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Appearance of fluorescent penetrant indications

Aviation Mechanic General (AMG) practice question 13 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

QUESTIONDuring a fluorescent penetrant inspection under black light, how do defects appear?

  1. AAs a deep blue-violet color against a yellow background
  2. BAs bright red lines on a smooth white developer coating
  3. CAs a brilliant yellow-green color
Show the answer and explanation

Correct answer: C. As a brilliant yellow-green color

  • A — incorrect Deep blue-violet is the appearance of the sound, defect-free areas, not of the defects.
  • B — incorrect Bright red indications on a smooth white developer coating describe the visible penetrant method, not the fluorescent method.
  • C — correct Under black light, fluorescent penetrant defects show up as a brilliant yellow-green color while sound areas appear deep blue-violet.

BACKGROUND

Penetrant visibility is increased by adding one of two types of dye: visible or fluorescent. The visible penetrant kit consists of dye penetrant, dye remover emulsifier and developer; when the developer dries to a smooth white coating, bright red indications appear where there are surface defects. The fluorescent kit adds a black light assembly consisting of a power transformer, a flexible power cable and a hand-held lamp. Under black light, defects show up as a brilliant yellow-green color and the sound areas appear deep blue-violet. The size of an indication shows the extent of the defect, and its brilliance is a measure of its depth.

STUDY TIP

Pair the color with the method: red on white means visible dye, yellow-green on blue-violet means fluorescent dye under black light.

KEY POINTS

  • Visible penetrant shows bright red indications on a white developer.
  • Fluorescent penetrant shows brilliant yellow-green defects under black light.
  • Sound areas under black light appear deep blue-violet.

SOURCES

  • FAA-H-8083-30B ch10 "Liquid Penetrant Inspection" and "Interpretation of Results"
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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.