William,

My guess is the S code is unique to the transponder, not the plane.


Actually, the S code is programmed into the transponder in setup mode
and can be changed any time. The code is issued by the aviation
authorities for an aircraft registration number. Or, in the case of
airline flights, the actual flight number is programmed into the
transponder, which, as you can imagine, changes quite a bit.

With our German GTX330 installation, the LBA (German FAA-equivalent)
issued a hex code upon installation for our aircraft which was then put
into the transponder.


--
Thomas Borchert (EDDH)