Narrative:

Immediately prior to my departure at jeffco county airport, a pilot ahead of me reported the tops of the clouds were 10300 ft. He also reported no trouble in the climb out and no ice. I even remember him saying he was witnessing a beautiful sunset. Based on this observation, I decided to take off. During my preflight, I verified all deicing system were working properly, also I did a weight and balance and determined the aircraft to be within limits. After takeoff we began to climb out as normal without any problem. At first, when in IMC we accumulated no ice whatsoever which seemed to confirm the pilot report. During the first 2000 ft or 3000 ft of the climb we still had no ice. Once we reached an altitude of approximately 9000 ft, we started to accumulate ice at an alarming rate. I reported this to ATC. They asked me if I wanted a different altitude and I elected to climb, as I knew it was clear above. Soon after my vertical speed went from a steady 500 FPM climb to about 200 FPM or 100 FPM. I was not utilizing maximum power at this time. I proceeded to apply maximum power and began to climb again. We gained another 500 ft or so and the ice was still accumulating at a surprising rate. I like to keep my operating temperatures below a certain level and they started to exceed my personal limits, so I elected to land at a nearby airport. ATC gave me a vector to greeley airport and I landed without incident. I believe that I encountered a patch of freezing rain, which accounted for the rapid buildup of ice. Hindsight is always 20/20, but I believe the aircraft ahead of me probably missed areas of freezing rain and temperatures. I believe he probably climbed faster than I did as well. Just because one plane does not gather ice doesn't mean another aircraft won't, especially in an environment as unpredictable as the foothills of the colorado mountains. Now that it is close to winter there will be airmets for icing every day. I don't believe this system is reliable enough to warn pilots of possible danger areas. I feel there should be a better scale for pilots to use when determining whether or not to take off.

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Original NASA ASRS Text

Title: C401 PLT ENCOUNTERED MODERATE TO SEVERE ICING IN THE ROCKY MOUNTAIN FRONT RANGE AREA IN ZDV CLASS E AIRSPACE.

Narrative: IMMEDIATELY PRIOR TO MY DEP AT JEFFCO COUNTY ARPT, A PLT AHEAD OF ME RPTED THE TOPS OF THE CLOUDS WERE 10300 FT. HE ALSO RPTED NO TROUBLE IN THE CLBOUT AND NO ICE. I EVEN REMEMBER HIM SAYING HE WAS WITNESSING A BEAUTIFUL SUNSET. BASED ON THIS OBSERVATION, I DECIDED TO TAKE OFF. DURING MY PREFLT, I VERIFIED ALL DEICING SYS WERE WORKING PROPERLY, ALSO I DID A WT AND BAL AND DETERMINED THE ACFT TO BE WITHIN LIMITS. AFTER TKOF WE BEGAN TO CLB OUT AS NORMAL WITHOUT ANY PROB. AT FIRST, WHEN IN IMC WE ACCUMULATED NO ICE WHATSOEVER WHICH SEEMED TO CONFIRM THE PLT RPT. DURING THE FIRST 2000 FT OR 3000 FT OF THE CLB WE STILL HAD NO ICE. ONCE WE REACHED AN ALT OF APPROX 9000 FT, WE STARTED TO ACCUMULATE ICE AT AN ALARMING RATE. I RPTED THIS TO ATC. THEY ASKED ME IF I WANTED A DIFFERENT ALT AND I ELECTED TO CLB, AS I KNEW IT WAS CLR ABOVE. SOON AFTER MY VERT SPD WENT FROM A STEADY 500 FPM CLB TO ABOUT 200 FPM OR 100 FPM. I WAS NOT UTILIZING MAX PWR AT THIS TIME. I PROCEEDED TO APPLY MAX PWR AND BEGAN TO CLB AGAIN. WE GAINED ANOTHER 500 FT OR SO AND THE ICE WAS STILL ACCUMULATING AT A SURPRISING RATE. I LIKE TO KEEP MY OPERATING TEMPS BELOW A CERTAIN LEVEL AND THEY STARTED TO EXCEED MY PERSONAL LIMITS, SO I ELECTED TO LAND AT A NEARBY ARPT. ATC GAVE ME A VECTOR TO GREELEY ARPT AND I LANDED WITHOUT INCIDENT. I BELIEVE THAT I ENCOUNTERED A PATCH OF FREEZING RAIN, WHICH ACCOUNTED FOR THE RAPID BUILDUP OF ICE. HINDSIGHT IS ALWAYS 20/20, BUT I BELIEVE THE ACFT AHEAD OF ME PROBABLY MISSED AREAS OF FREEZING RAIN AND TEMPS. I BELIEVE HE PROBABLY CLBED FASTER THAN I DID AS WELL. JUST BECAUSE ONE PLANE DOES NOT GATHER ICE DOESN'T MEAN ANOTHER ACFT WON'T, ESPECIALLY IN AN ENVIRONMENT AS UNPREDICTABLE AS THE FOOTHILLS OF THE COLORADO MOUNTAINS. NOW THAT IT IS CLOSE TO WINTER THERE WILL BE AIRMETS FOR ICING EVERY DAY. I DON'T BELIEVE THIS SYS IS RELIABLE ENOUGH TO WARN PLTS OF POSSIBLE DANGER AREAS. I FEEL THERE SHOULD BE A BETTER SCALE FOR PLTS TO USE WHEN DETERMINING WHETHER OR NOT TO TAKE OFF.

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.