When performing nondestructive inspection, which method is best suited for detecting surface and slightly subsurface cracks in ferromagnetic steel parts?
ACS code: AM.I.K
Correct answer: magnetic particle inspection
Rationale: Magnetic particle inspection relies on magnetizing a ferromagnetic part so that a crack distorts the magnetic field and creates leakage fields that attract iron particles, revealing the flaw. Because it works only on materials that can be magnetized, it is the preferred method for steel parts and can show surface and slightly subsurface defects. Liquid penetrant detects only flaws open to the surface, and ultrasonic gauging is primarily used to measure thickness rather than reveal small cracks visually.
Liquid penetrant inspection is capable of detecting defects only when those defects are:
ACS code: AM.I.K
Correct answer: open to the surface of the part
Rationale: Liquid penetrant inspection works by drawing dye into a discontinuity by capillary action, then drawing it back out with a developer to form a visible indication. The dye can only enter a flaw that breaks the surface, so the method finds only surface-connected defects. Subsurface flaws and any defect hidden under paint or primer cannot trap or release penetrant and so go undetected.
Which inspection method uses high-frequency sound waves to locate internal flaws and measure the thickness of a part?
ACS code: AM.I.K
Correct answer: ultrasonic inspection
Rationale: Ultrasonic inspection introduces high-frequency sound waves into a part and analyzes the energy that reflects from the back surface or from an internal discontinuity, allowing both flaw detection and thickness measurement. Eddy current uses induced electrical currents rather than sound, and radiographic inspection uses X-rays or gamma rays passing through the part to expose film.
Eddy current inspection detects discontinuities in a part by sensing changes in:
ACS code: AM.I.K
Correct answer: an induced electromagnetic field in the part
Rationale: Eddy current inspection passes alternating current through a coil to induce circulating eddy currents in a conductive part. A crack or change in conductivity alters those currents, changing the coil's electromagnetic field, which the instrument senses. Reflected sound is the basis of ultrasonic inspection, and drawing dye from cracks describes penetrant inspection.
When inspecting an engine cylinder for internal cracks and other defects without disassembly, a mechanic would most likely use a:
ACS code: AM.I.K
Correct answer: borescope
Rationale: A borescope is an optical instrument that allows a mechanic to view internal areas of an engine, such as cylinder walls and valves, through small access openings without disassembly, making it ideal for finding cracks, pitting, or other internal damage. A dial indicator measures small linear movement or runout, and a micrometer measures external or internal dimensions, neither of which provides a visual view inside the cylinder.
Radiographic (X-ray) inspection is particularly useful because it can reveal defects that are:
ACS code: AM.I.K
Correct answer: located internally within the part
Rationale: Radiographic inspection passes penetrating radiation through a part onto film or a sensor, where internal voids, cracks, and inclusions show as density changes. This makes it valuable for finding flaws buried inside a part that surface methods cannot reach. Surface-only flaws are the realm of penetrant inspection, and the method is not restricted to magnetic materials the way magnetic particle inspection is.
When tapping a bonded honeycomb structure during a coin-tap inspection, a dull or dead sound generally indicates:
ACS code: AM.I.K
Correct answer: a separation or void within the bonded area
Rationale: In the coin-tap (ring) test, a coin or light tapping tool is moved across a bonded or honeycomb structure while the inspector listens. A clear, sharp ring indicates sound bonding, while a dull or dead thud signals a disbond, delamination, or void beneath the surface. A dull sound does not indicate a good bond, and surface corrosion is detected by visual rather than tapping methods.
Good lighting and a clean part surface are important to a visual inspection primarily because they:
ACS code: AM.I.K
Correct answer: make small defects easier to see
Rationale: Visual inspection is the most widely used method, and its effectiveness depends on the inspector being able to see clearly. Adequate lighting and a clean surface free of dirt, grease, and old paint expose cracks, corrosion, and other small defects that would otherwise be hidden. Cleaning and lighting do not change how often an inspection must be done, and inspection results must still be documented in the maintenance records.
A dial indicator is calibrated to an accuracy of 0.001 inch. When using the gauge, you should
ACS code: AM.I.K
Correct answer: round the reading to the calibrated value of 0.001 inch.
Rationale: A measuring instrument can only be read meaningfully to its calibrated accuracy. Since the dial indicator is accurate to 0.001 inch, readings should be reported to that level; claiming additional decimal places implies precision the instrument does not have. See FAA-H-8083-30, Inspection Concepts and Techniques.
After magnetic particle inspection, how is residual magnetism removed from a steel part?
ACS code: AM.I.K
Correct answer: By degaussing (demagnetizing) the part
Rationale: Magnetic particle inspection leaves the part magnetized, so it must be demagnetized (degaussed) afterward by passing it through a decaying alternating field. Residual magnetism could otherwise attract metallic debris or disturb nearby instruments.
During a Rockwell hardness test, what dimension of the indentation is measured to determine hardness?
ACS code: AM.I.K
Correct answer: The depth of the indentation.
Rationale: The Rockwell test presses an indenter under a fixed load and reads hardness directly from the depth of penetration, with a deeper indent meaning a softer material. This differs from the Brinell and Vickers tests, which optically measure the diameter or diagonal of the impression rather than its depth.
On a hollow tubular structural member, a small dent or indentation is normally least acceptable when located
ACS code: AM.I.K
Correct answer: in the middle third of the tube's length.
Rationale: Per FAA-H-8083-30, on a hollow tube the center region carries the greatest bending stress, so an indentation there is the most damaging and is normally unacceptable. Small dents nearer the supported ends, in the outer thirds, are less critical because the bending moment and resulting stress concentration are lower.
When stop-drilling the end of a crack to arrest its propagation, what is the typical drill size used?
ACS code: AM.I.K
Correct answer: 0.125 inch
Rationale: Stop-drilling arrests crack propagation by removing the sharp stress concentration at the crack tip with a rounded hole; a hole of about 0.125 inch (1/8 inch) is the typical size used. A much smaller hole leaves too sharp a tip, while an oversized hole removes unnecessary material and weakens the part, per FAA-H-8083-30 inspection practice.
When taking an internal measurement with a vernier caliper, how is the dimension of the measuring jaws (nibs) that must be added to the reading determined?
ACS code: AM.I.K
Correct answer: By reading the dimension engraved on the instrument.
Rationale: When taking an internal measurement, the combined width of the caliper's measuring jaws must be added to the scale reading. That jaw dimension is established by the manufacturer and is engraved or stamped on the instrument, so it is read directly from the caliper rather than measured or assumed.
Why must test and inspection instruments be regularly calibrated and certified?
ACS code: AM.I.K
Correct answer: To ensure they perform within the required limits of accuracy.
Rationale: Calibration against a traceable reference confirms that an instrument still reads accurately within its specified tolerance, so any measurement or test made with it can be trusted, and certification records that check. The purpose is to prove the readings stay within required limits, not simply to exercise the instrument or its full measuring range.
The calibration intervals for inspection and test equipment
ACS code: AM.I.K
Correct answer: differ from one piece of equipment to another.
Rationale: Calibration intervals are established according to each instrument's type, stability, and how heavily it is used, so they differ from one piece of equipment to another rather than following a single fixed period. A twelve-month interval applies to some items but is not a universal rule.
The separation between the individual plies (layers) of a composite laminate is called
ACS code: AM.I.K
Correct answer: delamination.
Rationale: Separation between the plies of a laminate is termed delamination, whereas debonding refers to the adhesive bondline between separate parts, such as a skin and core, letting go. Because this concerns the layers parting, delamination is the correct term.
Which methods can be used to inspect fiberglass/honeycomb structures for entrapped water?
ACS code: AM.I.K
Correct answer: X-ray and back-lighting.
Rationale: Per FAA-H-8083-30, entrapped water in fiberglass/honeycomb panels is detected by X-ray, where the denser water shows as a shadow, and by back-lighting (shining a strong light through the translucent laminate) so trapped moisture appears as dark areas. Acoustic emission monitors crack growth under load and is not a moisture-detection method.
One method of inspecting a laminated fiberglass structure that has been subjected to damage is to
ACS code: AM.I.K
Correct answer: strip the damaged area of paint and shine a strong light through the structure.
Rationale: Fiberglass laminate is translucent, so per FAA-H-8083-30 a common damage inspection is to strip the paint and shine a strong light through it; delaminations, cracks, and resin-starved areas show up as differences in light transmission. Eddy current works only on conductive metals, and dye penetrant detects only surface-breaking flaws.
When inspecting a composite panel using the ring test (coin-tap) method, a dull thud may indicate
ACS code: AM.I.K
Correct answer: separation of the laminates.
Rationale: Per FAA-H-8083-30, in the coin-tap (ring) test a sound bonded laminate rings clearly while a dull or flat thud indicates a void or delamination, because the disbonded skin is not coupled to the core and damps the sound. The dull response specifically points to separation of the laminates.
With what would you check the bonded joints of a wooden aircraft structure for separation?
ACS code: AM.I.K
Correct answer: A feeler gauge.
Rationale: Glued joints in a wooden aircraft structure are checked for separation by attempting to insert a thin feeler gauge into the glue line; if the blade enters, the bond has opened or failed. A plastic strip or screwdriver lacks the calibrated thinness needed to assess the joint properly, per FAA-H-8083-30.
To carry out a full inspection of a fabric-covered wooden aircraft structure for deterioration, you would first
ACS code: AM.I.K
Correct answer: remove the fabric or cloth covering before inspection.
Rationale: A full inspection of a wooden structure for deterioration requires removing the fabric or cloth covering so the wood, glued joints, and fittings underneath can be seen and assessed, per FAA-H-8083-30. Hangaring or jacking the aircraft does not expose the structure, and the covering would still hide defects.
How is the moisture content within the wood of a wooden aircraft structure determined?
ACS code: AM.I.K
Correct answer: By inserting the probe of an electrical moisture meter.
Rationale: Moisture content of structural wood is measured by inserting the probe of an electrical moisture meter, which reads the wood's moisture directly and non-destructively in place. Judging water stains is unreliable, and weighing an assembled structure before and after drying is impractical, per FAA-H-8083-30.
To determine whether a wooden aircraft surface has compound curvature, you would use
ACS code: AM.I.K
Correct answer: a sheet of paper.
Rationale: A surface is single-curvature if a flat sheet of paper can be wrapped onto it without wrinkling, and compound (double) curvature if it cannot lie flat without creasing. Laying a sheet of paper on the surface is therefore the simple check for compound curvature.
A faint line running across the grain of a wood spar generally indicates
ACS code: AM.I.K
Correct answer: a compression failure.
Rationale: A faint line running across (at right angles to) the grain marks where the wood fibers have buckled under a compression overload. The FAA treats such compression failures as a serious, easily missed defect that drastically reduces strength; they are distinct from shear or decay, which show different indications.
Pin knot clusters are permitted in aircraft wood structure provided
ACS code: AM.I.K
Correct answer: they produce only a small effect on grain direction.
Rationale: The FAA permits pin-knot clusters in aircraft wood only when they are small enough to produce only a minor local effect on grain direction. If a cluster significantly disturbs the grain it concentrates stress and weakens the member, and is then rejected.
Compression failures in wood aircraft structures appear as buckled fibers that run
ACS code: AM.I.K
Correct answer: at right angles to the grain.
Rationale: A compression failure buckles the longitudinal fibers, producing wrinkle-like streaks that run across the wood, at right angles to the grain. Per the FAA, inspecting for these cross-grain streaks is the standard check for hidden compression damage in wooden spars.
A measuring tool is found to be reading outside its calibrated limits. The technician should
ACS code: AM.I.K
Correct answer: remove it from service, tag it unserviceable, and send it for recalibration.
Rationale: A tool found outside its calibrated limits must be removed from use immediately, clearly tagged unserviceable to prevent inadvertent use, and sent for repair or recalibration. The technician must not adjust it on site, and returning it to stock while still in service could allow defective measurements to be accepted.
The runout of a rotating shaft is most accurately measured using a
ACS code: AM.I.K
Correct answer: dial indicator with a surface plate and V-blocks.
Rationale: Runout is the total movement of a surface as the part is rotated, so it is read with a dial indicator. The shaft is supported on V-blocks set on a surface plate to provide a true axis of rotation while the dial indicator registers the variation. A micrometer or vernier caliper measures size, not rotational runout.
When using a vernier caliper with nibbed jaws to take an inside (internal) measurement, the technician must
ACS code: AM.I.K
Correct answer: add the combined nib width to the scale reading.
Rationale: The inside-measuring jaws (nibs) of a vernier caliper have a finite combined width, so for an internal measurement the nib width must be added to the scale reading to obtain the true bore dimension. For an external measurement the jaws close to zero, so nothing is added (FAA-H-8083-30, Inspection Concepts and Techniques).
A vernier height gauge measures using the same dual-scale principle as the
ACS code: AM.I.K
Correct answer: vernier caliper.
Rationale: A vernier height gauge measures by sliding a scribing jaw up a graduated beam and reading a vernier scale against the main scale, exactly the dual-scale principle of the vernier caliper. A bevel protractor measures angles and a depth micrometer uses a screw thread, so neither shares this reading principle (FAA-H-8083-30, Inspection Concepts and Techniques).
One complete revolution of the thimble of a standard inch (English) micrometer moves the spindle a distance of
ACS code: AM.I.K
Correct answer: 0.025 inch.
Rationale: An inch micrometer spindle has a 40-thread-per-inch screw, so one full turn of the thimble moves the spindle 1/40 inch, which equals 0.025 inch. The thimble is then divided into 25 parts, so each division reads 0.001 inch (FAA-H-8083-30, Inspection Concepts and Techniques).
On a standard inch-graduated micrometer, the pitch of the spindle screw thread is
ACS code: AM.I.K
Correct answer: 0.025 inch.
Rationale: An inch micrometer spindle has 40 threads per inch, giving a pitch of 1/40 inch, or 0.025 inch. One full revolution of the thimble therefore advances the spindle 0.025 inch. The 0.0001 and 0.050 inch values do not correspond to the standard 40-thread-per-inch micrometer screw.
The vernier scale on a standard inch-graduated vernier caliper is divided into
ACS code: AM.I.K
Correct answer: 25 equal divisions.
Rationale: On an inch vernier caliper the vernier scale is divided into 25 equal divisions that span 24 of the smallest main-scale divisions. This one-part difference per division yields the 0.001 inch reading resolution. The 40- and 50-division layouts belong to other instruments, not the standard inch vernier caliper.
The thimble of a metric micrometer is divided into
ACS code: AM.I.K
Correct answer: 50 equal divisions.
Rationale: The thimble of a metric micrometer is divided into 50 equal divisions. Because one thimble revolution moves the spindle 0.5 mm, each division represents 0.01 mm, which is the instrument's resolution. Twenty-five or forty divisions would not give the standard 0.01 mm metric reading.
The measuring capacity of a vernier caliper is equal to
ACS code: AM.I.K
Correct answer: the length of the main graduated scale minus the length of the vernier scale.
Rationale: A vernier caliper can read only where the vernier scale still overlaps the main graduated scale, so its usable measuring capacity is the length of the main scale minus the length of the vernier scale. Counting the full main scale or adding the jaw width would overstate what the instrument can actually measure.
V-blocks used to support round work for layout and measurement are manufactured
ACS code: AM.I.K
Correct answer: in matched sets of two and identified for use as a set.
Rationale: V-blocks are made and matched in pairs and marked so they are kept and used together, ensuring both blocks are exactly the same height to support a round workpiece accurately. Mixing a block with one from another pair could introduce a height difference and spoil the measurement, so they are not interchangeable.
On an inch vernier caliper whose vernier covers 24 main-scale divisions of 0.025 inch each, the length of the vernier scale is
ACS code: AM.I.K
Correct answer: 0.6 inch.
Rationale: The vernier scale spans 24 of the smallest main-scale divisions, each 0.025 inch, so its length is 24 multiplied by 0.025 inch, which equals 0.6 inch. The 1.2 and 2.45 inch figures do not correspond to 24 of those 0.025-inch divisions.
Which instrument is used to measure the depth of a blend after a corrosion repair?
ACS code: AM.I.K
Correct answer: A dial indicator.
Rationale: A dial indicator is set on a flat reference surface and its plunger run across the blended area to read the depth of the depression directly from the dial. A gauge-block set provides only fixed thicknesses and a vernier caliper measures lengths or diameters, so neither directly reads blend depth.
Why is a V-cut machined into the base of a surface gauge (scribing block)?
ACS code: AM.I.K
Correct answer: To trap any dirt or chips that may be on the surface of the layout plate.
Rationale: Per FAA-H-8083-30, a surface gauge must bed flat and square against the layout plate to scribe an accurate line. The V-groove in the base lets any small chips or dirt on the plate sit clear within the groove so the base still seats firmly, preventing the gauge from rocking on trapped debris.
A dial test indicator is most appropriately used for
ACS code: AM.I.K
Correct answer: checking a rotating round bar for bow or run-out.
Rationale: Per FAA-H-8083-30, a dial indicator reads small plunger movements relative to a reference. A round bar can be rotated against the stylus and any bow or run-out shows up as needle deflection. Its fine scale measures small relative variations, not coarse fixed steps and not absolute depths from a datum.
A key-seat rule is used for
ACS code: AM.I.K
Correct answer: scribing lines parallel to the axis of a round bar.
Rationale: Per FAA-H-8083-30, a key-seat rule has a stepped or angled section that registers against a round bar so a line can be scribed parallel to the bar's axis, as when laying out a keyway. A plain rule against flat stock or a driving dog serve other purposes and do not register on the curved surface of a shaft.
A three-point (bore) micrometer is designed to measure
ACS code: AM.I.K
Correct answer: internal dimensions, such as bore diameters.
Rationale: Per FAA-H-8083-30, a three-point micrometer has three measuring anvils that expand outward to contact a bore at three equally spaced points, self-centering in the hole to give an accurate internal-diameter reading. The three-point contact removes the alignment errors that two-point internal gauges can suffer.
To inspect the interior of a closed tubular structural member for corrosion attack,
ACS code: AM.I.K
Correct answer: ultrasonic testing is used to measure the remaining wall thickness.
Rationale: The inside of a closed tubular member cannot be seen directly, so ultrasonic testing is used to measure remaining wall thickness and reveal internal corrosion through the tube wall. Dye penetrant only finds surface-breaking defects, and not every form of test is suitable for a hidden bore. (FAA-H-8083-30, Inspection Concepts and Techniques.)
Corrosion is suspected in a thin composite flap panel. The most suitable nondestructive method to detect it is
ACS code: AM.I.K
Correct answer: low-voltage (soft) X-ray inspection.
Rationale: Corrosion in a thin composite flap panel is best revealed by low-voltage (soft) X-ray, whose longer wavelength gives good contrast for the low-density materials and corrosion products involved. High-voltage X-ray is suited to dense or thick metal, and a coin-tap test finds disbonds rather than corrosion. (FAA-H-8083-30, Inspection Concepts and Techniques.)