TCAS -TCAS COMPUTER
Purpose
The TCAS computer is the main component of the TCAS. It controls these functions:
*
Surveillance
*
Tracking
*
Advisory
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Air-to-air maneuver coordination.
The TCAS computer sends signals alert the flight crew to:
*
Maintain the current flight plan
*
Make flight maneuvers to avoid a possible collision with other airplanes in the area.
Physical Description
The TCAS computer is a 6 MCU size unit that weighs 28 lbs.
Functional Description
The TCAS computer transmits 1030 MHz pulse-coded interrogation signals. It receives 1090 MHz pulse-coded reply signals from intruder airplanes with a transponder.
Front Panel LED Indications
Two alphanumeric LEDs show fail conditions of the TCAS computer and systems that interface with the TCAS computer.
Front Panel Self-Test
Push the test switch on the front panel to start a test of TCAS. The applicable LED indications come on.
Software Loading
The TCAS computer is software loadable. Use the maintenance access terminal (MAT) to load the operational software into the TCAS computer.
Training Information Point
The TCAS computer receives data load information from the left central maintenance computing function (CMCF) only. You must use the left CMCF when you want to data load the TCAS computer.
Use the central maintenance computer switch control from the other functions menu on the MAT to select the active CMCF.
Front Panel Connectors
There are two connectors on the front panel. One for automated test equipment and one to load software. But, use the MAT to load software.
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TCAS -TRANSPONDER PANEL
General
The transponder panel controls the TCAS computer to send the selected display data to the AIMS.
Transponder Mode Selector
The transponder mode selector lets the flight crew select one of these two TCAS modes:
*
TA ONLY mode. In this mode, all intruder traffic except RAs show
*
TA/RA mode. In this mode, all intruder traffic shows. This is the normal mode of operation for TCAS.
Above-Normal-Below Switch
The above-normal-below (ABOVE-NORM-BELOW) switch controls the amount of altitude that shows for the TCAS display on the captain’s and first officer’s ND.
The switch has these three positions:
*
ABOVE; this makes the ND show intruder airplanes that are from 2700 feet below to 9900 feet above present airplane altitude
*
NORMAL; this makes the ND show intruder airplanes that are within 2700 feet below or above present airplane altitude
*
BELOW; this makes the ND show intruder airplanes that are from 9900 feet below to 2700 feet above present airplane altitude.
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TCAS -TCAS DIRECTIONAL ANTENNA
General
The TCAS uses a top and bottom directional antenna. The antennas are the same and interchangeable.
Physical Description
The directional antenna is a phased array antenna. Four array elements on the antenna make up the array. Each element has a color coded connector. The TCAS computer sends the array elements transmit interrogation signals with different phases. This makes the interrogation signal directional.
To attach the antenna, match the color of the coaxial cable with the color coded band on the array element connector.
Four screws fasten each antenna to the airplane. The radiation side of the antenna shows "FWD" and "DO NOT PAINT".
CAUTION: DO NOT PAINT THE RADIATION SURFACE OR THE BACKPLATE OF THE ANTENNA. PAINT DOES NOT PERMIT THE ANTENNA TO RADIATE OR RECEIVE RF SIGNALS.
CAUTION: TO PREVENT DAMAGE TO THE ANTENNA CABLES, DO NOT PULL ON THEM.
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 match the coax cable to the correct element, the TCAS computer reports an antenna fault.
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