Narrative:

I was initially enroute VFR with flight following to ZZZ2. Midway through my trip; ceilings were lowering and I asked center for an IFR clearance for the rest of the trip. I was in IMC soon after. I had anticipated the possible need for switching to IFR and pre-planned accordingly. Bqz was a good location to join the enroute structure because the westbound meas were substantially lower; and the terrain gentler; as it began to go down the colorado western slope. Weather in the clouds at 11;000 MSL was good IMC - 0 visibility but smooth; negative turbulence; negative icing. Approximately 50 NM east of che; we suffered a loss of power. I had just switched tanks and so switched them back. I turned on the auxiliary fuel pump. Pitot heat was already operating - even though temperatures were well above freezing; it is my SOP to do so upon entering sustained IMC. But; although we have not yet had the airplane checked mechanically for other possibilities; I believe I delayed applying carb heat long enough that serious carburetor ice formed and that; once applied; it took a long time for the ice to clear. We never lost power completely and; although I could not hold altitude; my impression is that we descended at a normal rate ~500 FPM. I don't think we ever went much below 8;000 MSL at which point power began to return. We made an uneventful landing. In my opinion; center did a great job and so many things about the system worked the way they are supposed to. I declared an emergency. Center gave me all the attention and help I required. ATC initially called out ZZZ1 as diversion airport (probably because it was the closest with an instrument approach). I initially turned that way; but I think we both realized at the same time that 'uphill' was not necessarily the best course of action. When ATC indicated my bearing and distance to ZZZ I elected to go there - it was closest 'downhill.' there were times that ATC and I were out of 2-way communication; and communications were relayed via other aircraft in the area. Human factors: they talk about brain lock and delayed reaction when there is an emergency. Although we check carb heat on every carbureted engine run-up; train for carb ice and teach and are taught to apply carb heat at the first sign of an unexplained loss of power; I had never experienced carb ice before - not even during instrument training in new england (summer and winter). Add to that I was at full throttle cruise flight; the prevalence of fuel injection and my flight in multiple types of aircraft (my last few flights have been part of a checkout in a fuel-injected debonair) and I think my form of brain lock was forgetting about carb heat. Whether it was just a minute or so or more; it's clear that it was long enough for what should have been a minor inconvenience to become a serious problem. On the other hand; there are parts of this that went well; even in terms of me (again; ATC was fantastic and there's no doubt that dumb luck played a big part). My general instrument training took over and loss of control (even though I have no autopilot) was never an issue. I had selected my entry into the system at a good location where terrain was becoming both lower and leveler. I recognized that the terrain toward ZZZ was 'downhill' - in fact I don't believe that I even received a terrain warning from my GPS - indicating that I was always at least 1;000' above the terrain. As a pilot; I know I will never forget the lesson this has taught me. As a CFI; my experience will be part of what I teach. It wouldn't have taken but one more bad thing to have changed the result of the experience.

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Original NASA ASRS Text

Title: PA-24 enroute over high terrain lost partial power due to carb ice; pilot declared an emergency and diverted with the aide of ATC. Total loss of altitude was approximately three thousand feet prior to regaining full power.

Narrative: I was initially enroute VFR with flight following to ZZZ2. Midway through my trip; ceilings were lowering and I asked Center for an IFR clearance for the rest of the trip. I was in IMC soon after. I had anticipated the possible need for switching to IFR and pre-planned accordingly. BQZ was a good location to join the enroute structure because the westbound MEAs were substantially lower; and the terrain gentler; as it began to go down the Colorado western slope. Weather in the clouds at 11;000 MSL was good IMC - 0 VIS but smooth; negative turbulence; negative icing. Approximately 50 NM east of CHE; we suffered a loss of power. I had just switched tanks and so switched them back. I turned on the auxiliary fuel pump. Pitot heat was already operating - even though temperatures were well above freezing; it is my SOP to do so upon entering sustained IMC. But; although we have not yet had the airplane checked mechanically for other possibilities; I believe I delayed applying carb heat long enough that serious carburetor ice formed and that; once applied; it took a long time for the ice to clear. We never lost power completely and; although I could not hold altitude; my impression is that we descended at a normal rate ~500 FPM. I don't think we ever went much below 8;000 MSL at which point power began to return. We made an uneventful landing. In my opinion; Center did a great job and so many things about the system worked the way they are supposed to. I declared an emergency. Center gave me all the attention and help I required. ATC initially called out ZZZ1 as diversion airport (probably because it was the closest with an instrument approach). I initially turned that way; but I think we both realized at the same time that 'uphill' was not necessarily the best course of action. When ATC indicated my bearing and distance to ZZZ I elected to go there - it was closest 'downhill.' There were times that ATC and I were out of 2-way communication; and communications were relayed via other aircraft in the area. Human factors: They talk about brain lock and delayed reaction when there is an emergency. Although we check carb heat on every carbureted engine run-up; train for carb ice and teach and are taught to apply carb heat at the first sign of an unexplained loss of power; I had never experienced carb ice before - not even during instrument training in New England (summer and winter). Add to that I was at full throttle cruise flight; the prevalence of fuel injection and my flight in multiple types of aircraft (my last few flights have been part of a checkout in a fuel-injected Debonair) and I think my form of brain lock was forgetting about carb heat. Whether it was just a minute or so or more; it's clear that it was long enough for what should have been a minor inconvenience to become a serious problem. On the other hand; there are parts of this that went well; even in terms of me (again; ATC was fantastic and there's no doubt that dumb luck played a big part). My general instrument training took over and loss of control (even though I have no autopilot) was never an issue. I had selected my entry into the system at a good location where terrain was becoming both lower and leveler. I recognized that the terrain toward ZZZ was 'downhill' - in fact I don't believe that I even received a terrain warning from my GPS - indicating that I was always at least 1;000' above the terrain. As a pilot; I know I will never forget the lesson this has taught me. As a CFI; my experience will be part of what I teach. It wouldn't have taken but one more bad thing to have changed the result of the experience.

Data retrieved from NASA's ASRS site as of April 2012 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.