Airframe Mechanic Certification Sheet Metal Structures 4 — Questions and Answers
Question 1: When performing a repair on aircraft skin using a flush patch, the patch material must be:
- One gauge thicker than the original to compensate for the cutout
- The same material type and temper as the original skin (Correct answer)
- A harder alloy than the original to provide additional strength
- Clad on one side only, with the clad side facing outward
Correct answer: The same material type and temper as the original skin
Repair patches must match the original material specification (alloy and temper) to maintain the structural and corrosion properties of the original design.
Question 2: A 'pilot hole' in sheet metal work is:
- A hole drilled at an angle to guide subsequent straight drilling
- A small-diameter starter hole drilled before final-size drilling (Correct answer)
- A hole in the fuselage skin used for avionics wire routing
- The first rivet hole in a row used to align subsequent holes
Correct answer: A small-diameter starter hole drilled before final-size drilling
A pilot hole is a small-diameter hole drilled first to guide the final-size drill and improve hole location accuracy.
Question 3: What does the 'T' designation (such as T3, T4, T6) indicate in aluminum alloy nomenclature?
- The thickness of the sheet in millimeters
- The temper (heat treatment condition) of the alloy (Correct answer)
- The tensile strength in thousands of PSI
- The temperature rating for sustained use
Correct answer: The temper (heat treatment condition) of the alloy
The T designation indicates the temper, which describes the specific heat treatment or work-hardening process applied to achieve desired mechanical properties.
Question 4: During a sheet metal repair, when must a doubler be used in addition to the filler patch?
- Whenever the damaged area exceeds the allowable limits for a simple filler patch (Correct answer)
- On all repairs to pressurized fuselage skin regardless of damage size
- Only when the original skin thickness is less than 0.032 inches
- When more than three rivets in a row must be replaced
Correct answer: Whenever the damaged area exceeds the allowable limits for a simple filler patch
A doubler is required when damage exceeds the limits for a simple filler patch, providing the additional material needed to restore original structural strength.
Question 5: Fretting corrosion between sheet metal components most commonly occurs due to:
- Dissimilar metal contact in the presence of moisture
- Slight relative motion between faying surfaces under vibration (Correct answer)
- Chemical attack from hydraulic fluid leaks
- Trapped moisture under paint causing blistering
Correct answer: Slight relative motion between faying surfaces under vibration
Fretting corrosion is caused by microscopic relative motion between tightly fitted surfaces under vibration, which wears away protective oxide layers.
Question 6: When laying out rivet rows, the transverse pitch (row spacing) should be at minimum:
- Equal to the edge distance
- 75% of the rivet pitch within the row (Correct answer)
- 3 times the rivet diameter
- Equal to the rivet pitch within the row
Correct answer: 75% of the rivet pitch within the row
Transverse pitch (distance between rows) should be at least 75% of the longitudinal pitch to maintain proper load distribution.
Question 7: What is the purpose of applying sealant between sheet metal faying surfaces in pressurized areas?
- To improve the strength of the riveted joint
- To prevent relative motion and reduce fretting
- To prevent cabin air leaks and provide corrosion protection (Correct answer)
- To electrically insulate dissimilar metals from each other
Correct answer: To prevent cabin air leaks and provide corrosion protection
Sealant on faying surfaces in pressurized areas prevents pressurized air from leaking and also inhibits corrosion by excluding moisture from the joint.
Airframe Mechanic Certification Sheet Metal Structures 4
When performing a repair on aircraft skin using a flush patch, the patch material must be: