Range View Aux OFF Bearing OFF Nav GPS1 Baro Set 29.92" VSI Bug 0 FPM Alt Bug 5000 FT Hdg Bug 270° Hdg Sync Range View SAC DTK 240° 19.1 NM 00:07:22 -20 -10 270 ° D E C R  I N C R HDG NAV APR REV ALT VS VS AP VSx100 HDG NAV D E C R  I N C R HDG NAV APR REV ALT VS VS AP VSx100 NAV 1 Enter the desired heading and engage the heading function. 3 As the autopilot captures the course, the heading function automatically  disengages, and the navigation function switches from armed to engaged. 2 Arm the navigation function. Figure 4-13. Flying an assigned heading to intercept a course. ILS Approaches Coupled Approaches RNAV Approaches With Vertical Guidance  The approach function is similar to the navigation mode, but  flies the selected course with the higher degree of precision  necessary for instrument approaches and allows glideslope  tracking in the vertical dimension. Most autopilots feature  a separate button that allows you to engage the approach  function, as shown in  Figure 4-14. (NOTE: Usually, this  mode is not used with most GPS receivers. The GPS approach  RNP (required navigation performance) of 0.3 induces the  necessary flight tracking precision. This mode is used only  if specifically stated as a command in the avionics handbook  for that equipment in that aircraft). Coupled ILS approaches make use of the autopilot’s  glideslope function.  Figure 4-15  shows the procedure for  one type of autopilot. Note that you cannot directly arm or engage the glideslope  function. The autopilot must usually be engaged first in  the approach and altitude modes. When the FD/autopilot  begins to sense the glideslope, the glideslope function will  automatically arm. When the aircraft intercepts the glideslope,  the glideslope function engages automatically, and uses the  aircraft’s pitch control to remain on the glideslope. It is  important to note that, generally, the glideslope function  can capture the glideslope only from below or on glideslope. Coupled RNAV approaches with vertical guidance work in  the same way as coupled ILS approaches. Lateral and vertical  guidance commands are generated by the FMS/NAV and  sent to the FD/autopilot. The same approach and glideslope  Like the navigation function, the approach mode can be used  to execute precision and nonprecision approaches that rely  on types of ground‑based navigation facilities (e.g., VOR,  VOR/DME, and localizer approaches). 4-12