FAA Aviation Mechanic Airframe (AMA)Airframe InspectionMedium
A technician needs to measure the remaining wall thickness of a corroded aluminum wing skin without removing or disassembling the panel. Which NDT method is best suited for this purpose?
- ACoin tap test
- BUltrasonic inspection
- CMagnetic particle inspection
- DDye penetrant inspection
Show answer & explanationAnswer & explanation
Correct answer: B. Ultrasonic inspection
Ultrasonic inspection uses high-frequency sound waves and measures the time for the echo to return from the back surface, allowing precise measurement of remaining material thickness without disassembly.
Why the other options are wrong
- A. Coin tap testing detects delamination in composites by sound differences, not metal thickness.
- C. Magnetic particle only works on ferromagnetic materials and detects surface/near-surface cracks, not thickness.
- D. Dye penetrant only detects surface-breaking defects, not thickness.
Ultrasonic Inspection (Thickness)
An NDT method using high-frequency sound waves to detect internal flaws and measure remaining material thickness by timing echo return.
- Measures thickness loss from corrosion
- Can detect subsurface flaws not visible externally
- Requires a couplant between the transducer and part surface
Memory trick: 'Ultrasonic bounces sound to measure how thin it's gone.'