Narrative:

ATC held us at FL290. We were encountering continual light to moderate turbulence. A few minutes later ATC cleared us to FL310. The autopilot was coupled in the VNAV mode. The captain dialed in the new altitude and pushed VNAV. We both confirmed the new altitude selection. I then noticed the plane was not climbing and that the autopilot was still indicating VNAV level instead of VNAV climb. I alerted the captain and he reselected VNAV. VNAV climb then displayed and the autothrottles pushed forward and a climb started. Shortly thereafter we heard a single loud thud accompanied by a buffet behind the cockpit. Initially we thought we might have hit a small pocket of air related to the turbulence we were in. We also questioned if perhaps something in the forward cargo hold had fallen over. Simultaneously we noticed the aircraft had quit climbing and that the EPR on the #1 engine was decaying with the egt rising. The captain then pulled the #1 engine back to idle and I requested a return to FL290. I then proceeded to go over the compressor stall checklist. The captain then took over the radios and declared an emergency. At idle the #1 engine had normal N1; N2; egt; oil press; and qty indications. The #1 generator stayed on line and the AC pack was functioning properly. I started the APU as a back up power source. After a brief conversation we decided that since we were about 100 miles from ZZZ descending down from FL300 that ZZZ was the most practical airport to return to. As I completed the compressor stall checklist I checked our single engine ceiling on the FMS. It showed 17700 ft. The captain then asked ATC for an altitude below 17000 ft. ATC then gave us a vector for ZZZ. As we continued our descent and turn I began the engine failure checklist. The captain and I ran the entire checklist but elected to leave the engine running at idle since it was providing electrical power and all other indications were within limits. After landing we secured the #1 engine and proceeded to the gate. After the passenger exited the captain and I went out to inspect the engine with the maintenance personnel. It appeared that the back half of the engine had come apart. There were numerous damaged turbine blades and stator vanes visible from the rear of the engine. No breach of the engine cowling was observed.

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Original NASA ASRS Text

Title: WHILE INCREASING THRUST FOR AN ENRTE CLB; AN MD80 ENG TURBINE FAILED BUT THE ENG CONTINUED TO OPERATE. AN EMER WAS DECLARED WITH A RETURN TO LNDG.

Narrative: ATC HELD US AT FL290. WE WERE ENCOUNTERING CONTINUAL LIGHT TO MODERATE TURBULENCE. A FEW MINUTES LATER ATC CLRED US TO FL310. THE AUTOPILOT WAS COUPLED IN THE VNAV MODE. THE CAPT DIALED IN THE NEW ALTITUDE AND PUSHED VNAV. WE BOTH CONFIRMED THE NEW ALTITUDE SELECTION. I THEN NOTICED THE PLANE WAS NOT CLBING AND THAT THE AUTOPILOT WAS STILL INDICATING VNAV LEVEL INSTEAD OF VNAV CLB. I ALERTED THE CAPT AND HE RESELECTED VNAV. VNAV CLB THEN DISPLAYED AND THE AUTOTHROTTLES PUSHED FORWARD AND A CLB STARTED. SHORTLY THEREAFTER WE HEARD A SINGLE LOUD THUD ACCOMPANIED BY A BUFFET BEHIND THE COCKPIT. INITIALLY WE THOUGHT WE MIGHT HAVE HIT A SMALL POCKET OF AIR RELATED TO THE TURBULENCE WE WERE IN. WE ALSO QUESTIONED IF PERHAPS SOMETHING IN THE FORWARD CARGO HOLD HAD FALLEN OVER. SIMULTANEOUSLY WE NOTICED THE ACFT HAD QUIT CLBING AND THAT THE EPR ON THE #1 ENGINE WAS DECAYING WITH THE EGT RISING. THE CAPT THEN PULLED THE #1 ENGINE BACK TO IDLE AND I REQUESTED A RETURN TO FL290. I THEN PROCEEDED TO GO OVER THE COMPRESSOR STALL CHECKLIST. THE CAPT THEN TOOK OVER THE RADIOS AND DECLARED AN EMER. AT IDLE THE #1 ENGINE HAD NORMAL N1; N2; EGT; OIL PRESS; AND QTY INDICATIONS. THE #1 GENERATOR STAYED ON LINE AND THE AC PACK WAS FUNCTIONING PROPERLY. I STARTED THE APU AS A BACK UP POWER SOURCE. AFTER A BRIEF CONVERSATION WE DECIDED THAT SINCE WE WERE ABOUT 100 MILES FROM ZZZ DSNDING DOWN FROM FL300 THAT ZZZ WAS THE MOST PRACTICAL ARPT TO RETURN TO. AS I COMPLETED THE COMPRESSOR STALL CHECKLIST I CHECKED OUR SINGLE ENGINE CEILING ON THE FMS. IT SHOWED 17700 FT. THE CAPT THEN ASKED ATC FOR AN ALTITUDE BELOW 17000 FT. ATC THEN GAVE US A VECTOR FOR ZZZ. AS WE CONTINUED OUR DSCNT AND TURN I BEGAN THE ENGINE FAILURE CHECKLIST. THE CAPT AND I RAN THE ENTIRE CHECKLIST BUT ELECTED TO LEAVE THE ENGINE RUNNING AT IDLE SINCE IT WAS PROVIDING ELECTRICAL POWER AND ALL OTHER INDICATIONS WERE WITHIN LIMITS. AFTER LNDG WE SECURED THE #1 ENGINE AND PROCEEDED TO THE GATE. AFTER THE PAX EXITED THE CAPT AND I WENT OUT TO INSPECT THE ENGINE WITH THE MAINTENANCE PERSONNEL. IT APPEARED THAT THE BACK HALF OF THE ENGINE HAD COME APART. THERE WERE NUMEROUS DAMAGED TURBINE BLADES AND STATOR VANES VISIBLE FROM THE REAR OF THE ENGINE. NO BREACH OF THE ENGINE COWLING WAS OBSERVED.

Data retrieved from NASA's ASRS site as of January 2009 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.