What does an aircraft tail number mean?

The short answer is that it means nothing about the aircraft. A US registration mark carries no year, no make, no model and no factory. It is a name, not a description.

What it does have is a completely specified format, and that is worth something: this page checks a mark against 14 CFR 47.15 and says precisely which rule a bad one breaks.

What the N means

“Each operator of an aircraft must display on that aircraft marks consisting of the Roman capital letter “N” (denoting United States registration) followed by the registration number of the aircraft.”

That is 45.23(a), and it is the only character in the whole mark that means anything. N is the United States. Everything after it is an assigned number.

The three shapes

“A U.S. registration number may not exceed five symbols in addition to the prefix letter “N”. These symbols may be all numbers (N10000), one to four numbers and one suffix letter (N 1000A), or one to three numbers and two suffix letters (N 100AB). The letters “I” and “O” may not be used. The first zero in a number must always be preceded by at least one of the numbers 1 through 9.”

Three sentences, and they are the entire specification:

A small thing, noted because this page reproduces the paragraph above verbatim: the CFR prints (N10000) with no space and (N 1000A) and (N 100AB) with one. That is the printing, not a rule. No mark has a space in it, and the tool strips spaces and hyphens before reading anything.

The letters I and O are never used

47.15(b) bars them outright. The regulation does not say why, and this page does not invent a reason for it. What can be said is what the tool does with them: if you have typed an I or an O, the character on the tail is a 1 or a 0, because a mark cannot contain either letter. That is the single most useful thing this page will tell most people.

Twenty-four letters are left, and a VIN excludes the same two, plus Q.

And a mark never starts with zero

“The first zero in a number must always be preceded by at least one of the numbers 1 through 9.” So N0123 is not a mark and never was. N1023 is fine — the rule is about the leading zero, not about zeros.

How many tail numbers are there?

This is arithmetic on the rule above, not a figure the FAA published. The working, since that is the point of this site:

That is what the regulation permits. It is not a count of what is available, or of what the FAA will actually issue — marks in use, marks reserved and marks locked out after a cancellation all come off it, and none of those numbers are in the regulation.

Why it cannot tell you the year or the model

Every other page on this site decodes something. This one spends most of its length explaining that there is nothing to decode, so it is worth being careful about how that is established. “The regulation does not mention a year” would be an argument from an absence, and those fall over the moment somebody finds the paragraph you missed.

It is not argued that way. 47.15(d) settles it positively:

“Any available, unassigned U.S. registration number may be assigned as a special registration number.”

Any available number. On any aircraft. The fee schedule at 47.17(a)(4) prices it: a special registration number costs $10.00, and changing or reserving one is another $10.00.

A mark that can be bought for ten dollars, moved to a different aeroplane and taken away again is not describing the airframe it is painted on today. What connects the two is the FAA Registry, which is public and free to search. That is a database, not a decoding, and this page does not keep a copy of it — a stale copy of a live register is worse than no copy at all.

Marks outlive aircraft, and aircraft outlive marks

When a registration ends, the mark does not die with it:

“If the request for reservation and fee are not submitted prior to cancellation, the registration number is unavailable for assignment for a period of five years.”

Five years locked out, then back into the pool. Reserve it instead and it is held a year at a time, renewable. So the same mark can be worn by several aircraft across decades, and one aircraft can wear several marks in a lifetime. Neither fact is readable from the characters, which is the same point again from the other end.

Temporary numbers are a different thing

14 CFR 47.16 creates temporary registration numbers, issued to manufacturers, distributors and dealers holding a Dealer’s Aircraft Registration Certificate — not to owners. The regulation gives them no character structure at all, so this page does not decode them and does not guess at one.

This is the first source here that delegates nothing

Five sources in a row on this site defined a structure and then handed one field of it to somebody else: the railway regulation to a European register, the Hallmarking Act to the Goldsmiths’ Council, 47 CFR 2.926 to an FCC office, the egg directive to each member state, and 40 CFR 1060.135 to EPA’s own guidance. It had begun to look like the way these things are always written.

It is not. 47.15(b) states the whole format in three sentences and sends you nowhere. There is no register to consult, no guidance document to find and no office that holds the missing half. It is the most complete source on this site — and the thing it completely specifies happens to mean nothing, which is its own kind of joke.

A note on where this came from

The text is the 2025 annual edition of the CFR, fetched from govinfo.gov as XML. The links above point at the eCFR instead, because that is the version a person can navigate — but the eCFR renders in JavaScript and serves an automated reader no regulation text at all, so what a machine checks and what a reader opens are deliberately two different things.

A work of the United States government carries no copyright, so nothing here needed anybody’s permission. 47.15 was last amended on 22 November 2022.