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Deicing planes: How does it work and why do airlines do it?

If you have flown in the winter, you may have encountered the phenomena of your plane being sprayed down before taking off. What you experienced was your plane being deiced. This is a crucial step that is sometimes needed during the cold winter months to allow planes to take off safely. 

Why it’s done

You might be wondering why airlines go through the trouble of deicing planes, especially if there is only a light layer of frost or ice. The answer has to do with physics, and the short version is that ice can affect the aerodynamics of the airplane and therefore takeoff. Airplane wings are designed in a specific shape to create lift and take off safely. A layer of ice or snow will disrupt the airflow around the wing and therefore affect the plane’s lift. 

Safety is the number one priority when flying, and deicing planes before takeoff is the safest option in icy or cold weather. The FAA has guidelines in place to ensure that the correct deicing fluids are applied properly and in the right circumstances. 

How it’s done

Deicing involves chemistry and engineering knowledge to know what solutions to use and where to apply them. There are extensive guidelines in place from the FAA that regulate deicing procedures for commercial aircraft. The typical way planes are deiced involves one or more solutions being sprayed onto key parts of the plane at high temperatures. The two different types are deicing and anti-icing solutions. 

Deicing solutions are liquid compounds made up of glycol, water and other additives. Chemical deicers like the ones used on the road, usually containing urea or chloride salts, cannot be used on aircraft because of their corrosive properties. Glycols work by lowering the freezing temperature of water. 

The deicers remove existing ice but don’t prevent ice from reforming. So, if there is active frozen precipitation, a second step may need to be taken. Anti-icing compounds are the same as the deicing compounds, but aren’t diluted with water, so they are thicker. This thicker solution sticks to the plane during takeoff.  Dye is usually added to anti-icing solutions so that it is easy to see if it is fading and therefore losing effectiveness. 

Deicing solutions are expensive and should be contained to prevent runoff into the water system.  While alternatives are being explored, it will be many years before alternate methods of deicing are used on commercial aircraft because of the rigorous testing required. It should be noted that all U.S. airports follow stringent practices to monitor and contain runoff to ensure that the deicing chemicals are managed carefully. Some airports have started using deicing fluid recovery systems that allow the glycols in the solutions to be recycled. 

And of particular note:  one of the most commonly misunderstood parts of the deicing process involves the timing of the actual deicing.  Passengers can experience frustration when they have boarded their flight, only to find out that the plane must be deiced prior to takeoff, which can create delays at times.  Why don’t the airlines deice prior to boarding the aircraft?  Deicing solutions have a limited time during which they are effective.  Therefore, applications must take place quickly and precisely just prior to takeoff. The allowable window of time in-between application and takeoff is called the holdover time, and if that time is surpassed the plane will need to be treated again.

What about when you’re in the air?

 Once in the air, planes have systems built-in for keeping ice off the surface of the aircraft. These are necessary year-round, because even in the summer it is below freezing at higher altitudes. Deicing systems on commercial aircraft usually include systems of pipes that carry hot air from the engines to the wings and tail to keep them warm and prevent ice from forming. These systems are effective for preventing ice accumulation in the air, but the plane still needs to be deiced before takeoff. 

Who does it?

It may come as a surprise that it is the airlines and not the airport who are responsible for deicing operations. Airlines either have their own deicing teams or may contract with a specialized company to handle the task. It is up to the airlines and pilots to make the call to deice depending on the weather and temperatures, adhering to FAA guidelines. 

So, the next time you are traveling in the winter and see the plane being sprayed with hot liquid, you’ll know exactly what is happening. Sit back and wait a bit – takeoff will happen as soon as the plane is ready.