PRI STAB TRIM FAIL
(Caution)

The primary channel of the stab trim has failed.

• With the SEC trim selected and operative, the indication will be a cyan 'STAB TRIM FAULT' advisory CAS message.
• The Primary channel Command and or Monitor path has failed.

NOTE: The Autopilot MDC Fault Codes will not show on the FGC diagnostic unless the fault is active. If the aircraft has been shut down the codes will not be there.

• Horizontal Stab Trim Electronic Control Unit (HST ECU) (A130)
• Motor Control Unit (MCU) (A131)
• Horizontal Stabilizer Trim Motor No. 1
• Proximity Sensor Electronic Unit (PSEU) (A9)
• Associated Wiring

Advisory Wire/Service Bulletin:

• AW300-27-0315 - PRI STAB TRIM FAIL EICAS message caused by CPLD U27
• AW300-27-0410 - “PRI STAB TRIM FAIL” EICAS message Troubleshooting

Forum Articles/Infoservice/Newsletter: None

Flight Operation Notifications Manual (FONM): None

NOTES:

• To clear the CAS message cycle the following circuit breakers (Weight On Wheels):

  • PRI STAB TRIM/RUD LIM, CB1 - B15
  • SEC STAB TRIM/RUD LIM, CB2 - B13
  • If the fault still exist, re-boot the entire aircraft

• Reset Procedure For Horizontal Stabilizer Trim Electronic Control Unit

This procedure provides instructions to the flight crew on how to clear Pitch Trim related fault messages when the aircraft is on ground. The HSTECU RESET PROCEDURE can be used whenever one of the following messages are posted:

PRI STAB TRIM FAIL (amber)
SEC STAB TRIM FAIL (amber)
STAB TRIM FAULT (cyan)

HSTECU RESET PROCEDURE

1. PTSS-----------------------------------------------------------------PRI
2. PRI STAB TRIM / RUD LIM CCB (CB1-B15)---------------------OPEN
3. PULL SEC STAB TRIM / RUD LIM CCB (CB2-B13)-------------OPEN
4. INSERT PRI STAB TRIM / RUD LIM CCB (CB1-B15)-----------CLOSED
5. INSERT SEC STAB TRIM / RUD LIM CCB (CB2-B13)-----------CLOSED
   Wait 45 seconds for HSTECU SPOST to complete. Ensure no pitch trim related faults are posted.
6. PTSS-----------------------------------------------------------------SEC
   Verify SEC STAB TRIM FAIL (amber) or STAB TRIM FAULT (cyan) are not posted.
7. PTSS-----------------------------------------------------------------PRI

Common Cause:
If the pilot disconnects the autopilot with the MSW switch on the yoke and hits it more than 2 times in 1½ seconds this can cause the primary stab trim to fail. The clue that this happened is brake #1 and #3 are posted as the faults. This has happened several times and the vendor confirmed the issue. It is also possible if the glareshield AP button was selected more than once also. Almost always seen during descent or approach.

Consequential Faults:
Mach trim, flap and spoiler configuration trim inoperative.

NOTE: Do not shut-down the aircraft. One will need to enter the FGC diagnostic page and retrieve the MDC Fault Codes.

NOTE: If CAS messages RUDDER LIMITER FAULT (Advisory), PRI STAB TRIM FAIL (Caution) and YAW DAMPER FAIL (Caution) are displayed at the same time and the TRIM PRI STAB (CBP1-LCBP) circuit breaker (CB) is tripped, access the Rudder Travel Limiter Actuator (RTLA) and disconnect it. Set the CB back to IN and apply power to the aircraft. If the CB does not trip, replace the RTLA.

1. Download PSEU Non-volatile Memory (NVM) and send to Bombardier CRC or to your FSR.
2. Interrogate the MDC as follows:

   1. On the cursor control panel, ensure the toggle switch is to the right and select Anti-Ice, ECS and Fuel buttons simultaneously. The MDC main menu should now be displayed on Display Unit #3.
   2. Using the joystick, select Current Faults (if the fault is active) or Aircraft History to research stored faults. From Aircraft History you can then select Fault Message History and locate the fault. Going into advanced diagnostics will provide an equation id for the fault identified.
   3. Select the MDC fault or equation from the drop down below to provide additional information to assist in troubleshooting.
      Select an MDC Fault Code/Message:B3-006857 - NO HSTECU OUTPUT TO IOC [HORIZ TRIM ECU]B3-006858 - INTERNAL FAULT [HORIZ TRIM ECU]B3-006871 - NO-BACK FAULT [HORIZ TRIM ECU]B3-006872 - HSTA MCU FAULT [HORIZ TRIM ECU]B3-006883 - RELAY FAILED [HST ENGAGE RELY1]B3-006884 - RELAY FAILED [HST ENGAGE RELY2]
   4. Return to MAINTENANCE MAIN MENU page of MDC
   5. Select REPORT DOWNLOAD line and push ENTER
   6. Select LRU NVM DOWNLOAD
   7. Move the cursor to the HST ECU and select ENTER
      NOTE: PITCH TRIM SWITCH WILL NEED TO BE IN SECONDARY TO PERFORM THIS DOWNLOAD.
   8. Forward NVM Download to Bombardier CRC or your FSR for evaluation.

3. Check wiring as outlined below:
4. The HSTA Motor brake 1 & 3 are controlled by primary channel and motor brake 2 & 4 are controlled by secondary channel. The motor brake coil resistance is 32-38 Ω at 70°F.
5. Interchange K44 (MCU control unit relay - left main bus power) AND K45 (right AUX Bus power supply to HST ECU) RELAYS. (K44 IS IN LEFT DCPC AND K45 IS IN RIGHT DCPC). Ref to IPC 24-61-81; Fig 1; Pg. 0 for K44 and IPC 24-61-81; Fig. 2; P. 2 for K45 location.
6. REF WM 27-41 For following Checks. On connector A131P1 on MCU, verify 28 VDC on pin B. While monitoring voltage, have assistant switch to SECONDARY. Ensure voltage is no longer present. Switch back to PRIMARY and ensure 28 VDC is present again.
7. Perform continuity check on primary trim wiring between the HST ECU and the MCU.
   

   HST ECU (A130)	MCU (A131)
   From:	To:	Expected Results:
   A130AP1 Pin 1H	A131P4 Pin 14	≈0 Ω
   A130AP1 Pin 1A	A131P4 Pin 11	≈0 Ω
   A130AP1 Pin 1B	A131P4 Pin 10	≈0 Ω
   A130AP1 Pin 1E	A131P4 Pin 22	≈0 Ω
   A130AP1 Pin 5K	A131P3 Pin 15	≈0 Ω
   A130AP1 Pin 5J	A131P3 Pin 13	≈0 Ω
   A130AP1 Pin 5H	A131P3 Pin 14	≈0 Ω
   A130AP1 Pin 5A	A131P3 Pin 11	≈0 Ω
   A130AP1 Pin 5B	A131P3 Pin 10	≈0 Ω
   A130AP1 Pin 5E	A131P3 Pin 22	≈0 Ω

8. Is the result correct?

   1. If YES, continue with the next step.
   2. If NO, repair wiring as required and do close out.

9. Check resistance values in the following tables. This can be done from the MCU (A131).
   

   RVDT Horizontal Stabilizer Trim 1
   From:	To:	Expected Results:
   A131P3 Pin 4	A131P3 Pin 5	113 - 150 Ω
   A131P3 Pin 5	A131P3 Pin 6	113 - 150 Ω
   A131P3 Pin 4	A131P3 Pin 6	113 - 150 Ω
   A131P3 Pin17	A131P3 Pin 2	30 - 40 Ω

10. Is the result correct?

    1. If YES, continue with the next step.
    2. If NO, replace the RVDT HST 1, and do close out.

11. Check resistance values for HST Motor 1

    Horizontal Stabilizer Trim Motor 1
    From:	To:	Expected Results:
    MPE44P1 Pin A	MPE44P1 Pin B	0.16 - 0.20 Ω
    MPE44P1 Pin A	MPE44P1 Pin D	0.16 - 0.20 Ω
    MPE44P1 Pin B	MPE44P1 Pin D	0.16 - 0.20 Ω

12. Is the result correct?

    1. If YES, continue with the next step.
    2. If NO, replace the HST Motor 1, and do close out.

13. Check resistance values for the RVDT HST 2

    RVDT Horizontal Stabilizer Trim 2
    From	To	Expected Results
    A131P4 Pin 4	A131P4 Pin 5	113 - 150 Ω
    A131P4 Pin 5	A131P4 Pin 6	113 - 150 Ω
    A131P4 Pin 4	A131P4 Pin 6	113 - 150 Ω
    A131P4 Pin 1	A131P4 Pin 2	30 - 40 Ω

14. Is the result correct?

    1. If YES, continue with the next step.
    2. If NO, replace the RVDT HST 2, and do close out.

15. Check resistance values for HST Motor 2

    Horizontal Stabilizer Trim Motor 2
    From:	To:	Expected Results:
    MPE44P2 Pin A	MPE44P2 Pin B	0.16 - 0.20 Ω
    MPE44P2 Pin A	MPE44P2 Pin D	0.16 - 0.20 Ω
    MPE44P2 Pin B	MPE44P2 Pin D	0.16 - 0.20 Ω

16. Is the result correct?

    1. If YES, continue with the next step.
    2. If NO, replace the HST Motor 2, and do close out.

17. Check RVDT Excitation Voltages per the following table.

    RVDT Excitation Voltage HST Motor 1
    MPE44P1 Pin 7	MPE44P1 Pin 8	≈5 VAC

18. Is the result correct?

    1. If YES, continue with the next step.
    2. If NO, repair as required, and do close out.

19. Check RVDT Excitation Voltages per the following table.

    RVDT Excitation Voltage HST Motor 2
    MPE44P2 Pin 7	MPE44P2 Pin 8	≈5 VAC

20. Is the result correct?

    1. If YES, continue with the next step.
    2. If NO, repair as required, and do close out.

21. Check resistance values of HSTA Motor 1 Brakes.

    HSTA Motor 1 Brakes
    From:	To:	Expected Results:
    A130AP1 Pin 11K	A130AP1 Pin 11A	32 - 34 Ω
    A130BP1 Pin 4K	A130BP1 Pin 4A	32 - 34 Ω

22. Is the result correct?

    1. If YES, continue with the next step.
    2. If NO, repair or replace as required, and do close out.

23. Check resistance values of HSTA Motor 1 Brakes.

    HSTA Motor 2 Brakes
    From:	To:	Expected Results:
    A130AP1 Pin 11J	A130AP1 Pin 11B	32 - 34 Ω
    A130BP1 Pin 4J	A130AB1 Pin 4B	32 - 34 Ω

24. Is the result correct?

    1. If YES, continue with the next step.
    2. If NO, repair or replace as required, and do close out.

25. Do close out.