Airplane De-Icing: Why They Spray & When You Should Worry

Airplane de-icing is a necessary part of aircraft maintenance that you might have seen happen before takeoff. But why do they spray and when should you worry?

Airplane de-icing is done to remove the accumulation of ice and frost from an aircraft, especially its wings. This buildup can alter the shape of the wings and affect flight. You shouldn’t need to worry about the de-icing process, but if you notice a spot they missed, feel free to speak up.

Aircraft are some of the most advanced pieces of equipment that have ever been built. Giant hunks of metal that fly effortlessly through the sky. It still gives me chills! They also require a lot of maintenance to maintain that effortless flight. One thing that’s necessary is to de-ice airplanes before takeoff to ensure a safe flight. In this article, you’ll learn everything you need to know about airplane de-icing so that you don’t worry when you see them spraying down your plane!

Here at SkyTough, we pride ourselves on providing our readers with the most accurate and up-to-date information you’ll find anywhere on the web. That includes our readers who are interested in learning all about airplane de-icing! For this article, we’ve taken our own aviation knowledge and brought in the opinions and input of other experts in the field along with hours of research to give you the best information we possibly can. Enjoy!

‍What Is Airplane De-Icing?

Have you ever been sitting at your gate in the terminal and looked outside and seen the workers spraying your plane with something? Or maybe you’ve even been on the plane itself and you noticed that they’ve started spraying a strange liquid all over the plane. Depending on what they’re doing, it looks like it’s orange and hot, or green and goopy. What are they doing?

Long story short, the answer is that they’re de-icing the airplane. As the name implies, airplane de-icing is a process that’s done to remove ice and the buildup of snow and frost from the surface of the airplane. It’s a completely normal process in the colder months, and shouldn’t be anything to concern you, so don’t worry! We’ll get more into the nuances of the process shortly. But you might have heard of a different term than just airplane de-icing.

What Is Airplane Anti-Icing?

You might have instead (or in addition to) heard of airplane anti-icing instead of, or alongside, airplane de-icing. You might be thinking that the terms are interchangeable and that the processes do largely the same thing. But the truth is, minus the fact that both processes have to do with ice and both look similar from your vantage point in the terminal or on the airplane, they’re actually completely different processes!

While the de-icing process is designed to remove the ice and other frozen build ups from the airplane’s surface, the anti-icing process prevents new stuff from accumulating. If you’ve ever actually been on an airplane that’s been treated with anti-icing spray, you’ll notice the entire thing is covered in green slime. That’s what you want to see; that’s the agent doing what it’s meant to do.

Now that you have a general idea of what these two processes are, let’s dive in a little deeper and see why it’s so important.

Why Is Airplane De-Icing Necessary?

Airplane de-icing works by spraying a pressurized de-icing solution over the surfaces of the airplane where snow and ice have built up. It’s incredibly important because aircraft are designed to fly with a “clean surface”. This does not mean the airplane needs to be washed, it means the surface needs to be free of all foreign debris and buildup to fly as designed.

During the cold winter months — especially at airports farther north — ice, snow, frost, and slush build up all over the surface of the aircraft. This is less than ideal anywhere on the aircraft, but especially on the wings. The shape of an aircraft’s wings is by far the most important part for flying, and any change in their shape will lead to different airflow characteristics.

And if the air is flowing over and around the wings in a different way than what they were designed to do, the expected areas of high and low pressure below and above the wings won’t work as expected. Without getting into the details of how airplane wings work, the way the air flows around them and creates pressure differences are basically what generates flight.

So as you can see, it’s of vital importance to remove this ice, frost, and snow from the wings of the airplane before takeoff. Otherwise, they might not generate the lift needed to fly.

How Does Airplane De-Icing Work?

As we’ve mentioned, de-icing is the first of two processes involved in the overall ice removal and prevention process on aircraft. Let’s take a look at how it works so you really know what’s happening when you see them spraying the airplane.

When they’re de-icing an airplane, the crews are using a special orange-colored fluid that’s known as Type I (Type 1). Usually, the fluid they use for de-icing is propylene glycol that’s been diluted with water and heated to around 150°F. The solution itself, combined with the heat and pressurized hose, breaks down snow, ice, and frost, in seconds and sends the debris flying.

The Type I fluid is automatically diluted with varying amounts of water depending on the conditions outside. Sensors on the trucks determine the weather conditions and then add in as much water as needed to ensure optimal de-icing. By spraying the solution at an angle (typically 45 degrees to the surface), the crews avoid any potential damage to the plane during the de-icing process.

The crews will typically spray the entire plane, at least the metal parts — fuselage, wings, nose, stabilizers, etc. — if necessary. They’ll avoid windows as much as possible, but pretty much any surface that has a build up of snow and ice is fair game. Well-trained crews will spray from the top of the plane down, allowing the fluid to run down the plane and do more on its own, saving time and money in the long run.

If it’s super cold or there’s a snowstorm going on, then the crew will switch over to the other solution on hand — the anti-icing solution.

How Does Airplane Anti-Icing Work?

In the most extreme winter conditions, de-icing the airplane isn’t going to be enough. If it’s cold enough or it’s snowing outside, then the snow and ice are just going to build right back up after the de-icing process while the plane is being boarded or taxiing. This is when the crew will begin the anti-icing procedure to prevent more build up from happening.

The anti-icing fluid is completely different from what the crews use for de-icing. This thick green slime-looking fluid is typically propylene glycol that is not heated or diluted with water. This solution, known as Type IV (Type 4) fluid, is far more viscous than the de-icing fluid. So instead of running off the plane after blasting snow and ice away, it actually coats the surface of the plane in itself.

This solution is designed to absorb water, so as snow falls or frost tries to accumulate, the Type IV fluid will automatically absorb it all and prevent it from freezing and building up on the aircraft. What really makes it special is that the solution is designed to slide off the airplane during takeoff, and by the time the plane is 1,000 feet in the air, it will be completely off the plane’s surface.

It’s pretty magical stuff that ensures the plane can safely make it into the air!

When Do They Spray The De-Icing Fluid On Airplanes?

As you now know, the importance of de-icing and anti-icing is most notable at takeoff. So the crews will usually spray the planes right before takeoff. It is typically done at the gates if the airport is operating efficiently, but they don’t like to block gates longer than they need to just to de-ice an aircraft.

So sometimes they’re sprayed after they pull back from the gates or on special de-icing pads at other locations around the airport. Another issue with spraying the planes at the gate is that they can't usually get to the entire plane. Due to the terminal and the jet bridge being in the way, they won’t be able to get to the front of the plane and de-ice the nose.

If there is a build up of ice in a location that they can’t access while the plane is at the gate, they’ll have to wait until the plane pulls back. Ideally, they’ll apply the anti-icing solution just before takeoff for maximum effectiveness.

Do Airplanes Always Have To Be Sprayed For De-Icing?

Chances are, the vast majority of flights you’ve been on, you’ve never seen the crews spraying the plane with anything. But considering how high airplanes fly and how cold it is up there — think around -65°F — you might be thinking that snow and ice will always build up on the airplane during flight. And if that’s the case, then won’t the plane always need to be de-iced before taking off?

Not usually. Even though the temperatures at those altitudes are incredibly cold, there typically is not a buildup of snow and ice due to the speed that the plane is moving; it’s tough for water to accumulate on the plane when it’s moving 500+ mph. So there typically won’t actually be a buildup after most flights. And if there is, it’ll just melt when the plane’s altitude comes back down if it’s not too cold out!

In most cases, planes will only have a build up of ice or snow during the winter months. And even then only at the airports more in the north where it’s actually cold enough for snow and ice to form. If there is no build up of ice or snow before takeoff, then there’s no reason to take the time and spend the money to use these solutions!

When Should Airplane De-Icing Concern You?

In general, the airplane de-icing and anti-icing processes are nothing to be concerned about. If you’re looking through the windows in the terminal or you’re sitting on the plane and notice they start spraying strange liquids everywhere, it’s understandable to be a little concerned if you’re not sure what’s going on.

But now that you’ve read all about the two processes, you’re a bit of an expert yourself and know that it’s actually a good thing that they’re spraying the aircraft down That said, if you notice snow and ice buildup on the aircraft after they’ve de-iced it — or if they haven’t done anything at all — then feel free to speak up and mentioned it to someone on the crew.

The only time the actual spraying process should really ever concern you is if you know that the crews are using ethylene glycol solution and you start to smell something similar to maple syrup. Ethylene glycol is toxic, and the crews should have closed off the plane’s outside air intake while using it. So if you can smell anything like that while they’re spraying, immediately let someone know and they’ll stop spraying and fix the vents!

Other than that, de-icing and anti-icing are both helpful and necessary — so don’t let it worry you too much!