Message Name:

VHF NAVIGATION SYSTEM NO DATA

The Very High Frequency (VHF) Navigation System cannot receive guidance data.

• Very High Frequency (VHF) Navigation Unit 1 (A3)
• Very High Frequency (VHF) Navigation Unit 2 (A4)
• Very High Frequency (VHF) Omnirange/Localizer (VOR/LOC) In-Line Filter 1 (FL7)
• Very High Frequency (VHF) Omnirange/Localizer (VOR/LOC) In-Line Filter 2 (FL6)
• Very High Frequency (VHF) Omnirange/Localizer (VOR/LOC) Antenna (E14)
• Very High Frequency (VHF) Omnirange/Localizer (VOR/LOC) Antenna Coupler (CP3)
• Glideslope Antenna Diplexer (CP2)
• Marker Beacon Antenna (E12)
• Marker-Beacon Antenna Diplexer (CP1)
• Marker-Beacon In-Line Filter (FL5)

Advisory Wire/Service Bulletin: None

Forum Articles/Infoservice/Newsletter: None

NOTE: When the radio system is initially energized (after a cold-start and during a WOW condition), it automatically starts the POST. The POST does an RMU test, RSB continuity test, and radio module test. The POST does not do a test of the antennas, in-line filters, diplexers, or coaxial cables.

1. If the RMU display shows CHK NAV 1-2-3 UNIT on the SYSTEM TEST RESULTS page, check that the correct VHF NAV units are installed and the switches on the audio panels are set correctly.
   NOTE: If the RMU display shows CHK RMU 1-2 or if the RMU displays are magenta, perform the troubleshooting for radio management units.
   NOTE: CHK NAV 1-2-3 UNIT can show that the VHF NAV unit is incorrect, not energized, or not installed.
2. Push the TST (test) pushbutton on the RMU to get the RADIO TEST RESULTS page from the SYSTEM TEST RESULTS page. Check if the RMU display shows NAV 1-2-3 UNIT and/or NAV 1-2-3 ERR.

   1. If the RMU display does not show NAV 1-2-3 UNIT and/or NAV 1-2-3 ERR, go to step 4.
   2. If the RMU display shows NAV 1-2-3 UNIT and/or NAV 1-2-3 ERR, continue with next step.

3. Perform the operational test of the RSB part of the digital bus system. On the CAIMS PMAT, perform the IBIT of the RSB part of the digital bus system.

   1. If the results of the RSB test are not satisfactory, repair the defective RSB wiring as required and do close out.
   2. If the results of the RSB test are satisfactory, continue with next step.

4. On the RMU display, look on the applicable maintenance log page(s) for the messages as follow:

   Event Description	Maintenance Page (Radio or cluster module)	Event Code
   CODE ERR	Cluster	A5
   COMPUTER	Cluster	06, 07, 08, 09, 86, 87, 88, 89, A4
   COMPUTER	Radio	06, 07, 08, 09, 25, 26, 86, 87, 88, 89, A5, A6
   DATA BUS	Cluster, Radio	03, 04, 05, 83, 84, 85
   FPGA ERR	Cluster	B0
   GS DATA	Radio	B3
   GS TUNE	Radio	2A, 2B, AA, AB
   LOC DATA	Radio	B2
   MKR RCVR	Radio	BC, C0, C1, C2
   NAV RCVR	Radio	3D, 3E, 3F, BD, BE, BF
   NAV TUNE	Radio	28, 29, A8, A9
   OVERHEAT	Radio	27, A7
   PWR SUPPLY	Radio	A1, A2, A3, A4
   RAM ERR	Cluster	A1, A2, A3, 2A
   RSB PRI	Cluster	AB
   RSB SEC	Cluster	AC
   RSB TX	Cluster	AD, AE
   STRAPS	Cluster	A6
   VOR DATA	Radio	AF, B0, B1

   1. If the messages are not found, do close out.
   2. If one or more of the given messages are found, replace the VHF NAV unit 1-2-3 and continue with next step.

5. On the RMU display, look on the applicable maintenance log page for the message as follows:

   Event Description	Maintenance Page (Radio or cluster module)	Event Code
   STRAPS	Cluster	A7

   1. If the given message is not found, do close out.
   2. If the given message is found, go to the NAV UNIT STRAPS page on the RMU which shows a list of straps that are cut (open). Check that the list of straps is correct for the aircraft configuration and continue with next step.

6. Perform a visual inspection of the VHF NAV system components such as VOR/LOC antennas, VOC/LOC couplers, VOC/LOC in-line filters, marker beacon antenna, marker beacon antenna diplexer, marker beacon in-line filters, glideslope antenna, glideslope antenna diplexer and related coaxial cables.

   1. If the defective components are not found, do close out.
   2. If the defective components are found, continue with next step.

7. Replace the defective VOR/LOC antennas, defective VOR/LOC antenna couplers, defective VOR/LOC in-line filters, defective Glideslope antenna, defective Glideslope antenna diplexer, defective Marker beacon antenna, defective Marker-beacon antenna diplexer, defective Marker-beacon in-line filter and defective coaxial cable.
8. Do close out.