B737 flight crew reported Oil Bypass Filter indication during cruise. Flight crew returned to departure airport and landed uneventfully.
Synopsis
B737 flight crew reported Oil Bypass Filter indication during cruise. Flight crew returned to departure airport and landed uneventfully.
Narrative
Shortly after established in cruise; we received an oil filter bypass light for the #1 engine. We completed the FM actions; which had us retard the thrust lever until the indication cleared; occurring near idle thrust. Assessing that we could no longer maintain altitude; we began drift down procedures and attempted to coordinate the decent with ATC over HF (High Frequency) radios. Coordination was difficult; as ATC kept saying that our transmissions were broken. Eventually we were able to coordinate a return to ZZZ. During coordination; the bypass indication returned and remained even at idle thrust. Following FM procedures; we executed an engine shutdown and advised ATC. Communications remained difficult until we were transferred back to VHF radios. Once all non-normal and normal checklists were completed; we notified dispatch; gave at brief report to the flight attendants; and the Captain made a PA notifying the passengers of the situation. The CA elected to assume pilot flying duties during the decent into ZZZ; and we continued using the modified checklists due to the shutdown. We executed the RNAV XX to a 15 Flap; MAX Auto-brake; full stop landing on the runway; followed by a shutdown of the operating engine. Crash/Fire personnel conducted an inspection of the engines and brakes; and after declaring all safe; we were towed to the ramp to park.
Second reporter narrative
While operating flight # ZZZ to ZZZ1 on Day 0 and shortly after reaching our cruise altitude of 34;000 feet; the #1 Engine OIL BYPASS FILTER indication came on. I the Captain was pilot monitoring and immediately executed the non-normal procedure for it which in short says to retard the affected trust lever until the OIL BYPASS FILTER indication disappeared or the trust lever was at idle. The first officer slowly retarded the thrust lever to idle and the indication disappeared for about 30 seconds. At this point with the #1 engine running at idle at 34;000 feet; airspeed started decaying; which led me to run the drift down QRC and checklist and start a descent to 20;000 after consulting the ENG OUT Altitude and airspeed with the FMC. We were on the Oceanic Track at the time so we offset 5 miles to the right so we wouldn't descend onto other traffic and made calls on XXX.X to advise nearby aircraft. We tried to get in contact with ZZZ Radio over HF radio which initially proved unsuccessful and unreliable as they couldn't us and we could barely hear them. That led me to try the backup HF frequency where we had a little better luck but communications between the radio operator; air traffic control and later dispatch we're perhaps the most challenging part of all of this. On the backup HF clearance we received clearance from air traffic control to return to ZZZ and descend to 20;000 and advise ATC. In the time that we had executed the driftdown QRC and communicated with ATC the OIL BYPASS FILTER indication had appeared and disappeared twice; and then it came on a third time which is when I made the decision to shut down the engine and run the inflight engine shutdown checklist. After we finished the shutdown and subsequent checklist was when ZZZ radio was able to get us a patch to dispatch. Dispatch was briefed although again we had troubles listening and speaking to dispatch on HF and so the call didn't last long and only key details were shared as well as a request coordinating the flight back in ZZZ. After; flight attendants were briefed and briefing was completed. At this point we had about 30 minutes to ZZZ so we prepared and briefed the approach; single engine landing and in case the single engine go around. Single engine Approach and landing were uneventful . We touched down with auto-brakes set to MAX and stopped on the runway to have the aircraft inspected before being towed to a stand. While the Airport Rescue and Fire Fighting team did not find any exterior damage to the engine; they determined that the brakes were hot and they brought out brake fans to cool them down before proceeding with a tow-in to a stand. Dispatch; Maintenance Control and Chief Pilot were debriefed after.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.