Despite the mild Autumn so far, all airline crews operating in the Northern Hemisphere will have refreshed their knowledge of the special “Cold Weather Operations” procedures applicable to their airliner. These procedures are applied when Ice, Slush and Snow are present at their airport.
The general principle is that all control surfaces must be free of all deposits of ice snow or slush. (Special dispensation is granted in the case of a thin layer of frost on the under-surfaces of the wings due to cold fuel in the tanks). This process is essential because all the performance calculations are based on the predictable smooth airflow over clean control surfaces.
All frozen water deposits must be removed by a process called ‘De-icing’. If more precipitation is forecast, the aircraft will be ‘Anti-iced” to prevent the fresh deposits from adhering to the control surfaces.
Taxying on snow and slush is done extremely slowly and with meticulous care.
If visible moisture is present in any form, engine fans are prone to icing up when the temperature is near freezing or lower. This means that engine anti-icing must be set to ON from engine start-up. Before takeoff in icing conditions, engines are run up to a mid value of power setting for several seconds to ensure that any ice is shed from the fans.
Take a look at this video of taxying and takeoff from Brussels when Cold Weather operating procedures were being used.