Getting Ready for Winter Operations
With the change of seasons it's important to prepare for the harshness of winter. More damage to aircraft occurs during winter from lack of knowledge of special procedures needed.
While there has been much written about cold-weather operations for power plants there has been little written about actual aircraft and systems operation and maintenance preparation for winter. This article will discuss both power plant and airframe and try to bring the two together for a common-sense solution to some potentially difficult and expensive situations encountered during winter.
Whether or not you elect to fly in the winter months, it's a bad idea to let snow sit for extended periods on the fuselage. It can promote corrosion.
A good quality wax is necessary to assist in removal or prevention of ice and snow while on the ground. Never rely on wax to prevent airframe icing in flight — ice can kill. Clean aircraft provide less of an opportunity for snow or ice to adhere to and make for easier removal with less chance of paint damage.
Fuel systems need special attention to purge all water including areas such as fuel strainers, gascolators, the carburetor float bowl drain and fuel tank drains. Especially important is draining the float bowl in the carburetor since moisture entering the carburetor tends to be trapped in the bottom of the float bowl, and stay until it is removed by draining.
Fuel tanks tend to trap water even if there are quick drains. Only some of the water is removed (above freezing) during preflight sump checks. It may be necessary to move the aircraft and rock the wings gently to allow the trapped water to reach the area of the quick drain and then drain an ample amount of fuel (1 quart or more) until the trapped water can be removed.
Frozen water in the fuel can lead to special problems such as plugging fuel strainers and filters, preventing fuel valves from operating properly, and even cause partial or complete engine failure due to fuel starvation in the fuel lines, carburetor or fuel injection finger strainer fuel inlet.
During winter it may be necessary to move an aircraft into a heated hangar or heat the area around the fuel drain to melt the ice so the liquid (water) can be removed. Attempting to force the quick drain open will most probably damage the drain and can damage the fuel tank or fuel bladder and cause a fuel leak. Moisture in aircraft hydraulic systems is also another problem and this is why it is important to use clean, fresh hydraulic fluid from a clean, sealed container.
Never reuse hydraulic fluid as contamination from water or foreign substances (dirt, etc.) can damage or prevent a hydraulic system from operating. Frozen water in hydraulic brake systems can only be corrected by warming the entire system (move to a heated hanger if you can move the aircraft). Heat the specific brake that is locked and then purge the system of water. Purging the hydraulic system of water prior to the onset of cold weather can save a lot of headaches.
Flight controls can also be influenced by cold weather not only with frozen controls, but control-cable tension may be reduced both from the fact that the entire aircraft shrinks slightly in cold weather but so does the cable itself, making adjustment necessary in extremely cold climates. When operating flight controls — especially during preflight checks — don't force controls if any resistance is felt. Investigate the reason for the restriction to movement.
Snow and ice packed between flight controls and wing or stabilizer surfaces can prevent normal operation and aircraft should not be operated nor flight controls moved until all snow or ice is removed from any control surface. Powered controls and surfaces such as flaps should be preflighted very carefully and any snow or ice removed from these surfaces or any flight control before operation.
Aircraft with powered flight controls, when operated with any obstruction such as snow or ice, can suffer expensive damage to the system. Cold weather and moisture also affect electrical systems with the battery power output reduced substantially during cold weather.
Properly servicing the aircraft battery with distilled water, fully charging the battery, and finally checking the specific gravity of each cell to be within allowable limits will provide maximum power from the battery. Replacing the aircraft battery if any cell tests below specific gravity specs can prevent a lot of anguish during starting attempts in cold weather.
During low-temperature operations, particularly during starting and initial warm up, it is important to have all the electronic equipment off to prevent voltage spikes from damaging avionics and allow full power to go to the starter. When the engine is stabilized after a few minutes then turn on the electrical equipment one at a time to prevent additional shock loading of the electrical system and alternator.
Auxiliary power from a warm, fully charged booster battery is very helpful and can be a real item of safety along with a fire extinguisher during cold weather starting. Consider the consequences of starting during cold weather with a weak battery and an engine backfire occurs.
If your battery will no longer turn the starter, you have no chance of sucking a fire into the engine — the standard procedure. Your aircraft can catch on fire. Even if you could extinguish the fire, damage to the aircraft will result from a fire and fire-extinguishing agent in the engine compartment.
When shutting down, turn off all unnecessary electrical loads and allow the battery to be charged for a short period of time to prevent a partially discharged battery from freezing in cold climates. Fully charged batteries will not freeze except in true arctic conditions and will provide the most energy for the next start attempt.
Drive belt tension for alternators and generators may be loose enough to cause slippage during high load conditions such as after engine starting or during landing when the rpm is lower and the landing lights are operating. Monitor alternator/generator output, especially after starting and during low rpm operations such as landing and taxi to verify that the system is being charged properly.
Allow extra time for the altitude encoder to warm up before flying as during cold weather this takes longer to warm up to proper operating temperatures. Some digital avionics displays go blank in cold weather (LCDs) and may require some heat to bring the display into view. Warm air preheat of the cockpit will help to prevent this.
Unfortunately, many times the aircraft heater will not supply enough heat to warm the cockpit sufficiently for the purpose of warming the radios so use of an auxiliary heater may be required. When selecting radio frequencies, especially with older navcoms, don't force the frequency change knobs to turn.
Slowly rock them back and forth or warm the radios as the frequency selector section of the radio can be damaged and could be very expensive to repair if parts are even available. You may want to select the frequency you are expecting to use next before you shut the radio off on the previous flight.
Landing gear is another often-forgotten airframe component that requires attention prior to the onset of cold weather. Wheel bearings require grease that will stay fluid in cold temperatures. Moisture trapped in bearing cavities mixes with old grease and freezes, occasionally "locking" a wheel.
Removing, cleaning and re-greasing wheel bearings with the proper approved grease will go a long way toward making an aircraft easier to tow. Use of synthetic greases like Mobil 28 (when approved) will make a noticeable difference both in terms of an easy turning wheel, and also make components such as actuators and motors work easier in cold conditions when the aircraft is greased with synthetic grease.
When using synthetic grease all of the old petroleum-based grease must be removed or purged as mixing greases can promote corrosion from acidic (combined) compounds. Some emergency extension systems may not operate correctly or at all with the improper grease or ice jamming the system.
Tires may also freeze to snow- or ice-covered surfaces after parking, when the warm tires thaw the snow or ice, which then refreezes. This can be prevented by ensuring the tires are properly serviced with the correct air (nitrogen) pressure, slowing your taxi speed, using the brakes sparingly and finally parking on a clean surface free of snow and ice or on a small piece of cardboard or wood.
If your aircraft tires are frozen to the surface it may be necessary to use a pre-heater to thaw the ice. The use of salt for deicing is not desirable as salt is corrosive to an aircraft and all aircraft systems. When taxiing your aircraft be careful to stay out of water or slush as any moisture on the landing gear has the possibility of freezing when the aircraft is flown to colder temperatures on climb out or when parked for the night.
Gear doors and components as well as brakes can freeze with no warning until you attempt to operate the system. Freezing of the landing gear can be reduced by staying out of the slush if possible, and when departing leaving the retractable landing gear down for a short period of time to blow the water off. Consider retracting and extending the gear after take off to remove or break any ice that may have formed.
Snow and Ice Removal
Winter covers for the wings and tail surfaces can make snow removal easy by just pulling the covers off. With heavy, wet snow or ice on the covers, they may not be able to be removed until some or all of the snow/ice is removed. Using a material such as plastic drop cloths or cheap plastic tarps may stick to the aircraft surface so a good quality material made for this purpose (canvas or similar) is necessary. When measuring for covers, allow for material to overlap the lower surface of the wing.
A local canvas shop can possibly make or advise on what material would be suitable for this purpose. Removing snow from an aircraft has been done in many ways, and while there is not one specific method to use, there are situations that will surely damage an aircraft and will not accomplish the job of complete snow or ice removal.
Ice is difficult to remove and especially dangerous if the aircraft is flown with any ice (or snow) on the aircraft aerodynamic surfaces — even frost can change flight characteristics.
This is why a very comprehensive preflight is necessary to detect and remove any ice or snow from the aircraft. Some methods to remove ice and snow that are inappropriate are sharp instruments such as screwdrivers, metal ice scrapers, mallets, hammers or broom handles. Sounds obvious, but I've seen it done.
The proper aircraft ground deice fluid is Type 1, which can often be found in cold country FBOs. It's not cheap, as this 5 gallon container was over $100.
Automotive chemicals such as windshield washer fluid, antifreeze, and aerosol spray deicers are not designed for aircraft use and can cause corrosion, damage paint, and damage or destroy plastic panels and windows. Unknown qualities of fluid adhering to a wing's surface can alter the aerodynamic characteristics and cause stall speeds to change as well as cause low-speed handling difficulties right after takeoff.
Unapproved fluids may also cause environmental problems entering the airport storm drains or ground water systems. Windshield washer fluid or hot water can refreeze after a short time and can be very dangerous to use. Frozen fluids such as these, in and around flight controls especially, can cause an aircraft to crash from loss of control or cause control flutter.
Light, fluffy, dry snow can be removed with a soft broom or other similar methods but be very careful not to damage antennas, gauge probes, fuel vents or Pitot tubes to name a few. Of utmost importance is that attempting to operate an aircraft with any snow, or ice on the lifting surfaces is asking for disaster.
Numerous aircraft have crashed with even minor amounts of lift-destroying snow or ice on the wings or tail surfaces. The weight of the snow or ice is also a concern but secondary to the loss of lift.
Parked aircraft can be damaged by the additional weight, especially the upper aircraft surfaces. Even if you don't plan on flying during winter, large amounts of snow must not be allowed to accumulate and at least the bulk of the snow should be carefully removed on a regular basis. Cessna owners should consider a tail stand of some type so as to prevent the tail from falling on the snow/ice covered tarmac and damaging the rudder and lower fuselage.
(click photo for larger version)
These new pistons only had 150 hours on them, but the engine was subject to a winter of cold starts, which caused the scuffing on the skirts.
Some aircraft owners not familiar with aircraft power plants don't consider the need for preheat necessary since automotive engines rarely need it. The principal difference is the fact that aircraft engines are air-cooled and are constructed largely of aluminum and some steel.
The rapid expansion of aluminum pistons in cold steel cylinders reduces the operating clearances, and the lack of proper lubrication at first start-up can cause damage to occur such as piston scuffing or worse. While the engine may run OK after it is warmed up, this damage (scuffing of the pistons) will become apparent at some point and shorten the life of the engine.
Another factor is that of the aluminum crankcase and steel parts such as steel crankshaft and connecting rods and that of expansion of these cold parts at a different rate than the aluminum crankcase. Cold motor oil takes many seconds to flow to the critical parts.
Even if the oil is warmed, the clearances are so small that proper oil flow to the unevenly expanding parts is nearly zero. Thus, it is very important that when engines are started in cold weather, even after preheat, that they be operated at a low rpm for several minutes to allow for full oil flow to all the critical parts of the engine internals.
Preheat can be done in many ways; it makes no difference to the engine if hot air is used, heat lamps, electric heating elements or any other combination is used. The actual temperature of all the internal parts of the engine is most important. Lycoming specifically recommends against dipstick heaters, by the way.
One method used years ago is that of using exhaust from an automobile or other combustion engine as a heat source. This produces little heat but lots of water vapor that is corrosive. Avoid this damaging and ineffective method.
Other problems in cold-weather starting are those of frosting over the spark plug electrodes after a failed starting attempt. With frosted plugs the spark plugs must be heated or removed, dried and replaced in order to start the engine.
Stiff or frozen engine control cables can be a real problem. Moisture between the outer shield and interior cable freezes, and locks the control.
A helpful procedure is to position the mixture and throttle controls to the starting position after shutdown. This will allow the engine to be started in below-freezing temperatures should a control be frozen or be stiff from the cold temperatures.
The tachometer drive cable should be lubricated with light oil to prevent the cable from freezing. Oil pressure supply lines should be purged and filled with light oil such as sewing machine oil. The oil pressure supply line should be bled to purge the trapped air in the line to the instrument panel. The light oil will ensure faster oil pressure indication after starting in cold-weather conditions.
During run-up it's important to operate a controllable pitch propeller several times at moderate rpm (1700 - 2000) to allow for oil to circulate in and out of the propeller and the propeller controls. It's not necessary to very deeply cycle the prop to achieve this oil circulation.
Another winter operation heightened danger is that of carbon monoxide poisoning from the entry of exhaust into the cabin. The immediate thought concerning carbon monoxide is that of leaking exhaust through the cabin heater and into the cabin.
Other areas that can allow entry of carbon monoxide into the cabin are through gaps or holes in the firewall. Areas where electrical cables and engine controls pass through the firewall may not be sealed or have sealant missing. Check each and every position in the firewall that could allow engine compartment "air" into the cabin.
Proper sealant should be able to withstand 400-degree heat for a period of time without any burn through or smoke being emitted.
Tail pipes and muffler outlets should not be modified and the position of the outlet should be turned exactly as specified in the aircraft maintenance manuals. Tail pipe extensions that are not "approved" modifications can be deadly in winter situations by allowing exhaust to find its way into the cabin.
Check for exhaust leaks anywhere in the engine compartment, such as leakage at the cylinder exhaust flanges, joints, and muffler attachment to the stacks. Correcting these leaks can prevent exhaust gas from entering the cabin.
The interior of the muffler is also important to check that the installed baffles (or flame cones in Bonanzas) are still intact. Missing baffles can reduce the heat output of the muffler that is used for both cabin and carburetor heat.
Even an inexpensive, disposable carbon monoxide detector can be helpful in preventing carbon monoxide poisoning, but never rely on this detector alone that things are OK. If you feel sleepy or groggy, turn off the heat, open a window slightly and land the aircraft. As an interesting aside, lean of peak operation results in almost no carbon monoxide production due to the nature of LOP combustion.
Those aircraft that are equipped with internal combustion heaters are also subject to problems and leaks. Be sure you know the procedures for proper operation of these heaters. For example, a cool-down period is necessary prior to shutdown of the aircraft and heater.
Shutdown of the combustion heater with the fire still on can crack the liner and allow flame into the cabin heat system. Turn off the fuel from the heater and allow the fan to operate for a period of time to cool the combustion chamber down.
The fan requires electrical power to operate so if the heat is not turned off early prior to shutdown and the master is turned off the electrical fan will not operate, possibly cracking the combustion chamber. Pressure decay checks can be made to check for combustion chamber cracks and several AD notes have been written requiring these tests on a regular basis.
Preparation for cold weather and winter operations definitely requires some proactive and modified procedures to assure both aircraft and personal long life. One of the best places to start is a thorough review of your operating manual.