Garmin Tips and Tricks #21
ADS-B Update
Keith Thomassen, PhD, CFII


With 3+ years until the ADS-B mandate kicks in, many are still weighing their options for equipping while others have made their choices and have installed “something”.  Part of the procrastination is hoping for newer and cheaper alternatives. But with all the new products recently -- the Lynx options by L3, and the GTX 3X5 choices from Garmin come to mind -- that course may provide diminishing returns.  Many pilots are still puzzling what will best work in their aircraft and with their installed equipment.  Compatibility with what you have is very important whether you’re trying to save money or not.
We’re all aware that airspace now requiring Mode C altitude reporting will require ADS-B (“Out” only) after Jan 1, 2020.  That includes airspace over 10,000’ altitude, Class C airspace, and airspace under the Class B veil – that one can catch you! We also understand our choices are a transponder (1090 ES) or a 978 Mhz transmitter (or transceiver).  In Class A airspace it has to be the 1090 Mhz option (Fig 1).


Figure 1.  Airspace requiring ADS-B “Out”, starting in 2020.

The transmission of your position via your ADS-B to ground stations must contain very specific additional parameters (see FAR 91.227) besides your PVT solution (position, velocity vector, and time) so that, among other things, the accuracy and latency of your position report can be judged as usable. This requires a WAAS-enabled position source (GPS) that is certified to work with your specific choice of transmitter. For example, if you have a Chelton EFIS using the FreeFlight 1201 WAAS GPS you can install a Trig TT31 ADS-B “Out” transponder, since the pair is on the “official list”. You cannot legally connect that TT31 to a GNS 480 without field approval, so check the FAA lists for compatibility ( 
Big brother is watching, and you can see what they see by asking for a report on your system performance.  Previously, an email to the right FAA address would trigger that report, but now  you fill out info on their website ( to see how your equipment is working.  Just enter the day (by the Zulu clock) of a flight (and equipment details) and you’ll likely get the report within hours. If any of the many parameters in the report are shown in red, those are failing and you should call your shop or expect a call from the Compliance folks.
So what are the main considerations as you ponder your choices?  First is frequency.  If you won’t go above 18,000’ you can go either way.  Second is whether you want traffic and weather from ADS-B “In”. Only the 978 Mhz channel has the bandwidth to provide weather, but you can get traffic on either frequency. Also, do you want this display on a panel mount or are you happy with the clutter of an iPad and portable ADS-B in the cockpit? That choice may be affected by what other systems you have, by cost, and personal preferences.
What traffic do you get? You will receive position reports directly from other aircraft that have ADS-B “Out” on whichever frequency you use for “In”.  It can be either one, or both if your unit has dual frequency inputs (common on portable systems).  If you have one frequency the ADS-B ground station will send you traffic on the other frequency (called ADS-R for rebroadcast). It will also send you traffic reports for mode C or S equipped aircraft that are not participating in ADS-B. Traffic sent by the ground station must have altitude reporting.
If you have TAS and Satellite weather, and you don’t mind the cost of a weather subscription, you may want to skip at least a panel mount ADS-B “In”. But note that the accuracy of the GPS position report from ADS-B “In” is far better than that from TAS or FAA radar (that’s why they’re doing it), Also, TAS sees Mode A traffic and ADS-B does not. So if you’re mainly interested in the “close calls” that could be a decider for you. Even if you have TAS and weather on a panel mount you may still want a dual frequency portable, if for no other reason than to have a backup.  After all, traffic and weather are probably two of the best products of the modern avionics revolution (maybe after never again being lost – or terrain awareness).
Some setups allow you to send both traffic sources (TAS, ADS-B) to the display and it selects the “best one”, by some algorithm.  If a your TAS unit doesn’t see a target you may still get it from ADS-B, or vice versa.  Or if both are seeing it, it may prioritize to the ADS-B for accuracy.  Check out this feature when reviewing equipment options.  Avidyne is awaiting FAA approval of their TAS units with built-in 1090 “In”, which will be merged with the TAS traffic.  The 1090 “In” will look for direct traffic having 1090 “Out” as well as rebroadcast (ADS-R) traffic from ground stations.
Weather from ADS-B is different from what the satellite systems give you -- the pixel density is greater for the region around you (a few hundred miles) than it is for weather further away.  This is not true for satellite weather, which has the same quality everywhere and some judge it to be superior (plus, you get it on the ground before you launch).  Some display units allow you to select either one if you have both sources coming into the unit.
The third consideration is the equipment choice.  If you have a Luscomb or a Cub and just want the lowest cost “Out” system, this doesn’t mean the choices are any easier.  What equipment are you starting with? Do you have a WAAS GNS 430 for example? That takes care of the position source, and it’s certified with a large choice of transmitters. If you don’t have a GPS, most ADS-B options today have a built-in WAAS GPS position source.  Many planes of this category are equipping with NavWorx units since costs are modest.  But check out all the manufactures; FreeFlight, Sandia, Trig, Avidyne, L3, Garmin, and others I may have overlooked here.
Maybe you’re able to treat yourself to “the best” at whatever cost.  Taking cost off the table still doesn’t make it easy either. Your options likely will still be influenced by what you already have, not simply what you want.  So at whatever price level, your task is the same – you must plow through a large set of options.  Evaluate all the equipment options, prices, and account for what you already have.  This can be a daunting job.
Lastly, do your homework on shops to get the best work done and the best prices. They’re all very busy right now, and both quality and price can vary significantly.  So don’t procrastinate too long. The FAA is quite concerned (rightly) that there is a huge backlog of aircraft that will probably equip, and time is becoming short.