The Trig TT31 Mode S Transponder is a cost-effective replacement for the Bendix/King KT-76C, especially since it is a direct replacement for KT-76A, KT-78A and KT-76C transponders with no installation changes.

For quick reference, please review the outline comparison of the KT-76C vs. TT31:

FEATURE	KT-76C	TT31
ADS-B Capable	No	Yes, 1090ES
Altitude Monitor	No	Yes
Current Draw (14V)	1.6 Amps	.63 Amps
Flight ID Display	No	Yes
GPS Input	No	Yes
Mode S	No	Yes, Level 2
Power	200 watts	240 watts
Solid State	No, PA Tube	Yes
Timer	No	Yes
TSO	C74c	C112
Warranty	2 Years	2 Years
Weight	2.4 lbs.	2.8 lbs.

Automatic Dependent Surveillance-Broadcast (ADS-B) is a component of the Next-Generation (Next Gen) Air Transportation System. ADS-B is an advanced surveillance technology that combines an aircraft’s positioning source (GPS), aircraft avionics, and a ground infrastructure to create an accurate surveillance interface between the aircraft & aircraft traffic control. ADS-B provides consistent position accuracy regardless of the aircraft’s range from the receiver.

The improved accuracy and update rate of ADS-B is a critical segment of the NextGen infrastructure.

The FAA has determined that it will be necessary for all aircraft operating in specific airspaces to be equipped with ADS-B Out by 2020. A nationwide infrastructure of ground stations is scheduled for completion during 2013.

As of June 2010, only ADS-B Out is being mandated. ADS-B Out provides the ATC with real-time position information. ADS-B In is the aircraft’s ability to receive and display other aircraft broadcasted information as well as the services provided by the ground stations.

ADS-B requires the use of a Positioning Source. As of June 2010, any positioning source is allowed; however, WAAS is the only positioning service that provides the equivalent availability required.

A Broadcast Link is also required for ADS-B functionality. There are two available options: 1090 MHz Extended Squitter (ES) or Universal Access Transceiver (UAT). FL 180 (the lower boundary of Class A airspace) is the ceiling for operating an aircraft equipped with UAT only.

ADS-B will eventually provide weather services, air traffic information, terrain maps and other flight information services for all pilots through satellite based data and ground stations. In accordance with NextGen, ADS-B will provide benefits that address some shortcomings over other, existing surveillance systems.

Some of these benefits include:

• Air-to-air surveillance capability
• Surveillance in remote areas where radar coverage is unavailable
• Real-time traffic information for aircraft not equipped with active traffic systems (ex. TCAS, TAS)
• Reduced separation between aircraft due to sharing of flight information between aircraft
• Better predictability in departure and arrival times
  
  Ultimately, ADS-B will allow aircraft to fly at safe distances from each another.

Click Here to View the official FAA NextGen Final Rule released on 5/28/10.

You may also View an SEA Summary of the FAA NextGen Final Rule (NOTE: this information has been altered for summary purposes and should be used as Reference Only).

The KT-79 is a basic digital Mode C transponder. Due to its age, components for the transmitter assembly are no longer available from Honeywell. Therefore, due to inevitable reliability and warranty issues, the KT-79 is not an ideal choice for a transponder installation. SEA offers many transponders available in the same price range with more features to consider.

SEA suggests the Trig TT31. The TT31 is a Mode S level 2 datalink transponder with extended squitter, which also supports growing ADS-B technology, available in the same price range as the KT-79.

KT-79

Trig TT31

Yes, you can connect any NMEA GPS position source to a Trig transponder, and with the correct configuration the transponder will broadcast ADS-B position squitters. However there are limitations with the NMEA data. The NMEA messages do not include Receiver Autonomous Integrity Monitoring (RAIM) information, which means that the position transmitted by the Trig transponder will be indentified as "low quality" on most traffic information systems. Please note that this type of NMEA GPS/transponder configuration will not meet forthcoming FAA ADS-B requirements, but in the end it will be rather beneficial for use in flight tracking and traffic avoidance.

As of 2010, Trig TT22 & TT31 transponders include support for Extended Squitter (ES) ADS-B Out. The software in the Trig transponders for the ES ADS-B Out provide all of the required parameters listed in EASA AMC20-24. AMC20-24 is ADS-B airworthiness approval for EASA. This "Acceptable Means of Compliance" spells out the performance requirements of such equipment.

In order to utilize the ADS functions of the Trig transponders, a GPS receiver meeting specific criteria must be interfaced with the transponder. As of 2010, the Freeflight 1201 and NexNav 3101 are the only GPS receivers that can be used with the Trig transponders for this function.

Please visit www.seaerospace.com for continuous updates on the ADS-B discussion and added features to the Trig transponders.

Extended Squitter (or 1090 ES) is the Mode S transport protocol for ADS-B operation. 1090 MHz extended squitter is an ADS-B link for air carrier, commercial, and private aircraft. With 1090ES, the Mode S transponder supports an extended squitter (ES) message. Currently, this message provides position, velocity, and heading information.

The ES versions of the Garmin GTX33, GTX-330, and GTX-330D transponders comply with FAA TSO C-166A which dictates the minimum performance standards (MPS) for 1090 MHz ADS-B equipment. Existing Garmin GTX Mode S transponders without ES can be upgraded through Garmin to include the Extended Squitter feature. On average the Extended Squitter option costs an additional $1000-$1500 USD.

It is very important to note that in order for the ES data to be broadcasted, the transponder must be interfaced to a compatible GPS that meets TSO C145a/C146a. These TSOs explains the performance standards for WAAS GPS receivers. As of 2009, the CNX80, GNS480, GNS400W/500W series and G1000 are the only Garmin GPS receivers that meet this criteria.

The following versions of the TRA-67A transponder are ADS-B compatible with Mode S extended squitter (also known as GPS squitter):

066-01127-1401
066-01127-1402
066-01127-1501
066-01127-1502
066-01127-1601
066-01127-1602

The word "squitter" refers to a random broadcast of data occurring usually in the absence of interrogation. As a component of the ADS-B system in the USA, Extended Squitter refers to a burst of extended data or message broadcasted on 1090 MHz. When connected to a GPS with the necessary integrity, a Mode S transponder with Extended Squitter capability will send a message providing position, velocity, and time.

As of June 2010, the TT31 can accept GPS information from the Garmin GNS 430/530 navigators; however the data from the GNS 430/530 does not meet the requirements of the FAA ADS-B Final Rule. The GNS 430/530 GPS does not export position integrity, which is now required by the new Rule. The Garmin GNS 430W/530W (WAAS) is an acceptable data source.

At this time, the Trig Transponders cannot accept input from the GNS 430/530W GPS. Trig is working to correct this integration issue & plans to have the software upgrade complete by end of 2010.

The software upgrade would allow the TT31 to extract the ADS-B parameters from the Garmin WAAS family of GPS navigators. This software will not be compatible with non-WAAS Garmin GPS units.

Configuration and programming of the TT31 transponder is simple. Hold down the FUNC button while switching on the transponder and the setup system will run. The setup includes the following configurations items: Mode S Address, VFR Squawk Code, VFR Flight ID, Aircraft Maximum Airspeed, Aircraft Category, Squat switch source, if installed, GPS position source, if installed, ADS-B parameters, Audio Output Volume, LCD Dimming Settings.

All programming is performed using the right hand knob and the ENT, BACK, FUNC buttons.

As of June 2010, the Trig Transponders do not currently meet the FAA's recently updated requirements.

However, in the near future Trig will be releasing several firmware updates for their ADS-B Transponders.

More information will be provided as soon as it becomes available. Transponder issues will be addressed as the FAA ADS-B requirements become more developed.

Southeast Aerospace & Trig Avionics will continue to be vigilant in notifying our customers of ADS-B requirements and solutions as soon as they become available. Customers can be assured that these solutions will be available well before the ADS-B requirements deadline.

Unfortunately, there is no other transponder that directly replaces the TDR-950 without mounting rack and connector change. Southeast Aerospace (SEA) recommends the Bendix/King KT-76A as a suitable Mode C alternative or the Trig Avionics TT31 Mode S transponder should you desire a more modern transponder with ADS-B capabilities.