NWS FAIL
(Caution)

The amber 'NWS FAIL' caution message indicates either:

• The Steering Control Unit (SCU) has detected an internal fault or a fault in an LRU.
• The SCU has detected a Nosewheel angle exceeding 65°, left or right.
• The SCU has been powered without or with low hydraulic pressure and with at least one NWSS component out of neutral.

The Nose Wheel Steering System (NWSS) will be disabled until the system is reset using the NWS PBA located on the TAWS/LG control panel.

NOTE: Switching the NWS PBA to OFF or removing power from the aircraft will clear the amber 'NWS FAIL' caution CAS message and reset any fault present in the system. An '0' (No Fault) will be displayed on the SCU's 7-segment display face when the NWS PBA is set to 'ON' if no faults are detected by the power-up test.

• Air trapped in the Nose Wheel Steering System (NWSS)
• Rotary Variable Transducer (RVT)
• Steering Control Handwheel (MT85)
• Rudder Pedal Transducer (MT86)
• Steering Manifold Electro-Hydraulic Servo Valve (EHSV) (V7)
• Steering Control Unit (SCU) (A73)
• Associated Wiring

Advisory Wire/Service Bulletin: None

Forum Articles/Infoservice/Newsletter: None

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

1. Before starting any troubleshooting, it is recommended to do a download of the SCU Non-Volatile Memory (NVM) and send it to Bombardier Customer Response Center (CRC) for analysis.
2. Make sure NWS PWR 1 (LCBP-C12) and NWS PWR 2 (RCBP-C12) Circuit Breakers are pushed in.
3. Make sure the Handwheel, Rudder Pedals, and Nose wheel are in their neutral position (0°)
4. Pressurize the left hydraulic system (AMM TASK 29-10-00-862-801).
   NOTE: Always establish Left Hydraulic System pressure before switching the NWS System (NWSS) to 'ON' as it may trigger and record a false 'NWS FAIL' CAS message if any NWSS component is out of its neutral position.
5. Set the SCU PBA to 'ON' (OFF legend is extinguished).
6. Wait 30 seconds for PBIT to finish.
7. Carry out the Operation Test of the Nosewheel-Steering System (AMM TASK 32-51-00-710-801), doing 10 full swings of the steering system using the handwheel and then rudder pedals, or until the "NWS FAIL' caution CAS message is displayed.

   1. If the fault message is not displayed, no maintenance action is required, but:
      → It is recommended to do a download of the SCU NVM and send it to Bombardier CRC for analysis.
      → It is recommended to carry out the Rigging of the NWS (AMM TASK 32-51-00-820-801) as it may solve spurious or intermittent faults.
   2. If the 'NWS FAIL caution CAS message is displayed, record the fault code(s) indicated on the SCU front face 7-segment display.
      Select the NWS fault code(s) from the SCU:SCU FAULT CODE 1 OR BLANKSCU FAULT CODE 1 AND *SCU FAULT CODE 2SCU FAULT CODE 3SCU FAULT CODE 3 & 4 OR 6SCU FAULT CODE 3 & 5SCU FAULT CODE 4SCU FAULT CODE 4 & 6SCU FAULT CODE 5SCU FAULT CODE 6SCU FAULT CODE 7SCU FAULT CODE 8SCU FAULT CODE ASCU FAULT CODE U
      NOTE: If there are multiple codes flashing on the SCUs 7-segment display combined with Fault Code '1', record the codes and troubleshoot them before addressing the Fault Code '1'.
      NOTE: If Fault Code '7' is flashing with another code, carry out Fault Code '7' troubleshooting before addressing any other fault.