What must an aircraft be equipped with for the TCAS system to identify it?

The TCAS (Traffic Alert and Collision Avoidance System) relies on transponder technology to function effectively. A transponder is a device on the aircraft that sends out specific information, such as position and altitude, which is then received by other aircraft and ground systems. When an aircraft is equipped with a transponder, it can communicate its identity and altitude to the TCAS unit, which analyzes this data to detect potential collision risks with nearby aircraft.

The TCAS system itself does not rely on radar, GPS, or a traditional altimeter for its primary function of collision avoidance. While radar can be part of broader air traffic control operations and GPS aids in navigation, they are not directly involved in the TCAS’s detection capabilities. An altimeter measures altitude but is not the medium through which TCAS identifies other aircraft. Thus, the transponder is critical for TCAS to operate and identify surrounding aircraft effectively.