What was found
DURING INSPECTION, THE AIRCRAFT WAS FOUND TO HAVE SEVERAL RIVETS LOOSE IN THE AREA OF THE SKIN DOUBLER, INSTALLED AS PART OF THE CABIN DOOR, STC SA2490S0. FURTHER INSPECTION REVEALED DEFECTIVE 'UPSET' HEADS ON MANY OF THE RIVETS INSTALLED DURING THIS MODIFICATION. FOUND NO EVIDENCE OF STRUCTURAL FAILURE. SUBMITTER FEELS THIS IS A CASE OF IMPROPER INSTALLATION TECHNIQUE DURING THE MODIFICATION. TO CORRECT THIS, THE DEFECTIVE RIVETS WERE REMOVED AND REPLACED WITH NEW. SUBMITTER'S ESTIMATION IS THAT APPROXIMATELY 30 PERCENT OF THE TOTAL NUMBER OF RIVETS USED TO ATTACH THIS DOUBLER REQUIRED REPLACEMENT. (X)