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Minimum blend-out length for a rework depression

Aviation Mechanic General (AMG) practice question 26 of 36 on Cleaning and Corrosion Control. ACS element AM.I.G.K7 · difficulty: applied. Want to answer it in a timed quiz? Use the Aviation Mechanic General (AMG) practice mode.

Question bank updated 2026-09-22

QUESTIONCorrosion rework leaves a depression 0.020 inch deep in an aluminum skin. Using the required length-to-depth ratio for a blended dish-out, what is the minimum length of the reworked area?

  1. A0.20 inch, or 10 times the depth
  2. B0.40 inch
  3. C4.0 inches, or 200 times the depth
Show the answer and explanation

Correct answer: B. 0.40 inch

  • A — incorrect Ten times the depth is the minimum width of the cleaned up area, not its minimum length.
  • B — correct Rework depressions are blended using a ratio of 20:1, length to depth, so 0.020 inch times 20 gives 0.40 inch.
  • C — incorrect No 200:1 requirement exists; this misplaces the decimal in the 20:1 length-to-depth ratio.

BACKGROUND

All depressions resulting from corrosion rework must be faired or blended with the surrounding surface. Rough edges and all corrosion are removed first, and every dish-out is made elliptically shaped, with the major axis running spanwise on wings and horizontal stabilizers, longitudinally on fuselages, and vertically on vertical stabilizers. Rework depressions are then formed as smoothly blended dish-outs using a ratio of 20:1, length to depth, while the width of the cleaned up area is at least 10 times the depth. In critical and highly stressed areas, all pits remaining after removal of corrosion products must be blended out to prevent stress risers that may cause stress corrosion cracking. Where multiple pits are closely spaced, the intervening material is removed as well to minimize surface irregularity or waviness.

STUDY TIP

Memorize the pair of ratios, 20:1 for length and 10:1 for width, and read the stem carefully to see which dimension is being asked for.

KEY POINTS

  • Blended dish-outs use a 20:1 length-to-depth ratio; width is at least 10 times depth.
  • Dish-outs are elliptical, with the major axis oriented by structure: spanwise, longitudinal, or vertical.
  • Pits in critical and highly stressed areas must be blended out to avoid stress risers.

SOURCES

  • FAA-H-8083-30B ch08 "Fairing or Blending Reworked Areas"
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SkyDrill is not affiliated with the FAA. This is an original practice item based on FAA-H-8083-30B Aviation Maintenance Technician Handbook – General, 14 CFR part 43 and part 65. Regulations and handbooks are revised; confirm details against the current edition.