Narrative:

While in cruise descent at approximately 2500 ft MSL the engine began to run rough. Planned to land at ZZZ; but diverted to ZZZ1. Placed '7700' squawk code and made contact with approach advising controller of situation. Applied carburetor heat; adjusted throttle and power restored. Landed at ZZZ1 without incident. Upon landing; noted right fuel cap loose and apparent trail of fuel seeping. Fuel cap not replaced to normal position by fueler. I should have made certain it was in proper position before takeoff.

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Original NASA ASRS Text

Title: AERO COMMANDER DARTER PLT EXPERIENCES ROUGH ENGINE. DECLARES EMERGENCY AND DIVERTS TO CLOSER ARPT.

Narrative: WHILE IN CRUISE DSCNT AT APPROX 2500 FT MSL THE ENG BEGAN TO RUN ROUGH. PLANNED TO LAND AT ZZZ; BUT DIVERTED TO ZZZ1. PLACED '7700' SQUAWK CODE AND MADE CONTACT WITH APCH ADVISING CTLR OF SIT. APPLIED CARB HEAT; ADJUSTED THROTTLE AND PWR RESTORED. LANDED AT ZZZ1 WITHOUT INCIDENT. UPON LNDG; NOTED R FUEL CAP LOOSE AND APPARENT TRAIL OF FUEL SEEPING. FUEL CAP NOT REPLACED TO NORMAL POS BY FUELER. I SHOULD HAVE MADE CERTAIN IT WAS IN PROPER POS BEFORE TKOF.

Data retrieved from NASA's ASRS site as of January 2009 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.