N404RS is taken. It's currently assigned to a 2001 Bombardier Inc BD-700-1A10 registered in Duluth, GA.
See the full aircraft record →A tail number only frees up if the owner deregisters the aircraft or moves it to a different N-number — and even then the FAA holds it before releasing it to the public.
N404RS has been worn before. Past registrations from FAA deregistration records:
Tails one nudge away from N404RS that aren't assigned or reserved: