What was found
(CAN) DURING CLIMBOUT AFTER TAKEOFF THE #2 ENGINE STOPPED WITHOUT WARNING. ENGINE FAILURE DRILLS WERE CARRIED OUT & AIRCRAFT RETURNED TO POINT OF DEPARTURE. POST FLIGHT INSPECTION REVEALED METAL FLAKES IN THE OIL FILTER & A GRATINGSOUND FROM THE ACCESSORY GEARBOX (AGB). THE AGB WAS REMOVED & THE INPUT COUPLING SHAFT WHICH COUPLES THE COMPRESSOR TO THE ACCESSORY GEARBOX WAS FOUND TO BE DECOUPLED CAUSING SEVERE DAMAGE TO THE INPUT GEARSHAFT & ITS SUPPORT BEARING IN THE AGB HOUSING. THE DECOUPLING WAS A RESULT OF THE BALL LOCK FEATURE BEING NOT PROPERLY LCOKED AT A PREVIOUS SHOP VISIT FOR REPLACEMENT OF THE STARTER GENERATOR GEARSHAFT.