N-Number Guide

N-Number Rules Explained

Every US civil aircraft wears an N-number, and only certain formats are valid. This guide covers the character rules, the patterns the FAA allows, and the quirks — like why the letters I and O never appear — with an example you can check for each rule.

The short answer

A valid N-number is the letter N followed by 1 to 5 characters: all digits, digits then one letter, or digits then two letters. The first character after the N must be 1–9 (no leading zero), and the letters I and O are never used because they look like 1 and 0.

The three valid patterns

After the N, an N-number follows one of three shapes. Tap any example to check its live status:

  • N12345All digits — up to five of them.
  • N1234AUp to four digits followed by one letter.
  • N123ABUp to three digits followed by two letters.

The character rules

  • Total length is 1 to 5 characters after the N (six including the N).
  • The first character after the N must be a digit 1–9 — no leading zero.
  • Letters, when used, come only at the end: one or two trailing letters, never in the middle.
  • The letters I and O are never used, to avoid confusion with 1 and 0.
  • Every N-number is unique: assigned, reserved, or available — never shared.

Common invalid examples

These break the rules and won't validate:

  • N0123 — starts with a zero.
  • N1I2 — contains the letter I, and puts a letter mid-number.
  • NAB12 — leads with letters instead of digits.
  • N123456 — too long (more than five characters after the N).

Check a tail number

Have a format in mind? See if it's available on the N-number availability checker.

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Frequently asked questions

What is a valid N-number format?

A US N-number is the letter N followed by 1 to 5 characters: all digits (N12345), digits then one letter (N1234A), or digits then two letters (N123AB). The first character after the N must be a digit 1–9, and the letters I and O are never used.

Why can't N-numbers contain the letters I and O?

The letters I and O are excluded because they're too easily confused with the numerals 1 and 0. This keeps tail numbers unambiguous when spoken over the radio or written by hand.

Can an N-number start with a zero?

No. The first character after the N must be a digit from 1 to 9. A leading zero is not permitted.

How many characters can an N-number have?

One to five characters after the N, for a maximum of six characters total including the N. The valid patterns are all digits, digits plus one letter, or digits plus two letters.

Can two aircraft have the same N-number?

No. Each N-number is unique — it's either assigned to one registered aircraft, reserved by one holder, or available. You can check the status of any tail against the FAA registry and reserved list.