background
x
loader
Troubleshooting
arrow By ATA By Message Color By Observed Faults by MDCBy Tips

Select color for CAS message that you wish to troubleshoot

(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.

This page includes :

For AOG assistance contact:

CRC Montreal (YUL)
Quick Links

11/04/24

Message Overview:

Message Name:

STUCK SWITCH INPUT

Message Code:

B3-681691

Associated CAS:

AT FAIL
(Advisory)

Reporting LRU: Autothrottle (AT) Computer
Effectivity: Post SB350-22-002
Aircraft 20937 and Subs
System Description: 22-30-00 - Autothrottle System (ATS)
Schematic Diagram: 22-30-00-801 - Autothrottle System
Wiring Diagram: 22-30-00-801 - Autothrottle System (ATS)

Message Description:

The Engage or Disconnect switches on the Throttle Quadrant Assembly (TQA) or the Autothrottle System (ATS) Test Switch are reported stuck or invalid by the Autothrottle (AT) computer. Either of the switches were detected active for more than 30 seconds.

Possible Causes:

  • Throttle Quadrant Assembly (TQA) (A51)
  • Autothrottle (AT) Computer (A252)
  • Associated wiring

Troubleshooting Tips:

Advisory Wire/Service Bulletin: None

Forum Articles/Infoservice/Newsletter: None

NOTE: The Left A Servo Current Fault could be a result of a broken wire or open connector within the aircraft harness, or a failure of the Servo Motor Clutch Pack (SMCP) or Autothrottle Computer.
NOTE: Review the Autothrottle "AT Diagnostic Information", to find details about the MDC Data Reader Labels & bits.
NOTE: Bombardier recommends referencing the elements one (1) through eleven(11) of the "Wiring & Connections" Troubleshooting Tips document. The intent of the document is to ensure the Maintenance Technician has the information needed to perform a comprehensive check of an aircraft system wiring circuit, while also doing checks found in the From - To tables called out in the Troubleshooting Recommendations element.

From - To Table (Example)
From To Expected Results Results
XXXX-XX XXXX-XX Continuity

Quick Links:

Removal of the Auto Throttle Computer AMM 22-30-01-000-801
Installation of the Auto Throttle Computer AMM 22-30-01-400-801
Functional Test of the Auto Throttle Computer AMM 22-30-01-720-801
Removal of the Throttle Quadrant AMM 76-10-01-000-801
Installation of the Throttle Quadrant AMM 76-10-01-400-801
Operational Test of the Throttle Quadrant AMM 76-10-01-710-801
Removal of the Servo Motor Clutch-Pack (SMCP) AMM 22-30-11-000-801
Installation of the Servo Motor Clutch-Pack (SMCP) AMM 22-30-11-400-801
Safety Precautions - Maintenance Practices SPM 20-00-01-02
Wire Repair - Maintenance Practices - ALL SPM 20-12-10-02
Electrical Connectors - Maintenance Practice SPM 20-20-00-02

Troubleshooting Recommendations:

  1. Inspect the Throttle Quadrant Assembly (TQA) Autothrottle (AT) Engage and Disconnect switches. Make sure they are not physically stuck depressed.

    1. If any of the Engage or Disconnect switches are stuck in a depressed state, replace the TQA (A51). Do close out.
    2. If the switches are not stuck, continue with next step.

  2. Remove the AT computer. Do a wire check on the engage switch circuit as follows:

    Condition From To Expected Result Result
    AT Engage Switch (S207) Open A252P1-6 Ground Open
    AT Engage Switch (S206) Open A252P1-11 Ground Open
    AT Engage Switch (S207) Depressed A252P1-6 Ground Continuity
    AT Engage Switch (S206) Depressed A252P1-11 Ground Continuity

  3. Are the results as expected?

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

  4. Does Fault persist?

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

  5. Clear the Label 353 NVM by pressing and holding both disconnect buttons for more than 10 seconds but less than 30 seconds, and then pressing and momentarily holding the Self-Test button. Did the Label 353 NVM clear?
    NOTE: Clearing the Label 353 NVM will validate the disconnect switches and wiring.

    1. If YES, continue with step 10
    2. If NO, continue with next step.

  6. Do wire check as follows:

    Condition From To Expected Results Results
    AT Disconnect Switch (S209) Open A51J1-x A51J1-c Open
    AT Disconnect Switch (S208) Open A51J2-x A51J4-c Open
    AT Disconnect Switch (S209) Depressed A51J1-x Ground Ground
    AT Disconnect Switch (S208) Depressed A51J2-x Ground Ground

  7. Are the results as expected?

    1. If YES, continue with next step.
    2. If NO, replace Throttle Quadrant (A51). Do close out. 

  8. Remove the DCU and do a wire check as follows:
    NOTE: Use the Diode selection on the multimeter. 

    From To Expected Result Result
    A14EP1-8K A252P1-12 Resistance Of Diode
    A14EP1-9K A252P1-14 Resistance Of Diode
    A252P1-12 A14EP1-8K Open
    A252P1-14 A14EP1-9K Open

  9. Are the results as expected?

    1. IF YES, continue with next step.
    2. If NO, repair wiring as required. Do close out.

  10. Replace Autothrottle Computer (A252). Do close out.

Registered and/or unregistered trademarks of Bombardier Inc. or its subsidiaries. © 2015 Bombardier Inc. All rights reserved.