G900X/G950 Installation and Maintenance Manual – GTX 33
Page 8-1
190-00719-00
Revision D
8 GTX
33
8.1 Equipment
Description
The Garmin GTX 33 rack mounted Mode S Transponder is a radio transmitter and receiver that operates
on radar frequencies, receiving ground radar or TCAS interrogations at 1030 MHz and transmitting a
coded response of pulses to ground-based radar on a frequency of 1090 MHz. The GTX 33 is equipped
with IDENT capability that activates the Special Position Identification (SPI) pulse for 18 seconds.
The GTX 33 replies to Mode A, Mode C and Mode S interrogation. Mode A replies consist of framing
pulses and any one of 4,096 codes, which differ in the position and number of pulses transmitted. Mode
C replies include framing pulses and encoded altitude.
Ground stations can interrogate Mode S Transponders individually using a 24-bit ICAO Mode S address,
which is unique to the particular aircraft. In addition, ground stations may interrogate a GTX 33 for its
Transponder data capability and the aircraft's Flight ID, which is the registration number or other call
sign. The GTX 33 makes the maximum airspeed capability (set during configuration setup) available to
TCAS systems on-board nearby aircraft to aid in the determination of TCAS advisories.
The unit features an altitude monitor and TIS traffic advisories. A voice or tone audio output announces
altitude and traffic alerts. The GDU 1040 Primary Flight Display screen displays the code, reply symbol
and mode of operation, depending on equipment connections and configuration selection.
The GTX 33 features multiple transmit/receive ARINC 429 and RS-232 data ports. The unit concentrates
data from three ARINC 429 inputs, gray code, RS-232 input data and discrete inputs to the high-speed
RS-232 data ports for display on the GDU 1040. Although multiple output capability is available, the
unit is designed to feed all outgoing data via RS-232 data ports. Two RS-232 data ports send and receive
data to/from the GIA 63W Integrated Avionics Units.