Free Airframe Mechanic Sheet Metal Structures Questions and Answers — Questions and Answers
Question 1: When fabricating a 90-degree bend in a piece of aluminum sheet metal with a radius of 0.125 inches and a thickness of 0.063 inches, what is the setback?
- 0.125 inches
- 0.063 inches
- 0.251 inches
- 0.188 inches (Correct answer)
Correct answer: 0.188 inches
For a 90-degree bend, the setback is calculated by adding the bend radius to the thickness of the material. In this case, Setback = Radius + Thickness = 0.125" + 0.063" = 0.188". Setback is a critical calculation for determining the starting point of the bend.
Question 2: An aircraft's aluminum skin shows signs of fine, worm-like lines of corrosion products beneath the paint film, particularly in a high-humidity environment. Which type of corrosion is most likely present?
- Pitting
- Filiform corrosion (Correct answer)
- Intergranular corrosion
- Stress corrosion cracking
Correct answer: Filiform corrosion
Filiform corrosion is characterized by its worm-like appearance as it forms tunnels of corrosion products under the paint. It is common on painted aluminum surfaces that are exposed to high humidity.
Question 3: During a repair of a stressed-skin structure, a small crack is found. What is the first procedural step to stop the progression of the crack before applying a patch?
- Rivet a patch directly over the crack.
- Apply a sealant to the crack.
- Drill a small hole at each end of the crack. (Correct answer)
- Blend out the crack using an abrasive pad.
Correct answer: Drill a small hole at each end of the crack.
To prevent a crack from spreading in a stressed-skin structure, a small hole must be drilled at each end of the crack. This technique, known as stop-drilling, relieves the stress concentration at the crack tips.
Question 4: What does the 'AD' in the rivet identification code AN470AD4-5 signify?
- The head style is countersunk.
- The material is 5056 aluminum alloy.
- The material is 2117-T aluminum alloy. (Correct answer)
- The rivet requires refrigeration.
Correct answer: The material is 2117-T aluminum alloy.
In the standard rivet identification system, the letter code following the head style indicates the rivet's material composition. 'AD' specifies that the rivet is made from 2117-T aluminum alloy.
Question 5: A technician is performing a flush patch repair on a pressurized fuselage skin. How should the thickness of the doubler and the filler (patch) relate to the original skin thickness?
- The doubler and filler should both be one gauge thicker than the original skin.
- The doubler should be one gauge thicker, and the filler should be the same thickness as the original skin. (Correct answer)
- The doubler should be the same thickness, and the filler should be one gauge thinner than the original skin.
- The doubler and filler should both be the same thickness as the original skin.
Correct answer: The doubler should be one gauge thicker, and the filler should be the same thickness as the original skin.
For a flush patch repair, the filler plug must be of the same gauge and material as the original skin to maintain a smooth surface. The doubler, which provides the structural reinforcement from the inside, should be made of material one gauge heavier (thicker) than the original skin.
Question 6: Which of the following is considered a major repair to an airframe sheet metal structure according to 14 CFR Part 43, Appendix A?
- Making a small patch not changing the contour.
- The repair of damaged areas in stressed covering exceeding six inches in any direction. (Correct answer)
- Repairing upholstery of the cabin interior.
- Replacing a side window that does not interfere with the structure.
Correct answer: The repair of damaged areas in stressed covering exceeding six inches in any direction.
According to 14 CFR Part 43, Appendix A, the repair of damaged areas in metal stressed covering that exceeds six inches in any direction is classified as a major repair and requires specific documentation and approval. The other options are listed as examples of preventive maintenance or minor repairs.
Free Airframe Mechanic Sheet Metal Structures Questions and Answers
When fabricating a 90-degree bend in a piece of aluminum sheet metal with a radius of 0.125 inches and a thickness of 0.063 inches, what is the setback?