• Ground Speed Display (GS): Notes:

  The source of ground speed information displayed on the HSI depends on the position of the HSI selector switch.

  
  HSI SW in VOR/ILS Position

  1.With the HSI SW in VOR/ILS the on-side IRU is the source of ground speed.
  
  2.The ground speed data from the IRU goes through the on-side DAA that feeds the respective HSI’s.
  
  HSI SW in NAV Position

  1.With the HSI SW in NAV the FMC is the source of ground speed.
  
  2.The ground speed data from the FMC goes through the on-side DAA that feeds the respective HSI’s.
  
  ADI INFORMATION:

  

  
  Circuit Breakers:

  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.

  DAA IRS #1 DC: P18-2 = D3.

  DAA IRS #1 AC: P18-2 = D2.

  DAA IRS #2 DC: P6-1 = D10.

  DAA IRS #2 AC: P6-1 = D9.

  IRS #1 AC: P18-2 = D4.

  IRS #1 DC: P18-2 = D5.

  IRS #2 AC: P6-1 = D11.

  IRS #2 DC: P6-1 = D9.

  
  Notes:

  With the on-side IRU in NAV and the FMC functioning normally, if ground speed data is not present with the HSI SW in either VOR/ILS or NAV, dashes will be in-view on the gnd speed display. Replace the on-side DAA first. If the gnd speed display is blank, the problem is most likely the indicator.

  
  
  The Ground Speed and Miles light modules are line replacable. The Aircraft Maintenance Manual can now be used as a reference for replacement of the modules. Ref to AMM 34-28-71-4.
  
  Applicable deferrals 34-35-04=HSI Ground Speed Display.

Training Only