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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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02/07/20

Message Overview:

SCU Fault Code:

'U'

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

Fault Description:

An SCU Fault Code 'U' on the 7-segment display indicates that the Nosewheel Feedback RVT detects a steering angle above 65°, left or right.

Possible Causes:

  • Steering traveled beyond 65°, left or right
  • Nosewheel Feedback Rotary Variable Differential Transducer (RVDT)
  • Steering Control Unit (SCU) (A73)

Troubleshooting Tips:

Advisory Wire/Service Bulletin: None

Forum Articles/Infoservice/Newsletter: None

Troubleshooting Tips:

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
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 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
Operational Test of the Nosewheel-Steering Control System AMM 32-51-00-710-801
Pressurize the Left and Right Hydraulic Systems AMM 29-10-00-862-801
Release Hydraulic Pressure - Left and Right Hydraulic Systems AMM 29-10-00-862-802
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. Set the NWS PBA to 'OFF' (legend is lighted).
  2. Align the Nose Steering Indicator with the 0° position on the nose wheel position placard by manually turning the Nosewheel.
  3. Pressurize the Left Hydraulic System (AMM TASK 29-10-00-862-801).
    NOTE: Always establish Left Hydraulic System pressure before switching the NWS System to 'ON' as it may trigger and record a false 'NWS FAIL' CAS message if any NWSS component is out of neutral position.
  4. Set the NWS PBA to 'ON' (legend is extinguished).
  5. Carry out the Operational Test of the Nosewheel-Steering System (AMM TASK 32-51-00-710-801).

    1. If SCU Fault Code 'U' is no longer present, no other maintenance action is required.
    2. If SCU Fault Code 'U' is still showing on the 7-segment display, continue with the next step.

  6. Depressurize the Left Hydraulic System per (AMM TASK 29-10-00-862-802).
  7. Visually inspect NWS feedback RVT linkage for damaged, bent, or broken components.

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

  8. Remove RVT and inspect for a broken shaft.

    1. If damage is found, replace RVT.
    2. If no damage is found, go to the next step.

  9. Replace SCU.
    nwss_block_diagramnwss_exploded_viewsteering_control_unit

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