PA-28 Cherokee/Archer/Dakota/Pillan/Warrior
Air Traffic Control Fully Certified
Situational Awareness
ATC Issue All Types; Inflight Event / Encounter Weather / Turbulence
Air Traffic Control Issued New Clearance
Weather; Human Factors; Procedure
A PA28 [was] traveling westbound on a vector to avoid high minimum IFR altitudes (MIA's). He was level at FL140 when the MSAW started to flash. I told SME we had a faulty MSAW alert. When I finished my traffic scan I noticed that he was at FL135; the MIA is FL138. I told him he was low and gave him the area's altimeter. He said he was picking up moderate icing and could not hold altitude and said he needed to turn around. I recommended a right 360 and issued the low altitude alert phraseology. He asked for a vector and I recommended a turn to the west which I misspoke then recommended an easterly heading. He wanted a vector to a nearby airport and I gave that to him when he cleared the high MIA. He then proceeded to the airport and landed. Nothing could prevent the situation; but I should have declared an emergency to better help him out.
Enroute Controller described an icing event that prohibited a PA28 from holding altitude and entering a below MIA situation. The reporter noted he should have declared an emergency for the aircraft in this situation.