pitot tubes
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Heater intakes
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Carburetor intakes
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Anti-torque and elevator controls
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Main wheel and tail wheel wells, where snow can freeze around elevator and rudder controls.
Fuel Vents
Fuel tank vents should be checked before each flight. A vent plugged by ice or snow can
cause engine stoppage, collapse of the tank, and possibly very expensive damage.
Taxi
Braking action on ice or snow is generally poor. Short turns and quick stops should be
avoided. Do not taxi through small snowdrifts or snow banks along the edge of the runway.
Often there is solid ice under the snow. If you are operating on skis, avoid sharp turns, as
this puts torque on the landing gear in excess of that for which it was designed. Also for
ski operation, make sure safety cables and shock cords on the front of the skis are carefully
inspected. If these cables or shock cords should break on takeoff, the nose of the ski can
fall down to a near vertical position which seriously affects the aerodynamics efficiency of
the aircraft and creates a landing hazard. If it is necessary to taxi downwind with either
wheels or skis and the wind is strong, get help or don't go. Remember, when you are
operating on skis, you have no brakes and no traction in a crosswind. On a hard-packed or
icy surface, the aircraft will slide sideways in a crosswind and directional control is
minimal particularly during taxiing and landing roll when the control surfaces are
ineffective.
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