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Circular magnetization and defect orientation

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

Question bank updated 2026-09-22

QUESTIONIn magnetic particle inspection, circular magnetization is produced by passing electric current through the part. Which defects does this field orientation locate?

  1. ADefects running roughly perpendicular to the part's axis
  2. BDefects at any angle, in a single magnetizing pass
  3. CDefects running roughly parallel to the part's axis
Show the answer and explanation

Correct answer: C. Defects running roughly parallel to the part's axis

  • A — incorrect Defects lying across the major axis are revealed by longitudinal magnetization, which is the second, separate magnetizing operation.
  • B — incorrect The lines of force must pass approximately perpendicular to a defect to reveal it, so one magnetizing operation cannot cover every possible defect angle.
  • C — correct Passing current through the part sets up concentric circles of force about and within it, which locates defects running approximately parallel to the axis of the part.

BACKGROUND

Magnetic particle inspection is a nondestructive test for ferromagnetic parts in which magnetic flux leaking at a discontinuity attracts fine particles and forms a visible indication. To locate a defect, the magnetic lines of force must pass approximately perpendicular to it, so the direction in which the part is magnetized decides which defects appear. Because defects can lie at any angle to the major axis of the part, two separate magnetizing operations are used: circular magnetization and longitudinal magnetization. Circular magnetization is induced by passing electric current through the part, producing concentric circles of force about and within it, and it locates defects running approximately parallel to the part's axis. Longitudinal magnetization supplies the other direction so that transverse defects are not missed.

STUDY TIP

Tie the method to the picture: current through the part makes rings of flux around the axis, and rings cut across defects that lie along the axis. If an inspection uses only one magnetizing direction, expect defects at the other orientation to be missed.

KEY POINTS

  • Magnetic flux must cross a defect roughly perpendicular for an indication to form.
  • Circular magnetization, made by passing current through the part, finds defects roughly parallel to the axis.
  • Two magnetizing operations, circular and longitudinal, are needed because defects lie at any angle.

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.