Garmin GDL 88 User Manual

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190-01122-03  Rev. A

GDL 88 ADS-B Transceiver Pilot’s Guide

The GDL 88 provides an Anonymous Mode which broadcasts a randomized

ICAO address in the ADS-B Out message. The Anonymous Mode, when armed,
will replace the Flight ID with a temporary randomized number for privacy while
the position information will still be provided. This randomized address allows
the  ADS-B  Out  message  to  not  be  tied  to  a  specific  aircraft,  much  like  a  VFR
squawk code of 1200 on a Mode A or Mode C transponder. The mode is armed 
via a switch in the cockpit or via a control on the display integrated with the GDL 
88. When a VFR squawk is present in the transponder and anonymous mode
is selected, then the GDL 88 operates in anonymous mode and no identifying 
information is provided in the ADS-B Out message. This mode will persist until 
the squawk code is changed or the Anonymous Mode control is turned to the off
state. 

Anonymous Mode is not available when installed in an aircraft with a Mode S 

transponder. 

If a weight on wheels or squat switch is installed, the GDL 88 will use that

input to determine air/ground status. If not, then air/ground status is purely based
on GPS-derived information.