B757 flight crew reported experiencing an EPR malfunction reducing its thrust while on a north atlan...

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 international relief officer 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.

Original NASA ASRS Text

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

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.

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.

Attributes
ACN	1359067
Time
Date	201605
Place
Locale Reference	ZZZZ.ARTCC
State Reference	FO
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Operating Under FAR Part	Part 121
Flight Phase	Cruise
Route In Use	Oceanic
Flight Plan	IFR
Component
Aircraft Component	Turbine Engine
Person 1
Function	Captain Pilot Not Flying
Experience	Flight Crew Last 90 Days 165
Person 2
Function	Relief Pilot Pilot Not Flying
Qualification	Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Total 9673 Flight Crew Type 1104
Events
Anomaly	Aircraft Equipment Problem Critical

B757 flight crew reported experiencing an EPR malfunction reducing its thrust while on a north atlantic crossing. Flight diverted with an uneventful landing.