B737-800
Air Traffic Control Fully Certified
Air Traffic Control Time Certified In Pos 1 (yrs) 1
Situational Awareness; Distraction
ATC Issue All Types; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter CFTT / CFIT
General None Reported / Taken
Procedure; Chart Or Publication; Human Factors; Airspace Structure
I took over the position with 3 aircraft going inbound. The first two were pretty close where I had to watch and issue speeds to maintain separation. The 3rd aircraft was already 'on approach' which was shown by the data block. When I took the position I had expectation bias that the aircraft was given a crossing restriction at or above 6000 feet for the ILS approach. The reason you give that clearance is due to the Minimum IFR Altitude(MIA) being 5600 feet near that area and then going into a 4;700 foot MIA prior to the Initial Approach Fix at 3;000 feet for the ILS. So; as I was ensuring separation with the first two aircraf;t I then looked at the third aircraft and they were through 5;600 feet going into the 4;700 foot MIA. They were past the terrain and over the ocean. I figured if I stopped them at that point; it would be a very abrupt maneuver. The previous controller should have ensured proper MIA clearance by giving the appropriate approach or a vector around the MIA.
A TRACON Controller reported soon after assuming control of the sector they observed an aircraft which had already been cleared for an approach descend below the Minimum IFR Altitude due to the previous controller not issuing the appropriate crossing restriction.