Laying out, drilling, riveting, repairing

Eight procedures. Guided first attempts are in AF-A Hands-on.

Everything here is subordinate to the structural repair manual. These procedures tell you how to execute; the SRM tells you what is permitted.

Procedure 1 — Assess damage and decide repairability (S14)

Before anything is cut or drilled.

1. Clean the area and establish what the damage actually is.
2. Establish its extent — choose an inspection method that can find the boundary (GEN-K Procedures Procedure 1). Cracks extend beyond what is visible.
3. Measure: length, depth, area, and distance to edges, fasteners and adjacent repairs.
4. Classify against the SRM: negligible, repairable, or beyond repair.
5. Check the zone restrictions — proximity to other repairs, to edges, to primary structure.
6. Decide and record the reasoning, not just the conclusion.

Check — mark the boundary of the damage physically and re-inspect outside it. If you find more, your boundary was wrong. Stopping at the visible edge is how a repair is built over a crack that continues underneath.

Failure — assessing extent by eye on a crack. GEN-K Concepts §1: visual inspection finds surface condition, and a tight crack is not reliably surface-visible.

Procedure 2 — Design a repair from the SRM (S5)

1. Confirm the SRM applies — model, effectivity, revision (GEN-B Procedures Procedure 1).
2. Find the repair scheme for that structure and that damage classification.
3. Read what it specifies: material, thickness, temper, fastener type and size, pattern, edge distance, sealing, and finish.
4. Lay out the repair on paper first (GEN-B Procedures Procedure 7).
5. Check the repair against the surrounding structure: existing fasteners, edges, other repairs, access.
6. If no scheme covers it, stop — that is approved data territory (GEN-I Procedures Procedure 2).

Check — name the SRM section and revision your repair comes from. If you cannot, you have designed a repair rather than selected one, and it is a major repair needing approved data.

Procedure 3 — Lay out a rivet pattern (S11, S7)

1. From the SRM or AC 43.13-1B, establish rivet diameter, edge distance, pitch and transverse pitch.
2. Mark the edge distance line on all sides first.
3. Divide the run to give even pitch — work from the center outward, not from one end, so any remainder is shared.
4. Mark each hole center and center-punch it.
5. Check the pattern against the limits before drilling anything.

Check — measure the two extreme rivets to their nearest edges. Layout errors accumulate along a run, so the ends are where edge distance goes out of limits, and after drilling it is too late.

Failure — laying out from one end. The accumulated error all lands on the last rivet.

Procedure 4 — Drill (K4)

1. Select the drill for the rivet, from the table — not by eye, and not by fraction where the table gives a number size (GEN-H Concepts §6).
2. Clamp or cleco the parts together so they cannot move or separate. Holes drilled separately do not line up.
3. Drill square to the surface, at the right speed, with steady pressure.
4. Deburr both sides of every hole.
5. Cleco as you go — every third or fourth hole — so the assembly stays aligned.

Check — look through the holes with the parts clamped. They should be round and aligned. An oval hole means the drill wandered or the parts moved.

Failure — drilling without clecoing. The parts creep, and by the end of the run the holes in the two sheets no longer align.

Procedure 5 — Countersink (S12)

1. Determine whether the joint is machine countersunk or dimpled — sheet thickness decides, and the SRM specifies.
2. Set the countersink stop and cut a test piece in the same material and thickness.
3. Cut, checking depth against the rivet head.
4. The head should sit flush to very slightly below the surface.

Check — fit a rivet dry and run a straightedge or a fingernail across it. Proud is wrong. Deep enough to leave a knife edge in the sheet is worse — you have thinned the material around the hole to nothing.

Failure — countersinking sheet too thin for it. Below the thickness the SRM specifies, the countersink cuts through and the joint must be dimpled instead.

Procedure 6 — Remove rivets without damaging the hole (S8, K8)

The hole is what you are protecting (AF-A Concepts §4).

1. Center-punch the rivet head — carefully, supporting the sheet from behind.
2. Drill the head only, with a drill the same size as the rivet shank, to about the depth of the head.
3. Break the head off with a pin punch used sideways.
4. Drive the shank out with a punch, supporting the structure behind.
5. Do not drill the shank out. The drill follows the softer path, which is the sheet.

Check — after removal, check the hole is still round and still the original size. If it is oversized, the repair now needs the next size rivet, which changes the pattern, the edge distance and possibly the repairability.

Failure — drilling straight through. It is faster, and it costs you the hole.

Procedure 7 — Install solid rivets (S1)

1. Check the rivet length: grip plus about 1.5 diameters.
2. Deburr, clean, and apply sealant or primer where the repair scheme calls for it (GEN-G Concepts §3).
3. Support the manufactured head with a bucking bar of appropriate weight, held square.
4. Drive with the correct set, square to the surface, in short controlled bursts.
5. Inspect the shop head — about 1.5 diameters across, 0.5 diameters high, concentric, no cracks.

Check — measure the shop head, at least until you can judge it. Too small means it is under-driven and the joint is not clamped; too flat means over-driven and the sheet may be damaged around the hole.

Failure — a bucking bar held at an angle, which produces a shop head offset to one side. It looks nearly right and clamps unevenly.

Procedure 8 — Install blind rivets (S2)

1. Confirm the blind rivet is permitted here. They are not universally interchangeable with solid rivets, and the SRM says where they may be used.
2. Confirm grip range against the material stack. Blind rivets have a narrow grip range and a rivet outside it will not clamp.
3. Set with the correct nose piece, square to the surface.
4. Inspect: stem broken off flush or within limits, head seated, no gap.

Check — the stem must break at the right point and sit within limits. A stem standing proud, or one that has pulled through, means the wrong grip length or the wrong tool setting.

The checks, collected

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