What are the two requirements for icing to occur?

Icing typically occurs when both visible moisture in the form of water droplets and temperatures at or below freezing (0°C) are present. This is because visible water can be in the form of rain, drizzle, or even cloud droplets which can lead to ice accumulation on aircraft surfaces when temperatures drop to or below 0°C.

When temperatures are above freezing, any moisture that comes into contact with the aircraft would tend to remain in liquid form and not freeze, reducing the risk of icing. Therefore, the combination of visible water and temperatures at or below 0°C is essential for icing to be a concern for aviation safety. The other options do not capture this critical combination; hence their descriptions do not represent the true conditions that lead to icing.