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190-00906-01 GTX 23 Installation Manual
Rev. C Page 1-1
1 GENERAL DESCRIPTION
1.1 Introduction
This manual is intended to provide mechanical and electrical information for use in the planning and
design of an installation of the GTX 23 into an aircraft. This manual is not a substitute for an approved
airframe-specific maintenance manual, installation design drawing, or complete installation data package.
Attempting to install equipment by reference to this manual alone and without first planning or designing
an installation specific to your aircraft may compromise your safety and is not recommended. The content
of this manual assumes use by competent and qualified avionics engineering personnel and/or avionics
installation specialists using standard aviation maintenance practices in accordance with Title 14 of the
Code of Federal Regulations and other relevant accepted practices. This manual is not intended for use by
individuals who do not possess the competencies and abilities set forth above.
NOTE
Garmin recommends installation of the GTX 23 by a Garmin-authorized installer. To the
extent allowable by law, Garmin will not be liable for damages resulting from improper or
negligent installation of the GTX 23. For questions, please contact Garmin Aviation
Product Support at 1-888-606-5482.
1.2 Equipment Description
The Garmin GTX 23 remote-mounted Mode S Transponder is a radio transmitter and receiver that
operates on radar frequencies. It receives ground radar and TCAS interrogations at 1030 MHz, and it
transmits a coded response of pulses at 1090 MHz. The GTX 23 replies to Mode A, Mode C, and Mode S
interrogations. 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 pressure
altitude. Mode S replies can contain various information such as the Mode A code, Mode C altitude,
ICAO address, and Elementary Surveillance and Enhanced Surveillance data described below.
Features of the GTX 23 include support for ADS-B, TIS-A, mutual suppression, IDENT functionality, SI
codes, elementary surveillance (ELS), and enhanced surveillance (EHS). ADS-B, TIS-A, and mutual
suppression are discussed in following sections. IDENT functionality activates a Special Position
Identification (SPI) pulse for 18 seconds in Mode A replies. This helps the air traffic controller confirm
your position on their radar screen. SI codes, ELS, and EHS better facilitate meeting various requirements
for operation in European airspace. SI codes uniquely identify ground radar with overlapping coverage.
Supporting SI codes enables reduction in ground infrastructure complexity. ICAO Annex 10, Volume IV,
Amendment 77, paragraph 2.1.5.1.7.1 mandated SI code support. Elementary and Enhanced Surveillance
provide additional aircraft parameters to ground radar systems (for ELS, see JAA TGL 13 rev 1 dated
June 01, 2003; for EHS, see AMC 20-13, which supersedes JAA NPA 20-12a). Elementary Surveillance
provides a detailed transponder capability report and aircraft identification data (e.g. Flight ID or radio call
sign). Additionally, TCAS II compatible transponders supporting ELS can provide resolution advisory
data if the aircraft is equipped with TCAS II. (ELS is Mode S BDS registers (1,0), (2,0), and (3,0).)
Enhanced Surveillance provides selected vertical intention, track and turn reporting, and heading and
speed reporting. (EHS is Mode S BDS registers (4,0), (5,0), and (6,0).)