What was found
HLN - FLT 2588 - LEFT ENGINE MADE LOUD BANG AFTER TAKEOFF AND ENGINE POWER DROPPED OFF. ENGINE THEN FAILED. CREW FOLLOWED CHECKLIST PROCEDURES AND RETURNED TO STATION. INTERNAL ENGINE FAILURE. SUSPECT HIGH SPEED PINION FAILURE OR COUPLING FAILURE. PROP CAN BE TURNED THROUGH WITHOUT ENGINE ROTATING IF THE GROUP IS AT A CERTAIN CLOCK ANGLE. WHEN MESHING THE TEETH TOGETHER, JUST AT THE EDGE OF THE DISCONNECT BETWEEN THE GEARBOX AND ROTATING GROUP, A METALLIC BUZZ ACN BE HEARD. SOUNDS LIKE TEETH MISSING ON HIGH SPEED PINION GEAR. (M)