Narrative:

I approached said aircraft. Found the mechanic checking the engine compartment and draining the fuel sumps. The cowls were open, so I got my flashlight (it was still dark) and checked the oil caps, which visually appeared secure. I then closed the cowls and completed the preflight. It was routine for the mechanic to check the oil the night before while the engine was still warm. We departed the ramp on time and took off. While climbing through 8000' we noticed a fluctuation on the right torque meter, followed by a drop in oil pressure (slow). Reaching 10000' we leveled off and set cruise power. The torque was continuing to fluctuate and oil pressure continued to drop. When the oil pressure dropped to 60-70 psi, we decided to make a precautionary engine shutdown (right engine) and return to shv. After making a single engine landing and taxiing in, the mechanic checked the engine only to find out that the oil cap had vibrated loose. The oil was replaced and the engine checked out ok. The oil cap appeared to function correctly. Because of this, I no longer assume that the mechanic has properly secured the cap, and physically check it myself.

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Original NASA ASRS Text

Title: FLT CREW ON A COMMUTER SMT DISCOVERED LOW OIL PRESSURE DURING CLIMBOUT FROM SHV. SHUT ENGINE DOWN AND RETURNED TO SHV.

Narrative: I APCHED SAID ACFT. FOUND THE MECH CHKING THE ENG COMPARTMENT AND DRAINING THE FUEL SUMPS. THE COWLS WERE OPEN, SO I GOT MY FLASHLIGHT (IT WAS STILL DARK) AND CHKED THE OIL CAPS, WHICH VISUALLY APPEARED SECURE. I THEN CLOSED THE COWLS AND COMPLETED THE PREFLT. IT WAS ROUTINE FOR THE MECH TO CHK THE OIL THE NIGHT BEFORE WHILE THE ENG WAS STILL WARM. WE DEPARTED THE RAMP ON TIME AND TOOK OFF. WHILE CLBING THROUGH 8000' WE NOTICED A FLUCTUATION ON THE RIGHT TORQUE METER, FOLLOWED BY A DROP IN OIL PRESSURE (SLOW). REACHING 10000' WE LEVELED OFF AND SET CRUISE PWR. THE TORQUE WAS CONTINUING TO FLUCTUATE AND OIL PRESSURE CONTINUED TO DROP. WHEN THE OIL PRESSURE DROPPED TO 60-70 PSI, WE DECIDED TO MAKE A PRECAUTIONARY ENG SHUTDOWN (RIGHT ENG) AND RETURN TO SHV. AFTER MAKING A SINGLE ENG LNDG AND TAXIING IN, THE MECH CHKED THE ENG ONLY TO FIND OUT THAT THE OIL CAP HAD VIBRATED LOOSE. THE OIL WAS REPLACED AND THE ENG CHKED OUT OK. THE OIL CAP APPEARED TO FUNCTION CORRECTLY. BECAUSE OF THIS, I NO LONGER ASSUME THAT THE MECH HAS PROPERLY SECURED THE CAP, AND PHYSICALLY CHK IT MYSELF.

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.