FAA Aviation Mechanic Powerplant (AMP)Engine InspectionMedium
A technician suspects a crack in a magnesium alloy engine crankcase half and wants to perform a nondestructive inspection to confirm it. Which method is appropriate for detecting surface cracks on this nonferrous casting?
- AEddy current inspection using a ferrous probe
- BMagnetic particle inspection
- CUltrasonic thickness testing only
- DDye penetrant inspection
Show answer & explanationAnswer & explanation
Correct answer: D. Dye penetrant inspection
Magnesium and aluminum alloy crankcases are nonferrous and cannot be magnetized, so magnetic particle inspection will not work; dye penetrant inspection is the standard NDI method for detecting surface cracks in nonferrous castings.
Why the other options are wrong
- A. Eddy current with a ferrous probe is not the standard method for crack detection on castings.
- B. Magnetic particle inspection only works on ferromagnetic materials, not magnesium.
- C. Ultrasonic thickness testing measures material thickness, not surface cracks.
Crankcase Crack Detection (Nonferrous)
Magnesium and aluminum crankcases require dye penetrant inspection for crack detection since they cannot be magnetized for magnetic particle testing.
- Magnetic particle inspection is limited to ferrous metals
- Dye penetrant works on both ferrous and nonferrous surfaces
- Crankcase must be clean and free of paint/oil before testing
- Fluorescent or visible dye penetrant kits are commonly used
Memory trick: 'Mag Won't Stick to Mag(nesium)' — magnetic particle fails on nonferrous metal, so use dye penetrant.