November 1, 1984
J. Jefferson Miller
Perhaps because there is psychological resistance to the very notion of winter, the chilly season often catches us unprepared. One mechanic at the Frederick, Maryland, airport, where AOPA has its headquarters, says that the first cold snap of winter will bring a line of pilots to his shop reporting flaccid tires, sagging struts and dead batteries. These unpleasant little surprises, and other considerably more serious problems, can be avoided by "winterizing" your airplane.
Winterization consists of a number of preventive maintenance procedures. The good news about winter maintenance is that, if you are so inclined, you can do much of it yourself and save money. Listed below are maintenance procedures you can accomplish on your own and those that can be performed legally only by a mechanic.
Coping with the cold also requires the pilot to adhere to specific cold weather operational procedures in three areas: the preflight inspection and engine start-up, the flight itself and the postflight securing of the aircraft. On this page and the following pages are guidelines to follow in these areas. These tips are printed in a set so that you can remove them and keep them in your flight kit.
Above all, when winter rolls around, pilots should be familiar with the cold weather procedures outlined in the operating handbook for their aircraft.
Ignition timing can fall out of specifications after a few months use. Improperly timed magnetos make starting harder and can lead to engine damage.
Temperature variations can change tension in control cables. Aluminum structures shrink slightly in cold weather, causing steel control cables (which shrink less) to slacken.
In aircraft equipped with heat exchangers that surround mufflers or other parts of the exhaust system, there is a danger of carbon monoxide seeping into the cabin. Remove heater shrouds, check for cracks in exhaust system and patch or replace questionable parts. Defective combustion heaters in twin-engine aircraft also can leak carbon monoxide into the cabin. These units also must receive close attention.
Pilot or Mechanic
Dirty, worn or improperly gapped spark plugs compromise engine efficiency and hinder engine starting. Plugs in this state produce weak sparks that lead to incomplete combustion. For an in-depth discussion of spark plug care, see "Facing the Firing Squad," November 1980 Pilot, p. 62.
If recommended by the aircraft's manufacturer, install baffles and oilcooler covers when temperatures drop to specified levels. Once installed, remember to observe temperature limitations for the devices. Some manufacturers allow temporary operations with the devices installed in warm weather.
Inspect insulation of all oil lines and hoses. Also check insulation of tanks in a dry sump system (external reservoir).
Burst hoses and loose fittings are among the major causes of maintenance-related accidents. Check all hose lines, flexible tubing and seals for deterioration. Non-airframe and powerplant mechanics can replace prefabricated fuel lines and any hose connection except for hydraulic connections. Retorque all damps and fittings to cold weather specifications.
Cold temperatures cause pressure in tires and struts to decrease. If the seal in the oleo strut is deteriorated, the strut will not hold air pressure. The seal must be replaced by mechanic.
This will reduce the likelihood that frozen substances will accumulate around wheels and brakes, possibly causing them to lock. There is, however, a second school of thought that holds that wheel pants should be left on a low-wing aircraft's main gear to prevent slush from flying up into flap assemblies and jamming them.
Oil should be changed every 50 hours of operation throughout the year. During the winter months, a thinner fixed-viscosity oil or a multiviscosity oil should be used. Fixed-viscosity oils can be used safely only within a rather narrow temperature range. Multiviscosity oils adapt their consistency to a wider range of temperatures.
Unless your engine is new or overhauled and requires straight mineral oil during the break-in period, a multiviscocity oil is preferred. Mineral oils have a fixed viscosity. Use the grade of oil specified by the aircraft or engine manufacturer. Also, follow the manufacturer's recommendations concerning changing the brand of oil used.
Remove the battery from aircraft. Use a hydrometer to determine the battery's specific gravity, which is a measure of its state of charge. A fully charged battery should have a specific gravity of about 1.265 and can stand temperatures as low as -60 degrees F without danger of freezing.
Normally, an aircraft's alternator or generator will keep the battery fully charged. A healthy battery should need charging only after several weeks of disuse. If the aircraft has been flown recently and the hydrometer test shows the battery in a state of discharge, a defect in the battery or charging system may be the cause.
Most automotive battery chargers can be used to charge an aircraft battery. Use low amperage over a long period of time. This is a slow charge and can take a day or longer. Do not exceed 10 ampere-hours of charge.
If water needs to be added, pour in just enough to cover the plates. Use only distilled water. Too much water causes the electrolyte to boil over. During the winter, perform the hydrometer test once a month and keep an eye on fluid levels. If the battery is two or more years old, it will probably need to be replaced.
Cycle the boot system once a week to prevent stiffening of the rubber, which can shorten boot life. Check deicing boots for cracks and cuts. With the assistance of a mechanic, shop air can be used to check boot inflation. The boot should feel hard when squeezed: It should not be easy to feel the metal leading edge of the wing when pressing your thumb directly into the inflated boot. Soft boots indicate the presence of leaks or other defects and will not shed ice properly.
BFGoodrich, which makes rubber boot deicing systems, recommends semiannual applications of a compound called Agemaster Number 1 to boots to slow the aging process of the rubber. Regular applications of a Goodrich product called Icex will enhance ice shedding by reducing the ability of ice to adhere to the boots.
A mechanic should check the pneumatic pump pressure by installing a pressure gauge in the outflow valve of the pump, and he should inspect the pump filters for cleanliness. Pneumatic pump air hoses also should be inspected for integrity. Check deicing fluid reservoirs.
Frost, ice and snow must be removed from all airfoil and control surfaces and around static system sensing ports. Alcohol or some other ice removing compound can be used,, or ice can be melted off in aheated hangar. Be sure water does not run into control surface hinges where it can refreeze.
Crankcase vapor can condense and freeze line shut. Visually inspect line to ensure that it is open. On many aircraft, the fine runs from the top of the engine through the bottom of the cowling. If the breather line is frozen shut, internal pressures may blow out oil seals, resulting in loss of oil pressure and possible engine stoppage.
Inspect all readily accessible hoses and tubing for integrity.
Thoroughly preheat entire engine. compartment when ambient temperature is below 250R This is a conservative practice but one that should ensure easy starting and save wear and tear on the engine and accessories. Coldstarts accompanied by immediate 1,500-rpm power blasts can significantly shorten the life of an engine.
For Continental and Lycoming piston engines, preheat is mandatory below 10 degrees F. One notable exception to this rule concerns the Lycoming O-320-H engine found in some Cessna 172s and Piper Seminoles, for which preheat is required below 20 degrees F.
There are two methods of preheating an engine: slow and fast. Slow methods include a variety of homemade and commercially available systems. Light bulbs under the cowling and electrically driven hot air blowers can be used successfully. One electrical system, the Tanis Aircraft Services TAS-100, consists of heating elements for sump and cylinders. It plugs into a standard 110-volt electrical source. Slow heating requires several hours.
Fast heating should take about 20 minutes. Car exhaust should be avoided, if possible, because its chemical components are not good for the engine in the long run. Portable preheaters such as Flame Engineering's Red Dragon are a better idea. Care must be taken to direct the hot air away from plastic components in the engine compartment that could melt.
Heated dipsticks are not a viable means of obtaining a fast preheat, because they only heat a portion of the oil. They are effective at retaining an engine's warmth after shutdown, if you plan to restart within a few hours. Start engine with normal procedures after a preheat.
Adhere to procedures in airplane's operating manual.
Rotating the propeller by hand should be done only with extreme caution — A switches off. Treat the propeller as if the ignition was hot: It may be, if a magneto ground wire has broken.
Normally aspirated engines usually require about six shots of primer. Consult any priming charts in the pilot's operating handbook. Operate primer slowly to ensure complete vaporization of each shot of fuel.
Do not overprime. This will wash oil residue off cylinder walls. Scoring may result. Overprinting can cause poor compression and hard starting. It also may cause a fire. Have an extinguisher handy. In the event of fire, keep cranking in an effort to draw flames back into the engine. If the fire continues, move the mixture to idle/cut-off. Know the emergency procedures specified in the pilot's operating handbook for engine fires.
Limit each cranking period to a maximum of 30 seconds. Cranking longer overheats the starter and leads to premature failure of the unit. Allow unit to cool for a few minutes before cranking again.
Under very cold conditions, it may be helpful to keep primer out and push it in when engine begins firing in order to maintain an extra rich mixture. In aircraft with fuel-injected engines, the boost pump can be set to the high position to maintain a good flow of vaporized fuel.
An engine that fires briefly and dies may have iced-over spark plug electrodes. Further attempts will be futile. The only remedy is to heat the entire engine or to remove the plugs and -warm them until no moisture is present.
The freezing point of jet-A, the most common turbine fuel, without additives, is -40 degrees C. When Prist, an antiicing, anti-bacterial compound, is added, the freezing point drops to -54 degrees C. Prist should be used year round, but is absolutely essential in winter Prist prevents the formation of ice crystals that can block fuel filters.
The freezing point of jet-Al, which is found in extremely cold regions, is -47 degrees C without additives. The freezing point of JP-4, which contains anti-icing additives, is -58 degrees C. JP-4 is used almost exclusively by the military.
These are generally very cold temperatures in the vicinity of -40 degrees C.
For Garrett turboprop engines, which are single shaft turbines and require more starting power than free turbines, a start with an external power source is the preferred method below 10 degrees C. If a battery start is to be attempted, dual battery systems should be used in a series circuit.
Pratt & Whitney does not specify a temperature for its five turbine engines below which external power must be used for starting. However, below -20 degrees C, the propeller of a Pratt & Whitney PT-6 turboprop engine should be secured before starting. The engine is then started and the oil allowed to warm to at least 0 degrees C before the engine is shut down and the propeller released. The engine is then restarted. Although this is the recommended.procedure, according to Pratt & Whitney of Canada, many operators ignore it without damaging their engines.
Check voltage. If battery voltage is insufficient, use external power for start. In some aircraft, battery voltage may be insufficient even for start with external power. For some Garrett engines, if voltage drops below 22 volts NiCad batteries must be recharged — a 24-hour or longer process. Having an extra set of charged batteries at your home base might be a wise policy.
Turbine engines can accumulate internal ice overnight and resist Atation when starting is attempted. With any indication of a locked rotor, low rpm or unusual sound, discontinue the start.
The engine may not produce suffident heat to keep spark plug elect-odes from icing over.
This will help prevent frozen accumulations from forming on wheels and brakes. If you feel you may have picked up slush or mud while taxiing in a retractable-gear model, after takeoff, leave gear down slightly longer than normal — the accumulations may blow off. Cycling gear may also remove accumulations.
Because engines are capable of developing more power as temperature decreases, extra care must be taken not to overboost turbocharged models.
If heat retention devices are installed, it is possible to overheat engine at normal climb speeds due to reduced cooling air flow. If temperature nears maximum limits, increase airspeed, open cowl flaps or do both.
In the descent it is necessary to guard against overcooling. It may be necessary to increase power, which may require extension of gear or flaps pitch, causing it to blow snow forward. to keep airspeed within limits.
Adhere to minimum temperature limitations as specified in pilot's operating handbook for for deicing equipment operation.
In turbine aircraft, upon landing on a snow covered runway, be alert for the potential of a "white out" when thrust reversers are used or when the aircraft's propellers are placed in reverse
Topping the -tanks will prevent condensation and water or ice accumulation in the fuel system. This procedure is important whether or not aircraft is placed in a heated hangar.
If the aircraft is left outside, install engine cowl plugs and pitot covers.
"Warming Up To Winter," by Thomas A. Horne, Pilot, September 1981, p. 37. Battery care, oil changes and other winterizing procedures.
"Coldstart," by Thomas A. Home, Pilot, February 1980, p. 62. Whys, whens, how-tos of preheating.
Information on icing.
"Safety Comer: Icing, brakeless Aztecs, Hiwas," by Mark M. Lacagnina, Pilot, October 1983, p. 94. "Ice Follies," by Mark M. Lacagnina, Pilot, December 1982, p. 61.
"On the Rocks," by Mark M. Lacagnina, Pilot, October 1982, p. 63.
"The Icing Options," by Thomas A. Horne, Pilot, September 1981, p. 43.
"Reflections on a Black Art: The known in known icing certification," by Thomas A. Horne, Pilot, February 1981, p. 52.
"Safety Corner. Understanding icing," by Thomas A. Horne, Pilot, February 1981, p. 80.
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