How planes handle the risks associated with snow and ice

As a major winter storm approaches the Northeast, we're exploring how pilots and aircraft manage snowy conditions.

With winter setting in, snow and ice become common in aviation. While they may look picturesque in your social media posts, icy conditions can create significant challenges for airlines and airports — and here’s why.

The incompatibility of ice and aviation

Aircraft achieve flight not solely due to their engines, but because of the lift produced by their wings. The engines simply propel the aircraft forward, enabling that lift. As the plane speeds down the runway, the airflow over the wings intensifies. Once this airflow reaches a certain threshold, the wings generate sufficient lift for the aircraft to become airborne and ascend into the sky.

Before every takeoff, we meticulously calculate the required engine power and speeds to ensure a safe lift-off. Once we reach the takeoff speed, referred to as Vr, we gently pull back on the control stick, allowing the aircraft to ascend. However, these calculations assume a "clean wing" that is free from any snow or ice contamination.

The wing design of an aircraft is the result of careful planning and engineering. Countless hours have been invested in perfecting the angle and shape to optimize lift as air moves over its smooth surfaces.

When snow or ice accumulates on the wing, the airflow becomes disrupted, which can cause it to separate from the wing’s surface. This leads to insufficient lift generation. Consequently, the speed we’ve calculated to ensure adequate lift will actually yield less lift in practice. As a result, greater speed is necessary to reach the critical takeoff velocity, which might exceed the available runway length.

In addition to the wings being contaminated, ice and snow can also interfere with the aircraft's external sensors.

To determine the speed, altitude, and various other parameters, the aircraft is equipped with several external sensors and probes. Among these, the pitot tubes play a crucial role.

Positioned to face the incoming airflow, these tubes measure the aircraft's speed through the air, providing pilots with essential information. If these probes become obstructed by ice or snow, they can produce inaccurate readings, leading to issues in the flight deck. Therefore, it is vital to ensure they are clear prior to takeoff.

Consequently, pilots take the issue of ice and snow contamination on the aircraft very seriously.

Prior to takeoff

Knowing that ice and snow pose significant risks to aviation, we implement several procedures to guarantee that the aircraft is safe for departure.

When there's a significant snowfall or it's actively snowing, getting the aircraft de-iced is essential. However, after a frost overnight, it can sometimes be tricky to distinguish between ice on the wing and mere condensation.

Even before officially starting our shifts, we’re already thinking several steps ahead. If it's early morning and you've had to scrape ice off your car, it’s likely the aircraft will also be covered in ice.

As we approach the aircraft, we often get a clear view of the airframe while climbing the steps or walking down the jetty. If visibility isn't great, peering out of the cabin windows can provide additional insights into the wing's condition.

Lastly, prior to every flight, one of the pilots conducts an external safety inspection, which includes checking the wings and fuselage. For smaller aircraft, accessing the wing is relatively easy, but for larger models like the 787 Dreamliner that I operate, the wing is somewhat out of reach.

If there's any uncertainty about whether the wing surface has ice or just condensation, engineers can use a specialized lift to closely examine it. In cases of doubt, we always prioritize safety and proceed with de-icing the wings.

What exactly does the de-icing procedure entail?

A two-step procedure

The de-icing procedure typically consists of two stages. First, we need to remove any ice and snow from the aircraft, which is the de-icing step. Next, we protect the wings and tail from further contamination before takeoff — this is the anti-icing step.

De-icing

To clear the ice and snow from the aircraft, it is sprayed with a heated mixture of glycol and water, effectively blasting off the icy residues from the wings. While this should theoretically prepare the aircraft for departure, if the temperature is around or below freezing and there's moisture in the air from fog or precipitation, there's a risk of more accumulation on the wings before takeoff. To prevent this, the anti-icing phase is performed.

Anti-icing

Anti-icing fluids are similar to de-icing fluids but also include polymeric thickeners. This creates a layer that resembles green or yellow slime on the wings, which prevents additional precipitation from accumulating. While effective at the time of application, this protection is temporary. Depending on the type of anti-icing fluid used and prevailing weather conditions, the effectiveness can range from a couple of hours to just a few minutes, referred to as the holdover time. Once this period expires, pilots cannot guarantee that the wings remain free from snow and ice, necessitating a repeat of the entire process.

On-stand treatment

In airports with milder winters, de-icing typically occurs at the gate. This process involves one or two specialized trucks arriving alongside the aircraft. Once the doors are secured and the air bridge is removed, the trucks begin spraying the aircraft. Depending on the contamination level and the skill of the de-icing crew, this can take anywhere from about five to thirty minutes. As soon as the anti-icing treatment starts, the holdover time countdown begins.

Remote treatment

Larger airports that frequently deal with cold weather usually have designated remote de-icing zones, typically located near the runway. The aircraft pushes back and starts its engines as usual, then taxis towards the remote de-icing area. If you find yourself taxiing to the runway with snow on the wings, there's no need for concern; you’re on your way to one of these remote zones. Once parked with the brakes engaged, de-icing vehicles commence spraying the aircraft. The key difference here is that the engines remain operational throughout this process. The primary benefit is that once de-icing is complete, the aircraft only needs to taxi a short distance to the runway, allowing for a quick takeoff, which is crucial when holdover times are short.

On the aircraft

Once the aircraft is airborne, while snow won't accumulate, ice buildup can pose a challenge. As the plane navigates through visible moisture like clouds and fog, ice can start to form in the engines and on the leading edges of the wings if the temperature drops sufficiently. To combat this, aircraft are equipped with several systems designed to prevent ice accumulation.

Automatic ice detection system

Aircraft like the Boeing 787 Dreamliner feature an automatic ice detection system that identifies icing conditions and sends signals to control the onboard anti-ice systems automatically. This system includes two detectors that measure the amount of liquid water in the atmosphere and utilize various temperature readings to assess whether icing conditions are present.

The wings

Depending on the type of aircraft, there are several strategies to prevent ice accumulation on the leading edge of the wings.

Most aircraft employ hot air from the engines, referred to as bleed air. This air is routed through ducts in the leading edge, warming it and melting any ice. While this method effectively removes ice, the use of bleed air reduces engine power and increases drag as it escapes into the atmosphere. These factors lead to higher fuel consumption to compensate for the decreased power and aerodynamic efficiency.

Modern aircraft, such as the 787 Dreamliner, employ an innovative method for wing anti-icing. This model utilizes a series of electrically heated blankets that are affixed to the interior of the leading edge structure. The warmth from these blankets effectively melts any ice that forms on the wing. This system is considerably more efficient, consuming about half the energy of a conventional bleed air system.

Moreover, since there are no bleed air exhaust openings, drag over the wing is minimized and noise levels are reduced, making the Dreamliner not only more fuel-efficient but also quieter during flight.

The engines

Although the engine exhaust is quite hot, pressure changes at the front of the engine can cause the temperature to drop, leading to ice formation. This typically occurs when air temperatures range from 10 to -40 degrees Celsius.

To prevent this, bleed air is utilized to increase the temperature. When icing conditions are detected, the engine anti-ice valves activate, allowing hot bleed air to flow into the engine inlet and core to prevent ice buildup. Once the aircraft exits the icing conditions, the valve automatically shuts off.

The system is designed to operate only when necessary, which helps minimize additional fuel consumption as previously mentioned.

Windows

Similar to car windows, the cockpit windows can also become icy. This is problematic not just for daily driving, but especially when landing an aircraft with 240 passengers onboard. To prevent ice buildup on the windshield, the glass is heated electrically.

The exterior surface is treated with anti-icing, while the interior features anti-fogging protection. These systems function continuously, whether the aircraft is on the ground or in flight.

Air conditioning inlets

In contrast to most aircraft, the cabin air in a 787 is sourced directly from outside. While this is beneficial for passenger health and comfort, it also makes the inlets susceptible to ice accumulation, much like the leading edges of the wings.

To prevent icing on these inlets, each one is equipped with an electric heater at the leading edge, which also helps minimize ice formation further down the air conditioning ducts.

Probes

As noted earlier, there are several probes and sensors located on the aircraft's exterior that are essential for measuring airspeed, altitude, and temperatures for display in the cockpit. To protect these instruments from ice, they are heated electrically while the engines are operating.

Final thoughts

Pilots fully understand the dangers that snow and ice can pose to flight safety. Prior to takeoff, we always make sure the aircraft is free of any snow and ice. Even after takeoff, ice remains a concern, but modern aircraft are equipped with various systems to prevent critical components from freezing. De-icing procedures can lead to delays, especially at airports where cold weather is infrequent, but those accustomed to harsh winters are usually well-prepared for extensive de-icing operations. While delays from de-icing can be frustrating, your pilots prioritize your safety above all else. When in doubt, we will always opt for de-icing.