04/26/21
Message Overview:
Message Description:
The amber 'G/S' caution flag identifies that the VHF Nav Glide slope is inaccurate or the Nav units can not cross compare to each other.
- Inaccurate information can be caused by weak signal, antenna, coax, or VHF Nav receiver.
- If the system 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 effect the VHF navigation system.
- Cross comparator problems could be associated with a bad IOC, VHF Nav receiver or Data bus failure.
- MDC troubleshooting information may help isolate data validity, prior to component replacement and data bus ring-out.
Possible Causes:
- L VHF Navigation Receiver (ADF VIR 1) (A47)
- R VHF Navigation Receiver (ADF VIR 2) (A48)
- ADF VIR Antenna
- Weak Signal
- Coax
- 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 |
| Standard Practices - Wire Repair | SPM 20-12-10-02 |
Troubleshooting Recommendations:
- None