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.
TCAS - FUNCTIONAL DESCRIPTION
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
· 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.
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.
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.
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.