Purpose of Tail/Ship Number
 

In addition to the registration, usually NXXXXX, airlines also add a ship or tail number to their aircraft. What is the purpose doing that? It seems any sort of database needs would do just fine using the registration. Why complicate matters?

There are many different formats for aircraft registrations. And the registration matters to the government bodies, not the airline. The back-office systems must work across all of them so they use a simple, consistent option instead. No harm, no foul. Doesn't matter at all to anyone.

And in some cases airlines even change the internal numbers without changing the registrations; I believe UA has a history of this with interior retrofits.

Don't know the exact reason, but a couple of guesses:

- A lot of the databases that airlines use tend to be on some old mainframes (black screen type systems) that might only be able to handle 3 or 4 letters and/or numbers. Very possible that it's a technical limitation
- Less confusion. For example, at Delta, the A319 fleet is N3xxNB, while the A320 fleet is N3xxNW or N3xxUS. The fleet numbers are 31xx for the 319s, 32xx for the 320s. Easier to remember that way than remember which last two letter clarification goes with each. As mergers have happened, you see a bit more of that type of overlapping since airlines aren't re-registering planes like they had done in some previous mergers. (Southwest is really the exception to this, as it's re-registered all the FL planes).

It's just irritating in threads that discuss interior/IFE updates on the fleets and airline insiders or enthusiast use the ship number instead of the registration. Most of us don't have access to internal information such as ship number but we can all look up the N number and see which aircraft type is being referenced.

I wonder why this is? The cost to register an airplane is $5... no matter if you are registering a Cessna 172 or a Boeing 747.

Simply for internal tracking purposes, nothing more.

Some airlines like Air Canada actually publish a table showing registrations and fin numbers http://www.aircanada.com/en/about/fleet/fin.html

Purpose of Tail/Ship Number
 

Your car has a license plate number - similar to an FAA registration number. Both cars and planes also have serial numbers (engines are also numbered as were propeller blades at least at one tine). But if your car is a company owned vehicle it likely also has a fleet number. And like cars, you can swap FAA registration numbers if you so desire. The FAA cares about N numbers, the manufacturer cares about airframe numbers and the airline cares about fleet numbers

Wait...you're telling me it costs more to register my car than a 747? That's crazy, I never would've thought that.

I'd bet it has to do with not having contiguous numbers in the range to move those fleets into. I don't believe any airline owns all the NnnnZZ numbers for its particular ZZ IATA code.

Solid distinction; thanks.

It's no different from a bus company assigning fleet numbers to their vehicles that are quite different from their government-issued number / licence plates. (Although historically in the UK many bus companies would request number plates where the digits wholly or partially matched the fleet number.)

A lot of airlines in countries that use the common all-letter format of aircraft registration use the last two and/or three letters of their planes' registrations as fleet "numbers" and typically repeat them on the tail, above the flight deck, on the nose gear doors.