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Stop drilling a crack in a transparent panel

Aviation Mechanic Airframe (AMA) practice question 19 of 30 on Non-Metallic Structures. ACS element AM.II.B.K27 · difficulty: standard. Want to answer it in a timed quiz? Use the Aviation Mechanic Airframe (AMA) practice mode.

Question bank updated 2026-09-22

QUESTIONAt the first sign of a crack developing in a transparent plastic panel, what action should be taken at the extreme ends of the crack?

  1. AApply a strip of tape across each end
  2. BDrill a small hole with a #30 drill
  3. CSand the area with fine abrasive
Show the answer and explanation

Correct answer: B. Drill a small hole with a #30 drill

  • A — incorrect Tape does not redistribute the strain concentrated at the crack tip, so the crack continues to split the panel.
  • B — correct A small hole drilled with a #30 or 1/8-inch drill at the extreme ends of a crack localizes it and distributes the strain over a large area.
  • C — incorrect Sanding and polishing address surface scratches; they do not relieve the stress concentration at the end of a crack.

BACKGROUND

Whenever possible, an extensively damaged transparent plastic part should be replaced rather than repaired, because a carefully patched part is not the equal of a new section either optically or structurally. At the first sign of crack development, a small hole is drilled with a #30 or 1/8-inch drill at the extreme ends of the cracks. This serves to localize the cracks and to prevent further splitting by distributing the strain over a large area. If the cracks are small, stopping them with drilled holes usually suffices until replacement or a more permanent repair can be made. Each crack occurring at any hole or tear is drilled in the same manner.

STUDY TIP

Treat stop drilling as a temporary measure that buys time, not as the finished repair. Remember the specific drill sizes, #30 or 1/8 inch, since the exam often tests the number.

KEY POINTS

  • Cracks are stop drilled at their extreme ends with a #30 or 1/8-inch drill.
  • The hole distributes strain and prevents further splitting.
  • Replacement is preferred over repair for extensive damage.

SOURCES

  • ama-airframe/ch07.txt "Repairs"
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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.