Chapter 8. Communication equipment

8.9. ATC radar beacon system

According to regulatory documents all Aircraft must be equipped aircraft with transponders(Air Traffic Control Radar Beacon System - ATCRBS). The main function of ATCRBS is receiving signals from ground-based radar, combining the information of the response message and send again back to the radar equipment (Fig. 130).

According to the mode of functioning there are three ATCRBS modes "A", "C", "S"

Fig. 130. The principle of ATCRBS

The signal responses of ATCRBS in mode "A" contains information only about the identification number of the aircraft(Fig. 131). Responses in the mode "C" contain information about barometric altitude of the AIRCRAFT (Fig. 131).

Fig. 131. Modes "A" and "C"

ATCRBS mode "S" allows to send through of the signal-response any information, as well as to address this information to specific Aircraft via a coded address (Fig. 132).

Fig. 132. Use of ATCRBS in Mode «S»

The frequency of a transmitter mode is 1090 MHz ± 0,06 in receiving - 1030 MHz. In addition, ATCRBS Mode «S» working with TCAS, answering his queries (Fig. 132). With the ability to transfer data and addresses to the recipient "S" mode is used by TCAS systems for the mutual exchange of data while selecting maneuvers to resolve the conflict.

One of the important functions assigned to "S" mode, is to ensure the functioning of the concept of ADS-B (Fig. 132). ATCRBS that supports 1090 ES after a certain period of time, generates and emits an informational message in a specific format. These messages contain information about the location of the aircraft, absolute altitude, aicrafts’ code and other data. The information transmitted in the mode of 1090 ES, is received by other aircraft equipped with appropriate equipment, and ground-based receiving station. The structure of the digital messages in ES format shown in Fig. 133.

Fig. 133. The structure of the digital messages in 1090 ES format

In general on-board equipment ATCRBS consists of two blocks, two antennas and remote control (Fig. 134). The remote control is usually combined with a remote control system TCAS II and placed in the cab Aircraft. Information about the actual altitude of aircrafts’ flight , ATCRBS receives from a barometric altimeter, and other information from the FMS and other avionics systems Aircraft. To ensure the reliability of using two antennas, which are usually placed below the Aircraft in the bow.

Fig. 134. Interaction ATCRBS with other systems of aircraft

The main manufacturers of ATCRBS are Rocwelcolins, Honywell, Thales and ACSS.

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Avionics training in details by
Ostroumov IvanOSTROUMOV Ivan, PhD
Associate Professor, www.ostroumov.sciary.com