Traffic Alert Collision Avoidance System (TCAS)

[Ref Jeppesen, FAA-H-8083-15B – Instrument Flying Handbook Page 5-30 to 5-34, FAA AIM]

What ‘s Traffic Alert and Collision Avoidance System (TCAS) ?

TCAS is an airborne collision avoidance system (ACAS), that is based on radar beacon signals which operates independent of ground-based equipment.

Traffic alert systems receive transponder information from nearby aircraft to help determine their relative position to the equipped aircraft. They provide three-dimensional location of other aircraft and are cost effective alternatives to TCAS equipage for smaller aircraft.

Difference between TCAS-I and TCAS-II?

TCAS- I: TA only ;


TCAS-I generates traffic advisory (TA) only – approximate bearing and relative altitude of aircraft with a selectable range;
TCAS-II generates traffic advisories (TA) , AND resolution (collision avoidance) advisories (a.k.a RA) in the vertical plane.


Resolution advisories (RA) –  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 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.
  2. 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.

TCAS does not respond to aircraft which are not transponder equipped or aircraft with a transponder failure, so TCAS alone does not ensure safe separation in every case

Airmanship! TCAS does not alter or diminish the pilot’s basic authority and responsibility to ensure safe flight.

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