eocvictim
If you witness the call sign and have evidence of an aircraft doing a circling approach well below MDA take it to casa.
There is nothing illegal about an IFR aircraft, in this case a Cat B aircraft descending below the circling MDA to 300 ft agl during daylight hours in VMC if they can maintain visual clearance from obstacles within the circling area and maintain visual contact with the runway and/or runway environment. It’s clearly laid out in the AIP.