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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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04/27/21

Message Overview:

Message Name:

APU INTERMITTENTLY RUNNING HOT

Identifier: 491OBS001
Effectivity: AIRCRAFT 20501 - 20999
System: APU
System Description: 49-10-00
Schematic Diagram: 49-61-00 Sh. 3
Wiring Diagram: 49-61-01

Message Description:

APU running hot intermittently 379°F on one leg 595°F on another leg, all temps are APU loaded up.

Possible Causes:

  • APU Surge Control Valve (V10)
  • Hot Outside Ambient Temperature

Troubleshooting Tips:

Advisory Wire/Service Bulletin: None

Forum Articles/Infoservice/Newsletter: None

APU Load Control and Surge Control Valve Control Logic

Quick Links:

Removal of the Auxiliary Power Generator Cooling Duct AMM 49-15-09-000-801
Installation of the Auxiliary Power Generator Cooling Duct AMM 49-15-09-400-801
General Visual Inspection of the Generator Cooling Duct AMM 49-15-09-210-801
Removal of the Bleed Air Duct AMM 49-16-01-000-801
Installation of the Bleed Air Duct AMM 49-16-01-400-801
General Visual Inspection of the APU Bleed Air Duct in the APU Enclosure AMM 49-16-01-210-801
Removal of the Bleed-Air Check Valve AMM 49-16-03-000-801
Installation of the Bleed-Air Check Valve AMM 49-16-03-400-801
Functional Test of the APU Bleed-Air Check Valve AMM 49-16-03-720-801
Removal of the Surge Valve Stub-Exhaust AMM 49-16-05-000-801
Installation of the Surge Valve Stub-Exhaust AMM 49-16-05-400-801
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:

  1. Remove and replace APU Surge valve.

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