Date: 201605
Location: ZZZZ.ARTCC, FO
Flight conditions: VMC
Light: Daylight
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Cruise
ATC / advisory: Center ZZZZ
Aircraft component: Turbine Engine
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Not Flying
Human factors: Troubleshooting
Second reporter function: Relief Pilot; Pilot Not Flying
Anomaly: Aircraft Equipment Problem Critical
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Issued New Clearance; Air Traffic Control Provided Assistance; Flight Crew Diverted
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: At FL340 [over North Atlantic] the right engine rolled back from commanded EPR (Engine Pressure Ratio) of 1.60 to 1.38. All other engine indications on the right engine decreased in proportion. We had no EICAS messages or other abnormal indications. Throttle movement had little effect on thrust. We were able to maintain altitude and airspeed but the left engine EPR increased to max EPR. We ran the checklist and called the IRO on break back to the cockpit.We tried to call dispatch on the SATCOM. We were unable to get SATCOM voice to work. We got a phone patch through ZZZZ1 radio on the HF; and started to conduct a conference call with dispatch and [Maintenance Control]. Halfway through the phone patch we were disconnected. The first officer sent an ACARS message to dispatch to call us on the SATCOM while I tried to reestablish communications with dispatch via the HF. The dispatcher was unable to call us on the SATCOM but we were connected again via HF. After consulting with [Maintenance Control] we [advised ATC of our situation]; offset 15 north of track initially descending to 33;500. We then got a clearance below the tracks from ATC; followed shortly by a clearance to proceed direct to ZZZZ. The landing was uneventful. We never regained more than approximately 25% thrust on the right engine.


Second narrative: I was on break in cabin asleep when a flight attendant woke me up and stated I was requested back on the flight deck as soon as possible.The airplane seemed to be holding altitude and speed when I first arrived; so we agreed that we should attempt to call Maintenance Control before diverting. I started looking for an appropriate QRH procedure; the flying FO flew the aircraft and the Captain handled communications. After describing the loss of thrust Maintenance Control asked us to reset the EECs. The two buttons that we reset however; were the Thrust Limit buttons. We stated that fact to Maintenance Control; but the phone patch got cut off. The Captain attempted another phone patch and got through to dispatch; but it was cutting in and out and was very hard to communicate. We had started to run the Engine Limit or Surge or Stall checklist before diverting; but flying the airplane and the degraded communications with Dispatch took precedent for a while. After diverting; we discussed several checklists to run since there was no EICAS; status messages or specific checklist heading that exactly fit our situation. We eventually ended up running the Engine Limit Surge or Stall checklist; but elected to keep the #2 engine running. We flew back to our alternate; checked the abnormal landing distance charts for and overweight landing since we were going to be about 2;000 lbs over weight and briefed a flaps 20 landing. The Captain also made a PA to the passengers explaining the situation and talked to the lead Flight Attendant several times. The flying FO made an uneventful; smooth landing and then we taxied to the gate.


Synopsis: B757 flight crew reported experiencing an EPR malfunction reducing its thrust while on a North Atlantic crossing. Flight diverted with an uneventful landing.