Narrative:

En route to dallas ft worth, flying an medium large transport, cruising at FL380 and passing st louis VOR, turbulence was encountered and I requested a clearance to FL310. The clearance was given by ZKC to FL310 and we began descending. The new flight level was programmed into the FMC. The aircraft was being operated by the FMC and automatic throttle computer. When the throttles were commanded to 'retard' for the descent at about 50% power the aircraft began to shake and a popping noise was heard. Automatic throttles were disengaged and power reduced on both engines. #2 engine showed a higher fuel flow and egt than #1 engine and vibrations continued to be felt in the airframe. The compressor stall checklist was completed and #2 engine seemed to operate normally at idle power. Power was increased on #1 and #2 to 80% N1 without vibrations and #2 engine egt was higher than #1 engine and #2 engine was slower to accelerate to 80% N1 than #1, so #2 was reduced to idle power and operated in this position for the remainder of the flight. During this engine evaluation period a clearance was requested for an approach to st louis and vectors with clearance to FL250 was issued by ZKC, the heading was to the northeast and a slow descent was initiated to FL250. Company maintenance in sfo and dispatch in ord were contacted concurrently through commercial radio. We discussed the engine problem and how #2 was operating at idle power and reduced thrust. The flight was now nearing the mid-point between stl and ord. Ord airport has excellent fire and rescue equipment, so I changed the landing field to ord and requested the fire and rescue teams to stand by on runway 14R at O'hare airport. WX was not a factor in the landing field decision. F/a's and passenger were briefed on the situation. The F/a's prepared the cabin for a possible emergency evacuate/evacuation. The flight proceeded to ord and landed without incident.

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Original NASA ASRS Text

Title: ACR ACFT RETURNS TO ARPT OF DEP RATHER THAN LAND AT NEAREST SUITABLE ARPT AFTER LOSING USE OF ONE OF THE 2 ENGINES.

Narrative: ENRTE TO DALLAS FT WORTH, FLYING AN MLG, CRUISING AT FL380 AND PASSING ST LOUIS VOR, TURBULENCE WAS ENCOUNTERED AND I REQUESTED A CLRNC TO FL310. THE CLRNC WAS GIVEN BY ZKC TO FL310 AND WE BEGAN DESCENDING. THE NEW FLT LEVEL WAS PROGRAMMED INTO THE FMC. THE ACFT WAS BEING OPERATED BY THE FMC AND AUTO THROTTLE COMPUTER. WHEN THE THROTTLES WERE COMMANDED TO 'RETARD' FOR THE DSCNT AT ABOUT 50% POWER THE ACFT BEGAN TO SHAKE AND A POPPING NOISE WAS HEARD. AUTO THROTTLES WERE DISENGAGED AND POWER REDUCED ON BOTH ENGINES. #2 ENGINE SHOWED A HIGHER FUEL FLOW AND EGT THAN #1 ENGINE AND VIBRATIONS CONTINUED TO BE FELT IN THE AIRFRAME. THE COMPRESSOR STALL CHECKLIST WAS COMPLETED AND #2 ENGINE SEEMED TO OPERATE NORMALLY AT IDLE POWER. POWER WAS INCREASED ON #1 AND #2 TO 80% N1 WITHOUT VIBRATIONS AND #2 ENGINE EGT WAS HIGHER THAN #1 ENGINE AND #2 ENGINE WAS SLOWER TO ACCELERATE TO 80% N1 THAN #1, SO #2 WAS REDUCED TO IDLE POWER AND OPERATED IN THIS POSITION FOR THE REMAINDER OF THE FLT. DURING THIS ENGINE EVALUATION PERIOD A CLRNC WAS REQUESTED FOR AN APCH TO ST LOUIS AND VECTORS WITH CLRNC TO FL250 WAS ISSUED BY ZKC, THE HDG WAS TO THE NE AND A SLOW DSCNT WAS INITIATED TO FL250. COMPANY MAINT IN SFO AND DISPATCH IN ORD WERE CONTACTED CONCURRENTLY THROUGH COMMERCIAL RADIO. WE DISCUSSED THE ENGINE PROBLEM AND HOW #2 WAS OPERATING AT IDLE POWER AND REDUCED THRUST. THE FLT WAS NOW NEARING THE MID-POINT BETWEEN STL AND ORD. ORD ARPT HAS EXCELLENT FIRE AND RESCUE EQUIPMENT, SO I CHANGED THE LNDG FIELD TO ORD AND REQUESTED THE FIRE AND RESCUE TEAMS TO STAND BY ON RWY 14R AT O'HARE ARPT. WX WAS NOT A FACTOR IN THE LNDG FIELD DECISION. F/A'S AND PAX WERE BRIEFED ON THE SITUATION. THE F/A'S PREPARED THE CABIN FOR A POSSIBLE EMER EVAC. THE FLT PROCEEDED TO ORD AND LANDED WITHOUT INCIDENT.

Data retrieved from NASA's ASRS site as of August 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.