A Comprehensive Guide to Aircraft De-icing

Why Do Aircraft Need De-icing?

Simply put, de-icing is necessary to prevent hazards to flight operations. Aircraft rely on their aerodynamic shape to generate lift, and if ice forms on the wings, it disrupts the airfoil shape, reducing flight safety. There have been accidents where foreign airlines experienced engine failures and crashes due to ice breaking off from wings and being ingested into engines. Additionally, large amounts of ice accumulating on the aircraft body add significant weight, which decreases aircraft performance and affects operational efficiency.

When Is De-icing Required?

I. Weather Conditions 

(1) De-icing must be considered when frost or snowfall occurs; 

(2) Any time when meteorological data indicates outside air temperature is below 5°C with visible moisture, such as: fog, rain, snow, sleet, or ice crystals with visibility below 1.5 kilometers, or when runways have water flow, slush, ice or snow. Or when outside air temperature is below 10°C and ambient temperature reaches or approaches the dew point, while frost, snow or ice has formed or is likely to form on the aircraft body and control surfaces; 

(3) Freezing rain and drizzle: Precipitation occurring when outside temperature is below 0°C, where supercooled raindrops form ice upon contact with the aircraft body; 

(4) Frozen precipitation, ice crystals: In cases of snow, rain mixed with snow, or hail, when outside air temperature is between -4°C and 1°C, with temperature and dew point usually within 1°C of each other, and wet snow accumulating on aircraft surfaces; 

(5) When outside temperature is around -8°C or below, with temperature and dew point differing by more than 5°C, and precipitation falling on aircraft surfaces;

II. Ground Conditions 

Ice accumulation can also result from ground operations or conditions. Even when weather conditions don't meet the temperature criteria for icing or snow, ice and snow can still adhere to aircraft surfaces in icy environments. For example: when aircraft operate on aprons, taxiways, or runways with moisture, slush, or snow; when ground winds, other aircraft operations, and ground support de-icing equipment continually blow snow around.

What Methods Are Used for De-icing?

Aircraft de-icing primarily uses the de-icing fluid method, which involves spraying the aircraft surface with heated de-icing fluid (containing ethylene glycol or propylene glycol) at around 82°C using specialized de-icing trucks to remove surface ice. When mixed with water, the de-icing fluid lowers the freezing point, similar to how water mixed with alcohol resists freezing. The mixture of de-icing fluid and water can lower the freezing point to about -50°C, preventing re-icing. However, this effect has a time limit, after which the anti-icing properties become ineffective and re-application is necessary.

Other de-icing methods include:

• Compressed air de-icing, which uses high-pressure air flow to blow ice off the aircraft surface. This method is suitable for dry snow that hasn't melted but is less effective for already-formed ice.

• Infrared heating de-icing is a new method. It uses high-power infrared generators arranged in clusters to emit infrared radiation onto the aircraft, melting ice and snow by heating the aircraft body. This process leaves no pollutant residue on the aircraft and is environmentally friendly, but requires significant equipment investment and is best suited for airports with long winter snow periods and high flight volumes.

• Hot water de-icing was commonly used in the past but has significant limitations. When ambient temperatures are well below 0°C, hot water quickly cools on the cold aircraft surface and may refreeze, affecting moving parts and blocking flight instruments. Therefore, it's only effective if takeoff occurs within 3 minutes of application.

What is Taxi De-icing?

Airports generally use three de-icing service modes: gate de-icing, centralized pad de-icing, and taxi de-icing.

Gate de-icing involves de-icing the aircraft at its parking position, with de-icing trucks coming to the aircraft. This method is suitable for airports with low de-icing frequency, as preparation and movement of de-icing trucks require considerable time.

The second method, centralized pad de-icing, involves setting up a de-icing pad near the runway takeoff position. Aircraft receive de-icing treatment at this pad before takeoff, eliminating the need for de-icing truck movement. This method is more efficient for high-traffic airports.

In both above methods, engines are shut down during the de-icing process.

Taxi de-icing is currently the most efficient de-icing method. It involves establishing a de-icing zone on the taxiway where aircraft queue for takeoff. Multiple de-icing trucks and other equipment are concentrated in this area. Aircraft receive de-icing treatment while queuing on the taxiway, with multiple trucks working simultaneously, completing the process in approximately 7-8 minutes per aircraft. After de-icing, aircraft can proceed directly to the runway for takeoff. Throughout the process, aircraft engines remain at idle power, hence the name "taxi de-icing." One key challenge of this method is preventing de-icing fluid from affecting engine operation.

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