De-icing liquid is a mixture of propylene glycol and water, heated to around 150 degrees, and sprayed under pressure onto the aircraft. It’s good for around 22 minutes so if there are delays in takeoff, one more application might be needed. It is important for aircraft to de-ice so that airflow can properly go over the wings and generate lift. It also allows instruments to work properly. Here is a VC-10 in 1:400 scale to demonstrate what it would the process would look like. Snowplows and other