Traffic Collision Avoidance System (TCAS)

or

Traffic Alert and Collision Avoidance System (TCAS)

Definition

Airborne Collision Avoidance System (ACAS). An aircraft system based on secondary surveillance radar (SSR) transponder signals which operates independently of ground-based equipment to provide guidance to the pilot on potential conflicting aircraft that are equipped with SSR transponders.

Source: ICAO Annex 10, vol. IV

Description

The Airborne Collision Avoidance System II (ACAS II) was introduced in order to reduce the risk of midair collisions or near midair collisions between aircraft. It serves as a last-resort safety net irrespective of any separation standards.