5.2 Sheet-Metal Repairs, Fasteners, and Riveting Judgment

Sheet-Metal Repairs: Making the Repair Match the Load

Sheet-metal repair is not a craft exercise separate from airworthiness. A patch, splice, doubler, or replacement part must carry load through the same structure without weakening the surrounding metal. The Airframe ACS includes layout, forming, drilling, rivet selection, rivet installation, and repair design because one poor detail can defeat the whole repair.

A typical repair starts with damage removal and boundary definition. The technician determines the full extent of the damage, removes cracked or corroded material as directed, and avoids leaving sharp corners. Round holes and smooth radii reduce stress concentration. The next step is selecting material that matches the approved data for alloy, temper, thickness, and protective finish.

Fasteners are selected for the joint, not for what is easiest to install. Solid rivets, blind rivets, and special-purpose fasteners have different uses. A blind rivet may be acceptable where backside access is not available, but only when the manual or structural repair data permits that fastener in that application. Substituting a fastener can change strength, clamp-up, galvanic behavior, and inspection requirements.

Use this checklist for a riveted repair scenario:

• Verify repair authority and damage limits before layout.
• Select compatible sheet, rivets, and corrosion protection.
• Lay out rivet spacing, pitch, row spacing, and edge distance from the approved source.
• Drill pilot holes accurately and support the work to prevent distortion.
• Deburr both sides and protect bare metal as required.
• Drive or pull fasteners with the correct tools and inspect shop heads or locking features.
• Check for skin waviness, cracks, loose fasteners, and proper documentation.

Rivet removal is a common test subject because it is easy to damage the hole. The normal logic is to center-punch carefully, drill through the head without enlarging the hole, remove the head, and drive out the shank with proper support. If the hole becomes oversized or elongated, the technician must not simply install a random larger rivet. The repair data must allow the next step.

Countersinking and dimpling also require judgment. A countersink that is too deep reduces sheet thickness around the hole. Dimpling forms the sheet but may be limited by material thickness and access. Forming operations require attention to bend radius and grain direction because cracking can occur when metal is bent too sharply or across an unfavorable direction.

Troubleshooting a bad repair means looking at the process, not only the final appearance. Rows that do not line up may indicate poor layout. Raised rivet heads may show poor driving technique or interference. A patch that oil-cans may not have enough support or may have been installed under stress. Corrosion around a repair can indicate poor sealing, incompatible metals, or damaged finish.

For the exam, choose answers that protect the original structure. The most defensible answer usually measures first, follows the structural repair manual, uses the specified fastener and material, and treats a questionable hole or crack as a condition requiring approved repair data.