Airframe Mechanic Certification Sheet Metal Structural Repairs 4 — Questions and Answers
Question 1: When performing a scab patch repair on aircraft skin, the patch material should be:
- One gauge thicker than the original skin
- The same material and temper as the original skin (Correct answer)
- A higher-strength alloy to compensate for stress
- Any available aluminum sheet of similar thickness
Correct answer: The same material and temper as the original skin
Patch material must match the original skin in alloy, temper, and thickness to ensure compatible strength and fatigue characteristics.
Question 2: Which tool is used to measure the diameter of a drilled hole to ensure it is the correct size for the rivet being installed?
- Micrometer caliper
- Telescoping gauge and micrometer
- Pin gauges or 'go/no-go' gauges (Correct answer)
- Vernier caliper only
Correct answer: Pin gauges or 'go/no-go' gauges
Pin gauges (go/no-go gauges) quickly verify that drilled holes fall within the acceptable tolerance range for the specified rivet diameter.
Question 3: What is the function of a 'joggle' in a sheet metal repair or splice?
- To increase the thickness of a sheet at a lap joint
- To allow one sheet to overlap another while maintaining a flush outer surface (Correct answer)
- To create a waterproof seal between panels
- To provide additional rivet hole locations
Correct answer: To allow one sheet to overlap another while maintaining a flush outer surface
A joggle is an offset formed in sheet metal so that a lap joint can be made flush on the outer surface without a protruding step.
Question 4: When removing a solid shank rivet, the drill bit diameter used should be:
- Equal to the rivet shank diameter
- Slightly smaller than the rivet shank diameter to avoid enlarging the hole (Correct answer)
- Slightly larger than the rivet shank to ease removal
- Equal to the rivet head diameter
Correct answer: Slightly smaller than the rivet shank diameter to avoid enlarging the hole
Drilling slightly smaller than the shank diameter allows the rivet head to be punched off cleanly without enlarging the hole for the replacement rivet.
Question 5: Which class of fit is required for structural rivet holes in primary aircraft structure?
- Clearance fit (0.004" oversize)
- Close tolerance fit (±0.001" of nominal) (Correct answer)
- Interference fit (rivet forced in)
- Loose fit for ease of installation
Correct answer: Close tolerance fit (±0.001" of nominal)
Structural rivet holes require a close tolerance fit so the rivet fills the hole properly when driven, ensuring maximum bearing strength.
Question 6: A 'tension head' (100° countersunk) rivet is used instead of a universal head rivet primarily when:
- The repair is in a high-vibration area
- A flush surface is required on the exterior skin for aerodynamic smoothness (Correct answer)
- The sheet thickness exceeds 0.080 inches
- The rivet must carry shear loads only
Correct answer: A flush surface is required on the exterior skin for aerodynamic smoothness
Flush (countersunk) rivets are used on exterior aerodynamic surfaces to minimize drag by maintaining a smooth, unbroken skin surface.
Question 7: What is the minimum number of rivets required in a single rivet row for a repair splice on primary aircraft structure according to AC 43.13-1B?
- Two rivets per side of the splice
- Three rivets per side of the splice (Correct answer)
- Four rivets per side of the splice
- One rivet per inch of splice length
Correct answer: Three rivets per side of the splice
AC 43.13-1B requires at least three rivets per side of the splice in any single row to ensure adequate load transfer in primary structure repairs.
Airframe Mechanic Certification Sheet Metal Structural Repairs 4
When performing a scab patch repair on aircraft skin, the patch material should be: