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Gas proof test of a flexible hose conducted underwater

Aviation Mechanic General (AMG) practice question 19 of 20 on Fluid Lines and Fittings. ACS element AM.I.D.K3 · 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 flexible hose assembly is to be proof-tested using dry, oil-free nitrogen. How is the test conducted?

  1. AWith the hose assembly clamped in an open vise
  2. BWith all trapped air bled from the assembly
  3. CWith the hose assembly submerged underwater
Show the answer and explanation

Correct answer: C. With the hose assembly submerged underwater

  • A — incorrect A vise holds the hose while it is cut to length and while the socket is screwed on during fabrication, not as the method for a gas proof test.
  • B — incorrect Bleeding trapped air before tightening the cap or plug applies when the proof-test medium is a liquid, not a gas.
  • C — correct Hose tests that use a gas as the proof-test medium are conducted underwater.

BACKGROUND

All flexible hose must be proof-tested after assembly by applying pressure to the inside of the hose assembly. The proof-test medium may be a liquid or a gas: hydraulic, fuel, and oil lines are generally tested with hydraulic oil or water, while air and instrument lines are tested with dry, oil-free air or nitrogen. When testing with a liquid, all trapped air is bled from the assembly before the cap or plug is tightened, and when testing with a gas the test is conducted underwater. In all cases, follow the hose manufacturer's instructions for the proof-test pressure and the fluid to be used for that specific hose assembly. A hose repaired or overhauled with existing hardware and new hose material should be tested to at least 1.5 times system pressure before it is installed on the aircraft.

STUDY TIP

Tie the method to the medium: liquid means bleed the trapped air first, gas means test underwater. Also remember the 1.5 times system pressure figure for a hose rebuilt with existing hardware.

KEY POINTS

  • Every flexible hose assembly is proof-tested after assembly by pressurizing the inside of the assembly.
  • A gas proof test is conducted underwater; a liquid test requires bleeding trapped air before capping.
  • Hose rebuilt with existing hardware and new hose material is tested to at least 1.5 times system pressure before installation.

SOURCES

  • FAA-H-8083-30B ch09 "Flexible Hose Testing"
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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.