"It's some kind of small craft," she announced a second later, "but I'm not getting a transponder code from it."

Can you notify him to change his transponder code?

The flight path was identical with the previous trip, and the transponder code was the same.

The transponder code for the cleared aircraft is selected at the remote control unit.

Am I correct in assuming you've been provided with a wide selection of transponder codes?

I'd just squawked the new transponder code when I saw a helicopter ahead at two o'clock.

On scope, the aircraft showed transponder code, or "squawk," 0357 and flight level 310.

She assigned him a transponder code, and he dialed in the number.

Aircraft can also signal an emergency by setting one of several special transponder codes, such as 7700.

Which is why we practically never sail under our own transponder codes until we're actually ready to make port.