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ADS-B FAQ’s

What do I need to get ADS-B?

If you have an existing Trig transponder then you already have one important part of your 1090ES ADS-B Out system. You may need to update your software to the latest version that offers the widest compatibility with third party avionics for full ADS-B Out capabilities.

If you are looking to select Trig and want to discover what other components you will need to create your ADS-B installation then this section provides the information you need. We understand you want an ADS-B system that’s reliable, easy to install and provides the best possible long term value.

Trig transponders meet these criteria, providing the hub to a 1090ES ADS-B Out solution

ADS-B Out typically requires;

  • A Trig TT31, TT22 or TT21 transponder – certified and ADS-B Out capable.
  • A suitable GPS Position Source – with associated cable and antenna. (In the U.S. if operating in 2020 rule airspace, Part 23 aircraft must use a certified WAAS unit GPS)
  • A Ground/Air determination method – Auto air/ground, Squat Switch, Airspeed Switch or Air Data Computer (this is mandatory in the U.S. but is not required in most countries – check with your local GA regulatory body)
  • Your transponder may require a new antenna if one is not already installed.
I’ve heard about the FAA mandate for 2020 but where can I find the actual regulations for ADS-B in the USA?

The FAA ADS-B Out requirements can be found online. Regulation FAR 91.227 tells you the performance requirements. FAR 91.225 defines the airspace in which ADS-B out is required. You can find more information about equipping with ADS-B here.

What are the requirements for an FAA 2020 rule compliant GPS?

In a certified aircraft you will require a certified TSO C145 position source that meets the requirements of AC20-165 Appendix 2 – such as the Trig TN70.

Trig has an FAA STC program that covers other GPS units. This includes Garmin 400 and 500 series WAAS GPS navigators which can be used with a Trig TT22 or TT31 transponder.

Light Sport, Experimental Aircraft and Gliders can use the TN72 as an approved position source in FAA 2020 rule airspace.  This product is certified and meets TSO C199 but is not approved for certified aircraft in the U.S. flying in 2020 rule ADS-B airspace.

Outside the USA, for ADS-B Out you will need:
  • An ADS-B Out capable transponder – TT21, TT22 or TT31
  • Depending upon local regulations you may be able to use our TN72 GPS Source, this is certified and highly affordable.
  • If you require a TSO-C145 WAAS GPS position source then you should use a TN70.
  • Alternatively our STC for the TT22 and TT31 allows the pairing with a  Garmin WAAS GNS or GTN Navigator.
How do I get an STC for ADS-B?

Trig has an established FAA STC program with Peregrine Avionics of Denver. We aim to cover as many aircraft and equipment combinations as possible.  Click on the STC link to view our current STC provision. Your Approved Trig Dealer (if Part 145 qualified) will be able to access the STC and provide this to you free of charge – as part of your transponder purchase and installation.

What are the key benefits of an aviation GPS source like the TN70 or TN72 compared to a consumer GPS receiver?

With good satellite coverage, both will give an accurate position fix – they use the same technology and the same GPS satellite sources.  The big difference is how they behave when coverage is poor or lost.  A consumer GPS will estimate a position and trajectory for some time after losing satellite data.  That gives the user apparent continuity when driving under bridges, or walking past tall buildings, but that behaviour is not suitable for safety critical applications, especially in a dynamic 3-D environment like an aircraft in flight.  An aviation GPS will perform fault detection and exclusion to remove poor satellite data from any position solution, and will report loss of position integrity or loss of position very quickly.  This may appear to users that the aviation GPS is “worse” than the consumer GPS, since it gives up reporting a position when the consumer GPS keeps running.  That is a deliberate safety design decision.

Why does my certified GPS take longer to find a position fix than my uncertified handheld device when I switch them both on?

Once it has locked on to the satellite transmissions, any GPS receiver needs data on the position of the satellites – called ephemeris data – to calculate the receiver position.  Each satellite transmits its own data every 30 seconds.  It takes 18 seconds to send the ephemeris data and the other 12 seconds in the cycle contains data about the rest of the satellite constellation.  Depending on where in the 30 second cycle the satellites were when the receiver was switched on, it could take between 18 and 30 seconds to acquire the ephemeris data.  The downlinked data has parity bits for error detection, but does not support error correction or higher integrity checks.  For a safety of life application like aviation, the solution is that a certified receiver must hear the same ephemeris data twice before it is allowed to use it.  This means a minimum acquisition time for each satellite of 48 to 60 seconds.  Total time will be longer than this taking into account system initialisation, interference, and other environmental factors, but a fix after a minute or so is normal.  So how does an uncertified GPS beat that?  The first speed gain is simple – consumer GPS doesn’t wait for the second copy of the ephemeris data, it simply believes what it was told the first time.  As a result, it can have a position fix in between 18 and 30 seconds.  But an even quicker solution is available to a GPS built into a phone or anything else with a data link – instead of waiting for the ephemeris data to be transmitted slowly from the satellite, it fetches the same data from an online server.  With a good data connection like a 3G phone, it might take only 1 or 2 seconds to receive all the ephemeris data over the line, and then a GPS position can be determined in less than 5 seconds.

Can I use my Pilot Aware GPS as a position source?

Yes, as long as you are not trying to meet any regulatory requirements.  Most Pilot Aware devices output GPS data using the NMEA protocol which is compatible with Trig transponders.

Note – this GPS source gives you SIL = 0 , which is ignored by certain ADS-B In traffic receivers. Additionally, for US customers, SIL = 0 does not qualify you for either a traffic or weather uplink.

Can I use my FLARM GPS as a position source?

Yes, as long as you are not trying to meet any regulatory requirements.  Most FLARM devices output GPS data using the NMEA protocol which is compatible with Trig transponders.

All Trig transponders look for $GPRMC NMEA messages.

Note – this GPS source gives you SIL = 0 , which is ignored by certain ADS-B In traffic receivers. Additionally, for US customers, SIL = 0 does not qualify you for either a traffic or weather uplink.

I fly in the U.S. and would like to install ADS-B Out in my glider. What products do I need?

Glider customers in the U.S. looking to get ADS-B equipped should look at our ADS-B gliding guidance document this highlights equipment and regulations for both certified and experimental gliders.

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