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Tubing material for 3,000 psi hydraulic systems

Aviation Mechanic General (AMG) practice question 7 of 17 on Fluid Lines and Fittings. ACS element AM.I.D.K1 · 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 mechanic is replacing a rigid line in a 3,000 psi hydraulic system that operates the landing gear. Which tubing material does the handbook describe as used extensively for this kind of service?

  1. A1100 H14 aluminum alloy, the general purpose tubing
  2. B5052-O aluminum alloy
  3. CCorrosion-resistant steel such as CRES 304
Show the answer and explanation

Correct answer: C. Corrosion-resistant steel such as CRES 304

  • A — incorrect 1100 H14 (1/2-hard) tubing is used for lines of low or negligible pressure such as instrument lines and ventilating conduits, not 3,000 psi hydraulics.
  • B — incorrect 5052-O, like 2024-T3 and 6061-T6, is used in low and medium pressure systems of 1,000 to 1,500 psi and for fuel and oil lines, not in 3,000 psi hydraulic systems.
  • C — correct The handbook states that corrosion-resistant steel tubing (annealed CRES 304, CRES 321 or CRES 304-1/8-hard) is used extensively in high-pressure hydraulic systems of 3,000 psi or more for landing gear, flaps and brakes.

BACKGROUND

Modern aircraft use aluminum alloy, corrosion-resistant steel (CRES) or titanium tubing in place of the copper used in early aviation. Aluminum alloys 1100 H14 and 3003 H14 serve low or negligible pressure lines, while 2024-T3, 5052-O and 6061-T6 serve low and medium pressure systems of roughly 1,000 to 1,500 psi. Corrosion-resistant steel (annealed CRES 304, CRES 321 or CRES 304-1/8-hard) is used extensively in high-pressure hydraulic systems of 3,000 psi or more that operate landing gear, flaps and brakes, and in fire zones. Its higher tensile strength permits thinner walls, so installed weight is not much greater than thick-wall aluminum tubing. Steel lines are also chosen where foreign object damage is a risk, such as landing gear and wheel well areas.

STUDY TIP

Link pressure ranges to materials: negligible pressure means 1100/3003, up to about 1,500 psi means 2024/5052/6061, and 3,000 psi or more means CRES or titanium.

KEY POINTS

  • CRES 304, 321 and 304-1/8-hard tubing is used in 3,000 psi and higher hydraulic systems.
  • Aluminum alloys 2024-T3, 5052-O and 6061-T6 serve 1,000 to 1,500 psi systems.
  • Steel is also used where FOD is a risk, such as landing gear and wheel wells.

SOURCES

  • FAA-H-8083-30B ch09 "Rigid Fluid Lines - Tubing Materials" (Aluminum Alloy Tubing, Steel)
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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.