Eclipse 500
Air Traffic Control Fully Certified
Air Traffic Control Time Certified In Pos 1 (yrs) 5.0
Situational Awareness
ATC Issue All Types; Deviation - Altitude Overshoot; Deviation / Discrepancy - Procedural Clearance; Inflight Event / Encounter CFTT / CFIT
Air Traffic Control Issued Advisory / Alert; Air Traffic Control Issued New Clearance
Human Factors; Airspace Structure
I issued an instruction for a pilot to cross a fix at 14;000 feet. Due to a departure I restated the instruction telling the pilot to descend at 2;000 feet per minute to and maintain 14;000 feet. The pilot read back 14;000 feet and descended. The radar screen showed the pilot level; and I went through a scan. When I next saw the aircraft he was descending through 13;300 feet with a minimum IFR altitude of 12;900 feet right below him. I climbed him to 14000 feet and he read it back. His next radar update went through 12;900 feet; so I issued a safety alert. The aircraft finally stopped descending and climbed back to 14;000 feet at 11;700 feet. The pilot read back properly; so I don't have anything.
ZLC Center Controller reported they observed an aircraft descend below their assigned altitude and below the Minimum IFR Altitude.