Message Name:

NO-BACK FAULT

Message Code:

B3-006871

Associated CAS:

PRI STAB TRIM FAIL
(Caution)

No-Back Fault detected by Horizontal Stabilizer Electronic Control Unit.

A failed HSTA No-Back can be detected if the following conditions are achieved in either the manual or autopilot trim mode.

• The HSTA load is above the HSTA static Back-Driving Load to reach a motor speed above 70 RPM AND

• The HSTA load is maintained within the No-Back Window (brake-off) for a time sufficient to reach the defined threshold (10.8 motor revs).

Consequently the failures described above will trigger in the MDC the corresponding HST ECU Label 352 bit 12.

• Horizontal Stabilizer-Trim Actuator (HSTA) (MPE44)
• Motor Control Unit (MCU) (A131)
• Horizontal-Stabilizer-Trim Electronic-Control Unit (HST ECU) (A130)
• Associated Wiring

Advisory Wire/Service Bulletin:

• AW300-27-0077 - Troubleshooting Guide for Spoiler Electronic Control Unit and Horizontal Stabilizer Trim Electronic Control Unit (20501 - 20999)
• AW300-27-0081 - Spoiler Electronic Control Unit (SECU) and Horizontal Stabilizer Electronic Control Unit (HSTECU) - Cold Temperature Circuit Breaker Reset Procedure (20501 - 20999)

Forum Articles/Infoservice/Newsletter: None

1. Aircraft on Ground: Pull the HST ECU breaker CB1 - B15 and CB2 - B13 reset after a couple seconds. This will re-boot the HST ECU. Is the fault still present?

   1. If YES, continue with next step.
   2. If NO, do close out.

2. Reboot the entire aircraft. Is the fault still present?

   1. If YES, continue with next step.
   2. If NO, do close out.

3. Perform the Functional Test of the HSTA No-Back. Is the fault still present?

   1. If YES, continue with next step.
   2. If NO, do close out.

4. Replace the Stab Trim Motor. Is the fault still present?

   1. If YES, continue with next step.
   2. If NO, do close out.

5. Replace the HST ECU.
6. Do close out.