• Navigation Flag (NAV): Notes:

  The source that affects operation of the NAV flag is determined by the position of the HSI source selector switches on the glareshield. With the HSI selector switch in VOR/ILS, the flag circuit is tied to the VHF Nav receiver. with the HSI selector switch in NAV, the flag circuit is tied to the FMC through the DAA.

  
  NAV Flag with HSI SW in VOR/ILS, VOR Freq tuned:

  1.Move VHF NAV XFR switch on P5 overhead panel to Capt on Aux or F/O on Aux (depending on the indicator that is flagged). On those acft with only two Nav receivers go to Both on 1 or Both on 2.
  
  2.If the NAV flag stays IN-VIEW when NAV XFR switch is moved to secondary nav source then the the indicator is the problem. To further verify the indicator failure, move the HSI selector switch to nav and verify that nav flag continues to show.
  
  3.If the NAV flag PULLS FROM VIEW when the NAV XFR switch is moved to secondary nav source then trouble shoot the VHF nav system. you can further verify a source problem by looking for a pointer flag on the RDDMI as well.
  
  NAV flag with HSI SW in VOR/ILS, ILS Freq tuned:

  1.With the HSI selector switch on the glareshield in the VOR/ILS position, observe the RUNWAY flag on the ADI directly above the HSI with the NAV flag in-view:
  
  2.If the RUNWAY FLAG IS NOT IN-VIEW on the ADI, then the problem is with the HSI. To further verify do one or both of the following:
  
  2a.Move the VHF Nav XFR switch on the P5 overhead panel to "Capt On Aux" or "F/O On Aux" and observe the NAV flag. If it stays inview with a different nav source then its the HSI at fault.
  
  2b.Run the ILS self-test on the VHF nav control panel and observe the indications on both the ADI and HSI. If the HSI NAV flag is in-view throughout the test but the ADI RUNWAY flag is not then the HSI is bad.
  
  

  3.If the RUNWAY flag on the ADI and the NAV flag on the HSI below are BOTH IN-VIEW, then you have a source problem. Do the following to verify:
  
  3a.Move the VHF Nav XFR switch on the P5 overhead panel to "Capt On Aux" or "F/O On Aux" and observe the RUNWAY flag on the ADI and NAV flag on the HSI. If both flags pull from view then the normal source feeding those indicators is at fault. proceed to trouble shoot the VHF Nav system.
  
  NAV Flag In-view (HSI SW in NAV):

  With the HSI selector switch in the NAV position the source of nav data to the indicator is the FMC:

  
  

  1.Place both CAPT and F/O HSI selector switches to the NAV position. If the NAV flag on BOTH HSI’s are in view, then trouble shoot the FMC.
  
  2.If the NAV flag is in-view on ONLY ONE HSI move the HSI selector switch from NAV to VOR/ILS and look for the following:
  
  3.If the nav flag remains IN-VIEW then the indicator is the most likely problem.
  
  4.If the nav flag is NOT IN-VIEW, then the DAA is the likely problem (#1DAA for the CAPT side, and #2 DAA for the F/O side).
  ADI INFORMATION:

  

  
  Circuit Breakers:

  VOR/LOC #1: P18-1 = A1.

  VOR/LOC #2: P6-1 = A15.

  Glide slope 2: P6-1 = A16.

  Glide slope 1: P18-1 = A2.

  FMCS CMPTR 1: P18-2 = E8.

  FMCS CMPTR 2: P6-1 = D16.

  F/O XFMR (ALT): P18-2 = B4.

  Capt cmps xfmr (ALT): P6-1 = B12.

  Instrument Transformer 2: P6-1 = A12.

  Instrument Transformer 1: P18-2 = A1.

  DAA FMC #1 DC: P18-2 = C5.

  DAA FMC #1 AC: P18-2 = D1.

  DAA FMC #2 DC: P6-1 = D13.

  DAA FMC #2 AC: P6-1 = D8.

  
  
  More Notes:

  The valid signals from either the FMC/DAA or the VHF Nav rcvr that control the NAV flag on the HSI go through the HSI selector switches. If you replace a HSI and the NAV flag is still in-view, check the wires going to the HSI selector switch.

  
  Applicable deferrals 34-17-04=VHF ILS System.
  34-17-01=VHF Navigation Systems (VOR System).
  34-36=Flight Management Computer System.

Training Only