TRAFFIC COLLISION AND AVOIDANCE SYSTEM
ANOTHER SET OF EYES IN THE SKY
ONE OF MANY systems you will find concurrently on turbojet aircraft is the Traffic Collision and Avoidance System, or TCAS. Following years of improvements and technological advances, TCAS provides basic and advanced aircraft avoidance through monitoring and interpreting of Mode C and Mode S transponders.
TCAS systems today can provide not only traffic information to supplement visual avoidance, but it can also provide escape guidance from the intruder aircraft. Early TCAS systems merely provided the azimuth of the intruder as well as its relative altitude. Now with the TA/RA mode equipped and enabled, you will receive a resolution advisory for the most expeditious way of escaping a collision.
Using escape path and trend information from each aircraft, the TCAS system determines whether a climb or descent is more appropriate for each respective aircraft. It then displays and aurally warns the crew by verbal and visual resolution advisories.
The TCAS systems of two equipped aircraft will even communicate to coordinate the escape. If one aircraft issues a descent advisory to the crew, the opposite crew will receive a climb advisory. The systems will continue to calculate the paths of the two aircraft to determine whether the current resolution is sufficient, or requires a higher rate of climb or descent. It will then issue a second advisory to either increase or decrease, or even maintain, a recommended vertical speed.
The FARs provide language involving a deviation of an ATC clearance in the event of a resolution advisory. The crew is to advise ATC as soon as practicable after such an incident. It is important to remember that nothing relieves the crew from being vigilant to see and avoid traffic; however, TCAS helps to identify and maintain visual contact with aircraft in high-traffic environments.