Originally Posted by
ATC Watcher
Ian W
On the horizontal plane, absolutely ,( GNSS is the "politically correct" term ), but the altitude part of ADS is still derived from Mode S transponder altitude, whose encoder is barometric, and unlikely to change in our lifetime if you ask me .
Of course.
I was just pointing out that the basic surveillance by ATC is slowly moving to dependence on GPS (GNSS's). This was the answer to the point about the precision switch being in DOD hands. This is mitigated somewhat by WAAS and LAAS which may be the reason that the precision switch is not so critical and discussed these days.