PLT OF A PA28R ON AN IFR FLT EXPERIENCED ICING AND LOSS OF AIRSPD RESULTING IN DECLARING AN EMER AND DIVERTING TO LAND.

Narrative

AT THE TIME OF DEP; THE LATEST WX AT PWK WAS RPTED AS VFR. A PIREP SOLICITED FROM AN ARRIVING ACFT RPTED 3000 FT CEILING. UPON DEP; INFLT CONDITIONS DETERIORATED RAPIDLY IN SNOW TO MVFR. AS A PRECAUTION; I HAD AN IFR FLT PLAN ON FILE; WHICH I ACTIVATED 3 MI W OF PWK AT 1900 FT MSL. I WAS CLRED TO CLB AND MAINTAIN 3000 FT ON A SW VECTOR WHICH TOOK ME TOWARDS DPA. I ENTERED THE BASE OF THE OVCST AT 2500 FT MSL. DURING THE NEXT 10 MINS; I PICKED UP 1/2 INCH OF RIME ICE. I DECIDED TO MAKE A PRECAUTIONARY LNDG AT DPA. THE DPA ATIS WAS RPTING 1100 FT CEILINGS. I INFORMED THE CTLR I WAS PICKING UP ICE AND I NEEDED TO LAND AT DPA. HE GAVE ME A VECTOR FOR THE ILS. WHILE OUTBOUND ON A PARALLEL COURSE TO THE ILS; THE CTLR ISSUED A 90 DEG L TURN THROUGH THE FINAL APCH COURSE FOR TFC. AT THIS POINT I DECLARED AN EMER TO PREVENT FURTHER DELAY. I CONTINUED TO PICK UP ICE; MY AIRSPD DECAYED 25 KTS; AND MY ALTIMETER AND VSI'S BECAME UNRELIABLE. PITOT HEAT WAS ON; AND I INFORMED CTLR OF THE PROB. I WAS CLRED TO DSND TO 2500 FT MSL FOR A VISUAL APCH. I BROKE OUT AT 2500 FT AND LANDED WITHOUT FURTHER INCIDENT. I USED MY HANDHELD GPS TO XCHK ALT DURING DSCNT. AUTOMATIC GEAR EXTENSION ACTIVATED DUE TO ICED UP PROBE. I DECIDED NOT TO OVERRIDE IT.