What was found
(AUS) DURING PREFLIGHT INSPECTION, THE NR 4 BLOCKER DOOR WAS FOUND NOT FULLY STOWED ON THE NR 1 ENGINE I/B REVERSER COWL. INVESTIGATION THEN FOUND THE BLOCKER DOORS LOWER HINGE BOLT WAS MISSING ANDTHE UPPER BOLT WAS LOOSE. FURTHER INVESTIGATION FOUNDTHE NR 2 AND NR 3 BLOCKER DOORS HAD LOOSE NUTS ON THE LOWER HINGE BOLTS AND MISSING NUTS AND WASHERS ON THE UPPER HINGE BOLTS. SUSPECT THE FASTENERS WERE IMPROPERLY TORQUED AT LAST BLOCKER DOOR REPLACEMENT. MAINTENANCE/PERSONNEL ERROR.