Date: 202202
Local time of day: 0601-1200
Location: ZZZ.Airport, US
Flight conditions: VMC
Light: Daylight
Aircraft: B737-800
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Cruise
Airspace: Class A ZZZ
ATC / advisory: Center ZZZ
Aircraft component: Turbine Engine
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: First Officer; Pilot Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Human factors: Troubleshooting
Second reporter function: Pilot Not Flying; Captain
Anomaly: Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural FAR; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Attendant; Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Provided Assistance; Flight Crew Diverted; Flight Crew Landed in Emergency Condition; Flight Crew Overcame Equipment Problem; Flight Crew Requested ATC Assistance / Clarification; General Flight Cancelled / Delayed; General Maintenance Action
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: We were cruising at FL360 when we felt several jolts coming from what appeared to be the #2 engine. We then encountered what felt like a strong vibration from the right side as well. At almost the same time that this was happening we received a call from the Flight Attendants who reported hearing loud banging coming from the right side of the aircraft. The only indication from the engine instruments that we observed was the N1 on the #2 engine dropping to approximately 54%. I was the Pilot Flying and disengaged the auto throttles and pulled the #2 thrust lever back until the vibration ceased which was when the thrust lever was at idle. The banging and vibration stopped and the engine seemed to have no further problems at idle. I did attempt one time to increase the thrust but felt the vibration return almost immediately; so I returned it to idle. We [advised] ATC and found that ZZZ was the nearest suitable airport. We requested a lower altitude and were given lower and vectors for ZZZ. I continued to fly the aircraft and the Captain ran the appropriate checklists and coordinated with ATC; Dispatch; the Flight Attendants and Passengers. We requested that ARFF meet us on the runway to inspect the engine. I flew a single engine visual approach to Runway XX at ZZZ and backed it up with the ILS. We stopped the aircraft on the runway and set the brakes. The Captain made the PA to remain seated and AARF came and checked the engine for visible damage or fire. None was detected; so we secured the engine and performed a single engine taxi to the gate with AARF in tow. The passengers were able to deplane via jet bridge. I do not think anything other than the maintenance issue caused the event or my role in the event. I do not think that anything can be done to prevent events like this.


Second narrative: After a step climb from FL340 to FL360; shortly after level off; we observed loud banging and some airframe vibration. The FO (First Officer) was the PF (Pilot Flying) and assumed control of the aircraft. Simultaneously we received a call from the Flight Attendants. They reported banging coming from the right hand side of the aircraft near the #2 engine. We observed that the N1 had dropped to around 45-55% on the #2 engine. The Auto throttle was disengaged and the #2 thrust lever was pulled to idle per the checklist. The engine then ran smoothly. It was determined that the vibration and banging returned when the #2 thrust lever was advanced beyond idle. We [requested priority handling] with ATC and requested a lower altitude. We then requested a diversion to ZZZ; the nearest suitable airport. While the FO flew; I completed the necessary checklists; communicated with ATC; the company; the passengers and the flight attendants. We made a visual; single engine approach to Runway XX and stopped the aircraft on the runway. ARFF observed the aircraft and saw no signs of fire or severe damage so we secured the #2 engine and single engine taxied to the gate. Passengers deplaned normally via the jet bridge and we rebooked on a later flight.


Synopsis: Flight Crew reported engine vibration and RPM decay resulted in a diversion and precautionary landing.