What color marking on aircraft tubing identifies it as fabricated from aluminum alloy that should be used for that application?
ACS code: AM.I.D
Correct answer: A stamped code and color band identifying the alloy
Rationale: Aircraft metal tubing is identified by markings stamped or coded on the tube indicating the material and, for aluminum alloy tubing, color bands or codes that identify the specific alloy (such as 1100, 3003, 5052, or 6061). A mechanic must verify the correct material before installation because each alloy has different strength and corrosion characteristics. There is no convention of a single full-length red stripe or a generic yellow end band serving as the material identifier.
When fabricating a replacement rigid fluid line, the bend radius should be kept as large as practical primarily to prevent which condition?
ACS code: AM.I.D
Correct answer: Flattening or wrinkling of the tube wall
Rationale: Bends in metal tubing must be made with as large a radius as practical, and tube benders are used so the tube is not flattened, wrinkled, or kinked. A flattened or wrinkled bend restricts flow and creates a stress concentration that can lead to cracking. Bend radius does not control fitting-nut tension, and the weight difference between a tight and generous bend is negligible.
A flared tube fitting forms its fluid-tight seal at which location?
ACS code: AM.I.D
Correct answer: Between the flare cone and the fitting seat
Rationale: In an AN/MS flared fitting, the tube end is flared to a cone, and the seal is made where that flared cone is compressed against the mating cone-shaped seat of the fitting by the sleeve and coupling nut. The coupling-nut threads only provide the clamping force; they do not seal. The sleeve backs up the flare but does not itself form the fluid-tight joint.
Which flare angle is standard for AN (Army-Navy) flared tube fittings used in aircraft fluid lines?
ACS code: AM.I.D
Correct answer: 37 degrees
Rationale: AN aircraft flared fittings use a 37-degree flare, whereas automotive and some plumbing fittings use a 45-degree flare. Mixing a 37-degree tube flare with a 45-degree fitting (or vice versa) produces a poor seal and can fail under pressure, so the mechanic must match the flare angle to the fitting. The 30-degree value is not a standard aircraft flare angle.
After cutting a length of metal tubing with a tube cutter, the next step before flaring should be to
ACS code: AM.I.D
Correct answer: remove burrs from the inside and outside of the tube
Rationale: After the tube is cut, the ends must be deburred (reamed) inside and out so the metal is smooth before flaring. Burrs left on the tube can cause a defective flare, restrict flow, or break loose and contaminate the system. Annealing every cut end is not required, and applying anti-seize before flaring would contaminate the seating surface.
A flareless (MS) tube fitting depends on which component to bite into the tube and form the seal?
ACS code: AM.I.D
Correct answer: A ferrule or sleeve that cuts into the tube
Rationale: Flareless fittings use a ferrule (sleeve) that, as the nut is tightened, bites into the outer surface of the tube to grip it and form the seal—no flare is made on the tube. This is why flareless tubing must not be over-tightened, which can cut the tube. By definition a flareless joint has no flared cone, and the seal is metal-to-metal through the ferrule rather than an O-ring in the nut.
A flexible hose marked with a lay line (a stripe running along its length) is checked at installation to confirm the hose is not
ACS code: AM.I.D
Correct answer: twisted
Rationale: The lay line is a stripe printed along the length of a flexible hose; if it spirals after installation, the hose has been twisted, which weakens it and can cause early failure. The mechanic installs the hose so the lay line stays straight. The lay line indicates twist, not length or service life—hose age and cure date are read from separate stamped markings.
On a fluid line that carries a hazardous or specific medium, the identifying decals or tape primarily tell the mechanic the
ACS code: AM.I.D
Correct answer: contents and function of the line
Rationale: Aircraft fluid lines are identified by color-coded tape, decals, or bands with words and symbols that indicate the contents (fuel, hydraulic, oxygen, etc.) and the function of the line. This lets a technician quickly recognize what a line carries and handle hazardous fluids correctly. The identification markings do not specify fitting torque or the tubing manufacturer.
Which practice is correct when routing and supporting a fluid line near a moving part or another line?
ACS code: AM.I.D
Correct answer: Support the line with clamps to prevent chafing
Rationale: Fluid lines must be secured with the proper clamps (often cushioned) at the recommended intervals so they cannot chafe against the structure, moving parts, or each other—chafing wears through the tube and causes leaks or failure. A line resting unsupported against structure will rub, and clamping a rigid line under tension induces stress; lines should be supported, not pulled tight.
In aircraft hydraulic systems, a flared-tube connection using a two-piece sleeve and nut is used in place of a one-piece fitting because it eliminates
ACS code: AM.I.D
Correct answer: the possibility of thinning the flare by wiping or ironing during tightening.
Rationale: In a two-piece sleeve-and-nut flare connection the separate sleeve bears against the flare while the nut turns freely on the sleeve, so tightening no longer rubs and thins the flare by wiping or ironing as a one-piece nut would. The flare must still be formed first, so it is the wiping of the flare, not the flaring operation, that is eliminated.
What does the dash number stamped on aluminum tubing fittings and on the size of rigid tubing represent?
ACS code: AM.I.D
Correct answer: The outside diameter in sixteenths of an inch
Rationale: Per FAA-H-8083-30, the size of rigid tubing and fittings is given by the outside diameter in sixteenths of an inch. A dash number such as -8 indicates 8/16 inch (1/2 inch) outside diameter.
Which material is most commonly used for rigid fluid lines carrying hydraulic fluid under high pressure in modern aircraft?
ACS code: AM.I.D
Correct answer: Corrosion-resistant steel
Rationale: Per FAA-H-8083-30, corrosion-resistant steel tubing (either annealed or 1/4-hard) is used extensively in high-pressure hydraulic systems because of its strength, and it does not have to be annealed for flaring or forming.
What is the standard included angle of an AN (Army-Navy) flare on aircraft tubing?
ACS code: AM.I.D
Correct answer: 37 degrees
Rationale: Per FAA-H-8083-30, AN standard fittings and the corresponding tubing flares use a 37-degree flare. This distinguishes AN flares from the 45-degree flares used in automotive and some plumbing applications.
What is the primary purpose of forming a tube bend or a loop in a rigid fluid line near a fitting?
ACS code: AM.I.D
Correct answer: To absorb vibration and allow for expansion and contraction
Rationale: Per FAA-H-8083-30, rigid tubing should not be cut or installed without some slack or a bend to absorb vibration and allow for expansion, contraction, and structural movement; a straight tight run is prone to cracking and fatigue failure.
When a rigid tube has been flattened, dented, or kinked during bending, what is the correct repair action?
ACS code: AM.I.D
Correct answer: Discard the bend and replace the damaged section of tubing
Rationale: Per FAA-H-8083-30, a kink or flattening from a poorly made bend weakens the tube and restricts flow; the damaged section should be removed and replaced rather than reused, because such a bend cannot be safely straightened.
What is the maximum allowable flattening of a tube bend, expressed in terms of the original outside diameter of the tube?
ACS code: AM.I.D
Correct answer: Flattening that reduces the diameter to less than 75 percent of the original OD is not acceptable
Rationale: Per FAA-H-8083-30, the minimum diameter through a bend (the small diameter of the flattened bend) should not be less than 75 percent of the original tube OD; flattening greater than 25 percent is cause for rejection.
A scratch or nick in aluminum alloy tubing is generally acceptable for continued service if it does not exceed what depth of the tube wall thickness?
ACS code: AM.I.D
Correct answer: 10 percent of the wall thickness
Rationale: Per FAA-H-8083-30, scratches or nicks not deeper than 10 percent of the wall thickness in aluminum alloy tubing, and not in the heel of a bend, may be repaired by burnishing; deeper damage requires replacement.
What is the purpose of a flareless (MS) fitting compared to a flared fitting?
ACS code: AM.I.D
Correct answer: It seals by a sleeve biting into the tube, eliminating the need to flare the tubing
Rationale: Per FAA-H-8083-30, flareless fittings (MS) eliminate the need to flare the tubing; instead a sleeve with a sharp cutting edge bites into the tube OD to form the seal, which saves time and is suited to high-pressure systems.
When presetting (preforming) the sleeve on a flareless fitting, how is the tube end prepared before assembly?
ACS code: AM.I.D
Correct answer: Cut square, deburred, and bottomed firmly in the fitting
Rationale: Per FAA-H-8083-30, the tube end must be cut square and deburred, then bottomed firmly in the fitting (or presetting tool) so that the sleeve's cutting edge bites into the tube as the nut is tightened a specified amount.
Which of the following identifies the color coding traditionally used to mark aircraft fluid lines for a HYDRAULIC system?
ACS code: AM.I.D
Correct answer: Blue and yellow
Rationale: Per FAA-H-8083-30, color-coded tape and decals identify line contents. Hydraulic lines are marked with a blue and yellow color band combination, distinguishing them from fuel, oil, and pneumatic lines.
What color is used in the standard color code to identify a FUEL line on an aircraft?
ACS code: AM.I.D
Correct answer: Red
Rationale: Per FAA-H-8083-30, the standard fluid-line identification color code assigns red to fuel lines. The bands of colored tape with the appropriate symbol are applied at intervals and near connections along the line.
In addition to color codes, what is also placed on aircraft fluid line identification tape to aid mechanics who may be color blind?
ACS code: AM.I.D
Correct answer: Geometric symbols and the name of the system
Rationale: Per FAA-H-8083-30, the line identification marking includes geometric symbols (and the word naming the system) in addition to color, so the system can be identified by personnel who are color blind or when working in poor lighting.
When installing flexible hose, why should it be installed with a slight slack (about 5 to 8 percent of the total length)?
ACS code: AM.I.D
Correct answer: Because hose shortens in length and expands in diameter when pressurized
Rationale: Per FAA-H-8083-30, flexible hose contracts in length and expands in diameter when pressurized, so it must be installed with slack (approximately 5 to 8 percent of its length) to prevent it from being pulled taut and stressing the fittings.
How should flexible hose be installed with respect to twisting?
ACS code: AM.I.D
Correct answer: It must be installed without twisting, indicated by a straight lay line
Rationale: Per FAA-H-8083-30, flexible hose must not be twisted on installation because pressure applied to a twisted hose can cause failure or loosen the connections. The lay line (identification stripe) printed along the hose should not spiral, indicating no twist.
The lay line (a stenciled stripe running lengthwise) printed on a flexible hose is used primarily to determine what?
ACS code: AM.I.D
Correct answer: Whether the hose has been twisted during installation
Rationale: Per FAA-H-8083-30, the lay line is a stripe printed along the length of the hose; if it spirals around the hose after installation, the hose has been twisted and must be reinstalled correctly.
What is the function of the support clamps used along a run of rigid tubing?
ACS code: AM.I.D
Correct answer: To secure the line to the structure and prevent vibration and chafing
Rationale: Per FAA-H-8083-30, support clamps secure tubing lines to the airframe structure to prevent excessive vibration and chafing; clamps with cushioned (synthetic rubber) inserts are used to protect the tubing.
When tightening a flared tube nut on an AN fitting, what is the result of overtightening?
ACS code: AM.I.D
Correct answer: It can split or crack the flare and cause leakage
Rationale: Per FAA-H-8083-30, overtightening a flared tube nut can split the flare or damage the fitting cone, causing leakage; the nut should be tightened to the specified torque using a torque wrench whenever possible.
When making up a flared-tube connection, what is the purpose of using a backup wrench on the fitting while tightening the tube nut?
ACS code: AM.I.D
Correct answer: To prevent the fitting body from turning and twisting the tube
Rationale: Per FAA-H-8083-30, a second (backup) wrench is held on the connector or fitting body to prevent it from turning while the nut is torqued; this avoids twisting and stressing the tube and the mating part.
What thread sealant or lubricant practice applies to tapered pipe-thread (NPT) fittings used in fluid systems?
ACS code: AM.I.D
Correct answer: Apply approved sealant to the male threads but keep it off the first two threads
Rationale: Per FAA-H-8083-30, an approved thread lubricant or sealant is applied to the male tapered pipe threads, but never to the first two threads, to prevent the sealant from entering and contaminating the system.
Aluminum alloy 1100 (1/2 hard) or 3003 tubing is generally used for fluid lines that carry fluid under what condition?
ACS code: AM.I.D
Correct answer: Relatively low pressure, such as instrument and vent lines
Rationale: Per FAA-H-8083-30, soft aluminum alloys 1100 and 3003 are used for lines carrying fluid at relatively low pressures, such as instrument lines and ventilation, while stronger alloys (2024-T, 5052-O) or steel are used for higher pressures.
After cutting rigid tubing with a tube cutter or hacksaw, what step is essential before flaring the tube?
ACS code: AM.I.D
Correct answer: Deburr the inside and outside of the tube end
Rationale: Per FAA-H-8083-30, the cut tube ends must be deburred (inside and outside) to remove sharp edges and burrs; failure to deburr can restrict flow and cause a poor flare that leaks.
Why should a fine-tooth hacksaw or a tube cutter, rather than a coarse-tooth blade, be used when cutting aircraft tubing?
ACS code: AM.I.D
Correct answer: To produce a square, clean cut with minimal burr and distortion
Rationale: Per FAA-H-8083-30, a tube cutter or a fine-tooth saw produces a square, clean cut with minimal burr and distortion; a coarse blade tends to tear the metal and leave excessive burrs that are difficult to remove.
When proof-testing a fabricated flexible hose assembly, the test pressure is generally set at what value relative to the hose's normal operating pressure?
ACS code: AM.I.D
Correct answer: Twice the maximum operating pressure
Rationale: Per FAA-H-8083-30, a newly fabricated hose assembly is proof-tested at twice (200 percent of) the maximum operating pressure to verify the integrity of the assembly before installation, without reaching the burst pressure.
What does a TEFLON (PTFE) flexible hose require special care to avoid after it has been installed and taken a set in a bent position?
ACS code: AM.I.D
Correct answer: It should not be straightened or rebent, because the liner can crack at the set
Rationale: Per FAA-H-8083-30, once a Teflon hose has been pressurized and has taken a permanent set, it should not be straightened or rebent, because the PTFE liner can crack or kink at the set; such a hose must be reinstalled in the same configuration.
Which statement about routing fluid lines relative to electrical wiring is correct?
ACS code: AM.I.D
Correct answer: Fluid lines should be routed below and away from electrical wiring
Rationale: Per FAA-H-8083-30, fluid lines (especially fuel, oil, and hydraulic) should be routed below and away from electrical wiring so that any leaking fluid will not drip onto wiring and create a fire or electrical hazard.
Bonding clamps used on metal fluid lines serve what purpose in addition to support?
ACS code: AM.I.D
Correct answer: They provide an electrical bonding path to the airframe for static charges
Rationale: Per FAA-H-8083-30, metal (unbonded) clamps used for bonding provide an electrical ground path so that static charges and stray currents are conducted to the airframe; the contact surfaces must be clean and free of paint or anodizing to ensure conductivity.
When a section of damaged rigid aluminum tubing must be repaired in the field and a replacement tube cannot be fabricated, what fitting may be used to splice in a repair section?
ACS code: AM.I.D
Correct answer: A standard flared-tube union joining a new flared repair section
Rationale: Per FAA-H-8083-30, a damaged tube section can be replaced or spliced using standard AN/MS unions (such as a flared-tube union) together with a new length of tubing flared at each end; the union connects the repair section to the existing line.