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Inspecting painted surfaces for hidden corrosion

Aviation Mechanic General (AMG) practice question 8 of 31 on Cleaning and Corrosion Control. ACS element AM.I.G.K21 · difficulty: recall. Want to answer it in a timed quiz? Use the Aviation Mechanic General (AMG) practice mode.

Question bank updated 2026-09-22

QUESTIONWhy must painted aircraft surfaces be inspected often for irregularities such as blisters, flakes, chips, and lumps?

  1. APaint always shrinks as it ages and exposes the bare metal beneath it
  2. BBlisters show that the paint was applied over a wet surface
  3. CCorrosion products occupy more volume than the original metal
Show the answer and explanation

Correct answer: C. Corrosion products occupy more volume than the original metal

  • A — incorrect The handbook does not attribute these irregularities to paint shrinkage; they result from expanding corrosion products under the film.
  • B — incorrect In the corrosion-inspection context, blisters are evidence of corrosion products accumulating under the paint, not of application over moisture.
  • C — correct Paint can mask the initial stages of corrosion, and because corrosion products occupy more volume than the metal they replace, they push the finish up into blisters, flakes, chips, and lumps that reveal the attack.

BACKGROUND

A good, intact paint finish is the most effective barrier between metal surfaces and corrosive media, but paint can also mask the initial stages of corrosion. Since corrosion products occupy more volume than the original metal, painted surfaces must be inspected often for irregularities such as blisters, flakes, chips, and lumps. Surface corrosion sometimes spreads under the coating without visible roughening or powder; closer inspection then shows the paint or plating lifted in small blisters by the pressure of the underlying corrosion products. Visual inspection, often with a flashlight, mirror, and 5 to 10X magnifying glass, is the most widely used technique.

STUDY TIP

Treat any raised or lifted spot in a paint film as a corrosion suspect until proven otherwise; the expansion of corrosion products is what makes it visible.

KEY POINTS

  • Intact paint is the most effective corrosion barrier
  • Paint can hide the early stages of corrosion
  • Corrosion products expand and lift the finish into blisters and lumps

SOURCES

  • FAA-H-8083-30B ch08 "Electrochemical Attack" (NOTE on paint)
  • FAA-H-8083-30B ch08 "Surface Corrosion"
Practice the Aviation Mechanic General (AMG) test →Timed 60-question exam, by ACS area, or review your misses. Free.
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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.