What was found
THE FUEL CONTROL UNIT , FCU, WAS SENT OUT FOR BENCH CHECK & REPAIR DUE TO A SUSPECTED FUEL FLOW PROBLEM. THE FCU WAS BENCH CHECKED & THE PROBLEM COULD IT WAS SLIGHTLY OUT OF RIG THAT MAY HAVE BEEN CAUSING A GOVERNOR INTERFERENCE PROBLEM. IT ALSO HAD THE DRIVE SPLINE INSPECTION PERFORMED ON THE FCU IAW THE REQUIREMENTS OF AD 2006-15-08 & COUNCIL 331 AMOC & APPROVED FOR RETURN TO SERVICE. THE UNIT WAS REINSTALLED & A GND RUN WAS ATTEMPTED. THE START WAS SLOW, BUT ACCELERATED PAST 60% WHERE THE TECHNICIAN ATTEMPTED TO PULL IT BACK FROM FLIGHT IDLE BACK TO GND IDLE, BUT IT CONTINUED TO ACCELERATE UNCONTROLLABLY THE TECHNICIAN IMMINENTLY PULLED THE STOP & FEATHERED & PREVENTED ANY ENG DAMAGE. AFTER SEPARATING THE FCU FROM THE FUEL PUMP THE FCU DRIVE HAD TWISTED OFF & SHEARED. THE TECHNICIAN NOTICED SOME BINDING WHEN TRYING TO TURN THE FCU DRIVE. SUSPECTS A BEARING FAILURE IN THE FCU. INSPECTION OF THE FCU WAS COMPLETED. THE PRIMARY CAUSE OF THE FAILURE TO INNER INPUT SHAFT WAS A BEARING PN 1412-612 CAUSING BEARING SEPARATION & LOCKING UP THE FCU DRIVE. A DETERMINATION OF THE BEARING FAILURE COULD NOT BE DETERMINED.