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Part# 11-12076
MFR Model# ASA-00259-SU


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.
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WARNING: Cancer and Reproductive Harm -


  • 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
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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.