On 2008-09-05, Thomas Borchert wrote:
Mode S transponder have the option of setting a flight ID or the tail
number in a data field designated for that info. This is broadcast with
the Mode S data packet and is independent of the unique transponder hex
code. In airline operations, the flight crew normally sets the flight ID
for each flight, e.g. UA011 for United flight 011. In GA operations, the
aircraft tailnumber is set by the installer.

In the US, the tail number is assigned an 8-digit octal number to be used as
the flight ID algorithmically by the FAA. I don't know what other countries
do. Since it's algorithmic, it's possible to go backward from ID 51577524 to
N55ZC.

Controllers with mode S radar equipment have the option of displaying
this data field next to the "blip". I do not know how common such
equipment is in the US, but it is getting more and more widespread in
Europe.

Apparently, it's not used in the US at all.

AFAIK, the big database correlating call signs and hex codes inside the
radar equipment is a myth.

If other countries do it the way the FAA does, there's no need for a
database.
--
Jay Maynard, K5ZC http://www.conmicro.com
http://jmaynard.livejournal.com http://www.tronguy.net
Fairmont, MN (FRM) (Yes, that's me!)
AMD Zodiac CH601XLi N55ZC