## The radio-navigation subsystem ILStest

The masked subsystem block ILStest, from the ILS sublibrary of the block-library NAVLIB, is called from within the masked Simulink block ILS, in order to check whether or not the localizer and glideslope signals are valid at the current aircraft position. The block ILStest is called from within the block ILS (Nominal ILS values). See the references for more information about ILStest.

### Inputvector: utst

      utst = [Gamma_loc Gamma_gs Rloc Rgs]'

      Gamma_loc: 2D-angle between line from c.g. of aircraft to lo-
                 calizer antenna and runway center-line (as seen from
                 above), [rad]
      Gamma_gs : 2D-angle between line from c.g. of aircraft to
                 glideslope antenna and runway center-line (as seen
                 from above), [rad]
      Rloc     : 2D-distance from aircraft's c.g. to localizer antenna
                 (as seen from above), [m]
      Rgs      : 2D-distance from aircraft's c.g. to glideslope anten-
                 na (as seen from above), [m]

### Outputvector: yils4

      yils4 = [LOCflag GSflag]'.

Note: GSflag = 0 if aircraft is in area where glideslope signals can be received with appropriate accuracy; LOCflag = 0 if the aircraft flies in area where the localizer signals are receivable. If the aircraft is too far away, GSflag and/or LOCflag are set to 1.

### References

Apart from the FDC user-manual, the following reference contains more information about the ILS signals:

1. M.O. Rauw: A Simulink environment for Flight Dynamics and Control analysis - Application to the DHC-2 'Beaver', part I: Implementation of a model library in Simulink. Delft University of Technology, September 1993