Small Aircraft
Air Traffic Control Fully Certified
Air Traffic Control Time Certified In Pos 1 (yrs) 11
Confusion; Situational Awareness
ATC Issue All Types; Deviation - Altitude Crossing Restriction Not Met; Deviation - Altitude Overshoot; Deviation / Discrepancy - Procedural Clearance; Inflight Event / Encounter CFTT / CFIT
General None Reported / Taken
Human Factors; Procedure
I thought I cleared Aircraft X to cross WARPU at or above 130 for the RNAV 16 at AFO. WARPU is on the border of 120 and 130 MIA (Minimum IFR Altitude) area. While calling traffic for other aircraft in the area; I noticed Aircraft X descending below 130. At the time the other aircraft was responding and before the frequency was free Aircraft X was over WARPU at 120. Aircraft X continued on the approach.Prioritize watching aircraft that are descending close to the MIA and be ready to correct them if they go below their cleared altitude.
ZLC Center Controller reported an aircraft descended below a crossing altitude at WARPU intersection.