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Substituting unapproved covering materials

Aviation Mechanic Airframe (AMA) practice question 4 of 30 on Non-Metallic Structures. ACS element AM.II.B.K8 · difficulty: recall. Want to answer it in a timed quiz? Use the Aviation Mechanic Airframe (AMA) practice mode.

Question bank updated 2026-09-22

QUESTIONAn aircraft is covered under an approved fabric covering process. What is the result of substituting a material that is not part of that approved system?

  1. AThe substitution is allowed if strength is equal
  2. BThe substitution only requires a logbook entry
  3. CThe aircraft becomes unairworthy
Show the answer and explanation

Correct answer: C. The aircraft becomes unairworthy

  • A — incorrect Equal strength does not authorize a substitution; the approval covers the specific materials together with the procedures for using them.
  • B — incorrect No record entry makes a forbidden substitution acceptable, because the covering approval is tied to the specific approved materials.
  • C — correct The handbook states that only the approved materials may be used and that substitution of other materials is forbidden and results in the aircraft being unairworthy.

BACKGROUND

For a fabric covering to be legal, the FAA must approve the fabric, tapes, threads, cords, glues, dopes, sealants, coatings, thinners, additives, fungicides, rejuvenators, and paints used. TSO-C15d, Aircraft Fabric, Grade A, prescribes the minimum performance standards approved aircraft fabric must meet, and fabric approved to replace Grade A cotton must meet the same criteria. Holders of a Parts Manufacturer Approval for the common polyester fabrics have also gained approval for the tapes, cords, threads, and liquids used with them. Those approved materials together with the procedures for using them constitute the supplemental type certificate for each covering process. Substitution of other materials is forbidden and makes the aircraft unairworthy.

STUDY TIP

Remember that a covering approval is a package of materials plus procedures, so mixing in a product from another system is not a paperwork problem but an airworthiness problem.

KEY POINTS

  • Only materials approved for the covering process may be used.
  • Substitution of other materials is forbidden.
  • An unapproved substitution renders the aircraft unairworthy.

SOURCES

  • FAA-H-8083-31B ch03 "Approved Aircraft Fabrics"
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MORE ON NON-METALLIC STRUCTURES

SkyDrill is not affiliated with the FAA. This is an original practice item based on FAA-H-8083-31B Aviation Maintenance Technician Handbook – Airframe, and 14 CFR part 43. Regulations and handbooks are revised; confirm details against the current edition.