SkyDrill

Maximum grain slope in repair wood

Aviation Mechanic Airframe (AMA) practice question 2 of 30 on Non-Metallic Structures. ACS element AM.II.B.K4 · difficulty: applied. Want to answer it in a timed quiz? Use the Aviation Mechanic Airframe (AMA) practice mode.

Question bank updated 2026-09-22

QUESTIONEvery wood species accepted for aircraft structural repair carries a maximum permissible grain slope of 1:15. Over a 30-inch length of spruce, what grain deviation does this permit?

  1. A1 inch across the 30-inch length
  2. B2 inches across the 30-inch length
  3. C4.5 inches across the 30-inch length
Show the answer and explanation

Correct answer: B. 2 inches across the 30-inch length

  • A — incorrect One inch is the allowance for only 15 inches of length; applying it to a 30-inch piece halves the permitted slope.
  • B — correct A slope of 1:15 permits 1 inch of deviation for every 15 inches of length, so a 30-inch piece may deviate up to 2 inches.
  • C — incorrect This treats 1:15 as 15 percent of the length, which is not how the handbook expresses grain slope.

BACKGROUND

Aircraft repair wood is graded on the direction of its grain because grain that runs out of the member carries load poorly. The handbook lists several species acceptable for structural repair and notes that the one item common to all of them is that the slope of the grain cannot be steeper than 1:15. Slope is expressed as a ratio of deviation to length, so 1:15 means one unit of sideways run for every fifteen units along the member. Spruce is the preferred choice and the standard against which the other species are measured. All four faces of a board must be checked to determine the actual divergence.

STUDY TIP

Practice converting grain slope ratios to inches over a given length, and remember that the 1:15 limit applies to every acceptable species, not just spruce.

KEY POINTS

  • Maximum permissible grain slope for aircraft repair wood is 1:15.
  • A 30-inch member may deviate up to 2 inches under that ratio.
  • Check all four faces of a board to measure divergence.

SOURCES

  • FAA-H-8083-31B ch06 "Suitable Wood"
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.