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Training Information Point

An antenna connection includes the coax cable and an antenna element. The TCAS computer checks the resistance of each antenna connection at power-up. The TCAS computer reports an antenna fault when it detects that the resistance of the connection is out of range. If you do not connect the coax cable to the correct element, the TCAS computer reports an antenna fault.






The TCAS computer transmits interrogations to and receives

replies from other airplanes. Airplanes that are tracked by

TCAS are called targets. The TCAS computer uses these

replies and data from other airplane systems to calculate if a target is a collision threat. The TCAS computer can communicate with other airplanes that have TCAS. The two TCAS computers can use the shared data to perform coordinated maneuvers and avoid potential collisions.

The TCAS computer also gets analog and digital inputs from other airplane systems. These inputs control TCAS and provide data for TCAS to track intruders. The TCAS computer sends display data to the common display system (CDS) display electronic units (DEUs).

The TCAS computer has these circuits:

Input/output (I/O)

Speech Processor

Central processing unit (CPU) and memory

Suppression circuit

Signal Processor



Beam steering and attenuator




The I/O circuit gets this on-board airplane systems data:

Magnetic heading data from the left ADIRU

Coordination and control data from the ATC transponder system

Barometric altitude from the left or right ADIRU from the

active ATC

Radio altitude from the radio altimeters

Resolution advisory status from the DEUs

Landing gear down discrete from the landing gear lever


Aural inhibit discrete interface with the GPWC

Aural inhibit discrete interface with the weather radar

Air/ground data from the PSEU.


Program pins set these parameters in the TCAS computer:

Altitude limits

Aural warning volume levels

Self test inhibits

Standby on ground

Intruders on ground disabled.

The I/O circuits send this data to the CPU.


The CPU gets the data from the inputs of the I/O and puts it into

memory. The CPU combines the input data and the data it

receives from the signal processor. The CPU makes the

necessary calculations for the TCAS displays and aural


The CPU sends TCAS display data to the CDS DEUs. It shows on these indicators:

Attitude indicators (AI)

Navigation display (ND)


The CPU sends the display data to the flight data acquisition unit (FDAU).

It also sends signals through the speech processor circuits to the REU to make TCAS aurals.

Signal Processor

The signal processor gets bearing information from the

receiver/processor and changes it to digital signals. The

signal processor does these functions:

Uses time measurement logic and the bearing information to calculate the intruder airplane range and bearing

Detects the mode C or mode S pulses

Controls the suppression circuit to send the suppression

pulse when TCAS transmits

Makes all signals necessary to receive and transmit mode S and ATCRBS interrogations through the receiver/transmitter circuits.



The suppression circuit sends a suppression pulse when the TCAS computer transmits. The TCAS computer receives a suppression pulse when an onboard ATC transponder or DME interrogator system transmits. This suppression pulse stops the TCAS computer receiver and transmitter circuits.

Speech Processor

When there is a TA, RA, or during a self-test, the TCAS computer sends signals to the speech processor. The speech processor sends the aural alerts to the REU. The REU sends them to the flight compartment.

During aural annunciations the GPWC sends an analog discrete to the TCAS computer to prevent TCAS advisories.

During predictive windshear annunciations the weather radar sends an analog discrete to the TCAS computer to prevent TCAS advisories.

Receiver Processor

The receiver gets the target replies from the antennas. The receiver uses the phase of the received signals to determine the bearing of the target. The receiver sends the signal to the signal processor to calculate the range to the target. The receiver decodes the target altitude from the reply signal. The receiver also receives and decodes coordination replies from targets equipped with TCAS.



The transmitter has a 1030 MHz output. The transmitter gets signals from the signal processor. The transmitter sends the formatted signals to the beam steering and attenuator (ATT) circuits. The transmitter controls the beam steering circuits and whisper/shout attenuator.

Date: 2016-03-03; view: 2083

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