Narrative:

The aircraft was a piper cherokee PA-28-180. During the aircraft preflight standard checklist items were checked including fuel sumps of each wing tank and the fuel strainer. Each sump location and a visible check inside the fuel filler cap revealed no contamination and light blue fuel color as expected. The aircraft started normally and was taxied short of the runway. Runup was performed with the engine at 2;000 RPM. Light contamination of the spark from the right magneto was observed as the RPM dropped to 1;800 RPM upon switching to the right magneto. The mixture was leaned for 5-10 seconds to clear the magneto; after this procedure the RPM drop was nominal at 1;900. Carb heat reduced engine to the nominal ~1;850 RPM level. About 45 seconds into the runup the tank selector was moved from the 'left' position to 'right' position. About ten seconds later the engine RPM reduced from 2;000 RPM to zero over about four seconds accompanied by light roughness. The engine was restarted on the right tank normally and the engine runup checklist was repeated with no issues. I believed that what I had observed was potentially a small amount of undetected water contamination in the tank reaching the engine and that no further issues could be expected. Takeoff clearance was granted thereafter. I pulled the aircraft on to the runway and allowed the engine to make maximum power with the brakes applied for 3-5 seconds before rolling on the runway; again no issues were experienced at this point or at any point during the ground roll. At about 300 ft AGL after departing the engine RPM dropped from 2;300 RPM to 2;000 RPM. I contacted tower and requested an immediate return to the traffic pattern which was granted. During the left downwind leg the engine RPM intermittently dropped from 2;000 RPM to 1;600 RPM for 2-3 seconds several times. During these brief periods of roughness I attempted corrective action with the mixture; magneto; and fuel pump controls but nothing seemed to affect the situation. Had the roughness persisted I would have switched fuel tanks and activated carb heat; however I did not have time to attempt all possible troubleshooting tasks. I requested and was granted landing clearance. The landing was uneventful. I taxied to the runup area a second time; and performed the runup checklist again. This time I switched the fuel tank selector to 'left' during the runup and no issues were experienced. I performed the runup checklist a second time and switched the tank to 'right' during the runup; roughly ten seconds later the engine RPM dropped from 2;000 to 1;600 RPM and a light roughness was observed for 3-4 seconds. At this point I stopped the runup checklist and taxied the aircraft to its parking spot and shut the aircraft down normally. I reported the details of the incident to the FBO and aircraft owner; who is also an a&P mechanic and is investigating the cause of the incident. The aircraft has been removed from rental use until it can be examined. I believe an issue exists in the fuel delivery system of the aircraft; perhaps localized to the fuel system of the right fuel tank. This may be due to fuel contamination or an obstructed filter; or perhaps another fault. An emergency or 'urgency' (pan-pan) was not declared as I received the necessary clearances from tower as they were requested. Had a delay potentially existed arising from ATC instructions; or complete engine failure occurred; I would have declared an emergency as the engine appeared to be very unreliable and seemed likely to fail at any moment after the 300 ft AGL engine trouble.

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Original NASA ASRS Text

Title: A PA-28-180 pilot reported engine roughness and loss of power after takeoff. He returned to departure airport for maintenance attention.

Narrative: The aircraft was a Piper Cherokee PA-28-180. During the aircraft preflight standard checklist items were checked including fuel sumps of each wing tank and the fuel strainer. Each sump location and a visible check inside the fuel filler cap revealed no contamination and light blue fuel color as expected. The aircraft started normally and was taxied short of the runway. Runup was performed with the engine at 2;000 RPM. Light contamination of the spark from the right magneto was observed as the RPM dropped to 1;800 RPM upon switching to the right magneto. The mixture was leaned for 5-10 seconds to clear the magneto; after this procedure the RPM drop was nominal at 1;900. Carb heat reduced engine to the nominal ~1;850 RPM level. About 45 seconds into the runup the tank selector was moved from the 'L' position to 'R' position. About ten seconds later the engine RPM reduced from 2;000 RPM to zero over about four seconds accompanied by light roughness. The engine was restarted on the right tank normally and the engine runup checklist was repeated with no issues. I believed that what I had observed was potentially a small amount of undetected water contamination in the tank reaching the engine and that no further issues could be expected. Takeoff clearance was granted thereafter. I pulled the aircraft on to the runway and allowed the engine to make maximum power with the brakes applied for 3-5 seconds before rolling on the runway; again no issues were experienced at this point or at any point during the ground roll. At about 300 FT AGL after departing the engine RPM dropped from 2;300 RPM to 2;000 RPM. I contacted Tower and requested an immediate return to the traffic pattern which was granted. During the left downwind leg the engine RPM intermittently dropped from 2;000 RPM to 1;600 RPM for 2-3 seconds several times. During these brief periods of roughness I attempted corrective action with the mixture; magneto; and fuel pump controls but nothing seemed to affect the situation. Had the roughness persisted I would have switched fuel tanks and activated carb heat; however I did not have time to attempt all possible troubleshooting tasks. I requested and was granted landing clearance. The landing was uneventful. I taxied to the runup area a second time; and performed the runup checklist again. This time I switched the fuel tank selector to 'L' during the runup and no issues were experienced. I performed the runup checklist a second time and switched the tank to 'R' during the runup; roughly ten seconds later the engine RPM dropped from 2;000 to 1;600 RPM and a light roughness was observed for 3-4 seconds. At this point I stopped the runup checklist and taxied the aircraft to its parking spot and shut the aircraft down normally. I reported the details of the incident to the FBO and aircraft owner; who is also an A&P mechanic and is investigating the cause of the incident. The aircraft has been removed from rental use until it can be examined. I believe an issue exists in the fuel delivery system of the aircraft; perhaps localized to the fuel system of the right fuel tank. This may be due to fuel contamination or an obstructed filter; or perhaps another fault. An emergency or 'urgency' (Pan-Pan) was not declared as I received the necessary clearances from Tower as they were requested. Had a delay potentially existed arising from ATC instructions; or complete engine failure occurred; I would have declared an emergency as the engine appeared to be very unreliable and seemed likely to fail at any moment after the 300 FT AGL engine trouble.

Data retrieved from NASA's ASRS site as of July 2013 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.