FAA Aviation Mechanic Airframe (AMA)Airframe StructuresMedium
A technician needs to inspect an aluminum casting for surface cracks, but the part is nonferrous and cannot be magnetized. Which nondestructive inspection method should be used?
- ALiquid (dye) penetrant inspection
- BUltrasonic through-transmission inspection
- CMagnetic particle inspection
- DRadiographic inspection only
Show answer & explanationAnswer & explanation
Correct answer: A. Liquid (dye) penetrant inspection
Liquid penetrant inspection is used to detect surface-breaking defects in nonmagnetic, nonferrous materials such as aluminum, magnesium, and nonferrous castings. Magnetic particle inspection only works on ferromagnetic materials.
Why the other options are wrong
- B. Ultrasonic inspection is typically used for internal or subsurface flaw detection, not the simplest choice for surface cracks.
- C. Magnetic particle inspection requires a ferromagnetic material that can be magnetized, which aluminum is not.
- D. Radiography can detect internal flaws but is more complex/costly than needed for surface crack detection.
Liquid (Dye) Penetrant Inspection
An NDI method using a visible or fluorescent dye penetrant to reveal surface-breaking cracks and defects in nonporous materials, including nonferrous metals.
- Works on any nonferrous or ferrous nonporous material
- Detects only surface-breaking defects
- Process: clean, apply penetrant, remove excess, apply developer, inspect
- Cannot detect subsurface flaws like ultrasonic or radiographic methods
Memory trick: Dye penetrant paints the crack for anyone to see.