Message Name:

ASCB AND-OR RSB MEMBER SYSTEMS CANNOT TRANSMIT ON THEIR RESPECTIVE BUS

The Avionics Standard Communication Bus (ASCB) Member Systems cannot transmit data through the ASCB and/or the Aircraft Radio Systems cannot transmit data through the Radio System Bus (RSB).

• Avionics Standard Communication Bus (ASCB) Isolation Coupler
• Integrated Avionics Computer Bus Controller

Advisory Wire/Service Bulletin: None

Forum Articles/Infoservice/Newsletter: None

For in depth ASCB BUS troubleshooting recommendations and test equipment detail, refer to the ASCB Fault Isolation Guide

1. For the ASCB, use the PMAT to access CAIMS. Perform the CAIMS test of the IAC system as per AMM 31-41-00-740-802. Monitor the EICAS and record any related ASCB fault messages.
2. Check if any EICAS messages were recorded:
   Select CAS MessageASCB FAILASCB ALL CTLR FAILASCB CTLR 1 FAILASCB CTLR 2 FAILASCB CTLR 3 FAILASCB FAULT

   1. If any CAS message are recorded, perform the corresponding troubleshooting procedure and continue with next step.
   2. If no CAS message are recorded, continue with next step.

3. For the RSB, on the RMU, after the POST has completed, monitor the pages that follow:

   • SYSTEM TEST RESULTS
   • RADIO TEST RESULTS

4. Record any related faults for the RSB and radio modules.
5. Check if any of the following messages are displayed on the RMU SYSTEM TEST RESULTS page:

   • CHK COM 1 (2) (3) UNIT
   • CHK NAV 1 (2) UNIT
   • CHK RMU 1 (2) UNIT
   • ADF 1 (2) ERR
   • ATC 1 (2) ERR
   • COM 1 (2) (3) ERR
   • COM 1 (2) (3) UNIT
   • DME 1 (2) ERR
   • NAV 1 (2) ERR
   • NAV 1 (2) UNIT
   • If the messages are displayed on the RMU SYSTEM TEST RESULTS page, troubleshoot the particular message and do close out.
   • If the messages are not displayed on the RMU SYSTEM TEST RESULTS page, do close out.

6. Do close out.