What is an intruder in the context of TCAS II?

In the context of TCAS II (Traffic Alert and Collision Avoidance System), an intruder specifically refers to any aircraft that meets the criteria for detection set by the system. TCAS II is designed to monitor the airspace around an aircraft for other transponder-equipped aircraft, providing alerts and guidance to help prevent mid-air collisions. When TCAS detects another aircraft that poses a potential traffic conflict, it identifies that aircraft as an intruder.

The criteria used by TCAS II for determining an intruder include the proximity of the aircraft, its altitude, and the potential for a conflict, based on the information received from transponders. This allows pilots and air traffic control to take action based upon reliable information, improving the safety of aviation operations. Understanding this definition is crucial for comprehending how TCAS II functions in real-time to enhance flight safety.

The other choices, while related to the context of aviation and radar systems, do not accurately describe what constitutes an intruder in TCAS II.