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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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Quick Links

04/27/21

Message Overview:

Message Name:

FLUTTERING OR POPPING SOUND AFTER APU START

Identifier: 491OBS002
Effectivity: AIRCRAFT 20501 - 20999
System: APU
System Description: 49-10-00
Schematic Diagram: 49-61-00
Wiring Diagram: 49-61-01

Message Description:

A fluttering or popping sound can heard after performing an Auxiliary Power Unit (APU) start.

Possible Causes:

  • Carbon deposits in combustor

Troubleshooting Tips:

Advisory Wire/Service Bulletin: None

Forum Articles/Infoservice/Newsletter: None

NOTE: Carbon formations originating in the combustion chamber can liberate and cause impact damage to turbine wheel blades and turbine nozzle and popping noises due to "surging".

Quick Links:

APU Safety Precautions AMM 49-00-00-910-801
Auxiliary Power Unit (APU) Pre-start Check AMM 49-11-00-740-801
Starting the Auxiliary Power Unit (APU) AMM 49-11-00-866-801
Inspection And Repair Manual 49-24-09

Troubleshooting Tips:

  1. Refer to the Honeywell APU Inspection and Repair Manual (49-24-09) to perform a Boroscope inspection of the APU. Look especially for carbon build up in the combustion chamber.
  2. Apply necessary recommended corrective actions if required.
  3. Do close out.

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