Highlight significant light sources, such as beacons and cities, out to a distance of at least how far?

Highlighting significant light sources, such as beacons and cities, out to a distance of at least 15 nautical miles is crucial for ensuring safe navigation in terrain flight operations. This practice helps pilots recognize these important visual references from a considerable distance, enhancing situational awareness and orientation during flight.

By observing these light sources from 15 nautical miles away, pilots can better prepare for approach and landing phases, as well as effectively navigate around populated areas and hazardous terrain, particularly at night or in low-visibility conditions. This distance provides a reasonable margin to make necessary adjustments to the flight path, ensuring a smoother and safer operation.

While shorter distances like 5 NM and 10 NM could assist in navigation, they may not offer the same level of safety as identifying light sources from further away, where pilots can make more informed decisions ahead of time. The option of 20 NM may be excessive since beyond a certain point, visual references become less useful due to limited resolution and detail. Thus, 15 NM strikes an effective balance between visibility and practicality for air navigation purposes.