FAA Aviation Mechanic Airframe (AMA)Airframe StructuresMedium
A technician repairing a damaged section of wing skin installs an external doubler plate that overlaps the surrounding parent skin on all sides, with rivets installed around the perimeter of the overlap. What type of joint does this repair create?
- ATongue-and-groove joint
- BScarf joint
- CButt joint
- DLap joint
Show answer & explanationAnswer & explanation
Correct answer: D. Lap joint
A lap joint is formed when one piece of material overlaps another and is riveted through the overlapping area, as is the case with a doubler plate installed over surrounding skin. A butt joint uses a separate splice plate to join two edge-to-edge pieces, and a scarf joint uses a tapered, feathered overlap typical of composite repairs.
Why the other options are wrong
- A. Tongue-and-groove is not a standard sheet metal riveted joint type.
- B. Scarf joints use a tapered, feathered surface typically for composite repairs, not overlapping metal doublers.
- C. A butt joint places two skin edges together and requires a separate splice plate underneath, not an overlapping doubler.
Lap Joint
A riveted joint in which one piece of sheet metal overlaps another, with fasteners installed through the overlapping area.
- Common in doubler and patch repairs
- Simpler to fabricate than a butt joint with splice plate
- Creates a step in the skin surface, unlike a flush butt joint repair
Memory trick: Lap joint = one sheet 'laps over' the other like a lap blanket