Some aircraft parked over New Year at Samedan were covered with snow overnight. These aircraft will surely have to be de-iced before being flown again.
When there are freezing conditions and precipitation, deicing an aircraft is critical. Frozen contaminants cause critical control surfaces to be rough and uneven disrupting smooth air flow and greatly degrading the ability of the wing to generate and increasing drag. This situation can cause a crash. If large pieces of ice separate when the aircraft is in motion, they can be ingested in engines or hit propellers and cause catastrophic failure. Frozen contaminants can jam control surfaces, preventing them from moving properly. Because of this potentially severe consequence, de-icing is performed at airports where temperatures are likely to drop below the freezing point.
De-icing techniques are also employed to ensure that engine inlets and various sensors on the outside of the aircraft are clear of ice or snow.
De-icing on the ground is usually done by spraying aircraft with a deicing fluid such as Propylene glycol. Ethylene Glycol is still in use for aircraft deicing in some parts of the world because it has a lower operational use temperature than Propylene Glycol and is more versatile in application, but Propylene Glycol is more common because it is classified as non-toxic, unlike Ethylene Glycol.