Narrative:

At an altitude of 14;000 ft we began to get an intermittent low oil pressure light on the left engine; but I had just experienced this indication a few weeks earlier and knew that shutting down the engine might be necessary. I pulled out my manual in case we had to shut it down. The captain started getting the weather to the closest airports. We both concluded the weather at option 1 was better and if we did an emergency that would be the ideal airport. The intermittent light was accompanied by the oil pressure needle bouncing between the green and yellow arcs. We concluded that we would have to shutoff down the left engine and the captain made a PA to the passengers letting them know. We received a master warning engine oil pressure and since my book was open I gave the airplane to the captain and accomplished the checklist per manual. After the engine was shutdown I took the airplane back and proceeded to our diversion airport. There were no other negative engine indications. We declared an emergency and got direct to the airport. We started our descent for the runway 21 until we saw the airport and entered the left base for runway 18 and landed with no other incidents. After we landed a mechanic opened the engine cowling and said the oil filler cap was not properly put on and was dangling. There needs to be some serious oversight on all oil services done. This is the second time that this has happened to me.

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Original NASA ASRS Text

Title: After an ATR72 oil pressure light illuminated the crew shut the engine down; declared an emergency and proceeded to their destination. The engine oil filler cap was not closed securely allowing engine oil drain during flight.

Narrative: At an altitude of 14;000 FT we began to get an intermittent low oil pressure light on the left engine; but I had just experienced this indication a few weeks earlier and knew that shutting down the engine might be necessary. I pulled out my manual in case we had to shut it down. The Captain started getting the weather to the closest airports. We both concluded the weather at option 1 was better and if we did an emergency that would be the ideal airport. The intermittent light was accompanied by the oil pressure needle bouncing between the green and yellow ARCs. We concluded that we would have to shutoff down the left engine and the Captain made a PA to the passengers letting them know. We received a master warning engine oil pressure and since my book was open I gave the airplane to the Captain and accomplished the checklist per manual. After the engine was shutdown I took the airplane back and proceeded to our diversion airport. There were no other negative engine indications. We declared an emergency and got direct to the airport. We started our descent for the Runway 21 until we saw the airport and entered the left base for Runway 18 and landed with no other incidents. After we landed a Mechanic opened the engine cowling and said the oil filler cap was not properly put on and was dangling. There needs to be some serious oversight on all oil services done. This is the second time that this has happened to me.

Data retrieved from NASA's ASRS site as of April 2012 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.