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Circular magnetization for axial defects

Aviation Mechanic General (AMG) practice question 14 of 21 on Inspection Concepts and Techniques. ACS element AM.I.K.K3 · difficulty: standard. Want to answer it in a timed quiz? Use the Aviation Mechanic General (AMG) practice mode.

Question bank updated 2026-09-22

QUESTIONA steel shaft is suspected of having a crack running approximately parallel to its long axis. Which magnetizing method is used to locate this defect?

  1. ALongitudinal magnetization by placing the part in a solenoid
  2. BResidual magnetization after removing the part from the demagnetizer
  3. CCircular magnetization by passing current through the part
Show the answer and explanation

Correct answer: C. Circular magnetization by passing current through the part

  • A — incorrect Longitudinal magnetization produces flux parallel to the long axis, which would run along rather than across an axial crack.
  • B — incorrect The residual procedure describes when the indicating medium is applied, not the flux direction, and the demagnetizer is used to remove magnetism after inspection.
  • C — correct Circular magnetization, achieved by passing electric current through the part, locates defects running approximately parallel to the axis of the part because the flux lines cross the defect nearly perpendicularly.

BACKGROUND

To locate a defect with magnetic particle inspection, the magnetic lines of force must pass approximately perpendicular to the defect. Because defects can lie at any angle to the major axis of the part, flux is induced in more than one direction using two separate magnetizing operations. Circular magnetization induces concentric circles of force about and within the part by passing electric current through it, locating defects running approximately parallel to the axis. Longitudinal magnetization produces a field parallel to the long axis by placing the part in a solenoid, so that the part becomes the core of an electromagnet, and it reveals defects lying across the axis.

STUDY TIP

Think of the flux needing to cut across the crack: an axial crack needs circular magnetization, a transverse crack needs longitudinal magnetization.

KEY POINTS

  • Flux must pass approximately perpendicular to a defect to reveal it.
  • Circular magnetization (current through the part) finds defects parallel to the axis.
  • Longitudinal magnetization (part in a solenoid) finds defects across the axis.

SOURCES

  • FAA-H-8083-30B ch10 "Effect of Flux Direction"
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SkyDrill is not affiliated with the FAA. This is an original practice item based on FAA-H-8083-30B Aviation Maintenance Technician Handbook – General, 14 CFR part 43 and part 65. Regulations and handbooks are revised; confirm details against the current edition.