What Is the De-Icing Solution Sprayed on Airplanes?

When boarding a flight in many parts of the U.S. during winter, it’s likely that a specialized team will apply de-icing fluid to the aircraft prior to takeoff, ensuring the removal of ice and snow (or preventing further accumulation).

Even minor deposits of snow, frost, or ice—referred to as ice contaminants in aviation—can pose significant risks for aircraft. These accumulations increase weight, complicating pilots' performance calculations, such as climb rate and runway clearance. Additionally, they disrupt airflow, diminishing lift and potentially obstructing vents or sensors.

In essence, de-icing ensures that passengers can travel safely during winter weather conditions. Here’s a comprehensive overview of how and why airlines perform de-icing before flights.

When do aircraft undergo de-icing?

De-icing primarily occurs between October and April each year; however, as Celley Buchanan, vice president of airport operations and customer service at Alaska Airlines, notes, “De-icing can be necessary at any time of the year, depending on the outside temperature.”

Both Buchanan and Catherine Morrow, a senior communications coordinator at Delta Air Lines, mentioned that inspections are conducted on all planes when temperatures fall below 50 degrees, even if only temporarily.

Morrow explained, “For instance, if the air is humid and temperatures drop overnight, there could be ice buildup the following morning, even if it warms up a little.”

After every flight in colder months, the flight deck crew checks the aircraft for any ice contaminants. If they find any, they’ll alert their de-icing team, which may include either staff or contract personnel. According to Perry Cooper, a media relations manager at Seattle–Tacoma International Airport, it is the airline's duty, not the airport’s, to ensure all planes in their network are ready for takeoff.

When a plane requires de-icing, this usually occurs after all passengers and crew have boarded, and the aircraft is ready for takeoff. This timing is crucial, as the de-icing solutions don’t offer indefinite protection, making prompt action necessary.

Buchanan stated, “In our industry, we refer to holdover time, which is determined by the flight deck crew using various factors such as the outside temperature and current weather conditions to assess how long after spraying an aircraft can safely take off.” Typically, she noted, this window is about 22 minutes from when the plane is treated to when it should depart.

The process of airplane de-icing

At some airports, de-icing takes place right at the gate. However, at others, particularly in regions with frequent snowfall like Boston and New York, planes will move away from the jet bridge to designated de-icing stations near the runway, where they are treated and can take off shortly thereafter.

The initial phase of de-icing involves spraying the aircraft with a heated solution of glycol (derived from ethylene, the chemical used in polyester and antifreeze) mixed with water. This de-icing fluid is applied under high pressure to effectively melt away contaminants. It's usually colored orange to help crew members track where they've sprayed. Although pilots turn off the aircraft’s ventilation system during this process, the scent of the fluid, reminiscent of maple syrup, may still reach the cabin; however, the U.S. Food and Drug Administration deems it safe.

According to Buchanan, this process is generally sufficient to ensure a safe departure, meaning no ice contaminants should be present on the wings or tail. However, under harsher conditions like sleet, freezing rain, or snowfall, airlines may choose to apply an anti-icing fluid. This additional measure provides extra time for takeoff before new ice can form. This second solution, also glycol-based but thicker due to less water, is green, unheated, and will slide off the wings once the plane begins to climb.

Despite the colder temperatures at cruising altitude—estimated by the National Institutes of Health to range from −92°F to −20°F—ice is not typically a concern during flight. This is because aircraft are equipped with systems that circulate hot engine air through pipes in the wings and tail, effectively preventing ice buildup while in the air.

Certain weather conditions on the ground, such as rapidly falling freezing rain, can complicate de-icing efforts and hinder a plane's ability to take off before accumulating more ice. In such instances, Buchanan emphasized that safety is the top priority. If it becomes clear that a safe departure isn’t possible within the plane's holdover time, the airline may opt to delay or cancel the flight.

When de-icing is executed successfully, the entire process typically takes between 5 and 10 minutes (not accounting for any waiting time behind other planes needing de-icing), depending on the aircraft's size. Buchanan noted that the procedure is generally consistent across different airlines.

Buchanan remarked, “One of the wonderful aspects of our industry is that safety isn’t seen as a competitive edge. Airlines are genuinely proactive in collaborating with one another. In fact, we gather annually to specifically discuss de-icing, sharing insights on trends and new technologies.”

The future of de-icing

While significant innovations in de-icing have been limited since its introduction in the 1950s, that may be on the verge of change in the coming years. The costs of de-icing fluids are substantial—some estimates suggest that treating a small jet can average around $1,300, while larger aircraft can exceed $13,000. Furthermore, these fluids have been criticized for their considerable carbon footprint. However, more airports have recently made efforts to recycle the fluids, prompting a growing interest among companies to find alternative solutions.

In December 2023, Air Canada became the first airline to adopt De-Ice technology, developed by a Boston-based startup, for an Airbus A320.

As explained by De-Ice, the system features tape-like strips affixed to the plane's exterior, linked to proprietary electronics inside. When the pilot activates the De-Ice system, it generates a high-frequency current that causes electrons on the aircraft's surface to vibrate, producing heat. This effectively melts away snow and ice during the boarding process, ensuring the aircraft is clear of ice by the time it is ready to depart from the gate.

De-Ice estimates that this system could reduce de-icing delays by an average of 30 to 45 minutes per flight. In a press release, Murray Strom, senior vice president of flight operations and maintenance at Air Canada, noted that the De-Ice system could greatly lower emissions, as less de-icing chemicals would need to be produced, transported, or heated, and it would minimize idling time during the de-icing process.

The De-Ice systems are currently undergoing regulatory testing. If approved, they could support airlines globally in achieving their net-zero emissions targets by 2050.