B737-800 flight crew reported engine shutdown inflight due to loss of oil.
Synopsis
B737-800 flight crew reported engine shutdown inflight due to loss of oil.
Narrative
Aircraft was on MEL 80-XX; Left (#1) Engine Start Valve. Manual procedures (maintenance personnel manually open and closing start valve from exterior of aircraft had to be used). Started #1 engine at gate in ZZZ1 following (O) procedures in MEL 80-XX. Engine started normally. During engine start; 'Start Valve Open' caution on Upper Display unit appeared when maintenance opened the start valve. 'Start Valve Open' caution on Upper Display unit extinguished when maintenance closed the start valve. Appeared just like a normal start. No abnormal indications. 'Blanked' lower display unit after both engines were started per AOM1. Takeoff; climb and initial cruise were uneventful. I was the FO and PF for this leg.About 140 NM west of ZZZ; lower display unit auto-displayed showing ENG (Engine) #1 oil QTY at zero (0) in reverse video. Followed QRH procedure 'Engine Low Oil Quantity'. Oil pressure and temperature were normal. QRH directed to 'operate engine normally'. Which we did. Engine continued running fine for about 15 min. At this point; oil pressure began dropping rather quickly; dipping into indicating band and below. Oil temperature was also rising. Returned to QRH; directed to go to 'Engine Low Oil Pressure' checklist. This checklist directed us to go to the 'Engine Failure or Shutdown Checklist'. At this time; Captain [requested priority handling] with ATC. We both decided we wanted to divert to ZZZ which was now just about 100 NM to our west. Completed 'Engine Failure or Shutdown Checklist' per QRH. Captain notified Dispatch; Flight Attendants; and made a Passenger Address. Landed uneventfully on Runway XXL in ZZZ. Taxied to gate. Parked; shutdown uneventfully.Maintenance arrived at the aircraft; opened the #1 engine cowling to inspect it. They reported that the engine starter had essentially destroyed itself; causing damage / leaving a hole in the accessory gearbox which had allowed all the engine oil to drain out.Cause: Unknown. Possible maintenance issue related to MEL 80-XX. Possible uncommented and un-annunciated opening of engine #1 start valve in-flight.
Second reporter narrative
FL350 noticed oil QTY on L ENG (Engine) was reading O [zero].Determined that message must have been result of bad sensor due to the oil pressure oil temp and ENG VIB's (Engine Vibration) were at normal levels.Ran checklist and decided to press on. Later; L ENG oil pressure started dropping with subsequent flashing indications.Reasoned that it was a possible cavitation issue near sensor due to the oil temp and ENG VIB's still showing normal.Later oil temp started to rise from roughly 108 (R ENG temp at the time) to 130 at which time we decided to descend out of FL 390 to FL 270 and perform a precautionary shutdown.Diverted to ZZZ and landed uneventfully. Determined that oil temp had not risen above 130 so after rolling out on [Runway] XXL decided to taxi to the gate. There were airport rescue vehicles checking our left side as we exited.Cause: My intuition had wanted to un-blank the lower engine display on takeoff; but did not want to distract the FO as it was his takeoff. That may have been a way to catch the oil leak before taking off. We did not get any Master Caution or 6 pack light warning until after the amber and red flashes for oil pressure started.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.