What was found
WING FLAPS WOULD NOT GO TO POSITION 40 WHEN SELECTED. MADE FLAPS 30 LANDING. INSPECTION REVEALED THAT THE NR 3 AND 6 FLAP JACKSCREWS HAD SURFACE CORROSION. THE JACKSCREWS AND BALLNUTS WERE REPLACED. THE NR 3 AND 6 JACKSCREWS AND BALLNUTS WERE REPLACED. THE AIRCRAFT WAS TESTED AND NO FAULTS WERE FOUND. UPON FURTHER INSPECTION IN THE SHOP IT WAS NOTED THAT THE CORROSION ON THE JACKSCREWS HAD COME FROM THE BALLNUTS. INTERNAL INSPECTION OF THE BALLNUTS REVEALED SEVERE PITTING AND CORROSION DUE TO FAILURE OF THE INTERNAL CHROME PLATING.