*
Mode S (squitter).
The TCAS detects, tracks, and monitors all of the airplanes that have ATCRBS or mode S transponders. The TCAS operates with the ATC/Mode S transponders to interrogate traffic airplanes and calculate if it is a threat.
All airplanes with TCAS can calculate coordinated commands to avoid possible collisions with traffic airplanes.
The TCAS does not track airplanes that do not have a transponder.
Whisper-Shout Interrogation
The TCAS uses an ATCRBS all-call whisper-shout interrogation to search for airplanes that have an ATCRBS transponder without TCAS. The whisper-shout technique changes the strength of the interrogation pulse to interrogate intruders at different ranges. The airplanes that are near detect the lower power (whisper) interrogations. The airplanes that are farther away detect the higher power (shout) interrogations.
Mode S Interrogation
The TCAS listens for mode S signal transmissions from airplanes that have mode S transponders. The signals contain a 24-bit airplane identification code. When the TCAS receives a valid airplane identification signal, the identification of that airplane goes on a roll-call list in the TCAS computer. The TCAS then interrogates the mode S transponder of the traffic airplane with the discrete 24-bit airplane address on the roll-call list.
TCAS Data Calculation
When the TCAS interrogates a traffic airplane with TCAS, the reply signal from the airplane contains the airplane identification and altitude.
The TCAS computer uses the round-trip time of the reply signal to calculate the range and range rate of the traffic airplane. It also uses direction of the reply to calculate bearing of the intruder airplane.
The TCAS computer uses the traffic airplane data to calculate if the traffic airplane is on a possible collision course with the flight path. If it is, the TCAS computer calculates traffic coordination maneuver data. AIMS uses this data to make the TCAS displays.
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TCAS -BASIC OPERATION
Mode S Data Link
After the TCAS computer calculates the traffic coordination maneuver data, it transmits this data in the mode S format to the mode S transponder of the traffic airplane. The ATC/Mode S transponder receives coordination data from the traffic airplane. This sets up the air-to-air mode S data link between two or more airplanes.
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TCAS -BASIC OPERATION
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TCAS -CONTROL AND DISPLAY
General
The EFIS control panel and the transponder panel control the TCAS data that shows on the PFD and ND.
EFIS Control Panel
To show the TCAS data on the ND, first put the mode control switch on the EFIS control panel in one of these modes:
*
Expanded approach
*
Expanded VOR
*
Expanded map
*
Centered map.
Then push the TFC (traffic) switch on the range selector to enable the ND to show the TCAS data. When you do this, the TFC message and all of the TCAS symbols shows on the ND.
To remove all of the TCAS messages and symbols from the ND, push the TFC switch again. To do this, the ND must be in one of these modes:
*
Expanded approach
*
Expanded VOR
*
Expanded map
*
Centered map.
Transponder Panel
The transponder panel sends control data through the selected ATC/Mode S transponder to the TCAS computer.
The TCAS computer sends the selected data to the AIMS for display on the NDs and PFDs.
Push the TFC switch to show TCAS data. If the function selector is not in the TA ONLY or TA/RA position, the ND has these changes:
*
Shows an amber message, TCAS OFF.
*
Does not show TCAS data.
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TCAS -CONTROL AND DISPLAY
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TCAS -NAVIGATION DISPLAY
General
The TCAS computer puts traffic into these four different groups with different symbols to show different types of traffic:
*
Other traffic shows as a white open diamond, and the altitude readout is small white text
*
Proximate traffic shows as a solid white diamond, and the altitude readout is small white text
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