Narrative:

At cruise altitude the first officer and I noticed (after 3 hours at cruise) the N1, N2, N3 of #1 engine were at minimal performance. Fuel flow was 2100 pounds and the EPR of the #1 engine was exceeding parameters at 2.03. Airspeed was decreasing, #2 engine was at maximum thrust (1.76 EPR limited). I immediately put anti-ice on and requested a descent from center. I had the first officer contact phx maintenance, reported the problem and reported the parameters of both engines. As we leveled off at FL280 the #1 engine returned to normal and no further problems arose for the duration of the flight. I made a logbook entry and labeled it 'information only.' maintenance in las met the aircraft and I further elaborated. I found out later that the same aircraft, same engine had rolled back in flight at FL390 just a few days prior. The sat at the time of the occurrence was -52 sat, well below rolls royce's recommended temperature for application of anti-ice (-40 degrees sat in cruise). Callback conversation with reporter revealed the following information: reporter stated the rollback was very slow. He also described it as insidious, only when airspeed started to decrease did they notice the lower N1, N2, and N3 indications. Engine of the B757 is rolls royce 211-535e4. Reporter was not certain the 535e4 was the exact version number. This engine was worked on by maintenance but no information was available to see if the problem was solved. Maintenance believes the rollback was caused by icing getting into one engine probe. Although the engine anti-ice does not have to be applied at temperatures below -40 degrees C, icing can occur.

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Original NASA ASRS Text

Title: A B757 FLYING AT 39000 FT IN ZAB AIRSPACE, SUFFERS ENG ROLLBACK AND SLOWLY DSNDS TO 28000 FT BEFORE THE ENG RECOVERS TO NORMAL PWR.

Narrative: AT CRUISE ALT THE FO AND I NOTICED (AFTER 3 HRS AT CRUISE) THE N1, N2, N3 OF #1 ENG WERE AT MINIMAL PERFORMANCE. FUEL FLOW WAS 2100 LBS AND THE EPR OF THE #1 ENG WAS EXCEEDING PARAMETERS AT 2.03. AIRSPD WAS DECREASING, #2 ENG WAS AT MAX THRUST (1.76 EPR LIMITED). I IMMEDIATELY PUT ANTI-ICE ON AND REQUESTED A DSCNT FROM CTR. I HAD THE FO CONTACT PHX MAINT, RPTED THE PROB AND RPTED THE PARAMETERS OF BOTH ENGS. AS WE LEVELED OFF AT FL280 THE #1 ENG RETURNED TO NORMAL AND NO FURTHER PROBS AROSE FOR THE DURATION OF THE FLT. I MADE A LOGBOOK ENTRY AND LABELED IT 'INFO ONLY.' MAINT IN LAS MET THE ACFT AND I FURTHER ELABORATED. I FOUND OUT LATER THAT THE SAME ACFT, SAME ENG HAD ROLLED BACK IN FLT AT FL390 JUST A FEW DAYS PRIOR. THE SAT AT THE TIME OF THE OCCURRENCE WAS -52 SAT, WELL BELOW ROLLS ROYCE'S RECOMMENDED TEMP FOR APPLICATION OF ANTI-ICE (-40 DEGS SAT IN CRUISE). CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATED THE ROLLBACK WAS VERY SLOW. HE ALSO DESCRIBED IT AS INSIDIOUS, ONLY WHEN AIRSPD STARTED TO DECREASE DID THEY NOTICE THE LOWER N1, N2, AND N3 INDICATIONS. ENG OF THE B757 IS ROLLS ROYCE 211-535E4. RPTR WAS NOT CERTAIN THE 535E4 WAS THE EXACT VERSION NUMBER. THIS ENG WAS WORKED ON BY MAINT BUT NO INFO WAS AVAILABLE TO SEE IF THE PROB WAS SOLVED. MAINT BELIEVES THE ROLLBACK WAS CAUSED BY ICING GETTING INTO ONE ENG PROBE. ALTHOUGH THE ENG ANTI-ICE DOES NOT HAVE TO BE APPLIED AT TEMPS BELOW -40 DEGS C, ICING CAN OCCUR.

Data retrieved from NASA's ASRS site as of July 2007 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.