What type of aircraft can use Mode S for communication?

Mode S, or Mode Select, is a radar transponder system that allows for selective communication between air traffic control and specific aircraft. It incorporates advanced functionalities such as Traffic Collision Avoidance System (TCAS) capabilities, which is critical for enhancing safety in busy airspace.

Aircraft using TCAS are equipped with this additional safety feature that relies on Mode S transponders to exchange information about their positions and velocities with other aircraft. This enables TCAS to provide timely alerts and advisories to pilots about potential traffic conflicts, thereby improving situational awareness and facilitating collision avoidance actions.

While other aircraft types might be able to use Mode S under specific circumstances, the question emphasizes the capability specifically linked to TCAS usage, which requires Mode S for effective functioning. This precise relationship illustrates why the correct response highlights aircraft that actively utilize TCAS within their operational systems.