What was found
(CAN) DURING PREPARATION FOR RUN-UP IT WAS NOTICED THAT THE PILOT OXYGEN MASK WAS HALFWAY OUT OF IT`S STORAGE POUCH. WHILE RE-STOWING THE MASK IT WAS NOTICED THAT THE REGULATOR ASSY HAD COME SEPARATED FROM THE MASK ASSY. UPON EXAMINATION IT WAS DISCOVERED THAT THE REGULATOR LOCK AND IT`S SCREW WERE MISSING. THE MASK WAS REMOVED FROM SERVICE AND WAS REPLACED BY A SERVICEABLE OXYGEN MASK ASSEMBLY. THE CO-PILOTS OXYGEN MASK ASSEMBLY WAS INSPECTED FOR CORRECT INSTALLATION OF THE REGULATOR LOCK ASSEMBLY AND NO DEFECTS WERE OBSERVED.