Narrative:

After departing cmh at gross takeoff weight and during our climb approaching 31000 a fluctuating oil pressure on the #1 engine was noticed. The oil pressure was in the caution range and did read slightly lower when the throttle was retarded and several times dipped to the red range -- approximately 20 psi, but no associated master warning occurred. We (the crew) immediately notified ATC that we wanted to return to cmh and wanted a lower altitude. We told them we thought we might have a faulty oil pressure gauge and was going to return to cmh as a precaution. Since we were over gross for a normal landing, we decided to hold to burn off fuel so we wouldn't have to make an over gross landing. We also said if we lost oil pressure below 25 psi (minimum operating) that we would land as soon as possible. After holding for approximately 1 hour 20 mins we notified ATC we would like to proceed to cmh to land. (We held at gunne intersection at 18000 ft). When we were handed off to cmh approach, they notified us that our operations wanted us to take the plane to spi where it could possibly be worked on if needed. Much to my reluctance, we told ATC we would proceed to spi. At that time, on our climb to a higher altitude, I retarded the throttle to flight idle, at which time the master warning for oil pressure on the #1 engine came on and went out 2 times. By bringing the throttle back up, the pressure stayed in the caution range. We notified ATC we were declaring an emergency and wanted to land at cmh. The landing was done with both engines operating. It was discovered the oil cap had been left off the engine when it was svced, which resulted in our loss of oil, which was the reason for the low oil pressure.

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Original NASA ASRS Text

Title: CPR FLC EXPERIENCES LOW OIL PRESSURE, DECIDES TO RETURN TO DEP ARPT -- HOLDS TO BURN FUEL TO GET TO LNDG WT.

Narrative: AFTER DEPARTING CMH AT GROSS TKOF WT AND DURING OUR CLB APCHING 31000 A FLUCTUATING OIL PRESSURE ON THE #1 ENG WAS NOTICED. THE OIL PRESSURE WAS IN THE CAUTION RANGE AND DID READ SLIGHTLY LOWER WHEN THE THROTTLE WAS RETARDED AND SEVERAL TIMES DIPPED TO THE RED RANGE -- APPROX 20 PSI, BUT NO ASSOCIATED MASTER WARNING OCCURRED. WE (THE CREW) IMMEDIATELY NOTIFIED ATC THAT WE WANTED TO RETURN TO CMH AND WANTED A LOWER ALT. WE TOLD THEM WE THOUGHT WE MIGHT HAVE A FAULTY OIL PRESSURE GAUGE AND WAS GOING TO RETURN TO CMH AS A PRECAUTION. SINCE WE WERE OVER GROSS FOR A NORMAL LNDG, WE DECIDED TO HOLD TO BURN OFF FUEL SO WE WOULDN'T HAVE TO MAKE AN OVER GROSS LNDG. WE ALSO SAID IF WE LOST OIL PRESSURE BELOW 25 PSI (MINIMUM OPERATING) THAT WE WOULD LAND AS SOON AS POSSIBLE. AFTER HOLDING FOR APPROX 1 HR 20 MINS WE NOTIFIED ATC WE WOULD LIKE TO PROCEED TO CMH TO LAND. (WE HELD AT GUNNE INTXN AT 18000 FT). WHEN WE WERE HANDED OFF TO CMH APCH, THEY NOTIFIED US THAT OUR OPS WANTED US TO TAKE THE PLANE TO SPI WHERE IT COULD POSSIBLY BE WORKED ON IF NEEDED. MUCH TO MY RELUCTANCE, WE TOLD ATC WE WOULD PROCEED TO SPI. AT THAT TIME, ON OUR CLB TO A HIGHER ALT, I RETARDED THE THROTTLE TO FLT IDLE, AT WHICH TIME THE MASTER WARNING FOR OIL PRESSURE ON THE #1 ENG CAME ON AND WENT OUT 2 TIMES. BY BRINGING THE THROTTLE BACK UP, THE PRESSURE STAYED IN THE CAUTION RANGE. WE NOTIFIED ATC WE WERE DECLARING AN EMER AND WANTED TO LAND AT CMH. THE LNDG WAS DONE WITH BOTH ENGS OPERATING. IT WAS DISCOVERED THE OIL CAP HAD BEEN LEFT OFF THE ENG WHEN IT WAS SVCED, WHICH RESULTED IN OUR LOSS OF OIL, WHICH WAS THE REASON FOR THE LOW OIL PRESSURE.

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.