Air Traffic Control Fully Certified
Air Traffic Control Time Certified In Pos 1 (yrs) 5.0
Confusion; Situational Awareness; Training / Qualification
ATC Issue All Types; Deviation / Discrepancy - Procedural Clearance; Inflight Event / Encounter CFTT / CFIT
Air Traffic Control Issued New Clearance
Airspace Structure; Chart Or Publication; Human Factors; Procedure
I was conducting OJTI (On Job Training) on combined sectors with a Radar Assist. The Radar Assist took a call from Approach regarding Aircraft X; who was at 5000 feet. Approach was asking if we were OK with Aircraft X at 5000 feet on his present route because the pilot wanted to stay as low as possible to avoid any potential icing. From my viewpoint it looked good. I heard the Radar Assist and Radar trainee discuss the 5000 foot Minimum IFR Altitude (MIA) in that vicinity and they seemed to concur on Aircraft X being good.A few minutes later after Aircraft X the MSAW (Minimum Safe Altitude Warning) begin to flash '058'. I quickly leaned in and noticed that Aircraft X had actually been inside the 5800 foot MIA for a few miles already but for some reason the MSAW (Minimum Safe Altitude Warning) didn't alert until now. He was about to re-enter the 5000 foot MIA anyway but we were already planning to climb Aircraft X for higher MIAs further ahead; so I told the Radar trainee to climb him to 071 feet as planned. This was sort of a glancing penetration of the 5800 foot MIA in this area; where the 5000 foot MIA was just west and south of the aircraft while the higher 5800 foot MIA sort of juts out from the east for a few miles. I would estimate he was about 2 miles inside the higher MIA for approximately 6-7 miles before climbing above it. In addition; the MIA values and boundaries were recently updated the area.Our MIAs and the associated boundaries are quite complex. It certainly reminded me of the importance of being extra vigilant in monitoring the proximity to these boundaries; especially while training and due to the recent changes that went into effect.
ZSE Center Controller reported they allowed an aircraft on a direct route to fly below the Minimum IFR Altitude.