Narrative:

The flight was a scheduled passenger operation from hot to hro. The first officer completed a normal preflight inspection and added a quart of turbine oil to the right engine. Just before departure I conducted a final walk-around inspection in which, among other things, I checked the security of all fuel caps, oil filler caps, door latches, etc. Takeoff and climb out were normal. After leveling at 6000' and completing the cruise checklist we were assigned 8000' by ATC. As we began the climb, I advanced the power levers to a normal climb setting. Almost immediately the right torque gauge began to fluctuate and behave erratically. Within 1 min the right oil pressure light illuminated and the right oil pressure indicator dropped below normal limits. We requested and were given clearance to return to hot. About this time a passenger came forward and advised us that there was transponder fluid seeping from the right engine. We told the passenger to return to his seat and fasten his seat belt. I reduced power on the right engine to near 0 thrust. The oil pressure held at about 40-50 psi and all other indications were normal. We were close enough to landing that no precautionary shutdown was warranted. A normal landing followed. Upon examination of the right engine, the oil cap/dipstick was found loose inside the cowling. No damage or injuries resulted and 7 qts of oil were required to return the engine to nominal. The first officer has no specific memory of reseating the oil cap after servicing. I am quite certain I opened the right cowling for the specific purpose of checking up oil cap security. I touched the cap/filler neck area. I cannot say whether I actually touched the cap or merely thought I had done so. It distresses me to think that after carefully checking hundreds of times uneventfully, the 1 time it mattered I failed to detect a problem. Note: a design factor which contributed to the occurrence is that the cowlings are hinged on the wrong side. As a result, I usually reach over the engines to check the oil caps because it is much quicker than walking around. However, from this position, access is poor and I must check more by touch than sight.

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Original NASA ASRS Text

Title: COMMUTER FO FAILED TO SECURE THE OIL CAP AFTER ADDING A QUART OF OIL. DURING CLIMB LOW PRESSURE OIL LIGHT CAME ON RESULTING IN RETURN LAND.

Narrative: THE FLT WAS A SCHEDULED PAX OPERATION FROM HOT TO HRO. THE F/O COMPLETED A NORMAL PREFLT INSPECTION AND ADDED A QUART OF TURBINE OIL TO THE RIGHT ENG. JUST BEFORE DEP I CONDUCTED A FINAL WALK-AROUND INSPECTION IN WHICH, AMONG OTHER THINGS, I CHKED THE SECURITY OF ALL FUEL CAPS, OIL FILLER CAPS, DOOR LATCHES, ETC. TKOF AND CLBOUT WERE NORMAL. AFTER LEVELING AT 6000' AND COMPLETING THE CRUISE CHKLIST WE WERE ASSIGNED 8000' BY ATC. AS WE BEGAN THE CLB, I ADVANCED THE PWR LEVERS TO A NORMAL CLB SETTING. ALMOST IMMEDIATELY THE RIGHT TORQUE GAUGE BEGAN TO FLUCTUATE AND BEHAVE ERRATICALLY. WITHIN 1 MIN THE RIGHT OIL PRESSURE LIGHT ILLUMINATED AND THE RIGHT OIL PRESSURE INDICATOR DROPPED BELOW NORMAL LIMITS. WE REQUESTED AND WERE GIVEN CLRNC TO RETURN TO HOT. ABOUT THIS TIME A PAX CAME FORWARD AND ADVISED US THAT THERE WAS XPONDER FLUID SEEPING FROM THE RIGHT ENG. WE TOLD THE PAX TO RETURN TO HIS SEAT AND FASTEN HIS SEAT BELT. I REDUCED PWR ON THE RIGHT ENG TO NEAR 0 THRUST. THE OIL PRESSURE HELD AT ABOUT 40-50 PSI AND ALL OTHER INDICATIONS WERE NORMAL. WE WERE CLOSE ENOUGH TO LNDG THAT NO PRECAUTIONARY SHUTDOWN WAS WARRANTED. A NORMAL LNDG FOLLOWED. UPON EXAMINATION OF THE RIGHT ENG, THE OIL CAP/DIPSTICK WAS FOUND LOOSE INSIDE THE COWLING. NO DAMAGE OR INJURIES RESULTED AND 7 QTS OF OIL WERE REQUIRED TO RETURN THE ENG TO NOMINAL. THE F/O HAS NO SPECIFIC MEMORY OF RESEATING THE OIL CAP AFTER SVCING. I AM QUITE CERTAIN I OPENED THE RIGHT COWLING FOR THE SPECIFIC PURPOSE OF CHKING UP OIL CAP SECURITY. I TOUCHED THE CAP/FILLER NECK AREA. I CANNOT SAY WHETHER I ACTUALLY TOUCHED THE CAP OR MERELY THOUGHT I HAD DONE SO. IT DISTRESSES ME TO THINK THAT AFTER CAREFULLY CHKING HUNDREDS OF TIMES UNEVENTFULLY, THE 1 TIME IT MATTERED I FAILED TO DETECT A PROB. NOTE: A DESIGN FACTOR WHICH CONTRIBUTED TO THE OCCURRENCE IS THAT THE COWLINGS ARE HINGED ON THE WRONG SIDE. AS A RESULT, I USUALLY REACH OVER THE ENGS TO CHK THE OIL CAPS BECAUSE IT IS MUCH QUICKER THAN WALKING AROUND. HOWEVER, FROM THIS POS, ACCESS IS POOR AND I MUST CHK MORE BY TOUCH THAN SIGHT.

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.