Airport Snow and Ice Operations: Keeping Runways Open in Winter

On a bitter February morning at Chicago O'Hare (ORD), the temperature hovers at minus 15 degrees Celsius and snow is falling at three centimeters per hour. Yet aircraft continue to land and depart on schedule — a seemingly routine miracle made possible by one of the most intensive and expensive operational challenges in all of aviation: airport snow and ice management. Every winter, airports across the Northern Hemisphere mobilize fleets of specialized vehicles, deploy thousands of liters of chemical agents, and coordinate complex choreographies between air traffic control, airlines, and ground crews to keep runways safe and open.

Why Snow and Ice Are So Dangerous

The fundamental threat of winter contamination on runways is loss of friction. An aircraft depends on friction between its tires and the pavement to steer during taxi, maintain directional control during takeoff, and decelerate during landing. Ice, compacted snow, or slush on a runway can reduce the coefficient of friction from a dry-pavement value of roughly 0.7 to as low as 0.05 — a level at which an aircraft has almost no braking capability.

History provides sobering examples of what happens when winter contamination is underestimated. In December 2005, a Southwest Airlines Boeing 737 overran Runway 31C at Chicago Midway (MDW) in the United States after landing on a snow-covered runway, sliding through the airport fence and onto a busy street, killing a six-year-old boy in a vehicle. The accident investigation found that the runway had not been adequately cleared and that the crew should not have attempted the landing. Events like this have driven continuous improvements in winter operations standards.

Measuring Runway Friction

Before any aircraft can land on or depart from a contaminated runway, the airport must assess the surface condition and report it to pilots and air traffic control. Historically, airports measured runway friction using decelerometers — instrumented vehicles that brake sharply on the runway surface and measure the deceleration. Modern standards, formalized by ICAO in 2021 under the Runway Condition Assessment Matrix (RCAM), have moved toward descriptive condition reports rather than numeric friction values.

Under RCAM, airport operations personnel inspect each third of the runway and assign a condition code from 6 (dry) to 0 (wet ice). These codes are combined into a Runway Condition Report (RWY CC) that is disseminated to pilots via ATIS (Automatic Terminal Information Service) and NOTAM (Notice to Air Missions). Pilots use the condition codes to calculate their required landing distance using tables or onboard performance computers, and if the required distance exceeds the available runway length, the landing is diverted to an alternative airport.

The Snow Removal Fleet

Major airports in snow-prone regions maintain enormous fleets of specialized winter maintenance vehicles. Helsinki-Vantaa (HEL) in Finland, which operates in one of the world's harshest winter climates, maintains a fleet of more than 60 snow removal vehicles that can clear all three runways in under 20 minutes — a capability that is essential when snowfall rates can overwhelm the pavement in less than an hour.

A typical snow removal operation involves multiple vehicle types working in formation:

• Snowplows: Heavy vehicles with angled blades that push snow off the runway surface to the edges. Airport plows are significantly larger than road plows, with blades up to six meters wide.
• Rotary snowblowers: Machines that ingest the snow banks created by plows and throw them well clear of the runway edges, preventing re-contamination by wind.
• Sweepers: Vehicles with rotating broom brushes that remove residual snow and slush that plows cannot reach, particularly important for cleaning the surface down to bare pavement.
• Chemical spreaders: Trucks that distribute runway de-icing chemicals — typically potassium acetate, sodium formate, or urea-based formulations — to melt remaining ice and prevent re-freezing.

At Chicago O'Hare (ORD), the snow removal fleet includes more than 180 vehicles and is staffed by over 300 workers during winter operations. The airport's annual snow removal budget exceeds $20 million, and in a severe winter with heavy snowfall, the total cost including overtime, chemicals, and equipment maintenance can approach $40 million.

The Clearing Choreography

Clearing a runway at a busy airport requires precise coordination with air traffic control. The standard procedure at most airports involves closing the runway for a defined snow period — typically 15 to 30 minutes — during which the vehicle fleet makes a complete pass. Air traffic control sequences arriving and departing aircraft to create this window, which means that snow removal directly impacts airport capacity.

At airports with multiple parallel runways, such as Atlanta (ATL) or Denver (DEN), controllers can keep some runways open while others are being cleared, maintaining partial operations throughout the storm. Single-runway airports face a starker choice: close for clearing and accept delays, or attempt to maintain operations on a contaminated surface with higher risk.

The formation in which snow removal vehicles operate resembles a military maneuver. Plows line up in an echelon (staggered diagonal) formation, with each plow's blade overlapping the path of the one ahead. This configuration clears the full runway width in a single pass, with sweepers and chemical spreaders following immediately behind. The entire convoy moves at 30 to 50 kilometers per hour, and communication between drivers, the operations center, and the control tower is continuous via dedicated radio frequencies.

Aircraft De-icing

Clearing the runway is only half the winter operations challenge. Aircraft themselves must be free of ice, snow, and frost before they can safely take off. Even a thin layer of frost on a wing can disrupt the airflow enough to reduce lift by 20 to 30 percent — a margin that can mean the difference between a safe rotation and a catastrophic stall.

Aircraft de-icing is performed using heated fluids applied by specialized trucks with articulating booms. The process uses two types of fluid, designated by color:

1. Type I fluid (orange): A heated mixture of propylene glycol and water applied at 60 to 80 degrees Celsius. Type I fluid melts existing ice and snow on contact and is typically used as the de-icing step.
2. Type IV fluid (green): A thickened glycol fluid that forms a protective film over the aircraft's surfaces. Type IV fluid is the anti-icing step: it prevents new ice from forming during the taxi to the runway. The fluid is designed to shear off during the takeoff roll, leaving the wing clean at rotation speed.

The holdover time — the period during which anti-icing fluid remains effective — depends on the ambient temperature, precipitation type, and precipitation rate. In light snow at minus 3 degrees Celsius, Type IV fluid provides a holdover time of roughly 45 to 80 minutes. In freezing rain, holdover time can shrink to as little as 5 to 15 minutes. If the holdover time expires before the aircraft reaches the runway, it must return to the de-icing pad for retreatment — a common source of delays during heavy winter storms.

Environmental Concerns

Both runway chemicals and aircraft de-icing fluids pose environmental challenges. Glycol-based de-icing fluids have a high biological oxygen demand (BOD), meaning they consume dissolved oxygen in waterways as they decompose, potentially harming aquatic life. Runway de-icing chemicals can contaminate groundwater and affect vegetation near the airfield.

Modern airports manage these impacts through dedicated stormwater collection systems that capture glycol-contaminated runoff from de-icing pads and route it to treatment facilities. At Denver (DEN), the airport operates its own glycol recycling plant that recovers and reprocesses spent de-icing fluid, reducing both environmental impact and procurement costs. Runway chemical manufacturers have also developed more environmentally benign formulations, with potassium acetate and sodium formate replacing the urea-based products that were common in the 1990s and caused significant nitrogen pollution.

The Nordic Approach: Winter as Routine

Airports in Nordic countries treat winter operations not as exceptional events but as a core competency. Helsinki (HEL), Oslo Gardermoen (OSL) in Norway, and airports across Sweden maintain some of the lowest weather-related delay rates in the world despite receiving far more snow than airports at comparable latitudes elsewhere. The key is investment: dedicated personnel trained specifically for winter operations, equipment maintained to operate reliably at temperatures below minus 30 degrees Celsius, and operational procedures refined over decades of continuous winter flying.

Finnish airports use a particularly sophisticated approach to runway surface management, combining continuous friction monitoring with predictive weather modeling to pre-treat runways before contamination occurs. This proactive strategy, rather than reactive clearing after snow accumulates, is increasingly being adopted by airports in milder climates that historically treated snow events as rare emergencies rather than routine operations.

The Cost of Winter

Winter operations represent a substantial financial burden for airports and airlines. The Federal Aviation Administration estimates that weather-related delays and cancellations cost the U.S. aviation industry more than $8 billion annually, with winter weather accounting for the largest share. Individual de-icing events cost airlines $3,000 to $15,000 per aircraft depending on the aircraft size and the severity of contamination. Airports that invest heavily in winter capabilities — like Toronto Pearson (YYZ) in Canada — can mitigate these costs by maintaining high completion rates even during storms, but the investment in equipment, chemicals, personnel, and infrastructure runs into tens of millions of dollars annually.

Despite these costs, the alternative — closing airports for the duration of winter weather — is unthinkable for the modern air transport system. The economic cost of grounding flights at a major hub for even a few hours dwarfs the investment in winter operations. And so, every winter, airports around the world mobilize their fleets, stock their chemical tanks, and prepare to fight the oldest adversary in aviation: ice.