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Why metallic pencils are barred on gas path parts

Aviation Mechanic Powerplant (AMP) practice question 1 of 13 on Turbine Engines. ACS element AM.III.B.R1 · difficulty: standard. Want to answer it in a timed quiz? Use the Aviation Mechanic Powerplant (AMP) practice mode.

Question bank updated 2026-09-22

QUESTIONWhy is the use of carbon alloy or metallic pencils not recommended for temporarily marking turbine engine parts?

  1. AThey burn off and leave no trace during operation
  2. BThey can cause intergranular corrosion attack
  3. CThey react with layout dye and blur the markings
Show the answer and explanation

Correct answer: B. They can cause intergranular corrosion attack

  • A — incorrect The concern is chemical attack on the metal, not that the mark disappears; the marks are for assembly, not for running.
  • B — correct Such pencils may cause intergranular corrosion attack, which can reduce material strength and lead to cracking.
  • C — incorrect Layout dye lightly applied is itself an acceptable marking material; the restriction on metallic pencils is about corrosion, not legibility.

BACKGROUND

Certain materials may be used for temporary marking during assembly and disassembly of the combustion section, and the manufacturer's information always governs. Layout dye applied lightly, a felt tip marker, or chalk may be used on parts that are directly exposed to the engine's gas path, such as turbine blades and discs, turbine vanes, and combustion chamber liners. A wax marking pencil may be used for parts that are not directly exposed to the gas path, but it must not be used on a liner surface or a turbine rotor. Carbon alloy and metallic pencils are not recommended anywhere on these parts because of the possibility of causing intergranular corrosion attack. That attack could result in a reduction in material strength and cracking.

STUDY TIP

Sort marking media into three buckets: acceptable on gas path parts, acceptable only off the gas path, and never acceptable. Remember that the reason metallic pencils are barred is corrosion leading to cracks.

KEY POINTS

  • Layout dye, felt tip marker, or chalk may mark parts directly exposed to the gas path.
  • Wax marking pencils are for non-gas-path parts only, never on liners or turbine rotors.
  • Carbon alloy and metallic pencils risk intergranular corrosion attack, reduced strength, and cracking.

SOURCES

  • FAA-H-8083-32B ch10 "Marking Materials for Combustion Section Parts"
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MORE ON TURBINE ENGINES

SkyDrill is not affiliated with the FAA. This is an original practice item based on FAA-H-8083-32B Aviation Maintenance Technician Handbook – Powerplant, and 14 CFR part 43. Regulations and handbooks are revised; confirm details against the current edition.