UAT ADS-B without a transponder

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Rich
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UAT ADS-B without a transponder

Post by Rich »

It occurs to me that there may be a case to be made for installing a 978UAT device in an aircraft lacking a transponder.

This would be to cover the case where one had an aircraft with no intention of entering airspace requiring ADS-B (which also requires an operating transponder) but would like to avail oneself of the benefits of ADS-B out (such as improving my ability to see you :) )

Why not just install a 1090ES transponder instead? Good question. The rationale would be to avoid the higher installation cost and that of needing to have the 24-month re-certification performed. Plus there's that anonymous mode available in UAT favored by the aluminum-foil-hat folks.

As far as I can tell, the requirements do not permit such a scenario and I certainly have not seen any products that provide for such an installation.

Why do I ask the question? Our local EAA chapter has acquired a partially-built Kitfox that we're working to finish. This particular one (from early 1990's) has perhaps the worst generator provision I could conceive of, save not having one at all. I thought it'd be a good thing to somehow provide for ADS-B and I actually question its ability to properly power a transponder of any kind.
2002 DA40-180: MT, PowerFlow, 530W/430W, KAP140, ext. baggage, 1090 ES out, 2646 MTOW, 40gal., Surefly, Flightstream 210, Orion 600 LED, XeVision, Aspen E5
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vontresc
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Re: UAT ADS-B without a transponder

Post by vontresc »

The reason a transponder is required is because legacy TCAS relies on a mode c reply. While newer avionics can see UAT, existing TCAS relies on a transponder.

987 got sold as a "cheap" retrofit for existing GA aircraft. Unfortunately the dual band implementation was handled terribly. What really drives me nuts are the GPS requirements. If I am in an experimental aircraft I can install a $400 GPS box, yet if I am certified it has to be a fancy $1200 box. All for the same access. The FAA really screwed up for folks on the lower end of the spectrum. Personally I'd love a small inexpensive box for my sailplane, but as of right now the best I can do is a Trig TT-22 and thankfully a TN-72 as mine is experimental racing. That's still a $2+k investment in a $12k sailplane.
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Rich
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Re: UAT ADS-B without a transponder

Post by Rich »

I don't recall 978UAT ever being touted as cheaper. I do know that there is concern over congestion in the 1090 band in some areas and the FAA has been encouraging 978UAT for that reason. Swapping transponders always seemed like the most straightforward approach. I know of folks with a balky existing transponder that needs replacing anyway. For them, the added cost of getting ADS-B out is probably the lowest cost approach.

Though not perfect I don't have a major problem with the way FAA put the requirements together. This Kitfox I mentioned (along with thousands of other aircraft) need not comply with the mandate. I just have come up with a use case outside the mandate that seems reasonable but I know of no solution under development that would support it. I could conceive of an approach to do so, but there might be too small a market to make it worthwhile to develop.

Note some of the areas where the FAA was "kinder and gentler" with this:
1. No requirement for ADS-B IN. This has allowed a plethora of low-cost portable solutions. In fact, in my plane a panel-mount ADS-B IN would be far inferior to my FF/Stratus setup OR it would have required a rework of the entire panel. Apparently a great many planes today equipped with ADS-B OUT are flying without ADS-B IN.
2. No requirement for periodic re-certification of your ADS-B OUT (as with your transponder). You can check it out any time you want at no cost.
3. Limited airspace requiring ADS-B/Mode C. Next year I have a trip planned from here in Central Oregon to Eastern Colorado and then on to Western Illinois. Were I not mandate compliant I could still make that trip by simply avoiding overflying Class C airspace of Boise and Lincoln, NB, the only mandate airspace even vaguely close to my intended route. There's something over 4 million cubic miles of airspace in the US that's not affected. (Though the barrier is unavoidable for those living in certain areas.)
4. There was a 10-year horizon provided for compliance. Plenty of time to budget for it. For years I've advised folks looking to buy an aircraft to budget the cost of compliance into their purchase decision. I implemented compliance 5 years ahead of time, with partial support (i.e., WAAS conversion of my GNS units) 8 years before that.
2002 DA40-180: MT, PowerFlow, 530W/430W, KAP140, ext. baggage, 1090 ES out, 2646 MTOW, 40gal., Surefly, Flightstream 210, Orion 600 LED, XeVision, Aspen E5
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