For all life on earth, nothing is as fundamental as the length of daylight. The tilt of the Earth’s axis affects the duration of daylight and plays a major role in our weather. It’s tilted at an angle of 23.44° to the plane of its orbit and because of this, at certain times during the orbit, it’s dark longer and we get cold weather. It’s a time of the year that produces fast moving fronts, icing conditions, strong and gusty winds with drifting snow and it’s like, you know, winter.
It took me a lifetime, but I have a nice airplane, a private hangar with an office, pre-heat equipment out the wazoo and reliable snow plowing. For this pilot, who keeps an artificially- lighted Christmas tree up all year long and cold weather gear at the ready, it’s a great season. My dad raised me to be an outdoorsman, to love the seasons. I have clothes for rain, cold, snow and wind – some might even get me through a torrent of frogs and locusts. Cold never bothered me as much as does heat and humidity. Just as southerners think we’re crazy to put up with cold and snow shoveling, the heat, humidity and bugs endured in the south are perplexing to a northerner. That’s why God made air conditioning – y’all say. And that’s fine if you like living in a cubicle indoors, but not me. Part of why we fly is freedom and the view. Let not a little thing like planetary tilt interrupt our flying schedule.
In the northern hemisphere, winter solstice always occurs around December 21st or 22nd. In the Southern hemisphere, it’s around June 20th or 21st. This year, it’s on December 21st at 5:44 A.M. EDT (10:44 UTC) and marks the official start of winter in the Northern Hemisphere and summer in the Southern Hemisphere. Winter solstice is the day with the fewest hours of sunlight during the whole year. Our shortest day this winter will last just nine hours and 15 minutes. The word solstice comes from the Latin words for “sun” and “to stand still.” In the Northern Hemisphere, the points on the horizon where the sun rises and sets advances southward each day and the high point across the sky, which occurs at local noon, also moves southward each day. At the winter solstice, the sun’s path has reached its southernmost position. The next day, the path will advance northward. However, a few days before and after the winter solstice, the change is so slight that the sun’s path seems to stay the same, or stand still – to “solstice.” The sun is directly overhead at high-noon on winter solstice along only one planetary marker: the latitude called the Tropic of Capricorn – it’s a bit south of the equator. Now that we’re astronomically up to speed about why it’s so cold and dark cold outside, onward to its relevance on our operations.
Temperatures in the North cause nostrils to momentarily stick closed and thin layers of snow will create a squeaky noise when you walk. Flying can be a bit more work for pilots: snow removal and preheating are added to the preflight list, taxi speeds are slower and low visibilities can be widespread. On the other hand, it’s the kind of weather the airplane loves: cold, dry air for the motor to breathe and tightly-packed molecules for the wings to finesse into lift. Compared to the hot, humid days of summer, it’s ideal. Traveling in our airplanes exposes us to wide-ranging temperatures and weather. This year, the National Weather Service is forecasting above-average temperatures and below-average precipitation for the southern part of the U.S. People in northern states should expect below-average temperatures and above-average precipitation. Forecasters expect the remaining U.S. to experience an average winter. The biggest wintertime changes for us occur during planning and preflight: preheating motors, adding a fuel system icing inhibitor (FSII) like Prist to our jet fuel when needed, using deice fluids, calculating holdover times and selecting alternates. When inflight, we’ll be using fuel heat and the anti-ice equipment. On arrival, flying low-visibility approaches and computing landing distances will be the norm and we’ll be diverting a couple of times. You’ve heard it all before, but stay with me; here comes the mandatory wintertime preflight stuff:
The Laundry List
Engine Oil – Check your aircraft manual for proper weight oil to be used in low temperature ranges. Warm it up before you start the motors. Use an oil cooler baffle if, and when, allowed.
Oil Breather – Assure that the breather system is free of ice. When crankcase water vapor cools, it condenses in the breather line and can freeze and clog. A number of engine failures have resulted from a frozen crankcase breather line. A clog can cause pressure to build up, sometimes blowing the oil filler cap off or rupturing a case seal, which causes the loss of the oil.
Hose Clamps, Hoses, Hydraulic
Fittings and Seals- inspect all hose lines, flexible tubing, and seals for deterioration and security.
Cabin Heater – Each year, accident investigations reveal carbon monoxide as a probable cause in accidents that have occurred during cold weather. It’s critical that a thorough inspection of the heater system be made to eliminate the possibility of carbon monoxide entering the cockpit or cabin. A pressure decay test on combustion heaters is mandatory for most and a great idea for the rest.
Control Cables – Because of contraction and expansion caused by temperature changes, control cables should be properly adjusted to compensate for the temperature changes.
Oil Pressure Controlled Propellers – Propeller control difficulties can be encountered due to congealed oil. Use caution when intentionally feathering propellers for training to assure that the propeller is unfeathered before the oil in the system becomes congealed.
Batteries – Wet cell batteries require special consideration during cold weather. Test, clean and charge the battery. A healthy battery should need charging only after several weeks of disuse. If the battery is two or more years old, it will probably need to be replaced.
Wheel wells – During thawing conditions, mud and slush can be thrown into wheel wells during taxi and takeoff. If frozen during flight, this mud and slush can create landing gear problems. The practice of recycling the gear after takeoff should be used as an emergency procedure only. The safest method is to avoid these conditions with retractable gear aircraft or to leave the gear extended an additional 5-10 seconds on takeoff when feasible. Make sure your anti-skid system is armed for takeoff and landing.
Inspect deicing equipment – Check deicing boots for cracks, cuts and holes. Cycle the boot system once each week to prevent stiffening of the rubber, which can shorten boot life. Use only cleaning and performance-enhancing products approved by the manufacturer of your system.
Preheat – Use a heated hangar when available both at home and on the road. A couple of hours above 50° F should be good. If not, oil pan heaters, kerosene-fueled torpedo heaters and individual electric-type cylinder heaters are good. Don’t leave the aircraft unattended, and keep a fire extinguisher handy. Don’t place heat ducting so it will blow directly on parts of the aircraft such as upholstery, canvas engine covers, flexible fuel lines or oil and hydraulic lines.
Been There, Done That
An employer over-primed an engine and caught it on fire, and I’ve done the same myself. I’ve had a wheel brake freeze, windshield heat failure, CADC probe heat failure, fuel heat failure, wing heat failure and one blade of prop heat failed. I’ve seen deicing personnel accidentally skip half of my airplane and have had fluid holdover times expire. Minimum takeoff fuel has been reached waiting in long lines. Make like a Boy Scout and be prepared. A wintertime addition of ten or twenty minute’s fuel above your summertime number is prudent. List an alternate (or two) if the weather is marginal or if the arrival airport has only one approach or one runway – snow plowing will close runways on a regular, and unpredictable, basis. Be ready for holding and a missed approach. Ask for braking action reports (use the Mµ chart from Owl Snot, T&T April, 2016) and calculate landing distance on every approach. Allow extra time to get yourself and the airplane ready. Ramps will be slippery – walk and taxi slowly. Airfield surface markings and signs are buried, covered or obscured, making incursions more likely. Aborting a takeoff on a slippery runway due to an incursion will exercise your judgment and adrenal glands.
This time of the year, dawn comes later, and dusk earlier. Light may be fundamental to life, but for us so is currency and proficiency. Just because it’s cold and dark, don’t solstice, son – get out of the tilted chair in your cubicle and go flying. Both you and the airplane need to stay aeronautically limber despite our astronomical condition. A condition that is a bit more work. That 23.44° tilt will, after all, make it, you know, like winter.