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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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11/04/24

Message Overview:

Message Name:

POWER SUPPLY FAULT

Message Code:

B3-681671

Associated CAS:

AT FAIL
(Advisory)

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

Message Description:

The Power supply fault indicates undervoltage within the Autothrottle Computer (AT). It could be caused either by a low voltage on the aircraft supply, or by a failure within the computer. The monitors are not able to reliable discriminate between an internal failure and a (external failure) loss of normal input power, and so this fault is reported separately from the " INTERNAL FAULT" [AT]. The fault is reported by the Autothrottle (AT) Computer.

Possible Causes:

  • Auto Throttle Computer (A252)
  • Power source
  • Associated Wiring

Troubleshooting Tips:

Advisory Wire/Service Bulletin: None

Forum Articles/Infoservice/Newsletter: None

NOTE: Review the Auto Throttle "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
Safety Precautions - Maintenance Practices - ALL SPM 20-00-01-02-01
Wire Repair - Maintenance Practices - ALL SPM 20-12-10-02
Electrical Connectors - Maintenance Practice - ALL SPM 20-20-00-02-01

Troubleshooting Recommendations:

  1. Make sure the Autothrottle (AT) Computer Circuit Breaker (CB2-A8) is set to IN.

    1. If the CB was set to OUT, investigate the reason and set it back to IN if possible, confirm faults related to the AT system have cleared and do close out.
    2. If the CB was already set to IN, continue with next step.

  2. Remove the AT computer. Perform a 28 VDC voltage and continuity to ground check as follows:

    From To Expected Result Result
    A252P1-30 Ground 28 VDC
    A252P1-22 Ground Continuity
    A252P1-9 Ground Continuity

    1. If results are as per table above, continue with next step.
    2. If 28 VDC or ground is missing, perform wiring checks and repair as required.

  3. Replace the AT computer (A252).
  4. Do close out.

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