Link between hexcode - registration or c/n?

[malc41]

Sorry if this has been asked before, but can't find anything in the search.

were is the link between the hexcode and that particular aircraft. does a particular c/n keep it's hexcode or will it chage if the aircraft is bought/sold by an airline?

[Spaice]

malc41, see Wikipedia for an explanation (transpoder (aviation)

ICAO 24-bit address

All modern aircraft are assigned a unique ICAO 24-bit address or (informally) Mode-S "hex code" upon national registration and this address becomes a part of the aircraft's Certificate of Registration. Normally, the address is never changed, however, the transponders are reprogrammable and, occasionally, are moved from one aircraft to another (presumably for operational or cost purposes), either by maintenance or by changing the appropriate entry in the aircraft's FMS system.

[DaveReid]

All modern aircraft are assigned a unique ICAO 24-bit address or (informally) Mode-S "hex code" upon national registration and this address becomes a part of the aircraft's Certificate of Registration. Normally, the address is never changed, however, the transponders are reprogrammable and, occasionally, are moved from one aircraft to another (presumably for operational or cost purposes), either by maintenance or by changing the appropriate entry in the aircraft's FMS system.

That's one of the worst explanations I've ever seen.

Firstly, it's by no means uncommon, as we all know, for an aircraft's Mode S address to change.  Although the ICAO guidelines say that this should only happen when an aircraft is re-registered in another country (because each country has a separate allocation of addresses) many countries such as the US, Canada, France, Germany, etc, will allocate a new Mode S code if, for example, an aircraft changes from one N-number to another N-number.

And as far as I recall from my aircraft maintenance days, the only way of moving a transponder or any other component from one aircraft to another is by taking it out, walking across the hangar and re-fitting it to the recipient aircraft.  You can't just push buttons on the FMS and expect the component to change itself  :-)

[Spaice]

Ouch! back to the day job for me;)

[malc41]

Thanks guys for the response. The reason I ask is, we really do not have any way of pinning down an exact aircraft registration to a s-code especially with the amount of re-registrations that take place everyday.

As there is no official list it is just down to enthusiasts like ourselves to try to maintain some sort of database and hope that somebody somewhere will share any changes?

Agree Dave, spent most of my life robbing one aircraft to fix another!

[DaveReid]

The reason I ask is, we really do not have any way of pinning down an exact aircraft registration to a s-code especially with the amount of re-registrations that take place everyday.

As there is no official list it is just down to enthusiasts like ourselves to try to maintain some sort of database and hope that somebody somewhere will share any changes?

Yes, but don't forget that for the countries I mentioned, and some others, the Mode S code is permanently tied to a specific registration.

So, for example, if you pick up a code in the US civil range (A00001 to ADF7C7) you will always be able to tie up the aircraft by looking up the corresponding N-number on the FAA's website.

[malc41]

Dave

Sorry for being thick, so once an aircraft is registered in the US and stays in that country it keeps the same N-number?

[DaveReid]

so once an aircraft is registered in the US and stays in that country it keeps the same N-number?

No, aircraft change N-numbers all the time. 

But according to the ICAO guidelines they should keep the same Mode S address while they are on the N register.

However the US has implemented a different system whereby it pre-assigns a fixed Mode S code to every N-number.

So if an aircraft changes N-number, its allocated Mode S address changes to the code associated with its new N-number.

[malc41]

Thanks Dave for the info