Narrative:

During the climb check the first officer turned on the air cycle machine (air conditioning) and the cabin and cockpit got a small amount of vapor from the vents. Thinking it was a malfunctioning air cycle machine I directed the first officer to turn it off then to go to the back of the airplane and check on everything. He returned saying it seemed like smoke, but he couldn't find a source. Since there was no smoke detector warning and the smoke went away after the acm was off, I elected to continue. Slightly after level off in clouds we noticed the left oil pressure fluctuating between 85 and 105 psi (the green range). A few mins later it was consistently below 85 psi, so I reduced power to less than 72% N1 as required and informed ZOA that I intended to land at chico, which was by now the nearest airport with an ILS. Within another few mins the oil pressure was nearing 40 psi confirmed by oil pressure light and engine inlet heat inoperative. When it went below 40 psi I shut the engine down as required, then declared an emergency with ZOA. We performed an ILS to chico, landed and brought the aircraft to a full stop on the runway. Nobody was coming toward us and instead of staying on the runway I decided it was safe to taxi to the gate where a mechanic was standing by. Preliminary inspection by a mechanic revealed a loss of 6 qts (9.3 total in system) of oil from a slow leak by a yet undetermined source. The mechanic thinks that the oil breather is clogged somewhere in the accessory case which caused the accessory gear case to pressurize and force oil out through the seals. Some of that oil was entering the engine at the air inlet, which is why when we turned the acm on there was smoke, because the acm uses compressor bleed air and if there is oil in that the acm will make some smoke.

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Original NASA ASRS Text

Title: DIVERT AND LAND WHEN ENGINE SHUT DOWN FOR LOW OIL PRESSURE.

Narrative: DURING THE CLB CHK THE F/O TURNED ON THE AIR CYCLE MACHINE (AIR CONDITIONING) AND THE CABIN AND COCKPIT GOT A SMALL AMOUNT OF VAPOR FROM THE VENTS. THINKING IT WAS A MALFUNCTIONING AIR CYCLE MACHINE I DIRECTED THE F/O TO TURN IT OFF THEN TO GO TO THE BACK OF THE AIRPLANE AND CHK ON EVERYTHING. HE RETURNED SAYING IT SEEMED LIKE SMOKE, BUT HE COULDN'T FIND A SOURCE. SINCE THERE WAS NO SMOKE DETECTOR WARNING AND THE SMOKE WENT AWAY AFTER THE ACM WAS OFF, I ELECTED TO CONTINUE. SLIGHTLY AFTER LEVEL OFF IN CLOUDS WE NOTICED THE LEFT OIL PRESSURE FLUCTUATING BTWN 85 AND 105 PSI (THE GREEN RANGE). A FEW MINS LATER IT WAS CONSISTENTLY BELOW 85 PSI, SO I REDUCED PWR TO LESS THAN 72% N1 AS REQUIRED AND INFORMED ZOA THAT I INTENDED TO LAND AT CHICO, WHICH WAS BY NOW THE NEAREST ARPT WITH AN ILS. WITHIN ANOTHER FEW MINS THE OIL PRESSURE WAS NEARING 40 PSI CONFIRMED BY OIL PRESSURE LIGHT AND ENG INLET HEAT INOP. WHEN IT WENT BELOW 40 PSI I SHUT THE ENG DOWN AS REQUIRED, THEN DECLARED AN EMER WITH ZOA. WE PERFORMED AN ILS TO CHICO, LANDED AND BROUGHT THE ACFT TO A FULL STOP ON THE RWY. NOBODY WAS COMING TOWARD US AND INSTEAD OF STAYING ON THE RWY I DECIDED IT WAS SAFE TO TAXI TO THE GATE WHERE A MECH WAS STANDING BY. PRELIMINARY INSPECTION BY A MECH REVEALED A LOSS OF 6 QTS (9.3 TOTAL IN SYS) OF OIL FROM A SLOW LEAK BY A YET UNDETERMINED SOURCE. THE MECH THINKS THAT THE OIL BREATHER IS CLOGGED SOMEWHERE IN THE ACCESSORY CASE WHICH CAUSED THE ACCESSORY GEAR CASE TO PRESSURIZE AND FORCE OIL OUT THROUGH THE SEALS. SOME OF THAT OIL WAS ENTERING THE ENG AT THE AIR INLET, WHICH IS WHY WHEN WE TURNED THE ACM ON THERE WAS SMOKE, BECAUSE THE ACM USES COMPRESSOR BLEED AIR AND IF THERE IS OIL IN THAT THE ACM WILL MAKE SOME SMOKE.

Data retrieved from NASA's ASRS site as of August 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.