COLD WEATHER OPERATIONS
Aircraft and their components are designed to operate within certain temperature ranges. If information about these ranges is not available, operators should consult the manufacturer as to precautions to be taken in extremely cold weather operations. Also the advice of operators and mechanics permanently located in the area of operation is of great value.
1. Aircraft Preparation For Cold Weather Operations
a) in extremely cold temperatures all oil lines, oil pressure lines and tanks, in aircraft with reciprocating engines, should be inspected for proper insulation to preclude the possibility of oil congealing. Insulation must be fireproof and the installation accomplished by an experienced mechanic.
b) baffles, winter fronts and oil cooler covers are recommended by some manufacturers (check for manufacturer’s approval)
c) check if oil and grease grades are as those specified by the manufacturer
d) special care is recommended during the preflight to assure that the crankcase breather system (reciprocating engines) is free of ice. Check if modification of the system is necessary and if yes, if it is approved.
e) inspect all hose lines, tubings, seals for any deterioration. Check all clamps and fittings.
f) inspect the cabin heater system to eliminate the possibility of carbon monoxide entering the cockpit/cabin.
g) check all control cables
h) remember that feathering of oil pressure controlled propellers, in extreme cold, may lead to the situation where congealed oil will not allow the propeller to be unfeathered.
i) if the airplane must be parked outside, wet cell batteries should be either kept fully charged or removed from the aircraft to prevent loss of power cause by cold temperatures. Dry cell batteries are resistant to power loss by freezing.
j) look out for any mud or slush which thrown into wheel wells, during taxi and takeoff, may freeze in flight and cause landing gear operational problems. If possible, avoid surfaces covered with mud or slush and remove wheel pants (fixed-gear aircraft) to prevent the possibility of frozen substance locking the wheels/brakes.
2. Preflight Actions
a) even in low temperatures, when conditions might entice the pilot to hurry the preflight phase, conduct full preflight inspection
b) check for fuel contamination which is very likely to happen when the aircraft was parked warm with half full tanks as this leads to water condensation in tanks. To check for contamination use all installed fuel sumps.
c) check for fuel source, use the best fuel available from modern fuelling facilities. If not available – filter the fuel as it goes into the tanks. Use good, commercial filter.
d) preheat the engine and cabin to minimise changes in the viscosity of oils, maximize the effectiveness of batteries and avoid situations when instruments stick.
e) to make preheating safe follow these precautions:
- preheat the aircraft by storing in a heated hangar,
- use only heaters in good condition and do not refuel the heater when it is operating,
- do not leave the aircraft unattended during the heating process.
- keep a fire extinguisher handy (fire extinguisher with CO2 should be fully charged)
- do not place heat ducting so it will blow hot air directly on combustible parts of the aircraft
- when using a “fire pot”, use a wire mesh in the ducting to prevent flaming pieces of carbon from entering the aircraft or engine compartment.
f) remove all frost, ice and snow from all airfoil and control surfaces and around the static system sensing point.
g) if an aircraft is parked in an area of blowing snow, put special attention to openings in the aircraft where snow can enter, freeze and then obstruct operations. There openings are:
- pitot tubes and static system sensing ports,
- fuel vents,
- heater intakes, carburettor intakes,
- wheel wells,
- tail wheel area (check for any frozen snow around the elevator and rudder controls).
h) in ski operation check all safety cables and shock cords.
i) if you are to fly over big, sparsely populated areas, consider carrying appropriate survival kits and proper clothing. It may save your life in case of forced landing.
3. Engine Start
a) in moderate cold an engine may be started without preheat. Use care as it may be difficult due oil being partially congealed.
b) avoid the tendency to overprime. It may lead to cylinder walls scoring, poor compression and hard starting. It may also be a cause of engine fire.
c) the reason for hard starting may be icing over sparkplug electrodes. To avoid it, heating is necessary and, if heat is not available then the plugs should be removed and heated to the point where no more moisture is present.
d) remember that during prolonged idling of the engine it may stop as insufficient heat is produced to keep the plugs from fouling out. When engine stops after long idling check plugs for icing.
e) remember that turbine engines can accumulate internal ice overnight and resist rotation when starting is attempted. Therefore with any indication of locked rotor, unusual noise or low RPM – discontinue the start.
a) in ski operation: exercise caution during downwind/crosswind taxiing and turning, especially when skis have no brakes.
b) in deep snow or on packed snow or ice, during wheel operation, braking action is poor.
c) avoid snow banks along the sides of runways as they may be frozen solid.
a) do not overboost supercharged or turbine engines. Use power charts for the pressure altitude and temperature to determine appropriate manifold pressure and engine pressure ratio.
b) remember that on multiengine aircraft the critical engine-out minimum control speed (Vmc) will be higher than the published figure.
c) with reciprocating engines use carburetor heat as required. On some occasions, in extremely cold weather, it may be advisable to use carburetor heat on takeoff.
d) use anti-ice and deice equipment as outlined in Flight Manual. In turbine powered aircraft remember that use of bleed air will, in most cases, affect aircraft performance.
a) in aircraft equipped with reciprocating engines, keep a close watch on cylinder head temperature. If the head temperature nears the critical stage, increase the airspeed or open the cowl flaps or both.
a) if You are to fly into snow shower be prepared to revert to instruments as visual reference may be lost.
b) if a “white out” (a condition in which there are no contrasting ground features in pilot’s visibility range) occurs - immediately shift to instrument flight.
c) in icing conditions use anti-ice equipment in the manner for which it was designed (anti-ice equipment is to prevent ice formation, not to eliminate which has already built-up)
8. Descent and Approach
a) during descent, there may be a problem keeping the engine warm enough. It may be desirable to use more power than normal, which may require extension of gear or/and flaps to keep the airspeed within limits. Use of carburetor heat may be necessary to prevent induction icing as well as to heat the carburetor to help vaporise the fuel.
b) keep in mind that two conditions are commonly associated with clear en-route weather: blowing snow and ice fog. Check the forecast carefully as these conditions are hazardous and may require alternate actions.
a) be aware of the potential for snow banks on the sides of the runways
b) try to obtain runway surface conditions prior to your landing decision. If such information is not readily available take your time to hold and wait for it.
c) remember that the use of reversible propellers or thrust reverses may reduce your forward visibility due to blowing snow.
10. After the Flight
a) during reciprocating engine shutdown a good practice is to turn off the fuel and run the carburetor dry. This lessens the fire hazard during preheat before next flight.
b) fill the tanks with the proper grade of fuel, especially if the aircraft is going to be parked in a heated hangar. Do it as soon as possible after the landing.
c) if the aircraft is to be left outside install engine and pitot tubes covers.
d) if snow or “clear and colder” conditions are forecast – install wing covers if available.
e) use control locks and tie down the aircraft if it is to be let outside.
f) check for manufacturer’s recommendations for engine oil dilution.
EGAST safety promotion leaflets for General Aviation pilots