Cold-Weather Flying, Part 1

Tuesday, February 6, 2018

Matt Gabbard, CFII, Ferry Pilot

Matt has been flying for over two decades and has extensive knowledge of different aircraft and avionics, he is a talented photographer and enjoys traveling, history and astronomy. 

Quote to live by: "Whatever you are, be a good one." ~ Abraham Lincoln


From my Desk to the Sky... Cold-Weather Flying, Part 1

At the time of this writing (early January), the temperature here at KLEX is a balmy 62 degrees F. Believe me, it feels great after a couple of weeks of sub-freezing temperatures and bone-chilling wind chills.

But as I like to say, when it’s this warm in January, you know we’re going to have to pay for it.

Sure enough, the forecast for this weekend calls for a low pressure system to move in from the southwest, move over the area, and bring with it the chance for significant ice and snow accumulations. On top of that, the temperature will crash and the wind will become gusty. Flying will just not be feasible, more than likely, for us GA pilots. So, in light of such a wild (and normal, for Kentucky) winter forecast, I’d like to offer some tips for staying safe during cold-weather flying operations. In this post, we’ll focus on pre-flight operations and considerations.

First, even though cold temperatures and low density altitudes are great for aircraft performance, the plane has to actually get in the air first. Obviously, for an airplane to fly it must develop lift, and to develop lift the airfoils need to be clear of frost, ice and snow.

Even just a small amount of frost (think of the texture of sandpaper) can not only cause undesirable effects such as an increase in drag by 40%, but, more dangerously, it can decrease the wing’s total lift (by 30%), decrease its critical angle of attack, and could even lead to an asymmetrical stall.

The best way to avoid this is to place the airplane in a heated hangar so frozen phenomena are not allowed to form at all. If the wings already have ice or frost on them, put the plane in a heated hangar for a while. Be careful, though, and don’t let any melted water on the wings re-freeze after you pull the airplane out for flight. I find it best to dry the wings after the frozen stuff has melted. If you can’t hangar the airplane, you may consider a whole-aircraft cover so that nothing frozen can form or fall on the aircraft surfaces.

If you are fortunate enough to have a de-ice/anti-ice system installed on your aircraft, making sure that the porous panels actually weep the glycol fluid is important. If the system hasn’t been used in a while, it’s possible it will need priming again to ensure proper functionality. The preflight is also a great time to listen to the fluid pumps working so you know they are doing their job. It’s best to do this on the ramp, though, as the fluid can make a hangar floor very slippery.

What about the engine? According to Teledyne Continental Service Information Letter SIL 03-1, “Preheating is required whenever the engine has been exposed to temperatures at or below 20° Fahrenheit / - 7 degrees Centigrade (wind chill factor) for a period of two hours….Failure to properly preheat a cold-soaked engine may result in oil congealing within the engine, oil hoses, and oil cooler with subsequent loss of oil flow, possible internal damage to the engine, and subsequent engine failure.”  For Lycoming (according to Lycoming Service Instruction No. 1505) the temperature varies a bit: “The use of pre-heat will facilitate starting during cold weather, and is required when the engine has been allowed to drop to temperatures below +10°F/-12°C (+20°F/-6°C for –76 series engine models).”

I think this is a good rule of thumb, although one could make the argument to do so at an even higher temperature.

So how should one pre-heat an engine? The best way to accomplish this is to use a heated hangar. After all, this option allows the wings to be free of frozen precipitation, the engine will be well above freezing, and it allows you as the pilot to complete your preflight inspection in relative (at least) warmth. But not everyone has this option, as many T-hangars are unheated, or worse yet, the airplane may be tied down on the ramp, exposed to the elements.

In these situations, preheating can be accomplished using a Tanis, Reiff or engine block heater, all of which are connected to an electrical extension cord and are able to warm the oil and engine components before flight. It may take a bit of time (probably several hours), but you will then be able to start the engine with the peace of mind of knowing that no engine parts will be harmed in the process.

This will make the jobs of both the starter and the battery much easier too because cranking won’t take as long. Other options for pre-heating the engine include propane forced-air heaters with ducting placed in the cowl air inlets, electric heaters and even a camping cooking stove (if you are somewhat desperate).

The engine is certainly a primary focus when it comes to heating, but not just because of the possibility of congealed oil. The crankcase, cylinders and other components, if exposed to extreme cold temperatures, are susceptible to wear and damage upon startup if not properly preheated.

Another very important component of the engine that should be thoroughly inspected is the crankcase breather tube.

If the end of this tube becomes plugged up due to ice - which is possible because water forms as a byproduct of combustion and therefore can freeze – your engine will try to vent the pressure in the crankcase by venting at the next weakest link: the crankshaft seal. The big fan at the front of your engine will probably quit for the day, leaving you sweating (even thought it’s freezing outside), and you’ll be looking for a place to land in a hurry. So make that part of your cold-weather pre-flight inspection, and keep that breather tube unobstructed.

As we’ve seen, allowing an airplane to sleep overnight in a toasty hangar is the best practice. Not only are the engine parts and oil warm, the instruments, control surfaces and electrical components will be warm as well, all of which will help provide optimal airplane performance.

We’ve discussed a few important pre-cold-weather-flight topics so far, but just about all have to do with the airplane. What about the pilot? Here are a few to consider. Let’s face it – we’re human, and because of that, we get cold during exposure to freezing weather. It is only natural, therefore, to rush through whatever activity we are doing so we can find a warm place to thaw out! It’s no different preparing for a cold-weather flight.

If you think about it, it’s a cold-weather preflight that should probably take probably longer than a warm-weather one.

Why? Because when you’re cold you tend to rush. When you rush, you may forget or overlook an item, and this could lead to very bad things happening.

It is advisable to prepare for the weather by dressing in layers, wearing hand and head protection, and taking your time. Not only will the extra layers help for the preflight, but if an off-airport landing occurs, you will be ready for the un-planned time spent on the ground.

In the next post, I’ll go through some tips and concerns for actually flying in cold temperatures and in the winter in general. In the meantime, stay warm, and check out these resources I used for this post:

 

https://www.faa.gov/documentLibrary/media/Advisory_Circular/ac91-13c.pdf

https://www.aopa.org/training-and-safety/active-pilots/safety-and-technique/weather/cold-weather-operations

http://www.avcanada.ca/forums2/viewtopic.php?t=78588

https://www.faa.gov/news/safety_briefing/2014/media/NovDec2014.pdf

http://www.boldmethod.com/learn-to-fly/aircraft-systems/three-ways-to-preheat-your-aircraft-this-winter/