Narrative:

I was level at 16000 ft in cloud with no ice accumulation; outside air temperature was -30 degrees C. Center had just told me that tops of the layer below had been reported at 12500 ft. With ATC's permission I left center frequency to get updated WX for stations along my route. I had my head down copying WX and hand-flying the airplane for approximately 2 mins while talking with flight watch. When I looked up to change frequency back to center; I noticed that the windscreen had become opaque with ice and that about 1/4 inch had accumulated on the leading edge of the gear mirror -- a telltale of the wing leading edge. Upon returning to center frequency; I could hear only static and an occasional spoken word; when syllables became audible; I could not tell whether center or an aircraft was transmitting. The same issue affected my second communication radio. After listening for about 10 seconds; I decided that effective 2-WAY communication with ATC would not be possible given current conditions; which I assumed was due to ice on the communication antennas. After briefly considering the alternatives; I chose to descend to seek an altitude between the layers. I broadcast in the blind to ATC that I had returned to the frequency and had left 16000 ft for lower. (I might have said; 'due to ice;' but my recollection is vague on that point.) at the same time; I looked at the en route chart to find local terrain elevation; nearby airways and MEA's. (I was off-airway; direct at the time.) during the descent; I could make out ATC assigning a frequency change to me; however once on the new frequency; I heard nothing but static. I returned to the original frequency and; after a short time; was able to reestablish communication. I leveled off between 2 cloud layers; and the ice that had accumulated slowly dissipated. (The outside air temperature was now -9 degrees C.) the remainder of the flight was normal. I continued without incident to my destination. I've reflected on this event from a couple of perspectives. First; I did not expect to accumulate ice at such a cold ambient temperature. I had read and been taught that; in stable air; airframe icing stopped at temperatures between -15 degrees to -20 degrees C; where the air was too cold to hold super-cooled water. How to prevent a recurrence? First; discard the idea that ice won't form below -20 degrees C. Also; once determining that unanticipated flight in cloud will be required above the freezing level; be quicker to talk with flight watch about WX and PIREPS. Finally; work with my avionics shop to ensure that I have at least one solid working radio in case of antenna icing.

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Original NASA ASRS Text

Title: C210 PLT ON AN IFR FLT PLAN ENCOUNTERED AIRFRAME ICING AND DEGRADED COM AT 16000 FT. PLT DSNDED TO AN ALT BTWN LAYERS; REESTABLISHED COM AND CONTINUED FLT WITHOUT FURTHER INCIDENT.

Narrative: I WAS LEVEL AT 16000 FT IN CLOUD WITH NO ICE ACCUMULATION; OUTSIDE AIR TEMP WAS -30 DEGS C. CTR HAD JUST TOLD ME THAT TOPS OF THE LAYER BELOW HAD BEEN RPTED AT 12500 FT. WITH ATC'S PERMISSION I LEFT CTR FREQ TO GET UPDATED WX FOR STATIONS ALONG MY RTE. I HAD MY HEAD DOWN COPYING WX AND HAND-FLYING THE AIRPLANE FOR APPROX 2 MINS WHILE TALKING WITH FLT WATCH. WHEN I LOOKED UP TO CHANGE FREQ BACK TO CTR; I NOTICED THAT THE WINDSCREEN HAD BECOME OPAQUE WITH ICE AND THAT ABOUT 1/4 INCH HAD ACCUMULATED ON THE LEADING EDGE OF THE GEAR MIRROR -- A TELLTALE OF THE WING LEADING EDGE. UPON RETURNING TO CTR FREQ; I COULD HEAR ONLY STATIC AND AN OCCASIONAL SPOKEN WORD; WHEN SYLLABLES BECAME AUDIBLE; I COULD NOT TELL WHETHER CTR OR AN ACFT WAS XMITTING. THE SAME ISSUE AFFECTED MY SECOND COM RADIO. AFTER LISTENING FOR ABOUT 10 SECONDS; I DECIDED THAT EFFECTIVE 2-WAY COM WITH ATC WOULD NOT BE POSSIBLE GIVEN CURRENT CONDITIONS; WHICH I ASSUMED WAS DUE TO ICE ON THE COM ANTENNAS. AFTER BRIEFLY CONSIDERING THE ALTERNATIVES; I CHOSE TO DSND TO SEEK AN ALT BTWN THE LAYERS. I BROADCAST IN THE BLIND TO ATC THAT I HAD RETURNED TO THE FREQ AND HAD LEFT 16000 FT FOR LOWER. (I MIGHT HAVE SAID; 'DUE TO ICE;' BUT MY RECOLLECTION IS VAGUE ON THAT POINT.) AT THE SAME TIME; I LOOKED AT THE ENRTE CHART TO FIND LCL TERRAIN ELEVATION; NEARBY AIRWAYS AND MEA'S. (I WAS OFF-AIRWAY; DIRECT AT THE TIME.) DURING THE DSCNT; I COULD MAKE OUT ATC ASSIGNING A FREQ CHANGE TO ME; HOWEVER ONCE ON THE NEW FREQ; I HEARD NOTHING BUT STATIC. I RETURNED TO THE ORIGINAL FREQ AND; AFTER A SHORT TIME; WAS ABLE TO REESTABLISH COM. I LEVELED OFF BTWN 2 CLOUD LAYERS; AND THE ICE THAT HAD ACCUMULATED SLOWLY DISSIPATED. (THE OUTSIDE AIR TEMP WAS NOW -9 DEGS C.) THE REMAINDER OF THE FLT WAS NORMAL. I CONTINUED WITHOUT INCIDENT TO MY DEST. I'VE REFLECTED ON THIS EVENT FROM A COUPLE OF PERSPECTIVES. FIRST; I DID NOT EXPECT TO ACCUMULATE ICE AT SUCH A COLD AMBIENT TEMP. I HAD READ AND BEEN TAUGHT THAT; IN STABLE AIR; AIRFRAME ICING STOPPED AT TEMPS BTWN -15 DEGS TO -20 DEGS C; WHERE THE AIR WAS TOO COLD TO HOLD SUPER-COOLED WATER. HOW TO PREVENT A RECURRENCE? FIRST; DISCARD THE IDEA THAT ICE WON'T FORM BELOW -20 DEGS C. ALSO; ONCE DETERMINING THAT UNANTICIPATED FLT IN CLOUD WILL BE REQUIRED ABOVE THE FREEZING LEVEL; BE QUICKER TO TALK WITH FLT WATCH ABOUT WX AND PIREPS. FINALLY; WORK WITH MY AVIONICS SHOP TO ENSURE THAT I HAVE AT LEAST ONE SOLID WORKING RADIO IN CASE OF ANTENNA ICING.

Data retrieved from NASA's ASRS site as of January 2009 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.