The regulations around ADS-B are pretty weird, basically because the FAA wants to require it of all aircraft but all the aircraft owners object because it's pre

The regulations around ADS-B are pretty weird, basically because the FAA wants to require it of all aircraft but all the aircraft owners object because it's pretty expensive to install it. So the FAA has kind of been taking a "death by a thousand cuts" approach where they never quite "mandate" ADS-B but they require it in more and more situations... So aircraft are perfectly allowed to not transmit ADS-B as long as they stay out of certain types of airspaces and outside of a certain distance of other types of airspaces and etc. So the effective result is pretty much that you need to have ADS-B if you ever want to land at a controlled airport but the details get a little weird. These rules have also been changing reasonably quickly in federal terms. The current set of ADS-B requirements only took effect the first of this year. Among other things, these rules require that any aircraft equipped with ADS-B out have it turned on at all times... but that's only been the rule as of recently (not sure if this revision or the previous one), so not that long ago it was acceptable to turn it on and off if you were outside of areas where it was required.