Garmin G3X Installation Manual page 779

34.1.4 Transponder
GTX 23ES/33/33ES/330/330ES transponders with software version 8.00 or later are compliant with
RTCA/DO-181D, which specifies that the selection of transponder ALT and GND modes may not be
controlled by the pilot. To allow the transponder to be operated in ALT mode while on the ground, for the
purposes of performing periodic testing in accordance with the requirements of 14 CFR Part 91.413, a
special transponder ground maintenance test mode is provided.
To access ground maintenance mode in a G3X Touch system with GDU 4XX displays:
1. Access the Transponder page, press the Menu key.
2. Select Enable Maintenance Test to force the transponder into ALT mode.
To access ground maintenance mode in a G3X system with GDU 37X displays:
1. Access the Transponder Setup page via the Main Menu.
2. Change the setting for Ground Maintenance Test to Enabled to force the transponder into ALT
mode.
Transponder ground maintenance mode will be cancelled following a power cycle, or if the aircraft is
determined to be airborne.
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Rev. AA
G3X/G3X Touch Installation Manual - Maintenance
Page 34-3