Why & How To Avoid Aircraft Icing

by Greg Gorak, CFII

This seems like an excellent time of the year to talk about icing.

When I started my career as a charter pilot in a Merlin III, I served my apprenticeship as copilot to a wonderful 24-year-old captain who taught me a great deal about weather. I asked him one day how he had obtained all of this knowledge at such a young age, and he explained that he had a degree in meteorology. But he tripped himself up one day in August (my starting month) by telling me how much he hated thunderstorms. He said the Merlin III could handle ice pretty well, but thunderstorms were another matter. Well low and behold, I drew the same captain the following February and he mentioned how much he hated ice because you could fly around thunderstorms, but icing was a completely different matter. So I guess the perspective depends on the season. Let’s start by reviewing the regulation on icing for general aviation pilots.

Part 91.527 titled “Operating In Icing Conditions” starts out emphatically by stating that no pilot may take off in an airplane that has frost, snow or ice adhering to any propeller, windshield, or powerplant installation or to an airspeed, altimeter, rate of climb or flight attitude instrument, or snow or ice adhering to the wings or stabilizing or control surfaces.

The next part of the regulation deals with all aircraft not certified for known icing. The FAR states: no pilot may fly under IFR into known or forecast moderate icing conditions or under VFR into known light or moderate icing conditions unless the aircraft has functioning de-icing or anti-icing equipment protecting each propeller, windshield, wing stabilizing or control surface, and each airspeed, altimeter, rate of climb or flight attitude instrument system. So we can immediately deduce that under IFR, we can fly into known light icing. It goes without saying that no pilot can fly into forecast severe icing conditions.

Now what about all this deicing equipment and aircraft certified for known icing?

I worked on a case of a P-Baron; that’s a Beechcraft Baron certified for known ice. This P Baron took off from the Mobile, Alabama area with two gentlemen, both in their mid-fifties, and two young ladies, both in their early twenties. The flight lasted only about 45 minutes and there were four fatalities due to an icing encounter. What was most interesting about the case was a statement by Beechcraft as to why they certify the aircraft for flight into known icing. The statement was as follows:

“We certify this aircraft for flight into known icing to allow the pilot to get out of the icing condition.”

I have owned only one aircraft certified for known icing and that was a Cessna 421 Golden Eagle. Owning this aircraft gave me a great deal of piece of mind from the standpoint that I know for a fact that if I landed the aircraft with some ice on it, the feds could not violate me.

My point is that although I have flown numerous aircraft certified for known ice, it is unwise to completely trust those systems. Why, you ask. Even if all of the parts are working during the preflight, doesn’t mean they will work once airborne. Here is a case in point.

I left Milwaukee Timmerman Airport one evening with a friend in a Cessna 310 bound for Bismarck, N.D. for the purpose of conducting a Flight Instructor Refresher Course the next day. We agreed that he was pilot in command (PIC) and I would work the radios. We were at 10,000 feet MSL in clouds about 100 miles out of Bismarck and picking up ice. I waited for some reaction from my friend, and even though we had lost 20 knots of airspeed, there was no reaction coming.

I reached the end of my patience by asking as casually as I could, “Fred, what do you think is the reason that we seem to have lost 20 knots of airspeed?” He indicated that he was not sure and tried to compensate by adding power.

As a side note, my friend had owned a Mooney 201 and had bragged to me how much ice the 201 would carry. I asked him if he would consider turning on the ice light and he said “okay.” He now ascertained that we were carrying a load of ice and turned the ice light off. Evidently, by the look in his eyes, that took care of the problem. I couldn’t believe that he still took no action. By the way, the tops were at 11,000 and clear above.

I now suggested that he consider operating the boots. He thought for a moment and then began operating the boots. Ala Kazan! We now gained 10 knots back, but still no further action.

By now you must know that some claim I have the patience of a saint. I then asked Fred if he would consider turning on the hot props. After thinking for a moment he acquiesced to my suggestion and now as the ice hit the sides of the nose of the aircraft, sounding like a 50 caliber machine gun, my friend who had bragged to me about how much ice his Mooney 201 could carry began to sweat precipitously. Let’s analyze the situation.

We are in moderate icing, utilizing the boots on auto sequence and the same for the electric props. But nothing else is happening. I now asked the $64,000 question. “Fred, would you consider asking me to ask Minneapolis Center for 11,000 feet, which should put us in the clear?” This is where Fred showed that he was a scholar of the regulations. He blurted out that 11,000 feet is the wrong altitude for our route of flight. (I thought to myself, I am flying with a Rhodes Scholar.) I asked him who would care 100 miles from Bismarck, N.D. at 11:00 pm at night and proceeded to ask Minneapolis Center for 11,000 and they responded by offering a block altitude should we need it. But the fun wasn’t quite over.

Upon landing at Bismarck, Fred demonstrated the worst landing I have ever experienced and when I asked him what happened, he stated that he forgot to put his landing glasses on. I guess he utilized three (3) different pairs of glasses depending on the mode of flight.

I appreciate your patience with my story, but Fred’s glasses were not the problem. After exiting the aircraft and proceeding to the empennage, I noticed that the right horizontal boot had not worked, thus setting up an imbalance and affecting airflow over the elevator on that side. I guess all is well that ends well.

Pilots, if you get into inadvertent icing conditions, take action. Utilize immediately what resources you have on the aircraft and work on a plan to allow you to exit the icing as soon as possible.

When does ice form? The most common form of icing occurs in visible moisture, namely clouds. It is generally accepted that cumulus clouds produce clear ice. We refer to this as the 2 c’s – cumulus equals clear. At what temperature does this occur? The average temperature necessary for clear ice is usually from 0 to minus 10 degrees Celsius. The biggest danger is the runback aft of the leading edge.

Clear icing is considered to be large droplet phenomena. Rime ice builds on the leading edge and forms in the minus 10 to minus 20-degree Celsius range. It is usually a smaller water droplet size and is the most common ice encountered. If you really want to get things interesting, you could encounter mixed icing, which of course is a mixture of clear and rime and usually forms at just below freezing. Most aircraft cannot handle freezing rain.

I worked on a case of an aircraft that was in freezing rain for 11 seconds and came to grief. We can most likely encounter freezing rain in warm frontal conditions. Large droplet or SLD (Super Large Droplet) is the worst kind of clear icing peculiar to the area around the Great Lakes and apparently responsible for the ATR-72 demise at Roselawn, Indiana. What’s interesting about SLD is that prior to Roselawn, most knew very little about SLD.

So you are planning a flight with the possibility of ice. Let us assume that you have an aircraft equipped with boots and prop de-ice, but it is not certified for known ice. Make sure you test all your equipment including pitot heat. Prior to external preflight, turn on the master and then turn on the pitot momentarily. You should notice a draw on the amp meter as an early indication that the pitot heat is working. Now turn the pitot heat off and there should be less of a draw on the amp meter. During the preflight, the pitot heat tube should be warm to the touch based on your previous action.

During the preflight, note the condition of the boots and especially look for punctures, loose patches, etc. If you have electric props, check the leads going to each blade. In those aircraft certified for known ice, you would also check the electric or alcohol windshield. If the aircraft is equipped with an alcohol windshield and props, check the alcohol reservoir and make sure it is full.

Also know the flow rates. Most aircraft will have two flow rates, which of course are utilized depending on the rate of icing and of course the max rate will diminish the amount of time spent in the icing encounter. During the engine run-up, also check the inflation of the boots and make sure everything is working.

The typical winter flying weather most often seen in the Midwest would be a ceiling of 600 to 800 feet with tops of 3,000 to 4,000 and clear above. The key in this scenario is to minimize the potential encounter. When climbing to VFR on top, utilize the best power and rate available, but remember that an excessive angle of attack can build ice on the bottom of the wing.

Every action taken must be balanced with the potential consequences of that action. Remember, once on top, some of the ice will be reduced through sublimation, namely simple friction will wear away the ice on the airplane.

One additional note: We have a tendency to think only of ice on the wing, but remember it isn’t called airframe icing for nothing. The weight of ice on the entire airframe is a factor to be dealt with.

EDITOR’S NOTE: Gregory G. Gorak is an 8,500-plus-hour Airline Transport Pilot and president and chief instructor of Gaits Aviation Seminars. Gorak’s experience as an aviation expert witness and past Milwaukee alderman enhances his presentation with real life, humorous anecdotes. The Federal Aviation Administration named Gorak “Flight Instructor of the Year “ for the United States in 1975. The National Association of Flight Instructors (NAFI) awarded Gorak Master Flight Instructor status starting in 1998 to the present time. Gorak received the Wright Brothers Master Pilot Award in September of 2012 and was inducted into the National Association of Instructors Hall of Fame in November of 2013.

DISCLAIMER: All information contained in this article and elsewhere in this magazine is based on the experience of the author, only. Readers are urged to seek out additional information from the Federal Aviation Administration and other sources. Neither the author nor this publication, its owners or anyone else or entity affiliated with this magazine are responsible for the reliance on information contained in this article or any other article published in this magazine.

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