Originally Posted by
Lost in Saigon
AFAIK the aircraft identity is not coded into the transponder. ATC enters the aircraft ident into their system when they assign the transponder code.
Wrong. The aircraft identity is coded into a Mode S transponder and cannot be changed. The Flight ID is separate and under the control of the crew, as is the squawk.
If you look at the registration record for any aircraft, you will see something like:
ICAO 24 bit aircraft address:Binary: 0100_00_000_000_01_0010110100
Hex: 4004B4
Octal: 20002264
Which will link back to the specific aircraft, whatever Flight ID or squawk is selected.
If you look at the full Mode S return on a screen, you will see the "4004B4" displayed.
Back to (bemused) watching brief.