Posted by: Korry | January 24, 2012

Techie Tuesday: Aircraft De-Icing

It’s winter and that means snow and ice, two things that do not go well with any airplane. If you’re a frequent traveler in the wintertime, you may have been on a plane that needed to be “de-iced.” Today for Techie Tuesday, I’m going to explain why planes need de-iced in the first place while also providing some insight into what the process entails.

The gist of the entire concept is this: to create lift, an airplane’s wings and tail must allow air to flow smoothly over and around them. Next week, I’ll explain how a wing actually works to create lift, but for today, lets just keep it simple. When air can flow smoothly over and around the wing, it makes lift. When the air can’t flow smoothly, the wing doesn’t create lift. No lift = no flying.

It’s not too hard to imagine that during a winter storm, snow or ice adhering to the wing and tail could disrupt the smooth airflow that’s needed. It doesn’t even take a lot of snow or ice to disrupt the needed airflow. In fact, even small amounts of frost can create major problems.

The issue on the ground then becomes twofold. First, we need to remove all snow and ice from the wings and tail (de-icing). And second, we need to prevent snow and ice from re-accumulating on the wings and tail before takeoff (anti-icing). (Once we’re airborne, the front of the plane’s wings–known as the leading edge–are heated or designed to break off any ice accumulation. It’s only the leading edge that is important since at high speeds only the front of the wing really ever impacts the snow, rain, etc.).

To do this, airlines spray various types of fluid onto the wings, tail and aircraft body. Most times, two fluid types are used. The first one is a very hot fluid designed to push and/or melt any snow or ice from the airplane’s surfaces. It includes some chemicals and alcohol which prevent the fluid from re-freezing. This fluid is usually red in color.

Here’s a video I found on YouTube that shows a simulation of aircraft de-icing:

Once the airplane is “clean” of snow and ice and if it is currently snowing/sleeting/raining/etc, it requires a second spray of anti-icing fluid to prevent accumulation of snow and ice before takeoff. This second fluid, however, is usually green and is much thicker, allowing it to “stick” to the wings. This fluid’s chemical makeup changes the temperature at which falling precipitation can freeze. This anti-icing fluid is also designed to “shed” as airspeed increases during takeoff so that the plane is not encumbered with the extra weight of the fluid in flight.

Of course, each fluid’s effectiveness decays over time, so the de-ice/anti-ice fluid manufacturer works with the FAA to determine how long the fluid can truly do its job well. If the plane hasn’t taken off by the end of this “holdover time”, the plane must get sprayed again, thus resetting the clock.

Airports and airlines go out of their way to recover the fluid that doesn’t stick to the plane during the application process for two main reasons: environmental and cost. With chemicals and alcohol a part of the fluids, the government specifies appropriate ways to discard de-ice and anti-ice fluids. Additionally, these fluids are expensive as hell! Depending on the product, these fluids can cost $8-12 PER GALLON! Considering that a large commercial plane could use anywhere from 500-1000 gallons during a single trip to the de-ice pad, it’s easy to understand why airlines have developed systems to recover, filter and re-use the fluids.

So that’s de-icing and anti-icing in general. Hopefully this helps you to feel more comfortable about why airplanes need this special treatment during wintry weather.

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  1. […] last week’s Techie Tuesday about De-icing, I wrote that the main reason airplanes get de-iced is so that the wings stay clean in winter […]

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