As the weather gets cooler this time of year, aircraft owners need to consider a few additional items in preparation for cold weather flying. Operating factors may include the proper use of winterization kits (as applicable), pre-heaters and defrosting concerns affected by the seasonal weather.
First of all, we need to remain aware that small aircraft engines work harder in cold temperatures, especially during the starting process. Lubricating oil is thick, normal fuel mixtures are compromised, battery cranking energy is reduced and the pilot’s patience is being tested. Mixture management may also come into play to combat the possibility of shock cooling the engine cylinders during power off descents. Controllable pitch propellers require more attention as actuating oil starts to congeal in the dome. These are merely a few of the items to be reviewed by owner/pilots as winter approaches. Once these items have been taken into consideration, the cold air actually enhances the winter flying experience.
One of the more misunderstood topics for most aircraft operators is the need for engine pre-heat. A thorough pre-heat on a cold soaked engine is essential to maintaining optimal condition and operation. A proper pre-heat will not only warm the oil but also stabilize the temperature of the engine metals knowing they are subject to various rates of thermal contraction and expansion. When the outdoor temperature drops somewhere between 5 and 10 degrees Celsius, the aircraft will require a pre-heat if not already stored in a heated facility.
Aircraft engine heating systems should include a means for heating the oil sump and all of the cylinders. Approved systems like Tanis, Reiff, and EZ heat can be permanently installed and are much more effective than portable external heaters which blow hot air into the cowling. Whichever method you choose must be complimented with a tightly secured cowl cover for insulation and even cowl inlet plugs. This procedure can be accomplished just a few hours before departure. Some of the latest systems can even be controlled remotely with a timing device and smartphone connection. Check with your local suppliers for the options available to accommodate your needs.
Winterization kits are another necessary supplement to several certified aircraft models. Instructions for use are detailed in the Pilot’s Operating Handbook (POH) for your aircraft. These kits may include a set of removable covers attached to the front cowl designed for restricting the cold incoming air. The kits may also include a cover designed for the oil cooler, vent tube or cowl outlet depending on model. Winter kits are designed to help maintain engine operation within its ideal temperature range which is usually about 165 – 225 degrees Fahrenheit. Check your Cessna crankcase vent tube breather for a relief hole aka a whistle slot which acts as a back-up in case the outlet of the tube freezes over in the airflow.
Consider maintaining full tanks to prevent moisture being formed through condensation. If fuel samples tend to drain slower than normal from the quick drains, then you can suspect ice in the fuel. In this case, the only resolution is to place aircraft in a heated hangar and sample again until fuel is free from moisture. Certain fuel additives (such as IPA) may also be approved to prevent icing in the fuel. Engine oil should be selected based upon seasonal requirements. Many operators will choose a multi-grade oil (such as Aeroshell 15W50 or Phillips 20W50) which is suitable for year round use in aircraft engines. Preference to single grade oils will require seasonal change to ensure the proper viscosity is used (such as 80 grade in winter and 100 in summer).
There is an annual requirement to perform a critical Airworthiness Directive (CF90-03R2) on the cabin heater to ensure that there are no leaks (every 12 months or 150 hours). Most small aircraft utilize the engine exhaust system as a source for cabin heat. The exhaust muffler can must be tested serviceable as the warm air contained in its cover shroud is delivered to the cabin. Ensure that this AD is completed in anticipation of the cold weather season. A common safety net to this inspection is to install a carbon monoxide detector on the aircraft panel. These small indicators are inexpensive and contain a spot which changes color when contaminated by carbon monoxide gas entering the cabin.
Several aircraft utility systems should also be inspected for condition and operation prior to cold weather flying. The pitot heater, aircraft de-icing systems (if equipped), carburetor heat system as well as the primer lines and nozzles on carbureted engine models. Plugged primer nozzles are often the culprit when the engine is difficult to prime or hard to start due to lack of fuel prime. Pre-heating the entire aircraft in a heated hangar ensures a more thorough preparation as it also ensures that aircraft instruments and avionics stabilize in temperature as well before operating in the cold.
Any time a cold soaked aircraft is brought inside for defrosting, be sure to remove any accumulated snow from all surfaces so that melting does not cause slippery conditions in the hangar. Once the aircraft has been defrosted in the hangar, be sure to wipe off moisture from all surfaces to ensure that it does not freeze again upon being re-exposed to the cold air. Never attempt to scrape frost off the windshield with the control lock or other objects. Just let it defrost so that it can be wiped dry with a soft cloth afterwards. Inspect control surfaces and belly or wing drain holes to ensure moisture escapes before potentially freezing again in flight.
Inactive aircraft should also receive suitable attention for cold weather storage. A warm hangar is always the ideal environment to protect your aircraft during longer periods of inactivity. If that is not possible, then you should consider removing the aircraft battery and ELT for storage in a warm facility. A lead acid aircraft battery will gradually discharge in the cold even if it has recently maintained its specific gravity. A frozen battery will most likely cause internal damage rendering the unit unserviceable.
Engine preservation is another effective consideration when anticipating an inactive aircraft for longer periods of time (such as through the winter months). There are procedures to install a special inhibiting oil which serves to protect exposed internal surfaces while in storage. This is something that trained maintenance personnel can assist with for pre and post storage preparations.
The material covered here identifies some of the primary concerns for winter operations and may inspire further research specific to your make and model of aircraft. Feel free to contact the Flying Club for more information or accommodations at the Brantford Airport over the winter season.