Skyhawk 172/Cutlass 172
Air Traffic Control Fully Certified
Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Clearance; Inflight Event / Encounter CFTT / CFIT
Air Traffic Control Issued New Clearance
Procedure; Weather
I was working the RADAR position on Sector X. I had precipitation displayed west of the departure airport; but not along the route the C172 as traveling. The C172 was en route from their departure airport direct to their destination at 100 in an area with a 099 MIA (Minimum IFR Altitude). The C172 declared he was in icing conditions and needed to descend. I stood up from my chair to check the MOCA (Minimum Obstruction Clearance Altitude) the airway the C172 was over-flying. I made the decision to turn the aircraft 30 degrees to the right which would direct the aircraft to an area with a 072 MIA. I began to issue the clearance when I noticed the MSAW (Minimum Safe Altitude Warning) alert flashing. I issued a Low Altitude Alert as well as a 30 degree turn to the aircraft. The C172 was descending without clearance so I restated the MIA altitude and told the aircraft to maintain FL100. Soon after the aircraft entered the area with the 072 MIA he advised he was returning to his departure airport and canceled IFR. The weather that is displayed should be updated more often and needs to be more accurate. If the precipitation was displayed I could have issued it to the pilot and issued a heading around the area.
Enroute Controller described a below MIA event when IFR traffic encountered icing and initiated a descent below the MIA; the reporter noting improved weather information may have provided a heads-up on the existing condition.