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Detecting a twisted flexible hose

Aviation Mechanic General (AMG) practice question 13 of 17 on Fluid Lines and Fittings. ACS element AM.I.D.R4 · difficulty: recall. Want to answer it in a timed quiz? Use the Aviation Mechanic General (AMG) practice mode.

Question bank updated 2026-09-22

QUESTIONHow can a mechanic determine whether a flexible hose has been installed with a twist?

  1. AThe hose shows deep, permanent impressions under its clamps
  2. BThe lay line or stripe spirals around the hose
  3. CThe hose is shorter and larger in diameter under pressure
Show the answer and explanation

Correct answer: B. The lay line or stripe spirals around the hose

  • A — incorrect Deep permanent impressions from clamps or supports are cold flow, a sign of deterioration, not evidence of twist.
  • B — correct Twisting is determined from the identification stripe that runs along the length of the hose; the stripe should not spiral around the hose.
  • C — incorrect Contracting in length and expanding in diameter when pressurized is normal hose behavior, which is why slack is provided; it does not indicate twist.

BACKGROUND

Hoses must be installed without twisting to avoid possible rupture of the hose or loosening of the attaching nuts; high pressure applied to a twisted hose may cause failure or loosen the nut. Swivel connections at one or both ends relieve twist stresses. Lay lines and identification markings are printed along the hose in the natural lay (no twist) and are repeated at intervals of not more than 9 inches, so twisting can be determined from the identification stripe running along the hose length: the stripe should not spiral around the hose. Separately, cold flow describes deep permanent impressions produced by clamps or supports and is a reason for replacement.

STUDY TIP

Sight along the lay line after installation; a straight stripe means no twist, a spiraling stripe means the hose must be reinstalled.

KEY POINTS

  • A twisted hose may rupture or loosen its attaching nuts under high pressure.
  • The lay line printed along the hose should run straight, not spiral.
  • Swivel connections at one or both ends relieve twist stresses.

SOURCES

  • FAA-H-8083-30B ch09 "Installation of Flexible Hose Assemblies - Twisting"
  • FAA-H-8083-30B ch09 "Hose Identification"
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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.