Combating Icing in General Aviation Aircraft

By Sarah Rovner, Master CFI, CFII, MEI, ATP, Owner of FullThrottle Aviation LLC

January 2018

As winter weather reaches the majority of the United States, it brings a unique set of weather phenomena. The colder temperatures and frozen precipitation pose an exceptional threat to general aviation aircraft. Although general aviation aircraft range in size and capability to handle cold weather conditions, careful thought must go into planning when the threat of icing is present. As an international ferry pilot who has flown 115 different aircraft in 15 different countries and taken small aircraft across the North Atlantic to Europe, there are many tools and strategies that I have come to use that many general aviation pilots may benefit from.

Icing poses risks to aircraft beyond the loss of control situations that pilots have read about in accident reports. Even small amounts of ice accumulation will degrade aircraft performance significantly. I’ve picked up small amounts of ice climbing through thin clouds, and even a minuscule amount of ice can equate to significant losses of airspeed which eats into fuel reserves. For North Atlantic crossings in most small aircraft, the longest legs are just shy of 700nm between Canada and Greenland, and then Greenland to Iceland. Most of the airplanes I’ve flown across have a range of just slightly more than that with reserves. Therefore, it’s absolutely critical that there is no ice accumulation or there is the risk of running out of fuel before reaching shore.

Not all ice will sublimate. When ferrying a King Air across the North Atlantic, I picked up ice while climbing through clouds on the way to Iceland from Greenland. After waiting for the proper amount of ice accumulation, I engaged the de-ice boots but not all ice came off, nor did it come off completely evenly. Just that small accumulation caused a decrease in performance, but luckily the tailwind allowed the flight to continue with sufficient reserves. The ice didn’t come off for the entire 4-hour leg, with temperatures around -40°C (-40°F) at 25,000ft. The dangers of icing and its effect on performance are serious, and pilots should not anticipate that the ice they pick up on the climb will go away once they are clear of clouds.

Although not all clouds will cause icing in winter, there is a high probability that a general aviation aircraft will begin to accumulate ice when the temperature drops to around 0°C (32°F) and there is visible moisture present. FAA Advisory Circular 91-74B¹ discusses how clouds and visible moisture at temperatures below freezing are often mixed with frozen liquids (super cooled clouds) and ice particles. Ice accumulation is often greatest at temperatures just below freezing where there is a high quantity of liquid water content, and nearly negligible when the temperature is below about -20°C (-4 °F) as most clouds are made up entirely of ice particles. As the temperatures start to get colder, it is critical that pilots ensure they are staying within the operating limitations of their aircraft. Not all piston airplanes can handle the extreme cold, so pilots must consult their aircraft manufacturer for temperature limitations to include pre-heat and engine temperature limitations. Additionally, many general aviation airplanes equipped with TKS systems also have temperature limitations and a specific operating envelope where protection is effective.

Ferrying small aircraft for long distances has little to do with flying itself – it’s all about planning. A great tool that many general aviation pilots are not aware of is the GRAMET, which is a graphical vertical flight path weather forecast based on the Global Forecast System. This tool combines prognostic charts, AIRMETS, SIGMETS, winds aloft tables, and many other tools into a graphical representation of weather along a specific flight path and altitude at a specific time. In many cases, pilots are not able to attain a temperature range suitable for operation in clouds due to altitude limitations, so the GRAMET is helpful to get an idea of where the clouds actually are in relation to their path in order to choose a path that would keep them clear of visible moisture in a dangerous temperature range. The Autorouter is a free tool that can generate a GRAMET for pilots by inputting their route and flight plan information, and can be found at: https://www.autorouter.aero.* Although the Autorouter is primarily for European pilots that look for route and flight planning tools, the tool does work for any ICAO airport. By selecting the GRAMET link on the upper right hand side (which does not require an account), a user can input their flight plan information, time and altitude and it will generate a GRAMET immediately. Since the tool is more geared toward Europe, not all North American fixes will be recognized but most airports should be. OGIMET is another tool that can be used to generate a GRAMET and it can be found at http://www.ogimet.com/home.phtml.en.* OGIMET is not as easy to use but it does provide the same data and even has an Android App (but not for iPhone).

Icing poses a severe threat to aircraft and can significantly degrade performance and aircraft control. Avoiding icing conditions with a high probabiity of ice accumulation is important for the safe completion of any General Aviation flight. Proper pre-flight planning using all available information and tools is a very important part of icing avoidance. While enjoying the cooler temperatures this winter, make sure you are taking into account all aspects of winter weather while planning your flights. Fly safe this winter and remember that cold weather isn’t to be avoided completely; but it is to be respected.

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¹https://www.faa.gov/documentLibrary/media/Advisory_Circular/AC_91-74B.pdf

Sarah Rovner holds an ATP certificate with a CL-65 type rating and is currently a FAA Safety Team Lead Representative, Master Instructor, Captain and FTD instructor/evaluator with a Part 121 airline. Since changing careers after years as a senior network engineer for the oil & gas industry, Sarah has obtained her ATP, CFI, CFII, MEI and has flown over 3800 hours. As the owner of an international ferry pilot company, FullThrottle Aviation LLC, Sarah has flown over 115 different types of general aviation airplanes in 15 different countries, including oceanic crossings in small aircraft. She continues to stay involved in general aviation through mentoring and education; volunteering at many different events and presenting original seminars on aviation safety and human factors. Although much of her flying is now professional in nature, she still enjoys flying a Super Cub on her days off. As a regular attendee of EAA AirVenture and local fly-ins, she enjoys the company and camaraderie that general aviation brings.

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