What was found
(CAN) DURING CRUISE FLIGHT, THE CREW NOTICED THAT THE CABIN PRESSURE WAS FLUXUATING ABNORMALLY. THE CREW SELECTED MANUAL OPERATION AND SELECTED THE NR 1 SOURCE AND CONTINUED THE FLIGHT TO DESTINATION. MAINTENANCE FOUND THAT THE NR 1 SUPERCHARGER HAD FAILED. BOTH ROTORS WERE MISSING LARGE SECTIONS OF ROTOR MATERIAL AND THE DRIVE QUILL SHAFT WAS SHEARED. THE FAILED SUPERCHARGER HAD UNDERGONE AN OPERATOR INSTIGATED ROTOR INSPECTION AT 500 HRS TSO WITH NO DEFECTS NOTED.