B737 air carrier Captain and Dispatcher reported an engine oil quantity decrease during cruise. The Captain diverted to an alternate airport; landed safely and was towed to the gate after fire rescue noted oil leaking from the engine.
Synopsis
B737 air carrier Captain and Dispatcher reported an engine oil quantity decrease during cruise. The Captain diverted to an alternate airport; landed safely and was towed to the gate after fire rescue noted oil leaking from the engine.
Narrative
While at cruise approximately 100 miles south of ZZZ at FL350. My First Officer (FO) observed an inverse oil quantity display showing 17%. We read low oil quantity in chapter 0 of the Flight Manual (FM) Engine Anomalies which states; There are no non-normal checklists for engine oil quantity and no minimum oil quantity limit (no amber or red line limit). After engine start there are no inflight operating limitations for the engine oil quantity; therefore; there are no pilot checklists based solely on a response to low oil quantity." Other than our right engine quantity being low; no other parameters were out of range. We discussed landing alternates if the situation deteriorated and we agreed ZZZ was our best option. We discussed what would be our minimum quantity of oil to divert and we decided 10% was our bingo number. I contacted Dispatch and Maintenance Control to advise what was going on. While on the radio with them we observed our oil quality continuing to drop. By the end of the call the number 2 engine was at 10%. We advised Dispatch we were [requesting priority] and were proceeding to ZZZ. We [requested priority] with center and ask immediately vectors to ZZZ. I asked the First Officer to fly the aircraft and communicate with ATC. I coordinated with Dispatch; briefed the Flight Attendants and talked to the Passengers. ATC asked if we would need assistance at ZZZ and I initially said no. However the oil quantity continued to drop and was now reading 0. Prior to this we briefed the single engine approach and landing had data ready if the engine had seized on final. Since the quality was now reading zero I advised ATC to roll crash fire rescue. Tower asked if able to clear the runway and once clear set the brake and gave us a frequency to talk directly to crash fire rescue. Immediately after landing; I shut the right engine down to prevent any further damage. We cleared the runway and crash fire rescue advised we had a significant oil leak out of the right engine and it would have to be cleaned up before we could move. Since there was a large amount of crash fire rescue around the aircraft they ask that we shut down engine one and we would be towed to the gate. I called the Flight Attendants to advise we were okay and not in any danger but we would be on a taxiway waiting on a tug. I made a PA to the passengers advising them we were fine and there would be Company people at the gate to assist. We were tugged to the gate with no issues. We were debriefed by the Chief Pilot and were deemed to be fatigued from the event and long duty day. Within 5 minutes crew scheduling was called and asked if we would extend and operate another flight to ZZZ. This was unsafe and unacceptable in my opinion and scheduling should have never called. Our Flight Attendants were reassigned to operate the next leg with the passengers to ZZZ1. Due to the amount of different personnel meeting the aircraft; I was never able to debrief the Flight Attendants to see if they were emotionally okay. They should not have been assigned without someone checking if they were safe to operate another leg. It is important to note several factors surrounding this flight. 1) This was a reassignment after a four hour sit in ZZZ2 after we operated ZZZ1 ZZZ2 and were supposed to be going to the hotel for rest. My subsequent rest was planned for a XA:00 am report and one leg day. 2) The engine in question had just been changed in ZZZ the morning of the incident. The prior Captain called Maintenance Control and questioned them why the engine had been changed and felt he never was given an answer. 3) The was a two day pairing and we were told we had to operate our next flights ZZZ1-ZZZ3-ZZZ1. No one from Company ever called to see if we were safe to operate. We did operate the next two legs."
Second reporter narrative
In the vicinity of ZZZ4 the flight sent Dispatch an ACARS stating that the #2 engine oil quantity had dropped to 12% and was falling rapidly. This message was rapidly followed up by a request to call them via ARINC. Once contact was made with the flight on ARINC; the flight requested conference with Maintenance Control. They reported to Maintenance Control that the oil quantity had dropped to 10% but the oil pressure remained normal. Due to this; the decision was made to divert to ZZZ and keep the engine running until the oil quantity ran out or oil pressure became abnormal. The flight [requested priority] with ATC and landed at ZZZ where it was met by Crash / Fire Rescue. The aircraft was able to taxi off the runway on its own power but shut down all engines after vacating the runway. It was reported by Crash Fire Rescue that large amounts of oil were seen leaking from the #2 engine and pooling underneath the engine. Due to this the aircraft did not restart the engines and was towed to the gate. Upon debriefing with the crew; it was discovered that the oil quantity had reached 0% on the affected engine on short final for ZZZ. It was also discovered that the engine in question had been replaced 2 cycles earlier.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.