Strategies for managing winter storms with approved ramp and runway deicing chemicals
Reprinted from the September 2005 issue of Ground Support Magazine
Proper management of snow and ice at airports is essential for on-time winter operations. These functions always include commercial aircraft movements during pushback, taxi and takeoff. But maintenance personnel must also ensure safe working conditions for luggage and cargo handling, airport security, FBOs and a myriad of other airside activities happening during what are often brutal winter storm conditions.
Delays and employee injuries resulting from ineffective snow and ice control cost airlines, airports and their customers precious time and revenues in what today are fragile economic times for the industry. And at the same time officials must manage chemical outfall and potential environmental impacts.
Use Mechanical Equipment as the First Option
Today"s high-speed broom and plow techniques offer the best first strategy for removing snow and ice deposits from airport surfaces. Keeping ahead of the storm using proper mechanical means minimizes chemical usage and can provide adequate friction for safe operations. Mechanical removal is preferred at low temperatures, below 15 degrees Fahrenheit, when snow is dry and does not bond or adhere to gate areas, ramps and runways.
Choosing the Right Deicer
Deicers are used when plows and brooms are not sufficient. Deicers are used to prevent bonds from forming between snow and ice and moisture in the pavement, or to break those bonds once formed. The remaining frozen deposits can then be removed mechanically. When choosing the right deicer, review the certification, the effectiveness and how the deicer works.
Deicer Certification Required from the Vendor
Ramp and runway deicers should be certified to airport approved specifications. Deicers must pass airframe material compatibility, corrosion, concrete, paint, storage stability and other standards established by airline, airport and government officials. The liquid specification is SAE AMS 1435 and the solid is SAE AMS 1431.
Urea is a nitrogen-heavy, granular fertilizer and should not be used. Because it is approximately 46 percent nitrogen by weight most major airports have stopped using it for environmental pollution reasons.
Deicers lower the melting point of ice and snow turning them into liquid brine solutions. When the brine makes contact with the surface it flows outward and breaks the bond between ice deposits and the pavement. A deicer"s type and active ingredient concentration determine how quickly brine forms, and the product"s residual or staying power and effectiveness.
Airports must know when to use liquid and solids. Lambert-St. Louis International Airport uses primarily liquid potassium acetate on its runways but often switches to solids on ramps and walkways. Airfield Administrator Bill Korte comments, ""the St. Louis area experienced one of the worst winter storms we have seen in the past three years. By the time we officially called off our snow crews, we had 7.9 inches of snow mixed with almost two inches of freezing rain and ice.
"We used NAAC (solid sodium acetate anhydrous) on our elevated ramps, drives and sidewalks in front of the terminals from the beginning of the storm event. After the ice hit and temperatures dropped to the single digits, we mixed NAAC with sand and applied it in conjunction with E36 (liquid potassium acetate) on our tug roads and in the airline gate areas."
"The results, in every case, were extraordinary. We were able to maintain 80 to 90 percent "bare pavement" conditions in these areas throughout the storm."
Understand How Deicers Work
Liquid deicers are generally used as "anti-icers." This means they are applied before frost, ice or snow accumulate and have a chance to bond to the pavement. The technique prevents frozen deposits from adhering - like Pam® on a frying pan, allowing any remaining snow and ice to be removed more easily with mechanical equipment. The first anti-icing application is generally made just before the event starts, again as needed during the storm -following mechanical removal- to prevent bonding.
Solid deicers are generally used as "deicers." This means they are applied after snow and ice have fallen and bonded to the surface. Solids bore holes through the accumulated pack to the pavement as the deicer changes form from solid to liquid. Some solids like sodium acetate anhydrous actually give off heat (exothermic reaction) as they dissolve. It causes the solid to work faster than an endothermic product such as urea.
Solid deicers come in two forms, pellets and granules. Pelleted deicers are harder and therefore, are less dusty. And because of their even size they tend to spread more uniformly. Both deicers adhere to the surface and have less bounce during application when applied on wet or light snow covered surfaces.
Generally, anti-icing techniques are more efficient than deicing, because it requires far less energy to prevent a bond from forming than to break it. Think of holding two magnets close together but not joined. It takes little energy to keep them apart. But once the magnets are linked "like ice bonded to the pavement " it takes a lot of energy to break them apart. And so it is with anti-icing versus deicing techniques. Less chemical is required to prevent the bond than to break it. In a typical winter storm, both techniques may be necessary to provide safe working conditions.
Pavement surface temperature, ambient temperature and pavement chemical concentration levels are all variables that affect pavement refreeze. Refreezing occurs when ice control chemicals dilute sufficiently that the brine solution turns to ice. Monitoring the variables closely allows for timely reapplication before refreeze.
Sand use may cause friction levels to improve in the short term. However, sand has little long-term value in an on-going storm. There are also accompanying clean-up costs and a real concern for sand ingestion into airplane engines.
Choose the Right Application Equipment
Choosing the right deicer spreader and sprayer provides accurate, cost effective applications. Ground speed control, the right spray nozzle configuration and calibration are important for accurate chemical delivery. Spreader covers should be used to protect dry deicers.
Training Is Important
All the best chemicals and state-of-the-art equipment are useless if maintenance personnel do not know how to properly use them. Initial and refresher training for both anti-icing and deicing strategies are often provided by quality manufacturers.
Efficient, effective airport ice and snow control is clearly a difficult task particularly in raging winter storms. Yet timely movement of aircraft and safe working conditions are imperative for successful winter operations by airlines and other airport customers.
Maintenance personnel have a wide range of storm-fighting strategies available to them. Their "tool box" includes first the use of mechanical removal whenever that alone achieves desired friction levels. But when conditions are such that chemicals are required, only "airfield certified" deicer formulations should be used.
Good training before winter hits will help ensure the right anti-icing and deicing techniques are fully understood and effectively practiced. Field maintenance managers should look to their purchasing departments for qualified vendors, certified deicers and ample training to help ensure this most difficult task is managed correctly.
Deicers commonly used by airports include: