Flight crew of an light transport returned to land after 1 engine oil pressure was below acceptable ...

Attributes
ACN	338513
Time
Date	199606
Day	Fri
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : gij airport : mke
State Reference	MI
Altitude	msl bound lower : 11000 msl bound upper : 11000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Operator	common carrier : air carrier
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 135
Flight Phase	cruise other other other
Route In Use	enroute airway : zau
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	other other : other pilot : cfi pilot : atp
Experience	flight time last 90 days : 120 flight time total : 3300 flight time type : 1100
ASRS Report	338513
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	aircraft equipment problem : critical other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : unspecified other flight crewa
Consequence	Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	other

Narrative:

I was the PF while the captain was writing down information for an engine monitoring trend. (This engine trend is done for our maintenance department once a day in VMC between 20000-10000 ft MSL.) ZAU told us to descend from 11000 ft to 9000 ft MSL. Just then I noticed that the right oil pressure gauge was reading about 30 psi. (Normal operating range is 90-120 psi and caution is 60-90 psi.) I then reduced the power on the right engine to idle and brought both propellers to maximum RPM. After a short discussion, the captain and I decided not to shut the engine down. There was no secondary indication of low oil pressure. The right oil pressure low light was not on. (We tested the light and it was working normally.) the right oil temperature was in the green and about 5 degrees C lower than the left, the torque and oil pressure gauges were not fluctuating (both measure oil pressure), and there was not visual indication of a leak. The emergency checklist calls for (in the event of a low oil pressure indication) either a precautionary shutdown or minimum power to sustain flight. Because there was no secondary indication and because milwaukee was IFR (300 ft ceiling and 1 1/4 mi visibility) we elected to not shut down the engine. The captain informed ZAU of the problem. We decided not to declare an emergency. However, we decided to return to mke. About 15 NM southeast of mke the captain became PF. The captain elected to have the crash fire rescue equipment standing by. After intercepting final for the ILS runway 7R at mke the captain elected to feather the right engine (and keep it running). We landed without incident. After investigating the problem, our mechanics found that the oil level was normal and there were no broken lines. An engine runup was performed. It was then determined that the probable cause was either a bad gauge or a bad sender unit. The aircraft was signed off with a new gauge and sender. No further problems occurred.

Original NASA ASRS Text

Title: FLC OF AN LTT RETURNED TO LAND AFTER 1 ENG OIL PRESSURE WAS BELOW ACCEPTABLE LIMITS AND ALL PRECAUTIONARY CHKLIST PROCS WOULD NOT BRING IT BACK. HOWEVER, SINCE THERE WERE NO OTHER INDICATIONS OF AN ACTUAL ENG MALFUNCTION THE ENG WAS LEFT RUNNING.

Narrative: I WAS THE PF WHILE THE CAPT WAS WRITING DOWN INFO FOR AN ENG MONITORING TREND. (THIS ENG TREND IS DONE FOR OUR MAINT DEPT ONCE A DAY IN VMC BTWN 20000-10000 FT MSL.) ZAU TOLD US TO DSND FROM 11000 FT TO 9000 FT MSL. JUST THEN I NOTICED THAT THE R OIL PRESSURE GAUGE WAS READING ABOUT 30 PSI. (NORMAL OPERATING RANGE IS 90-120 PSI AND CAUTION IS 60-90 PSI.) I THEN REDUCED THE PWR ON THE R ENG TO IDLE AND BROUGHT BOTH PROPS TO MAX RPM. AFTER A SHORT DISCUSSION, THE CAPT AND I DECIDED NOT TO SHUT THE ENG DOWN. THERE WAS NO SECONDARY INDICATION OF LOW OIL PRESSURE. THE R OIL PRESSURE LOW LIGHT WAS NOT ON. (WE TESTED THE LIGHT AND IT WAS WORKING NORMALLY.) THE R OIL TEMP WAS IN THE GREEN AND ABOUT 5 DEGS C LOWER THAN THE L, THE TORQUE AND OIL PRESSURE GAUGES WERE NOT FLUCTUATING (BOTH MEASURE OIL PRESSURE), AND THERE WAS NOT VISUAL INDICATION OF A LEAK. THE EMER CHKLIST CALLS FOR (IN THE EVENT OF A LOW OIL PRESSURE INDICATION) EITHER A PRECAUTIONARY SHUTDOWN OR MINIMUM PWR TO SUSTAIN FLT. BECAUSE THERE WAS NO SECONDARY INDICATION AND BECAUSE MILWAUKEE WAS IFR (300 FT CEILING AND 1 1/4 MI VISIBILITY) WE ELECTED TO NOT SHUT DOWN THE ENG. THE CAPT INFORMED ZAU OF THE PROB. WE DECIDED NOT TO DECLARE AN EMER. HOWEVER, WE DECIDED TO RETURN TO MKE. ABOUT 15 NM SE OF MKE THE CAPT BECAME PF. THE CAPT ELECTED TO HAVE THE CFR STANDING BY. AFTER INTERCEPTING FINAL FOR THE ILS RWY 7R AT MKE THE CAPT ELECTED TO FEATHER THE R ENG (AND KEEP IT RUNNING). WE LANDED WITHOUT INCIDENT. AFTER INVESTIGATING THE PROB, OUR MECHS FOUND THAT THE OIL LEVEL WAS NORMAL AND THERE WERE NO BROKEN LINES. AN ENG RUNUP WAS PERFORMED. IT WAS THEN DETERMINED THAT THE PROBABLE CAUSE WAS EITHER A BAD GAUGE OR A BAD SENDER UNIT. THE ACFT WAS SIGNED OFF WITH A NEW GAUGE AND SENDER. NO FURTHER PROBS 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.

Flight crew of an light transport returned to land after 1 engine oil pressure was below acceptable limits and all precautionary checklist procedures would not bring it back. However, since there were no other indications of an actual engine malfunction the engine was left running.