Narrative:

In the planning of an IFR flight from paine field, everett to reno international in a C310 along with 2 passenger, I decided to go on a day that had a lull in the WX along the route. Both pae and rno had VFR forecast for the period. The flight went well as we had a smooth ride between layers of clouds, but experienced problems about 10 mins from our destination (rno). At that point, we were flying an assigned altitude of 14000 ft, when, over a period of approximately 5 mins, we experienced a significant buildup of rime ice. Over that period of time I noticed that our aircraft performance degraded to the point where I could no longer maintain our assigned altitude. I adjusted the aircraft's airspeed and found a point that minimized the rate of descent without compromising my ability to control the aircraft and advised ATC of the situation. They advised me that a lower assigned altitude of 10700 ft would be available in approximately 9 mi (3-4 mins). In the meantime I was able to stop the rate of descent and level out at approximately 11600 ft. I held this altitude until a clearance was received to descend and maintain 10700 ft. I was then able to maintain all subsequent altitude assignments, successfully completing the ILS approach and landing without further incident. In reviewing my preflight planning and WX briefing printout for this flight, I discovered that I had overlooked an airmet on icing for the rno area. To avoid this kind of problem in the future, I plan to more carefully scrutinize preflight planning and WX briefing to do all I can to avoid icing conditions. A general rule that I plan to use in the future is not to fly in clouds of precipitation when the freezing level is on the ground along the planned route. It is amazing how the performance of a high performance aircraft can be seriously degraded by the buildup of ice on the airframe.

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Original NASA ASRS Text

Title: A C310 PLT, ON A TRIP FROM PAE TO RNO, ENCOUNTERED FORECAST ENRTE WHICH CAUSED HIM TO MAKE SPD ADJUSTMENTS AS HE WAS UNABLE TO MAINTAIN ASSIGNED ALT.

Narrative: IN THE PLANNING OF AN IFR FLT FROM PAINE FIELD, EVERETT TO RENO INTL IN A C310 ALONG WITH 2 PAX, I DECIDED TO GO ON A DAY THAT HAD A LULL IN THE WX ALONG THE RTE. BOTH PAE AND RNO HAD VFR FORECAST FOR THE PERIOD. THE FLT WENT WELL AS WE HAD A SMOOTH RIDE BTWN LAYERS OF CLOUDS, BUT EXPERIENCED PROBS ABOUT 10 MINS FROM OUR DEST (RNO). AT THAT POINT, WE WERE FLYING AN ASSIGNED ALT OF 14000 FT, WHEN, OVER A PERIOD OF APPROX 5 MINS, WE EXPERIENCED A SIGNIFICANT BUILDUP OF RIME ICE. OVER THAT PERIOD OF TIME I NOTICED THAT OUR ACFT PERFORMANCE DEGRADED TO THE POINT WHERE I COULD NO LONGER MAINTAIN OUR ASSIGNED ALT. I ADJUSTED THE ACFT'S AIRSPD AND FOUND A POINT THAT MINIMIZED THE RATE OF DSCNT WITHOUT COMPROMISING MY ABILITY TO CTL THE ACFT AND ADVISED ATC OF THE SIT. THEY ADVISED ME THAT A LOWER ASSIGNED ALT OF 10700 FT WOULD BE AVAILABLE IN APPROX 9 MI (3-4 MINS). IN THE MEANTIME I WAS ABLE TO STOP THE RATE OF DSCNT AND LEVEL OUT AT APPROX 11600 FT. I HELD THIS ALT UNTIL A CLRNC WAS RECEIVED TO DSND AND MAINTAIN 10700 FT. I WAS THEN ABLE TO MAINTAIN ALL SUBSEQUENT ALT ASSIGNMENTS, SUCCESSFULLY COMPLETING THE ILS APCH AND LNDG WITHOUT FURTHER INCIDENT. IN REVIEWING MY PREFLT PLANNING AND WX BRIEFING PRINTOUT FOR THIS FLT, I DISCOVERED THAT I HAD OVERLOOKED AN AIRMET ON ICING FOR THE RNO AREA. TO AVOID THIS KIND OF PROB IN THE FUTURE, I PLAN TO MORE CAREFULLY SCRUTINIZE PREFLT PLANNING AND WX BRIEFING TO DO ALL I CAN TO AVOID ICING CONDITIONS. A GENERAL RULE THAT I PLAN TO USE IN THE FUTURE IS NOT TO FLY IN CLOUDS OF PRECIPITATION WHEN THE FREEZING LEVEL IS ON THE GND ALONG THE PLANNED RTE. IT IS AMAZING HOW THE PERFORMANCE OF A HIGH PERFORMANCE ACFT CAN BE SERIOUSLY DEGRADED BY THE BUILDUP OF ICE ON THE AIRFRAME.

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.