Definition
A description of the operational capability of TCAS I (Traffic Alert and Collision Avoidance System, Version I), which detects nearby transponder-equipped aircraft and issues Traffic Advisories (TAs) alerting the pilot to their position and approximate altitude, but does not issue Resolution Advisories (RAs) telling the pilot how to maneuver to avoid a collision.
Plain English
TCAS I tells the pilot that another aircraft is nearby and where it is, but it does not tell the pilot what to do about it. The pilot must decide how to avoid the traffic.
Context Anchor
Seen in aircraft equipment descriptions, traffic-alert system discussions, and cockpit alerts during flight near other aircraft.
Derivation
TCAS stands for Traffic Alert and Collision Avoidance System. The Roman numeral I marks it as the first and simplest version of the system. A more capable version, TCAS II, adds resolution advisories that tell the pilot to climb or descend.
Why Pilots Care
Pilots must visually locate and avoid traffic themselves since the system provides no guidance on what maneuver to fly.
Intuition Check
Do not assume all TCAS equipment gives avoidance commands. TCAS-I gives traffic alerts only; it does not tell the pilot to climb or descend.
Example Sentence 1
Because the aircraft was equipped with TCAS I, the crew received a traffic advisory but had to visually locate the other aircraft and decide on their own avoidance action.
Example Sentence 2
During the preflight briefing the instructor noted that TCAS-I generates traffic advisories only and requires the pilot to maintain visual separation.