Date: 202104
Local time of day: 1201-1800
Location: ZZZ.ARTCC, US
Flight conditions: VMC
Light: Daylight
Aircraft: B737-800
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Cruise
Airspace: Class A ZZZ
ATC / advisory: Center ZZZ
Aircraft component: Powerplant Lubrication System
Component problem: Failed
Reporter organization: Air Carrier
Reporter function: Pilot Not Flying; First Officer
Reporter qualification: Flight Crew Instrument; Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP)
Human factors: Troubleshooting; Workload
Anomaly: Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Maintenance
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Provided Assistance; Aircraft Aircraft Damaged; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Inflight Shutdown; Flight Crew Landed in Emergency Condition; General Maintenance Action
Contributing factors: Procedure; Aircraft; Human Factors
Primary problem: Procedure

Narrative: I was the Pilot Monitoring on this leg; approximately after 30 min of TOC; the lower display popped up showing Eng 2 low oil qty (3 qts); the Captain asked me to pull the QRH and look if there was a NNC (Non Normal Checklist); and we found out that there is no NNC for low oil quantity; upon searching our manuals we found information regarding this situation; explaining that there is not a min oil qty per se; but that oil temp and oil press are governing; and both indications we normal matching Eng 1. The Captain and I discussed the previous write up that the airplane had regarding low oil qty upon TOD; and how Maintenance personnel had previously drained the oil tank; filled it up again and checked for leaks. Since oil temperature and pressure indications were normal on Eng 2; we assumed it was an oil qty indication issue and decided to continue the flight closely monitoring Eng 2 oil temperature and pressure indications. In the following 10 to 15 mins the oil qty dropped to 0; but all other indications remained normal. Approximately 30 mins after the oil qty indication had shown 0 the Eng 2 oil pressure started to oscillate down and back up in a normal range; gradually getting lower every time; once it remained in the amber range the Captain and I started to anticipate a precautionary engine shutdown. Once the Eng 2 oil pressure indication entered the red range at approximately 14 PSI; the Captain called for the LOW OIL PRESS QRH NNC; we followed the NNC and proceeded to the ENG SHUTDOWN QRH NNC; we informed ATC and Dispatch of our mayday status and proceeded to ZZZ. After completing the ENG SHUTDOWN QRH; we proceeded to the ONE ENG INOPERATIVE NNC; dispatch sent us the landing data for ZZZ RWY XX We landed in ZZZ without further incident; stopping on the RWY and being towed to the ramp.The engine had developed an oil leak that went undetected.I understand the ZZZ1 Maintenance refilled the oil and perform an engine dry run; and then checked for leaks; perhaps the leak would have been discovered if the engine had been started and ran for several minutes.




Synopsis: B737 First Officer reported decreasing oil quantity followed by total loss of oil pressure caused an inflight shut down and a precautionary landing at destination airport.