During surveillance mode, how active is TCAS with transponder transmissions?

In surveillance mode, TCAS (Traffic Alert and Collision Avoidance System) operates in a passive manner. This means that it primarily listens for transponder transmissions from surrounding aircraft rather than actively sending out its own signals. By monitoring these signals, TCAS can gather information about nearby aircraft's altitude, position, and intentions, which is essential for assessing potential collision threats.

The primary purpose of this approach is to enhance situational awareness without causing additional radio traffic, allowing for a more effective monitoring of the airspace around the aircraft. This passive listening mode plays a crucial role in maintaining safety by ensuring that the TCAS can quickly identify nearby traffic based on the responses received from active transponders.