Planes can fly in the snow, but only within a strict framework of procedures and limitations designed to ensure safety. Commercial flight operations during winter weather require specialized infrastructure and minute-by-minute decision-making by pilots and air traffic control. Every step, from taxiing to takeoff, is carefully managed to maintain the integrity of the aircraft and the safety of the runway environment.
Why Snow Poses a Threat to Aircraft
Snow, frost, or ice adhering to an aircraft’s surfaces poses a significant aerodynamic risk, often summarized by the “clean aircraft concept.” Even a thin layer of frozen contamination disrupts the smooth flow of air over the wings and control surfaces. This rough texture drastically reduces the lift the wing can generate while simultaneously increasing aerodynamic drag.
The resulting performance degradation is dramatic, potentially reducing lift by up to 30 percent and increasing drag by as much as 40 percent. This loss of performance raises the aircraft’s stall speed and severely impairs handling qualities during the critical low-speed phase of takeoff. Furthermore, frozen deposits add weight to the airframe and can jam moving parts, such as flap mechanisms, or cause instrument probes to report false airspeed data.
Snow and slush also threaten the jet engines. Ingestion of heavy snow or slush from the ground, particularly during taxiing, can contaminate the engine’s core and fan blades. As this ice sheds during high thrust application for takeoff, large chunks can damage the fan and compressor blades, potentially causing a loss of thrust or an engine flameout. Pilots must ensure all critical surfaces and engine intakes are completely free of frozen contamination before takeoff.
Ground Operations: Keeping Flights Moving
To counter contamination, airports and airlines use a two-pronged approach involving de-icing and anti-icing fluids. De-icing is the initial step of removing existing frozen contaminants, typically using heated, low-viscosity Type I fluid sprayed at high pressure. This fluid is primarily composed of glycol and quickly runs off the aircraft, taking the ice and snow with it.
Anti-icing is the second step, involving the application of a thickened Type II or Type IV mixture that remains on the aircraft’s surfaces. These high-viscosity fluids form a protective film, preventing new frost, ice, or snow from adhering until the aircraft is airborne. The fluids are designed to shear off the wing during the takeoff roll as airflow increases, restoring the clean wing profile for flight. These procedures significantly lengthen the time required between a flight’s arrival and departure.
Maintaining safe runway and taxiway conditions is equally important. Airport crews use specialized equipment for snow plowing and high-speed sweeping to clear surfaces. To prevent ice formation and maintain adequate braking action, they apply chemicals, often freezing point depressants, to the pavement. Air Traffic Control regulates the flow of aircraft and issues notices detailing the current runway conditions and any temporary closures needed for clearing.
Operational Limits and Cancellations
When the rate of snowfall or other weather factors overwhelm ground operations, regulatory limits are quickly reached, leading to delays and cancellations. A key factor is the “holdover time” (HOT), which is the estimated duration the anti-icing fluid remains effective under prevailing weather conditions. This time is determined by the fluid type, concentration, temperature, and the intensity of precipitation.
If the rate of snowfall is too heavy, the anti-icing fluid can become saturated and lose effectiveness before the aircraft reaches the runway. If snow falls too fast for the fluid to remain active during the taxi, flights must be halted until the precipitation rate decreases. This scenario forces a flight back for a repeat treatment, causing delays across the airport schedule.
Heavy snowfall also reduces visibility below the minimums required for safe takeoff and landing. Commercial carriers must adhere to specific visibility minimums, often measured by Runway Visual Range (RVR). For large commercial aircraft, this minimum is typically around one-half to one statute mile; if the weather drops below this threshold, flights cannot legally depart or arrive.
Air traffic control must reduce overall airport capacity during snow events due to these combined factors. Slower taxi speeds, the need for de-icing, and reduced landing and takeoff rates decrease the number of aircraft the system can safely handle per hour. To balance demand with capacity, Air Traffic Control implements flow management strategies like Ground Delay Programs, which mandate delays on flights departing for the affected airport, leading to widespread cancellations.