B737-800 flight crew reported a split N1 condition during climb followed by engine failure. Flight crew returned to departure airport.
Synopsis
B737-800 flight crew reported a split N1 condition during climb followed by engine failure. Flight crew returned to departure airport.
Narrative
On Day 0 the Captain and I reported to fly Aircraft X from ZZZ-ZZZ1. During our sit at ZZZ; we reviewed the AML (Aircraft Maintenance Logbook) for the aircraft and saw a repeat writeup regarding split N1s during takeoff and the inability of two previous crews to match N1s by manually manipulating the thrust levers. Both previous crews stated that N1s matched upon reaching 3;000 feet and the autothrottles continue to work accurately throughout all phases of flight from that point. When we arrived at the airplane; maintenance was on board and informed the Captain that the autothrottle system would be MELd; something the Captain and I discussed and determined we were comfortable with. Upon stating that I had not experienced much flying without autothrottles at this airline; the Captain briefed me on procedures for takeoff and initial climb prior to autopilot engagement where I as the FO and PM would manipulate the thrust levers to set takeoff thrust and make necessary changes declared by the Captain as PF.The Captain and I conducted preflight duties without incident and pushed back from gate XX and received taxi instructions for an intersection takeoff from runway XXR at [taxiway] 1. We were cleared for takeoff and the Captain commenced the takeoff roll. I noted and verbalized an approximately 5% split in N1s with the #1 engine operating at a lower N1. I advanced the #1 thrust lever to attempt to match the #2 engine; which was operating at takeoff power. Advancing the #1 thrust lever did not change the N1 percentage of the engine. I announced to the Captain that the N1 split remained and that the thrust levers were split and he continued the takeoff roll without incident. We rotated on schedule and began our initial climb. After the Captain called for flap retraction and after takeoff checklist; I completed the requested tasks and verbalized them as complete. I then remarked that we would see if the N1s would match upon reaching 3;000 feet as previously written up. Our initial climb clearance was to 5;000 feet and we leveled off there. As I was reducing power; I noticed that the N1 split remained at about 5%. Our level off was brief and we were cleared to climb to 15;000 and then switched to ZZZ Center with a further climb to FL230.Passing through roughly 12;000 feet; I told the Captain that the N1 split remained in the climb and was about 7% now with the #1 engine still showing lower N1 than the #2 engine. The Captain engaged autopilot and took control of the thrust levers. He moved the #1 thrust lever forward of the #2 thrust lever and noted the N1 split remained and asked my opinion. I informed the Captain I was not comfortable continuing to ZZZ1 with uneven fuel burn and an engine possibly incapable of producing maximum power. The Captain felt the same way and passed aircraft control to me so he could talk to ZZZ Center and inform the flight attendants of the return to ZZZ. We received a clearance to level off at 15;000 feet so we could troubleshoot and determine our next steps.At the same time; I informed dispatch via ACARS that we were returning to ZZZ because of an N1 split. The Captain then informed me to request priority handling with ZZZ Center and to have ARFF (Airport Rescue and Firefighting) standing by upon our return out of an abundance of caution. I requested priority with Center and they cleared us back to ZZZ via radar vectors.After informing the flight attendants of the diversion; the Captain made a PA and began running the QRH procedure. At this time; the Captain passed the radios to me so he could run the checklist. Center queried us for souls and fuel remaining on board which I passed back; then they cleared us to descend to 13;000 feet; then 10;000 feet. I started the descent with idle power and used level change to set speed to 250 knots. I saw a master caution light illuminate and immediately turned toward the engine gauges and saw ENG FAIL on the #1 N1 gauge. I called; Myaircraft" and informed the Captain that we had an engine failure on the #1 engine. The Captain verified what I saw and immediately turned to the Engine Failure QRH procedure.At the same time; dispatch sent us an ACARS message asking if we intended to enter a hold to burn fuel or immediately land; which would put us approximately 12;000 lbs over maximum landing weight. I informed the Captain about the message and he told me we would be landing. I wanted to ensure that we would not be rushed and had time to finish checklists; and we continued toward ZZZ.The Captain continued the Engine Failure checklist; completed the Before Landing checklist and started the overweight landing checklist. I again asked if we should pick up a hold; but we continued toward ZZZ and received clearance for the ILS XXC and then clearance to land XXC with ARFF standing by.I mistakenly called for flaps 25 near the FAF and the Captain selected flaps 25. I remembered that single engine landing calls for flaps 15; so I called for flaps to 15 which the Captain selected. I reselected VRef as I initially was set up for a flaps 30 landing. This selection was made prior to the engine failure. We landed on runway XXC without incident and taxied clear onto taxiway 2 so ARFF could inspect our #1 engine from both the front and back. After finishing their inspection and seeing no abnormalities; we called for taxi clearance to our new gate XY. We taxied back to the gate and parked and shutdown without incident.I think ultimately the handling of the emergency procedure was good and we safely returned the passengers and aircraft without any damage; however I think there was some room for improvement.With the benefit of hindsight; I think calling for an aborted takeoff and taxi back to the gate could have been a better decision. We already had the autothrottles MELd and saw that this did not fix the problem but continued the takeoff roll. Even though the N1 split was only 5% and there were no directional control problems; it was a sign that something else was wrong.Additionally; I think continuing directly to the airport for landing compressed the timeline and we could have benefited from a brief hold to make sure all checklists were completed and any further briefing items were taken care of.The brief hold could have corrected my error of calling for flaps 25 and the Captain selecting them. We ultimately trapped the error and corrected the situation; but I feel the decision to proceed straight back to the runway led to this error."
Second reporter narrative
At the departure gate; we discussed about the AML (Aircraft Maintenance Logbook) history of the auto throttle issue with maintenance personal and accepted the aircraft with auto throttle MELed. I was PF and FO was PM; we tookoff from XXR ; middle of takeoff roll; PM stated split N1 condition like previous writeup condition; I felt normal acceleration and no aircraft control issue; so decision was made to continue. I was hand flying; PM kept trying to match the N1. About passing through 10000ft; flying condition was normal but still N1 split condition exist; not like previous writeup condition. We discussed about if we should continue or return to ZZZ and decided to go back to ZZZ . I transfer the control to FO and told him to request priortity handling and start to prepare for landing while I started to run Engine Limit or Surge or Stall; and other check lists. During the descent; FO stated that we lost the left engine; so I continued the Engine Failure or Shutdown and One Engine Inoperable Landing check lists. Initially; landing was prepared for 2 engine; so we went momentarily flaps 25; but went back to flaps 15 landing. Approach and landing were uneventful; but that was overweight landing. After exterior check out by ARFF (Airport Rescue and Firefighting); we taxi to gate with them. Parked at the gate and completed necessary AML entry and talked with my dispatcher and maintenance chief for event details. Overall; we handled this event properly.Few possible improvements are takeoff decision; my decision was part of expecting bias from previous writeup which condition improved as continue climb. Time management; we executed all check lists but that was little bit rushed we should consider to ask brief holding for better management and prevent the mistakes.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.