What was found
ON ANNUAL INSPECTION OF RUDDERS AT THE CENTER ATTACH FITTING AFT SPAR MOUNT, SLIGHT RUST WAS NOTED. FURTHER INSPECTION REVEALED 5 OUT OF THE 8 ATTACH NUTS ON THE SPAR ATTACH WERE CRACKED THROUGH TO THE BOLT THREADS. THESE NUTS ARE CRACKED ONLY O THE BOTTOM AREA OF NUT. LOOKING DOWN AT THE ATTACH NUTS WILL NOT SHOW CRACKS. TELL TALE RUST ON THE BOLT THREADS IS THE ONLY TOP SIDE INDICATOR. RECOMMEND THAT NAS679A NUT BE INSPECTED OR REPLACED WITH MS21042 OR MS21083N. THESE NUTS ARE USED IN OTHER LOCATIONS ON THE PLANE. EXPOSED NUTS ARE MORE SUSCEPTIBLE TO CRACKING.