In article , Big John
wrote:

With that background, what does FAA use today? If they do not use
'skin paint' why can't the 'glass' birds with a wooden prop, turn off
their transponder and fly through all the restricted areas unseen?

at least some restricted areas augment the FAA radars with
primary radars that are better suited to the air defense role
than the FAA radars.

--
Bob Noel