SP-TPA and SP-TPU and OK-WYI are Polish and Czech Calibrators.
Also there's YR-CAA from Romania and YU-BTC from Serbia.
All are visible on Flightradar24 and sometimes can be heard on some feeds covered by LiveATC.
Thanks for this Sagdiyev! I will try to follow one of these and get some clips from LiveATC
Thanks for the clip Victor.
I did not know about these flights.
From the controllers' reaction/questions it seems they had not been properly briefed. For instance, the first one did not appreciate that for the calibration to be valid the flight could not be deviated to make way for other traffic.
How often do calibration checks take place?
You're welcome Geoff!
Calibration flights (And I'm talking about Europe. Don't really know in the US) are planned two days before the DOF. The flight planning is sent to Eurocontrol and has to be validated. As you said, for the calibration to be perfectly issued the aircraft has to do what it has to do. No vectors allowed usually. That's why NOTAMS and ATIS are important when calibration is taking place because some big delays can be caused. I remember the CLB26 in Madrid LEMD and more than 10 aircraft holding because it had to do an ARC crossing the localizer twice and at a certain low altitude (to check radio signals and errors).
I don't really know how often they are done. I do know in Madrid was done because of a runway re-construction that took more than a month. The whole surface was replaced. I know they also calibrate after strong storms specially of hail. Antennas get broken, they are fixed and need to be re-calibrated.
Maybe some here knows how often, regularly without conditions, they take place
