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Minimum airworthy breaking strength of aircraft fabric

Aviation Mechanic Airframe (AMA) practice question 14 of 30 on Non-Metallic Structures. ACS element AM.II.B.K7 · difficulty: applied. Want to answer it in a timed quiz? Use the Aviation Mechanic Airframe (AMA) practice mode.

Question bank updated 2026-09-22

QUESTIONAn aircraft was certificated with a covering fabric whose new breaking strength is 80 pounds. At what breaking strength does that covering become unairworthy?

  1. A46 pounds, the intermediate figure
  2. B56 pounds
  3. C40 pounds, half the new strength
Show the answer and explanation

Correct answer: B. 56 pounds

  • A — incorrect The 46-pound figure belongs to fabric with a 65-pound new breaking strength, not to fabric rated at 80 pounds new.
  • B — correct Fabric is airworthy until it falls below 70 percent of the new strength required, and 70 percent of 80 pounds is 56 pounds.
  • C — incorrect The airworthiness threshold is 70 percent of the new strength, not one half of it.

BACKGROUND

An aircraft is certificated with a particular fabric based on its wing loading and its never exceed speed. The higher the wing loading and the never exceed speed, the stronger the fabric must be. Fabric is considered airworthy until it deteriorates to a breaking strength less than 70 percent of the strength of the new fabric required for that aircraft. Grade A cotton has a new breaking strength of 80 pounds, so the covering becomes unairworthy at 56 pounds. If a stronger polyester fabric is used to re-cover the same aircraft, it must still exceed 56 pounds to remain airworthy.

STUDY TIP

Practice the 70 percent calculation on each of the three published pairs: 80 and 56, 65 and 46, 50 and 35. The percentage never changes, only the starting strength.

KEY POINTS

  • Fabric is unairworthy below 70 percent of the required new breaking strength.
  • Grade A cotton starts at 80 pounds and fails airworthiness at 56 pounds.
  • The required grade depends on wing loading and never exceed speed.

SOURCES

  • ama-airframe/ch03.txt "Fabric Strength"
Practice the Aviation Mechanic Airframe (AMA) test →Timed 100-question exam, by ACS area, or review your misses. Free.
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.