Jeremy Lew wrote:

Really, they have no business "approving" a frequency change if you're not
in their airspace. Do they have radar there?

Some yes, some no.

MMU and CDW "sort of" do, but they don't really use it. More accurately,
they don't assign squawks and differentiate traffic that way. CDW, at
least, cannot. Both MMU and CDW get feeds of RADAR from EWR.
Unfortunately, there's this ridge which creates a shadow that blocks at
least some of the pattern at CDW.

Further, the system at CDW doesn't show transponder codes. It'll
differentiate between VFR and IFR (one slash or two) and it'll show idents.
But nothing else. I've never visited the MMU tower, so I don't know
whether they've a better feed.

Other D airports have and use RADAR: TEB and RDG come to mind. In those
airspaces, you get a squawk.

- Andrew