A Boeing plane takes off or lands every two seconds, somewhere in the world! Any given point of time more than 12,000 aircraft are airborne. So how do they avoid mid-air collision? TCAS (Traffic Collision and Avoidance System) in an aircraft is designed to avoid mid-air collisions between aircraft. It scans the surrounding airspace once each second and communicates automatically with other aircraft equipped with a corresponding active transponder. It sends out interrogation signal and responds to other aircrafts’ TCAS interrogation signals. If potential collision is noticed, TCAS II will issue a Resolution Advisory (RA) to the pilots on both aircraft a verbal and visual corrective or preventive vertical maneuvering commands to avoid a collision. TCAS II measures the intruder in terms of time interval rather than distance. TCAS is mandatory on aircraft carrying more than 19 passengers.
Usually intruder threat region is 4minutes. The timing is dependent on aircraft speed and altitude. On the display unit, the position, shape and color determines the intruders threat level and position.
