Transponder -Central Maintenance Computing Function Interface
Each transponder has a maintenance interface to the central maintenance computing function (CMCF) of the AIMS cabinets.
The transponders continuously send ATC system maintenance data to the CMCFs in the AIMS cabinets.
The central maintenance computing function (CMCF) in the left AIMS cabinet sends data to both transponders to do these functions:
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Define flight legs for the non-volatile memory (NVM) in the transponder

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Command the ATC/Mode S transponder to start an ATC/ Mode S transponder system test.

Use the maintenance access terminal (MAT) to start the ATC system test through the CMCFs.
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ATC/MODE S TRANSPONDER SYSTEM -MAINTENANCE INTERFACE

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ATC/MODE S TRANSPONDER SYSTEM -TCAS INTERFACE AND PROGRAM PINS

Program Pins
Each ATC/Mode S transponder has these types of program pins:
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Airplane mode S address program pins

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Source destination indicator (SDI) program pins

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Maximum true airspeed program pin.

There are 24 airplane address program pins on each transponder. A program switch module connects to the program pins. The program switch module supplies the open and ground connections necessary to make the 24 bit unique airplane identification.
The SDI defines the transponder as a left or right ATC/Mode S transponder.
The maximum true airspeed pins define the maximum true airspeed for the airframe. The transponder formats and sends the maximum true airspeed to the TCAS computer.
Digital Data to TCAS
The active ATC/Mode S transponder sends this data to the traffic alert and collision avoidance system (TCAS) computer:
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The 24-bit mode S airplane identification. TCAS needs the airplane mode S identification for maneuver coordination

*
Barometric altitude

*
Maximum true airspeed

*
TCAS coordination message data

*
ATC/Mode S transponder system failure data.

TCAS to Active Transponder
The TCAS computer sends this data to the active transponder:
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General TCAS operational data

*
Coordination update data.

Digital Data to the AIMS Cabinets
The ATC/Mode S transponders send the airplane unique 24-bit mode S airplane identification to the AIMS cabinets for use in other systems.
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ATC/MODE S TRANSPONDER SYSTEM -SUPPRESSION INTERFACE

General
The ATC/Mode S transponders, TCAS, and the DME interrogators operate in the same frequency band. There is a suppression interface between these units. This prevents damage to the receiver circuits during a signal transmission.
The first unit to transmit sends a suppression pulse through the supression splitter to the other units. This suppression pulse prevents the operation of the receiver circuits in the other units.
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ATC/MODE S TRANSPONDER SYSTEM -SUPPRESSION INTERFACE

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ATC/MODE S TRANSPONDER SYSTEM -ATC/MODE S TRANSPONDER

General
The ATC ground station interrogates the ATC/Mode S transponder with a pulse-coded signal at a frequency of 1030 MHz.
The transponder responds with pulse-coded signals at a frequency of 1090 MHz.
Characteristics
The transponder responds to air traffic control radar beacon system (ATCRBS) mode A and mode C interrogations. The transponder also responds to the TCAS computer with the mode select (mode S) format.
The ATC/Mode S transponder has a non-volatile flight-fault memory.
Front Panel Indications
The light emitting diode (LED) status indicators on the front panel show:
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TPR LED, if there are no LRU failures

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TPR LED, if there is an LRU failure

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ALT, if the altitude input from the AIMS cabinets fail

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DATA IN, if the transponder input fails

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TOP, if the top antenna fails

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BOT, if bottom antenna fails

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TCAS, if the interface with TCAS fails

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MAINTENANCE, not used

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