Garmin G5 Pilot's Manual page 62

AFCS
At 50 feet from the Selected Altitude, the flight director automatically transitions
from Selected Altitude Capture to Altitude Hold Mode and holds the reference altitude.
As Altitude Hold Mode becomes active, the white 'ALTS' annunciation moves to the
active vertical mode field and flashes green for 10 seconds to indicate the automatic
transition.
Setting the selected altitude:
Use the ALT SEL Knob on the GMC 507 to adjust the selected altitude.
Or
1) Press the Selection Knob to display the Menu.
2) Select Altitude and use the Selection Knob to change the Selected
Altitude.
Syncing to the current altitude:
Press the ALT SEL Knob on the GMC 507.
Or
1) Press the Selection Knob to display the Menu.
2) Select Altitude and press and hold the Selection Knob to sync the Selected
Altitude to the current altitude
Changing the Selected Altitude while Selected Altitude Capture Mode is active
causes the autopilot to revert to Pitch Hold Mode with Selected Altitude Capture Mode
armed for the new Selected Altitude.
3.3.3.3 ALTITUDE HOLD MODE (ALT)
Altitude Hold Mode can be activated by pressing the ALT Key; the AFCS maintains
the current aircraft altitude (to the nearest 10 feet) as the Altitude Reference. Altitude
Hold Mode active is indicated by a green 'ALT' annunciation in the G5 Autopilot Status
Box.
Altitude Hold Mode is automatically armed when in Selected Altitude Capture Mode.
Selected Altitude Capture Mode automatically transitions to Altitude Hold Mode when
within 50 feet of the Selected Altitude. In this case, the Selected Altitude becomes the
Altitude Reference.
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G5 Electronic Flight Instrument Pilot's Guide for Certified Aircraft 190-01112-12 Rev. F