The Cost of Frost on Runways

A Look at Heated Pavement Technology

Source: FAA Safety Briefing Mar/Apr 2021

By Jennifer Caron

As an early December 2020 storm complicated an already tricky landing with ice and snow, Spirit Airlines Flight 696 touched down at Baltimore/Washington International Airport (KBWI) safely, but during their taxi to the terminal, skidded off the icy taxiway into the grass. Luckily no one was hurt, and all aboard departed with what will likely be a colorful “there-I-was” travel story. Not all such events turn out so well.

Every year, snow, ice, and freezing rain pose a serious challenge to pilots and airport operations.

To further enhance runway surface safety, the FAA, through the Center of Excellence Partnership to Enhance General Aviation Safety, Accessibility, and Sustainability (PEGASAS), looked at the method of using heated pavements on airport surfaces to melt ice and snow. This method is not only innovative, but also economical, since it would re-purpose shelf-stable technology and products from other industries. Read on to learn more about these hot (ahem) technologies.

Slush Fund

Some see a crisp blanket of glistening white snow as pure delight. For others, the mere forecast of white stuff evokes muttered curses, as it portends the dreaded chore of back-breaking shovel work. For pilots, flight crews, airport managers, and equipment operators, inclement weather means lots of preparation. Long before the first flurries touch the tarmac, pilots and air traffic controllers monitor the weather. Airport personnel stand ready to clear ice and snow from runways, taxiways, and aprons. Conventional snow removal systems consist of well-practiced teams operating the equipment that plows, blows, and sweeps hundreds of feet of asphalt, while the long arms of de-icing trucks dispense liquid chemicals to deprive frozen precipitation of its traction-stealing power.

But snow removal is quite costly for airports. Snow plows run around a million dollars apiece, with vehicles, brooms, and sand adding to the price tag. De-icing chemicals deal another blow to airport budgets, costing as much as $20,000 or more per use. When you factor in the cost and facilities to collect contaminated ice and snow, garages to house the equipment, maintenance costs, round-the-clock staffing, and flight delays and cancellations, you’re looking at quite a hefty expense. There is also potential for environmental damage from de-icing chemicals.

Age-Old Problem Meets Age-Old Solution

Imagine a practical and cost-effective way to deal with the time-consuming, expensive, essential task of clearing airport surfaces. What if that technology was already in use, poised to cross into the aviation community? That’s where heated pavements come into play.

Similar to the technology we already use in our cars to de-ice windows and warm chilly seats, this technology lends itself to using heated pavements on airport surfaces. PEGASAS studied this idea to de-ice frozen apron areas and, potentially, taxiways and runways to improve traction and safety for critical surface operations. The collaborative FAA/PEGASAS research team includes Matthew Brynick in the FAA’s Airport Pavement Research and Development division at the William J. Hughes Technical Center, and university lead Dr. Halil Ceylan of Iowa State University.

Heated pavement systems (HPS) are not a new technology. They are already used by hospitals, offices, and shopping centers to keep sidewalks and parking areas slip and fall free. Heated pavements work in one of two ways, either by hydronic (water-based) or electric heating.

Hydronic HPS is the most established technology, primarily used in bridges and at many U.S. and European airports. It works by circulating hot fluid, namely glycol antifreeze, through a series of pipes running through the pavement. The challenge with this technology is two-fold. First, if any of the embedded tubing cracks or breaks, corrosive liquid can leak, damaging concrete and posing the same threat to the environment as de-icing chemicals. Second, large boilers are needed to heat the circulating liquid, thereby increasing energy and maintenance costs. It also requires a large space to house the components.

Electrical HPS uses basically the same principle as defrosting windows in your car. Comparable to the black lines you see layered in the glass of your rear window, electrical HPS uses a grid of heating cables embedded in the bottom of a pavement system. The drawback is that these cables have to be placed at the very bottom layer of pavement, forcing heat to travel through the entire thickness of the concrete before it can reach the top layer to melt ice and snow. The result is higher operating costs and reduced efficiency.

But there’s a more effective solution. Adding electrically conductive materials such as carbon fiber and graphite directly into the concrete mix, the entire pavement becomes a heat source and starts generating heat at the very top layer where it’s needed. “That’s why from the very beginning we focused our research on electrically conductive concrete, or ECON for short,” says Dr. Halil Ceylan, who has been the PEGASAS lead on this project for over seven years. “The advantage of this technology is that we don’t have to heat the entire thickness of the pavement, thereby reducing the downtime required to melt the ice and snow,” he explains.

Heated Pavements in Action

Dr. Ceylan and PEGASAS researchers have conducted an on-site demonstration of ECON in action. The world’s first, full-scale ECON slabs at a U.S. airport were installed in the general aviation (GA) apron area at the Des Moines International Airport (KDSM) in Des Moines, Iowa in November 2016 (see Figure 1).

Throughout the evaluation period (2016-2017 and 2017-2018 winters), the ECON pavement system consistently provided uniform heat distribution and prevented snow and ice accumulation on the surface. Here’s how it works. When the system is activated, it generates enough heat to melt a one-inch thick layer of snow in about 30 minutes. You can see the system at work with the thermal imaging shown in Figure 2.

“The period between when the system is turned on and the snow and ice is melted depends on the atmospheric conditions at the time, such as the rate of snowfall, air temperature, relative humidity, and wind velocity,” notes Dr. Ceylan, “but we were able to demonstrate that our technology works under harsh winter conditions to quickly melt any frozen precipitation on contact and keep the surface temperature above freezing.” It has no adverse impacts on aircraft communication or sensitive equipment, and airports can activate it ahead of a snow storm or automate start and stop times. Dr. Ceylan recommends that airport managers use this system proactively, activating it up to two hours before any expected winter weather event.

Ramp Up the Heat

Alternate snow removal strategies like ECON have the potential to keep both commercial and GA airports operational during severe cold weather. They also allow airports to reduce or eliminate dependence on traditional snow removal equipment and de-icing chemicals, saving time and money. “One of the goals of the research project is to help smaller airports clear runways during winter storms,” says Dr. Ceylan. Although GA airports focus more on specialized services (EMS, air cargo) than part 139 airports, maintaining winter operations in these smaller hubs will increase their operating revenue resulting in substantial cost advantages.

In addition, ECON installation will have benefits in congested ramp/apron areas where most employee slip and fall injuries occur. Runways are long, straight strips, much easier and faster to clear with heavy equipment than aprons, where clearing and hauling snow is more time consuming and complicated due to the mix of ground staff and equipment. “You can’t send a large snow plow into an apron area, which is why it makes the most sense to implement ECON in these congested areas first, and then expand it into other areas of the airport, such as high-speed taxiways, where most of the skidding events take place,” explains Dr. Ceylan. “Snow plows leave a thin layer of snow and ice behind when they clear any airport surface, but with our technology, the skid resistance is much higher, providing better operational safety in these critical areas,” he added.

Clearance to Proceed

“To further advance and demonstrate this technology, the next logical step is to build upon the progress shown at the airport in Des Moines, and implement larger-scale heated pavement systems,” says Dr. Ceylan. Additional research involves a multi-pronged approach that examines anti-icing systems such as a full-scale demonstration of electrically conductive asphalt concrete pavement systems, superhydrophobic (super-water-repellent) coatings, phase change materials, and hybrid heating. The next expected outcome of this research is an update to FAA Advisory Circular 150/5370-17, Airside Use of Heated Pavement Systems, which will provide guidance to airport owners, engineers, operators, and contractors to design, construct, and maintain heated pavement systems. “Our ultimate goal,” says Dr. Ceylan, “is to keep airfield pavement systems safe, open, and accessible during winter weather events.”

Jennifer Caron is FAA Safety Briefing’s copy editor and quality assurance lead. She is a certified technical writer-editor in the FAA’s Flight Standards Service.