N4DU is reserved. Fee-paid reservation held by Short-N-Numbers — if it isn't renewed, the FAA releases it on May 8, 2027 (in about 10 months).
Reserved by an individual or company for $10 per year.
Reservations lapse more often than you'd think. Check back around May 8, 2027 — if the holder doesn't renew, it becomes available. See everything scheduled to free up in May 2027.
N4DU has been worn before. Past registrations from FAA deregistration records:
Tails one nudge away from N4DU that aren't assigned or reserved: