The Go/No-Go Decision In Winter

I tracked directly over the old DYE-2 radar site at Raven, its characteristic ball-shaped dome reflecting the dancing blue and orange colors of the aurora borealis. [To learn about flying in Greenland, read "Extreme Flying!" from Pilot Journal Nov/Dec 2008 at our online home.] As I cleared the ice cap, Sondre Strom appeared in the distance, a tiny beacon of light seemingly suspended in an expanse of perpetual black. Predictably, Sondre Strom took a while to negotiate, but I finally got off in time to arrive in Iqaluit by 7 p.m. local time. Iqaluit was bitter-cold, minus-35 degrees C, though again, as so often happens in the far north during a cold snap, the weather was severe clear.

After topping the tanks for the fourth time that day, I asked about a heated hangar for the night, knowing it wouldn't be cheap. The local airline, First Air, had a huge, empty hangar available, large enough for a 737. The service manager said he thought the rate was $75 Canadian, but he'd have to check. Wow, I thought, that's incredibly cheap, only about $60 U.S. We walked into his office, he pulled out a rate sheet and verified, "Yep, I was right. It's $75 per hour."

Tired and dispirited, I said "thanks anyway" and filed a flight plan for Wabush, Newfoundland, 600 miles south, where I knew the temperature wouldn't be a problem. I hiked back to the Baron through the cold and dark, and launched for the fourth leg of the day. I wasn't about to leave the near-new Baron to cold soak overnight in minus-30 degree C temperatures. I arrived at Wabush at midnight, after a longer day than I had planned. Flying that last leg was a decision I wouldn't have had to make in summer.

As some readers may know, I now live in Southern California, where anything colder than 0 degrees C is considered a return to the Ice Age. The "yeah, but!" is that I grew up flying Civil Air Patrol in Alaska and, these days, I fly regular trips through northeastern Canada in winter practically every year. Accordingly, I know many of the mistakes with airplanes in that part of the world because I've made virtually all of them.

The go/no-go decision becomes more difficult in winter for a variety of reasons. The most obvious is simply the temperature. It's colder (duh!), and pilots, weather and airplanes become less friendly when the thermometer falls. For our part, pilots tend to take shortcuts when the weather is cold/wet/snowy. Perhaps the easiest shortcut is to treat winter like summer, but that's pretty unrealistic if you plan to survive until spring. Another philosophy is simply to lock the hangar door and not fly again until the weather is warmer. That also may not be a practical alternative if you hope to realize the utility of an airplane.

The inconveniences of winter begin with the preflight. Differences appear with simply untying and unchocking the airplane, what my old buddy Bob Pyle used to call "the most important part of the preflight." Ropes are less pliable in winter, sometimes stiff and inflexible, and chains can be cold and miserable to work with. Checking the fuel caps on a high-wing airplane becomes a lot less fun when the steps on the strut are covered with ice and your fingers are too numb to grab the handgrip on the cowling, so some pilots simply skip it.

Similarly, checking the fuel sumps on a low-wing airplane becomes less fun when you must go down on one knee and have that knee come up wet. Hardly anyone will spend the proper time checking all those things under the airplane that present less of a challenge in summer: wheels and tires, flashing beacons or strobes, antennas, exhaust stacks or cowl-flap security. Snow or ice on the windshield is another problem you don't normally face in summer, and considering the temperamental nature of Plexiglas, scraping is ill-advised. Break all the credit cards you wish chipping ice off the wings or tail, but windshields are off limits for anything abrasive.

The old cliché that the worst abuse you can inflict on an engine is starting it goes double in winter. All those moving parts out front are cold and unlubricated (a good argument for installing a preoiler if there's one available), and rubbing metal upon metal causes surfaces to wear each other down, reduces tolerances and eventually contributes to failure. Starting procedures vary from engine to engine, but one general rule is that you can't overprime an engine in extreme cold. You can avoid most of the start problems completely by paying for a comprehensive preheat at temperatures below freezing, an intelligent investment.
The rules for taxiing change slightly in winter, when ramps may be partially snow- or ice-covered. In any significant wind, keep speed slower than normal and do all braking in a straight line. Similarly, make absolutely certain the engine is up to a normal operating temperature before adding power for takeoff.

While it's true most piston engines perform better in cold weather, extreme cold can make them perform a little too well. Fly around the northern states or Canada in winter, and you may be faced with a density-altitude problem---exactly the opposite of summer. At minus-35 degrees C, for example, flying from a field elevation of 1,000 feet MSL, the density altitude is minus-5,500 feet, the equivalent of flying more than a mile below sea level. That means a typical normally aspirated engine will pull something like 34 inches of manifold pressure, easily enough to start bending parts and breaking things. Bush pilots who fly the far north in winter know to monitor the manifold pressure on takeoff to avoid an overboost.

Virtually everything on the airplane suffers when the OAT takes a dive. Batteries are less efficient, so starters have less cranking power, an excellent argument for a cart start. Tires become less elastic in cold weather and can even develop flat spots in extreme conditions. Lubricants sometimes don't lubricate, restricting things that should move freely to immobility. Brakes can become glazed and useless in cold, wet conditions. Switches don't work as well, door locks may freeze, sun visors can embrittle and even landing gear can cycle slower or not at all.

IMC becomes notably less clement in the gap between about 0 and minus-25 degrees C, then often begins to improve as it gets really cold. Below minus-25 degrees C, the air can become so dry that it may not support the formation of clouds. In summer, the worst possible weather system is a thunderstorm, an unquestionably formidable opponent. The only good news about thunderstorms is that they're often predictable and usually fairly visible, and most pilots don't have to wonder if it's safe to fly into a huge cumulonimbus cloud with lightning sparking out the sides.

Winter weather is less predictable and more insidious. The question is often how bad is too bad? Overcasts are sometimes lower and generally thicker, weather systems are often larger, and in-flight icing can represent a definite no-go situation. The wind tends to be stronger both on the ground and in flight, sometimes bad enough to compromise safety all by itself. In parts of the Midwest and East, winter weather can go from manageable to deadly in a heartbeat.

The big question that most pilots must answer is how to handle airframe icing. If icing is forecast and your airplane isn't fitted with approved deice equipment, either pneumatic or liquid, your decision is made for you. Technically, you can't just go up and "take a look." Depart into known icing without proper equipment, and you may get away with it, but if you don't and survive the encounter, the FAA may have some embarrassing questions.

In flying the ocean several times each winter, icing is always one of my biggest challenges, and I start considering an exit strategy the instant it appears. Ice is to winter what thunderstorms are to summer. Airframe icing is caused by supercooled water droplets that adhere to the airplane when they contact the surface. If the limit of your deice equipment is pitot heat, or even if you have a full set of approved pneumatic boots, the rule is, don't go there.

So what do you do if you encounter inadvertent icing? The type of ice dictates how you handle it. Climbing, descending (if the terrain below will allow) or a 180 are the options. Freezing rain is the worst and demands the most respect and immediate action. The rate of accretion can be unbelievably fast.

Several years ago in Anchorage, Alaska, the crew of a corporate King Air 200 from North Carolina was briefed on the possibility of freezing rain on a flight to Sitka. The captain had never flown in significant icing conditions before and took off anyway, assuming his Super King Air was super enough to handle anything. It wasn't. Ten minutes later, he staggered down the ILS back into Anchorage under nearly full power, barely able to make the runway because of a load of ice that deformed the wings and tail and nearly turned the big corporate turboprop into an icicle.

Clear ice, often most evident in cumulus clouds and other types with vertical development, is the second most serious. Clear ice is tougher to remove with pneumatic boots. Rime is perhaps the most common and least severe form of icing, often filled with air pockets and generally the easiest to crack off with boots. These days, more and more airplanes are being fitted with a TKS system, laser-drilled titanium panels fitted to the leading edge of wings and tail that exude a special glycol-based liquid.

I have a good friend in the Northeast who flies his Mooney 201 all year round with his aftermarket TKS system constantly enabled to protect him from evil, even in severe icing conditions. He spends a fortune on TKS fluid, but in 10 years of operation during some nasty winter storms, he's never seen any significant accumulation of ice.

For a more in-depth analysis of icing, Robert N. Buck's excellent book, Weather Flying, has the best advice I've read. Avoidance is the best remedy.