Chapter 7. Navigation and surveillance systems

7.8. Traffic Collision and Avoidance System TCAS

Systems of warning of dangerous encounters of aircraft in the air (Traffic Collision Avoidance System - TCAS) intended to help pilots of aircraft in collision avoidance in airspace [9; 14]. There are four types of TCAS [56]: TCAS I, TCAS II, TCAS III, TCAS IV.


Reports to pilots of the plane about air traffic around (TA). TCAS I system is a remote monitoring system that periodically emits signals of request being taken by other aircraft. Plane responders mode «S» process the received signal and send the signal response containing information about your plane. This information is taken on board, processed and shown on the display of pilot. In addition, estimates trajectory parameters and the possibility of a collision that also displays with corresponding encoded characters.

Modern TCAS I system focused on the use the concept of ADS-B to inform the pilot of the aircraft that are nearby and can pose a threat of collision. According to this board equipment receives signals from aircraft responders mode "1090 ES" and indicates to pilot the location of the aircraft who sent it. TCAS I widely used in avionics systems of light aviation. In particular is mandatory for light aviation means of the United States (with the number of passengers from 11 to 30). In general, on the means of light aviation used integrated systems and usually feature of TCAS I follow the on-board computer system.

The use of a combined system that performs all aeronautical features can reduce the cost, dimensions and weight of equipment.


Provides overview of the surrounding airspace in case of detecting other aircraft with display them on the screen (TA). Moreover, TCAS II assesses the potential collision in the air with other aircraft in case of presence such a threat generates a message (RA) for both pilots, allowing aircraft to breed in the vertical plane and avoid a collision.


TCAS III project in addition to advisory information on air traffic (TA) should provide recommendations for avoiding collision threat (RA) in the vertical and horizontal planes.

Avoiding collision threat in the horizontal plane closely related to accuracy of the whereabouts of the conflicting aircraft. Used principles of remote monitoring in the construction of TCAS systems do not provide the desired accuracy of the relative angular coordinates. Therefore, avoid conflicts by maneuver in the horizontal plane is very risky. Because it turned technically difficult to create and implement this type of TCAS, the project was rejected.


Systems project TCAS IV involves the use GNSS with functional additions EGNOS (WAAS) and inertial navigation systems for accurate information on the location of the aircraft [54]. Based on the location of the exact coordinates will be possible to generate a trajectory of maneuver to avoid conflict in the horizontal and vertical planes. Project TCAS IV based on the use of the concept of ADS-B and digital data network for the exchange of information between the conflicting aircraft.

One of the possible options for implementing concept of TCAS IV is to create a collision avoidance function PC consisting Flight management system (FMS) (Fig. 91).

Fig. 91. The principle of the TCAS IV

During the flight ATCRBS aircraft operating in the "1090 ES", emits information about your location. Board equipment ADS-B receives these signals and after decoding provides information on the location of the aircraft, which are near to the FMS. Further FMS displays labels of adjacent planes on display of electronic display system. Moreover, function of collision warning is in continuous tracking of trajectory of movement of aircraft and checking of them to possibility of intersection with own trajectory. In case of such fact FMS automatically associated with other conflict aircraft FMS through digital line data transmission such as VDL, SATCOM or other, to compare the planned trajectories. In the case of the planned crossing 4D trajectories of aircraft collision avoidance algorithms adjusted for individual characteristics of the aircraft. New trajectory of movement provided to pilots to familiarize and approval. Thus, achieved early prevention and resolution of potential conflict between aircrafts.

Due to the unavailability of air navigation flight support to the requirements of TCAS IV, this concept is in project form. Moreover it is necessary to introduce available digital channels of data exchange, global deployment of ADS-B concept and reduce errors global satellite navigation system that takes a lot of effort associated with the deployment of terrestrial infrastructure stations differential corrections.

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Ostroumov IvanOSTROUMOV Ivan, PhD
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