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Why weather matters for pilots

Weather can be a force for good, not just an obstacle course for pilots. After all, “Bra vind i ryggen er best.” (“A fair wind at our back is best.”)

As warm oceanic currents and humid air from the Gulf Stream ripple across the Atlantic and collide with the cool mountainous landmass of Scandinavia – particularly along Norway’s northwestern coastline – dramatic weather ensues. Fog, ice, snow and turbulent air are just some of the climatic by-products that challenge the operational flow of airlines.

But Scandinavian travelers have always taken temperamental weather in stride. A millennium ago, when skies darkened and storm clouds rolled in, the sun – which Viking sailors relied upon for navigation – suddenly became obscured. To regain their bearings, they augmented their terrain-reading skills with a clever device to keep their drakushiffen (dragonships) on-course – a “sunstone,” believed to be made of ­calcite crystal, that enabled mariners to polarize the diffused sunlight and locate the hidden sun with pinpoint accuracy.

‘In cold weather, the output of the engines and the aerodynamic capabilities increase’

Viking ingenuity must have trickled down the generations, because today’s flight crews apply the same formula to understand Scandinavia’s unique topography and climate. They use technology (much updated, of course) to tackle weather, thereby sticking to schedules, and aligning with SAS’ strategic mandate to “simplify the travel experience and take care of passengers’ time.”

“In Scandinavia, the weather changes quickly, often with sub-zero temperatures in winter. Runways become slippery, so it’s important to learn the local conditions from experienced colleagues,” says Captain Marie Stridh, who pilots all variants of SAS’ Boeing 737 fleet. 

‘In Scandinavia, weather changes quickly, often with sub-zero temperatures in winter’

“Once, we flew to Tromsø and snow showers were forecast. We brought plenty of extra fuel and upon reaching Tromsø they’d closed the runway for snow clearance and four other aircraft were in a holding pattern above the airport. After 30 minutes, the runway reopened and aircraft ahead of us landed, but when our turn came, it started snowing heavily and the airport was closed again. We diverted to nearby Evenes airport and waited an hour before Tromsø opened again between the snow showers.”  

Carrying extra fuel is just part of the process of monitoring, anticipating and preparing for the unpredictable. SAS aircraft are equipped with weather ­radars which scan for rain, thunderstorms and turbulence. 

“There’s a weather display in front of each pilot, which helps us avoid bad weather,” Stridh explains. “There’s also another display showing wind at present position and altitude. If there’s turbulence and we need to alter the flight level, it’s helpful to know the winds at other altitudes.” 

The anticipatory nature of flight planning has prompted an addition to the pilot’s toolbox. “A few years ago, we started using iPads in the cockpit. All pilots carry these with apps which help analyze weather. At the hotel we can meet for coffee with our tablets before pick-up time and sit together to plan the day,” explains SAS First Officer Jostein Sørli. This might involve preparing three or four alternative flight plans in case the weather changes significantly.

‘Jet streams are ribbons of air that travel up to 320km/h from west to east’

“We try to plan the most optimal route, taking in various factors, including jet streams,” Sørli says. Jet streams are ribbons of air that travel up to 320km/h from west to east, 9–16km above the ground. “If we know there’s a jet stream, or possible headwind, we’ll plan accordingly to make the flight time faster and use less fuel.”

Winds are part of a pilot’s calculations all year round, but Scandinavian winters offer another operational advantage. “In cold weather, the output of the engines and the aerodynamic capabilities increase, which is important to keep in mind when calculating takeoff and climb performance. In cold temperatures, aircraft can take off with a bigger payload, using a shorter runway,” Stridh says.

Of course, mastering weather also means collaborating with air traffic control colleagues. Complementing the pilot’s onboard tools, a recent initiative at Scandinavian airports provides useful data to pilots as they prepare to land. “Avinor has developed a weather model to predict potentially slippery runway conditions,” says Marit Rabbe, an expert in aviation meteorology at Avinor, which is responsible for most of Norway’s airports. 

This model, called IRIS (Integrated Runway Information System) is in use at Oslo Airport, and is based on six scenarios known to cause slippery conditions. The model receives weather information from instruments along the runway – wind, visibility, current weather, air temperature, runway temperature, dew point and pressure.

‘When runways are covered with snow and ice, we get information on how slippery the runway is’

Up in the cockpit this information is invaluable, ­according to Stridh. “When runways are covered with snow and ice, we get information on how slippery the runway is on a scale, and we can use that number to put in a program on our iPads. We put in braking ­action, wind, weight of the aircraft, and it tells us the landing distance.”

So the next time you board a SAS flight and perhaps catch a glimpse of the pilots tapping on their tablets, rest assured – they’re just getting on top of the weather. 

Text: Paul Sillers

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