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Traffic Collision Avoidance System

In aviaation industry a system commonly known as TCAS (Traffic Collision Avoidance System) was developed in order to eleminate the risk of mid air collisions between aircraft. It is a promising computerised technology that monitors the monitors the airspace around an aircraft, independent of air traffic control, and warns pilots of the presence of other aircraft which may present a threat of mid-air collision (MAC).

It is an implementation of the Airborne Collision Avoidance System mandated by International Civil Aviation Organization to be fitted to all aircraft over 5700 kg or authorised to carry more than 19 passengers.

In modern glass cockpit aircraft, the TCAS display may be integrated in the Navigation Display; in older glass cockpit aircraft and those with mechanical instrumentation, a TCAS display replaces the mechanical Instantaneous Vertical Speed Indicator (which indicates the rate with which the aircraft is descending or climbing).

TCAS strategically maintains communication between all aircraft equipped with an appropriate transponder. Each TCAS-equipped aircraft "interrogates" all other aircraft in a determined range about their position (via the 1030 MHz radio frequency), and all other craft reply to other interrogations (via 1090 MHz). This interrogation-and-response cycle may occur several times per second.

Through this constant back-and-forth communication, the TCAS system builds a three dimensional map of aircraft in the airspace, incorporating their bearing, altitude and range. Then, by extrapolating current range and altitude difference to anticipated future values, it determines if a potential collision threat exists.

It should be noted that TCAS and its variants are only able to interact with aircraft that have a correctly operating transponder. The next step beyond identifying potential collisions is automatically negotiating a mutual avoidance maneuver between the two (or more) conflicting aircraft. These avoidance maneuvers are communicated to the flight crew by a cockpit display and by synthesized voice instructions.

There are some variations of TCAS such as TCAS 1, TCAS 2, TCAS 3. TCAS I is the first generation of collision avoidance technology. It is realtively cheap technology but less capable than the modern TCAS II system, and is mainly intended for general aviation use. TCAS II is the second and current generation of TCAS, used in the majority of commercial aviation aircraft. It offers all the benefits of TCAS I. TCAS III was the "next generation" of collision avoidance technology which underwent development by aviation companies such as Honeywell.

Compiled by Edward Apurba Singha

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