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Maximum permissible grain slope in aircraft wood

Aviation Mechanic Airframe (AMA) practice question 12 of 30 on Non-Metallic Structures. ACS element AM.II.B.K3 · difficulty: recall. Want to answer it in a timed quiz? Use the Aviation Mechanic Airframe (AMA) practice mode.

Question bank updated 2026-09-22

QUESTIONFor every wood species listed as acceptable for aircraft structural repair, what is the steepest permissible slope of the grain?

  1. A1:20 for every listed species
  2. B1:8, except for spruce
  3. C1:15
Show the answer and explanation

Correct answer: C. 1:15

  • A — incorrect A 1:20 slope is not the published limit; the handbook gives the same 1:15 figure for each acceptable species.
  • B — incorrect No species is allowed a grain slope as steep as 1:8, and spruce is held to the same 1:15 limit as the others.
  • C — correct The one item common to all the listed species is that the slope of the grain cannot be steeper than 1:15.

BACKGROUND

The handbook lists the wood species acceptable for structural repair of aircraft, with spruce as the preferred choice and the standard against which other species are measured. Douglas fir, noble fir, western hemlock, northern white pine, Port Orford white cedar, and yellow poplar are compared to spruce for strength, workability, and suitability for gluing. Each entry also carries a maximum permissible grain deviation. The one item common to all the species is that the slope of the grain cannot be steeper than 1:15. All woods used for structural repair of aircraft are classified as softwood.

STUDY TIP

Do not try to memorize every species comparison; learn that spruce is the standard at 100 percent strength and that 1:15 is the single grain-slope limit shared by all of them.

KEY POINTS

  • Spruce is the standard against which other aircraft woods are compared.
  • Grain slope may not be steeper than 1:15 in any acceptable species.
  • All woods used for structural repair are classified as softwood.

SOURCES

  • ama-airframe/ch06.txt "Suitable Wood"
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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.