"Climb! Climb Climb!" - TCAS explained

Imagine two aircraft at the same altitude flying towards each other. If there was no TCAS, the situation would end in a sad and tragic disaster.

Unfortunately, accidents need to happen that gaps can be filled and technology further developed. Several mid-air collisions took place in the 90‘s and due to this the TCAS came to life.

The Traffic Collision Avoidance System is carried by most of the airplanes nowadays and prevents mid-air collisions with other aircraft. TCAS scans and receives signals from transponders of other aircraft and can determine the flight direction and altitude. As soon as the TCAS detects a threat, it automatically commands aircraft 1 to immediately descend, while aircraft 2 receives the command to climb.

What is a transponder?

The transponder is a must-have communication device in busy airspaces and gives information about the current aircraft and flight. It sends signals, which are then received by the air traffic controllers. As a pilot, you will receive a transponder code of four digits by the tower of the airport of departure. This is from now on your identification number. With your transponder code, the ATC can identify you on their radar with your current altitude, cruise speed, and flight direction.

How could a TCAS look?

Now let us have a closer look at the TCAS and find out what these symbols mean:

White bordered diamond	Non-Threat Traffic – Outside of protected range – Currently 1’000 feet above and climbing
White filled diamond	Proximity Intruder Traffic – Within protected range – Currently 1’100 feet below and climbing – Not considered as a threat
Orange circle	Traffic Advisory (TA) – Within protected range – Currently 1’000 feet above and descending – Pilots being alerted that traffic is in range (“Traffic!, Traffic!“)
Red square	Resolution Advisory (RA) – Within protected range and considered as a threat – Currently 100 feet below and climbing – Pilots receiving aural command to immediately climb or descend (“Climb! Climb! Climb!” or “Descend! Descend! Descend!“)