N566 is taken. It's currently assigned to a 1979 Loutrel David MYSTERY SHIP 2 registered in Fairbanks, AK.
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.
N566 has been worn before. Past registrations from FAA deregistration records:
Tails one nudge away from N566 that aren't assigned or reserved: