What does a secondary radar system provide that a primary does not?

A secondary radar system enhances the capabilities of surveillance and tracking by providing additional information that a primary radar system does not. Particularly, secondary radar systems rely on transponders in aircraft that respond to interrogations from the radar system, allowing for the transmission of more detailed data.

The key differentiator is that secondary radar systems, through their interaction with the transponder, can offer identity—confirming which aircraft it is based on the unique codes each transponder sends—and altitude information, which is essential for air traffic control and maintaining safe distances between aircraft. This contrasts with primary radar, which primarily detects the position of objects and provides distance and azimuth (direction) data based on the reflection of radar signals.

Identity is crucial for air traffic management, as it allows controllers to track specific aircraft more efficiently and helps in the identification of potential conflicts. Altitude data is equally important to ensure that planes are flying at designated flight levels, facilitating safe separation and efficient routing in busy airspaces. Thus, secondary radar systems are vital for modern aviation operations due to their capability to convey both identity and altitude, aspects that primary radar alone cannot provide.