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Choosing penetrant for a nonmagnetic part

Aviation Mechanic General (AMG) practice question 19 of 21 on Inspection Concepts and Techniques. ACS element AM.I.K.R3 · 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 mechanic suspects a surface crack in an aluminum landing gear fitting. Which nondestructive inspection method is appropriate for finding a surface crack in this nonmagnetic material?

  1. ALiquid penetrant inspection
  2. BMagnetic particle inspection
  3. CMagnaglo inspection under black light
Show the answer and explanation

Correct answer: A. Liquid penetrant inspection

  • A — correct Penetrant inspection detects defects open to the surface in any nonporous material, including aluminum, whereas magnetic particle methods are not applicable to nonmagnetic materials.
  • B — incorrect Magnetic particle inspection works only on ferromagnetic materials such as iron and steel and is not applicable to aluminum.
  • C — incorrect Magnaglo is a fluorescent variant of magnetic particle inspection and likewise requires a ferromagnetic part.

BACKGROUND

Selecting an inspection technique begins with the material of the part. Magnetic particle inspection detects invisible cracks and other defects in ferromagnetic materials such as iron and steel, but it is not applicable to nonmagnetic materials. Liquid penetrant inspection detects defects open to the surface in parts made of any nonporous material and is used with equal success on aluminum, magnesium, brass, copper, cast iron, stainless steel and titanium. When a part is made of magnetic material, the handbook recommends magnetic particle inspection instead of penetrant because penetrant cannot find subsurface defects.

STUDY TIP

Decide by material first: nonmagnetic metals such as aluminum go to penetrant or eddy current, magnetic steels go to magnetic particle.

KEY POINTS

  • Magnetic particle inspection is limited to ferromagnetic materials.
  • Penetrant inspection works on aluminum and other nonporous nonmagnetic materials.
  • For magnetic parts, magnetic particle is generally recommended over penetrant.

SOURCES

  • FAA-H-8083-30B ch10 "Liquid Penetrant Inspection"
  • FAA-H-8083-30B ch10 "Magnetic Particle Inspection"
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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.