TRAFFIC COLLISION AND AVOIDANCE SYSTEM is a system that provides the visual and Aural warning to the pilots flying in the vicinity of another a/c, and even guides the a/c to maneuver safely to prevent a collision. The TCAS can only see the A/c that has Transponder on board, the A/c with no Transponder or with faulty Equipment on board remains invisible to the system.
TCAS has a display screen installed in the cockpit or the inputs can be displayed on an Airborne Weather radar screen, or an EFIS system. The pilot is guided to maneuver the a/c safely from the potential traffic, with continuous information of altitude and bearing of the other traffic.
Hollow White or Black Diamond means Other Traffic = Caution of position of traffic that is at least 6 N.M away from the a/c and is more than 1200 feet above or below the a/c altitude.
Solid White or Black Diamond means Proximate Traffic = Caution of position of traffic that is less than 6 N.M from the a/c and is less than 1200 feet above or below the a/c altitude.
Yellow Circle means Traffic Advisories (TA) = Warning of position of traffic that is approximately 30-50 seconds away from potential collision.
Red Square means Resolution Advisories (RA) = Warning of position of traffic that is approximately 15-30 seconds away from potential collision.
TCAS 1- gives Traffic Advisories only, it does not give Resolution Advisories, it can only display the information of the other traffic operating in the vicinity of the a/c, if traffic has Mode “A” Transponder it displays bearing of the a/c and will also show Relative Altitude (Relative Altitude = Altitude with reference to a/c’s own altitude), if the traffic has Mode “C” Transponder on board.
It does not give a course of action to avoid the collision.
TCAS 2- Same as TCAS 1 it also gives Traffic Advisories as well as Resolution Advisories in vertical plane. It can only give a course of action to avoid the collision from traffic in vertical plane, it can not give a course to maneuver the a/c in horizontal plane.
It requires both a/c to have Mode “S” transponder on board.
It uses Vertical Speed Indicator to show the required maneuver to avoid collision in Green and the dangerous maneuver turning Red.
Example – if the required maneuver to avoid collision is to climb at 1000 feet per minute. All of the area at VSI indicating Descent or below 1000 feet climb turns Red and only area above 1000 feet climb on VSI will remain green.
TCAS 3- Same as TCAS 2, it also gives Traffic Advisories as well as Resolution Advisories in vertical plane as well as in horizontal plane. It can give a course of action to avoid the potential collision from traffic in vertical plane as well as horizontal.
It requires both a/c to have Mode “S” Transponder on board.
Indian Regulations require that-
1. All Twin Jets having seating capacity of less than 10 passengers or Maximum certified Take off mass below 5700 kg should have TCAS 1 on board
2. All a/c having seating capacity of 10-19 passengers or Maximum certified Take off mass below 5700 kg should have TCAS 1 on board.
3. All a/c having seating capacity of 20-30 passengers or Maximum certified Take off mass in excess of 5700 kg should have TCAS 2 on board
4. All a/c having seating capacity of 30 passengers or Maximum payload capacity of 3 tons should have TCAS 2 on board.