Garmin GDL 88 Pilot's Manual

Also see for GDL 88: Installation manual

Garmin GDL 88 Pilot's Manual Manual pdf 18 page image

3-2Garmin GDL 88 ADS-B Transceiver Pilot’s Guide 190-01122-03 Rev. CThe following table describes the aircraft that will be observed by a GDL 88equipped aircraft according to the level of equipment installed in the other aircraft.Other Aircraft Equipage Viewable by GDL 88Equipped Aircraft1090ES Out Equipped YesUAT Receive Only Capable NoUAT Transmit Equipped YesNo Transponder, No ADS-B NoNon ADS-B Equipped, but with Mode C or S Transponder Yes (see Note)Table 3-1 Aircraft Available for Viewing by an ADS-B Equipped OwnshipNOTE: Only when in ADS-B ground station coverage and when the otheraircraft is in ATC radar coverage.3.2 Self-InterrogationFor installations with a digital interface between the GDL 88 and the installedtransponder, the transponder acts as a single control to enter the transpondersquawk code, IDENT, and emergency status.When a digital interface is not available, the GDL 88 is configured to utilizeself-interrogation. The GDL 88 has a small, ultra low power 1030 MHz transmitterintegrated into the unit that interrogates the transponder installed in the aircraft.This interrogation looks exactly like the interrogations received from groundbased surface search radars and the transponder replies like it is designed to do,to include the squawk code, IDENT status, and emergency status. The GDL 88receives this reply and sets the corresponding ADS-B Out message values to matchthe received data.3.3 Pressure Altitude Broadcast Inhibit (PABI)Much like with Mode C transponders, a method is required to be available tothe flight crew to inhibit the transmission of pressure altitude in the ADS-B Outmessage. This could be used for certain surface operations, in the event of a failureof an altitude source in the ownship, etc. This control may either be integratedinto the controlling display or as a stand-alone switch installed in the cockpit.While conducting operations within airspace requiring ADS-B Out compliantOut transmissions, per 14 CFR 91225, PABI should not be activated unlessdirected by ATC.