Saturday, January 06, 2007


Depending on where you are flying, deicing can be a routine event. The FAA requires that planes not attempt to takeoff with anything adhering to the upper sides of the wings and tail (there is a minor exception for the underside of the wing) because it can significantly effect the ability of the wing to generate lift. The way this is accomplished is through the application of deicing fluid prior to departure.

Many larger airports in climates where deicing is a major event have setups where the plane taxis to a pad near the departure runway and is deiced with its engines running. That way, there is minimal time between the deicing and the takeoff. These pads are also usually designed to recover excess deicing fluid both for reuse (after reprocessing) and to prevent it from entering the surrounding environment through runoff.

Anything on the wing is initially taken off through the application of what is known as "Type I" fluid. This is a heated glycol/water mixture that is very effective at removing any contaminants from the wing. Unfortunately, though, it doesn't do much when it comes to further accumulation.

Enter "Type II" and "Type IV" fluids. Now these are very cool! Their viscosity is directly proportional to the speed of the air passing over them! This means that at slow wind speeds, this fluid is "sludgy" and sits on the wing. Any snow or ice accumulates on top of the fluid. At about 60 knots of speed during the takeoff roll, this "sludge" becomes "liquid" and shears off the wing, taking any accumulated ice and snow with it. This allows for much safer operations when there is significant snowfall.

So now you know a little more about what they are doing during the next blizzard in Denver!

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