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Trig TT21 Mode S Transponder

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Part# 11-07999
MFR Model# 00710-00


Note: The TT21 does not meet FAA Approval for ADS-B Out in the USA. For USA aircraft, please order the Trig TT22.

Trig makes the world’s smallest and lightest Mode S certified GA transponders. The TT21 Trig compact transponder can fit into to the tightest panel space. This allows general aviation, light sport and glider pilots to fit other instrumentation or displays that otherwise might not have been possible. The TT21 is a class 2 transponder and our most popular compact transponder model.
  • Compact size - takes minimal panel space, fits in a standard instrument hole
  • Integrated altitude encoder
  • Certified for IFR / VFR flight
  • Certified class 2 transponder 130 watts nominal output
  • Low weight – 440g (0.8 lbs)
  • Low power consumption
  • 1090ES ADS-B Out capable
  • EASA ETSO and FAA TSO Certification – includes TSO C166b the latest ADS-B standard
  • Unbeatable value and quality – designed and manufactured in the U.K.
  • Two year worldwide warranty
The TT21 is a two part transponder with a compact control head; this includes an inbuilt altitude encoder - saving further space and expense. A separate hardware box can be installed anywhere in the airframe. The mounted control head is only 54mm (2 3/25”) deep and can be fitted in panel using a 57mm (2 ¼”) round hole or smaller compact mount, the unit ships with the necessary fittings for both install options. The TT21 unit is highly efficient and is ideal for use via an auxiliary battery in gliders, balloons and foot launched flight.

Trig’s TT21 is a popular compact transponder with 130 watts nominal power output. This is a class 2 transponder which meets international standards for 1090ES ADS-B Out (TSO C166b). The TT21 is ideal for use in flight where a light weight Mode S solution is required and is suitable for IFR and VFR use.

Older mode A and C transponders are now being replaced by Mode S, technology which is optimised for tomorrow’s airspace requirements. The TT21 transponder is easy to operate and with a crisp, bright display it is also easy to read in all lighting conditions. The transponder control head is splash proof too so it’s ideal for open cockpit and seaplane operations.

(Please note in the U.S. to comply with the FAA’s 2020 mandate for ADS-B Out a certified Class 1 transponder is required after 2020, the Trig TT22 matches this requirement being a higher powered Class 1 device).

All Trig products come with a two year warranty, supported by our global network of Approved Trig Dealers and Approved Trig Service Centers in the U.S. and Australia.


  • Low Weight
  • Minimal Panel Space
  • Low Power Consumption
  • 130 Watts Nominal Output
  • Integrated Altitude Encoder
  • Simple Installation
  • Easy to Use Rotary Knobs
  • Support for ADS-B Out


  • Type: Class 2 Mode S Level 2 Datalink
  • Certification: ETSO 2C112b, C88a, TSO C112, C88b
  • Compliance: ED73B, DO160E, DO178B level B, DO254, DO181C, DO260A
  • Supply Voltage (DC): 10 – 33 V
  • Typical Current Consumption: Idle: 0.15 A
  • (at 14V) Active: 0.28 A
  • Transmitter Power: 130W nominal at connector
  • Operating Temperature: -40 to +70 C
  • Cooling Requirement: No fan required
  • Weight: 1.0 lb (450 g)
  • Dimensions: Controller: 64 x 45 x 45 mm
  • Transponder: 62 x 45 x 141 mm

In The Box

  • TT21 Control Head
  • TT21 Transponder
  • Connector Kit
  • Tray
  • Accessories
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I bought the TT-21 over 12 years ago. It has been on the aircraft and flying for around 900 hrs. In all sorts of environments, rain sleet sun night you name it. I can strongly attest to the units reliability and service. Not a single problem ever and for a mode S transponder that to this day I am not sure what it does differently than a plain mode C,,,,,. It worked perfectly. It was easy to install I did it myself as an A&P, cant be any simpler. I have yet to install the ADSB add-on but that is next. You want a great reliable transponder this is the one you ought to buy.

Ron M
December 11, 2018


Please note, Aircraft Spruce Canada'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 Canada 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: Can you tell me what is the standard length of wire is linking the controller to the transponder?

The TT21 & TT22 does not come with a wire harness. They do come with connector kit (wire not included) so you can wire them as all applications will vary giving the installer the ability to make the best fit in the aircraft.

Q: Does the TT21 Mode S Transponder meet the year 2020 ADS-B requirements?

The FAA’s 2020 mandate for ADS-B Out a certified Class 1 transponder is required. The Trig TT22 matches this requirement by being a higher powered Class 1 device. Keep in mind that your aircraft must have a Certified WAAS GPS receiver as the position source.

Q: Can a Stratus 2 or a Garmin GDL 39 supply the WAAS data to the TRIG TT21 MODE S TRANSPONDER?

A portable WAAS GPS cannot legally supply WAAS data to any transponder to be ADS-B out compliant.

Q: Can I use the new Dynon 2020 GPS antenna with this transponder for the ADS-B?

No, the Dynon antenna can only be used with a Dynon Skyview system and the Dynon mode s transponder to be ADS-B out.

Q: Does the TT21 include an antenna? If not, which antennae will work? My light sport aircraft has an aluminium skin fuselage and I am after the simplest antenna.

The TT21 does not include an antenna. We recommend Rami part number AV-22 stub antenna for certified aircraft. For experimental, the TED antenna is available, see part number 11-17995.

Q: What is the difference between the TT21 & TT22 transponders? Do they only have the ASD-B out capability, not ASD-B IN?

The TT22 wilt meet the requirements for the ADS-B out only if wired to a GTN 650 or GTN 750 as well as a GNS 430W or 530W unit. Trig also makes a TN 70 which when wired will make the TT22 ADS-B out. The TT21 has a lower watt output and does not meet the 2020 ruling.

Q: What is included in the Trig TT21 package?

The TT21 kit includes the transponder, remote controller, mounting tray, installation manual, and connector kit.

Q: What is included with the Trig tt21 PART # 11-07999?

This will include the transponder, the tray, connector kit and the control head.

Q: Is the TT21 control head included?

Yes, this kit includes the control head, the transponder, the connector kit, and the tray.

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