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Scratch depth limit for burnishing aluminum alloy tubing

Aviation Mechanic General (AMG) practice question 16 of 20 on Fluid Lines and Fittings. ACS element AM.I.D.K2 · difficulty: standard. Want to answer it in a timed quiz? Use the Aviation Mechanic General (AMG) practice mode.

Question bank updated 2026-09-22

QUESTIONA mechanic finds a scratch in a length of aluminum alloy tubing, located away from the heel of any bend. Burnishing the scratch out with hand tools is an acceptable repair only if the scratch is no deeper than

  1. A20 percent of the tube wall thickness
  2. B10 percent of the wall thickness
  3. C50 percent of the tube wall thickness
Show the answer and explanation

Correct answer: B. 10 percent of the wall thickness

  • A — incorrect The 20 percent figure in the handbook applies to a dent measured against the tube diameter, not to scratch depth in the tube wall.
  • B — correct Scratches or nicks not deeper than 10 percent of the wall thickness in aluminum alloy tubing, and not in the heel of a bend, may be repaired by burnishing with hand tools.
  • C — incorrect No such allowance exists; damage that deep is beyond the shallow burnishing repair and the line would be replaced.

BACKGROUND

Rigid tubing can pick up minor surface damage in service, and the handbook distinguishes between damage that may be dressed out and damage that requires replacement of the line. For aluminum alloy tubing, scratches or nicks that are not deeper than 10 percent of the wall thickness and are not located in the heel of a bend may be repaired by burnishing with hand tools. A separate limit covers dents: a dent of less than 20 percent of the tube diameter is not objectionable unless it is in the heel of a bend. Damage limits for hard, thin-walled corrosion-resistant steel and titanium tubing are considerably less than for aluminum, and the aircraft maintenance manual must be consulted. Lines with severe die marks, seams, or splits are replaced rather than repaired, and any crack or deformity in a flare is cause for rejection.

STUDY TIP

Memorize the two percentages separately: 10 percent of wall thickness for scratches and nicks, 20 percent of tube diameter for dents. Also remember that both allowances disappear when the damage is in the heel of a bend.

KEY POINTS

  • Scratches or nicks up to 10 percent of wall thickness in aluminum alloy tubing may be burnished out by hand.
  • The allowance does not apply to damage located in the heel of a bend.
  • A dent of less than 20 percent of the tube diameter is not objectionable, a limit based on diameter rather than wall thickness.

SOURCES

  • FAA-H-8083-30B ch09 "Rigid Tubing Inspection & Repair"
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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.