Narrative:

I was pilot flying. This was our first flight together as a flight crew. Upon review we noticed that same morning the aircraft was signed off for a new air turbine starter on the left (number 1) engine. We briefed that as a threat for the flight since we were the first crew to fly this aircraft since that maintenance was completed.the flight was completely normal until we were holding short; number 1 for takeoff. At this time the left oil level lo status message posted. I pressed the menu button on the EICAS control panel and it said the left engine oil quantity was 47%. I pulled out the QRH and it advises to write it up at 37%. So I cleared the status message and we agreed to continue to [destination]; paying close attention to the oil level in flight.we took the runway and took off. When [the first officer] called for the after takeoff checklist; when it states 'EICAS - checked and cleared;' I pressed the menu button on the EICAS control panel again. At this time the left engine oil quantity was 34% and the right engine oil quantity was 85%. We noted the significant decrease and discussed that this might have been due to the increased deck angle on climb out and/or the higher power setting. After just 2 minutes I pressed the menu button on the EICAS control panel again and it said the left engine oil quantity was now 32% and the right engine oil quantity was 85%. We discussed the fact that this was abnormal and potentially an indicator for a possible engine issue in the next few minutes.I asked [the first officer] if it would be alright with him if we circled over the area to stay close to the [nearby] airports. He thought that was a good idea too. I let him know to please advise ATC for that request while I would be off communication 1 to send a few ACARS messages to dispatch and maintenance. At this time the left engine oil quantity had fallen to 22%. I messaged dispatch 'oil level on no.1 engine went from 47 to 22.' I immediately followed that ACARS message with 'due to 22 percent oil what airport we will divert.' the reasoning for this was the significant and rapid drop in oil quantity on the left engine.[approach] asked if we were [declaring] and I told [the first officer] to [advise ATC]. [First officer] provided the souls and fuel onboard. Dispatch ACARS replied to us with 'so U want to return to either ZZZ or ZZZ1;' to which I replied 'which do you prefer'. Dispatch wrote 'back to ZZZ.' I called the flight attendants and told them that there was an issue with our left engine so we are circling and will most likely not continue on to [destination]. I also mentioned it is a rapidly developing situation so I would get back to them shortly with more details. I then made a PA to the passengers advising them of the low engine oil quantity on our left engine and that we are circling to determine the best course of action.at this point the oil quantity stabilized with the left engine at 15% and the right engine at 87%. I looked at the gauges and noted the engine indications were normal; so I mentioned to [the first officer] it was a possibility that we were dealing with an indication error. I brought this to our dispatcher's and maintenance's attention by sending this via ACARS: 'normal indications on engines would you prefer we continue or play it safe with a return to ZZZ.' to this dispatch replied; 'with such a long flight would probably go back to ZZZ.'around this point; the left engine oil pressure began to decline; from 65 psi to 40 psi and this is where the situation started to become more time sensitive and urgent. I mentioned my concerns to [the first officer] by stating with two system indications agreeing with each other; we most likely have an actual issue occurring. Within 60 seconds the left engine oil pressure fell into the red (around 20 psi) and we received the triple chime; master warning message left engine oil press and the aural 'engine oil.' I pulled out the QRH for 'engine oil press.' [first officer]and I worked together through that and the following QRH procedures at a slow; deliberate pace.when the procedure asks the crew; 'are any two of the following three indications displayed? - Left or right engine oil press warning message; - affected engine oil pressure is below limits; - affected engine oil temperature is increasing or decreasing abnormally.' we agreed 'yes' to the first two items; which led us to 'complete 'engine failure / in-flight engine shutdown.'' we proceeded to run that procedure; shutting down the left engine. Before starting the APU I decided it would be an appropriate break in the procedure to notify the flight attendants and passengers of our situation. [First officer] advised ATC we would like vectors to the ILS.I messaged dispatch and maintenance with 'left engine oil press single engine emergency 20 mins ETA.' dispatch copied that message and asked 'will it be ZZZ or ZZZ1.' after briefing the approach and preparing to land; on a 10 mile final I wrote back 'touching down at ZZZ in 2 minutes single engine.'[first officer] and I referenced the 'single engine approach and landing' to finish up all associated checklists. [First officer] conducted an approach briefing; we ran the descent and approach checklists; then I made one last call to the flight attendants and PA to the passengers 5 minutes before touchdown.it was an uneventful landing. Tower asked if we required any assistance; to which our answer was 'no.' we cleared the runway and I had [the first officer] call operations to confirm our gate and to also send a [gate agent] to meet the aircraft. While taxiing to the gate I checked the oil quantity. The left engine oil quantity was 15% and the right engine was 87%. We parked at the gate and ran the shutdown checklist. One last check of the oil quantity was 15% on the left engine and 100% on the right engine. We opened the main cabin door and I called the [gate agent] over before I [made] an announcement to the passengers. He advised me all passengers and bags were rerouted onto a flight leaving to [destination] in 30 minutes. I passed this information onto the passengers and also apologized for the inconvenience. All passengers were appreciative of this news and for the safe ending of our flight.

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Original NASA ASRS Text

Title: CRJ-900 flight crew reported a deterioration of the oil quantity and pressure in the left (#1) engine led to the engine being shut down and a successful return to the departure airport.

Narrative: I was Pilot Flying. This was our first flight together as a flight crew. Upon review we noticed that same morning the aircraft was signed off for a new air turbine starter on the left (number 1) engine. We briefed that as a threat for the flight since we were the first crew to fly this aircraft since that maintenance was completed.The flight was completely normal until we were holding short; number 1 for takeoff. At this time the L OIL LEVEL LO status message posted. I pressed the MENU button on the EICAS Control Panel and it said the left engine oil quantity was 47%. I pulled out the QRH and it advises to write it up at 37%. So I cleared the status message and we agreed to continue to [destination]; paying close attention to the oil level in flight.We took the runway and took off. When [the First Officer] called for the After Takeoff checklist; when it states 'EICAS - Checked and Cleared;' I pressed the MENU button on the EICAS Control Panel again. At this time the left engine oil quantity was 34% and the right engine oil quantity was 85%. We noted the significant decrease and discussed that this might have been due to the increased deck angle on climb out and/or the higher power setting. After just 2 minutes I pressed the MENU button on the EICAS Control Panel again and it said the left engine oil quantity was now 32% and the right engine oil quantity was 85%. We discussed the fact that this was abnormal and potentially an indicator for a possible engine issue in the next few minutes.I asked [the First Officer] if it would be alright with him if we circled over the area to stay close to the [nearby] airports. He thought that was a good idea too. I let him know to please advise ATC for that request while I would be off COM 1 to send a few ACARS messages to Dispatch and Maintenance. At this time the left engine oil quantity had fallen to 22%. I messaged Dispatch 'OIL LEVEL ON NO.1 ENGINE WENT FROM 47 to 22.' I immediately followed that ACARS message with 'DUE TO 22 PERCENT OIL WHAT AIRPORT WE WILL DIVERT.' The reasoning for this was the significant and rapid drop in oil quantity on the left engine.[Approach] asked if we were [declaring] and I told [the First Officer] to [advise ATC]. [First Officer] provided the souls and fuel onboard. Dispatch ACARS replied to us with 'SO U WANT TO RETURN TO EITHER ZZZ OR ZZZ1;' to which I replied 'WHICH DO YOU PREFER'. Dispatch wrote 'BACK TO ZZZ.' I called the Flight Attendants and told them that there was an issue with our left engine so we are circling and will most likely not continue on to [destination]. I also mentioned it is a rapidly developing situation so I would get back to them shortly with more details. I then made a PA to the passengers advising them of the low engine oil quantity on our left engine and that we are circling to determine the best course of action.At this point the oil quantity stabilized with the left engine at 15% and the right engine at 87%. I looked at the gauges and noted the engine indications were normal; so I mentioned to [the First Officer] it was a possibility that we were dealing with an indication error. I brought this to our Dispatcher's and Maintenance's attention by sending this via ACARS: 'NORMAL INDICATIONS ON ENGINES WOULD YOU PREFER WE CONTINUE OR PLAY IT SAFE WITH A RETURN TO ZZZ.' To this Dispatch replied; 'WITH SUCH A LONG FLIGHT WOULD PROBABLY GO BACK TO ZZZ.'Around this point; the left engine oil pressure began to decline; from 65 PSI to 40 PSI and this is where the situation started to become more time sensitive and urgent. I mentioned my concerns to [the First Officer] by stating with two system indications agreeing with each other; we most likely have an actual issue occurring. Within 60 seconds the left engine oil pressure fell into the red (around 20 PSI) and we received the triple chime; master warning message L ENG OIL PRESS and the aural 'ENGINE OIL.' I pulled out the QRH for 'ENG OIL PRESS.' [First Officer]and I worked together through that and the following QRH procedures at a slow; deliberate pace.When the procedure asks the crew; 'Are any two of the following three indications displayed? - L or R ENG OIL PRESS warning message; - Affected engine oil pressure is below limits; - Affected engine oil temperature is increasing or decreasing abnormally.' We agreed 'yes' to the first two items; which led us to 'Complete 'Engine Failure / In-Flight Engine Shutdown.'' We proceeded to run that procedure; shutting down the left engine. Before starting the APU I decided it would be an appropriate break in the procedure to notify the Flight Attendants and passengers of our situation. [First Officer] advised ATC we would like vectors to the ILS.I messaged Dispatch and Maintenance with 'L ENG OIL PRESS SINGLE ENGINE EMERGENCY 20 MINS ETA.' Dispatch copied that message and asked 'WILL IT BE ZZZ OR ZZZ1.' After briefing the approach and preparing to land; on a 10 mile final I wrote back 'TOUCHING DOWN AT ZZZ IN 2 MINUTES SINGLE ENGINE.'[First Officer] and I referenced the 'Single Engine Approach and Landing' to finish up all associated checklists. [First Officer] conducted an approach briefing; we ran the Descent and Approach checklists; then I made one last call to the Flight Attendants and PA to the passengers 5 minutes before touchdown.It was an uneventful landing. Tower asked if we required any assistance; to which our answer was 'no.' We cleared the runway and I had [the First Officer] call Operations to confirm our gate and to also send a [Gate Agent] to meet the aircraft. While taxiing to the gate I checked the oil quantity. The left engine oil quantity was 15% and the right engine was 87%. We parked at the gate and ran the Shutdown checklist. One last check of the oil quantity was 15% on the left engine and 100% on the right engine. We opened the main cabin door and I called the [Gate Agent] over before I [made] an announcement to the passengers. He advised me all passengers and bags were rerouted onto a flight leaving to [destination] in 30 minutes. I passed this information onto the passengers and also apologized for the inconvenience. All passengers were appreciative of this news and for the safe ending of our flight.

Data retrieved from NASA's ASRS site 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.