Narrative:

On climb out from addison airport, in IMC. I looked to my left and found oil streaming back from the engine. The instruments indicated oil pressures and temperatures to be fine. I immediately told departure controller that I needed to go back to addison and proceeded to shut down the left engine. I declared an emergency and flew the ILS approach into addison airport and landed safely. The oil cap was found to be loose. The only logical explanation is that the line person who refueled/filled the oil on the engines did not put the cap on tight. I did not notice that the cap was loose. No damage to persons or property occurred.

Google
 

Original NASA ASRS Text

Title: A PA31-310 PLT RPTED THAT OIL WAS STREAMING OUT OF HIS L ENG, CAUSING HIM TO SHUT IT DOWN AND LAND AT ADS AFTER DECLARING AN EMER.

Narrative: ON CLBOUT FROM ADDISON ARPT, IN IMC. I LOOKED TO MY L AND FOUND OIL STREAMING BACK FROM THE ENG. THE INSTS INDICATED OIL PRESSURES AND TEMPS TO BE FINE. I IMMEDIATELY TOLD DEP CTLR THAT I NEEDED TO GO BACK TO ADDISON AND PROCEEDED TO SHUT DOWN THE L ENG. I DECLARED AN EMER AND FLEW THE ILS APCH INTO ADDISON ARPT AND LANDED SAFELY. THE OIL CAP WAS FOUND TO BE LOOSE. THE ONLY LOGICAL EXPLANATION IS THAT THE LINE PERSON WHO REFUELED/FILLED THE OIL ON THE ENGS DID NOT PUT THE CAP ON TIGHT. I DID NOT NOTICE THAT THE CAP WAS LOOSE. NO DAMAGE TO PERSONS OR PROPERTY OCCURRED.

Data retrieved from NASA's ASRS site as of July 2007 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.