That was what I thought for a long time too, until Todd's post made me go look up 91.215. 91.215(b) says that you need a transponder in in the airspaces you list above. So that's in agreement. I also thought that if you had a transponder, it had to be on, and of course if it was on, it had to meet the requirements of 91.413. But for the life of me right now I can't find the requirement that "if you have a transponder in the plane, it must be turned on". Where is that? Am I going senile? 91.215(c) says that ... Oh, Crap - there it is... the "or in all controlled airspace" clause in 91.215(c) - missed that the first time checking.
Originally Posted by FlyingRon
If you have a transponder, it must be on except in class G airspace, and if it's on, you need a 91.413 check.
Thanks for making me look again...
And if you have an ADSB-out box, it must be on at all times, even Class G and when taxiing. (91.225(f))
Originally Posted by Marc Zeitlin