Reply #219: As a current air traffic controller, that's not accurate.

[MercutioATC]

This has been discussed as nauseum here, but I'll give you the basics:

The ATC system is based almost entirely on user compliance. It's a safety system, not a security system. As such, if a user chooses to turn off his/her transponder, our computers no longer correlate the primary radar target with the flight plan data that identifies the flight.

It's not "IMPOSSIBLE", it's a known limitation of the system.