AN MD80 CREW EXPERIENCED A L ENG BOOM; LOW OIL QUANTITY; HIGHER EGT REMAINING WITHIN LIMITS. DECLARED AN EMER AND RETURNED TO DEP ARPT.

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DURING CLBOUT THROUGH 19500 FT WE HAD EXITED ICING CONDITIONS AND WERE SECURING ENG AND WING ANTI ICE WHEN WE HEARD A LOUD BOOM AND THE ACFT SHUDDERED. I LOOKED AT THE ENG INSTRUMENTS AND NOTICED A L ENG OIL PRESSURE 'LOW' LIGHT AND L ENG EGT HIGHER THAN THE R; BUT STILL WITHIN LIMITS. N1 AND N2 WERE SPINNING AND WE HAD OIL PRESSURE ON THE L ENG. OIL QUANTITY WAS APPROX 1 QUART. I TURNED OFF THE AUTOTHROTTLES AND RETARDED THE L ENG TO IDLE. I ASKED THE FO TO DECLARE AN EMER AND TO REQUEST CLRNC BACK TO ZZZ. FLT ATTENDANT CALLED AND SAID A DEAD HEADING CAPT LOOKED AT THE ENG AND SAID HE COULD SEE NO APPARENT DAMAGE. FLT ATTENDANTS DID NOT RPT ANY UNUSUAL VIBRATION; SOUNDS; OR SMELL AFTER THE INITIAL BOOM. WE COMPLETED APPLICABLE PORTIONS OF ENG OIL PRESSURE LOW CHKLIST AND REVIEWED INFLT ENG FAIL/DAMAGE CHKLIST. I STARTED THE APU AND DECIDED TO KEEP THE L ENG AT IDLE BECAUSE THERE WAS NO INDICATION OF DAMAGE OR SEIZURE AND WE HAD OIL PRESSURE. I BRIEFED THE FLT ATTENDANTS AND THEN MADE A PA LETTING THE PAX KNOW WE HAD HAD AN ENG PROB AND WERE RETURNING TO ZZZ; AND THAT I WOULD UPDATE THEM AFTER LNDG. WE MADE A FLAPS 28 DEG LNDG USING SINGLE ENG PROCEDURES WITH THE L THROTTLE AT IDLE TO RWY XX AT ZZZ. DURING ROLLOUT; WE SHUT DOWN THE L ENG AND TAXIED CLR OF THE RWY. I ASKED ARFF TO INSPECT THE L ENG AND THEY RPTED NOTHING UNUSUAL EXCEPT AN OIL LEAK VISIBLE ON THE L COWLING. WE THEN TAXIED TO THE GATE. SUPPLEMENTAL INFO FROM ACN 647209: WE DEPARTED FROM ZZZ IN ICING CONDITIONS. CALLBACK CONVERSATION WITH RPTR ACN 647481 REVEALED THE FOLLOWING INFO: PLT STATED THAT FEEDBACK FROM HIS ACR MAINT INDICATED THE #3 COMPRESSOR THRUST BEARING FAILED. HIS VISUAL INSPECTION OF THE ENG AT THE GATE REVEALED A NORMAL LOOKING COMPRESSOR SECTION; BUT A COMPLETELY BLOWN OUT TURBINE SECTION.