Narrative:

Roughly 8 mins into flight; level at 6000 ft the oil pressure started to fluctuate and was occasionally in the yellow (below 60 psi). About 14 mins into the flight after descending to 3000 ft and with visual of the airport; and flaps set at 8 degrees we got a red 'left engine oil pressure low' cas with no time to review the checklist and in a good position to land we chose to land; and monitored the oil pressure knowing that 50 psi is a magic number; which it never went below. Upon completion of the pre-landing checklist and landing safely we shut down the left engine. Taxied into the ramp and shut down the rest of the plane. Once we got out to check the physical condition of the left engine; we found it covered in oil from the oil service door back. Opening the door the oil dipstick was in the hole but not locked down and it was very obvious that was the source of the oil leak. Safely got the airplane on the ground with no further damage. We had checked the oil on the preflight; found it the normal operations range. After checking the oil; felt the cap had been secured; however it appears later it may not have been. Be sure the oil dipstick cap is totally secured. When in low light conditions double-check it with a bright flashlight; to make sure the small tab is visible in the hole; and that the yellow index lines match up.

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Original NASA ASRS Text

Title: A LEARJET-45 WITH TFE-731SER TYPE ENGINES EXPERIENCED FLUCTUATING LOW OIL PRESSURE. ACFT LANDED SAFELY. OIL DIPSTICK CAP FOUND NOT LOCKED DOWN.

Narrative: ROUGHLY 8 MINS INTO FLT; LEVEL AT 6000 FT THE OIL PRESSURE STARTED TO FLUCTUATE AND WAS OCCASIONALLY IN THE YELLOW (BELOW 60 PSI). ABOUT 14 MINS INTO THE FLT AFTER DSNDING TO 3000 FT AND WITH VISUAL OF THE ARPT; AND FLAPS SET AT 8 DEGS WE GOT A RED 'L ENG OIL PRESSURE LOW' CAS WITH NO TIME TO REVIEW THE CHKLIST AND IN A GOOD POS TO LAND WE CHOSE TO LAND; AND MONITORED THE OIL PRESSURE KNOWING THAT 50 PSI IS A MAGIC NUMBER; WHICH IT NEVER WENT BELOW. UPON COMPLETION OF THE PRE-LNDG CHKLIST AND LNDG SAFELY WE SHUT DOWN THE L ENG. TAXIED INTO THE RAMP AND SHUT DOWN THE REST OF THE PLANE. ONCE WE GOT OUT TO CHK THE PHYSICAL CONDITION OF THE L ENG; WE FOUND IT COVERED IN OIL FROM THE OIL SVC DOOR BACK. OPENING THE DOOR THE OIL DIPSTICK WAS IN THE HOLE BUT NOT LOCKED DOWN AND IT WAS VERY OBVIOUS THAT WAS THE SOURCE OF THE OIL LEAK. SAFELY GOT THE AIRPLANE ON THE GND WITH NO FURTHER DAMAGE. WE HAD CHKED THE OIL ON THE PREFLT; FOUND IT THE NORMAL OPS RANGE. AFTER CHKING THE OIL; FELT THE CAP HAD BEEN SECURED; HOWEVER IT APPEARS LATER IT MAY NOT HAVE BEEN. BE SURE THE OIL DIPSTICK CAP IS TOTALLY SECURED. WHEN IN LOW LIGHT CONDITIONS DOUBLE-CHK IT WITH A BRIGHT FLASHLIGHT; TO MAKE SURE THE SMALL TAB IS VISIBLE IN THE HOLE; AND THAT THE YELLOW INDEX LINES MATCH UP.

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.