Small Aircraft
Communication Breakdown; Situational Awareness
ATC Issue All Types; Inflight Event / Encounter CFTT / CFIT; Inflight Event / Encounter Weather / Turbulence
Air Traffic Control Provided Assistance; Flight Crew Landed As Precaution
Human Factors; Weather
Aircraft X contacted ZID to report they were picking up light rime icing and requested a descent. I looked at the MVA and the lowest for his course of flight would eventually be 4;500 ft. MSL. Aircraft X started to descend. At 4;500 ft. MSL; Aircraft X got out of the icing temporarily. I issued weather to the pilot to expect moderate precipitation for next 100 miles. I asked the pilot if they had any de-icing or anti-icing equipment on board. They said Negative. I suggested to the pilot an airport at their 8-7 o'clock and 5 miles; to land at due to the weather up ahead. I also said there were 4-5 airports he could land at along his route. He came back with they were just getting out of the icing and a +1 degree Celsius and liked lower. I descended them to 4;000 ft. MSL. Another aircraft; Aircraft Y; requested to speak; I let them; Aircraft Y spoke and told the aircraft to 'take his advice; land; it's not worth it.' I descended Aircraft X to the MVA 3;700 ft. MSL. I told Aircraft X about the several airports he could land at including Scott Municipal at a 200 heading and 18 miles. I told the pilot that if he were to continue to SCX; that the lowest I could go in that area was 4;500 ft. MSL unless he [advised ATC]. Aircraft X decided that he wanted to divert to SCX and [advised ATC]. I read the SCX airport weather to him; there was only 1 NOTAM not pertinent to the safety of flight that was not read. I asked if he could climb to at least 4;500 MSL to attempt the approach (The approach actually required to be started at 4;800 MSL). Aircraft X said negative. I cleared Aircraft X to COPEP and told him to expect the RNAV 23 approach into SCX. He read it back; but never turned. COPEP turned Aircraft X back into the weather and kept him in the freezing conditions longer. Aircraft X started to descend. I asked Aircraft X if they had ground contact. They said no; and then when the aircraft was leaving 2;800 ft. MSL they said they could see the ground. I told them that the SCX airport was now a 195 heading and 4.8 miles. They called the airport in sight at 2;500 ft. MSL. I said Roger; paused; key up and cleared Aircraft X for the visual approach. I attempted to ask several times for the souls on board and fuel on board remaining. I was able to get 2 souls on board; but no report of FOB remaining. I called in the blind for Aircraft X Charlie a few times to ask their progress; and a [air carrier] keyed up to say they could hear Aircraft X trying to call Center on our frequency to say they landed safely.	SME airport was another option the aircraft could navigate to; with better weather and the possibility of not descending below the MVA to reach the airport and stay out of icing conditions. I did not call a Low Altitude Alert clearance to Aircraft X when he descended below the MVA. Given the situation would rise again; I should take all the options into consideration.
ZID ARTCC Controller reported that an aircraft was in icing conditions and the process that was taken to get the aircraft safely on the ground.