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Slack provided when installing flexible hose

Aviation Mechanic General (AMG) practice question 17 of 20 on Fluid Lines and Fittings. ACS element AM.I.D.K3 · difficulty: recall. Want to answer it in a timed quiz? Use the Aviation Mechanic General (AMG) practice mode.

Question bank updated 2026-09-22

QUESTIONWhen installing flexible hose, how much slack or bend should be provided in the hose line to allow for the change in length that occurs when pressure is applied?

  1. A10 to 15 percent of its total length
  2. B2 to 4 percent of the installed length
  3. C5 to 8 percent of its total length
Show the answer and explanation

Correct answer: C. 5 to 8 percent of its total length

  • A — incorrect This is more slack than the handbook calls for; the stated allowance is 5 to 8 percent.
  • B — incorrect This is less slack than the handbook calls for, and too little slack puts a mechanical load on the hose as it contracts under pressure.
  • C — correct The handbook directs that slack or a bend of 5 to 8 percent of the hose's total length be provided when installing flexible hose.

BACKGROUND

Flexible hose contracts in length and expands in diameter when it is pressurized, so a hose installed tight between two fittings would be placed under a mechanical load in service. To prevent that, the handbook requires slack or a bend in the hose line amounting to 5 to 8 percent of the hose's total length. Hose assemblies must never be stretched tightly between two fittings, and flexure should not occur at the end fittings, with the hose remaining straight for at least two hose diameters from each fitting. Hose must be supported at least every 24 inches, though closer supports are desirable. Flexible hose also has to be protected from excessive temperatures, either by routing it away from heat or by installing shrouds around it.

STUDY TIP

Remember the pair of ideas together: hose gets shorter and fatter under pressure, so slack of 5 to 8 percent of total length is built in. Do not confuse that figure with the 24-inch maximum spacing between hose supports.

KEY POINTS

  • Provide slack or a bend of 5 to 8 percent of the hose's total length when installing flexible hose.
  • Flexible hose contracts in length and expands in diameter when pressurized.
  • Hose must never be stretched tightly between two fittings and must be supported at least every 24 inches.

SOURCES

  • FAA-H-8083-30B ch09 "Installation of Flexible Hose Assemblies — Slack"
  • FAA-H-8083-30B ch09 "Installation of Flexible Hose Assemblies — Clearance"
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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.