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No, this article has nothing to do with flying your model during an ice storm. I thought because of the weather we’ve had recently, you would like to know what it’s like to fly in icing conditions -- in a full size airplane. (Now do not worry, I’m not trying to impress you with a “War” story.) You may wonder how the “Big Boys” fly the commercial planes during wintry weather. Well, even the air carrier guys have to cancel a flight from time to time because of heavy snow or icing conditions. An iced-over airplane setting on the tarmac is bad enough, but an in-flight buildup of ice can be a truly "memorable" experience! The first step for a pilot before a flight is to get a weather briefing -- not from the local TV station but from an FAA aviation weather briefer who can tell you about the current and forecast conditions for your particular flight, such as known hazardous weather aloft and at your destination airport, winds aloft which include temperatures, the altitude of the "freezing level" if there is precipitation enroute, "PIREP’s," and "NOTAM’s." NOTAM’s are Notices to Airmen which is important timely information about departure and destination airports such as closed runways/taxiways, out of service navigation aids, or any information different than that shown on navigation charts (communication or navigation frequencies including approach courses, minimum approach altitudes, and so on). PIREP’s are "Pilot Reports" that pilots pass along mostly about hazardous in-flight weather such as turbulence, icing, wind shear, birds, etc. (Pilots helping pilots). After filing an IFR Flight Plan* and doing a thorough pre-flight (walk around) inspection of the airplane, you get in and go. In the climb-out and into the clouds, you keep an eye on the outside air temp (OAT) indicator because every 1000 ft. of climb translates to a temperature drop of roughly 4 degrees F. This temp’ drop is called the "adiabatic lapse rate" which is a fancy term for decreasing temperature with increasing altitude. As you notice the OAT approaching the freezing point in IMC (Instrument Meteorological Conditions), anti-ice protection is switched on. Otherwise there is a strong probability that your plane will begin collecting ice. IMC (Instrument Meteorological Conditions) is another fancy term for flying in the clouds with no outside visual attitude references. Lots of fancy terms and acronyms in the aviation language. Not all aircraft are certified for flight into known icing. Most single engine planes and many light twins are not approved for this. Invariably a hapless pilot without an "Instrument" rating or with limited experience will wander into IMC either on purpose or by accident. Emphasis on accident! There are two types of ice: Bad and Badder! Actually the two are "Rime" ice and "Clear" ice. Rime ice has a “milky” appearance because air is mixed in as it freezes. Clear ice is, well, clear and is the worst of the two because "Clear" ice is all water (no air mixed), and it sticks like Gorilla glue to aircraft surfaces! The clear stuff is found in and around thunderstorms or from freezing rain. You’re thinking: "Why on Earth would anyone want to fly through a thunderstorm?" Well, this happens too, and it makes front page news! Some thunderstorms, as you know, produce hail and while I have never been there, I’ve heard that a flight through an area of large hail can be one of the scariest rides known to man. Even pea-size hail has an incredible amount of energy when it hit’s an airplane doing 500 mph. Hail can cause severe damage mainly to leading edges and to the cockpit windshield -- or much worse! Back to freezing rain: Have you heard the term "super-cooled" water droplets? This "below freezing" water or precipitation is in an unnatural liquid state because of agitation. When these water droplets find an airplane (or any other object for that matter), an immediate change to ice occurs. The pilot must take evasive action if his airplane’s anti-ice gear is not keeping up with this onslaught of ice accumulation. What kind of evasive action? You might think descending to a lower altitude (toward a relatively warmer temp‘) would be the thing to do, but this is not always the right direction. When a winter weather front moves through a region of the country, there is usually a "wedge" of colder air in it’s wake at the surface -- this cold air mass will likely be below freezing. The boundary between the colder air on the surface and the warmer air above it, is called an “inversion” and the temperature difference can be from five to fifteen degrees. This temperature change occurs quickly -- usually within only a few hundred feet of altitude. Ok, so now that you are armed with this weather information, should our pilot climb or descend to leave the ice? You can see the importance of a thorough weather briefing as well as possessing all the weather knowledge that you can stand. In the above scenario, I would climb a couple of thousand feet (and level off) to thaw and shed the ice collection and then mentally sort things out while at an above freezing altitude. However, you may not have this option since climbing and holding consumes more precious fuel. In any case, the worst thing to do is nothing when your plane is loading up with ice. What does an ice build-up do to your airplane? The answer is: Everything BAD! The plane changes shape, in particular the wings and since propellers are airfoils they too will take on a different (less efficient) shape. Jet engine intakes can ice-up just like any other exposed aircraft part and cause a flame-out. External aircraft inlets and ports can get plugged with ice causing loss of critical instrument readings. As ice accumulates, aircraft weight increases. In other words, just about every crucial function of an airplane in flight is adversely affected. In addition to all the above, a pilot’s outside visibility is reduced or could even be zero with an iced-over windshield. And -- all this can happen at night! An ice load can be removed or prevented if the de-ice or anti-ice systems (respectively) are on and working properly. Properly, meaning Murphy’s Law applies to ice protection systems (among other aircraft systems), but I won’t get into that. Have you heard the phrase: "Discretion is the better part of Valor?" Or -- "I’d rather be on the ground wishing I were in the air, than in the air wishing I were on the ground!" Sometimes it’s best not to make that flight. But then, there are times during a climb through the gray you suddenly break out "on top" (in the clear) and watch the sublimation* process evaporate that load of ice while it is still a solid! Or flying an instrument approach at night, in the soup, and breaking out under the overcast -- in a perfectly straight line to the runway, as brilliant strobe lights lead you in on the last few hundred feet of your flight. It’s a Great feeling! It’s all a part of the "package deal." And it doesn’t take very long for a new pilot to develop a deep respect for Mother Nature. Her weather can be beautiful, ugly, awesome, dreaded, pleasant, but (I think) always interesting and fascinating. I learned early in my 30 years of flying that Ma Nature’s weather is not malicious, just indifferent -- to creatures such as we. Knowledge and a healthy respect for weather is one way of staying healthy as a pilot. One more thing ... My Fighter-Pilot friend Bill Womble helped me with advice in writing this article -- Thanks Bill. Keep ‘em Flying Brad ------------------------------------------------------------------------------------------------------------* IFR Flight Plan: Instrument Flight Rules flight plan. Legally flying in the clouds under the direct control of Air Traffic Control. ATC is responsible for the separation and sequencing of IFR aircraft in controlled airspace. * Sublimation: The process of a solid substance changing directly to a gas, bypassing the liquid state of matter. Frozen Carbon Dioxide (Dry Ice) evaporating is an example. |