Already a member? Please login below for an enhanced experience. Not a member? Join today
Menu

Out in the coldOut in the cold

Stay safe and warm to enjoy winter weather flying

I arrive at the Fargo Jet Center just in time to see a student walking out to a Cessna 172; dressed in a heavy winter coat; hood up over his hat; thick mittens; and heavy, insulated boots. The temperature is minus 5 degrees Fahrenheit, the sky bright and clear, the wind about 15 miles per hour from the west. The wind chill, on the old scale, is 42 degrees below zero.
Big Chill
Illustration by Allan Davey

This is his second lesson, and the preflight is going to be brutal. Then again, there is probably no happier person on the planet. The air is thick and smooth and bright and clear; no bumpy thermals at all. The fields around Fargo are snow-covered and bright, the rivers frozen solid. Trees look like black-and-white photographs.

Winter air is different than summer air. It’s thicker, denser, and in some ways more stable. January can be just as windy as July, but there’s little of the convection that leads to cotton-ball clouds—and none of the flying that feels like you’re driving down a deeply rutted gravel road.

Simply put, winter flying on the northern plains is fun. Every airplane feels like a sports car. Turns are tight. There’s no haze, and you feel like you can see forever. Winter, though, requires its own awareness. A great many things about flying are the same year-round. But a great many things about flying in winter are unique.

“There are a bunch of things we do differently in winter,” says Steve Schlangen, assistant chief flight instructor at the Fargo Jet Center. “And one of the first is talk about how the students are dressed.”

I vaguely remember advice about not wearing flip-flops, but I don’t recall anyone ever talking about appropriate pilot-wear.

“Think about it,” Schlangen says. “Right now it’s just below zero. The wind chill is whatever it is, but it’s very cold. Now imagine you need to put down in a field for some reason. You have to wait half an hour for the sheriff to arrive. Or worse, you have to exit the airplane because of some post-landing fire or such. So you’re standing in the field, exposed until someone arrives. Yes, how you’re dressed matters.

“I had a student show up in ankle socks and a light windbreaker once,” he says. “I threatened to make him stand outside on the windward side of the building for half an hour. I didn’t do that, but he got the point.”

Mike Paulson, flight school manager and chief flight instructor, agrees. “And it’s not just the college kids,” he says. “Businesspeople come out in winter in dress pants and thin shoes. They’re not going to be well-protected either.”

Paulson points to a bright orange snowmobile suit hanging on the back of his office door. Remembering winter flights in a Cessna 150 and 152, I am suddenly jealous.

Fred Remer, professor of atmospheric science at the University of North Dakota, has a story about winter clothing.

“In 1991,” he says, “I was part of a group of five or six airplanes that flew from Grand Forks up to Churchill, Manitoba, to see the polar bears. Airplane just jumped off the runway. Really just a joy to fly those days. Sky was crisp blue.

“I had a [Piper] Comanche 250 back then. Single engine. Of course we had brought survival [equipment], and it was so cold in the backseat my wife jumped into the sleeping bag. Heater didn’t reach back that far.”

Remer and I are sharing winter stories. He’s just sent me an email, a picture of his computer monitor—numbers on a screen, taken with his cellphone. The numbers show a density altitude of 4,700 feet below sea level. I can’t help but wonder what this would mean when I’m rolling down the runway, about to pull back on the yoke.

There are a thousand lessons about winter flying you learn only by experience. They are not in the pilot’s operating handbook (POH). They are not part of the training curriculum. For example, when you’re sitting on the taxiway, slightly turned to the side, pushing the throttle in for a run-up, you might learn that if you’re sitting on ice, it does not matter how hard you push on the brakes. And you might feel that wonderful cardiovascular awareness for a moment, too. Trust me.

I remember a winter flight years ago, renting a Cessna 172; the afternoon was profoundly cold. The guys at the Fargo Jet Center were kind to me—the airplane was still in the hangar when I arrived, all warm and cozy. I did the preflight in shirtsleeves (my heavy winter coat on the right seat). Then we opened the doors, pulled the airplane outside. I got in and fired it up.

Everything looked wonderful. All I had to do was wait for the oil temperature to come up. So I waited. And waited. And waited. This was an old-school panel with round gauges. The oil-temperature needle moved, but it did not center in the green. I waited so long I finally got out my phone and called Mike Paulson. “If the needle’s come up a bit, you’re good,” he told me. “The oil temperature will come up the rest of the way once you start flying.”

Winter flying demands an understanding of temperature and metal. Pilots know the rule that if oil does not drip from the dipstick during preflight, the engine is too cold to start. It will likely turn over easily enough, but you’ll do damage to the cylinders on the way. At the jet center, the 172s have red thermal coverings over the cowlings when they are parked outside, and Tanis heaters plugged in to warm the engines. Yet neither of these is foolproof.

“There can be a gap in the cover,” Schlangen says. “And the heater may have come unplugged.” Schlangen teaches his students to place their hands on the engine during preflight. If it does not feel warm, it’s not.

“Have you ever heard of shock cooling?” he asks me. I confess I have not. “You know what happens when you put hot metal in water, or a skillet directly into the sink. There’s all that noise and steam and the metal contracts rapidly.”

I nod. This much I know.

“Now, imagine you’re at the point in lessons when you want to teach power-out gliding. What do you think will happen if you suddenly pull the throttle out? The cylinder-head temperatures are somewhere between 300 and 400 degrees and the air is 15 degrees below zero. Suddenly, there’s no heat at all going into that engine. The first two cylinders are getting all that cold air. That’s a really good way to hurt your engine.”

“What do you do?” I ask.

“Wait for a day that’s not so cold.”

Mike Paulson, flight school manager and chief flight instructor at the Fargo Jet Center, shows off his winter flying clothes. It’s important to dress for the possibility of an off-airport landing, and a very long walk in sub-zero temperatures.Schlangen and I start wondering about performance charts. Stall speeds do not change with temperature; landing and takeoff speeds do not change—but just about everything else does.

The standard performance tables in the Cessna 172 POH only go 20 degrees below standard temperature. Standard temperature is 15 degrees Celsius, or 59 degrees F. Minus 5 C is only 23 degrees F. This isn’t even close to winter flying on the northern prairie. While the jet center does not generally allow lessons or rentals when the air temperature is lower than 10 or 15 degrees below zero, it has reached 40 below.

For grins, we plug minus 40 and an altitude of 1,000 feet (Hector International Airport is actually 900) into an E6B flight computer. We use the current pressure: 29.79 inches mercury. Density altitude: minus 5,967 feet.

“Here’s another thing,” Schlangen says. “Carbon monoxide. You’ve seen those little stick-on things that change color if there’s carbon monoxide? Think about the heaters in a small airplane. Outside air is ducted over the muffler, which is very hot, and then vented into the cabin. If there’s a pinhole leak in the muffler, suddenly you have carbon monoxide in the air you’re breathing. You’d never notice in summer because that same air is ducted back outside the aircraft.”

“Is this common?” I ask, worried.

“If there’s a hole, it should be caught during an annual,” Schlangen says.

A handheld can of Type 1 deicing fluid is often used to spray the wings and other surfaces of small airplanes that have been sitting outside in cold weather.“Why doesn’t the 172 have those stickers?” I ask.

Schlangen smiles. “The G1000 [digital avionics suite] has a carbon monoxide warning.”

Schlangen asks me if I’ve heard of the runway condition scale. I tell him I’ve heard reports about marginal braking and such, but not about a scale.

“It’s part of the FICON, field condition reports,” he says. He shows me a page on his computer, the Runway Condition Assessment Matrix (RCAM). A code of 6 is a clear and dry runway. Code 3 is slippery when wet. Code 1 is ice. Code 0 is wet ice, slush over ice, water on top of compacted snow, dry snow, or wet snow over ice.

“Always plan your winter landings as if you have no brakes at all,” Schlangen says. “That’s the length you need. Because if you’re landing on ice, you really don’t have any brakes at all.”

“And tires,” he continues. “You can bald-spot tires really fast if you’re on ice and pressing on brakes, then hit a patch of dry runway.”

I remember a winter flight when the air was very cold and ice crystals hung at eye level. I remember asking if there was such a thing as clear-air icing. It seemed to me that if I could see the ice, could feel it sticking to my nose and eyes, then it might be sticking to wings as well.

No, I learned. There is no such thing as clear-air icing. And the fact that I could see crystals meant the water was already solid. It would bounce off the wings. Icing is when liquid or vapor water hits a cold wing and freezes, turns to solid immediately.

Deicing is the obvious topic for winter flying. And according to Jeremy Sobolik, line manager at Fargo Jet, the very best deicing is hangar space.

“Beyond that,” he says, “There is Type 1 and Type 4 deicing fluid. Type 1 is deicing. It’s a heated fluid, propylene glycol, very similar to an antifreeze. Type 4 is an anti-ice. It’s thicker than Type 1 and applied cold. It helps create a barrier so precipitation does not stick.

“It has a shear factor,” Sobolik says. “As the wind moves over the wing, it thins the fluid out so it become very viscous.”

Type 1 is what they spray on a 172 that’s been sitting outside.

Cold air is dry air. I ask Schlangen about carburetor ice. Frankly, he says, there’s less of a problem in winter than in summer. The air is that dry, at least in the upper plains. That’s not necessarily the same in the Ohio Valley and New England. But the routine, the habits of mind and hands, should be the same.

There is one wrinkle to hangared airplanes, though. Moving an airplane from a nice, warm hangar into cold air can cause condensation on the engine and carburetor. This can cause carb ice. You likely won’t know it until runup.

“Low temperature means low water vapor content,” Remer says. “Relative humidity plummets. It’s very easy to saturate cold air and any addition of moisture can cause rapid saturation.”

“Do you know about the ideal gas law?” Remer asks.

“Perhaps,” I say.

If you can, you want to avoid long stretches of remote areas. If something does go wrong, you want to be near someone who can help. Even a walk of a quarter mile when the temperature is below zero and the wind is strong can be life-threatening.“The atmosphere is a mixture of gasses. And there are three variables in the ideal gas law,” he says. “Pressure, temperature, and density. Those three are always jockeying with each other, always changing in the atmosphere. And the three always respond to each other. So when we get these really cold Canadian high-pressure systems coming through in winter, when pressure goes way up and temperature goes way down, you know that density is going to be high, too.

“Dense air,” he continues, “has more molecules per volume of air. There is more oxygen in a given volume of air. That changes the mixture you’re sending to the engine. If you’ve not adjusted, you’re probably running a bit leaner than you think you are. But that greater amount of oxygen means you’ve got greater combustion. Your engine is running better.

Big Chill“An aircraft works much better with the lift equation in winter,” he says. “There’s an increase to both lift and drag but not to weight.”

A bit like a first solo, I think, when everything is just the same except there’s a lot less weight—the CFI isn’t there any more—and the flying is so much fun.

Winter advice comes from experience. Some of it is practical. For example, if you’re flying to a small airport, call ahead to get field conditions. The runways may be plowed by volunteers and it can be several days after a storm until they get out of their own driveways and over to the field. Even at a popular airfield, remember that frost on a taxiway can cause an airplane to slide.

Airports often put sand down on taxiway ice, but they don’t use chemicals to melt the ice. If you taxi too close behind another airplane, especially a turboprop, you can find yourself in a minor sandstorm.

When sumping fuel, it’s possible that nothing will come out. Not a drop. That means water in the fuel has iced up inside the tank.

Airplane heaters, especially in older airplanes, are often more hoped-for than real, especially with little 80- or 100-horsepower engines. Paulson tells a story of reaching for a bottle of water he had in the back of a 152 and finding it frozen. Small airplanes in general don’t have defroster fans—it’s all ram air—and window fogging can be a real problem.

On the plus side, snow blowing across the runway makes crosswind detection easier.

Some of the advice is more personal. I remember a winter sightseeing flight several years ago. My goal was to fly north of Fargo, turn west when the Red River of the North met the Sheyenne River, and then follow the Sheyenne, banking left and right with the river bends, for as long as the afternoon light lingered. The air was cold and clear and as gentle as I could dream. As I was walking out the door, Paulson called to me. “Climb out at 90 instead of 80,” he said. I must have looked confused. “At 80,” he said, “in this air you’ll be a rocket.”

Likewise, route planning should favor FBOs that can service common problems, such as a leaking seal around the front strut or a flat tire.

Some of the advice can save your life. “Flying cross-country,” Paulson says, “in terms of route planning up here on the prairie, should be different. In summertime you just fly point A to point B. In winter, we tend to follow roads a bit more. If you can, you want to avoid long stretches of remote areas. If something does go wrong, you want to be near someone who can help. Even a walk of a quarter-mile when the temperature is below zero and the wind is strong can be life-threatening.”

I ask Paulson for favorite winter flying stories and he tells me about winter fly-ins at Minnesota lake resorts where someone has taken a plow to a frozen lake and cleared a runway of 10,000 feet or more as well as alternate runways, taxiways, parking areas, and more than 100 airplanes—sometimes as heavy as a Cessna 310—arrive for chili or barbecue. “That really is a fun adventure,” he says.

But then he pauses. “The visibility at night,” he says, “is astounding. The air is so clear. A town you would think is 20 miles away is really 60. And the northern lights! Dim down your cockpit lights and there is no better way to see the auroras than from an airplane cockpit.

“If you can stand the cold of the preflight,” Paulson says, “winter flying is pretty special.”

W. Scott Olsen is an English professor at Concordia College in Moorhead, Minnesota.

Related Articles