Date: 201603
Local time of day: 0001-0600
Location: ZZZ.Airport, US
Flight conditions: VMC
Aircraft: B777 Undifferentiated or Other Model
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: Failed
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Flying
Human factors: Other / Unknown
Second reporter function: Pilot Flying; First Officer
Anomaly: Aircraft Equipment Problem Critical
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Diverted; Flight Crew Inflight Shutdown; Flight Crew Landed in Emergency Condition; General Maintenance Action; General Flight Cancelled / Delayed
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: I was on my scheduled crew rest break back in a cabin seat when I heard and felt a heavy vibration that began quickly and was felt thru out the entire aircraft. The Flying First Officer and I immediately called the flight deck. The relief pilots reported that they were seeing no abnormal indications with the engines or flight controls including no EICAS; Status messages of any kind; engine vibration indications were 0.4. Since I was already in the cabin I asked that the aircraft be slowed down from Mach .83 to Mach .80. This appeared to make it worse; returned to Mach .83. I requested the wing lights be turned on. The flying first officer and I used heavy beamed flashlights and began assessing the wings and engine cowlings for anything obvious. Initially I suspected a flight control problem. I did not see anything obvious except the left position light was shaking more than the right directing my attention to something on the left side of the aircraft. The flying first officer and I immediately returned to the flight deck.Once I was back in the seat as expected I did not see any indication as to what was causing this continuous heavy vibration throughout the aircraft. Dispatch was contacted with a maintenance patch. There was no information that maintenance was able to share at that time to help with this very concerning situation. There continued to be normal indications from the engine and flight controls; no EICAS or Status messages of any kind. Again both engine vibrations were 0.4. all normal. A continuation of diagnosing our problem continued trying to think of anything. There was now a period of time that has passed with no obvious clues; maintenance was still of very little help. At that point in time ZZZ was our [alternate]. I wanted to keep all nearby airports completely in our back pockets so to speak in case we needed to get on the ground quickly. At this point a request was made thru Controller Pilot Datalink Communications (CPDLC) to divert direct to ZZZ1 and a lower altitude of 22;000 feet so we could verify if it was an engine problem. Once at 22;000 feet I began pulling back throttles beginning with the left engine. Once reduced to 60 percent N1 we felt relief from the cabin vibrations. We continued to operate at 60 percent N1. All engine indications remained normal including engine vibrations were now 0.6. Very low. At this point maintenance mentioned that he was now possibly seeing Left Engine Bearing indications problems however they were intermittent. All appropriate check list were run including single engine checklist etc. I had continually been making PAs to our customers thru out the flight keeping them up to date as best as possible. A single Engine Approach was made with a normal taxi to the gate.Throughout the 2.5 hours to ZZZ1; numerous messages were sent to dispatch regarding our passengers and the companies plan for them. Once on the ground I had yet understood what the plan was; there was no information as of yet. As my crew and I were securing this information; trying to talk with Maintenance etc. Flight OPs called my Cell. I answered; she introduced herself as an Airbus Captain and was not really familiar with the Boeing Vibration monitors; yet immediately wanted to be debriefed.  She wanted to know detailed information including engine parameters and especially about Engine Vibration monitors and what they were recording. I asked her if this was a debrief as I have never been debriefed in this manner. I had yet had a chance to secure our passengers including PA information etc. as I normally would; I have yet been debriefed by maintenance; and have yet secured the aircraft and talked to the ground personnel and the Purser.She explained that this is all in the Ops Manual and that I was to give her all pertinent information. She was on my speaker phone for all four very tired pilots as we listened; I myself received no sleep through the entire flight; I was very tired. I became very disappointed and taken back at how this whole conversation transpired. What my crew needed to hear from her at this point is how can we support you. All of the rest will come out in time; this is not the time. Maintenance entered the cockpit with pictures taken from the tail cone of the Left engine showing very large internal engine parts thru out the cone and cowling area. With this information she abruptly ended the conversation. As I walked out into the terminal our customers were not being told much of anything yet. I felt that our operations had 2.5 hours to prepare for our arrival and as to what the plan would be for customs etc. At that time I than began informing our customers from the terminal PA system as to what I knew in terms of customs procedures and tried to answer their questions as best I could. Three days after this event and a safe landing into ZZZ1 I have yet to receive a phone call from the Chief pilots office asking if myself or my crew my have any needs or support.


Second narrative: Pronounced aircraft vibration occurred suddenly and without localization. No Caution or Master Warnings. No EICAS or Status messages. No change in aircraft configuration or operation. All Engine Instrumentation in normal operating range.  Communication was established with the Captain who was on rest break. Captain and First Officer returned to the flight deck and assumed operational positions on flight deck.  Captain communicated with Dispatch and Maintenance to diagnose the issue. Decision was made to declare an Emergency and begin the diversion process to ZZZ1. Diversion Guide and required checklist items were completed.As the flight continued to ZZZ1; vibration began changing in reference to power changes. Left Engine was operated in Flight Idle for the remainder of the flight. Single-Engine Procedures were adhered to. Vibration increased on the Engine Monitor as we approached ZZZ1.  Uneventful approach and landing was completed. Taxi; parking and shutdown were uneventful. Mechanic boarded aircraft and confirmed physical damage and debris in the Left Engine. Captain debriefed the crew and made further contact with the company.


Synopsis: A B777 crew reported feeling a heavy vibration with no other indications initially. They decided to divert and the left engine was identified as the source of the vibration; they executed a successful single engine approach and landing.