Date: 202003
Local time of day: 1201-1800
Location: ZAU.ARTCC, IL
Aircraft: Commercial Fixed Wing
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Descent
ATC / advisory: Center ZAU
Reporter organization: Government
Reporter function: Enroute; Instructor
Reporter qualification: Air Traffic Control Fully Certified
Human factors: Time Pressure; Confusion
Second reporter function: Enroute; Trainee
Anomaly: ATC Issue All Types; Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter CFTT / CFIT
Detector: Person Air Traffic Control
When detected: In-flight
Result: Air Traffic Control Issued Advisory / Alert
Contributing factors: Airspace Structure; Human Factors; Procedure
Primary problem: Human Factors

Narrative: I entered the area with my D-side trainee. We were informed that there was an emergency in the sector we were about to train on so we hurried to get in. Due to low traffic; the R-side did not request a D-side; but with the emergency situation we jumped in quickly. The R-side was informing us of the situation as we fumbled to get our headsets on and plugged in. He has already ran the emergency checklist; pointed the aircraft out to Approach Control and forwarded necessary information [to] the next Approach Controller who would be accepting the aircraft. As we were about to call for a brief; the aircraft requested descent to 5;000 feet; the R-side quickly re-coordinated the point out and apreqed (Approval Request) the descent. The R-side then responded to aircraft that were checking on frequency while he coordinated and the aircraft then again asked for a descent to 3;000ft. I told my D-side to make the call now. The R-side was aware that the emergency was a divert to an airport with better weather due to anti-icing issues on the aircraft so he gave the emergency aircraft the clearance they requested. My trainee then referenced the point out descending to 3;000 and the controller sounded confused. In order to make sure there was no confusion I keyed over my trainee to ask if there are any MSAs in the area that we should be aware of. The controller assured us 3;000 is the MIA. We then called the next Approach Controller to APREQ the aircraft descending to 3;000 feet which was approved. We shipped and dropped the aircraft as deadwood. When time allowed; I looked at maps and realized there is an MIA of 3;100 feet in that area. The R-side pulled up the data block and we observed the aircraft level at 3;100 feet. We are unaware if the aircraft went below and climbed; or if they were leveled prior by Approach Control. Our airspace goes down to 11;000 feet at the lowest. We are not aware of MEAs/MIAs/MVAs/MSAs/MOCAs or any other minimum altitudes other than 11;000 feet. For situations like this; I think it is important to be aware. I will be aware in the future and encourage my trainees and fellow area controllers to be aware.


Second narrative: I came back from break and was told there was an emergency aircraft.  As I was sitting down to work the D side I heard the emergency aircraft quest 5000. I heard the radar controller call Rockford Approach to APREQ the descent due to us only owning down to 13000. Shortly after; the aircraft requested 3000 I had not yet signed into position and got a briefing; but I made the call to Rockford Approach to APREQ the descent which was approved and then my trainer overrode the line to ask if there was any minimum safe altitudes in the area. The Rockford Approach Controller said 3000 was the lowest they could go to. I then called Madison Approach to APREQ the descent and they approved it. I told the R side and he descended the aircraft. I then logged into position and got a briefing. The aircraft had been headed to ZZZ but due to anti-icing issues couldn't land at ZZZ and had to divert to MSN. The radar controller shipped the aircraft to Madison Approach descending to 3000. Afterwards; we looked at the overhead maps and realized there was a MIA in the area of 3100 and RFD as well as MSN Approach should have been aware. We pulled the aircraft back up and saw that it was stopped at 3100. I'm not sure if the aircraft ever descended below the MIA. Not sure what to recommend in this case. My trainer did ask the Rockford Controller is there was a minimum altitude in the area. I could've signed in quicker and got a briefing quicker. Due to the emergency aircraft not having control issues I think its possible it would have been better to ship the aircraft to RFD instead of working the aircraft that low in their airspace.


Synopsis: ZAU Instructor and developmental reported descending an aircraft 100 feet below the MIA.