B757 Flight Crew experiences degraded engine performance at FL350. The problem cannot be remedied and the crew descends to a lower altitude and continues to destination at reduced thrust.
Synopsis
B757 Flight Crew experiences degraded engine performance at FL350. The problem cannot be remedied and the crew descends to a lower altitude and continues to destination at reduced thrust.
Narrative
While cruising at FL350 for approximately 5 hours a deterioration in performance was encountered on the R engine. EPR dropped to a mid level value with corresponding engine parameters. There were no abnormal indications; vibrations or any associated EICAS or lights. The autothrottle was disengaged and continuous ignition was selected; later followed by flight ignition. Also engine anti-ice was selected for approximately 3 minutes. There was no change in engine performance. The throttle was then advanced full with no increase in EPR. At this point while approaching ETP 2; SATCOM was established with company; it was determined that there were no QRH applicable procedures available for the given situation. Preparation was made for a possible divert if any further deterioration would have occurred. The R engine continued to run at a reduced EPR; a lower altitude was selected and the flight continued to final destination while routing paralleled with the route to the diversion alternate. On descent the throttle was retarded and the engine lagged in response but did decelerate; also an increase was attempted and the engine did respond but at half the rate and thrust output. Preparation was made for a possible single engine landing and/or go around in the event it would of become necessary for the engine to be shut down. A full briefing was given to the flight attendants of possible intentions; fortunately an emergency was not justified at the time. A normal landing ensued with both engines running and there were no further events. The R engine never did recover to normal thrust and response.
Second reporter narrative
We were at cruise altitude and all parameters were normal with no EICAS messages. The Captain noticed the control wheel was slightly tilted and retrimmed the aircraft. Right after doing that he looked at the right EPR indicator gauge and noticed it was slightly lower than the left EPR indicator gauge. The degradation of the right EPR continued to go lower; stopping at approximately 1.44 EPR. The corresponding engine indications matched; with no oil; temperature; vibration or any other indications out of sync or limits and there were no EICAS indications of any kind. At this point we were at our second ETP.The Captain disengaged the auto throttles and turned on continuous ignition. He also tried anti-ice although that did not make any difference in the engine performance. He pushed the right throttle slowly full forward to try and get the most out of the engine but got almost no increase in EPR. We called the IRO up to the cockpit and he helped with looking for QRH and other solutions. We spoke with the company to discuss the situation. There was no specific QRH applicable procedures that we could find directly relating to this situation. We talked about various solutions and no one had any specific ideas and we were not going to do anything to jeopardize the engine getting any worse! The Purser was fully briefed and made aware of a possible diversion. We made preparations to divert if the engine shut down or lost significantly more power but aside from EPR going up or down slightly; it remained stable. (1.44 to 1.38) We were now well past our second ETP. The engine continued to run at approximately half its rated power. The second ETP diversion route paralleled our route of flight until almost the beginning of our descent; so it was decided to continue on unless the engine lost more power or failed. Upon speaking with ATC and establishing radar contact; we called Pan; Pan; Pan to make sure we had priority handling. We prepared for a single engine arrival and briefed a single engine go-around in case either was needed. Fortunately; the engine continue to run at reduced power all the way to an uneventful and smooth landing. We do not know why the engine lost power although it may have been a fuel control unit.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.