Narrative:

Severe carburetor icing was suddenly encountered en route. Unable to maintain altitude, even with carburetor heat, I advised bdl approach that I was in a descent and required immediate clearance to 4000'. This was granted. At 4000' I was VFR, sorted things out, cancelled IFR and continued to my destination--4v8 with flight following. Before leaving bdl airspace I was asked to call bdl approach on landline when on the ground. Upon calling I was informed by the supervisor that approach control had declared an emergency even though I had not. I was told that there had been less than minimum IFR traffic sep during my descent due to other traffic in the area, and that bdl would be filing an incident report. Human performance--perceptions: during descent it appeared to me that I was in a right turn, which I didn't understand why. It appeared that I had a gyro INS failure or possibly a pitot static source blockage. All of the above was reported to ATC, along with light rime airframe ice. I was mainly concerned with airspeed and vertical speed, and not heading. I discovered that somehow I had inadvertently put the autoplt into a right turn, while I thought the aircraft should be wings level. In retrospect I now realize that the attitude indicator and turn and bank were tracking properly. Any reporting of INS malfunction or pitot static port blockage was in error.

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Original NASA ASRS Text

Title: SMA REQUESTED IMMEDIATE DESCENT BECAUSE OF CARBURETOR ICE. HE THEN FAILED TO MAINTAIN ASSIGNED HEADING DURING DESCENT.

Narrative: SEVERE CARB ICING WAS SUDDENLY ENCOUNTERED ENRTE. UNABLE TO MAINTAIN ALT, EVEN WITH CARB HEAT, I ADVISED BDL APCH THAT I WAS IN A DSCNT AND REQUIRED IMMEDIATE CLRNC TO 4000'. THIS WAS GRANTED. AT 4000' I WAS VFR, SORTED THINGS OUT, CANCELLED IFR AND CONTINUED TO MY DEST--4V8 WITH FLT FOLLOWING. BEFORE LEAVING BDL AIRSPACE I WAS ASKED TO CALL BDL APCH ON LANDLINE WHEN ON THE GND. UPON CALLING I WAS INFORMED BY THE SUPVR THAT APCH CTL HAD DECLARED AN EMER EVEN THOUGH I HAD NOT. I WAS TOLD THAT THERE HAD BEEN LESS THAN MINIMUM IFR TFC SEP DURING MY DSCNT DUE TO OTHER TFC IN THE AREA, AND THAT BDL WOULD BE FILING AN INCIDENT RPT. HUMAN PERFORMANCE--PERCEPTIONS: DURING DSCNT IT APPEARED TO ME THAT I WAS IN A RIGHT TURN, WHICH I DIDN'T UNDERSTAND WHY. IT APPEARED THAT I HAD A GYRO INS FAILURE OR POSSIBLY A PITOT STATIC SOURCE BLOCKAGE. ALL OF THE ABOVE WAS RPTED TO ATC, ALONG WITH LIGHT RIME AIRFRAME ICE. I WAS MAINLY CONCERNED WITH AIRSPD AND VERT SPD, AND NOT HDG. I DISCOVERED THAT SOMEHOW I HAD INADVERTENTLY PUT THE AUTOPLT INTO A RIGHT TURN, WHILE I THOUGHT THE ACFT SHOULD BE WINGS LEVEL. IN RETROSPECT I NOW REALIZE THAT THE ATTITUDE INDICATOR AND TURN AND BANK WERE TRACKING PROPERLY. ANY RPTING OF INS MALFUNCTION OR PITOT STATIC PORT BLOCKAGE WAS IN ERROR.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.