Rime Time

It is that time of the year again. Houses are covered in holiday lights, hangars in festive layers of snow, and your airplane? If you are lucky, it is covered by a heated hangar. Otherwise, you will spend quite a bit of time doing de-icing procedures before you can fly into the clouds.

People will tell horror stories about things freezing over, engines and flight instruments struggling with the cold, and tales of extreme turbulence.?

I love to fly on instruments in the winter. Airplanes and airfoils perform better in cold air, and the weather is a more definite thing – it is either okay or so terrible you would not change it.

You may have to pay closer attention to weather reports and forecasts, but thunderstorms are not the big problem they were just a few months ago. Airframe, engine, and probe icing are just as possible in summer as in winter, depending on your altitude.?

One last advantage to winter instrument flying over summer is that big-front low-cloud winter weather tends to keep the amateurs out of the sky. When it is two hundred and a half in moderate snow, you can be sure that only instrument pilots are with you. No pop-up VFR traffic to worry about.

The main problem that pilots run into during the cold months is that frozen stuff that clogs pitot tubes and, more importantly, your wings and empennage.?

FAR Part 91 does not specify how much icing you can carry on your airplane. Chapter five of the Aeronautical Information Manual has some good, non-regulatory guidance on what kind of condition your aircraft should be in before flying on an icy day.

“Critical and Lift-Generating” are the terms used to describe the areas you should ensure are clear of ice. To most people, this would be the wings, control surfaces like the elevators and ailerons, induction areas and propellers, etc.

The standard for frost now is that it should be totally removed from your airplane with only a little allowed on the bottom of the wing, where small amounts of it sometimes form because of the cold fuel in the wing mixing with lower, warmer, and wetter air.

I’ve witnessed almost every strange technique pilots use to avoid paying a de-icing charge or a fee to put their bird in a heated hangar. I have seen pilots sweep snow off of their wings with brooms. I’ve seen them sit on the tail of their airplanes so the snow would slip off.?

Getting the frozen stuff off your wings is the main idea, but what about the rest of the ice? Control surfaces generally have hinges, and cable attach points. Are they all clear and usable throughout their entire range? A jammed elevator is far more challenging than frost on your wing.

Even if you are de-iced by professionals, I suggest a quick walk-around after the procedure is done if you can do that before you taxi out. A hurry-up or cheap de-icing job sometimes means they have gotten the ice chunks off your horizontal stabilizer but hosed the gunk into your elevator hinges. Most de-icing efforts quite rightly concentrate on the upper surfaces of an airplane. If you get the chance for that post-de-icing walk around, make sure the landing gear and gear wells aren’t packed with snow.????

During your walk around in the crisp and snowy holiday air, pay close attention to the probes on your airplane. On big aircraft, they are all heated. The general aviation airplanes most of us fly only are required by FAR to have a heated pitot if you are operating in icing conditions.

They say nothing about a heated static port. Static ports are generally in areas of an airplane that doesn’t get in-flight icing. The key phrase here is “in flight” If your aircraft was parked outside the night before, all bets are off if there was frozen precip or rain that later froze. Also, de-icing people rightly don’t aim their hoses at static ports and pitot tubes.

Ice in the pitot is another instrument flying horror story, but if you have a GPS on board and practice a little with the difference between ground speed and airspeed, you can use your groundspeed readout and factor in the wind. If you don’t have a GPS, you can practice no airspeed indication approaches and the like using pitch and power settings.

Antennas aren’t lifting surfaces but can be essential to your instrument flying. Iced-over nav and comm antennas can be more than annoying; they can be dangerous. While many probes on bigger airplanes – like angle of attack vanes, Total Air Temperature probes, and static ports – are heated, most antennas are not.?

?If you fly large transport or executive aircraft, you have more places to look during your preflight – sink and water drains. Sink drain masts are normally de-iced electrically, but a clogged drainage system can make your flight with the boss very uncomfortable.

Now that we’ve gone through the lengthy and expensive process of de-icing our airplane and totally rethinking our stance on how expensive that heated hangar rent is, we need to talk about the frozen stuff you are likely to fly into there.?

In the long list of things you are dealing with – if you are encountering significant icing, getting out of it is your first priority. Bumpy air and grouchy controllers won’t make your airplane fall out of the sky out of control – in-flight icing will.

There are basically two kinds of aircraft icing: Rime and Clear. This sounds like a great new song for Sesame Street Muppets, but it really is that simple. There are three ways to avoid it: go up or down or turn-around.?

You will typically run into rime ice in stratus clouds. It happens when tiny water droplets instantly freeze on your airplane’s surfaces. It is china white and opaque, and it builds up quickly on the leading edges of your aircraft. Irregular in shape when it does freeze, it can break up the airflow over your wings and controls very quickly.?

If the ice is clear, it is almost impossible to see on a wing, so it might take a long time before you notice a problem. Clear Ice is a product of large water droplets like you might find in cumulous clouds or freezing rain, which is deadly and deserves its own little discussion.

Two problems with ice on your airplane are weight and drag. Anybody who has carried one of those cardboard pallets of drinking water out to a soccer practice will tell you that water is heavy.

Drag is probably one of the best self-describing words in the English Language. A thin layer of ice on your airplane can reduce lift by 30% and drag by 40%.?

?Icing can be avoided with a bit of planning and is usually easy to get out of if you accidentally encounter it.?

Please get out there and fly this winter. The weather during the next few months is why you got your instrument rating in the first place. File and fly and enjoy the beautiful winter weather.