Fault Message:

RAD_ALT_2/WRG/DAU #4 INACTIVE

Fault Code:

3147111DAU

Associated CAS:

None

A Radio Altimeter malfunction, or radio-altitude display malfunction occurs and is identified by one or more of the conditions that follow:

• Red RAD flag (radio altitude failure) shows on the Pilot (Copilot) Primary Flight Display (PFD)
• Amber RAD flag (radio altitude miscompare) shows on the Pilot (Copilot) PFD
• Radio altitude display does not show on the Pilot (Copilot) PFD
• Radio-altitude low-altitude awareness (brown shading as the ground) is not on the altitude tape on the Pilot (Copilot) PFD

• Radio Altimeter (RA) Transceiver 2 (A68)
• Radio Altimeter (RA) Transmit Antenna 2 (E17)
• Radio Altimeter (RA) Receive Antenna 2 (E18)
• Data Acquisition Unit (DAU) 4 (A31)
• Associated Wiring

Advisory Wire/Service Bulletin: None

Forum Articles/Infoservice/Newsletter: None

• A metallic or reflective surface (Water, Ice, metal plates, metal grills, etc...) underneath the RA antennas when aircraft is on the ground can cause erratic readings and cause the unit to fail. The first thing that should be attempted is move the A/C a few feet and test the system again
• The radio altimeter (RA) supplies altitude signals to other systems. When one of these signals does not show, the smart LRU will send a fault (CAIMS) report about the RA. You can get access to the active faults on the CAIMS PMAT to find the fault messages and the fault isolation procedure. If there are more than one CAIMS fault message about a RA, the RA is the most possible cause
• The radio altimeter operates an internal self-test that continuously monitors the health of the unit. The unit reports the status on the digital output bus

1. Swap RAD alt transceiver 2 with RAD alt transceiver 1. Is the fault still present?

   1. If system checks are good, go to step 12.
   2. If fault remains, continue with next step.

2. Check if the mounting tray connector is defective.

   1. If YES, replace the mounting tray connector and do close out.
   2. If NO, continue with the next step.

3. Check if the radio altimeter connector is defective.

   1. If YES, go to step 12.
   2. If NO, continue with the next step.

4. Remove the radio altimeter transceiver 2 to get access to the connector A68P1. Check if there is 28 VDC between the pins of the connector as follows:

   From	To	Result
   A68P1-9	A68P1-11

   1. If there is 28 VDC, go to step 6.
   2. If there is no 28 VDC, continue with the next step.

5. Remove the SPDA 3 to get access to the connector A15P4. Perform a continuity check as follows:

   From	To	Result
   A68P1-9	A15P4-F

   1. If there is continuity, check power source and do close out.
   2. If there is no continuity, repair or replace defective wiring as required and do close out.

6. Perform a continuity check as follows:

   From	To	Result
   A68P1-58	GS778
   A68P1-40	GS778
   A68P1-21	GS778
   A68P1-24	GS778

   1. If there is continuity, repair the configuration wiring of the radio altimeter and do close out.
   2. If there is no continuity, continue with next step.

7. Check the coaxial cable between the radio altimeter transceiver and the antennas. Check the coaxial connectors and cable are satisfactory.

   1. If NO, replace the defective coaxial cable and do close out.
   2. If YES, continue with the next step.

8. Replace the defective radio altimeter antenna. Is the fault still present?

   1. If YES, go to step 12.
   2. If NO, continue with the next step.

9. Perform a continuity check of the ARINC 429 between the DAU and the transceiver as follows:

   From	To	Result
   A68P1-2	A31CP1-H6
   A68P1-10	A31CP1-J6
   GM42-B (GND)	SH (Shield)

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

10. Perform a continuity check as follows:

    From	To	Result
    A31CP1-H6	Ground
    A31CP1-J6	Ground

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

11. Swap DAU 4 with DAU 3. Is the fault still present?

    1. If NO, replace DAU 4 and do close out.
    2. If YES, continue with next step.

12. Replace radio altimeter transceiver.
13. Do close out.