Small Transport; Low Wing; 2 Turboprop Eng
Air Traffic Control Fully Certified
Air Traffic Control Time Certified In Pos 1 (yrs) 2
Situational Awareness
Deviation - Altitude Crossing Restriction Not Met; Deviation / Discrepancy - Procedural Clearance; Inflight Event / Encounter CFTT / CFIT
Air Traffic Control Issued New Clearance
Procedure; Chart Or Publication; Human Factors; Airspace Structure
I gave aircraft X an approach clearance to maintain at or above 3;500 feet until established at (SANLY) on the localizer ILS 31 Approach into STC. The pilot read it back; however descended to 3;000 feet which is 500 feet below the Minimum IFR Altitude (MIA). I climbed the plane back up to 3;500 feet.Do pilots know the MIAs? Do their flight management systems know?
ZMP Center Controller reported an aircraft descended below its assigned altitude and went below the Minimum IFR Altitude (MIA).