We all have been told that no two snowflakes are alike. But in 1988, Nancy Knight from the National Center for Atmosphere Research, using a microscope, found two that were. Can you imagine her in a freezing cold room sorting snowflakes for months? How did she even move from one flake to the next without damaging them? In modern vernacular, snowflake is used to describe a very sensitive person; someone easily hurt or offended by the statements or actions of others; sometimes inclined to flip-flop their position but not inclined to take criticism for doing so. For this story, snowflakes are ice crystals – not sensitive to anything but aircraft anti-icing equipment, liquid deicing fluids, atmospheric conditions and those molding them into snow forts, snowballs and snowmen – sorry, snow people.
“A day without sunshine is like, you know, night.”
Steve Martin
For all life on earth, nothing is as fundamental as the length of daylight. The tilt of 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 degrees 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. For us aviators, 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. The term solstice comes from the Latin words sol (sun) and sistere (to stand still) because, during the solstice, the angle between the sun’s rays and the plane of the equator (declination) appears to stand still. In the Northern hemisphere, the winter solstice always occurs around December 21 or 22. This year, it’s on Tuesday, December 21 at 10:59 am EST 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 year. Our shortest day this winter will have 9 hours and 13 minutes of daylight. 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 solstice, the change is so slight that the sun’s path seems to stay in the same place 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. Now that we’re up to speed astronomically and understand why it’s so cold and dark outside, onward to its relevance to our operations.
With the exception of the Northeast having a stormy January and a tranquil February, the Farmers’ Almanac (more accurate than an Ouija board, horoscope and some meteorologists) says the rest of the continental United States will see a “flip-flop” winter with larger than normal temperature swings with a near-normal amount of snow. With the extreme weather patterns seen lately that have been attributed to climate change, their forecast seems intuitive. Winter flying can be more work for pilots: snow removal and preheating are added to the preflight list, taxi speeds are slower and low visibilities can be widespread. Temperatures in the North may cause nostrils to momentarily stick closed, and thin layers of snow will create a squeaky noise when we walk. But, compared to the hot, humid days of summer, from the airplane’s anthropomorphic position, it’s ideal – the kind of weather it loves: cold, dry air for the motor to breathe and tightly-packed molecules for the wings to finesse into lift.
Traveling in our airplanes exposes us to wide-ranging temperatures and weather, even without the flip-flop forecast. 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 monitoring fuel temperatures and using the anti-ice equipment. On arrival, flying low visibility approaches and computing landing distances will be the norm, and we may be diverting a couple of times. You’ve heard it all before, but stay with me – here comes the mandatory wintertime review.
The Laundry List
Engine Oil – Check your aircraft manual for proper weight (viscosity) 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.
Hoses – Hose clamps, hydraulic fittings and seals: inspect all 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 good 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 or to leave the gear extended an additional 5 to 10 seconds on takeoff when feasible.
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 degrees 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 once over-primed an engine and caught it on fire. I’ve had a wheel brake freeze, windshield heat failure, CADC probe heat failure, fuel heat failure, wing heat failure and electric heat on one blade of a three-bladed prop fail. I’ve seen deicing personnel accidentally skip half of my airplane, had fluid holdover times expire and minimum takeoff fuel has been reached waiting in long lines. Make like a Boy Scout and be prepared. A wintertime addition of 10 or 20 minutes worth of 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, a missed approach and a divert. Ramps will be slippery – walk and taxi slowly. Airfield surface marking and signs may be buried, covered or obscured, making incursions more likely. Aborting a takeoff due to an incursion, especially on a contaminated runway, will exercise your judgment and adrenal glands.
This time of year, dawn comes later and dusk earlier. Light may be fundamental to life, but for pilots, so is currency and proficiency. Just because it’s cold and dark, don’t solstice – get out of that tilted chair in your office and go flying. Both you and the airplane need to stay aeronautically limber despite our astronomical condition – a condition that creates more work for pilots. Don’t be a snowflake about cold weather – or my comment about snowflakes. Earth’s 23.44-degree tilt will, after all, make it, you know, like winter.
