Message Name:

INCORRECT OR ERRATIC RADIO ALTITUDE VALUE ON COPILOT PFD

Radio Altimeter System 2 do transmit correct radio altitude information. May be associated to a RAD amber flag if Pilot and Copilot Primary Flight Display (PFD)s values disagree.

• Radio Altimeter Unit 2 (A68)
• Radio Altimeter Transmit Antenna 2 (E17)
• Radio Altimeter Receive Antenna 2 (E18)
• Associated Wiring

Advisory Wire/Service Bulletin:

• 700-34-023 - Modification - Radio Altimeter System - Radio Altimeter Antenna Corrosion Protection
• 700-1A11-34-008 - Modification - Radio Altimeter System - Radio Altimeter Antenna Corrosion Protection

Forum Articles/Infoservice/Newsletter: None

1. Before proceeding with troubleshooting, remember that while on ground radio altitude displayed values may be affected by the ground surface material or surrounding equipment near the antennas. If the condition is only present on ground, the aircraft may me moved to another location to monitor the effect.
2. 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 reported by the Flight Control Unit (FCU), DAU, HUD, GPWS about a RA 2 loss of communication, that Radio Altitude system itself (Radio altimeter, antennas/ coax/strapping) is the most possible cause.
3. Water may collect around the radio altimeter’s transmitter and receiver antennas location. This water may cause corrosion of the connectors, premature/ intermittent failure of the radio altimeter antennas.

Service bulletins 700-34-023/700-1A11-34-008 (9002 to 9139) introduces self-contouring sealing pads and water deflectors to prevent corrosion, divert water and prevent failure of the antennas. Other aircraft were modified in production.

CAIMS messages may be associated to the AMBER and NOT RED RAD flag are:

Extract from the Rockwell Collins installation manual (ALT-4000 Radio Altimeter System CPN: 523-0777765).

1. Initiated self test and monitor results on altitude display:
   Indicated altitude of 50 feet=TEST PASS, no fault detected.
   Reported Fault Condition Codes Table

   • Additional information to the Reported Fault Condition Codes Table. On the GEX ALT-4000 antenna monitoring function is enabled (P1-21 ground)

     • The Antenna Fault monitoring as detected an out of tolerance impedance value for one of both antennas. Suspect coaxial cables or antennas. (Follow Smart fix troubleshooting related to coaxial cables or antennas)
     • The Power Supply Fault monitoring function from the internal power supply. Replace the Radio altimeter
     • The Invalid Strap monitoring function detects an invalid strap configuration with the Aircraft Installation Delay (AID) strapping, the Modulation Frequency strapping, or the Analog Format strapping (Follow Smart fix troubleshooting related to wiring strapping)
     • The Internal Fault monitoring function detects an internal failure. Replace the Radio altimeter

2. ARINC 429 maintenance label monitoring:
   ARINC 429 Data Bus Word 350 Maintenance Code Definitions Table

   • Additional information to the ARINC 429 Data Bus Word 350 Maintenance Code Definitions Table (bit 17 is the LSB) for the fault code definition bit 17 to 24

     • As examples: 0010 0001 (LSB)=21 HEX, 33 Code. 0100 0000 (LSB)=40 HEX, 64 Code

   • Additional information to the ARINC 429 Data Bus Word 350 Diagnostic Code Definitions Table
   • Most failures are internal and would point to the Radio Altimeter replacement, except for the following CODEs which are indicative of external faults:

     • 33, 34, 35; for the specific receive or transmit antenna, suspect coaxial cables or antennas (Follow Smart fix troubleshooting related to coaxial cables or antennas)
     • 64, 65, 67; Aircraft Installation Delay (AID) strapping, the Modulation Frequency strapping, or the Analog Format strapping (Follow Smart fix troubleshooting related to wiring strapping)

1. Swap RAD ALT 2 with RAD ALT 1.

   1. If system checks are good, replace RAD ALT 2 and do close out.
   2. If fault remains, continue with next step.
      NOTE: Radio altimeter system can also be interrogated for internal/external, current active failures by the following two methods (since the radio altimeter is not CAIMS compliant):

      1. Initiated self test and monitor results on altitude display:

         1. Apply a ground to radio altimeter connector P1 pin 25. This can be done via Junction box 6 test point: JB6-PCB5, TP-15
         2. After ten seconds, an altitude value that is the sum of the fault conditions specified in Reported Fault Condition Codes Table and follow the table information for next steps for troubleshooting.

      2. ARINC 429 maintenance label monitoring:

         1. Access any of the four radio altimeter A429 output buses. As an example remove the GPWS computer and connect a Data track (refer to wiring diagram 34-44-00).
         2. In low speed, monitor label 350 and decode using the information specified in ARINC 429 Data Bus Word 350 Maintenance Code Definitions Table and ARINC 429 Data Bus Word 350 Diagnostic Code Definitions Table and follow the table information for next steps for troubleshooting procedure.

2. Perform wiring checks between Radio Altimeter 2 strappings and ground.

   1. If wiring checks are not good, repair defective wiring as required and do close out.
   2. If wiring checks are good, continue with next step.

3. Perform wiring checks between both Radio Altimeter 2 antenna coaxial cables: the extension adaptors (if installed), shield isolation using Megger or equivalent.
   CAUTION: For isolation check, ensure that the antennas and Rad Alt unit are not connected.

   1. If wiring checks are not good, repair defective wiring as required and do close out.
   2. If wiring checks are good, continue with next step.

4. Check both Radio Altimeter 2 antennas coaxial cables, the extension adaptors (if installed) for any loose connections and proper shield connection to the connectors.

   1. If fault remains, repair as required and do close out.
   2. If system checks are good, continue with next step.

5. Verify for any moisture contamination at/in the connectors. Perform Cleaning and Corrosion Protection of Electrical Connectors and Component as necessary.

   1. If fault remains, repair as required and do close out.
   2. If system checks are good, continue with next step.

6. Perform both antennas bounding check.

   1. If there is no incorrect antenna installation, signs of corrosion and moisture accumulations, go to step 8.
   2. If there is incorrect antenna installation, signs of corrosion or moisture accumulations, continue with next step.

7. Perform installation of Service Bulletin (Radio Altimeter Antenna Corrosion Protection (700-34-023/700-1A11-34-008 (9002 to 9139)) listed in Troubleshooting Tips.

   1. If system checks are good, do close out.
   2. If fault remains, continue with next step.
      NOTE: Pay attention to the self courting pad that prevents moisture ingress between fuselage connector hole and the antenna base. Also verify that the lower fuselage two drain holes - (one on the outside skin panel, one on the inner skin panel (this one can only be seen if the outside panel is removed or under the main battery) between the aft compartment assess door and the fwd (RA 1 antenna) are clear of obstruction (i.e. dirt, paint, coax cable obstruction) that would prevent proper water drainage.

8. Replace RA2 antennas.
9. Do close out.