How pilots adjust their takeoff procedures in snowy conditions

While a snowy Christmas might bring cheer to many, it presents unique challenges for those in aviation.

Snow on wings, ice in engines, and slush on runways can create serious risks for aircraft, necessitating thorough evaluations by pilots before takeoff. Modifications in our aircraft preparation, taxiing to the runway, and the actual takeoff process are essential to ensure a safe departure for both the plane and its passengers.

At the airport gate

Flight preparation in wintry weather starts well before we head to the runway. Many pilots monitor the snowfall from home or their hotel, contemplating its impact on the upcoming flight. If it's been a while since I've operated in snowy conditions, I usually take this time to review winter operations specific to the Boeing 787 Dreamliner and the departure airport.

As we board the plane, we use the jet bridge windows to inspect the wing and the ground conditions. We're on the lookout for any signs of ice or snow that could impact takeoff performance.

An aircraft achieves flight not solely due to its engines but because of the lift created by air moving over the wings. Engineers design wings to optimize airflow, so any disruption caused by ice or snow can lead to a significant decrease in lift.

Pre-flight inspection

Prior to each flight, one of the pilots performs an external safety inspection of the aircraft. In cold weather, certain areas require special attention.

The pitot tubes and static ports, located near the nose of the aircraft, are crucial for providing various flight deck information, such as airspeed and altitude. If they become blocked by snow or ice, it can lead to incorrect readings.

We also inspect the air conditioning inlets and outlets, engine intakes, fuel tank vents, and APU inlets to ensure they are clear of ice and obstructions. Additionally, we examine the landing gear doors for any ice build-up.

After takeoff, when we retract the landing gear, any large ice chunks that have accumulated could fall to the ground below – which isn't great if you live near the airport. This is why Japan has implemented specific regulations for arriving aircraft to prevent ice from landing in populated areas.

De-icing aircraft

To clear snow and ice from the aircraft's surfaces, specialized de-icing trucks spray heated fluid onto the aircraft. This not only melts the contaminants but also helps prevent additional build-up for a limited duration. Typically, this process involves two steps.

Getting ready for de-icing

Before we begin spraying the aircraft, we need to adjust its configuration. Although it may seem like a sealed metal tube, an aircraft has many (intentional) openings. These allow air to enter and exit. If the de-icing fluid were to enter these ducts, it could potentially damage the aircraft's systems and release fumes into the cabin.

Therefore, prior to starting the de-icing process, we must follow the de-icing checklist to configure the aircraft. Each aircraft type has its own specific procedure due to variations in system designs, but generally, it involves sealing all external inlets to prevent de-icing fluid from entering the aircraft.

This obviously includes the cabin doors. While it might be convenient to de-ice the aircraft while passengers are boarding, the risk of fluid entering the jet bridge and the aircraft is too significant to ignore.

De-icing can be performed either at the gate or, at airports where winter de-icing is common, at designated remote de-icing areas.

On-gate vs. remote de-icing

Depending on the airport's infrastructure, aircraft de-icing can take place either at the gate or on a remote de-icing pad.

On-gate de-icing is the simplest way to remove ice and snow from the aircraft. Once all passengers are onboard and the pilots have set up the aircraft for spraying, one (or sometimes two) de-icing trucks begin the operation.

Although the de-icing process is the same whether done at the gate or on a remote pad, it can create challenges for the airport. Spraying can only start after all passengers have boarded, and there may not be enough de-icing trucks available for all the aircraft that require treatment.

This leads to delays for departing aircraft, which in turn causes hold-ups for arriving flights that must wait for a gate to open up.

At major airports where winter de-icing is routine, like Munich and Montreal, there are dedicated remote de-icing pads. These function similarly to a drive-through de-icing station.

When it's time to depart, we push back from the gate as usual and start the engines. We then taxi to the remote de-icing pad, where we are guided into one of the de-icing bays. Here, in communication with the de-icing controller, we engage the parking brake and let them know when the aircraft is prepared for spraying, just like at the gate.

The main difference in this scenario is that the engines remain running during the spraying process. This poses a significant risk for those on the ground, so we must stay extremely alert while this operation is underway.

Moving the aircraft or revving the engines before the de-icing team has completed their task could be dangerous for the truck operators.

The de-icing procedure

The decision on which parts of the aircraft to spray lies with the pilots. However, due to limited visibility of the entire airframe, we typically consult the de-icing truck operator for their evaluation of the contamination.

At a minimum, we usually treat the wings and tail, but if there's significant ice or snow on the fuselage, we will de-ice the entire aircraft.

During the first step, a heated mixture of glycol and water is sprayed onto the aircraft's surfaces; this effectively melts and blasts away the ice and snow from the airframe. Once this is complete, the aircraft is theoretically ready for departure. However, if temperatures are near or below freezing and moisture is present, such as fog or precipitation, there's always a risk of new contamination settling on the wings before takeoff. To mitigate this, the anti-icing phase is performed.

Anti-icing fluids resemble de-icing fluids, but they also include polymeric thickeners. This creates a layer that often appears as green or yellow slime on the wing surfaces, helping to prevent any falling precipitation from accumulating. While effective at the time of application, its efficacy is limited.

The effectiveness of the anti-icing fluid depends on the type used and the prevailing weather conditions, with holdover times ranging from a couple of hours to just a few minutes. Once this time elapses, pilots cannot guarantee that the wings remain clear of snow and ice, necessitating a complete re-treatment.

Pushback and engine startup

When pushing back from the gate in cold weather, there's a high likelihood that the stand and taxiway may be icy. While the pushback tugs are quite powerful, reduced traction can make it difficult for them to move the aircraft, especially if the engines are running.

Therefore, we often wait until the pushback is fully completed and the tug is disconnected before we start the engines.

Typically, on the Boeing 787, we initiate both engines simultaneously. The autostart system oversees the process and notifies us of any abnormal parameters that might need our attention.

However, when the outside temperature drops below 41 degrees Fahrenheit, Boeing advises that we start one engine at a time. Using the autostart function, we let the first engine stabilize before starting the second. In these conditions, oil pressure may take longer to rise, and the initial pressure could be higher than usual.

This process takes additional time, but it's crucial to properly care for the engines during this vital phase of their operation.

Taxiing

Before we begin taxiing, we carefully consider whether to deploy the flaps. According to our Standard Operating Procedure (SOP), we should set the takeoff flaps before leaving the gate area.

However, in winter conditions, if the aircraft hasn't been de-iced at the gate, the flap drive mechanisms could be frozen. Activating them under these circumstances might cause damage, leading to significant delays and repair costs.

If the aircraft has been de-iced while parked, slush and snow on the taxiways can still infiltrate the flap system's components, potentially causing ice build-up. This could result in flap malfunctions when we attempt to retract them after takeoff.

For remote de-icing, we keep the flaps up until the de-icing is complete. After this process, we assess the taxiways to determine if it's safe to deploy the flaps immediately or if we should wait until just before takeoff.

In either case, if we opt to postpone setting the flaps, it's crucial to remember to do so before we reach the runway. Historical data indicates that taking off without the appropriate flap configuration often leads to catastrophic outcomes.

Engine run-ups

Maintaining engine health is essential in winter weather, so we must closely monitor engine conditions as we taxi toward the runway.

Before every flight, regardless of the weather, the engines need five minutes post-start to achieve their optimal operating temperature. However, in cold conditions, additional procedures must be followed.

When temperatures range from 37 degrees F to 19 degrees F, and if the engines have been running for an hour prior to takeoff, we are required to conduct an engine run-up. This process involves halting the aircraft and applying approximately 50% power for 30 seconds. This is to ensure that any ice that may have formed in the engine is dislodged before takeoff. This procedure must be repeated every hour.

If the temperature drops below 19°F, we only have one attempt at this. If we still haven't taken off after another hour (which is not unusual at airports like JFK), we must return to the gate, shut down the engines, and have them manually de-iced by an engineer.

Bottom Line

A snowy airport may appear picturesque, but it can create significant challenges for everyone involved in the operation. Delays can occur as aircraft awaiting de-icing block the gates, and planes may require additional de-icing if their holdover time expires.

Ultimately, the safety of the aircraft rests with the pilots. We determine how to prepare the aircraft and the extent of de-icing that is carried out. Snow and ice are likely to cause delays, and while we understand the frustration, especially for passengers with connections, our priority is to ensure the aircraft travels safely from point A to point B, and we will not compromise on that.

Featured Image by Andreas Gebert/picture alliance via Getty Images