US N-numbers: structure, assignment and FAA registry lookup

You are standing at the fence in Los Angeles, a Boeing 777 rolls past, and on the tail you read N2331U. A few minutes later comes a Cessna with N and four digits, then a freighter with UP at the end. Anyone collecting US N-numbers for the first time quickly notices: the system works completely differently from German D- registrations. There are no weight classes, no hyphen and plenty of digits instead. This guide explains the structure, the FAA’s assignment rules and the history behind NC and NX, and shows you how to look up any US aircraft in the open FAA registry.

N-numbers: the short answer

An N-number consists of the country prefix N and at most five further characters. Digits always come first, the first of them between 1 and 9. Up to two letters may follow at the end, with I and O off limits. Formally, that is all there is: unlike in Germany, the registration tells you nothing about weight, number of engines or aircraft category. Whether N12345 is a jet, a Piper or something else entirely is only revealed by the registry of the Federal Aviation Administration (FAA).

The N itself is the nationality mark of the USA. How the prefixes are distributed worldwide is explained in the overview of country markings on aircraft. The basics of reading registrations in general are in the article Understanding aircraft registrations.

The three permitted patterns

The rules are set out in the US regulation 14 CFR § 47.15, and the FAA summarizes them on its page on forming N-numbers. There are exactly three forms:

Pattern	Example	Structure
Digits only	N12345	one to five digits
Digits plus one letter	N1234Z	one to four digits, then one letter
Digits plus two letters	N123AZ	one to three digits, then two letters

Three additional rules apply:

• No leading zero. Before the first zero, there must be a digit from 1 to 9. N01Z is invalid, N10Z is correct.
• No I, no O. Both letters are dropped so nobody confuses them with 1 and 0.
• N1 to N99 belong to the FAA. According to the agency, these short numbers are reserved exclusively for internal use.

This gives you a practical reading aid: letters never appear between digits. If you read something like N12A4 at the fence, you misread it or assigned a character wrongly. And because at most two letters are allowed, N123ABC is not a valid US registration.

What an N-number reveals – and what it doesn’t

In the German system, even the first letter after the D tells you a lot: D-A means a heavy aircraft over 20 tonnes, D-E a single-engine light aircraft. The guide to German registrations and weight classes explains this in detail. The US system has no such class logic. A number is assigned when it is free, regardless of whether an airliner or a light aircraft gets it.

A nice example: according to the FAA registry, N100 is a Piper J3C-65 built in 1940, a classic Cub trainer from Piper Aircraft. And behind N12345, probably the most obvious number of all, the registry lists a small drone. The shortness or beauty of a number says nothing about the size of the aircraft.

What the number can still reveal to you is the operator. Many US airlines have blocks of numbers with a fixed suffix assigned to them. A few examples we checked in the FAA registry (as of October 2026):

Registration	Type per registry	Owner per registry	Pattern
N570UP	Boeing 747-400F	United Parcel Service	suffix UP
N601FE	McDonnell Douglas MD-11F	Federal Express	suffix FE
N801DZ	Boeing 737-900ER	Delta Air Lines	suffix DZ
N8701Q	Boeing 737-8	Southwest Airlines	digits plus Q
N77012	Boeing 777-200	United Airlines	digits only
N2331U	Boeing 777-300ER	United Airlines	suffix U

For UPS and FedEx, the suffix is almost a trademark. At Delta, you come across the ending DZ, at United digit-only registrations mix with those ending in U, and at Southwest, for example, a Q at the end. Such patterns are airline habits, not regulations. They help you classify quickly but don’t replace a look at the registry.

When a bank is listed in the registry

When you look up an airline aircraft, the owner listed is not always the airline. For N101NN, an Airbus A321 built in 2013, and N901NN, a Boeing 737-800 from 2012, the registry names a trust company as the registered owner. This is common for leased or financed airliners. The background includes the FAA’s eligibility rules: those allowed to register include US citizens, US companies with predominantly American management and voting rights, government agencies or, under certain conditions, foreign-controlled US companies whose aircraft fly mainly in the USA. Trust structures close the gap for foreign owners and lessors. Why aircraft are registered in particular countries in the first place is explained in the article on offshore registrations and leasing.

How the FAA assigns N-numbers

The FAA’s Aircraft Registration Branch is responsible. The process is surprisingly unbureaucratic, and the fees have been low for years.

Vanity numbers and number changes

Anyone who wants a specific number picks it from the list of available numbers and pays 10 US dollars for assignment or reservation. The reservation is valid for one year and can be renewed annually for another 10 US dollars. If the vanity number is to move to an aircraft that already carries a different N-number, another 10 US dollars is added for the change.

This matters to spotters because numbers move around. When a number is canceled, the last owner can reserve it for one year. Otherwise, under the regulation, it stays blocked for five years before it can be assigned again. One and the same N-number can therefore have been on completely different aircraft over the decades. When you compare an old sighting with a current one, always check serial number and type. More on this topic is in the article Aircraft re-registrations.

Size and position on the aircraft

Where the number must be displayed is regulated by 14 CFR Part 45. On fixed-wing aircraft, there are two options: horizontally on both sides of the vertical stabilizer or horizontally on both sides of the fuselage between the trailing edge of the wing and the horizontal stabilizer. On airplanes and helicopters, the characters must generally be at least 12 inches tall, with a width of two thirds of the height.

For you at the fence, this means: on US airliners you will usually find the number on the rear fuselage or the tail, sometimes quite small relative to the size of the aircraft. For light aircraft there are exceptions with characters only 3 inches tall, for example for gliders, for certain experimental aircraft such as homebuilts with a cruising speed of up to 180 knots, and for older aircraft with grandfathered status. Such mini registrations are often hard to read in photos. A comparison of the rules in different countries is provided by the article Where the registration must be placed on an aircraft.

NC, NX, NR, NL: history in the registration

On vintage aircraft at airshows or in museums, you sometimes see registrations like NC12345 or NX211. The second character is a historic category letter. Until the late 1940s, US aircraft often carried it directly after the N, for example C for civil and commercial operation, X for experimental, R for restricted or L for limited. Today the FAA no longer issues numbers with NC, NX, NR or NL. According to the FAA, however, older aircraft may continue to display them.

Important for your collection: the category letter is not part of the actual number. NC12345 and N12345 designate the same registration. In the registry, you therefore search without the C.

The most famous example hangs in Washington: Charles Lindbergh’s Spirit of St. Louis carried the marking N-X-211, the X standing for the experimental category of the one-off aircraft. You can see the original in the National Air and Space Museum. For comparison with the German development, the article on the history of German aircraft registrations is worthwhile.

And one more distinction: military aircraft of the US armed forces do not carry N-numbers but serial numbers of their own. How to read them is explained in the guide to US military serials.

Looking up the FAA registry: step by step

The best thing about the US system for spotters: the registry is public and free. At registry.faa.gov/aircraftinquiry, you can look up any registration in seconds. According to the FAA, the data is updated at midnight on every federal business day.

The search options

The Aircraft Inquiry offers several entry points:

• N-Number: the standard case, you can leave out the N
• Serial Number: search by manufacturer serial number, ideal for number changes
• Name: all aircraft of an owner, such as an airline
• Make / Model: all registered examples of a type
• Engine, Dealer, Document Index: for special research
• State and County, Territory and Country: regional analysis

Under N-Number Availability, you can also check whether a number is available, reserved or assigned.

What the result shows

A query gives you, among other things:

• Status (for example Valid) as well as issue and expiration date of the certificate
• Manufacturer, model, year of manufacture and serial number
• Type of registration (individual, corporation, government agency) and the registered owner
• the Mode S code in octal and hexadecimal
• notes on pending number changes and airworthiness information

From the year of manufacture, you can directly judge how old an aircraft is. How that works for registrations from other countries is shown in the article Finding out an aircraft’s age. You can find a comparison of different national registries under Looking up aircraft registries.

The downloadable database

If you want to dig deeper, you can download the complete registry database. The FAA provides it as a ZIP archive with comma-separated text files. Included are, among others, the main file of all registered aircraft, the deregistered aircraft, a type reference and an engine reference as well as the reserved numbers. The archive is updated daily. For spotters who love spreadsheets, it is a goldmine, for example for finding all examples of a rare type in the USA.

N-number and hex code: the link to ADS-B

Every aircraft broadcasts a fixed 24-bit address via its Mode S transponder, the so-called hex code. How this address works in general is explained in the article ICAO 24-bit address (hex code). In the USA, the code is firmly tied to the N-number: the FAA registry shows it for every entry. The examples checked in the registry all lie in the block with the leading digit A; N100 has the code A004B3, for instance, and N8701Q the code ABF8E0.

Two practical consequences follow:

• If the N-number changes, the hex code changes too. An aircraft you are searching for using old ADS-B data shows up under a new address after a re-registration.
• Hex and registration can be checked against each other. If your receiver shows a code, you can look in the registry to see which N-number belongs to it. How to track an aircraft specifically by registration or hex is described in the guide Tracking an aircraft by registration.

LADD and PIA: when aircraft want to be invisible

Two FAA programs mean that some US aircraft are missing from flight tracker sites or hard to match. Through LADD (Limiting Aircraft Data Displayed), owners or operators can request that their flight data be filtered out of the FAA data streams for public tracking services. With PIA (Privacy ICAO Address), eligible aircraft get an alternative, temporary 24-bit address that is not linked to the owner in the registry. For this, they use a third-party callsign instead of the N-number. If you see a hex code for which the registry returns nothing, such a program may be behind it. How callsigns and registrations differ is explained in the article Callsign and flight number.

Typical mistakes when reading N-numbers

• Noted O instead of 0. There is no O in a US registration. What looks round is a zero.
• Read I instead of 1. Same principle: a vertical stroke is always the digit 1.
• Searched with the category letter. For NC or NX registrations on vintage aircraft, you search the registry without the second letter.
• Added a hyphen. N-12345 doesn’t exist in that spelling, even if some databases show it differently.
• Confused owner with operator. If a bank or trust is listed in the registry, the aircraft still flies for an airline.
• Linked an old sighting to a new number. Numbers are reassigned after a waiting period. The serial number brings clarity.

Plane spotting in the USA with N-numbers

Anyone traveling to the USA collects N-numbers by the dozen. At spots like the In-N-Out Burger in Los Angeles at LAX or at Gravelly Point Park in Washington, airliners pass over you by the minute. What is allowed there and what to keep in mind is covered in the guide Plane spotting in the USA. The article Plane spotting trip to the USA helps with preparing your tour.

A practical tip: because US registrations on airliners are often comparatively small at the tail, a telephoto lens with some reach is worthwhile. Photograph the number separately to be safe, even if the overall picture isn’t perfect. In the evening, you then match everything against the registry.

Conclusion

US N-numbers are simply built: N, then digits without a leading zero, and at the end at most two letters without I and O. There are no content classes like in Germany, but airline suffixes often reveal the operator. The FAA assigns standard numbers free of charge, vanity numbers for 10 US dollars, and registered aircraft need a new certificate every seven years. The biggest advantage for spotters is the open FAA registry: type, year of manufacture, serial number, owner and hex code are just one query away.