FAA Aviation Mechanic Airframe (AMA)Airframe StructuresMedium
A technician needs to inspect a high-strength steel landing gear axle for surface and near-surface fatigue cracks without disassembling the axle further. Which nondestructive inspection method is appropriate for this ferromagnetic part?
- ADye penetrant inspection
- BMagnetic particle inspection
- CRadiographic inspection only
- DEddy current inspection
Show answer & explanationAnswer & explanation
Correct answer: B. Magnetic particle inspection
Magnetic particle inspection is used on ferromagnetic materials to detect surface and near-surface discontinuities by magnetizing the part and applying iron particles that cluster at flux leakage points caused by cracks. It cannot be used on nonferrous materials like aluminum.
Why the other options are wrong
- A. Dye penetrant only detects flaws open to the surface and works on nonporous materials but does not use magnetic flux.
- C. Radiographic inspection can find internal flaws but is not the typical first-choice, lower-cost method for surface/near-surface cracks in ferromagnetic parts.
- D. Eddy current is best suited to thin, nonferrous conductive materials and near-surface flaws, not typically the primary choice for thick steel axles.
Magnetic Particle Inspection (MPI)
An NDI method limited to ferromagnetic materials where the part is magnetized and fine iron particles are applied; particles cluster at cracks due to magnetic flux leakage, revealing the flaw.
- Works only on ferromagnetic metals (iron, steel, nickel, cobalt)
- Detects surface and near-surface discontinuities
- Part must be demagnetized after inspection
- Common for landing gear and engine steel components
Memory trick: Magnets stick to steel — MPI sticks to ferromagnetic flaws.