Message Name:

TRAFFIC/COLLISION AVOIDANCE SYSTEM (TCAS) FAIL

The Primary Flight Displays (PFDs) and/or Multi Function Displays (MFDs) show the Traffic/Collision Avoidance System (TCAS) Fail legend.

• Traffic/Collision Avoidance System (TCAS) Directional Antenna (Top) (E1)
• Traffic/Collision Avoidance System (TCAS) Omnidirectional Antenna (Bottom) (E2)
• Traffic/Collision Avoidance System (TCAS) Receiver/Transmitter (A7)
• Associated Wiring

Advisory Wire/Service Bulletin:

• SB700-23-002 - Modification - Third Very High Frequency (VHF 3) Communication System - Installation

Forum Articles/Infoservice/Newsletter: None

1. Access the TCAS unit. Push the "PUSH TO TEST" button on the front panel of the TCAS unit. The table that follows shows the possible IBIT results. Monitor all 10 LEDs and record those that come on.
   NOTE: Initially, the IBIT does a test of all 10 LEDs on the front panel. The LED test result is satisfactory only when all 10 LEDs come on for 3 seconds (The TCAS PASS LED is green and the other LEDs are red).Wait for the IBIT to complete. At that time, one or more LEDs come on for 10 seconds to show the general condition of the TCAS components and interfaces.

   LED Name	TCAS Condition
   TCAS PASS	IBIT results are satisfactory and the TCAS receiver/transmitter is serviceable. If other LEDs come on, there is a fault in the identified subsystem or aircraft wiring.
   TCAS FAIL	The IBIT results are unsatisfactory and the TCAS receiver/transmitter is unserviceable.
   TOP ANT	DC resistance test shows that the directional (top) antenna and/or related interface is defective.
   BOT ANT	DC resistance test shows that the omnidirectional (bottom) antenna and/or related interface is defective.
   TA DISP	TA display discrete signal 1 and/or 2 show that a DU and/or a related interface is defective.
   RA DISP	TA display discrete signal 1 and/or 2 show that a DU and/or a related interface is defective.
   RAD ALT	RAD ALT 1 and/or 2 transmit incorrect data, are not energized, or are defective.
   XPDR BUS	Transponders 1 and/or 2 transmit incorrect data, are not energized or are defective.
   ATT	Not applicable
   HDG	Not applicable

   1. If the green LED for TCAS PASS comes on but the red LEDs does not, perform the operational test of the TCAS and continue with next step.
   2. If the green LED for TCAS PASS comes on and a red LED comes on, continue with the next step.
      NOTE: To do the IBIT again, wait until all 10 LEDs go off before pushing the PUSH TO TEST push-button (If it is not waited for the LEDs to go off, the IBIT results from a flight that occurred before will show off).

2. Check if one of the fault indications that follow is recorded:
   For the TCAS receiver/transmitter (A7):

   Name of Display Unit	Activity Fault
   TCAS receiver/transmitter	Unsatisfactory LED test (one or more LEDs do not come on for 3 seconds)
   TCAS receiver/transmitter	TCAS FAIL

   1. If one of the fault indication is recorded, perform the maintenance tasks and continue with the next step.
   2. If the fault indications are not recorded, continue with the next step.

3. Perform the voltage check on the transmitter/receiver (A7) connector as follows:

   TCAS Transmitter/Receiver	Expected Result
   A7CP1-10	+28 VDC

   1. If there is no +28 VDC, repair or replace defective wiring as required and do close out.
   2. If there is +28 VDC, continue with the next step.

4. Check for which of the red LEDs come on.

   1. If the red LED comes on for omnidirectional (BOT) antenna, continue with step 7.
   2. If the red LED comes on for TA and/or RA, continue with step 9.
   3. If the red LED comes on for RAD ALT, continue with step 10.
   4. If the red LED comes on for XPDR BUS, continue with step 11.
   5. If the red LED comes on for directional (TOP) antenna, continue with the next step.

5. Remove the TCAS receiver/transmitter. Perform a DC resistance check between the center pin and the shield of each coaxial cable connector from the mounting tray side as follows:

   TCAS Transmitter/Receiver	Expected Result	Result
   A7AP1-1 (0 degree port)	1000 ±100
   A7AP1-2 (270 degree port)	8060 ±800
   A7AP1-3 (180 degree port)	4020 ±400
   A7AP1-4 (90 degree port)	2000 ±200

   1. If the resistance check is not satisfactory, continue with the next step to isolate a cable or an antenna.
   2. If the resistance check is satisfactory, continue with the step 7.

6. Disconnect the four coaxial cables from the Directional (top) Antenna (E1). Perform the DC resistance check of each coaxial antenna connector as follows:

   TCAS Directional Antenna	Expected Result	Result
   E1P1 (0 degree port)	1000 ±100
   E1P2 (270 degree port)	8060 ±800
   E1P3 (180 degree port)	4020 ±400
   E1P4 (90 degree port)	2000 ±200

   1. If the resistance check is satisfactory, replace the defective coaxial cable and/or connectors and do close out.
   2. If the resistance check is not satisfactory, replace the defective Directional Antenna (E1). 

7. Remove the TCAS receiver/transmitter. Perform a DC resistance check between the center pin and shield of the coaxial connector from the mounting tray side as follows:
   For the TCAS receiver/transmitter (A7):

   TCAS Transmitter/Receiver	Expected Result	Result
   A7BP1-1	50 ohms maximum

   1. If the resistance check is not satisfactory, continue with the next step.
   2. If the resistance check is satisfactory, continue with step 9.

8. Disconnect the coaxial cable from the omnidirectional (bottom) antenna. Perform the DC resistance check for the coaxial antenna connector as follows:
   For the omnidirectional (bottom) antenna (E2):

   TCAS Omnidirectional Antenna	Expected Result	Result
   E2P1	50 ohms maximum

   1. If the resistance check is satisfactory, repair or replace the defective wiring as required. Connect the coaxial cable to the omnidirectional (bottom) antenna and do close out.
   2. If the resistance check is not satisfactory, replace the defective omnidirectional (bottom) antenna and do close out.

9. Perform the continuity check between the connectors TCAS UNIT (A7EP1), IAC 1 (A11CP1), IAC 2 (A10CP1), IAC 3 (A12CP1) as follows:
   
   For IAC 1 (A11):
   

   From	To	Result
   A7EP1-7C	A11CP1-65
   A7EP1-7D	A11CP1-66
   Ground	Shield

   For IAC 2 (A10):

   From	To	Result
   A7EP1-7G	A10CP1-65
   A7EP1-7H	A10CP1-66
   Ground	Shield

   For IAC 3 (A12):

   From	To	Result
   A7EP1-7C	A12CP1-65
   A7EP1-7D	A12CP1-66
   Ground	Shield

   1. If there is no continuity, repair or replace the defective wiring as required and do close out.
   2. If there is continuity, continue with the next step.

10. Perform a continuity check between the connectors TCAS UNIT (A7EP1), RADIO ALTIMETER UNIT 1 (A67P1), TCAS UNIT (A7FP1), RADIO ALTIMETER UNIT 2 (A68P1) as follows:
    For RAD ALT 1 (A67):

    From	To	Result
    A7EP1-13H	A67P1-55
    A7EP1-13J	A67P1-52
    Shield (Ground)	Shield (Ground)

    For RAD ALT 2 (A68):

    From	To	Result
    A7FP1-3D	A68P1-55
    A7FP1-3E	A68P1-52
    Shield (Ground)	Shield (Ground)

    1. If there is no continuity, repair or replace the defective wiring as required and do close out.
    2. If there is continuity, continue with the next step.

11. Perform a continuity check between the connectors TCAS UNIT (A7EP1), TCAS UNIT (A7CP1), VHF COMM UNIT 1 (A1P1), VHF COMM UNIT 2 (A2P1) as follows:
    For VHF COM unit 1 (A1):

    From	To	Result
    A7EP1-14F	A1P1-55
    A7EP1-14G	A1P1-87
    A7EP1-15J	A1P1-90
    A7EP1-15K	A1P1-104
    Shield (Ground)	Shield (Ground)
    A7CP1-12	A1P1-94

    For VHF COM unit 2 (A2):

    From	To	Result
    A7EP1-14H	A2P1-55
    A7EP1-14J	A2P1-87
    A7EP1-14A	A2P1-90
    A7EP1-14B	A2P1-104
    Shield (Ground)	Shield (Ground)
    A7CP1-12	A2P1-94

    1. If there is no continuity, repair or replace the defective wiring as required and do close out.
    2. If there is continuity, continue with the next step.

12. Check if the TCAS aural warning function operates.

    1. If the TCAS aural warning function operates, do close out.
    2. If the TCAS aural warning function does not operate, continue with the next step.

13. Perform a continuity check between the connectors TCAS UNIT (A7EP1), AUDIO PANEL 1 (A8P2), AUDIO PANEL 2 (A9P2) and AUDIO PANEL 3 (A215P2) as follows:
    For the audio panel 1 (A8) and audio panel 2 (A9):

    From	To	Result
    A7EP1-3F	A8P2-t
    A7EP1-3G	A8P2-Z
    Ground	Shield
    A7EP1-3F	A9P2-t
    A7EP1-3G	A9P2-Z
    Ground	Shield

    For the audio panel 3 (A215):
    On A/C Post SB 700-23-002

    From	To	Result
    A7EP1-3F	A215P2-t
    A7EP1-3G	A215P2-Z
    Ground	Shield

    1. If there is no continuity, repair or replace the defective wiring as required and do close out.
    2. If there is continuity, continue with the next step.

14. Replace the defective TCAS receiver/transmitter.
15. Do close out.