Demystifying deicing (just in time for winter)
Due to the frequent snow and low temperatures associated with Aspen area winters, aircraft at the Aspen/Pitkin County Airport (ASE) often undergo a procedure to remove ice, snow and frost (often referred to as “contamination”) from the aircraft. Because aircraft surfaces are engineered to be a very specific shape and associated control surfaces are designed to move precisely per input from the pilot, they can be very susceptible to even small amounts of this contamination.
The surfaces most impacted include:
- Control surfaces (wings, tail, ailerons, slats, flaps, horizontal stabilizers, rudder)
- Antennas and sensors
- Landing gear and gear doors
When snow, ice, and frost buildup on these surfaces they change the way in which air flows around them and can also restrict their movement. In addition, this contamination can alter the airflow around the fuselage of the aircraft creating drag and turbulence, impacting overall aircraft performance. To eliminate the contamination, and at times prevent additional buildup, aircraft often go through a de-ice and anti-ice process prior to takeoff.
At the Aspen/Pitkin County Airport, aircraft are only treated for contamination buildup on a designated “de-ice pad,” located at the southern portion of the airfield. The dedicated use of this location serves two fundamental purposes. First, since aircraft de-icing uses a mixture of chemicals and water, the spent fluid is collected through a series of drains on the pad to prevent it from reaching waterways and can be properly disposed. Second, this location places the aircraft de-ice operation as close to the departure end of the runway as possible, limiting the opportunity for additional contamination buildup following removal.
The airport’s de-ice pad can handle several aircraft simultaneously, if needed. At the discretion of the pilot, the aircraft will enter the de-ice pad and shut down the engines. This engine shutdown is to prevent de-ice fluid from being ingested into the interior mechanical workings of the engine and reduce the odor of de-ice fluid on passengers. At ASE, the airlines perform their own de-icing while general aviation aircraft are serviced by the Fixed Base Operator (FBO).
Two types of fluids are used to de-ice and prevent additional contamination buildup at ASE:
- Type I – (De-Icing) A fluid mixture of water and glycol (antifreeze) heated to approximately 150-degrees F. Typically dyed orange.
- Type IV – (Anti-Icing) A fluid, similar in composition to Type I, but with a polymeric thickening agent added allowing the fluid to remain in place on aircraft surfaces until after takeoff (This prevents the buildup of contamination after the application of Type I fluid). Typically dyed green.
Initially, the aircraft will go through a de-ice process where Type-I fluid is applied to any areas covered in snow, ice, or frost. This process typically involves a specialized truck which applies the heated fluid at a high pressure. Some de-icing trucks have an added feature where compressed air accompanies the fluid to help remove contamination and reduce the amount of fluid needed.
If, during the de-icing process, weather conditions (snow, freezing rain) which could add additional contamination exist, the Type IV fluid (anti-ice) will be applied to specific critical aircraft surfaces to prevent re-contamination. Dependent on the outside ambient air temperature, if the aircraft cannot depart within a specific amount of time (referred to as “holdover time”), the de-ice/anti-ice process must be repeated. The colder the temperature, the shorter the amount of holdover time allotted to the aircraft before takeoff.
The spent fluids are directed by gravity on the de-ice pad towards special drains. These drains lead to a 20,000 gallon underground holding tank where it is held until it can be disposed. Access to the holding tanks are controlled via a series of valves. These valves prevent regular snow melt from entering the tanks causing them to fill prematurely with water. During times of excessive inclement winter weather, the holding tanks will near their capacity within a day or two, and the spent fluid will be removed by a third party contractor. Because ASE is reliant on aircraft de-icing during the winter season, and access to the facility could be impacted by road conditions and regional closures, the airport has an additional 20,000-gallons of above ground storage to offer additional reserve capacity. Unfortunately, the used fluids cannot be re-used and must be disposed of and are often repurposed for use as auto windshield fluid.