N843 is taken. It's currently assigned to a I.C.A.-Brasov (Romania) IS-28B2 registered in Helena, MT.
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.
N843 has been worn before. Past registrations from FAA deregistration records:
Tails one nudge away from N843 that aren't assigned or reserved: