What is the primary purpose of beacons at airports?

The primary purpose of beacons at airports is to provide navigational guidance at night. Beacons emit light signals or radio waves, which help pilots navigate to and from the airport, particularly in low visibility conditions such as nighttime or adverse weather. These signals can indicate the location of the airport and assist in aligning the aircraft for approach and landing.

Additionally, while the other choices involve aspects of airport operations, they do not capture the primary function of beacons. For instance, indicating runways and marking the perimeters are accomplished through different types of signage and lighting systems. Signalling to other aircraft is typically done using radio communications or transponder systems rather than visual beacons. Thus, the role of beacons is fundamentally rooted in enhancing navigational safety and efficiency, particularly when visibility is compromised.