Narrative:

While in cruise at FL330 in still air; the aircrew felt a subtle vibration and slight rumbling noise. We checked the vibration gauges and noted nothing unusual (both around 1.0) with all other engine indications normal. The vibrations sounded almost like the engines were out of sync. The captain attempted to adjust the thrust levers to attempt to eliminate the vibration. After no change to the vibration and having stabilized the thrust levers back around 85%; in less than two minutes; there was a rumble with a moderate pop accompanied by a brief smell of smoke (while deplaning; a passenger reported seeing a 5 foot long flame emerge from the exhaust). Subsequently; the engine rolled back to about 50 percent N1. The captain reduced the thrust to idle and believing the engine was in the process of failing; called for the engine failure/shutdown checklist. The first officer pulled out the QRH and the aircrew proceeded to accomplish the checklist. We were about 100 miles north of ZZZ and told ATC we would like to divert to ZZZ. We started our descent and got vectored towards ZZZ. We completed the engine failure/shutdown checklist; calculated the performance for a one engine inoperative landing; the oei descent and landing checklists; diversion checklist; and proceeded to land in ZZZ. We informed dispatch via ACARS of our situation and diversion decision as well as to expect an overweight landing. The flight attendants and passengers were notified that we had a maintenance problem and were diverting to ZZZ. The first officer informed the flight attendants that we would be executing a single engine landing and to expect a completely normal landing with no evacuation or other abnormalities expected. Upon landing and stopping on the runway; we had arff check the aircraft for any indication of fire; fuel leaks; hot/smoking brakes or anything else out of the ordinary. Upon an all clear from them; we taxied to the gate without any further assistance.

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Original NASA ASRS Text

Title: B737 flight crew reported an engine malfunction in cruise resulting in an inflight shutdown and diversion to a nearby airport.

Narrative: While in cruise at FL330 in still air; the Aircrew felt a subtle vibration and slight rumbling noise. We checked the vibration gauges and noted nothing unusual (both around 1.0) with all other engine indications normal. The vibrations sounded almost like the engines were out of sync. The Captain attempted to adjust the thrust levers to attempt to eliminate the vibration. After no change to the vibration and having stabilized the thrust levers back around 85%; in less than two minutes; there was a rumble with a moderate pop accompanied by a brief smell of smoke (while deplaning; a Passenger reported seeing a 5 foot long flame emerge from the exhaust). Subsequently; the engine rolled back to about 50 percent N1. The Captain reduced the thrust to idle and believing the engine was in the process of failing; called for the Engine Failure/Shutdown Checklist. The FO pulled out the QRH and the Aircrew proceeded to accomplish the checklist. We were about 100 miles north of ZZZ and told ATC we would like to divert to ZZZ. We started our descent and got vectored towards ZZZ. We completed the Engine Failure/Shutdown Checklist; calculated the performance for a One Engine Inoperative Landing; the OEI Descent and Landing Checklists; Diversion Checklist; and proceeded to land in ZZZ. We informed Dispatch via ACARS of our situation and diversion decision as well as to expect an overweight landing. The Flight Attendants and Passengers were notified that we had a Maintenance problem and were diverting to ZZZ. The FO informed the Flight Attendants that we would be executing a Single Engine landing and to expect a completely normal landing with no evacuation or other abnormalities expected. Upon landing and stopping on the runway; we had ARFF check the aircraft for any indication of fire; fuel leaks; hot/smoking brakes or anything else out of the ordinary. Upon an all clear from them; we taxied to the gate without any further assistance.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.