What does a paired primary target signify?

A paired primary target indicates that an aircraft is being tracked by secondary radar, which means that the aircraft's transponder is providing information to the radar system. Secondary radar is used to receive data such as aircraft identification, altitude, and other data that primary radar alone cannot provide. This is critical for air traffic control as it enhances situational awareness and allows controllers to manage air traffic more effectively.

In contrast, primary radar merely detects the object's physical presence and returns a radar echo, without additional information such as the aircraft's altitude or identity. Hence, option B is correct because paired primary targets show that the aircraft has a secondary radar contact and is actively transmitting its transponder signal, allowing controllers to maintain better communication and tracking of the aircraft's progress.

The other options do not accurately define what a paired primary target represents. For instance, an aircraft on final approach is not specifically indicated by the status of being paired; secondary radar contact doesn’t inherently mean the aircraft is below safe altitude, nor does it directly indicate proximity to controlled airspace. Thus, the context of radar tracking and transponder usage clarifies that the essence of a paired primary target is centered on secondary radar contact.