Final answer:
Aircraft icing primarily requires the presence of visible moisture and temperatures near or below freezing. Freezing point depression is a method used to combat icing on aircraft surfaces. The icing process is influenced by atmospheric conditions like temperature and moisture levels.
Step-by-step explanation:
The two most important conditions necessary in the formation of aircraft icing are visible moisture, such as clouds or precipitation, and temperatures near or below the freezing point. When an aircraft flies through moist air at cold temperatures, the moisture can freeze on the aircraft's surfaces, leading to ice accumulation. The temperature and pressure condition where the liquid and solid phases of water are in equilibrium is known as the melting point of ice, which is crucial to understanding aircraft icing.
Freezing point depression is a phenomenon that causes the freezing point of a liquid to be lowered by the presence of another substance, such as the salts used on roadways and aircraft surfaces to combat icing. Additionally, when water vapor rises in the atmosphere, it cools and condenses, potentially forming precipitation that can freeze upon contact with an aircraft, thereby contributing to icing. In contrast, warmer air can facilitate a faster exchange of heat, which can help in melting snow or ice.