Aircraft De-Icing: Why They Spray Aircraft

Aircraft De-icing - Aerosavvy

Happy De-Ice Season! (It’s winter somewhere)

When flying during the cold weather months, passengers often see aircraft being de-iced. Ever wonder why the airline chose to delay your flight to wash their airplane with slimy green goop?

Aircraft de-icing is really important. Here’s how and why airlines do it…

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Aircraft De-icing - Aerosavvy
Photo Source: Helen Cook

Aviation rules require that an aircraft’s wings and tail be free of snow, ice and frost before takeoff. I’ll explain with a quick beginner aerodynamics lesson.

Really easy aerodynamics… I promise!

The flow of air above and below an aircraft wing produces lift (high school students blame it on Bernoulli and Newton). Anything on the wing’s surface that changes the shape or texture of the wing will disrupt the airflow and the wing won’t provide the amount of lift that the aircraft designers promised.

Now, back to the snow, ice, and frost. Frozen precipitation is dangerous because it changes the shape and texture of the wing. The top of the wing needs to be smooth for optimum performance. Frost changes the wing texture to something like sandpaper. Snow is even worse, it changes the aerodynamic shape of the wing.

Aircraft De-icing - Airflow over the wing.
A little frost can really mess up the airflow over the top of a wing!    Source:

On a “clean” wing, the air flows smoothly.  On a wing “contaminated” with frost or snow, the air has trouble sticking to the wing surface. The air separates and becomes turbulent. When this happens, we lose lift; and that could be the start of a very bad day.  If you see airliners being de-iced on a clear, chilly morning, it’s probably because they have frost on the wings.

Aircraft De-icing - SWA Deicing
De-ice Pad. Source:

Aircraft de-icing procedures vary from airport to airport. Smaller airports will de-ice the aircraft at the gate (like the picture at the top) or just after the aircraft pushes back onto the taxiway.  Big airports often have a “de-icing pad” where all aircraft are de-iced. De-ice pads are nice because the airport authority can collect the used fluid for proper disposal or recycling. The fluids used are typically complex concoctions based on propylene or ethylene glycol (similar to automotive antifreeze).

Aircraft De-icing is a one or two-step process depending on the weather.

  • Step 1: “De-ice” removes ice, frost, and snow.
  • Step 2: “Anti-ice” protects the wings from new ice, frost, and snow.

Step #1:   De-Icing – Remove The Bad Stuff!

Aircraft De-icing - Aerosavvy

Spraying the aircraft with very hot, high pressure fluid removes snow, ice, or frost adhering to the wings. Fluids are tinted to make them easier for pilots and ground crews to identify.

The stuff typically used to remove existing snow is called “Type-1” and is tinted orange. Type-1 fluid is easy to spot because it’s hot and produces a lot of steam when sprayed.

If the snow has stopped falling, the process is complete after de-icing. The flight crew can taxi to the runway and safely takeoff.  If it’s still snowing, there is more to do…

Step #2:    Anti-Icing – Protection From NEW Bad Stuff!

Aircraft De-Icing - Aerosavvy
Type-4 de-ice. Source:

The weather is crummy and the snow fall continues. While Type-1 fluid does a great job of removing snow and ice, it doesn’t protect the wings from new snow. Even during a short taxi, dangerous accumulations of snow can build up on the aircraft.

To protect the wings from further contamination, the de-ice crews will apply a coat of “Type-4” fluid (may vary internationally). Type-4 is super thick, super slimy, and green (think lime jello). Instead of being sprayed at high pressure, it dribbles out of the hose: glug, glug, glug.

Aircraft De-icing - Green
Coated with Type-4.

Type-4 is interesting stuff. It grabs any new snow and ice and holds it until the takeoff roll. It’s designed to maintain its jello-like consistency until the aircraft reaches about 110 mph. At that point the fluid (and accumulated snow) begins to shear off the wing. By the time the aircraft nose lifts, all the bad stuff is gone.

If you get the “green stuff” on a flight, watch the wing during the takeoff roll. You’ll see it do its thing!

Who does the spraying?

Airlines have a few options for de-icing. It depends on the airport and facilities available. Large airlines sometimes have their own equipment. Many cold-weather airports, like Winnipeg, have a central de-icing facility operated by the airport authority to handle all de-icing. Pilots taxi the aircraft to the facility, get sprayed, then continue to the runway.

Most airports have at least one Fixed Base Operator (gas station for aircraft) that provides de-icing services for small and large aircraft.

De-icing services are expensive. Find out how much it costs in Jennifer’s article about fees airlines have to pay.

What happens to the excess fluid?

Aircraft de-icing crews do a great job of spraying the airplanes, but inevitably, some of the spray misses the aircraft and ends up on the ground. Airports collect this yucky runoff and either recycle, or dispose of it in an environmentally safe manner.

Now you’re totally AeroSavvy about aircraft de-icing! If you need a little visual stimulation to bring it all together, check out the two short videos below.

Video time!

Here’s a video of a WestJet aircraft having frost removed in Winnipeg. It surprises many passengers that aircraft are de-iced for such small amounts of frost. The reason is that we really don’t know how much frost it takes to negatively impact performance (and we’d rather not find out!).

My sincerest apologies for the cheesy flight attendant announcements.

This video shows both steps of the de-ice/anti-ice process. During the first half of the video you can see the high pressure, hot & steamy Type-1 being applied. Then they switch to the low pressure, green Type-4.

Further Reading:

Aircraft Ice Detection


    • Not that I am aware of. Typically, the flight crew informs the passengers that it’s a procedure to remove ice and snow before takeoff. Thanks for the comment!

  1. Another good article, but ‘smaller airports’, like ORD? On one of flights back to Germany the AA 767 was anti-iced at the gate. 🙂

  2. I sat through this from Venice airport Sunday evening (18th December 2016) in thick freezing fog and in all honesty I was nervous watching it and trying to come to terms with the fact we were taking off, after the pilot decided to test the engines 3 times before we actually took off. We sat on the plane for 2 hours while it kept icing over 🙁 However I am grateful that they did this to ensure our safe journey home.

    • Hi Wendy,

      I know it can be frustrating, but it sounds like your airline and crew followed procedures to assure your safety. A properly de-iced and anti-iced aircraft can takeoff with absolutely no problem. It’s interesting that you mention the pilot “tested” the engines. What I suspect was happening is the crew was performing a “Static Run-up” with the engines. During a frozen precipitation event on the ground, engine manufacturers often require us to run up the engines to a fairly high power setting to clear any ice buildup from the big fan blades in the front of the engine. Our operating manual tells us how often the engines need the run-up during icing conditions. Some engines need the run up as often as every few minutes.

      Thanks for reading!

  3. Quite interesting. Another good article. Could you please also explain how they clean runway before take off and landing at the time of heavy snow?

  4. Waiting for my plane to take off. They are using this technique. Thanks for the article; I saw these trucks outside and googled about it. Thanks for keeping us safe.
    Traveling from Minneapolis to Houston.

    • Hi Beth,

      Critical areas of aircraft wings & tail are often heated either electrically or with hot bleed air from the engines. This type of heating system is for in-flight use when the aircraft encounters icing conditions in clouds.

      The problem with ice and snow on the ground is that it covers the entire airplane. When an aircraft needs to be de-iced, all wing and tail surfaces must be clear of ice and snow. If the fuselage has more than a light coating, it must be removed as well. It would be far too costly (and add too much weight) to have a heating system that heats the entire aircraft exterior. It would also take too long. A de-ice truck can blast a 1/4″ of ice off of an aircraft fairly rapidly.

      Thanks for reading!

  5. Currently sitting on the runway while this is happening. Had to google. Never witnessed this before. Baltimore to Dallas.

    • First a great explanation. Waiting for the process to complete Den to SJC. The flight had just arrived, and no fresh snow, still requires de-icing.

  6. They just did it to my flight. Cold but clear weather with no snow or ice or any precip accumulated or present. It seems to me that they just added to the problem. They applied water to a dry surface, sat still for 15 minutes, then took off. Enough time to refreeze. Am I missing something /wrong?

    • Hi Adam, the crew likely spotted some frost on the wings or tail that had to be removed (frost loves cold/clear weather). They weren’t using water. It was an alcohol or glycol based product.

  7. Very interesting stuff . Thanks for the information. I witnessed 4 trucks approach the A380 going from Germany to dubai and was totally puzzled on what was going on. It took 15 minutes to clear all the frost and we are about to departure. Adios amigo!

  8. I saw this robot outside the plane washing the wings ! Here for learning. Thank you for easing my anxiety 😬

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