Do you need a transponder with ADS-B?

[rv8ch]

The FAA website says this:

Mode S transponder-based (1090 MHz) ADS-B equipment must meet the performance requirements of Technical Standard Order TSO-C166b. For aircraft operating at or above FL180 (18,000 feet), you must be equipped with a Mode S-transponder-based ADS-B transmitter. For aircraft operating below 18,000 feet and within U.S. airspace, you must be equipped with either a Mode S transponder with Extended Squitter
or
Universal Access Transceiver (UAT) equipment must meet the performance requirements of TSO-C154c. UAT equipment provides the ability to receive traffic and weather data provided by the FAA ADS-B network.

Does this mean that a transponder is never needed if you have a UAT? Apologies if this is a dumb question!

[rleffler]

Originally Posted by rv8ch

The FAA website says this:



Does this mean that a transponder is never needed if you have a UAT? Apologies if this is a dumb question!

It's talking about a transponder feature, not the transponder itself. You need extended squiter (available on some transponders) or a UAT device. In both cases, you still have a transponder.

[GalinHdz]

Two different issues.

1 - You require a transponder to fly in certain airspaces.
2 - Additionally, you will require an ADS-B out signal to fly in certain airspaces starting in 2020

Some transponders fulfill both requirements while others don't. If your transponder doesn't fill the ADS-B requirement you can use UAT (within the US) to fulfill the ADS-B out requirement. No UAT out box fulfills the transponder requirement.

[rv8ch]

Thanks for the feedback - looks like that Trig TT22 is still on the avionics shopping list.

[BobTurner]

And, to make it easy to remember, you must have a mode C (or S) transponder in exactly the same airspace where you will need ADSB-out in 2020. BTW, the logic is that airliners have a transponder-based collision avoidance system which is the backup if ADSB goes down. The FAA doesn't want any GA aircraft running into them.
I put in the TT22 (with gps coming from a G420W) and am happy with it.