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Lay line repeat interval on flexible hose

Aviation Mechanic General (AMG) practice question 18 of 20 on Fluid Lines and Fittings. ACS element AM.I.D.K5 · difficulty: recall. Want to answer it in a timed quiz? Use the Aviation Mechanic General (AMG) practice mode.

Question bank updated 2026-09-22

QUESTIONLay lines are printed along flexible hose to show the hose's natural lay. These lines are repeated along the length of the hose at intervals of not more than

  1. A24 inches
  2. B4 inches
  3. C9 inches
Show the answer and explanation

Correct answer: C. 9 inches

  • A — incorrect Twenty-four inches is the maximum spacing at which flexible hose must be supported after installation, not the spacing of the printed lay line.
  • B — incorrect Four inches is the maximum width of the color-code band painted on small aluminum tubing to identify the alloy, and has nothing to do with hose lay lines.
  • C — correct FAA-H-8083-30B states that the markings indicating the natural lay (no twist) of the hose are repeated at intervals of not more than 9 inches along the length of the hose.

BACKGROUND

A lay line is a contrasting-colored line printed lengthwise along a flexible hose, together with identification markings made up of lines, letters, and numbers. The line shows the natural lay of the hose, that is, the position the hose holds when it is not twisted, and it is repeated at intervals of not more than 9 inches along the hose. Because a hose must be installed without twisting to avoid rupture of the hose or loosening of the attaching nuts, this printed line is the witness mark a mechanic reads after an installation to confirm the hose is lying naturally. Twisting of the hose can be determined from the identification markings, so a lay line that spirals around the hose instead of running straight shows the assembly was twisted as the fittings were tightened. The same markings also carry the hose type, the quarter and year of manufacture, and a five-digit manufacturer code.

STUDY TIP

Memorize 9 inches as the lay line repeat interval and keep it separate from the 24-inch maximum hose support spacing, since both numbers belong to flexible hose installation. When you see a question about reading marks on an installed hose, think lay line first.

KEY POINTS

  • Lay lines show the hose's natural lay, meaning no twist.
  • They repeat at intervals of not more than 9 inches along the hose.
  • Do not confuse this with the 24-inch maximum hose support spacing.

SOURCES

  • FAA-H-8083-30B ch09 "Hose Identification"
  • FAA-H-8083-30B ch09 "Installation of Flexible Hose Assemblies — Twisting"
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MORE ON FLUID LINES AND FITTINGS

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.