Definition
A nondestructive testing method used to find cracks, voids, and other surface or near-surface flaws in ferrous (iron-based) metal parts. The part is magnetized and then coated with fine iron particles, often suspended in a liquid. Any flaw in the metal disrupts the magnetic field, and the particles gather along the disruption, making the flaw visible to the inspector.
Plain English
A way of finding hidden cracks in steel parts by magnetizing them and sprinkling on iron powder. The powder collects at any crack, so the crack stands out and can be seen.
Context Anchor
Seen in aircraft maintenance, especially during inspections or overhaul of steel engine, propeller, and landing gear parts.
Derivation
From 'magnetic' (relating to a magnet's field) and 'particle' (a small piece of matter, here the iron powder). The name describes exactly what the method does: it uses magnetic fields and iron particles to reveal flaws.
Why Pilots Care
Reveals hidden damage in critical metal parts before it can lead to in-flight failure.
Analogy
Think of iron filings clustering around the seam of a magnet. A crack in a magnetized part acts the same way -- it becomes a mini-magnet, and the iron particles pile up along it and reveal it.
Intuition Check
Do not assume this works on every metal or finds every hidden flaw. It only works on materials that can be magnetized, and it is best for cracks at or just below the surface.
Example Sentence 1
After the hard landing, the landing gear axle was sent to the shop for magnetic particle inspection before being returned to service.
Example Sentence 2
Propeller blades receive magnetic particle inspection during overhaul to confirm they are free of cracks.