Small Aircraft; High Wing; 1 Eng; Fixed Gear
Air Traffic Control Fully Certified
Air Traffic Control Time Certified In Pos 1 (yrs) 6
Situational Awareness; Troubleshooting; Distraction
Deviation - Altitude Excursion From Assigned Altitude; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance; Inflight Event / Encounter Weather / Turbulence
Air Traffic Control Issued New Clearance; Air Traffic Control Provided Assistance; Flight Crew Returned To Clearance
Aircraft; Weather
Aircraft X was on V611 going to LWT.  He was supposed to be level at 8;000 feet.  I observed him at 7;700 feet shortly before losing him on radar and asked his altitude.  He said 8;000 feet.  I advised him of the LWT altimeter setting.  He then asked for lower.  I told him to maintain 8;000 feet until ESTRO and cleared him for the VOR 8 approach.   When I reacquired him on radar he was still showing low.  I suggested he climb 700 feet.  He was observed turning off course.  I provided a heading to rejoin the airway; he reported he was picking up ice and having difficulty maintaining altitude. The aircraft had no DME to get an accurate position report and by then I had lost him on radar again.  I did not want to contribute to the workload by trying to get him to tune in another VOR so I advised him of the minimum VFR altitudes east of LWT and told him not to deviate from the airway.  Aircraft maintained 6;000 feet until LWT VOR and then did the procedure turn.  Inbound he reported the field in sight and I attempted to give him a visual approach and he said he might not be able to maintain visual contact so I re-cleared him via the VOR 8 approach.  The aircraft landed safely.Strongly suggest to GA pilots that they avoid flying hard IFR in underpowered; under equipped small aircraft.  Better radar coverage at LWT.
ZLC Controller reports of an aircraft under ATC control that is not at the required altitude and the Controller advises and issues altimeter. Aircraft cannot hold altitude and is off and on radar contact. Pilot reports of icing and Controller gets the aircraft turned toward airport for a visual; but pilot reports the might not be able to maintain the airport insight. Controller then clears aircraft for a VOR approach.