Garmin G3X Touch Pilot's Manual page 302

AFCS
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 Touch: Ensure that LOC1 is the selected navigation source. The HSI
should automatically slew the needle to the correct course.
3) G3X Touch: From the PFD, touch the autopilot and touch NAV to activate
LOC Mode.
Or: Press or the NAV Key on the GMC 305
If the localizer deviation is less than half-scale when NAV is touched
or when the NAV Key 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 Touch 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.
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Garmin G3X Touch Pilot's Guide 190-01754-00 Rev. E