What conditions are necessary for ice to form on an aircraft?

For ice to form on an aircraft, the presence of visible moisture is crucial, and this moisture must come into contact with a surface that is at or below 0 degrees Celsius (32 degrees Fahrenheit). When the temperature of the aircraft's surface is below freezing, the liquid droplets in visible moisture can freeze upon contact, causing ice accumulation.

This requirement emphasizes the significance of both temperature and moisture conditions. Specifically, even if the air temperature is above freezing, if the aircraft's surfaces are cold enough due to prior flight conditions or other factors, ice can still form when visible moisture, such as clouds, drizzle or rain, interacts with those surfaces.

Understanding these conditions is vital for pilots, as ice can severely affect an aircraft's performance by adding weight, disrupting airflow, and increasing drag. Hence, monitoring both moisture presence and surface temperature is essential in avoiding icing conditions.