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Main disadvantage of penetrant inspection

Aviation Mechanic General (AMG) practice question 12 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

QUESTIONWhat is the main disadvantage of liquid penetrant inspection?

  1. AIt can be used only on ferromagnetic materials such as steel
  2. BThe defect must be open to the surface
  3. CIt cannot be used on nonmetallic materials such as plastics
Show the answer and explanation

Correct answer: B. The defect must be open to the surface

  • A — incorrect Penetrant inspection works on any nonporous material, including nonmagnetic metals such as aluminum and titanium; the ferromagnetic limitation applies to magnetic particle inspection.
  • B — correct The handbook states that the main disadvantage of penetrant inspection is that the defect must be open to the surface so the penetrant can enter it.
  • C — incorrect Penetrant inspection may be used on ceramics, plastics, molded rubber and glass, so this is not a limitation of the method.

BACKGROUND

Liquid penetrant inspection is a nondestructive test for defects open to the surface in parts made of any nonporous material. It is used with equal success on aluminum, magnesium, brass, copper, cast iron, stainless steel and titanium, and may also be used on ceramics, plastics, molded rubber and glass. It detects surface cracks and porosity caused by fatigue cracks, shrinkage, cold shuts, grinding and heat-treat cracks, seams, forging laps and bursts, and can indicate lack of bond between joined metals. Its main disadvantage is that the defect must be open to the surface, which is why magnetic particle inspection is generally recommended for parts made of magnetic material.

STUDY TIP

When a question mentions subsurface defects, rule out penetrant inspection; it only finds what is open to the surface.

KEY POINTS

  • Penetrant inspection works on any nonporous material, metallic or not.
  • The defect must be open to the surface for the penetrant to enter.
  • For magnetic materials, magnetic particle inspection is generally recommended instead.

SOURCES

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