Narrative:

About 15 minutes into flight at 3500 ft MSL; experienced engine roughness. Turned immediately back toward my departure airport; climbing which addressing engine problem. Saw that scattered in direction of destination airport had gone broken. Continued slight climb with intention of crossing a nearby field in case engine quit before getting to my departure airport. Found a good clear area to descend through broken layer but did not recognize terrain once down to approximately 1000 ft AGL. Circled around some as engine had smoothed out. Trying to locate my departure airport; in as much as it looked like I was going south of it; in direction of ZZZ; I turned to 360 and almost immediately saw the field and landed without incident. I think I may have gotten into the upper ring of class C on my descent. I believe I was well below the 2000 ft MSL ring most of the time; while busy with my situation. I do remember the ATC frequency I was monitoring was quiet. At no time did I hear radio transmissions; which would in anyway be in reference to my aircraft; after I got closer to the class C. I normally do not contact ATC for my local flying in the area outside class C. I felt it was more important for me to get on the ground as soon as possible then try and contact ATC about my predicament. My aircraft was squawking 1200 VFR with altitude encoding. Earlier in the flight; before engine problem; I heard ATC call my position to a crossing aircraft so I know my encoder was ok. This incident would not have occurred if either factor (engine problem; weather) were not in the equation. I gave up night flying years ago because it offered fewer options for emergency landing. I will be staying below even scattered henceforth in my local flying without ATC contact. Another item of note: I was so rusty on my GPS; that I had forgotten how to access a more helpful screen; which would have kept me clear of class C. In retrospect; I think my anxiety about this engine had 100% of my focus. In any event; I am re-reading the GPS manual. In monday morning quarterbacking this thing; I should have put the airspace screen on the GPS prior to takeoff instead of the course intercept screen; which required me to interpret numbers and bearings while addressing and engine problem.

Related reports:

Google
 

Original NASA ASRS Text

Title: An experimental aircraft's engine appeared to run rough. The pilot returned to land but after descending did not immediately identify his airport and may have incurred nearby Class C airspace.

Narrative: About 15 minutes into flight at 3500 FT MSL; experienced engine roughness. Turned immediately back toward my departure airport; climbing which addressing engine problem. Saw that scattered in direction of destination airport had gone broken. Continued slight climb with intention of crossing a nearby field in case engine quit before getting to my departure airport. Found a good clear area to descend through broken layer but did not recognize terrain once down to approximately 1000 FT AGL. Circled around some as engine had smoothed out. Trying to locate my departure airport; in as much as it looked like I was going south of it; in direction of ZZZ; I turned to 360 and almost immediately saw the field and landed without incident. I think I may have gotten into the upper ring of Class C on my descent. I believe I was well below the 2000 FT MSL ring most of the time; while busy with my situation. I do remember the ATC frequency I was monitoring was quiet. At no time did I hear radio transmissions; which would in anyway be in reference to my aircraft; after I got closer to the Class C. I normally do not contact ATC for my local flying in the area outside Class C. I felt it was more important for me to get on the ground as soon as possible then try and contact ATC about my predicament. My aircraft was squawking 1200 VFR with altitude encoding. Earlier in the flight; before engine problem; I heard ATC call my position to a crossing aircraft so I know my encoder was OK. This incident would not have occurred if either factor (engine problem; weather) were not in the equation. I gave up night flying years ago because it offered fewer options for emergency landing. I will be staying below even scattered henceforth in my local flying without ATC contact. Another item of note: I was so rusty on my GPS; that I had forgotten how to access a more helpful screen; which would have kept me clear of Class C. In retrospect; I think my anxiety about this engine had 100% of my focus. In any event; I am re-reading the GPS manual. In Monday morning quarterbacking this thing; I should have put the airspace screen on the GPS prior to takeoff instead of the course intercept screen; which required me to interpret numbers and bearings while addressing and engine problem.

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.