N421UA is reserved. Post-cancellation hold held by Cancelled/Not Assigned — if it isn't renewed, the FAA releases it on Nov 1, 2029 (in about 3.3 years).
This tail was recently cancelled. The FAA holds cancelled N-numbers before releasing them back to the public.
Reservations lapse more often than you'd think. Check back around Nov 1, 2029 — if the holder doesn't renew, it becomes available. See everything scheduled to free up in November 2029.
N421UA has been worn before. Past registrations from FAA deregistration records:
Tails one nudge away from N421UA that aren't assigned or reserved: