Garmin GTX325 Mode C Transponder FAA TSO

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Part# 11-17184
MFR Model# 010-01083-01


Offering a simple, affordable replacement for standard Mode C transponder units in aircraft that don’t fly in ADS-B mandated airspace — or that will be equipped with a separate UAT ADS-B transceiver solution — the GTX 325 transponder is a reliable, TSO-certified problem solver. Its solid-state design works to maximize service life and assure dependable ATC traffic surveillance.

Note: For ADS-B compliance, the GTX 325 requires that the aircraft is equipped with a UAT ADS-B solution, like the GDL 82.


A Smarter Way to Squawk
Featuring an easy-to-read LCD display designed for optimal viewing in all lighting conditions, GTX 325 offers a number of useful timing and display functions. Timers include trip time, flight time, count-up and count-down, while display functions include readouts for density and pressure altitude as well as static (outside) air temperature. In addition, the altitude monitor function displays the current deviation from the chosen altitude, as well as provides a “leaving altitude” alert when the deviation exceeds the preset limit. Dedicated push buttons numbered 0 through 9 make for quick and easy squawk code entry, while a dedicated VFR button pulls up the VFR code with a single keystroke. Compatibility with the GTN 750 and GTN 650 series of integrated GPS/Nav/Comm systems also enables transponder code selection and control from your navigator’s touchscreen display.

Altitude Encoding Made Simple
The GTX 325 transponder can also be paired with an optional Garmin altitude encoder to satisfy Mode C data transmission requirements for IFR. The external Garmin altitude encoder mounts separately on the install rack. So, if the transponder ever requires removal, there’s no need for the static line to be disconnected. In turn, that eliminates the need for a follow-on leak check — and thus helps minimize ongoing service costs.

Keeps Your Stack Intact
No matter how your aircraft is currently equipped, our GTX 325 offers a simple, all-bases-covered transponder upgrade solution. The standard size and form factor of the 1.65” high unit assures a straightforward replacement for most existing stack-mount transponders — preventing extra avionics rework and installation downtime. See your authorized Garmin installation center for more details on the GTX 325 upgrade for you


  • Physical dimensions (unit, rack, connectors); depth is measured from face of instrument panel: 1.68” x 6.30” x 10.07” (42 x 160 x 256 mm)
  • Display type: Digital
  • Weight (unit, rack, connectors) 2.9 lbs (1.32 kg)
  • Voltage range: 14/28 VDC (14 W max)
  • Transmit power: 200 W minimum
  • Temperature: -40° C to +70° C
  • Operating altitude: To 55,000 ft (16,800 m)
  • Cooling input: Not required
  • Environmental compliance (TSO Approved): DO-160G
  • Software compliance (TSO Approved): DO-178 Levels B, C, D
  • Hardware compliance (TSO Approved): DO-254 Level C; TSO compliance (Approved): TSO-C88b (w/opt. alt. encoder); TSO-C74d
  • Mount type: Panel
  • Transponder type: Mode A/C
  • Squawk code selection: Push-button


  • Solid state transmitter (more efficient, longer life): yes
  • Aural alerts: yes
  • Total air temperature (TAT): yes
  • Pressure altitude readout: yes
  • Altitude monitor function: yes
  • Density altitude readout: yes
  • Built-in timers: yes
  • Automatic ALT/GND mode: yes

  • Optional:

  • Pressure altitude encoder module (mounts to connector back-plate)
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Please note, Aircraft Spruce's personnel are not certified aircraft mechanics and can only provide general support and ideas, which should not be relied upon or implemented in lieu of consulting an A&P or other qualified technician. Aircraft Spruce assumes no responsibility or liability for any issue or problem which may arise from any repair, modification or other work done from this knowledge base. Any product eligibility information provided here is based on general application guides and we recommend always referring to your specific aircraft parts manual, the parts manufacturer or consulting with a qualified mechanic.

Q: Does the GTX Mode C Transponder come complete with wiring plug at rear?

This part number, 11-17148, does not come with a harness. the connector kit is included for building the wiring harness.

Q: Is this direct replacement for GTX 327 transponder? a simple remove and replace?

No. These two are different sized units. the GTX 325 was made to "replace" the GTX 327 in terms of functionality but will require a new tray and connector to be installed.

Q: Does this Garmin GTX 325 transponder it come with its own digitizer and antenna?

No, it does not include an internal digitizer, however the GAE12 altitude encoder can attach to the back of the tray. It will not include an antenna, a common antenna would be the CI 105.

Q: What encoder is recommended with the Garmin GTX 325?

The Garmin encoder for this transponder is part number 11-14162.


No, this is a mode C transponder. The addition of the WAAS GPS does not make this compliant for ADS B Out.

Q: Can the GTX325 interface with the G3X? To transfer transponder code and pressure altitude information from G3X to this unit?

Yes, the GTX 325 can interface to the G3X. Yes, the G3X can send pressure altitude info to the transponder and control the squawk code.

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