I have scoured this and other forums looking for information about the usefulness of mode C transponders after the FAA's 2020 mandate to convert to ADS-B. I am in the process of rebuilding a 601 after an unfortunate nose wheel collapse after a hard landing. I have a Garmin 320A transponder to install, but after January 1, 2020, will I need an entirely new system or can I retrofit an ADS-B device to my existing transponder /aircraft. I can't seem to find any straight answers. 

I am sorry for my ignorance to this subject. I would rather have a fix in place while the aircraft is still grounded for repairs. Someone did mention a wingtip mounted option know as the SkyBeacon. How does this all fit together? Will I need my mode C system? Do/can/will they need to communicate (the garmin and skybeacon). 

This forum has been incredibly helpful with my quest to restore my plane. Thanks for your patience. 


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Well, I'm no expert but have been researching this as well. The SkyBeacon and similar devices can be programmed to read information from your mode C transponder(I understand Garmin is suing uAvionix for copyright infringement of how they read the transponder data). They then use this to provide your ADS-B "out" information. I've been looking at uAvionix's tail lamp model since it looks like easier to retrofit to my 601 XLB. I have a Garmin 327 and together they should provide ADS-B out.

Yes, you'll still need your current (or replacement) Mode C-reporting device.  As Charles noted, there's the SkyBeacon by uAvionix that mounts on the wing tip or tail that uses RF (or bluetooth?) to read what the transponder is emitting from the antenna, then piggybacks the ADS-B out information. 

There are also wired units by both uAvionix and Garmin (GDL 82) that basically just takes GPS info from an included antenna puck and then feeds that to your existing transponder.

Thanks gentlemen. See, where I was getting confused was the need for a wired connection to an existing transponder. That is what Garmin appears to be doing with their system (or at least one of them). The tail mounted sky beacon seems to be the logical answer because it is a self contained unit. Initially I dismissed this option because all I saw was the wingtip mounted version. Now I see there is a rudder mounted version that appears to be suitable for my 601 XLB. I also see there is a $500 dollar rebate that began last month. I hope to be in the air next fall.

Thanks again!!


Yes as others have said you may keep your current Mode C equipment and retrofit an acceptable solution.  Some good info here as well https://www.faa.gov/nextgen/equipadsb/resources/faq/#q35 that includes the statement that  the need for any transponder at all someday in the future is being debated by the FAA.  


I beta-tested the skyBeacon for uAvionix and it requires and is compatible with any Mode C or S transponder - same for tailBeacon.  Originally, the skyBeacon got it's squawk code and barometric data from the transponder's squawk via wireless reception with its built-in antenna - no wifi or bluetooth is used for transponder data, but the skyBeacon and tailBeacon's functioning can be configured and monitored (even in-flight!) via wifi on a smartphone app.  The current production models of the skyBeacon and tailBeacon obtain squawk code via the existing power wiring to the nav/strobe or tail light - not quite sure how they do it (maybe the wiring functions as an antenna or the rf output of the transponder induces a detectable pulse in the wires?), but apparently it works.  I believe the current production models also have a barometric pressure chip on-board so they no longer depend on the transponder for that data. (ADSB compares barometric altitiude to GPS altitude as one of its many data integrity parameters.)

Currently, the $500 rebate is possible for experimental aircraft, but only for installation of TSO'd equipment.  The increased cost of a TSO'd unit would likely negate the advantage of the $500 rebate since you could yourself install a less expensive, non-TSO'd ADSB in an experimental aircraft.



(uAvionix beta tester, but no business affiliation)

If I'm reading the FAA doc correctly, the best real-world option - for those of us who never go into A/B/C airspace - may be to simply remove our transponders (if so equipped), and be done with it...

In the 6 years since I've had my plane flying, I've only needed a Transponder when I was based at my original First Flight / Phase One airport, which was located inside a Mode-C veil, and for which I only could fly a direct route "out", transponder or not.

Since then, I've stayed out of controlled airspace.


Of course, if you never go into controlled airspace, the transponder is of little use to you from your perspective.  However, even when you're not in controlled airspace,  if you happen to be in radar coverage your transponder is being pinged and your air traffic position is relayed via the ADS-B ground stations to ADS-B "in" equipped aircraft, so you are getting some modicum of increased safety since it aids others to see and avoid you even though they may not be communicating with ATC, either.

ADS-B "in" equipped aircraft are becoming increasingly common since you can equip with a Stratux receiver for very little expense - less than $150 for a DIY kit.


Patrick, I suggest you keep your transponder and have it on at all times when airborne. Even if you are not talking to a controller your transponder is letting people know (both in ATC controller stations and via ADSB information to other plane's pilots) where you are and what altitude you are at. It can save your life (it may have already saved your life) and you will never know it happened.

Also, your Mode C transponder (IF it is turned on -- I cannot strongly enough urge all of you good people to keep your transponder on and sending Mode C data at all times when you are airborne) is always talking to any nearby planes that have TCAS or TCAD equipment. That equipment reads your altitiude and position and alerts the pilot of the equipped plane of your presence. If a collision is about to happen the equipment actually gives the pilot of the TCAS equipped plane instructions on how to avoid the collision. Pretty cool!!

I flew big iron for 38 years (now retired for over a decade) and when TCAS first came out we were cynical about it. But it did not take long at all to love that particular electronic gadget. But in order for it to know you are there, you MUST have your transponder on and sending the Mode C altitude signal. It does not matter if you are talking to someone who is going to look at your transponder or not, always have it on when airborne!!

End of sermon..........

Just to add another data point to this discussion..

I guess it depends somewhat on where you fly but any type of transponder gives you access to Flight Following. Here in northern CA where the there is a lot of both commercial and GA traffic outside of Class B or D airspace. To my mind flight following is a huge increase in safety of flight.

ADSB out or not, a transponder is a valuable benefit to any aircraft. Now and into the near future.  


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