TT31 Mode S Transponder

Part No: TT-31

Shipping calculated at checkout.
Options: w/ Rack


Trig’s TT31 transponder is the perfect retro-fit for popular Bendix King KT76A and KT78A transponders. The TT31 is a certified Class 1 Mode S transponder which will ‘plug and play’ straight into the existing Bendix King tray. It is now possible to install the TT31 and configure ADS-B Out using the original tray. This significantly reduces both installation time and cost. It provides pilots with class leading Mode S technology that is 1090ES ADS-B Out capable.

Now STC'd for interface with Garmin GNS400W/500W series navigators for full ADS-B compliance. Please see STC AML for aircraft and equipment applicability.

The TT31 stack transponder has unparalleled installation benefits and class leading performance.

Trig’s TT31 transponder is the ideal retro-fit for the popular Bendix King legacy transponders. The TT31 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 1 Mode S technology that is also 1090ES ADS-B Out capable too – to the latest international standard.

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.

Talk to your Approved Trig Dealer now to find out how the TT31 can feature in your aircraft. Our Express Lane Service now provides customers in the U.S. with the fastest installation pathway to ADS-B, in as little as 5-8 hours. This service is offered by participating dealers, identified by a stop-watch symbol on our U.S. dealer page.

  • Improved retrofit performance – ‘plug and play’ Mode S installation for KT76A, KT76C and KT78A
  • Certified for IFR / VFR flight
  • Amongst the lowest power consumption in class
  • 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)
  • 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


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, up-linked from approach radars. TIS traffic can be displayed on a variety of portable and panel mount displays, coverage includes most US terminal areas. The latest performance upgrades are available during the life of your product via Trig software upgrades, avoiding the need for expensive hardware upgrades.


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 class leader, 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 traffic transmissions in the U.S. the FAA requires a functioning certified ADS-B Out device.


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.


In North America ADS-B is required by most pilots.

Our TT31 transponder provides a highly practical 2020 ADS-B upgrade option. With the right avionics in your aircraft and our latest TT31 software you can get ADS-B installed up to three times faster than alternative solutions – saving time and money.

To find our more watch the video below and visit our ADS-B Express Lane page:

Specification TT31 Transponder
Type Class 1 Mode S Level 2 els
Certification ETSO C166A, 2C112B and TSO-C112, C166b
Compliance ED-73B, DO-160E, DO-178B Level B, DO181C, DO-260B Class B1S, DO-254 Level C
Supply Voltage (DC) 11 – 33 V
Typical Current Consumption (at 14V) idle: 0.22 A, active: 0.45 A
Nominal Transmitter Power 240 W at connector
Operating Temperature -20°C to + 70°C
Cooling Requirement No fan required
Weight 1.35 kg
Dimensions In tray – H 40 x W 160 x L 239 mm
In tray – H 1.57 x W 6.30 x L 9.4 inches

Questions & Answers

See below for answers to our most popular questions.

Have a Question?

Product Reviews from Verified Customers