The deicer sprayed on planes before takeoff is a glycol-based fluid, essentially a specialized antifreeze mixed with water and heated to high temperatures. It melts ice and snow on contact and, depending on the type, leaves a protective layer that prevents new ice from forming while the plane taxis to the runway. There are four types of deicing fluid, each designed for different aircraft and weather conditions.
What Deicing Fluid Is Made Of
Aircraft deicing fluids are built on either propylene glycol or ethylene glycol, the same family of chemicals used in car antifreeze. The glycol is mixed with water at varying concentrations to lower the freezing point well below 0°C. A 50/50 glycol-to-water mix can stay liquid down to roughly -12°C to -14°C, which is enough for most winter operations. Thickening agents, surfactants, and corrosion inhibitors round out the formula.
Propylene glycol is more common in North America because it’s less toxic than ethylene glycol, which matters when thousands of gallons wash off aircraft and onto airport surfaces during a busy winter day.
The Four Types of Deicing Fluid
Each type is color-coded so ground crews can identify it at a glance, and they differ mainly in thickness and how long they protect the aircraft.
- Type I is the thinnest fluid. It’s heated to 60–80°C and sprayed at high pressure to blast away existing ice and snow. Because it’s so thin, it blows off the aircraft at relatively low speeds (around 60 knots), so it doesn’t offer long-lasting protection. Type I works on any aircraft and is the most widely used fluid in North America.
- Type II contains thickening agents that let it cling to surfaces longer, providing extended protection against new ice formation. It requires a rotation speed of at least 100 knots to shear off during takeoff, so it’s limited to larger jets.
- Type III sits between Type I and Type II in viscosity. It was designed specifically for smaller commuter aircraft that take off at lower speeds (60 knots or higher) but still need longer protection than Type I can offer.
- Type IV is the thickest fluid and provides the longest protection window. It meets the same specifications as Type II but can keep ice from forming for significantly more time, making it the go-to choice when there’s a long wait between deicing and takeoff.
How the Deicing Process Works
If you’ve watched from a window seat, you’ve seen the process: a truck with a cherry-picker arm pulls up and sprays the plane with steaming fluid, often bright orange or green. What you’re watching is either a one-step or two-step procedure.
In a two-step process, the crew first sprays heated Type I fluid to melt and wash away all existing ice and snow. Then they apply a second coat of thicker fluid (Type II, III, or IV) to prevent new ice from building up before takeoff. The protection clock starts ticking at the beginning of that second spray. This method is standard in North America, and it’s required for U.S. and Canadian airlines operating in snow when using Type I fluid.
The one-step method combines deicing and anti-icing into a single application, using heated fluid to remove contamination while simultaneously leaving a protective layer. This approach is more common in Europe, typically using Type II or IV fluids. It’s faster, but the protection window is shorter since the clock starts as soon as spraying begins.
Holdover Time: The Protection Window
Every deicing fluid has a “holdover time,” or HOT, which is how long the fluid will keep preventing ice from forming. This varies based on the fluid type, how heavily it’s diluted, the temperature, and the type of precipitation falling. If conditions are bad and the holdover time runs out before the plane reaches the runway, the crew has to go back for another round of deicing.
Federal regulations require that an aircraft be completely free of frozen contaminants on wings, control surfaces, engine inlets, and all other critical surfaces before takeoff. Only trained and qualified personnel are allowed to perform deicing, and airlines must maintain approved programs with specific holdover time tables and inspection procedures.
What It Costs
Deicing fluid typically runs $20 to $75 per gallon, and a single application on a large commercial jet can use hundreds of gallons. A 55-gallon drum of concentrated Type I fluid costs airports around $2,000 to $3,000. During severe winter storms, prices spike. One documented case in Washington, DC saw charges reach $75 per gallon during peak conditions. Airlines absorb these costs, which is one reason winter operations are significantly more expensive.
How Planes Handle Ice in Flight
Ground deicing fluids blow off during takeoff, so they offer zero protection once the plane is airborne. Aircraft rely on entirely different systems to deal with ice at altitude, where temperatures can drop far below freezing and supercooled water droplets freeze on contact with the airframe.
Large jets and turboprops typically use bleed air systems that channel hot air from the engines to the leading edges of the wings, tail, and other ice-prone surfaces. This keeps those areas above freezing so ice never gets a chance to form. Many smaller propeller aircraft use inflatable rubber boots along the wing’s leading edge instead. These boots rapidly inflate and deflate, cracking accumulated ice so the airflow peels it away.
Some aircraft use chemical anti-icing systems, sometimes called weeping wings, that push a glycol-based fluid through tiny holes in the wing’s surface. The fluid spreads across the leading edge, preventing ice from bonding. These systems are common on smaller general aviation aircraft and protect vulnerable spots like fuel vents and sensor probes.
Environmental Concerns
Airports spray enormous volumes of glycol during winter, and that fluid has to go somewhere. When it washes into nearby waterways, microorganisms break it down and consume large amounts of dissolved oxygen in the process. This oxygen depletion can suffocate aquatic life, making runoff from deicing operations a significant environmental concern. Most major airports now collect spent deicing fluid through drainage systems built into their ramp areas, either recycling the glycol or treating it before it reaches local water systems.