What is the primary function of beacon anti-collision lights?

The primary function of beacon anti-collision lights is to signal the presence of an aircraft, especially in critical phases of flight where awareness of the aircraft's position is crucial for safety. These lights, typically mounted on the top and bottom of the aircraft, serve to make the aircraft visually detectable to other aircraft and individuals on the ground, particularly during low visibility conditions.

While it is essential to indicate when an aircraft is operational and to enhance visibility, the beacon lights do not particularly focus on signaling that the engines are running as one of their primary functions. Instead, they are designed to alert nearby aircraft and ground personnel to the aircraft's presence and potential movement. This is especially important when the aircraft is taxiing, taking off, or landing, enhancing overall safety in crowded airspaces.

Other options like illuminating runways or signaling for ground navigation or enhancing passenger visibility do not align with the core purpose of beacon anti-collision lights, which is primarily centered around the aircraft's presence and collision avoidance.