B737 Flight Crew reported the Number 1 Engine Oil Bypass Light illuminated during the climb out. After conferring with Dispatch and Maintenance; the decision was first made that the engine did not need to be shut down. However; as the flight continued to the destination and the Oil Bypass Light would not extinguish; the engine was then shut down.
Synopsis
B737 Flight Crew reported the Number 1 Engine Oil Bypass Light illuminated during the climb out. After conferring with Dispatch and Maintenance; the decision was first made that the engine did not need to be shut down. However; as the flight continued to the destination and the Oil Bypass Light would not extinguish; the engine was then shut down.
Narrative
On climb-out from ZZZ through about 26;000 ft.; the No 1 Engine Oil Bypass Light illuminated. We followed the Engine - Oil Bypass Light QRH. The Bypass Light went out with the Number 1 Engine at about 77% N1. The checklist says to confer with Dispatch and Maintenance about safest course of action.I sent a message to Dispatch; Call me;" on Commercial Radio frequency. Dispatch quickly responded with a frequency; but we had to wait about 10+ minutes since another aircraft was handling a medical issue with a passenger. Once they were finally done and the frequency was clear; we were able to establish a phone patch with Dispatch and Maintenance. By this time; we were nearly over the top of ZZZ1.After explaining what happened; telling them the checklist we followed; and after having a brief discussion with Dispatch; Maintenance; and the FO (First Officer); we all agreed it was safe to continue to ZZZ2 as long as the Number 1 Engine parameters stayed within normal limits; and it did not need to be shut down. Maintenance suspected it was an instrumentation issue since we had oil pressure and oil temperature within normal limits. We all agreed it was not necessary to [request priority handling] with the Number 1 Engine operating at reduced thrust; so we did not do so at this point.I called the flight attendants to give a briefing. Person A answered. I told her; I need to give you a briefing. Her exact response was; "But; I am right in the middle of my service." I told her this was more important; and she put Person B on the phone. I had to repeat to Person B that I needed to give her a briefing; and she seemed better prepared for one - asking me to wait just a moment while she got ready to take notes on her link device.Once she was ready; I advised her that one of our engines was operating at reduced power because of an oil issue. It was still running; and we were still continuing to ZZZ2; but there was a chance we would divert with only 20+ minutes warning to the cabin if the engine performance significantly degraded. I told her we had about an hour to go; there was no need to prep for an evacuation; I had no special instructions; and I would update her if things changed.We reviewed the Engine Shutdown Checklist; kept the fuel balanced; checked the single-engine performance page of the FMC; and continued to monitor the engine. The Bypass Light reilluminated about every 3 - 5 minutes during flight and go out when the throttle was slightly reduced. Each time the N1 needed for the light to go out was a little lower. I sent a maintenance write-up and info report; logging the multiple N1 numbers when the Bypass Light came on; and what setting it went off. Per the Oil Bypass Light Checklist and our conversations with Dispatch / Maintenance; we continued towards ZZZ2. It appeared more likely that we would end up shutting down the engine; so I called the flight attendants and gave an updated briefing. I told her we were about 10 - 15 minutes of committed to continuing to ZZZ2; and to consider no news is good news on the need to divert. Fortunately; ATC needed a slower than normal speed from us; as we would not have been able to hold a fast; 0.78 mach or 300+ kt. if they needed it.We requested to descend early so the Number 1 Engine could operate at a further reduced setting. Just after the start of descent; the Oil Bypass Light came on again; and did not extinguish with the throttle at idle. The Oil Bypass checklist directed us to the Engine Failure or Shutdown Checklist. We followed the checklist; shut down the engine; advised Dispatch we were shutting down the engine; and about to [request priority handling]. After shutting down the Number 1 Engine; [requested priority handling] with ATC.After completing the checklist to the descent briefing portion; I did another briefing with the flight attendants and made a PA to the passengers. I did not have the flight attendants prepare the cabin for an evacuation - as we would be landing on a dry; long runway it did not seem necessary. In my view; "Prepare the Cabin" meant briefing the passengers on brace positions; and additional briefings with the passengers in the exit rows. Discussions with Person B after landing determined that she thought "Prepare for Evacuation" simply meant being more spring-loaded to evacuate herself; but no extra briefings of the passengers. There was obviously a big gap between what they think and what we think "Prepare for Evacuation" means in an immediate situation and this should be looked at and further addressed. I calmly told the passengers to expect a little faster than normal landing; they would see fire trucks follow us; and despite all this; we would still have them into ZZZ2 early; and I will see them at the gate. We had the checklist completed well before joining the approach to [Runway] XXL. We landed and fire / rescue confirmed there was no smoke / no evidence of abnormalities / no hot brakes before we taxied into the gate."
Second reporter narrative
Normal ground operations and checks; with uneventful takeoff and initial departure out of ZZZ. Around XA:38; while climbing through approximately 23;000 ft. MSL for FL290 the Captain's side; Number 1 Engine Oil Bypass Light illuminated. Oil pressure was normal; RPM was normal; Number 1 Engine Oil Temperature was noted as slightly warmer - approximately N1 - 95 degrees; N2 - 77 degrees. Captain directed execution of 737 FM Non-Normal procedures. Checklist was accomplished in order; condition and light was confirmed. Autothrottle was disengaged; LNAV and VNAV remained engaged. Thrust lever was confirmed; then retarded slowly until approximately 77% N1 when the light extinguished. Light had extinguished so we proceeded. The Captain then contacted Dispatch and Maintenance after we discussed factors and positive control of the aircraft was passed to me. Dispatch and Maintenance recommendation was to continue; Captain and I used CRM / TEM (Threat and Error Management) and discussed possible threats to continuing the flight; and made the decision we concurred the flight could continue. After the Captain completed discussion with Dispatch / Maintenance he conducted a briefing with the FA (Flight Attendant) then took back control of the aircraft. Shortly after the Oil Filter Bypass Light illuminated again at approximately 77% N1; thrust was reduced to 75% N1; and the light extinguished. The decision was made to continue the flight in accordance with the current game plan while while we discussed CRM / TEM for possible engine failure and divert options. Decision point was made that prior to beginning descent into ZZZ2; an engine failure would be addressed by diverting to either ZZZ3 or ZZZ4. Once on the arrival at current altitude we would continue to ZZZ2. As we continued; the light illuminated again and another N1 reduction of approximately 2% was accomplished with the light extinguishing once again. The frequency of this trend then began to increase initial reduction to reillumination of the light was about 5 minutes between and by the time we began descent for the arrival we had decreased from 71% N1 to 68% and the light only remained off for approximately 1 - 2 minutes. By 27;000 ft. in the descent the light would illuminate again after only 30 seconds from each thrust reduction and Engine 1 Oil Temperature was noted as rising from 99 to 107 degrees Celsius as thrust was reduced all the way to idle closed. Once closed; step three of the Engine Oil Filter Bypass was conducted; following Oil Filter Bypass Light stays illuminated and Engine Failure or Shutdown Checklist for the NG; 737 FM was then executed per the publication. At this time the Captain [requested priority handling] with ZZZ2 Center. ZZZ2 Center kept us initially on the arrival but lifted all speed restrictions and gave a hard altitude of 14;000 ft. MSL for our descent. The Captain passed controls one more time with good confirmation to allow him to update the FAs; Dispatch / Maintenance; and review the arrival brief while covering CRM / TEM threats and mitigation. Once complete; controls were passed back to the Captain. I completed the remainder of the Engine Failure or Shutdown Non-Normal procedure; then proceeded to the Once Engine Inoperative Landing Non-Normal Checklist 737 FM. At this point ZZZ2 Approach had passed us to a single channel Approach frequency with a dedicated control and cleared us for the Visual XXL per our request as as that was our expected arrival and was loaded in the system. The checklist was completed in its entirety and the approach to landing was without incident and in accordance with all procedures and very much so reflected exactly the situations and training that we receive at the training center in the simulators. Airport & Rescue Firefighting (ARFF) was able to inspect the brakes and do a general safety check once we cleared the runway and an uneventful taxi to the gate was accomplished followed by shutdown. Training; support from ATC; Approach; Tower; Dispatch; Maintenance; and ARFF was all expertly and professionally handled with no issues detracting from the safe accomplishment of the flight. Training and checklist usage and the 737 FM were excellent tools for the situation with one suggestion in regards to the FM Checklist and Fuel Balance. By short final or landing rollout my best recollection was our fuel was at an imbalance of approximately 600 lb. with about 4;200 lb. on the Engine 1 side and 3;600 lb. on the Number 2 side. Although in tolerance and not unsafe this was a larger split than intended and the Captain and I had discussed a game plan for management and monitoring. The checklist however only mentions it one time during Step 9 of FM well prior to final landing; where much time might be spent with a growing imbalance of fuel. I recommend Balance Fuel as Needed" be added to the end of the engine failure again; prior to Step 15 on FM; and then again add "Balance Fuel as Needed" prior to deferred items on FM during the Engine Inoperative Landing Non-Normal Checklist."
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.