Flight crew reported erratic oil pressure and quantity indications on number 2 engine during descent which had previously been reported and deferred per MEL. The flight crew continued to the destination after coordinating with ATC for an expedited arrival.
Synopsis
Flight crew reported erratic oil pressure and quantity indications on number 2 engine during descent which had previously been reported and deferred per MEL. The flight crew continued to the destination after coordinating with ATC for an expedited arrival.
Narrative
This was the first leg of our 4 day trip. Commuted from ZZZ3 to ZZZ2; took the train to ZZZ1 and waited about 4 hours before my trip with First Officer (FO); Person A. The first leg; ZZZ1-ZZZ was scheduled to leave at XA00. The aircraft did not get towed over to gate until almost XB30 though it had been ready since the previous night. We were all slightly tired and rushed already. During our briefing it was mentioned that this aircraft had an MEL for keeping a watch on the oil for number 2 engine as previous flight consumed quite a bit and Maintenance could not find a leak; and therefore released the aircraft on a MEL requiring a close look before each flight. We also had a new hire jump seat observation flight; and were helping to explain a lot to him along the way. During the taxi out the flight attendants (FAs) (thankfully) reported to us that all the pilot meals smelled awful and were spoiled. We decided to deal with that later. Then came the final weights issue. Despite calling everyone we possibly could someone eventually figured out how ramp did not properly close out the weights. This resulted in further delaying our flight. Finally; we were airborne and on our way to ZZZ. The cruise portion became rather busy. We were explaining a lot of things to our observation rider and Dispatch was sending us a number of updated TAFs about the deteriorating ZZZ weather conditions. In all honesty; I do not think any of us looked very much at the oil quantity # 2 during that flight. I saw it once during early cruise and it looked ok all things considered. The unfortunate reality is I see these various maintenance watch items too much and become a little numb to giving them enough attention they deserve which you will soon discover they do. Moving on... just as we were done briefing our arrival; and RNAV Z approach for XXR into ZZZ; we made our PAs; and let the FAs know to clean up a little early for a possible bumpy descent. The observer was asking about some VNAV items which I began to address and that is when we noticed the oil problems. My First Officer noticed it. The number 2 engine was showing 0 QTY. I quickly shifted into pre urgent mindset mode. We observed all other engine related items and agreed everything else at the moment was actually fairly normal. I asked Person A to see if there was a QRH item for LOW OIL QTY. He was able to find the correct checklist but since we did not have an actual engine failure; high temp or pressure in the red area the checklist did NOT provide much more guidance. A moment later ATC gave us the initial descent and it was then we were able to see a very significant drop in oil pressure with reduced thrust. I told Person A I was going to advise ATC and asked if he agreed which he did. I gave the flight controls to him and advised ZZZ Center. We were able to get priority handling and vectors for the approach. Even though we were set up for the RNAV Z; we discussed that the ILS would be a better choice if we were to have the engine quit or were forced to shut it down. Lacking anything but excessive oil pressure fluctuations; I decided that keeping it running was the better of two choices.... the risk of it getting so hot and possibly catching on fire; but also; the risks of shutting it down and doing a single engine approach down to practically minimums. Ultimately we thought it would be best to run it until something worse presented itself. After putting the gear down; I told Person A that if we were to lose the engine this low we would continue the approach; select Flaps 15; secure the engine if needed; and fly an appropriate single engine flap speed rather than doing a go around southeast in IFR conditions. We both agreed that was what we were going to do. I know other pilots would choose a different strategy but this was my pilot in command (PIC) safest decision at the moment and was agreed on with Person A as well. In the end; the engine gave us power all the way to the ground. Once we were clear of runway with our times; we shut down the number 2 and taxied in uneventfully.
Second reporter narrative
Just prior to the top of descent on arrival into ZZZ; the Captain pointed out something on his FMC to the jump seater (JS). The JS was a new hire completing an observation flight. I looked down and noticed the solid white box around the right engine oil quantity. It was already reading 0. I notified the Captain and he asked me to check the QRC then QRH for the appropriate procedure. I noted there after checking I noted there was no procedure; but found a paragraph in the Flight Manual (FM) stating there was no non-normal checklist. We monitored the oil pressure and temperature as we continued our descent. We noted that the right oil pressure had begun to fluctuation. We continued to monitor until we saw the oil pressure flashed amber. At that point we advised ATC and got vectors to the ILS in ZZZ. During the vectors we reviewed the procedure for a red oil pressure light and discussed what we would do if we had to secure the engine. The controls were transferred to me while the Captain managed the situation. We made an uneventful landing at ZZZ and taxied to the gate on the left engine. We left the engine running during the descent to landing as it was providing thrust and not in the red for oil pressure yet. After landing; the Captain informed me that the oil pressure had intermittently fluctuated into the amber and red a couple times on final but elected to not distract me while landing was imminent.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.