top of page

TCAS (Traffic Alert and Collision Avoidance System)

Mar 6, 2023

Close encounters in flight.

Written by: Luz Rubio, Nahuel Terenzi, Facundo Rocha


Air transportation industry has proven resilient to external shocks, proof of which is the current accelerated recovery from COVID-19, the worst crisis in aviation history. Continued growth in operations means that our skies are becoming increasingly congested, with multiple aircraft flying at the same time in close proximity to each other, requiring safer operations and technological advances. In the 1980s, this became evident, so TCAS was introduced to the industry to help pilots and air traffic controllers avoid collisions by alerting the pilot and indicating the evasive maneuver, independent of air traffic control (ATC) and navigation systems.


What is TCAS?

The ‘Traffic Alert and Collision Avoidance System’ (TCAS) is designed to scan for, detect, and interrogate the transponders of other aircraft in the nearby airspace vicinity. When TCAS detects that an aircraft’s distance or closure rate becomes critical, it generates aural and visual annunciations for the pilots. Since 2000, TCAS is mandatory on all aircraft types which carry more than 30 passengers.

How does it works?

The correct operation of the TCAS system depends directly on the Transponder. Each aircraft has a Trasponder, whose function is to provide air traffic control personnel with information about the aircraft in flight, such as its identification, position, speed, etc. Thanks to this, the TCAS system of each aircraft interrogates the Trasponders of the other aircraft in operation and collects information about their distance, speed and altitude. After processing this data, TCAS can send two different alerts. In case of an aircraft in the vicinity it sends an alert called TA (Traffic Advisory), these warnings are indicated to the crew by an audible message "Traffic, Traffic" and by amber signals on the navigation screen indicating the position of the intruder aircraft. On the other hand, in the case of an intruder aircraft too close to its own, it sends a type of RA (Resolution Advisory) alert indicating what evasive maneuvers the pilots of each aircraft should perform to avoid collision. A Resolution Advisory is indicated to pilots by an audible message indicating the type of vertical maneuver to perform ("Climb", "Descent", "Hold", "Adjust", "Monitor", etc.), Green and red zones on the Vertical Speed Indicator (VSI) materializing the 'fly-to' and 'forbidden' vertical speed areas and finally, red signals on the Navegation Display materializing the threat aircraft.

Safety is essential in aviation.

Since its implementation, TCAS has brought more safety to aviation, as its alerts and indications help pilots to perform more precise and safer maneuvers. Even so, the aviation world continues to work on improving aircraft safety systems and incorporating new and safer technologies. A clear example of this is the U.S.-developed NextGen program, which through a series of interrelated programs, portfolios, systems, policies and procedures is fundamentally changing aviation communications, navigation and surveillance. Within its scope are airport infrastructure improvements, new air traffic management technologies and procedures, and environmental and safety-related improvements.

The future is today....

Airbus developed a new system called AP/FD TCAS, which complements the role played by the TCAS system, allowing the aircraft to resolve the issued alert on its own. In other words, the basic TCAS systems required pilots to disconnect the Auto Pilot and perform the evasive maneuver manually. With this new system, the Auto Pilot/Flight Director is automatically in charge of responding to the indications issued by the TCAS, so pilots alone must monitor the situation and be alert in case they are required to take control. The maneuver will be performed by the aircraft by itself, as long as the AP (Auto Pilot) is connected. Otherwise, the TCAS sends an alert and the indications to follow are sent to the FD (Flight Director), since it is a system that pilots are confident to and it is easier for them to resolve the alert.

An indispensable element for the installation of the AP/FD TCAS system is to have the ADS-B (Automatic Dependent Surveillance Broadcast) system. In this system, the aircraft determines its position through GPS signals. This information can be received by air traffic control ground stations as well as other aircraft to provide nearby traffic information. ADS-B equipment is currently mandatory in the United States and Europe.

To wrap up.

As frequent airline passengers, it is important for us to be aware of the active role that aviation authorities and manufacturers play in continually developing a safer flying environment for people and goods. TCAS was one of the first attempts to increase flight safety, and now, 40 years after its first development, it is still very important for flight safety and has been complemented by other safety systems such as ADS-B or NEXT GEN that will further increase it.

So let's keep flying and contributing to the evolution of the magnificent air transport industry.


Fast 45 & 52 magazine - Airbus

bottom of page