Air Traffic Control Fully Certified
Air Traffic Control Time Certified In Pos 1 (yrs) 5.0
Confusion; Situational Awareness
Airspace Violation All Types; Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural FAR; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter CFTT / CFIT
Air Traffic Control Issued New Clearance; Air Traffic Control Provided Assistance
Chart Or Publication; Aircraft; Procedure; Manuals
I was working the Radar position at the beginning of the session. Two aircraft were IFR inbound to an airport. Aircraft Y was slightly behind and at 5;000 feet and direct to the airport. Aircraft X was slightly closer and at 6;000 feet setup to execute the RNAV approach into the airport. When Aircraft X checked in I informed him that I would have to issue holding instructions as the approach would make him later to the airport but if he wanted to execute a Visual Approach we could get him inbound first. Aircraft X said he would take the visual so I cleared him inbound direct; cleared him to descend to 4;100 feet which is the Minimum IFR Altitude (MIA). I told them to report the field in sight for a Visual Approach.Aircraft Y was informed that he was number 2 and would have to climb to 5;100 feet to provide separation between him and his friend both inbound at the same time. Aircraft Y then turned 90 degrees to the north (right at Aircraft X) and asked if he should go direct to the initial approach fix for the RNAV approach. I told him no and that I saw his turn and that he needed to continue westbound for the moment until we had altitude separation before I could issue a turn to the north. While this is happening Aircraft X crosses my boundary and I issue 3;900 feet which is my MIA and I inform him if he is unable to get the field in sight we may have to go to plan B as there were no lower altitudes I could provide. Aircraft X then proceeds to descend below 3;900 feet all the way to 2;100 feet and I asked him 'Do you have the airport in sight?' Aircraft X responds 'I have the ground in sight.' I am then getting my supervisor's attention to let her know what is going on (now about both aircraft) and that I need to have the brasher warning so I could provide it to them.  While I am getting her attention Aircraft X says field in sight cancel IFR... I accept his cancellation and then clear Aircraft Y inbound on the RNAV as it was obvious to me that 3;900 feet was not able to provide visual conditions to the field. I then give a briefing to the relieving controller and came here to report what had happened.Both pilots need a refresher as to what IFR means and maybe take a break for a bit. One pilot almost had an IFR to IFR conflict by turning without instruction; the other could have had collision with terrain as he descended below his assigned altitude... ridiculous!
An aircraft was descended to 3;900 feet for a Visual Approach. The aircraft descended on its own to 2;100 feet which is below the Minimum IFR Altitude before cancelling IFR. Another aircraft was climbed to 5;100 feet for separation. Instead the aircraft turned 90 degrees to the right on its own.