Air carrier flight crew reported during cruise the number 2 engine vibrated with an increase in EGT. Flight crew diverted and after landing a fuel fire in engine was extinguished before taxi to the gate.
Synopsis
Air carrier flight crew reported during cruise the number 2 engine vibrated with an increase in EGT. Flight crew diverted and after landing a fuel fire in engine was extinguished before taxi to the gate.
Narrative
While cruising at FL280; the number 2 engine vibrated and engine speed decreased with an increase in EGT. I immediately disengaged the auto throttle and retarded the number 2 throttle to keep EGT from rising higher. The throttle was near idle at this point with acceptable EGT; so I tried advancing the throttle. Upon throttle advancement; the engine shuttered and vibrated. I immediately pulled the throttle to idle which erased the shuttering and vibration. We accomplished the appropriate checklist while [requesting priority handling].The engine was at idle power with no vibration so we decided to leave it running. All other engine indications were fairly normal except the oil temperature was higher than usual. We diverted into ZZZ. After clearing the runway; we shut the engine down. After stopping on the taxiway; the fire trucks inspected the engine and advised us of a small fuel fire in the bottom of the engine. They promptly extinguished it. Mechanics were called to inspect the engine. After the inspection; we were cleared to taxi to the gate.
Second reporter narrative
Preceding the incident; both engines had been running normally with no indications of an impending failure. The Captain was the flying pilot and I; the FO; was the pilot monitoring. We also had a jumpseater qualified in the 737. The autopilot and autothrottles were ON; LNAV/VNAV engaged. The flight had been subject to a near constant light chop for about an hour with a period of occasional moderate turbulence that ultimately caused us to descent from FL340 to FL280 where we encountered smooth air for what may have been 20 minutes. We had also just begun to enter a line of weather with reported tops around FL250 but we were in smooth air; IFR conditions; with radar showing light echoes on our path. I can't remember the time although I know it was below -40F. I do remember seeing minimal and normal icing on the windshield wiper for the conditions being experienced. The ENG Anti-Ice had been on for the descent to FL280 but it was turned off once level due to the temperature being below -40F.At the moment of the incident; I felt Aircraft X mildly yaw and immediately observed; announced the #2 N1 rollback to an RPM that may have been 50-60%. The CA clicked off the autothrottles and reduced the #2 throttle. The EGT was observed to be increasing despite the throttle being reduced. The APU was started; and we turned on ignitors with ENG-Anti Ice. No compressor stall was felt however; the engine was behaving as if it that had been the issue; so we determined that to be the correct procedure. The CA continued to fly as I read the checklist; and we performed the remaining procedural steps. After a brief discussion about our situation and options; we quickly [requested priority handling] with ATC with XXX SOB (Souls on Board) and 110 minutes of fuel remaining. ATC gave us a few divert options to consider; and we ultimately settled on ZZZ due to the favorable conditions; support available; and relative location in consideration of our altitude. Due to the loss of power and performance; we asked for a lower altitude to allow for a drift-down in order to keep our speed as we maneuvered through the weather. I sent an ACARS message to dispatch about our situation and intentions. The CA briefed the FA's.Once procedures and plans had begun to settle into place; the CA made attempts to increase the throttle from idle to explore remaining power available. When N1 was increased by about 10% we could feel some vibration and a very subtle popping from the motor; indicative of a possible compressor stall. I also remember that with the N1 around 45%; the EGT steadily increased to peak at about 760C but the temperature eventually came down to a more normal range after 5 or more minutes at idle. During the descent; the small amount of power available deteriorated to idle as the only option for smooth operation. Additionally; the jumpseater noticed that the oil temperature had been slowly and steadily climbing; ultimately peaking at 115 degrees before finally starting to come down after 5-10 minutes. Although the engine wasn't behaving as expected for a compressor stall event; we suspected this was at least partly the case agitated by the possibility of a mechanical issue. We elected to keep the engine running under the circumstances but also prepared for a complete failure by opting to perform the one engine inoperative flaps 15 landing procedure. [Priority handling] equipment was requested and later verified to be in place. The jumpseater got the ATIS; prepared the Captain's iPad for the approach; and provided a useful crosscheck of our situation. On final about 3;000 AGL; a right engine OIL FILTER BYPASS indication occurred with no other associated indications; so no actions were performed on short final. The landing was uneventful.On the ground; we cleared the runway and shutdown the #2 engine. CFR (crash fire rescue) was quickly on scene and determined the #2 engine to have experienced a post-shutdown fire; reportedly dueto pooled fuel in the tailpipe. I opened the window to communicate directly with CFR and we were asked to shut down the left engine as well. CFR extinguished the fire and notified us there was no appearance of any further danger as they continued to monitor the engine. ZZZ Company coordinated maintenance to come open the #2 cowling for further CFR inspection. Maintenance determined that we could restart the #1 engine and safely taxi.During the approximately 1 hour on the ground; one passenger was reported; by the FA's; to be causing a security risk with a variety of vulgar comments that included a witness later reporting that he yelled into his phone to customer service; I'm going to break your f…..g neck." I coordinated ZZZ police meeting us at the gate and the customer was not allowed to continue to ZZZ with the remaining passengers. That situation was resolved without further confrontation.This incident; although undesired; was an incredible success by so many involved. FA's performed amazing calming passengers while performing duties; ATC vectored us around weather and coordinated a significant portion of our divert; our jumpseater was proof of how beneficial another trained person is in that situation; CFR response was robustly professional and reassuring; Dispatch clearly had begun solving many divert related issues before our arrival making the experience much better than expected for everyone; ZZZ ops was amazing to adapt to all of our needs; the ZZZ police were immediately responsive to defuse and resolve our security situation; the Company maintenance team that just happened to be on-site adapted and responded to our need immediately as well as being the solution well after the parking brake was set at the gate. I'm sure many more people need to be credited from our training department to the hotel desk and I hope Company can take the time to share our appreciation as the supported flight crew. THANK YOU!"
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.