What happened
The pilot received two weather briefings prior to the flight, both of which indicated icing conditions en route to Hays. Additionally, both briefings included a SIGMET for reported moderate-to-severe icing in freezing rain below 4500 feet MSL. Before departure, the pilot contacted both dispatch and the chief pilot; the consensus among these parties was that the weather had not developed as forecast and that adverse conditions appeared to be located east of Hays.
While descending into Hays, the aircraft accumulated ice rapidly. Upon reaching the minimum descent altitude (MDA), the pilot could not see the airfield and executed a missed approach. Following the missed approach, the pilot was unable to climb out of the icing conditions. The aircraft subsequently settled to the ground while operating at full power.
The investigation
The investigation revealed that the aircraft was not equipped for flight into known icing conditions. While the aircraft incorporated STC SA2573CE, which installs synthetic rudder strips on the wing and tail leading edges designed to be sprayed with glycol to help prevent ice build-up, it did not meet the necessary requirements for such environments. The pilot noted that the owner had represented this STC as meeting FAR 135.227 standards for flight into icing conditions.