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(WARNING)
RED MESSAGE (CAUTION)
AMBER MESSAGE (ADVISORY)
CYAN MESSAGE (STATUS)
WHITE MESSAGE Require immediate crew attention. These messages are accompanied by flashing master warning, triple chime attenson with or without voice message or dedicated tone. Require immediate crew awareness and future crew action may be required in the form of alternate system selection or performance limitation. These message are accompanied by flashing master caution and a single chime. Indicate safe or normal system operation which require crew awareness, over and above the dark cockpit philosophy. Indicate minor failures or reduction in systems capability, which require no crew action.

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For AOG assistance contact:

CRC Montreal (YUL)
Quick Links

02/07/20

Message Overview:

SCU Fault Code:

'3'

Associated CAS:

NWS FAIL
(Caution)

DDG Reference: None
Reporting LRU: Steering Control Unit
System Description: 32-51-00
Schematic Diagram: 32-51-00
Wiring Diagram: 32-51-01
32-51-13
32-51-29

01/05/22

Message Description:

A '3' on the 7-segment display indicates either:

  • A fault in the Electro Hydraulic Servo Valve (EHSV), located on the Steering Manifold or associated wiring.
  • The SCU has been powered without or with low hydraulic pressure and with at least one NWS component out of neutral.

NOTE: A '3' combined with a '5' on the 7-segment display indicates that the SCU is not able to isolate the fault to a specific LRU. Use the combined '3 & 5' troubleshooting page.

NOTE: If SCU Fault Code '7' is flashing with another code, carry out SCU Fault Code '7' troubleshooting before addressing any other fault.

Possible Causes:

  • Electro-Hydraulic Servo Valve (EHSV)
  • Rotary Variable Transducer (RVT)
  • Steering Control Unit (SCU) (A73)
  • Associated Wiring

Troubleshooting Tips:

Advisory Wire/Service Bulletin:

SB100-32-25 - Special Check/Modification - Nosewheel-Steering Control System - Replacement of the Steering Manifold

Forum Articles/Infoservice/Newsletter: None

Troubleshooting Tips:ATA 32-51-00 NOSEWHEEL STEERING SYSTEM

Quick Links:

Automatic Download of the Steering Control Unit (SCU) Non-Volatile Memory (NVM) AMM 32-51-01-970-801
Manual Download of the Steering Control Unit (SCU) Non-Volatile Memory (NVM) AMM 32-51-01-970-802
Pressurize the Left and Right Hydraulic Systems AMM 29-10-00-862-801
Operational Test of the Nosewheel-Steering Control System AMM 32-51-00-710-801
Removal of the Steering Control Unit AMM 32-51-01-000-801
Installation of the Steering Control Unit AMM 32-51-01-400-801
Removal of the Steering Manifold AMM 32-51-13-000-801
Installation of the Steering Manifold AMM 32-51-13-400-801
Removal of the Rotary Variable Transducer AMM 32-51-29-000-801
Installation of the Rotary Variable Transducer AMM 32-51-29-400-801
Rigging of the Rotary Variable Transducer AMM 32-51-29-820-802
Standard Practices - Continuity and Insulation Check SPM 20-12-01-05
Wiring - Maintenance Practices - ALL SPM 20-12-00-02
Wire Repair - Maintenance Practices - ALL SPM 20-12-10-02
Electrical Connectors - Maintenance Practice - ALL SPM 20-20-00-02

Troubleshooting Recommendations:

Fault Isolation Procedure:

  1. Before starting the following Fault Isolation Procedure, make sure the SCU Fault Confirmation Procedure is carried out to ensure the correct fault code is being addressed.
  2. Verify the EHSV connector and receptacle is free of contamination/oxidation. Clean or repair the connector as required.
  3. Measure resistance at the EHSV receptacle per the following table:

    FROM TO EXPECTED RESULTS
    1 2 Between 450Ω - 537Ω
    3 4 Between 160Ω - 220Ω
    5 6 Between 340Ω - 400Ω
    3 5 OPEN (∞Ω)
    3 Chassis OPEN (∞Ω)
    1 Chassis OPEN (∞Ω)

    1. If values are not within range, replace Steering Manifold.
    2. If values are in range, go to next step.

  4. Using a Megger, measure the insulation resistance at 50 VDC for 1 minute between pins 1, 3, and 6 of the EHSV receptacle and one of the mounting bolts.

    1. If value is lower than 50 MΩ, replace Steering Manifold.
    2. If No Fault Found, go to next step.

  5. Carry out a wiring check per the following table:

    FROM EHSV TO A73P2 (SCU) RESULTS
    Pin 1 Pin B
    Pin 2 Pin C
    Pin 3 Pin a
    Pin 4 Pin N
    Pin 5 Pin Y
    Pin 6 Pin L

    1. Repair wiring as required.
    2. If No Fault Found, go to next step.
      NOTE: The reason for verifying the Nosewheel Feedback RVT with an SCU Fault Code '3' is that the excitation voltage comes from the same oscillator for both, the EHSV and the RVT, and the SCU cannot always determine which component has failed.

  6. Verify the RVT connector and receptacle are free of contamination/oxidation. Clean or repair the connector as required.
  7. Measure resistance at the RVT receptacle per the following table:
    FROM RVT TO RVT EXPECTED RESULTS
    Pin 1 Pin 2 Between 125Ω - 155Ω
    Pin 1 Pin 6 OPEN (∞Ω)
    Pin 1 Chassis OPEN (∞Ω)

    1. If values are not within range, replace RVT.
    2. If values are in range, go to next step.

  8. Carry out a wiring check per the following table:

    FROM RVT TO A73P2 (SCU) RESULTS
    Pin 1 Pin S
    Pin 2 Pin P

    1. Repair wiring as required.
    2. If No Fault Found, go to next step.

  9. If No Fault Found at this point, the EHSV may have a mechanical jam or may be contaminated. It is recommended to do a download of the SCU NVM and send it to Bombardier CRC for analysis.
  10. Replace Steering Manifold.
  11. If fault persists, replace SCU.
    steering_manifoldsteering_manifold_2scu_with_layoutnwss_electrical_schematic

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