"Thomas Borchert" wrote in message
...
Paul,

Is it normal practice for a Mode S transponder to display the aircraft
tail number to ATC?


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.

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.

It doesn't exist anywhere in the US. I seriously doubt it will ever be
implemented as ADS-B which has a much more robust datalink capability will
be the shape of things to come.