AT72 EXPERIENCES INCREASING LEVELS OF TORQUE SURGES DURING CLB. FLT CREW SHUTS DOWN AND RETURNS TO DEP ARPT.

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DURING THE CLBOUT; THE CREW NOTICED A SLIGHT SURGING OF THE #2 ENG AT ABOUT 5000 FT. INITIALLY THE SURGING WAS SMALL; ABOUT 5% TORQUE. CLBING THROUGH ABOUT 6500 FT; THE SURGING GREW WORSE; ABOUT 10-20% TORQUE. AT ABOUT 7000-8000 FT; THE ENG SURGING GREW MUCH WORSE; 30-40% TORQUE LOSS AND THEN REGAIN WITH NOTICEABLE YAW IN THE ACFT. FINALLY; THE TORQUE DROPPED TO 0% AND THEN BACK UP TO CLB TORQUE. I TOLD THE FO TO PULL OUT THE PRECAUTIONARY SHUTDOWN CHKLIST AND WE SHUT DOWN THE #2 ENG. WE DECLARED AN EMER WITH ZZZZ DEP CTL. WE ADVISED THE FLT ATTENDANT THAT WE WERE RETURNING TO ZZZZ AND TO PREPARE FOR LNDG. WE EXECUTED THE APCH INTO ZZZZ AS THE WX WAS 1800 FT OVCST WITH WINDS 040 DEGS AT 20 KTS. WE LANDED THE ACFT UNEVENTFULLY AND RETURNED TO THE GATE WHERE I THEN MADE A PA TO THE PAX EXPLAINING WHAT HAD JUST HAPPENED. MAINT NEEDS TO FIGURE OUT WHY ENG HAD THIS RECURRING ENG SURGE PROB. SURGING WAS PREVIOUSLY WRITTEN UP ON OCT/WED/05 AND THEN AGAIN ON OCT/SUN/05 BY SAME CREW THAT HAD THIS INCIDENT AFTER CORRECTIVE MAINT WAS DONE.