It’s that time of year again; days are getting colder and the nights are getting longer. With winter, along come seasonal climate changes that create considerations and challenges for pilots.
So how does winter weather affect commercial flying?
Low visibility operations are common in the winter for airline pilots. This is when the visibility falls below the usual limits required for an approach and landing. An airport will enforce ‘Low Visibility Procedures’ when the horizontal visibility falls below 550m or when the height of the clouds above the aerodrome falls below 200ft. These procedures allow an airport to continue operating, with some changes:
Once a year pilots must be tested on at least two automatic landings, which takes place in a full flight simulator.
One of the most fatal air accidents in history was partly due to low visibility. In the so-called “Tenerife Disaster” the Captain believed he was cleared for take-off when in fact there was still an aircraft on the runway ahead of them. On clear day, the other aircraft would have been in full view.
The main cause of the low visibility at airports is Radiation Fog. It is the most common type of fog that forms away from the coast and it occurs when the earth’s surface loses heat overnight and cools the air close to the surface to something called the ‘dew point’, i.e. when there is moisture in the air and it appears dense, visibly creating the fog.
Snow looks magical, but it comes with its considerations for pilots. It sure is great for skiing on, but it is not so good for landing, taking off or taxiing on. When there is snow or ice on the runway, this is known as ‘runway contamination’.
Much like a car stopping distance is affected by ice on the road, both the landing and take-off distances will be increased if a runway is contaminated. If it begins to snow at an aerodrome, the runway will have to be temporarily shut to clear the snow as it falls. This means that aircraft will have to enter holding patterns before landing, or wait for take-off.
Pilots need to plan for these changes. More fuel may need to be taken to absorb delays and avoid a diversion. Learn more about planning a commercial flight here.
After landing, care will need to be taken when taxing as surfaces will be slippery.
In winter climates, the aircraft will be exposed to ice forming on it, or ‘icing’, especially when flying through moisture at temperatures below 0 degrees and climbing through clouds in colder air. This is why commercial aircraft have multiple systems for dispelling ice, for example on the wings and in the engines.
Ice is very detrimental to aircraft performance for example; a contaminated engine as slush and snow will enter, resulting in decreased engine efficiency.
Pilots must inspect the aircraft thoroughly before departure to ensure that the wings are clear of ice. Different airfields have different de-icing procedures and so pilots will familiarise themselves with these.
Sometime de-icing is conducted close to the runway and sometime it is done on stand,
De-Icing is when the aircraft has ice removed from its surface and anti-icing is a fluid that will prevent further icing for during holdover time.
Pilots must pay attention to the ‘holdover time’ – this is the amount of time that the anti-icing fluid will prevent any further ice build-up. If this time has gone past, and the plane still hasn’t taken off, the aircraft must return to be de-iced and anti-iced once more.
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