Trig Avionics


TT21 - Compact Transponder

TT21 - Class 2 – Mode S and 1090ES ADS-B Out transponder

Trig makes the world’s smallest Mode S certified GA transponders. The TT21 Trig compact transponder can fit into to the tightest panel space. This allows other instrumentation or avionics to be accommodated, providing a genuine benefit in any installation.

To order your TT21 contact your Approved Trig Dealer now.

Product features

The TT21 is a class 2 transponder and our most popular compact transponder model, with the following features:

  • Takes minimal panel space, fits in a standard 57mm round instrument hole or smaller compact mount
  • Comes with integrated altitude encoder
  • Certified for IFR / VFR flight
  • Certified class 2 transponder 130 watts nominal output
  • Manual dimming feature (adjustable backlight)
  • Low weight – 440g (0.8 lbs)
  • Low power consumption
  • 1090ES ADS-B Out capable
  • Free European Minor Change approvals
  • 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

Product description

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, ideally suited for use via an auxiliary battery in either gliders, balloons or foot launched flight.

Trig’s TT21 has a 130 watts nominal power output, making it a class 2 transponder that 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 both 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 easy to read in all lighting conditions and features manual dimming. The transponder control head is splash proof too so it’s ideal for open cockpit and seaplane operations.

You may wish to consider our TN70 product line, this contains all the main components to provide an ADS-B Out solution in one box and can be specified with a TT21. Customers in the U.S. should be aware that FAA, Federal Aviation Regulations (FAR) 91.227 requires that a compliant ADS-B Out solution uses a Class 1 transponder. The TT22 is a Class 1 device and meets this requirement. The TT21 is a Class 2 device and does not meet this regulation.

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.

Contact your nearest Approved Trig Dealer now and benefit from our smart, affordable and future proof avionics.

What are the differences between the TT21 and TT22?

Both models have the same physical dimensions and advantages of size and ease of installation. The TT21 is a 130 watt Class 2 transponder; this makes it ideal for light sports and regular GA use. The TT22 is a 250 watt Class 1 transponder, ideally suited to higher performance and/or high altitude performance types.

In the U.S. the FAA has stated that Class 1 transponders must be used to be ‘2020 compliant’ For U.S. customers Trig recommends the TT22 unit for this reason.

How does the compact fit or full round installation work?

Complete units ship with the necessary parts to enable you to choose to install the transponder either as a compact mount or 2 ¼ “ full round. The kit includes a template to assist you in cutting an accurate compact mount hole in the panel. If a full round mounting is required then you simply fit the plastic blanks above and below the body on the TC20 controller (included in the box). Once installed the full round is a tough and durable solution and is particularly suited to classic and vintage types.

Is the controller display visible in all lighting conditions?

Yes! The LCD display is clear and crisp in all lighting, full sunlight generates a very clear contrast and in dull or dark lighting the inbuilt lighting ensures the unit remains clear and legible. The controller has a backlight and manual dimming can be selected to increase or decrease brightness.

Is the controller easy to use?

Yes! One handed operation is simple. The Squawk code is easily entered using fingers to rotate the ‘CODE’ dial whilst the thumb is used to press the ‘ENT’ key. All operations can be performed whilst wearing flying gloves.

Can I use the transponder in open cockpit flying?

The TC20 controller is splash proof. This makes it suitable for use in open cockpit aircraft, where the weather can sometimes be in the cockpit and not just outside it!

When I buy a TT21 or TT22 transponder what comes in the box?

When you purchase a TT21 or TT22 transponder (complete kit) you will receive the following items: control head, hardware 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.

In Europe how do I get a free minor change?

Free minor changes for the TT21 and TT22 are available, see our minor change library. You may also consider the alternative EASA approval called CS-STAN this is especially suited to VFR aircraft.

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