DALLAS — During winter, you may see a truck spraying liquid on planes. What is that liquid, and what does it do?
For the Winter 2024-25 season, major airlines are significantly expanding their flight offerings and making strategic adjustments to meet the growing global demand for air travel. Of course, winter storms can significantly impact commercial flying, causing disruptions and safety concerns for airport operations and aircraft.
In this article, we want to explain the de-icing process, its purpose, the fluid types, and everything you need to know about this critical process in aviation.
De-icing 101
We refer to de-icing as removing the ice from the plane. Usually, this process has to be done before the plane takes off because ice or snow on the principal flight surfaces can affect the aerodynamics of the aircraft, resulting in accidents like SAS Flight 751, Continental Airlines Flight 1713, and Air Ontario Flight 1363.
All those accidents happened due to icing on the aircraft surfaces.
The surfaces of a plane are designed to be aerodynamic, allowing the wind to travel along the fuselage or wings without any effort. This means less drag and more speed and lift. However, when ice or snow covers these surfaces, the aircraft's performance is affected due to the drag it produces; in other words, the snow makes the flight surfaces less aerodynamic.
The International Civil Aviation Organization (ICAO) says snow on the wings can reduce lift by approximately 30% and increase drag by 40%. For example, snow can interrupt the wind flow over the wing, causing the aircraft to stall and end, like Arrow Air (JW) Flight 1825R.
The primary considerations for de-icing aircraft are:
- Visible contamination: De-icing is required when there is visible ice, snow, or frost on the aircraft's critical surfaces, particularly the wings.
- Active precipitation: If there is ongoing snow, sleet, or freezing rain, de-icing is often necessary.
- Wing temperature: Some airports use advanced systems like DTN Aircraft IceGuard, which combines weather data with wing temperature forecasts to determine the need for de-icing. Wing temperature can be up to 8 degrees colder than the surrounding air.
- Type of precipitation: Dry snow may not require de-icing if it's not sticking to the aircraft, while wet snow or freezing rain would necessitate treatment.
- Holdover time: This is the estimated time that de-icing fluid will prevent ice formation. If this time expires before takeoff, the aircraft may need to be de-iced again.
- Airline policies: Some airlines have stricter policies and may require de-icing even in borderline conditions.
The final decision to de-ice typically rests with the flight crew, who assess the conditions and consult with ground personnel.
There are different ways to prevent icing formation on flight surfaces: fluids or plane de-icing systems. For small planes, it can be done manually, but we will only discuss the de-icing fluids here.
Types of De-icing Fluids
Before explaining the types, we need to know that all de-icing fluids are typically composed of ethylene glycol (EG) or propylene glycol (PG), with thickening agents, wetting agents, corrosion inhibitors, UV-sensitive dyes, and colors for their identification. All of them have to be applied hot.
The principal purpose of using these chemicals is to lower the freezing point; the water has a 32ºF freezing point, and the de-icing fluids have a freezing point between -18 and -67 ºF.
Type I fluids have a low viscosity. 45% is the de-icing mixture, and the other 55% is water. To remove the ice and snow, the fluid must be sprayed hot at high pressure. The fluid's temperature must be between 130 and 180 °F. The Type I fluids are dyed orange for easy identification during application. The freezing point of this fluid is -19 ºF.
Type II fluids are pseudoplastic liquids, meaning they have a polymeric thickening agent preventing them from quickly flowing off the plane. Due to this, the Type II fluid is mixed in 75% water and 25% mixture, making it feel like jelly. This one can be used to de-icing the plane or prevent the formation of ice on it. It does not have any color for identification.
Type III fluids were created as a middle ground between Type I and Type II. They are usually yellow and used on slower planes with a rotation speed of less than 100 knots.
Type IV fluids were created as more potent Type II fluids. For this reason, Type IV is not diluted in water, resulting in a highly viscous substance. This fluid is usually applicable for ice prevention. The type IV fluids are tinted a light green.
After applying the de-icing fluid, another fluid layer must be sprayed to prevent the formation of new ice or snow during the waiting time or the takeoff; Type II or Type IV fluids can be used for this.
Where, When, and How Is De-icing Done?
All airports in cold countries have a specific zone reserved during the winter for this procedure. These zones are called de-icing pads and are located near the runways or in the taxi routes from the gate to the runway.
De-icing can also be done at the gate or stand. For this procedure, the aircraft must be closed, cleared of any handling equipment, and the engines off.
Let's take Frankfurt Airport (FRA) as an example. This airport has two de-icing pads, one located at the side of runway 18 and another in front of Terminal 1. FRA is also permitted to do a de-icing process at the gates.
De-icing must be done before the plane takes off. As said in the previous part, it can be done at the gate or the de-icing pads. Ice or snow on the aircraft surfaces can affect takeoff due to increased drag and lift reduction.
EASA and FAA check the maximum time to take off after the de-icing fluid application every year to prevent any accidents.
Special trucks are used to apply the de-icing fluid. These trucks have a hydraulic boom with an open bucket or a cabin attached to it where an operator is located. The trucks have a heated tank where the fluids are stored and are already heated for use.
These tanks are equipped with a pumping system powered by the truck engine. The operator can correctly spray all the fluid over the plane with the help of the adjustable nozzle located outside the cabin or the bucket.
The de-icing process takes at least 10 minutes, and usually, more than one plane is waiting for the de-icing pad to be available; this can cause delays, but remember, this was created to make aviation safer.
In such a situation, you must wait patiently and remember that those 10 minutes will bring you safely home.
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