What was found
AIRCRAFT ON PART 91 FLIGHT RETURNING TO BASE, PILOT OBSERVED A TORQUE SPLIT OF APPROXIMATELY 12-15 PERCENT. PILOT MATCHED TORQUE WITH TRIM SWITCH, NOTICED NR 2 ENGINE RUNNING HOTTER AND FASTER THAN NR 1. PILOT REDUCED POWER TO KEEP ENGINES IN NORMAL OPERATING RANGE. FLEW 15 MINUTES TO RETURN TO BASE. AFTER SHUT DOWN, INSPECTION SHOWED F.O.D. DAMAGE TO NR 12 COMPRESSOR. A 'AN3' BOLT WAS FOUND IN THE AIR BOX, ORIGIN UNKNOWN. ALL HARDWARE IN AIR BOX ACCOUNTED FOR.