Garmin G3X Pilot's Manual page 306

Integrated Autopilot
LOCALIZER APPROACH (NO GS)
LOC Mode is used to fly a localizer only approach (no glideslope).
Selecting LOC Mode for a localizer only approach:
1) EXTERNAL NAVIGATOR: Tune and activate the desired LOC frequency,
2) G3X: Ensure that LOC1 is the selected navigation source (use the CDI
SRC Softkey on the PFD or PFD Page to cycle through external navigation
sources if necessary). The HSI should automatically slew the needle to the
correct course.
3) G3X: From the PFD, press the HDG/ROLL Softkey to access the autopilot
lateral modes and then press the AP NAV Softkey to activate LOC Mode.
If the localizer deviation is less than half-scale when the AP NAV Softkey
is pressed, the autopilot will activate LOC Mode and track the localizer,
otherwise LOC Mode is armed and the pilot is responsible for intercepting
the localizer. In some cases it may be necessary to use HDG Mode with
LOC Mode armed to follow a vector to the localizer.
BACKCOURSE APPROACH
NOTE: When making a backcourse approach, set the Selected Course to the
localizer front course.
'
NOTE: BC' will not be displayed on the G3X HSI.
Backcourse Mode captures and tracks a localizer signal in the backcourse direction.
Backcourse is indicated by 'BC' in the autopilot status box.
If GS and LOC Mode are armed, the autopilot can only capture the localizer front
course, indicated by 'LOC' in the autopilot status box. If only LOC Mode is armed (not
GS Mode), the autopilot will capture either the front course or the backcourse based
on the angle at which the aircraft intercepts the localizer.
Selecting BC Mode:
1) EXTERNAL NAVIGATOR: Tune and activate the desired LOC frequency.
2) G3X: Ensure that LOC1 is the selected navigation source on the (use
the CDI SRC Softkey on the PFD or PFD Page to cycle through external
navigation sources if necessary). The HSI should automatically slew the
needle to the correct course.
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Garmin G3X Pilot's Guide 190-01115-00 Rev. G