Narrative:

While deviating around a large weather system; we heard a sharp and loud bang and noticed that our right engine egt was 700 degrees C while our left engine was around 400 degree C. We received immediate reports of the loud bang and the presence of smoke in the cabin. While keeping the cabin in communication; I moved the right engine to idle and began a descent to FL200. I turned on the anti ice (since it was not previously required for cruise flight in -57C sat). As we descended; we received a report that the smoke had dissipated immediately after the throttle was moved to idle. We discussed whether we had severe damage to the right engine or a compressor stall; surge. Upon level off at FL200 (good single engine cruise altitude) I determined that while the problem may have been a compressor stall; the egt indications were abnormal relative to the left engine. I proceeded to the precautionary shutdown checklist because in my judgment; the severity of the detonation/explosion and the presence of the smoke in the cabin exceeded the description of a simple compressor stall/surge. We completed all necessary checklists and I chose to proceed to dfw (our intended destination) due to marginal weather at ZZZ and other enroute suitable airports. On descent; the APU flamed out and I was unable to restart it. The landing was uneventful and arff was called and an emergency was declared. Later in a conference call with our company engineers; it was determined that the engine had developed a P1 leak in the EPR system and had provided us with a lower than normal egt. When the right engine was being compared with the left for signs of abnormality; the comparison was based on a lower than normal egt in the 'good engine' skewing the severity of 'bad engine.' this was a compound emergency with three system failures. (1) P1 leak in the left engine; (2) engine surge/stall in the right engine; (3) APU flameout/inability to restart.callback conversation with reporter revealed the following information: examination by maintenance revealed that the right engine had experienced a stall/surge but was undamaged and fully operational. The P1 leak in the left engine apparently developed at about the time of the right engine stall. This leak caused the eec to gradually reduce fuel flow to the left engine to maintain limits; and at the same time auto thrust was gradually increasing thrust to maintain airspeed. Why the right engine stalled has not been determined but the low egt of the left engine led the reporter to believe the right engine was over temperature. The APU failure was completely independent. The best estimate from maintenance was that this P1 leak resulted in a 25% reduction in available thrust. Had the right engine not stalled this deficit would have been detected by the crew and the eec could have been turned off to restore normal operation.

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Original NASA ASRS Text

Title: B757 Captain reports R engine compressor stall at FL340. After comparison with good L engine. Engine is shut down. APU fails during descent. Uneventful landing ensues at destination. Maintenance discovers P1 leak on good engine which skewed both EPR and EGT readings in flight.

Narrative: While deviating around a large weather system; we heard a sharp and loud bang and noticed that our R engine EGT was 700 degrees C while our L engine was around 400 degree C. We received immediate reports of the loud bang and the presence of smoke in the cabin. While keeping the cabin in communication; I moved the right engine to idle and began a descent to FL200. I turned on the Anti Ice (since it was not previously required for cruise flight in -57C SAT). As we descended; we received a report that the smoke had dissipated immediately after the throttle was moved to idle. We discussed whether we had severe damage to the right engine or a compressor stall; surge. Upon level off at FL200 (good single engine cruise altitude) I determined that while the problem may have been a compressor stall; the EGT indications were abnormal relative to the L engine. I proceeded to the precautionary shutdown checklist because in my judgment; the severity of the detonation/explosion and the presence of the smoke in the cabin exceeded the description of a simple compressor stall/surge. We completed all necessary checklists and I chose to proceed to DFW (our intended destination) due to marginal weather at ZZZ and other enroute suitable airports. On descent; the APU flamed out and I was unable to restart it. The landing was uneventful and ARFF was called and an emergency was declared. Later in a conference call with our company Engineers; it was determined that the ENG had developed a P1 leak in the EPR system and had provided us with a lower than normal EGT. When the R engine was being compared with the left for signs of abnormality; the comparison was based on a lower than normal EGT in the 'good engine' skewing the severity of 'bad engine.' This was a compound emergency with three system failures. (1) P1 Leak in the L engine; (2) Engine surge/stall in the R engine; (3) APU flameout/inability to restart.Callback conversation with reporter revealed the following information: Examination by maintenance revealed that the right engine had experienced a stall/surge but was undamaged and fully operational. The P1 leak in the left engine apparently developed at about the time of the right engine stall. This leak caused the EEC to gradually reduce fuel flow to the left engine to maintain limits; and at the same time auto thrust was gradually increasing thrust to maintain airspeed. Why the right engine stalled has not been determined but the low EGT of the left engine led the reporter to believe the right engine was over temperature. The APU failure was completely independent. The best estimate from maintenance was that this P1 leak resulted in a 25% reduction in available thrust. Had the right engine not stalled this deficit would have been detected by the crew and the EEC could have been turned off to restore normal operation.

Data retrieved from NASA's ASRS site as of April 2012 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.