B737 flight crew reported excessive engine vibration and return to departure airport.
Synopsis
B737 flight crew reported excessive engine vibration and return to departure airport.
Narrative
During the climb out of ZZZ enroute to ZZZ1; the crew noticed the #1 engine vibe was at 4.3. The Captain (PF) passed the controls and radios to the FO (First Officer) and went to the 'Engine High Vibration' checklist in the FM (Flight Manual). The level off at cruise altitude of FL380 coincided with the checklist step of 'retarding thrust' to try and bring the vibe within limits. As the thrust reduced below 95%; the vibe started to decrease. At cruise altitude (.76M) the vibe maintained between 1.7-2.3 (82-88% N1). All other engine indications were normal. After completion of the 'Engine High Vibration' checklist; the Captain (PM) coordinated a call with Dispatch and Maintenance Control. After discussions with this team and with the FO; the Captain made the decision to return to ZZZ and treat the engine as if it could not produce full thrust. The Captain (PM) took the radios back; requested priority handling and coordinated a return to ZZZ. He then spoke with the FAs (flight attendants) and then the passengers to inform them of our return to ZZZ due to a mechanical issue. The crew ran the 'One Engine Inoperative Landing' checklist to set up for an approach/landing with a reduced thrust engine (flaps 15). ATC asked what runway was preferred and we coordinated for Runway XXR due to its location on the west side of the field. At a good breaking point in the 'One Engine Inoperative' checklist the crew briefed the approach/landing plan. When everyone was comfortable and passing 12000' the Captain took the controls back and the FO resumed PM duties. ATC vectored the aircraft to a 15 NM final for the visual approach XXR (with ILS backup). Emergency equipment was not requested; but was standing by on the field. The Captain completed an uneventful flaps 15 landing and then taxied to the gate. After shutdown; Maintenance inspected the #1 Engine and noted several fan blades that had broken off and damaged the abradable shroud. The crew (pilots and FAs) were all moved to another aircraft and successfully completed the flight to ZZZ1.
Second reporter narrative
Normal takeoff and climb out of ZZZ. At approximately FL370; the First Officer noticed an engine vibration out of limits on the number one engine. I noticed an indication of 4.3 units. Upon leveling at FL380; the power levers retarded and the engine returned to within limits; however still indicating higher than engine two. I passed the controls to the First Officer and informed him to handle routine comms. I opened up the engine high vibration checklist. As instructed by the checklist I initiated a call with my Dispatcher and Maintenance Control. Maintenance Control verified that a 4.3 indication is an exceedance. I asked him for a recommendation to continue or turn around from a maintenance standpoint as the aircraft would be down for maintenance wherever we landed. He informed me that Maintenance Control is not allowed to make recommendations. I identified the threat being unable to achieve max continuous thrust on the number one engine; and I recalled that in the FM (Flight Manual); I would need to complete the one engine inoperative landing checklist and land flaps 15. I discussed this with the First Officer and we checked our fuel requirements to return to ZZZ. We agreed that this was the most conservative action and to execute the return. I informed Dispatch via radio that we would be returning to ZZZ. I chose to request priority handling due to not knowing if the number one engine condition would worsen leading to an engine shutdown. We received an immediate 180 degree turn; and proceeded directly to ZZZ. I then took time to inform the flight attendants that we would be landing back in ZZZ due to an engine malfunction; approximately 45 minutes till landing and that there was no intent to evacuate. I also made a PA announcement to the passengers; trying to be honest but not cause anyone to panic about the engine malfunction; and that we would work with the company to get them back to ZZZ1 after landing. The First Officer did a great job keeping me informed of ATC clearances and flying the aircraft with no auto throttles. I ran the one engine inoperative landing checklist as we descended back into ZZZ. XXR was in use per ATIS. We calculated landing distance from the charts and found XXR to be sufficient. We could have requested XXL which would have given us an extra 4000 ft of landing distance. I briefed the visual XXR backed up with the ILS. I completed the deferred items descent checklist; and took the controls. In hindsight I should have taken the controls back then asked for the deferred items. We received vectors to final XXR; configured to flaps 15 and completed an uneventful approach and landing. We checked engine indications after landing and elected to taxi to the gate coordinated by Dispatch. CFR (Crash Fire Rescue) met us on the taxiway and followed us to the gate. We debriefed in the aircraft and reviewed required calls and reports per the FOM. Maintenance came to the flight deck and showed us pictures of multiple fan blades missing from the number one engine.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.