Airframe Mechanic Certification Sheet Metal Structures 5 — Questions and Answers
Question 1: A cracked sheet metal skin panel that extends to within one rivet pitch of a stringer attachment must be repaired by:
- Stop-drilling the crack ends only
- Replacing the damaged skin section and using the stringer as part of the repair boundary (Correct answer)
- Applying a bonded external doubler over the crack
- Stop-drilling and installing a single row of rivets across the crack
Correct answer: Replacing the damaged skin section and using the stringer as part of the repair boundary
When a crack extends near structural members, the repair design must incorporate those members as boundaries and cannot rely on stop-drilling alone.
Question 2: What information is found on a sheet metal part's material callout such as '2024-T3 ALCLAD .040'?
- Alloy, temper, cladding type, and sheet thickness in inches (Correct answer)
- Alloy series, temper, surface finish code, and weight per square foot
- Alloy, treatment, application area code, and thickness in millimeters
- Alloy family, heat code, layer count, and thickness in gauge number
Correct answer: Alloy, temper, cladding type, and sheet thickness in inches
The callout '2024-T3 ALCLAD .040' specifies the aluminum alloy (2024), temper (T3), that it has alclad corrosion-resistant cladding, and the sheet thickness is 0.040 inches.
Question 3: When inspecting a riveted skin splice for serviceability, which condition would require immediate repair?
- A shop head that is 5% smaller than the nominal driven diameter
- A manufactured head with 2° of tilt from perpendicular
- A crack emanating from a rivet hole (Correct answer)
- A rivet with slight surface corrosion on the manufactured head
Correct answer: A crack emanating from a rivet hole
A crack emanating from a rivet hole is a critical defect that requires immediate repair because it will grow under fatigue loading.
Question 4: The 'neutral axis' of a sheet metal bend is important because:
- It is the surface that must face outward on all formed parts
- It is the layer that experiences neither compression nor tension and has no change in length (Correct answer)
- It defines the maximum bend angle before cracking occurs
- It indicates the location where the bend radius is measured
Correct answer: It is the layer that experiences neither compression nor tension and has no change in length
The neutral axis is the theoretical line within the material that is neither stretched nor compressed during bending, and its location determines bend allowance.
Question 5: Which rivet installation defect is called a 'clinched' rivet?
- A rivet whose shank has been expanded but not fully driven
- A rivet whose shank has bent over instead of forming a proper shop head (Correct answer)
- A rivet installed at an angle to the sheet surface
- A rivet with an oversized manufactured head
Correct answer: A rivet whose shank has bent over instead of forming a proper shop head
A clinched rivet occurs when the shank bends sideways rather than mushrooming outward, resulting in a bent shank and poor joint quality.
Question 6: What is the correct procedure when a drilled rivet hole is found to be oversize beyond acceptable limits?
- Install a rivet of the next larger diameter, using the SRM for the next standard oversize (Correct answer)
- Fill the hole with epoxy and re-drill to the correct size after curing
- Install the original rivet size and apply sealant to fill the gap
- Mark the hole as non-structural and leave it open
Correct answer: Install a rivet of the next larger diameter, using the SRM for the next standard oversize
An oversize hole must be filled with a rivet of the next standard oversize diameter as specified in the Structural Repair Manual.
Question 7: Stress corrosion cracking in high-strength aluminum alloys is most likely to initiate when:
- The alloy is exposed to salt spray during ground operations
- Sustained tensile stress acts on the material in a corrosive environment (Correct answer)
- Compressive residual stresses are introduced by shot peening
- The material is heated above its recrystallization temperature
Correct answer: Sustained tensile stress acts on the material in a corrosive environment
Stress corrosion cracking requires the simultaneous combination of sustained tensile stress and a corrosive environment to initiate and propagate.
Airframe Mechanic Certification Sheet Metal Structures 5
A cracked sheet metal skin panel that extends to within one rivet pitch of a stringer attachment must be repaired by: