SkyDrill

Minimum fabric breaking strength

Aviation Mechanic Airframe (AMA) practice question 8 of 30 on Non-Metallic Structures. ACS element AM.II.B.K16 · 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 Grade A cotton fabric having a new breaking strength of 80 pounds. At what point does the covering become unairworthy?

  1. ABelow 46 pounds, which is 70 percent of 65
  2. BBelow 56 pounds of breaking strength
  3. CBelow 72 pounds, which is 90 percent of 80
Show the answer and explanation

Correct answer: B. Below 56 pounds of breaking strength

  • A — incorrect The 46-pound figure comes from intermediate grade fabric with a new strength of 65 pounds, not from Grade A cotton.
  • B — correct Fabric is airworthy until it deteriorates below 70 percent of the new strength required, and 70 percent of 80 pounds is 56 pounds.
  • C — incorrect The handbook uses a 70 percent threshold, not 90 percent, to decide when covering fabric is no longer airworthy.

BACKGROUND

The strength of fabric coverings must be determined at every 100-hour and annual inspection, and minimum breaking strength is what decides whether an aircraft needs re-covering. 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. For an aircraft certificated with Grade A cotton at 80 pounds new, that threshold is 56 pounds. If a stronger polyester fabric is used to re-cover the same aircraft, it must still exceed 56 pounds to remain airworthy. Aircraft requiring intermediate grade fabric have a new strength of 65 pounds and a minimum of 46 pounds.

STUDY TIP

Memorize the 70 percent rule and the paired figures of 80 and 56 pounds for Grade A, then work the same arithmetic for the other grades.

KEY POINTS

  • Fabric strength is checked at every 100-hour and annual inspection.
  • Fabric is unairworthy below 70 percent of new breaking strength.
  • Grade A cotton at 80 pounds new becomes unairworthy below 56 pounds.

SOURCES

  • FAA-H-8083-31B ch03 "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.