Fault Message:

FWC3 INTERFACE

Fault Code:

3030601HBM

Associated CAS:

None

It is unusual that the Air Data Sensor/Probe Heaters are on when the Engines are off, the airspeed is less than 50 knots and the Aircraft is on the ground. The Heater/Brake-Temperature Monitoring Unit (HBMU) receives ARINC data about the Engines on/off status and the airspeed, and the Aircraft air/ground status (WOW) from the Landing Gear Electronic Control Unit (LEGCU). If the HBMU does not receive any one of these data, the Sensor/Probe/Actuator Heaters can become hot on the ground.

If the HBMU is de-energized or the Data Acquisition Unit (DAU) is unserviceable, all of the related Sensor/Probe Heaters will become hot.

The HBMU is a CAIMS member and reports on other defective Line Replaceable Unit (LRU).

• Data Acquisition Unit (DAU) 1 (A17)
• Data Acquisition Unit (DAU) 2 (A18)
• Engine Electronic Controller (EEC) 1
• Engine Electronic Controller (EEC) 2
• Micro-Air Data Computer (MADC) 1 (A27)
• Micro-Air Data Computer (MADC) 2 (A28)
• Electrical Management System Control and Display Unit (EMS CDU) 1 (A94)
• Electrical Management System Control and Display Unit (EMS CDU) 2 (A91)
• Heater/Brake-Temperature Monitoring Unit (HBMU) 1 (A121)
• Heater/Brake-Temperature Monitoring Unit (HBMU) 2 (A93)
• Associate Wiring

Advisory Wire/Service Bulletin: None

Forum Articles/Infoservice/Newsletter: None

1. Check if the following CAS messages are displayed on the EICAS primary display. Select displayed message from menu below:
   Select the CAS message:DAU 1A FAILDAU 1B FAILDAU 2A FAILDAU 2B FAILADC 1 DEGRADEDADC 1 FAILADC 2 DEGRADEDADC 2 FAILADC 3 DEGRADEDADC 3 FAIL

   1. If any of these messages are displayed, troubleshoot them first and do close out.
   2. If none of these messages are displayed, continue with next step.

2. Check CAIMS active or stored faults for the following messages "LEFT HBMU or RIGHT HBMU".

   1. If fault message is found, replace the defective HBMU and do close out.
   2. If fault message is not found, continue with next step.

3. Check CAIMS active or stored faults if internal faults for the ADC, DAU, EEC or EMS CDU are found.

   1. If an internal fault is found, troubleshoot or swap the affected unit.
   2. If no internal fault is found, continue with next step.

4. Check if the following CAIMS active fault messages are displayed. Select displayed message from the menu below:
   Select the CAIMS message:27660271SX - AIR DATA CMPTR #3/ BUS #1 FAULT27660272SX - AIR DATA CMPTR #3/ BUS #2 FAULT27660281SX - AIR DATA CMPTR #2/ BUS #1 FAULT27660282SX - AIR DATA CMPTR #1/ BUS #2 FAULT27660291SX - AIR DATA CMPTR #1/ BUS #1 FAULT27660292SX - AIR DATA CMPTR #2/ BUS #2 FAULT

   1. If any of these messages are displayed, troubleshoot them first and do close out.
   2. If none of the messages are displayed, continue with next step.

5. Disconnect HBMU 1 connector A121P2 and remove DAU 1 or disconnect HBMU 2 connector A93P2 and remove DAU 2. Perform a continuity check as follows:
   For HBMU 1:

   From	To	Result
   A121P2-5	A17CP1-A9
   A121P2-6	A17CP1-A10
   A121P2-33	A17CP1-K1
   A121P2-34	A17CP1-K2

   For HBMU 2:

   From	To	Result
   A93P2-5	A18CP1-A9
   A93P2-6	A18CP1-A10
   A93P2-33	A18CP1-K1
   A93P2-34	A18CP1-K2

   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 next step.

6. Perform a continuity check as follows:
   For HBMU 1:

   From	To	Result
   A121P2-5	Ground
   A121P2-6	Ground
   A121P2-33	Ground
   A121P2-34	Ground

   For HBMU 2:

   From	To	Result
   A93P2-5	Ground
   A93P2-6	Ground
   A93P2-33	Ground
   A93P2-34	Ground

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

7. Swap HBMUs.

   1. If system checks are good, replace the defective HBMU and do close out.
   2. If fault remains, continue with next step.

8. Access CAIMS active or stored faults and check if an EEC INTERFACE fault is displayed.

   1. If fault message is not found, go to step 12.
   2. If fault message is found, continue with next step.

9. Remove DAU 1 and disconnect L ENG FIREWALL connector 1JA2 for HBMU 1 or remove DAU 2 and disconnect L ENG FIREWALL connector 1JB4 for HBMU 2. Perform a continuity check for open circuit or short circuit between the pins of the connectors as follows:
   For HBMU 1:

   From	To	Result
   A17CP1-B5	1JA2-6
   A17CP1-C5	1JA2-17
   A17CP1-H9	1JA2-18
   A17CP1-J9	1JA2-36

   For HBMU 2:

   From	To	Result
   A18CP1-B5	1JB4-6
   A18CP1-C5	1JB4-17
   A18CP1-H9	1JB4-18
   A18CP1-J9	1JB4-36

   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 next step.

10. Perform a continuity check as follows:
    For HBMU 1:

    From	To	Result
    A17CP1-B5	Ground
    A17CP1-C5	Ground
    A17CP1-H9	Ground
    A17CP1-J9	Ground

    For HBMU 2:

    From	To	Result
    A18CP1-B5	Ground
    A18CP1-C5	Ground
    A18CP1-H9	Ground
    A18CP1-J9	Ground

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

11. Swap DAUs.

    1. If system checks are good, replace the defective DAU and do close out.
    2. If fault remains, continue with next step.

12. Access CAIMS active or stored faults and check if an EMS CDU INTERFACE/WRG fault is displayed?.

    1. If fault message is not found, go to step 18.
    2. If fault message is found, continue with next step.

13. Perform the operational test of the EMS CDU.

    1. If it is not satisfactory, check CAIMS active or stored faults for EMS CDU related messages and perform the troubleshooting and do close out.
    2. If it is satisfactory, continue with next step.

14. Remove DAU 1 and disconnect EMS CDU 1 connectors A94P1 and A94P2 for HBMU 1 or remove DAU 2 and disconnect EMS CDU 2 connectors A91P1 and A91P2 for HBMU 2. Perform a continuity check for open circuit or short circuit between the pins of the connectors as follows:
    For HBMU 1:

    From	To	Result
    A17CP1-D9	A94P1-3
    A17CP1-E9	A94P1-4
    A17CP1-H5	A94P2-3
    A17CP1-J5	A94P2-4

    For HBMU 2:

    From	To	Result
    A18CP1-D9	A91P1-3
    A18CP1-E9	A91P1-4
    A18CP1-H5	A91P2-3
    A18CP1-J5	A91P2-4

    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 next step.

15. Perform a continuity check as follows:
    For HBMU 1:

    From	To	Result
    A17CP1-D9	Ground
    A17CP1-E9	Ground
    A17CP1-H5	Ground
    A17CP1-J5	Ground

    For HBMU 2:

    From	To	Result
    A18CP1-D9	Ground
    A18CP1-E9	Ground
    A18CP1-H5	Ground
    A18CP1-J5	Ground

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

16. Swap EMS CDUs.

    1. If system checks are good, replace the defective EMS CDU and do close out.
    2. If fault remains, continue with next step.

17. Perform a operational test of the air data probes and sensors anti-ice system. Check if the EMS CDU INTERFACE fault is displayed.

    1. If fault message is not found, do close out.
    2. If fault message is found, continue with next step.

18. Access CAIMS active or stored faults and check if an ADC INTERFACE/WRG fault is displayed.

    1. If fault message is not found, do close out.
    2. If fault message is found, continue with next step.

19. Remove DAU 1 and the pins of the connector ADC 1 (A27P1) for HBMU 1 and remove DAU 2 and the pins of the connector ADC 2 (A28P1) for HBMU 2. Perform a continuity check for open circuit or short circuit between the pins of the connectors as follows:
    For HBMU 1:

    From	To	Result
    A17CP1-G1	A27P1-30
    A17CP1-J1	A27P1-34

    For HBMU 2:

    From	To	Result
    A18CP1-G1	A28P1-30
    A18CP1-J1	A28P1-34

    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 next step.

20. Perform a continuity check as follows:
    For HBMU 1:

    From	To	Result
    A17CP1-G1	Ground
    A17CP1-J1	Ground

    For HBMU 2:

    From	To	Result
    A18CP1-G1	Ground
    A18CP1-J1	Ground

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

21. Perform the operational test of the air data probes and sensors anti-ice system. Access CAIMS Active or Stored faults and check if an ADC INTERFACE fault is displayed.

    1. If fault message is not found, do close out.
    2. If fault message is found, continue with next step.

22. Replace the defective MADC.
23. Do close out.