Narrative:

I was on autopilot at 15000 feet in IMC. In fact I had just encountered snow and turbulence. Suddenly and dramatically; the aircraft slowed and began to descend. I initially thought I had structural icing and reported the inability to maintain altitude to ATC but went through the checklist. Carburetor heat was applied but seemed to have little effect initially. Actual inspection by flashlight revealed only a trace of snow on the tires and the engine was obviously struggling by now with perhaps some help with carburetor heat. I informed ATC that it was not a structural ice problem; likely carburetor ice; but I was still unable to maintain altitude. I am very familiar with the route and knew I was clear of high terrain and made [visual] contact with the ground at about 10500. I canceled IFR but asked to stay on for flight following. I did not declare an emergency. Unfortunately; when I reduced power the engine quit. I lost additional altitude but did get a restart with full rich mixture and carburetor heat still on. I noted I had an engine temp reading below the green arc. The engine ran with no roughness at this point; full rich and carburetor heat on. I would not have made [destination] when the engine quit. I maneuvered in the area briefly and ascertained that the wind was directly out of the north; at right angles to the long runway. [Destination airport] is uncontrolled and I was not sure if emergency services were available. I elected to continue to [alternate airport].

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Original NASA ASRS Text

Title: A C182 pilot reported diverting to an alternate airport after experiencing loss of power and engine roughness enroute in instrument conditions.

Narrative: I was on autopilot at 15000 feet in IMC. In fact I had just encountered snow and turbulence. Suddenly and dramatically; the aircraft slowed and began to descend. I initially thought I had structural icing and reported the inability to maintain altitude to ATC but went through the checklist. Carburetor heat was applied but seemed to have little effect initially. Actual inspection by flashlight revealed only a trace of snow on the tires and the engine was obviously struggling by now with perhaps some help with carburetor heat. I informed ATC that it was not a structural ice problem; likely carburetor ice; but I was still unable to maintain altitude. I am very familiar with the route and knew I was clear of high terrain and made [visual] contact with the ground at about 10500. I canceled IFR but asked to stay on for flight following. I did not declare an emergency. Unfortunately; when I reduced power the engine quit. I lost additional altitude but did get a restart with full rich mixture and carburetor heat still on. I noted I had an engine temp reading below the green arc. The engine ran with no roughness at this point; full rich and carburetor heat on. I would not have made [destination] when the engine quit. I maneuvered in the area briefly and ascertained that the wind was directly out of the north; at right angles to the long runway. [Destination airport] is uncontrolled and I was not sure if emergency services were available. I elected to continue to [alternate airport].

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.