How do pilots take off in a snowstorm?

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Editor’s note: This post has been updated with new information.

It’s that time of the year again: Deep winter in the Northern Hemisphere means major airports face disruptions from snow, sleet and extreme weather. If you flew through New York’s John F. Kennedy International Airport (JFK) in 2018, you might still have bad memories of the bomb cyclone that shut down the biggest gateway to the U.S.

If you transit through Chicago’s O’Hare International Airport (ORD) regularly, you know very well the pain of winter-weather delays. London’s Heathrow Airport (LHR) is not immune, either. Chances are you’ve found yourself on an airplane sitting on a taxiway, waiting — and waiting — as snow swirled outside. Or you’ve had your flight canceled due to fog.

Another such storm is developing just ahead of the busy Christmas travel rush, and it’s threatening to bring poor weather to hubs in the Great Plains, Midwest and East Coast.

Travelers must grapple with the disruption at the airport — or on their phones as they try to rebook — but what about pilots?

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What do these types of weather events look like from the cockpit? And how exactly do airline pilots cope with tough winter weather, from snowstorms to strong winds? What weather events, if any, do pilots fear more than others? For the answers, we turned to an expert: a pilot who flies Boeing 787s for a major international airline and has seen all kinds of weather worldwide.

In an email, he told us all about flying in tough winter conditions. We have omitted his name so he could speak as freely as possible. We lightly edited for brevity and clarity. Here’s what he had to say.

Snow is the worst

Different types of weather bring their own challenges. Strong winds can create bumpy conditions on the departure and approach. If the wind is across the runway, we must fly “crabbed” into the wind to keep us tracking straight. The test of our skill comes when the aircraft is just feet above the runway. Using one of a few approved techniques, we have to straighten the nose while keeping the aircraft tracking down the centerline. Ask a pilot what their most satisfying time at work is, and most will tell you a good crosswind landing.

Fog, too, gets us thinking. When you’re hurtling down the runway at 195 miles per hour and you can only see 250 feet ahead, you need to bring your “A” game. Rigorously practiced procedures for situations like this ensure that we keep all on board safe.

However, it’s probably snow and ice conditions that provide the biggest challenge to our skills as professionals.

While you’re in a cab on your way into the airport, your pilots are also heading in, thinking about the challenges ahead. Bad-weather days require extra focus and thought.

During a pilot’s initial training, there is a large focus on weather and how it can affect flights. We’re taught from a very early stage to respect the weather and never to take any chances with it. Mother Nature is a powerful force.

How heavy is the snowfall? What’s the temperature? What kind of snow is it? What’s the wind doing? All these questions will run through our heads before we even arrive at the airport.

The main threat to flight safety during snowy conditions is contamination on the flying surfaces. The design of the wings is so advanced that any snow or ice on the surface can massively affect the aircraft’s performance.

To create lift and climb away from the runway, the aircraft requires airflow over the wing. It’s this airflow that actually makes us fly — the engines merely create the forward motion. For every flight, the pilots calculate the speed required to lift off safely. This is based on the aircraft weight, weather and runway conditions at departure time. When we reach this speed, known as “Vr,” we ease back on our controls and the aircraft rotates into the air.

However, this speed is based on a clean wing, free from any snow and ice contamination. Build-ups on the flight surfaces can affect the airflow and, consequently, the lift, making the calculated Vr speed too slow — with potentially disastrous consequences.

Before every flight, one of the pilots walks around the aircraft to check its physical condition. During snowy weather, a major part of this is to see what contamination exists. The engines, wings and external sensors all come under close scrutiny. Often, the only way to check the upper surface of the wing is by looking out of a cabin window, so don’t be surprised if you see a pilot doing this — it’s a good sign!

From these checks, we know what kind of de-icing procedure to follow to make the aircraft safe for departure. If there’s any doubt as to how bad the contamination is, we will always consider the worst case. Too much de-icing is better than too little.

An aeroplane undergoes de-icing before taking off at the Düsseldorf Airport in Düsseldorf, Germany, 10 December 2017. Photo: David Young/dpa (Photo by David Young/picture alliance via Getty Images)
A British Airways Airbus A319 undergoes de-icing before taking off at the airport in Dusseldorf, Germany. DAVID YOUNG/GETTY IMAGES

De-icing on the cake

We want to be home with our families and friends as much as you do. However, while we are always mindful of punctuality, we are very aware that it can quite often be pulling in the opposite direction of safety. It’s our job to manage that balance.

Sitting at the gate, waiting to be de-iced, we know you have connections. We know you have meetings. We know you just want to get home. However, aviation history is littered with incidents where pilots cut corners to try and save a few minutes, only to regret that decision later on.

Why does de-icing take so long, though?

There are two ways aircraft can be de-iced: either with the engines shut down at the gate or with engines running in a remote de-icing area. This depends on the airport and on what facilities are available. Airports that experience snow and ice regularly tend to have remote de-icing facilities. Montreal-Trudeau International Airport (YUL) is a great example. Airports that experience these conditions only a few times a year, such as Newark Liberty International Airport (EWR), tend to have trucks that de-ice aircraft at the gate.

Now, I can already hear you asking why these big airports like Newark don’t just have better facilities. It comes down to a matter of space and cost. Remote de-icing pads cost much more and take up a lot of space. Would you spend thousands of dollars on a fancy electric snow-clearing device for your home when you know that, for the few days a year it snows, a shovel will be just fine?

The de-icing process can take anywhere from a few minutes to 30 minutes, depending on how much snow and ice is on the aircraft. When there are only a limited number of de-icing trucks, you can see why delays build up quickly.

All this time, we remain relaxed in the flight deck. You can’t rush these things. Let the trained professionals do their jobs and when the de-icing is done, it’s done.

Once de-icing has been completed, the clock is ticking. If snow is still falling, it’s only a matter of time before it accumulates on the wing again. This time is called the holdover time; we work out how long we have before we need to be airborne or get de-iced again. This time depends on the de-icing fluid used, the air temperature and what kind of precipitation is falling.

While there seems to be a race against time in this situation to get airborne, once again, we are the gatekeepers of safety. If the taxi to the runway takes too long and our holdover time runs out, we have to return to be de-iced again. More delays and more frustration for you, but we are doing our best to keep you safe.

Related: How aircraft de-icing works

Yes, you can take off on a snow-covered runway*

Once we make it near the runway, our focus steps up another level. We’re listening closely to air traffic control. When we can’t see landing aircraft because of poor visibility caused by the snow, we have to build a mental picture in our heads of where other aircraft are.

It’s for this reason that ATC should always speak in English, the official language of aviation. By listening to instructions issued to other aircraft, we can tell if there is one about to land, or another taking off farther down the runway.

ATC will also give us information about the runway conditions, which is where my asterisk comes in. You can take off on a snow-covered runway … depending on how slippery it is and how much snow has accumulated.

There are different kinds of snow. It can be quite wet or very dry. This depends mostly on the air temperature. If the snow is very dry, as it often is in areas such as northern Canada and Scandinavia, there can be times when it’s possible to take off with visible snow on the runway. This depends on how slippery the runway is.

Most airports have special vehicles with a roller on the back that can measure just how slippery the runway is. This information is then passed to pilots who use this to work out their aircraft’s performance for takeoff and landing, as mentioned earlier.

However, the wetter the snow, the more slippery the runway. This is typical of snowstorms on the Eastern Seaboard in the U.S. when the air temperature isn’t too cold. When the runway is slippery like this, it has to be cleared and treated with anti-ice.

Naturally, this can take time — during which we can do very little except wait. Once again, it’s all for your safety.

DULLES, VA - JANUARY 24:Snow removers clear the runways at Dulles International Airport in the aftermath of the big blizzard on January, 24, 2016 in Dulles, VA. (Photo by Bill O'Leary/The Washington Post via Getty Images)
Snow removers clear the runways at Dulles International Airport after a blizzard on Jan. 24, 2016. BILL O’LEARY/GETTY IMAGES

When approaching the runway to take off, we are constantly assessing the weather to ensure that the performance we calculated earlier is still valid. If things have changed, we must redo the performance calculations, which takes time.

Only when we’re happy that the aircraft is free from all snow and ice — and that the performance is still valid — will we tell ATC we’re ready for departure.

Bottom line

When we line up on that runway with 200-plus lives on board, we want to know that we will take off safely. By abiding religiously by all these procedures, we ensure you get to your destination safely — even if it’s a few hours late.