Chapter 15 Ice and Rain Protection Ice Control Systems Rain, snow, and ice are transportation’s longtime enemies.  Flying has added a new dimension, particularly with respect  to ice. Under certain atmospheric conditions, ice can build  rapidly on airfoils and air inlets. On days when there is  visible moisture in the air, ice can form on aircraft leading- edge surfaces at altitudes where freezing temperatures  start. Water droplets in the air can be supercooled to below  freezing without actually turning into ice unless they are  disturbed in some manner. This unusual occurrence is partly  due to the surface tension of the water droplet not allowing  the droplet to expand and freeze. However, when aircraft  surfaces disturb these droplets, they immediately turn to ice  on the aircraft surfaces.