Narrative:

In level cruise initially at 8000' MSL, in and out of clouds. Encountered increasing turbulence but didn't feel it necessary to change altitude until ice started to form. Called approach controller, who authority/authorized descent to 6000' per my request. I started the descent. At time of starting descent, turbulence in clouds increased significantly, such that control became difficult, both as to attitude and airspeed. While attempting to keep wings level and airspeed out of the yellow, with throttle pulled back to just above gear horn mp I was about to lower gear as an emergency measure. Then noticed that I was at 5000', mp of 12', and IAS 170 KTS in an small aircraft. I then called controller, told him of my deviation and requested 4000'. I was immediately cleared to 4000', and I don't think this caused any problems for the controller as the frequency was quiet due to the gusty winds that day, and I was in a fairly remote area as far as approach paths to rfd are concerned. In retrospect, descending earlier and getting out of the clouds before ice was noticeably might have prevented inadvertent altitude deviation, but I had initially climbed to 8000' to avoid turbulence that I knew was present lower down. Not having a non-flying passenger would have avoided the distraction of advising him that he might hear a gear horn go off, and not to worry about it, might have helped me spot the high descent rate (1500 + FPM) sooner. Note: ice was not a factor in this, other than my desire to get out of it. While at 8000', I asked for lower when I had only a few crystals on the windshield and none on the wings. Approach had cleared me to lower before any appreciable buildup of ice had occurred.

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Original NASA ASRS Text

Title: SMA, DESCENDING IFR, OVERSHOT HIS ASSIGNED ALT.

Narrative: IN LEVEL CRUISE INITIALLY AT 8000' MSL, IN AND OUT OF CLOUDS. ENCOUNTERED INCREASING TURB BUT DIDN'T FEEL IT NECESSARY TO CHANGE ALT UNTIL ICE STARTED TO FORM. CALLED APCH CTLR, WHO AUTH DSCNT TO 6000' PER MY REQUEST. I STARTED THE DSCNT. AT TIME OF STARTING DSCNT, TURB IN CLOUDS INCREASED SIGNIFICANTLY, SUCH THAT CONTROL BECAME DIFFICULT, BOTH AS TO ATTITUDE AND AIRSPD. WHILE ATTEMPTING TO KEEP WINGS LEVEL AND AIRSPD OUT OF THE YELLOW, WITH THROTTLE PULLED BACK TO JUST ABOVE GEAR HORN MP I WAS ABOUT TO LOWER GEAR AS AN EMER MEASURE. THEN NOTICED THAT I WAS AT 5000', MP OF 12', AND IAS 170 KTS IN AN SMA. I THEN CALLED CTLR, TOLD HIM OF MY DEVIATION AND REQUESTED 4000'. I WAS IMMEDIATELY CLRED TO 4000', AND I DON'T THINK THIS CAUSED ANY PROBS FOR THE CTLR AS THE FREQ WAS QUIET DUE TO THE GUSTY WINDS THAT DAY, AND I WAS IN A FAIRLY REMOTE AREA AS FAR AS APCH PATHS TO RFD ARE CONCERNED. IN RETROSPECT, DSNDING EARLIER AND GETTING OUT OF THE CLOUDS BEFORE ICE WAS NOTICEABLY MIGHT HAVE PREVENTED INADVERTENT ALT DEVIATION, BUT I HAD INITIALLY CLBED TO 8000' TO AVOID TURB THAT I KNEW WAS PRESENT LOWER DOWN. NOT HAVING A NON-FLYING PAX WOULD HAVE AVOIDED THE DISTR OF ADVISING HIM THAT HE MIGHT HEAR A GEAR HORN GO OFF, AND NOT TO WORRY ABOUT IT, MIGHT HAVE HELPED ME SPOT THE HIGH DSCNT RATE (1500 + FPM) SOONER. NOTE: ICE WAS NOT A FACTOR IN THIS, OTHER THAN MY DESIRE TO GET OUT OF IT. WHILE AT 8000', I ASKED FOR LOWER WHEN I HAD ONLY A FEW CRYSTALS ON THE WINDSHIELD AND NONE ON THE WINGS. APCH HAD CLRED ME TO LOWER BEFORE ANY APPRECIABLE BUILDUP OF ICE HAD OCCURRED.

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.