What condition is optimal for detecting icing conditions?

The optimal condition for detecting icing is when there is visible moisture at or below freezing temperatures. This is because icing typically occurs when supercooled water droplets are present in the atmosphere, which can happen at temperatures below freezing. These supercooled droplets remain in liquid form despite being below the freezing point, and when an aircraft flies through this environment, the droplets can freeze upon contact with the aircraft's surfaces, leading to ice accumulation.

In contrast, cruising altitude with dry air does not typically present icing conditions since there is an absence of moisture necessary for ice formation. Warm, humid air can lead to cloud formation and so forth, but if temperatures are above freezing, icing is less likely to occur. Lastly, clear weather conditions generally indicate a lack of significant moisture, decreasing the likelihood of encountering icing conditions. Therefore, for optimal detection of icing, the presence of visible moisture coinciding with freezing temperatures is crucial.