>>10965763 (lb)
>can someone make whatever callsign they want?
Yes
I don't know what Air3 is.
But, ADS-B systems transmit a fixed identifier.
Traffic control will then assign a filled callsign.
ex: Airline aircraft have registration numbers like all aircraft, the ADS-B transmitters are programmed with the aircraft registration, Traffic control will then assign the requested callsign that you see on flight trackers.