Air Traffic Control Fully Certified
Air Traffic Control Time Certified In Pos 1 (yrs) 1
Situational Awareness; Confusion
ATC Issue All Types; Aircraft Equipment Problem Less Severe; Deviation - Altitude Excursion From Assigned Altitude; Inflight Event / Encounter Weather / Turbulence; Inflight Event / Encounter CFTT / CFIT
Air Traffic Control Issued New Clearance; Air Traffic Control Provided Assistance; Air Traffic Control Issued Advisory / Alert; Flight Crew Landed in Emergency Condition; Flight Crew Diverted
Human Factors; Airspace Structure; Weather; Aircraft
Aircraft X checked on my frequency as a pop up IFR requesting a clearance to ALB.  He requested 4;000 feet for altitude; I told him he would need to climb to 5;000 feet for a clearance to ALB.  I cleared him reaching 6;000 feet cleared to ALB airport via direct.  Reaching 6;000 feet he told me he was picking up icing and requested 8;000 feet.  I climbed him to 8;000 feet and asked him the type and intensity of ice.  He said Light Rime.  I had my Supervisor put the pilot report in the computer.I then noticed Aircraft X  descending instead of climbing. I verified he was in the climb.  He said he was having a problem with his auto pilot.  I told him he was descending and that he needs to climb.  He continued descending at which point I gave him a low altitude alert and told him my minimum IFR altitude in the area is 3600 feet an he needs to climb to 6000 feet.  He continued to descend so I asked him if wanted vectors to the closest airport.  He said he had the airport in front of him in sight.  I asked if he wanted to land there. He said yes.  I cleared him for a Visual Approach.  I asked if he was requesting priority handling.  He said yes.  I read him the NOTAMs.  I asked him how many people were on board.  He didn't reply.  He was low and close to the airport.  I told him to change to advisory frequency and report his cancellation.
ZBW Center Controller reported an aircraft that reported light rime ice and a malfunctioning auto pilot descended instead of climbing and flew below the Minimum IFR Altitude. The aircraft diverted to the nearest airport and landed safely.