FAA Aviation Mechanic Airframe (AMA)Airframe StructuresMedium
A technician needs to inspect a thick aluminum wing spar cap for internal subsurface cracks and delaminations without disassembling the structure. The inspection method uses high-frequency sound waves transmitted into the material, with reflections analyzed to detect discontinuities. Which NDI method is this?
- ALiquid penetrant inspection
- BMagnetic particle inspection
- CEddy current inspection
- DUltrasonic inspection
Show answer & explanationAnswer & explanation
Correct answer: D. Ultrasonic inspection
Ultrasonic inspection sends high-frequency sound waves through a material; discontinuities reflect the sound back to a transducer, allowing detection of subsurface flaws such as cracks and delaminations in thick sections, which surface methods like dye penetrant or magnetic particle cannot detect.
Why the other options are wrong
- A. Dye penetrant only detects flaws open to the surface, not internal defects.
- B. Magnetic particle inspection only works on ferromagnetic materials and detects surface/near-surface flaws.
- C. Eddy current is effective mainly for surface and near-surface flaws in conductive materials, with limited depth penetration.
Ultrasonic Inspection
A nondestructive inspection method using high-frequency sound waves to detect internal flaws, thickness variations, and delaminations in materials.
- Detects subsurface defects in thick materials
- Uses transducer and reflected sound wave analysis
- Works on metals and composites
Memory trick: Ultrasonic = 'echo location' finding hidden cracks deep inside