Traffic Alert and Collision Avoidance System (TCAS I…

AIM Text

TCAS I provides proximity warning only, to assist the pilot in the visual acquisition of intruder aircraft. No recommended avoidance maneuvers are provided nor authorized as a direct result of a TCAS I warning. It is intended for use by smaller commuter aircraft holding 10 to 30 passenger seats, and general aviation aircraft.
TCAS II provides traffic advisories (TA) and resolution advisories (RA). Resolution advisories provide recommended maneuvers in a vertical direction (climb or descend only) to avoid conflicting traffic. Transport category aircraft, and larger commuter and business aircraft holding 31 passenger seats or more, are required to be TCAS II equipped.
1. When a TA occurs, attempt to establish visual contact with the traffic but do not deviate from an assigned clearance based only on TA information.
2. When an RA occurs, pilots should respond immediately to the RA displays and maneuver as indicated unless doing so would jeopardize the safe operation of the flight, or the flight crew can ensure separation with the help of definitive visual acquisition of the aircraft causing the RA.
3. Each pilot who deviates from an ATC clearance in response to an RA must notify ATC of that deviation as soon as practicable, and notify ATC when clear of conflict and returning to their previously assigned clearance.
Deviations from rules, policies, or clearances should be kept to the minimum necessary to satisfy an RA. Most RA maneuvering requires minimum excursion from assigned altitude.
The serving IFR air traffic facility is not responsible to provide approved standard IFR separation to an IFR aircraft, from other aircraft, terrain, or obstructions after an RA maneuver until one of the following conditions exists:
1. The aircraft has returned to its assigned altitude and course.
2. Alternate ATC instructions have been issued.
3. A crew member informs ATC that the TCAS maneuver has been completed.
  
  NOTE-
  
  TCAS does not alter or diminish the pilot's basic authority and responsibility to ensure safe flight. Since TCAS does not respond to aircraft which are not transponder equipped or aircraft with a transponder failure, TCAS alone does not ensure safe separation in every case. At this time, no air traffic service nor handling is predicated on the availability of TCAS equipment in the aircraft.

Source: FAA Aeronautical Information Manual · current edition · paragraph 4-4-16.

The short answer

This AIM section is FAA advisory guidance on TCAS I and II. TCAS I gives proximity warnings only; TCAS II adds traffic advisories and resolution advisories with vertical maneuvers. It explains pilot response duties and the requirement to notify ATC of any RA-driven deviation, complementing 14 CFR 91.123 and 91.113.

Research Notes

Common Questions

What is the difference between TCAS I and TCAS II?

TCAS I provides proximity warning only, for commuter aircraft holding 10 to 30 passenger seats and general aviation. TCAS II provides traffic advisories (TA) and resolution advisories (RA) with vertical maneuvers, and is required on aircraft holding 31 passenger seats or more.

How should a pilot respond to a TCAS resolution advisory?

When an RA occurs, pilots should respond immediately and maneuver as indicated unless doing so would jeopardize safe operation. For a TA, attempt visual contact but do not deviate from an assigned clearance based only on TA information.

Do I have to tell ATC if I deviate for an RA?

Yes. Each pilot who deviates from an ATC clearance in response to an RA must notify ATC of that deviation as soon as practicable, and notify ATC when clear of conflict and returning to the previously assigned clearance.

4-4-16. Traffic Alert and Collision Avoidance System (TCAS I & II)