In good weather, how many miles away can lookouts typically spot planes with the naked eye?

Lookouts can typically spot planes with the naked eye at a distance of about 15 miles in good weather conditions. This range is influenced by several factors, including visibility, the size and altitude of the aircraft, and the observer's line of sight. In ideal conditions, such as a clear day without obstructions, trained lookouts can often see aircraft well before they approach for landing or takeoff, making this distance a commonly accepted standard in aviation.