HighFlyingA380
Cleared for Takeoff
Hey Mark, what's generally going on behind the scenes when you get assigned a new code mid-flight? I'd understand the occasional change, but once I got 4 xpndr changes in a 127nm flight: 1- The code for departure when I picked up my clearance, and told to expect a different one; 2- Initial contact with ZAU after departure I got the expected change; 3- Another change about halfway along with ZKC; 4- Final change when switched to St. Louis approach. Just curious as to what causes that...The TRACON ARTS system picks up flight plan information, including beacon code, from the ARTCC computer. When a pre-determined time arrives, the ARTS computer forwards the departure track and beacon information to the appropriate sector's tab list. That way, when radar acquires the beacon code, it automatically associates track information and produces a data block on the display. Once that happens, the TRACON computer forwards the departure time to the ARTCC computer.
When an incorrect beacon code pops up, we usually see a Mode C intruder tag. That's when you hear ATC request a new code, and everyone has a happy day. Sometimes, that incorrect code belongs to another departure. That's when things get interesting. Now I have to verify that the automation is erroneous. Once I've done that, after fixing the erroneous data, I call the appropriate ARTCC controller and advise them the aircraft they think they are expecting is a ghost. We call that a "scratch and hold."
It happens every day, and takes all of a few keystrokes and phone calls to fix. If a pilot departs on a VFR code, the only difference is that there is no chance of an erroneous tag.
Maybe it's not such a bad idea to ensure the transponder gets a 1200 code prior to shutdown?