Narrative:

During cruise; three hours into the five-hour flight; I heard one of the engines start to roll back. It was as if we were losing power and the plane had some yawing. The cockpit was dark and I could not clearly see the throttles. I reached out and I touched the throttles; I felt the left throttle on its own had moved back about two inches from where it had been initially set. I pushed the left throttle back up to where it should have been. Then the left engine started continuously surging. The plane also started shuddering and shaking very violently. The captain took over the throttles and shortly after turned off the auto throttles. We started losing the automation for directional control; the captain turned off the autopilot; and hand flew the aircraft. As I tried to figure out why we were losing automation the flight attendants started calling the flight deck and told me passengers were screaming about the left engine and said the left engine was on fire. The flight attendants and passengers could see flames coming out of the engine. We did not get any type of engine fire indications in the cockpit. I told the captain about the fire and saw [a possible alternate] was approximately one hundred miles away. I suggested it to the captain and he agreed. I [advised] ATC of our situation and we turned toward the [alternate]. I believe the captain had pulled the power off the engines since we were close to the airport and at twenty eight thousand feet. Some of the shuddering and shaking dissipated for the moment. I ran the qrc quick reference checklist for: 'engine limit or surge or stall' and that directed me to the QRH where I did the appropriate check list. I was also coordinating with ATC. I had ATC notify the company about our situation. I was later also able to notify the company via ACARS. While I was setting up the plane for landing; I asked [our jumpseat pilot] if he could pull up the appropriate approach plates and he gladly helped. I set up for the ILS. As we started to configure for landing the engine power was increased and the shuddering and violent shaking came back along with an unfamiliar and very uncomfortable sound from the left engine. The captain pulled the left engine to idle and it seemed to help. We completed the before landing checklist and landed single engine.we stopped on the runway; the captain spoke with the passengers and I coordinated with [ground personnel]. [Ground personnel] said the engine was not on fire at that time. It was a fiasco/ complete failure; trying to get hold of operations and get a gate. During this the captain was talking with [ground personnel]; I was talking with the tower and [our jumpseat pilot] once again helped out and tried getting contact with operations.once we got a gate; we taxied to park with [ground personnel] following us where the passengers deplaned without any further issues.cause: unforeseen engine issues.suggestions: have our stations better trained for emergencies and make it mandatory for someone to always be able to respond to the operations radio. Having to call multiple; multiple times when you are under pressure to make sure passengers are safe is inexcusable.

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Original NASA ASRS Text

Title: B737-800 First Officer reported diverting to an alternate airport after experiencing an inflight engine stall and surging.

Narrative: During cruise; three hours into the five-hour flight; I heard one of the engines start to roll back. It was as if we were losing power and the plane had some yawing. The cockpit was dark and I could not clearly see the throttles. I reached out and I touched the throttles; I felt the left throttle on its own had moved back about two inches from where it had been initially set. I pushed the left throttle back up to where it should have been. Then the left engine started continuously surging. The plane also started shuddering and shaking very violently. The Captain took over the throttles and shortly after turned off the auto throttles. We started losing the automation for directional control; the Captain turned off the autopilot; and hand flew the aircraft. As I tried to figure out why we were losing automation the flight attendants started calling the flight deck and told me passengers were screaming about the left engine and said the left engine was on fire. The Flight attendants and passengers could see flames coming out of the engine. We did not get any type of Engine Fire indications in the cockpit. I told the Captain about the fire and saw [a possible alternate] was approximately one hundred miles away. I suggested it to the Captain and he agreed. I [advised] ATC of our situation and we turned toward the [alternate]. I believe the Captain had pulled the power off the engines since we were close to the airport and at twenty eight thousand feet. Some of the shuddering and shaking dissipated for the moment. I ran the QRC Quick Reference Checklist for: 'Engine Limit or Surge or Stall' and that directed me to the QRH where I did the appropriate check list. I was also coordinating with ATC. I had ATC notify the company about our situation. I was later also able to notify the company via ACARS. While I was setting up the plane for landing; I asked [our jumpseat pilot] if he could pull up the appropriate approach plates and he gladly helped. I set up for the ILS. As we started to configure for landing the engine power was increased and the shuddering and violent shaking came back along with an unfamiliar and very uncomfortable sound from the left engine. The Captain pulled the left engine to idle and it seemed to help. We completed the before landing checklist and landed single engine.We stopped on the runway; the Captain spoke with the passengers and I coordinated with [ground personnel]. [Ground personnel] said the engine was not on fire at that time. It was a fiasco/ complete failure; trying to get hold of Operations and get a gate. During this the Captain was talking with [ground personnel]; I was talking with the Tower and [our jumpseat pilot] once again helped out and tried getting contact with Operations.Once we got a gate; we taxied to park with [ground personnel] following us where the passengers deplaned without any further issues.Cause: Unforeseen engine issues.Suggestions: Have our stations better trained for emergencies and make it mandatory for someone to always be able to respond to the operations radio. Having to call multiple; multiple times when you are under pressure to make sure passengers are safe is inexcusable.

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.