Trig Avionics


TT31 – Transponder - Class Leader

TT31 – Class 1 - Mode S and 1090ES ADS-B Out transponder

Trig’s TT31 transponder is the ideal retro-fit for the popular KT76A, KT76C and KT78A transponders. The TT31 is a Class 1 transponder which will ‘plug and play’ straight into an existing KT76A, KT76C and KT78A tray. This significantly reduces both installation time and cost. It provides pilots with class leading Mode S technology that is also 1090ES ADS-B Out capable too.

Our latest upgrade includes TIS traffic enhancements and enables ADS-B Out to be configured using the existing tray. The TT31 is compatible with many popular GPS position sources including Garmin GNS and GTN navigators and the Trig TN70. This makes installation flexibility the best in class. A free FAA STC allows the TT31 to be installed as a compliant ADS-B Out solution in 650 aircraft types for further information see our U.S. ADS-B page.

To order your TT31 contact your Approved Trig Dealer now.

Product features

  • Improved retrofit performance – ‘plug and play’ Mode S installation for KT76A, KT76C and KT78A
  • Certified Mode S and 1090ES ADS-B Out capable
  • Certified for IFR / VFR flight
  • Amongst the lowest power consumption in class
  • 240 watts nominal output
  • TIS traffic capabilities – portable and/or panel mounted avionics
  • Backlit LED display
  • No cavity tube – no warm up time required (no need for dropper resistors)
  • EASA ETSO and FAA TSO Certification – TSO C166b the latest ADS-B standard
  • Free European Minor Change approvals
  • Free FAA ADS-B STC for 650 aircraft types
  • Software provides the widest compatibility with third party avionics
  • Unbeatable value and quality – designed and manufactured in the U.K.
  • Two year worldwide warranty

Product description

The TT31 is a highly efficient class leading transponder. It’s easy to use and operate, with a clear bright display and simple user interface. Features include a flight timer, stop watch and altitude monitor (can alert you of a deviation from your selected altitude). The TT31 includes data link support for the U.S. TIS traffic service, uplinked from approach radars. TIS traffic can be displayed on a variety of portable and panel mount displays, coverage includes most US terminal areas.

Mode A and C transponders are now being replaced by Mode S transponders, this technology is optimised for tomorrow’s airspace requirements. The introduction of ADS-B surveillance technology means the modern transponder has now become the hub of future airspace compliance requirements. Here the TT31 remains the transponder of choice, it was the world’s first transponder certified to TSO C166b. This is latest FAA standard for the U.S. 2020 ADS-B mandate and demonstrates Trig’s advanced levels of compliance. It’s worth remembering that to receive all ADS-B In transmissions in the U.S. the FAA requires a functioning certified ADS-B Out device, fitting a Trig TT31 ensures a full ADS-B In picture.

The TT31 uses half the electrical power of legacy transponders, whilst still transmitting at a higher signal power, its efficient design reduces waste heat in the avionics stack. This reduces the load on the aircraft electrical system improving overall reliability. The flexible power input means that both 14 and 28 volt systems can be used without special configuration or dropper resistors (we recommend that any dropper resistor fitted for a previous transponder should always be removed). The TT31 is compatible with both parallel and serial altitude encoders; it can even act as a serial altitude repeater to provide a convenient altitude source for your GPS.

All Trig products come with a two year warranty, supported by our global network of Approved Trig Dealers and Trig Service Centers. Contact your nearest Approved Trig Dealer now and benefit from our smart, affordable and future proof avionics.

Why do you call the TT31 the class leader?

The TT31 was also the first transponder in the world to achieve FAA TSO C166b certification. It is the easiest retro-fit transponder on the market for the popular KT76A, KT76C and KT78A. Mode S is ‘plug and play’ and configurable serial ports enable the fastest ADS-B Out install, using the existing BK tray. The latest TT31 software also provides the widest compatibility with other third party avionics. In use the TT31 is one of the world’s most energy efficient transponders, producing less heat and using less power. This improves the overall reliability of your entire avionics stack.


How does “plug and play” work?

The TT31 has been specifically designed as a slide in replacement for the Bendix King KT76A, KT76C and KT78A. The transponder and can utilise the existing mounting tray, electrical connector and antenna connector.

The TT31 is also “plug and play” with the KT-76C. The  mounting tray can sometimes be a snug fit as the size varies depending on the age of the KT-76C unit.

Should I buy a Trig tray with a new transponder?

If your old transponder is a different model than the KT76A, KT76C or KT78A, or if the condition of the tray is in doubt we would recommend that it’s best to buy a TT31 tray.

Can I get Mode S using my existing tray?

Yes – the TT31 really does provide Mode S straight out of the box. We would of course remind you to ensure compliance with local installation requirements via an approved facility if you have a certified aircraft. The latest version of the TT31 provides the most flexible installation options, that can include installing ADS-B Out using the original tray (this is subject to local STC regulations).

In Europe how do I get a free minor change?

We have an extensive list of free minor changes within our site available to download. If your aircraft type is not included give us a call, we usually know of other third parties who have a TT31 minor change that may be available. You may also consider the alternative EASA approval called CS-STAN this is especially suited to VFR aircraft.

When I buy a TT31 what comes in the box?

When you purchase a TT31 Transponder (complete kit) you will receive the following items:  TT31 unit and tray, install kit, installation and user manuals (in English, German and French) and an EASA Form 1. You will need to supply wiring and have an existing or new antenna.

The TT31 can also be ordered as a kit without the Trig tray.

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