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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

04/26/21

Message Overview:

Message Name:

LOCALIZER FLAG (Caution)

Identifier: 345OBS004
Effectivity: AIRCRAFT 20501 - 20999
System: Navigation
Associated CAS: None
System Description: 34-51-00
Schematic Diagram: None
Wiring Diagram: 34-51-01
34-51-05

Message Description:

The amber 'LOC' caution flag identifies that the VHF NAV Localizer is inaccurate or the NAV units can not cross compare to each other.

Possible Causes:

  • VOR/LOC Antenna
  • Poor Antenna Bonding
  • Static Wicks
  • Control Surface Bonding
  • Input/Output Concentrator (IOC) (A4-IOC)
  • L VHF Navigation Receiver (ADF VIR 1) (A47)
  • R VHF Navigation Receiver (ADF VIR 2) (A48)
  • Data Bus Failure
  • Associated Wiring

Troubleshooting Tips:

Advisory Wire/Service Bulletin: None

Forum Articles/Infoservice/Newsletter: None

Quick Links:

Removal of the VHF Navigation Receiver AMM 34-51-01-000-801
Installation of the VHF Navigation Receiver AMM 34-51-01-400-801
Removal of the VOR/LOC Antenna AMM 34-51-13-000-801
Installation of the VOR/LOC Antenna AMM 34-51-13-400-801
Removal of the Input/Output Concentrator Unit (IOC) AMM 31-45-05-000-801
Installation of the Input/Output Concentrator Unit (IOC) AMM 31-45-05-400-801
Wiring - Maintenance Practices - ALL SPM 20-12-00-02
Wire Repair - Maintenance Practices - ALL SPM 20-12-10-02

Troubleshooting Recommendations:

  1. MDC troubleshooting information may help isolate data validity, prior to component replacement and data bus ring-out.
  2. Inaccurate information can be caused by weak signal, antenna, coax, or VHF NAV receiver. If the condition checks good on the ground with test equipment and still fails in the air from a known good source, poor antenna bonding, static wicks, and control surface bonding will affect the VHF navigation system.

    • Check Antenna bonding.
    • Check Antenna resistance value and compare with other side.
    • A Time Domain Reflectometer (TDR) may be used to check the Antenna Coaxial cable.

  3. Cross comparator problems could be associated with a bad IOC, VHF NAV receiver or data bus failure.
  4. Swap the VHF NAV units. Replace defective VHF NAV Unit if necessary.
  5. Do close out.

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