Everyone has at some point in their life looked out their window and been overjoyed at the sight of snow outside. But seeing snow through an airplane window brings many threats with it; so what exactly are they and can an airplane take off into snow?
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Or you may have a holiday to the sun coming up, and are frightened the sudden snowfall will prevent your plane from taking off and flying to that warm and sunny destination you’ve been dreaming of for the past few months. Will your flight get cancelled due to snow?
The answer is that snow might be hazardous, but it does not prevent take-off or landing. As long as all of these threats can be mitigated, the flight can continue as planned. The primary concerns that accompany it are the threat of icing, reduced visibility and compromised braking distance.
Snow Management Before Takeoff
Doing the walkaround, the pilot’s job is to ensure all critical surfaces of the aircraft are contamination and damage-free – checking they are not covered with ice, snow or any bird guts.
If left on the plane, snow will essentially change the shape of the wing, presenting the same dangers as ice. So if snow or ice is found it must be removed either manually or with the aid of a de-icing rig. Check out our article on icing, for a deeper look at ice and how it is removed.
In the case of snow, the best tool for the job is often a trusty broomstick. Even an ordinary kitchen broom will do! However, scrapers, squeegees and ropes can also be used to manually decontaminate the airplane.
Snowy weather can also make the taxiways and parking areas slippery with slush or ice. This video shows a couple of clips of people finding this out the hard way!
Snow In The Engines
During winter airplanes frequently fly in snow, and from the cockpit it looks like you are jumping into hyperspeed! So snow can of course be ingested into the engines during flight without any impact on the performance.
Although snow usually melts once inside it, in some situations snow can cause a flameout. This is when the flame inside the engine, producing the power, is blown out.
Often an engine can be recovered from this, so manufacturers suggest that crews leave the igniters on during such weather so that the engine can be quickly reignited.
Most flights that get cancelled ‘due to snow’ are actually due to the poor visibility that comes with it. Snow can seriously reduce visibility and cause what is known as ‘whiteout’. This is when a dense blizzard changes the way light is reflected so that only very dark objects may be seen; when this occurs it becomes impossible to tell the ground from the sky.
This can happen anywhere, but in places such as the arctic, where the snow is particularly fine, the powder can be whipped up quickly and change the sky from CAVOK (ceiling and visibility OK) to a white blank in a matter of minutes.
Aircraft that are autoland capable will have no problems landing in this environment, but as yet no commercial airliners are able to take-off automatically. So they must delay take off until the visibility improves. In the near future however, crews may be able to conduct auto take offs, as Airbus demonstrated their first automatic takeoff in January this year.
Whiteouts are thankfully only experienced in very severe winter weather. Flat light however, is a much more common occurrence. Also known as ‘partial whiteout’, flat light is an optical illusion that makes depth perception extremely difficult. This illusion is not just limited to snow; it can also occur in sandy environments and on glassy water.
As with a white-out, flat light makes the pilot lose the ability to judge closure rate, terrain features and distinguish between climbing/descending and level flight. This phenomena is insidious and so many aircrews have not realized their error until it was too late.
Whilst you should never take off in white out conditions, flying in flat light is possible and done frequently by seaplane and arctic pilots.
Taking Off On Snow
So lots of precautions must be taken when planning a take off in snow, but what about a take off on snow?
Snow can have a huge impact on landing distance and take-off distance, but unless we are dealing with wet ice, most aircraft are still able to meet these requirements on commercial runways.
But for some heavily loaded aircraft, such as the C130, a little boost is occasionally needed. In this case, the little boost comes in the form of 8 rockets. Other aircraft have been donning skis to aid their handling, allowing exploration of more remote locations, including frozen lakes.
Replacing wheels with skis extends the takeoff roll by roughly 10%. Wet or very deep powder snow may increase this further. As you would expect, flying in these snowy areas has its dangers.
Phenomena such as flat white light are frequent and pilots are advised to wear orange-lensed goggles and keep sight of at least one reference point during the take-off. For landing, pilots often drop red flags on the landing site before landing to aid their depth perception.
On frozen lakes, pilots must beware of ‘overflow’. This is when water from the lake below, seeps up and flows over the ice, saturating the snow on top. This slush makes it impossible to get the airplane moving fast enough to take off again.
In these chilly environments, it is absolutely essential that the pilot thoroughly checks out the landing area, even performing ‘touch and go’s’ to ensure that the surface is suitable.
The Antarctic Circle
People living in the antarctic circle have not had the convenience of having supplies flown in until fairly recently. Finding runway materials that would withstand the environment was exceptionally difficult and being over 1238km away from the nearest land mass, trying to find a plane that was able to make the journey and land was impossible.
Now ‘blue ice runways’ provide a much easier way for scientists to be sent much-needed supplies. Although the idea has been around since the 1950s, the first strip wasn’t built until 1987. Blue ice occurs further inland than the typically brilliant white ice of the Antarctic plains, and is so much darker that it can be seen from space.
Ice runways are exceptionally slippery and so they must be around 3000m long and require pilots to use reverse thrust only. Using brakes on an ice runway will just cause the plane to skid, so using aerodynamic braking is actually much more efficient!
Take a look at this video on the Wilkins Runway:
Air Florida Flight 90, 1982
One Air Florida flight in 1982 however, broke nearly every rule in the book regarding snow. It was departing from Washington National Airport heading for Fort Lauderdale-Hollywood International Airport. The snowfall was moderate and the outside air was -4℃.
When attempting to push back from the stand, the crew used reverse thrust to try to push themselves back from the stand. This was against Boeing’s advice at the time. Once finally on the taxiway, they held there for over 45 minutes.
They now had a considerable snow cover on the wings, but instead of deicing, they used the jet blast from the aircraft in front to melt the snow. Unfortunately this had the opposite effect, blocking instrument probes and melting the snow into a slushy mixture which then solidified on the leading edge of the wings.
At any point, the crew could have used the onboard anti-ice system, but they did not. On take-off the engines had differential thrust but the crew continued the take off. Unable to climb, it crashed into a frozen lake.
One of these issues on its own would not have led to the catastrophe that day, but combined they caused a very serious incident. The hours of delays we experience on winter nights in snowy airports may be frustrating, but they are to prevent events like Flight 90; proof that it pays to follow the rules.
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