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API Documentation: ATC TCAS Panel


The aircraft has two ATC transponders (XPDR) which are controlled by a control panel (ATC/TCAS) on the center pedestal.

Only the selected XPDR operates.

The XPDR automatically responds to requests:

  • From the ATC, to ensure effective air traffic surveillance.
  • From other aircraft that have a TCAS, to ensure that traffic alerts are triggered.

The XPDR is capable of elementary surveillance (ELS) and enhanced surveillance (EHS). It transmits the following data to the ATC center:

  • Supplied by the ADRs:
    • The aircraft 24 bit address
    • The aircraft altitude
    • The flight number
    • The RA report
    • The indicated airspeed
    • The Mach number
    • The barometric vertical speed
  • Supplied by the IRs:
    • The magnetic heading
    • The roll angle
    • The ground speed
    • The track angle
    • The track angle rate
    • The inertial vertical speed
  • The selected altitude and barometric reference settings supplied by the FCUs.


Mode Selector

  • STBY:
    • Both XPDR are electrically supplied but do not operate.
  • ON:
    • Selected XPDR operates.
  • AUTO:
    • In flight : Selected XPDR operates.
    • On ground : Selected XPDR only operates in mode S (Selective aircraft interrogation mode).

XPDR Selector

This switch selects XPDR 1 or 2.

Currently, only 1 is available in the FBW A32NX for Microsoft Flight Simulator.


  • ON:
    • The XPDR sends barometric standard altitude data.
  • OFF:
    • No altitude data transmission. If the TCAS is installed, the upper ECAM displays "TCAS STBY" in green.

IDNT Switch

  • The flight crew presses this button to send the aircraft identification signal.

Code Display

  • The window displays the selected code.


  • The flight crew uses the keypad to set the code assigned by ATC.


  • The flight crew uses this key to clear the code display.
  • Note: As long as the four figures of the new code are not entirely written, the previous code remains.


  • This light comes on if the selected XPDR fails.


TCAS knows the following threat categories:

  • Other intruders - white outlined diamond
  • Proximate intruders - white diamond
  • Traffic Advisory (TA) - amber circle
  • Resolution Advisory (RA) - red square

TCAS mode selector:

  • TA/RA:
    • If the ALT RPTG switch is ON and the transponder is not on STBY RAs, TAs and proximate intruders are displayed. Default position.
  • TA:
    • TCAS only provides Traffic Advisory. Used in case of degraded aircraft performance (engine failure, landing gear extended, or approach on parallel runways).
    • All RAs are converted into TAs. TAs, proximate and intruders are displayed if the ALT RPTG switch is ON and the transponder is not on STBY.
    • "TA ONLY" memo is displayed on the NDs.
  • STBY:
    • TCAS is on standby.


  • THRT:
    • Proximate and other intruders are displayed only if a TA or RA is present, and they are within 2700 ft above and 2700 ft below the aircraft.
  • ALL:
    • Proximate and other intruders are displayed even if no TA or RA is present (full time function).
    • The altitude range is – 2700 ft to + 2700 ft.
  • ABV:
    • Same as ALL, except that the other intruders are displayed if within 9900 ft above and 2700 ft below the aircraft.
  • BLW:
    • Same as ALL, except that the other intruders are displayed if within 9900 ft below and 2700 ft above the aircraft.

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