AMT Sheet Metal Structural Repair 3 — Questions and Answers
Question 1: Which repair method restores the greatest percentage of original strength in a damaged aircraft skin panel?
- Plug patch repair
- Flush patch repair (Correct answer)
- Scab patch repair
- Overlay patch repair
Correct answer: Flush patch repair
A flush patch (insert patch) restores close to 100% of original strength because it maintains the original skin thickness and aerodynamic surface.
Question 2: What is the correct sequence for laying out rivet holes in a sheet metal repair pattern?
- Mark rivet locations, drill patch, cleco, drill structure (Correct answer)
- Drill structure, cleco patch, drill through patch
- Cleco patch, drill through all layers simultaneously
- Mark on patch, drill patch, transfer marks, drill structure
Correct answer: Mark rivet locations, drill patch, cleco, drill structure
Rivet holes are laid out on the patch first, drilled, then the patch is clecoed to the structure and used as a template to drill the structure.
Question 3: Which type of corrosion is most likely to occur between aluminum aircraft skin and a steel fastener?
- Uniform surface corrosion
- Galvanic corrosion (Correct answer)
- Intergranular corrosion
- Stress corrosion cracking
Correct answer: Galvanic corrosion
Galvanic corrosion occurs when dissimilar metals (aluminum and steel) are in electrical contact in the presence of an electrolyte.
Question 4: What is the purpose of using a cleco fastener during a sheet metal repair?
- To permanently fasten the repair patch
- To temporarily hold parts in alignment while drilling and riveting (Correct answer)
- To countersink holes for flush rivets
- To measure hole diameter before drilling
Correct answer: To temporarily hold parts in alignment while drilling and riveting
Clecos are temporary spring-loaded fasteners used to hold sheets in position while remaining holes are drilled and rivets installed.
Question 5: When cutting a repair patch from aluminum sheet stock, the corners of rectangular patches should be:
- Left as sharp 90-degree angles
- Clipped or radiused to reduce stress concentration (Correct answer)
- Cut at 45-degree angles only
- Left raw and not deburred
Correct answer: Clipped or radiused to reduce stress concentration
Square corners on repair patches create stress concentrations that can initiate cracks, so corners must be radiused or clipped.
Question 6: What does the 'T' designation in an aluminum alloy temper (e.g., 2024-T3) indicate?
- The alloy has been tin-plated for corrosion protection
- The alloy has been thermally treated (Correct answer)
- The alloy thickness in thousandths of an inch
- The tensile strength rating in ksi
Correct answer: The alloy has been thermally treated
The 'T' temper designation indicates the alloy has been thermally treated (heat treated) to improve mechanical properties.
Question 7: When using a countersink tool to prepare holes for flush rivets, what angle is used for standard 100-degree countersunk (AN426) rivets?
- 82 degrees
- 90 degrees
- 100 degrees (Correct answer)
- 120 degrees
Correct answer: 100 degrees
AN426 (MS20426) rivets have a 100-degree head angle, so countersunk holes must also be cut to 100 degrees to achieve a flush fit.
AMT Sheet Metal Structural Repair 3
Which repair method restores the greatest percentage of original strength in a damaged aircraft skin panel?