N646 is taken. It's currently assigned to a 2023 Cirrus Design Corp SR22T registered in Graham, TX.
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.
N646 has been worn before. Past registrations from FAA deregistration records:
Tails one nudge away from N646 that aren't assigned or reserved: