A TCAS II provides the intruder relative position (Traffic advisory and proximate traffic) and possibly an indication of a collision avoidance maneuver (Resolution Advisory) within the vertical plane only, by comparing the mode C pressure altitudes of the aircraft. The instrument determines the bearing of an intruder by using two specific antennas. The TCAS II can only operate normally with a fully operational transponder since it uses the replies from the transponders of other aircraft. Therefore, if other aircraft do not have a serviceable transponder no protection will be provided against them. In the same way, if any of the concerned aircraft does not have the altitude reporting capability from the mode C transponder, the TCAS II will only issue Traffic Advisories (TA).

The TCAS II can display up to 30 traffic simultaneously. This means that the system can handle a significant number of traffic alerts and resolution advisories at the same time, providing crucial information to the flight crew for collision avoidance. The display of these advisories is essential for the safe operation of the aircraft, especially in busy airspace where multiple aircraft may be in close proximity.