FAA Aviation Mechanic Airframe (AMA)Airframe StructuresMedium
A technician is selecting solid wood stock to repair a wing spar and must ensure the material meets aircraft structural grade requirements. Which characteristic would disqualify a piece of Sitka spruce from use in this repair?
- AA grain slope of 1 in 20 relative to the edge
- BA slope of grain of 1 in 10
- CA moisture content of 12 percent
- DUniform, straight-grained wood with no visible defects
Show answer & explanationAnswer & explanation
Correct answer: B. A slope of grain of 1 in 10
Aircraft-grade wood such as Sitka spruce must have a slope of grain no steeper than 1 in 15; a slope of 1 in 10 is steeper than allowed and would disqualify the piece. A slope of 1 in 20 is acceptable, 12 percent moisture content is within the acceptable range, and straight, defect-free grain is the desired characteristic.
Why the other options are wrong
- A. A 1-in-20 slope is less steep than the 1-in-15 limit and is acceptable.
- C. 12 percent moisture content is within the acceptable range for aircraft wood.
- D. Straight, defect-free grain is exactly what is required, not a disqualifier.
Aircraft Wood Grading
Structural wood such as Sitka spruce must meet specific grading standards for grain slope, moisture content, and defects before use in aircraft repair.
- Maximum slope of grain is 1 in 15
- Acceptable moisture content is typically 12 percent or less
- Wood must be free of decay, compression wood, and excessive knots
Memory trick: 'Fifteen or finer, or the spar's a liar.'