The reason for a certified "detect and avoid" system is that the UAS can detect and avoid conflicting traffic/bird concentrations/parachutists/ para gliders etc, just as if it was being navigated visually. If it can do that in Class G airspace, Class D presents no problem for UAS to be operated in accordance with VFR, albeit it will be able to do it more efficiently than the MK1 eyeball of a manned aircraft pilot. The UAS is controlled by a Remote Pilot who communicates with ATC on the appropriate RTF frequency to obtain CAS entry clearance.