What does TCAS I primarily provide?

Answer: B — Proximity warning.

TCAS I, or Traffic Collision Avoidance System I, primarily provides proximity warnings to the pilot about nearby aircraft that may be in a potential conflict situation. It is designed to alert the crew regarding the proximity and potential risk of collisions with other aircraft based on their relative positions and altitude. This system is focused on enhancing situational awareness by providing alerts that allow pilots to visualize and react to surrounding traffic. In contrast, other options refer to functionalities that are characteristic of more advanced versions of the TCAS system. For example, TCAS II offers traffic and resolution advisories as well as recommended maneuvers to avoid conflicting traffic. Additionally, while altitude alerts do provide critical information, they are not the primary function of TCAS I. Instead, these alerts come from other onboard systems aimed at maintaining altitude awareness. Overall, the emphasis of TCAS I on proximity warnings is crucial for pilots in maintaining safety by being aware of nearby traffic.