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3-2
GDL 88 ADS-B Transceiver Pilot’s Guide
190-01122-03 Rev. A
The following table describes the aircraft that will be observed by a GDL 88
equippedaircraftaccordingtothelevelofequipmentinstalledintheotheraircraft.
Other Aircraft Equipage Viewable by GDL 88
Equipped Aircraft
1090ES Out Equipped Yes
UAT Receive Only Capable No
UAT Transmit Equipped Yes
No Transponder, No ADS-B No
Non 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 Ownship
NOTE: Only when in ADS-B ground station coverage and when the other
aircraft is in ATC radar coverage.
3.2 Self-Interrogation
ForinstallationswithadigitalinterfacebetweentheGDL88andtheinstalled
transponder, the transponder acts as a single control to enter the transponder
squawkcode,IDENT,andemergencystatus.
Whenadigitalinterfaceisnotavailable,theGDL88isconguredtoutilize
self-interrogation.TheGDL88hasasmall,ultralowpower1030MHztransmitter
integrated into the unit that interrogates the transponder installed in the aircraft.
This interrogation looks exactly like the interrogations received from ground
based 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88
receives this reply and sets the corresponding ADS-B Out message values to match
the received data.
3.3 Pressure Altitude Broadcast Inhibit (PABI)
MuchlikewithModeCtransponders,amethodisrequiredtobeavailableto
the flight crew to inhibit the transmission of pressure altitude in the ADS-B Out
message. This could be used for certain surface operations, in the event of a failure
of an altitude source in the ownship, etc. This control may either be integrated
into the controlling display or as a stand-alone switch installed in the cockpit.
WhileconductingoperationswithinairspacerequiringADS-BOutcompliant
Out transmissions, per 14 CFR 91225, PABI should not be activated unless
directed by ATC.