TT21 Class 2 Transponder (complete system)

Artikkelnr.: 00710-00

Fitting in the tightest panel space the innovative design saves weight and space.

NOK36 332,00 inkl. mva.
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Chosen by pilots around the world Trig’s compact transponders are the best choice for good reason.

Fitting in the tightest panel space the innovative design saves weight and space. Trig is ‘better by design,’with Mode S technology that makes you visible to commercial, military and GA traffic, as a result transiting busy airspace becomes more predictable and stress free. Trig transponders are future proof too – the growing use of ADS-B further enhances your visibility and flight safety. Unlike other brands Trig transponders meet the very latest certification standard for ADS-B, FAA TSO-C166b.

Designed to be easier to use, with a clear bright display the controller even comes with a built in altitude encoder!  Join other pilots who have made Trig their compact transponder of choice – you’ll be in great company.

  • Compact form factor – takes minimal panel space, fits in a compact or standard 57mm instrument hole.
  • Minimal depth – create space on your panel for other avionics.
  • Integrated altitude encoder
  • Certified for IFR / VFR flight
  • Manual dimming feature (adjustable backlight)
  • Low power consumption
  • EASA ETSO and FAA TSO Certification – includes TSO-C166b the latest ADS-B standard
  • Free European Minor Change approvals
  • Free FAA ADS-B STC for 576 aircraft types
  • Unbeatable value and quality – designed and manufactured in the U.K.


Trig’s compact transponder is in two parts 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. Our compact transponders are highly efficient, whilst used in a wide range of GA types they are ideally suited for use in gliders and balloons, via an auxiliary battery.

Trig’s compact transponders are easy to operate and have a crisp, bright display that’s easy to read in all lighting conditions and is equipped with manual dimming. The transponder control head is splash proof too, so it’s ideal for open cockpit and seaplane operations.


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.


ADS-B enhances safety and visibility – your investment in a TT22 transponder is future proof. Trig has a matching certified GPS position source that is highly affordable called the TN72. This is ideal for ADS-B voluntary equipage and the TN72 can even be used to meet the 2020 mandate by light-sport, experimental and homebuilt types in the U.S.

Our TN70 GPS position source is suitable for certified Part 23 aircraft that need a TSO-C145 position source, for operations in 2020 rule ADS-B airspace using a TT22 transponder.

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.

Product Model Type Meets TSO-C166b Suitable for 2020 ADS-B rule airspace (US) Transmitter Output Sales Part Number
TT21 Class 2
Mode – S and 1090ES      ADS-B Out capable
Yes No – FAR 91.227 requires a Class 1 device – select the TT22. 130 W at connector 00710-00
TT22 Class 1
Mode – S and 1090ES    ADS-B Out capable
Yes Yes 250 W at connector 00772-00
Specification TT21 Transponder TT22 Transponder
Type Transponder Class 2 Mode S level 2els ADS-B Class B0 Transponder Class 1 Mode S level 2els
ADS-B Class B1S
Certification ETSO C88A, C112C, C166A
TSO C88b, C112c, C166b, approved for IFR and VFR flight
Compliance ED-73C, DO-160F, DO-178B Level B, DO-254
Level C, DO-260B, DO-181D
Supply voltage (DC) 9-33 V
Typical consumption (at 14v) idle: 0.15 A active: 0.28 A idle: 0.15A active: 0.34 A
Nominal Transmitter Power 130 W at connector 250 W at connector
Operating temperature for the transponder -40°C to +70°C
for the controller -25°C to +70°C
Cooling requirement no fan required
Weight (hardware back box) 440g / 0.8 lbs
Weight (TC20 control head) 90g / 0.11 lbs
Dimensions (mm) controller: H 44 x W 63 x L 54 mm
transponder in tray: H 48 x W 68 x L 160 mm
Dimensions (inches) controller: H 1.8 x W 2.4 x L 2.1 inches
transponder in tray: H 1.8 x W 2.6 x L 6.2 inches


  • All Trig products come with a two year warranty, starting from the day of installation
  • Installation manual and Operating manual (in English, German and French)
  • Installation kit (including plastic brackets for round mounts)
  • Tray
  • EASA Form One


What is the difference between the TT21 and the 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 complaint’ For U.S. customers Trig recommends the TT22 unit for this reason.

Is the controller display visible in all lightling 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.

How does the compact fit or the round mount installation work?
The transponder control head, the TC20 can be installed either as a space saving compact mount or in a 57 mm round hole. Click on the 'specification tab' of this web page to see an image of the installation kit, in the technical images area. This photo features all the components contained in the install kit. This includes the two plastic blanking plates and long screws that are used to fit the TC20 control head into a 57 mm round hole. Once installed, the full round mount is a tough and durable solution, it looks great in both modern and vintage aircraft. The kit also includes a template to assist you in cutting an accurate compact mount in the panel, if that is required.

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!

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.

Does the TT22 have an STC?
Yes, Trig has a free STC with an AML list of over 576 types.

You can find the TT22 STC here -

In the U.S. installing a compliant ADS-B Out solution (in a certified aircraft) requires your Trig transponder to utilise a certified WAAS GPS, this provides a compliant ADS-B position source. The FAA also requires that a certified ADS-B installation is completed in accordance with an FAA STC approval (Supplementary Type Certificate).

Our ADS-B STC’s are available free of charge and cover hundreds of aircraft types. Trig STC approvals allow the use of popular WAAS GPS navigators too – making installation more practical and cost-effective. Our TA70 GPS antenna has also been added to our STC equipment list.