Date: 201301
Local time of day: 0601-1200
Location: ZZZ.ARTCC, US
Flight conditions: VMC
Weather elements / visibility: Thunderstorm
Aircraft: B777 Undifferentiated or Other Model
Operator: Air Carrier
Operating under: Part 121
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: Captain; Pilot Not Flying
Second reporter function: Relief Pilot; Pilot Not Flying
Anomaly: Aircraft Equipment Problem Critical
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Landed in Emergency Condition; General Declared Emergency
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: We were being rerouted for thunderstorms affecting airports in the area. Initially; we were at FL320; in and out of turbulence. We descended to FL280 for a better ride. Shortly after level cruise; we felt a jolt; like wake turbulence. I saw no aircraft on TCAS that could have been the cause. So we didn't think anything more about it. A little while thereafter; we heard a banging noise; and we looked at the engine gauges but could not determine which engine might have been the cause. I turned the right throttle off; thinking that might have been it. We retarded the throttle slightly to see if that would identify the cause. It ran smoothly; so we re-engaged the right autothrottle. As the engine was coming up; we got the bang again and noticed the fluctuation on the left engine. At that point; we turned off the left autothrottle and retarded the left engine. At that point; we decided we needed to run the checklist for that engine. We declared an emergency and asked for vectors to destination. We thought that was the best option because thunderstorms were at the field at our alternate and also between us and the alternate. We followed all checklists and accomplished a safe landing. We asked for fire trucks to meet us on landing; they checked out the aircraft; and we continued our taxi to the gate.


Second narrative: We were approximately 120 NM northeast of destination at FL280 when we heard an unidentified rumbling noise followed shortly thereafter by a second one. We suspected it was a compressor stall be didn't know for sure which engine. After another short descent and thrust addition another stall occurred and a rise in EGT was identified on the left engine. The Captain ran the appropriate non-normal checklist and elected to leave the engine running at idle power; the First Officer flew the aircraft and I contacted Dispatch and Maintenance to advise them of our situation. Maintenance checked the down link information from the aircraft but did not notice any exceeded limits. Dispatch advised of some thunderstorm activity passing through and suggested we vector around to the northwest for an approach to the southeast. I informed the flight attendants and passengers that we had an engine problem that was now stable and we would be landing shortly. The Captain declared an emergency; we completed all our checklists; and I reviewed the landing distance required with a single engine. We deviated around some moderate rain and were vectored for an approach. After landing we taxied off the runway and were inspected by emergency crew. No visible damage or indication of fire was noted and so we shut the engine down and taxied to the gate.


Synopsis: B777 flight crew experiences compressor stalls in the left engine during initial descent for landing. The engine is allowed to continue running and an uneventful landing at destination ensues.