What was found
AIRCRAFT EXPERIENCED A LEFT ENGINE POWER FLUCTUATION DURING CRUISE AT 3,500 FEET, EN ROUTE FROM ROTA (GRO) TO SAIPAN (GSN). THE PILOT-IN-COMMAND (PIC) OBSERVED MANIFOLD PRESSURE FLUCTUATIONS BETWEEN 28-22 INCHES OF MERCURY AND NOTED INCONSISTENT ENGINE POWER. WHITE/BLUE SMOKE WAS SUBSEQUENTLY OBSERVED EMANATING FROM THE LEFT ENGINE. THE AIRCRAFT RETURNED TO ROTA (GRO) WITH THE LEFT ENGINE OPERATING AT APPROXIMATELY 75% POWER. POST-FLIGHT INSPECTION REVEALED A SHEARED AND SEPARATED TURBINE ASSEMBLY WITHIN THE LEFT ENGINE TURBOCHARGER. THE TURBOCHARGER, OVERHAULED BY APPROVED TURBO COMPONENTS (U5AR184Y), HAD ACCUMULATED 392.7 HOURS SINCE OVERHAUL. THE AIRCRAFT HAD UNDERGONE A PHASE CHECK THE PREVIOUS DAY, WITH 0.9 HOURS FLOWN SINCE INSPECTION. NO ABNORMALITIES WERE NOTED DURING THE PRECEDING INSPECTION.