What condition does the Airport Surveillance Radar (ASR) primarily monitor?

The Airport Surveillance Radar (ASR) primarily monitors terminal airspace, which encompasses the area surrounding an airport where aircraft are in controlled flight during takeoff, landing, and while taxiing. The ASR is designed to provide air traffic controllers with real-time information about the positions and movements of aircraft operating within this critical zone, helping to ensure safe and efficient operations.

In addition to monitoring aircraft positions, ASR systems can detect and display the trajectories of aircraft, which is crucial for managing the flow of air traffic, especially in busy airport environments. This capability allows controllers to make informed decisions regarding aircraft separation, sequencing for takeoffs and landings, and overall airspace management in the terminal area.

While other choices hint at relevant aspects of air traffic control, such as en route aircraft positions or ground traffic, they don't capture the primary function of the ASR, which is specifically focused on the terminal airspace. Similarly, while weather changes are a significant concern for aviation safety, they are typically monitored by meteorological systems and not the ASR. Thus, the emphasis of the ASR on terminal airspace is what makes it a critical component of ensuring safe aircraft operations near airports.