Airframe Mechanic Certification Sheet Metal Structural Repairs 3 — Questions and Answers
Question 1: When laying out a rivet pattern for a patch repair, the transverse pitch (row spacing) should typically be:
- Equal to the rivet diameter
- 0.75 times the longitudinal pitch
- 0.866 times the longitudinal pitch (for staggered rows) (Correct answer)
- 2 times the edge distance
Correct answer: 0.866 times the longitudinal pitch (for staggered rows)
For staggered rivet rows, transverse pitch is 0.866 times the longitudinal pitch to maintain proper load distribution.
Question 2: What is 'chem-milling' used for in aircraft sheet metal fabrication?
- Chemically treating rivets before installation
- Selectively removing material from sheet metal using chemical etching to reduce weight (Correct answer)
- Applying corrosion-inhibiting primer to bare metal
- Cleaning metal surfaces before welding
Correct answer: Selectively removing material from sheet metal using chemical etching to reduce weight
Chem-milling uses controlled chemical etching to precisely remove material from selected areas to reduce weight while maintaining structural integrity.
Question 3: A rivet that has been improperly driven and shows a cracked or split tail should be:
- Left in place if the head is still flush
- Reinforced with epoxy adhesive
- Removed and replaced (Correct answer)
- Peened again to close the crack
Correct answer: Removed and replaced
A cracked or split rivet tail indicates a faulty installation; the rivet must be drilled out and replaced with a new one.
Question 4: Which aluminum alloy is most commonly used for aircraft skin panels due to its excellent strength-to-weight ratio and corrosion resistance when alclad?
- 2024-T3 (Correct answer)
- 7075-T6
- 6061-T6
- 5052-H32
Correct answer: 2024-T3
2024-T3 aluminum is the most widely used aircraft skin alloy, offering high strength, good fatigue resistance, and excellent workability when alclad coated.
Question 5: When using a hand squeezer to set rivets, which type of rivet set should be used to avoid damaging the surrounding sheet surface?
- A flat set only
- A crowned set only
- Either a flat or crowned set depending on rivet head type (Correct answer)
- A dimple die set
Correct answer: Either a flat or crowned set depending on rivet head type
Flat sets are used for universal (round) heads and crowned sets for brazier heads; the correct set prevents marring the surrounding sheet.
Question 6: What is the maximum allowable depth of a gouge or scratch that can remain on aluminum aircraft skin without repair per AC 43.13-1B?
- 10% of the material thickness
- 25% of the material thickness (Correct answer)
- 50% of the material thickness
- Any depth if polished smooth
Correct answer: 25% of the material thickness
Scratches or gouges exceeding 10% of sheet thickness typically require repair; however, AC 43.13-1B allows up to certain limits depending on location—always verify with the SRM.
Question 7: Fretting corrosion between aluminum skin and a steel fastener is best prevented by:
- Using a larger diameter fastener
- Applying a wet-installation sealant or corrosion inhibiting compound (Correct answer)
- Increasing rivet spacing
- Using an aluminum fastener instead
Correct answer: Applying a wet-installation sealant or corrosion inhibiting compound
Wet installation with sealant or corrosion inhibiting compound prevents galvanic contact and moisture intrusion between dissimilar metals.
Airframe Mechanic Certification Sheet Metal Structural Repairs 3
When laying out a rivet pattern for a patch repair, the transverse pitch (row spacing) should typically be: