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Thursday, March 27 2014 23:27

Preparing for Winter

Written by  Mike Berry
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October 2005

While it may seem early to write about the coming winter, fall is the season to prepare. Preparing your aircraft will make operating during winter much easier, safer and also save you some money.

Even if you don't plan on flying during the winter season it is important to prepare for winter. If you live in the sunny South or Western United States, winter still can bring some surprises and, don't forget that even if it is sunny and warm on the ground it may be freezing at altitude.

The two problems with winter are that of frozen precipitation and cold temperatures. While we can't control the weather we can prepare for the battle and minimize the effects of the winter season.

Airframe preparations: A clean aircraft is always good, but most importantly is that of preparing for cold weather operations. Washing and waxing your aircraft can prevent ice and snow from sticking, or at least allow for easy removal. While not a guarantee of ice not adhering to your aircraft, proper cleaning and protecting of the entire exterior of the aircraft with a good quality wax will help significantly.

De-ice boots can be cleaned and treated with approved materials to soften the boots, aid in ice removal and lengthen the useful life of the pneumatic de-ice boots. Check with the manufacturer of the boots for the proper treatment and care. Do not use automotive chemicals on aircraft unless specially approved for aircraft use as the materials on aircraft equipment are different than automotive.

Plastic windows should also be cleaned and treated to allow for easy removal of ice and snow. Never use chemicals intended for use on glass on aircraft windows even if the windows are glass (most aircraft windows are plastic.) Glass aircraft windows also require special cleaning techniques and chemicals; always refer to manufacturers' recommendations. Heated windows and ice plates also require special care, cleaning techniques and chemicals used according to the manufacturers' specs.

Aircraft control cable tensions are subject to significant change during extreme temperature changes and require adjustment according to operating temperature. Most manufacturers' maintenance manuals include charts reflecting temperature variation and adjustments to tension.

In addition to tension differences, moisture on cables can freeze if not protected. It is important to inspect fairleads and protective boots for condition so as to not allow water to enter these areas and freeze. Especially important is to be aware of this potential problem when moving an aircraft out of a heated hangar into frigid conditions as liquid water may freeze after takeoff and restrict movement of flight or engine controls or even cause fuel system blockage with ice crystals. Properly lubricating and purging any areas of moisture during warm weather conditions can prevent control lockup due to frozen moisture.

Aircraft batteries should be checked for serviceability with checks of the specific gravity of each cell after charging. Batteries with defective cells must be replaced with a fully charged battery—keeping in mind that a fully charged battery will not freeze unless subjected to unusually cold temperatures.

Aircraft tires, wheels, brakes and wheel bearings should be properly serviced prior to winter weather. Wheel fairings should be removed for winter operations, as fairings can trap snow or ice, increase aircraft weight and disrupt airflow.

Wheel bearings are particularly susceptible to damage from liquid water and ice formation. Bearings should be thoroughly cleaned to remove all old grease and re-greased with approved lubricant. The use of synthetic grease (when allowed by manufacturer's maintenance manuals) will greatly enhance resistance to water mixing with grease and allow for freedom of movement during cold weather operations.

Tires need to serviced with nitrogen or dry air, as water vapor in air used to service not only tires but oleo struts can freeze and rust internal parts. Mechanics over the years have encountered cold weather problems with hydraulic systems, including brakes due to frozen moisture in the hydraulic fluid. It is important to occasionally purge hydraulic systems with fresh clean hydraulic fluid.

Never re-use hydraulic fluid as this can introduce contaminants (including moisture) to the system. Spend the money and use approved fluid from a clean, properly marked container. Locked brakes due to frozen moisture in the hydraulic system are a real hazard especially in cold weather and can happen at any time when operating below freezing with moisture in the fluid.

As a common sense approach and cold weather operational technique, do not ride the brakes during taxi but rather use the brakes to slow the aircraft, release the brakes for a short while and then re-apply. This technique prevents excessive brake, wheel and tire heat buildup, increases the life of associated components and prevents excessive heat from melting ice and snow re-freezing later, especially in retractable gear aircraft when the landing gear is retracted.

Always use chocks and tiedowns (instead of parking brakes) when parking, especially in cold weather for any more than a few minutes because heat generated during landing and taxi can melt ice and snow causing brakes to freeze, and heat migration to tires can "freeze" tires to the ramp.

Also pay attention to the fuel systems; these systems should be checked for proper operation with special attention paid to fuel valves and quick drains. Fuel caps should have seals or gaskets in good pliable condition with no cracks or gaps in the seals to allow liquid water into the fuel tanks and later freezing. Drains around the fuel tank caps should be checked for proper operation, as blockage can allow water into fuel tanks.

Prior to the onset of freezing temperatures, drain all sumps for longer than the normal quick check. Also important is to move the fuel selector to the OFF position and back to ON to allow for any accumulation of moisture to be purged from the fuel system. Then make one final sump check after waiting a few minutes for contaminants to enter the sump area.

Make absolutely certain that the fuel valve is in fact positioned back in the ON position, as sometimes an intermediate valve position can allow an engine to run on the ground, but when using full power as during take off, cause fuel starvation due to insufficient fuel flow.

If a fuel valve is difficult to operate when it is warm, then it is going to be much more difficult to move when it is cold. Repair or replace binding or stiff fuel valves before you really need to use them—during an engine fire, for example.

Engine backfires during cold weather starts are somewhat common and there is risk of fire during these operations: shut off the fuel and continue to crank/start the engine, sucking the fire out.

When draining sumps during freezing temperatures or when operating the fuel selector, you discover a drain or valve blocked with ice, do not attempt to use force to open the drain or valve as force will not clear the ice, but only damage the drain or valve.

Never operate an aircraft with a damaged sump or fuel selector valve, especially in cold conditions as when ice changes to liquid, a serious fuel leak or introduction of water into the engine could result in engine failure.

For those operators using auto fuel, do not store or park your aircraft for extended periods with auto fuel in the tanks, carburetor, or any part of the fuel system. Auto fuel does not store well and forms gums. In addition certain chemical additives evaporate after a short time causing detrimental changes to the fuel. Drain the fuel systems of auto fuel and use Avgas when parking or storing.

Another tip on preparing for winter is to examine the instruments in your panel for signs of moisture inside the glass. If you see fog or liquid inside any instrument remove the gauge, purge the system of moisture and send it to an instrument shop for repair. Moisture in instruments is bad, as ice (and rust) can form, stopping the operation of the instrument.

Pitot static instruments are particularly susceptible to introduction of moisture into the system during warm, humid conditions. Also important is that when any connection to the pitot/static system is removed, a re-certification of the system is required before transponder/encoder operation.

As a final statement regarding preparing airframes for winter operation, I would suggest that the aircraft maintenance and operating manuals be studied and followed both in terms of preparing for winter and operating during winter or storage of an aircraft. The time and money spent "doing your homework" will save much grief and money in the long run.

Powerplant Preparation: While there is a wealth of information regarding preparing and operating your power plant during winter a few of the basics are:

1) Change engine oil and replace with engine oil of the proper grade for cold weather.
2) Proper maintenance of the engine components (ignition timing, spark plug gap and fuel delivery systems) is very important and may make the difference between being grounded or having a pleasant winter flight experience.
3) Proper inspection and maintenance of the exhaust, cabin heater and carb heat/alternate air systems is of extreme importance.
4) Thorough winter preheat, proper warm up and operation of the powerplant can reduce or eliminate premature wear associated with cold weather operations.
5) If you do not intend to operate your aircraft/power plant during the winter, then prepare for storage using the methods recommended by the manufacturer to include special preservative oil in place of aviation motor oil.
As an aircraft owner, you can do much of the preparation for winter yourself. However; it is always good to work with a mechanic that is familiar with your particular type of aircraft and the operations in which you are engaged.

Winter flying can be enjoyable, but like anything else in life preparation is necessary. Spend some time reading the sections of your operating and maintenance manuals that deal with cold weather operations, and if necessary, storage. Start on the preparations BEFORE the cold weather arrives and enjoy fall and winter flying!

Read 1413 times Last modified on Tuesday, May 27 2014 19:10

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