What does prevailing visibility refer to?

Prevailing visibility is defined as the greatest distance at which objects can be seen throughout at least half of the horizon circle. This measurement is crucial for pilot and air traffic control operations as it provides a clear indication of the visibility conditions affecting flight safety. It typically considers the most favorable conditions and is important for determining whether weather conditions are suitable for various flight operations, including takeoff and landing.

In contrast, the other definitions do not capture the complete picture needed for prevailing visibility. The greatest distance visible in a specified sector pertains to visibility in a limited area rather than the entire horizon, which may not reflect overall conditions. The maximum distance runway or lights can be seen focuses on specific reference points rather than accounting for visibility across the horizon. Lastly, the greatest distance visible into total obscuration does not directly relate to prevailing conditions, as it deals with scenarios involving obscured visibility rather than a clear maximum distance across the horizon. The concept of prevailing visibility specifically requires assessment throughout more than half of the horizon, which aligns precisely with the correct definition provided.