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Iran CAO Part-66 AMT Theory study materials
Iran CAO Part-66 AMT Theory study resources

Iran CAO Part-66 AMT Theory practice questions

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Question 1Mathematics

An aircraft maintenance engineer converts a torque value of 55 N·m into pound-force inches using 1 N·m ≈ 8.851 lbf·in. Which result is correct to three significant figures?

  1. 487 lbf·in Correct answer.
  2. 46.5 lbf·in
  3. 0.00114 lbf·in
  4. 6.21 lbf·in

Explanation

Multiplying 55 by 8.851 gives approximately 486.8 lbf·in, which rounds to 487 lbf·in to three significant figures. The conversion factor multiplies newton-metres to obtain pound-force inches, so the numerical value must increase.

Question 2Mathematics

A rectangular access panel on an engine cowling measures 0.42 m by 0.18 m. What is its area in square centimetres?

  1. 7 560 cm²
  2. 0.0756 cm²
  3. 75.6 cm²
  4. 756 cm² Correct answer.

Explanation

Convert each dimension to centimetres first: 0.42 m = 42 cm and 0.18 m = 18 cm. Multiplying 42 by 18 gives 756 cm². Squaring the linear conversion factor of 100 is equivalent and confirms the result.

Question 3Mathematics

A component weighs 3.6 kg and its centre of gravity lies 0.25 m from a datum. Taking g as 9.81 m/s², what is the moment of its weight about the datum?

  1. 35.3 N·m
  2. 88.3 N·m
  3. 8.83 N·m Correct answer.
  4. 0.90 N·m

Explanation

Weight equals mass times gravitational acceleration: 3.6 × 9.81 ≈ 35.3 N. The moment is weight times the lever arm: 35.3 × 0.25 ≈ 8.83 N·m. Note that the moment uses force, not mass, so the gravitational factor must be applied.

Question 4Mathematics

A hydraulic actuator develops a force of 12 500 N acting on a piston area of 0.005 m². Expressed in bar, what pressure does the fluid exert?

  1. 2 500 bar
  2. 25 bar Correct answer.
  3. 250 bar
  4. 2.5 bar

Explanation

Pressure equals force divided by area: 12 500 ÷ 0.005 = 2 500 000 Pa, that is 2 500 kPa. Since 1 bar equals 100 kPa, dividing by 100 gives 25 bar. Checking the units confirms the result is physically reasonable for an aircraft hydraulic system.

Question 5Physics

An aircraft climbs at a constant 5 m/s while its horizontal ground speed is 12 m/s. What is the magnitude of its velocity relative to the ground?

  1. 60 m/s
  2. 7 m/s
  3. 13 m/s Correct answer.
  4. 17 m/s

Explanation

The vertical and horizontal velocity components are perpendicular, so they combine as the hypotenuse of a right triangle: v = sqrt(5^2 + 12^2) = sqrt(169) = 13 m/s. Simple addition of the components would only be valid if they acted along the same line.

Question 6Physics

A maintenance trolley of mass 40 kg is pushed across a level hangar floor with a constant horizontal force of 120 N. Friction is negligible. What is the acceleration of the trolley?

  1. 4.8 m/s^2
  2. 3.0 m/s^2 Correct answer.
  3. 4800 m/s^2
  4. 0.33 m/s^2

Explanation

Newton's second law states that the resultant force equals mass times acceleration, so a = F/m = 120 N / 40 kg = 3.0 m/s^2. Because the force is horizontal and friction is negligible, the whole applied force produces acceleration.

Question 7Physics

A sealed hydraulic jack has a small piston of area 5 cm^2 and a large piston of area 200 cm^2. A force of 80 N is applied to the small piston. Ignoring losses, what force is produced at the large piston?

  1. 2 N
  2. 320 N
  3. 3200 N Correct answer.
  4. 16 000 N

Explanation

Pascal's principle states that pressure is transmitted undiminished through a confined fluid, so F1/A1 = F2/A2. The area ratio is 200/5 = 40, hence F2 = 80 N x 40 = 3200 N. The force is multiplied by the same ratio as the piston areas.

Question 8Physics

A body is in translational equilibrium under the action of several coplanar forces. Which statement must be true?

  1. The vector sum of all forces is zero and the sum of moments about any point is zero Correct answer.
  2. The sum of moments about the centre of gravity is zero, but the forces may have a resultant
  3. The forces must all act through a single common point
  4. The vector sum of all forces is zero, but moments need not balance about every point

Explanation

For complete static equilibrium, both conditions must hold: the resultant force must be zero and the resultant moment about any chosen point must also be zero. If moments balanced about only one point while a couple existed, the body would rotate. Concurrent forces are sufficient for force balance but do not by themselves guarantee moment balance.

Question 9Electrical Fundamentals

In an aircraft DC circuit, a resistor carries a current of 2 A when the potential difference across it is 24 V. What is the resistance of the resistor?

  1. 48 Ω
  2. 0.083 Ω
  3. 12 Ω Correct answer.
  4. 6 Ω

Explanation

Ohm's law states that resistance equals voltage divided by current, so R = V / I = 24 V / 2 A = 12 Ω. This is the fundamental relationship used when checking resistive loads and circuit protection in aircraft DC systems.

Question 10Electrical Fundamentals

Which statement correctly describes the behaviour of a capacitor in a steady DC circuit once it is fully charged?

  1. It behaves as an open circuit and blocks further steady current. Correct answer.
  2. It behaves as a short circuit and carries full current.
  3. It behaves as a fixed resistor of low value.
  4. It behaves as a voltage source that reverses polarity.

Explanation

A capacitor stores energy in its electric field; once the voltage across it equals the applied DC voltage, no further charging current flows, so it acts as an open circuit to steady DC. This blocking property is why capacitors are used for DC isolation and filtering in avionics supply lines.

Question 11Electrical Fundamentals

Two resistors of 6 Ω and 3 Ω are connected in parallel across a 12 V supply. What is the total current drawn from the supply?

  1. 6 A Correct answer.
  2. 1.33 A
  3. 9 A
  4. 4 A

Explanation

In a parallel circuit each branch sees the full 12 V, so the branch currents are 12/6 = 2 A and 12/3 = 4 A, giving a total of 6 A. Equivalently the equivalent resistance is 2 Ω, and 12 V / 2 Ω = 6 A.

Question 12Electrical Fundamentals

An inductor of 0.5 H carries a current that increases steadily at 4 A per second. What is the magnitude of the induced back EMF across the inductor?

  1. 0.5 V
  2. 2 V Correct answer.
  3. 8 V
  4. 0.125 V

Explanation

The induced EMF in an inductor is given by e = L × (di/dt). Substituting L = 0.5 H and di/dt = 4 A/s gives e = 2 V, opposing the change in current according to Lenz's law.

Question 13Electrical Fundamentals

In a purely capacitive AC circuit, how does the current relate to the applied voltage?

  1. Current is in phase with the voltage.
  2. Current leads the voltage by 90 degrees. Correct answer.
  3. Current lags the voltage by 90 degrees.
  4. Current leads the voltage by 45 degrees.

Explanation

In a capacitor, current is proportional to the rate of change of voltage, so the current reaches its peak a quarter cycle before the voltage. This gives a 90-degree phase lead of current over voltage, described by the mnemonic CIVIL for capacitive circuits.

Question 14Electrical Fundamentals

A transformer has 400 turns on its primary winding and 100 turns on its secondary. If the primary is supplied with 230 V AC, what is the secondary voltage, assuming an ideal transformer?

  1. 57.5 V Correct answer.
  2. 920 V
  3. 575 V
  4. 92 V

Explanation

For an ideal transformer the voltage ratio equals the turns ratio: Vs/Vp = Ns/Np. Here 100/400 = 0.25, so Vs = 230 V × 0.25 = 57.5 V, a step-down result consistent with fewer secondary turns.

Question 15Electrical Fundamentals

A three-phase aircraft AC generator is connected in star (wye). If the phase voltage is 115 V, what is the line voltage?

  1. 199 V Correct answer.
  2. 66 V
  3. 115 V
  4. 230 V

Explanation

In a star connection the line voltage equals the phase voltage multiplied by the square root of three, so 115 V × 1.732 ≈ 199 V. This relation is why 115 V phase systems produce roughly 200 V line-to-line, a standard aircraft AC supply value.

Question 16Electrical Fundamentals

A series RLC circuit is at resonance. Which statement best describes its behaviour at that frequency?

  1. The impedance is at a maximum and the current is at a minimum.
  2. Inductive reactance exceeds capacitive reactance and the circuit is inductive.
  3. The impedance equals the resistance and the current is at a maximum. Correct answer.
  4. The total reactance is doubled and the power factor is zero.

Explanation

At resonance the inductive and capacitive reactances are equal in magnitude and cancel, so the net reactance is zero and impedance reduces to the resistance alone. The circuit is therefore purely resistive, the power factor is unity, and the current reaches its maximum for a given supply voltage.

Question 17Electronic Fundamentals

In a Part-66 avionics context, a bipolar junction transistor is described as a current-controlled device. Which terminal current actually controls the collector current in the active region?

  1. Emitter current
  2. Substrate leakage current
  3. Base current Correct answer.
  4. Collector current

Explanation

In the active region the base-emitter junction is forward biased and the collector-base junction is reverse biased. The collector current is set by the base current multiplied by the forward current gain hFE, so the base is the control terminal. Emitter current is the sum of base and collector currents, not the controlling quantity.

Question 18Electronic Fundamentals

A maintenance technician measures the forward voltage of a silicon rectifier diode in a circuit and reads about 0.7 V while it conducts. What does this reading primarily indicate about the junction?

  1. The junction is forward biased and conducting normally. Correct answer.
  2. The diode is operating in avalanche breakdown.
  3. The diode is reverse biased and leaking.
  4. The diode has failed short circuit.

Explanation

A forward-biased silicon PN junction develops a barrier potential of roughly 0.6 to 0.7 V when conducting. Reading approximately 0.7 V across a conducting silicon diode is therefore the expected normal condition. A shorted diode would show almost zero volts, and a reverse-biased or avalanching device would not sit at this value.

Question 19Electronic Fundamentals

An aircraft DC generator feeds a load through a bridge rectifier. Compared with a half-wave rectifier using the same transformer, what is the principal electrical advantage of the full-wave bridge configuration?

  1. It removes the need for a smoothing capacitor entirely.
  2. It doubles the peak inverse voltage seen by each diode.
  3. It produces ripple at twice the supply frequency with a higher mean output. Correct answer.
  4. It allows the output to be taken without a return path.

Explanation

A full-wave bridge rectifies both half cycles, so the output ripple repeats at twice the input frequency and the mean DC level is higher for the same secondary voltage. Each diode still only sees approximately the peak secondary voltage in reverse, which is lower than in a centre-tapped arrangement. Smoothing is still required to reduce ripple.

Question 20Electronic Fundamentals

A zener diode is used to regulate a 12 V rail. The measured rail rises to 12.9 V when the load is disconnected. Which explanation best fits this observation?

  1. The zener is operating below its knee current and cannot clamp.
  2. The zener has been installed with reverse polarity.
  3. The zener voltage tolerance and dynamic resistance allow a small rise at light load. Correct answer.
  4. The zener is being run at a current above its rated maximum.

Explanation

A real zener has a tolerance band and a finite dynamic resistance, so the clamped voltage rises slightly as current falls toward the knee. A 0.9 V rise at no load is consistent with a device whose nominal value is near 12 V. Operation below knee current would cause a much larger rise toward the unregulated input.

Question 21Electronic Fundamentals

Which statement correctly describes the function of the lightly doped collector drift region in a power MOSFET designed for aircraft power switching?

  1. It provides the channel in which inversion occurs.
  2. It isolates the gate from the source metallisation.
  3. It stores charge to speed up turn-off.
  4. It increases the breakdown voltage while adding on-resistance. Correct answer.

Explanation

In a vertical power MOSFET the lightly doped drift region supports most of the reverse voltage, raising the breakdown rating. Because it is lightly doped it also contributes significantly to the drain-source on-resistance. The inversion channel forms in the body region under the gate oxide, not in the drift region.

Question 22Electronic Fundamentals

An operational amplifier used as an inverting amplifier has an input resistor of 2 kΩ and a feedback resistor of 20 kΩ, with a 0.2 V input. Assuming ideal behaviour, what output voltage appears?

  1. +0.02 V
  2. -0.02 V
  3. +2.0 V
  4. -2.0 V Correct answer.

Explanation

For an inverting amplifier the gain is minus the feedback resistance divided by the input resistance, here -20 kΩ / 2 kΩ = -10. Multiplying the 0.2 V input by -10 gives -2.0 V. The negative sign reflects the phase inversion inherent to this configuration.

Question 23Electronic Fundamentals

A logic circuit on an aircraft indication panel is required to output HIGH only when input A is HIGH and input B is LOW. Which single gate implements this function directly?

  1. NAND
  2. XOR
  3. NOR
  4. A AND NOT B Correct answer.

Explanation

The required truth condition is A true together with B false, which is the Boolean expression A·B̄. This is realised by an AND gate with an inverter on the B input. NAND, NOR and XOR all produce a HIGH output for other input combinations as well.

Question 24Electronic Fundamentals

During fault diagnosis of a digital engine indication circuit, a technician finds that a two-input gate outputs LOW for every input combination. Assuming the device is functional, which condition explains this behaviour?

  1. An open-circuit input is floating at a logic HIGH level.
  2. The gate is an XOR driven by identical input levels. Correct answer.
  3. Both inputs are permanently tied to logic HIGH on an AND gate.
  4. The gate is a NOR driven by one HIGH and one LOW input.

Explanation

An XOR gate outputs LOW whenever its two inputs are at the same logic level, so driving both inputs identically gives a constant LOW. This is a known diagnostic trap when a stuck input is suspected. An AND gate with both inputs HIGH would output HIGH, and a NOR with mixed inputs would also output LOW but only for that combination, not for all four.

Question 25Digital Techniques / Electronic Instrument Systems

In a typical electronic flight instrument system (EFIS) using ARINC 429 data buses, how is a 32-bit word structured for transmission?

  1. It is encoded as a Manchester-coded message of variable length
  2. It is transmitted as 32 discrete parallel lines clocked by a strobe
  3. It is sent as 32 sequential bits preceded by a label and followed by parity Correct answer.
  4. It is sent as four 8-bit bytes in a single serial frame with a parity bit per byte

Explanation

ARINC 429 transmits each word as a sequence of bits over a twisted pair: an 8-bit label identifies the parameter, followed by the data and status bits, and a final parity bit. Transmission is unidirectional and serial, so each receiver decodes the label to know what the following data represents.

Question 26Digital Techniques / Electronic Instrument Systems

On an EFIS primary flight display, the flight director command bars are shown as a single centred cross when the autopilot is engaged in which condition?

  1. The attitude gyro is being aligned on the ground
  2. The aircraft is exactly on the selected flight path and the commands are satisfied Correct answer.
  3. The pilot has selected a raw-data-only display mode
  4. The flight director computer has failed and no guidance is available

Explanation

Command bars indicate the steering commands the flight director is generating; when the aircraft is tracking the selected path, the commands reduce to zero and the bars centre. A centred cross therefore means the guidance is satisfied, not that a failure has occurred.

Question 27Digital Techniques / Electronic Instrument Systems

An electronic instrument system uses a digital data bus to connect an air data computer to several displays. Which characteristic is the main reason digital transmission is preferred over analogue synchro wiring for this link?

  1. It removes the need for any power supply to the displays
  2. It guarantees that no data latency can occur
  3. It eliminates the need for any transducer calibration
  4. It allows many parameters to share one bus with high noise immunity and self-checking Correct answer.

Explanation

Digital buses carry many labelled parameters over a shared pair of wires, and the discrete coding plus parity/CRC checking gives strong resistance to noise and detection of corruption. Analogue synchro systems need dedicated wiring per parameter and are more susceptible to induced errors.

Question 28Digital Techniques / Electronic Instrument Systems

A flight crew reports that the standby attitude indicator shows a slowly increasing pitch error after a long period of straight-and-level flight. Which maintenance action is the most appropriate first step for an electrically driven standby gyro?

  1. Recalibrate the air data computer static source
  2. Replace the display CRT without further testing
  3. Perform the manufacturer's caging and erection check and inspect the power supply to the instrument Correct answer.
  4. Adjust the flight director command bar gain

Explanation

A slow drift in an electrically driven standby gyro points to an erection or power-supply problem, so the prescribed caging/erection test and supply check come first. This isolates whether the gyro itself or its electrical supply is at fault before any replacement.

Question 29Digital Techniques / Electronic Instrument Systems

In a glass cockpit, the symbol generator that drives a display unit fails. What is the typical design provision that maintains presentation of critical attitude information?

  1. All display units blank and the crew relies on standby instruments only
  2. The display unit reverts to a dedicated internal or standby symbol generator Correct answer.
  3. The data bus automatically increases its transmission rate to compensate
  4. The display freezes on the last valid image until repaired

Explanation

Certification practice requires that loss of one symbol generator does not remove essential attitude information, so displays can switch to an alternate or standby symbol generator. This redundancy keeps a valid attitude presentation available to the crew.

Question 30Digital Techniques / Electronic Instrument Systems

An engineer is tracing why an EFIS display shows a red horizontal line across the attitude area. Which interpretation and action pair is correct?

  1. The line indicates an active flight director command and requires no action
  2. The line is an attitude validity flag indicating invalid attitude data, so the attitude source and its wiring should be investigated Correct answer.
  3. The line shows the selected altitude bug and the bug setting should be changed
  4. The line is a radio altitude scale and the radio altimeter should be tested

Explanation

A red horizontal line replacing the attitude sphere is a standard invalid-data flag, meaning the display is not receiving trustworthy attitude information. Maintenance should therefore check the attitude source, its power and the data path to the display.

Question 31Digital Techniques / Electronic Instrument Systems

An aircraft has an electronic centralized aircraft monitoring system presenting engine and system data. Which statement best describes its role compared with the EFIS displays?

  1. It concentrates system and engine parameters and generates alerts for abnormal conditions Correct answer.
  2. It replaces the primary flight displays for attitude information
  3. It performs the air data computations for the primary flight display
  4. It provides the sole navigation solution for the flight management system

Explanation

Centralized monitoring systems gather engine and system parameters and generate caution/warning messages when limits are exceeded. They complement rather than replace the EFIS attitude and navigation displays, and they do not compute air data.

Question 32Digital Techniques / Electronic Instrument Systems

A maintenance team is testing a display unit fed by a fibre-optic link. The display intermittently loses data. Which inspection point is most specific to a fibre-optic installation?

  1. Measuring the DC resistance of the outer screen
  2. Verifying the ARINC 429 label parity setting
  3. Checking the connector end-face cleanliness and minimum bend radius of the cable Correct answer.
  4. Checking the synchro rotor-to-stator continuity

Explanation

Fibre-optic links are sensitive to contaminated connector end-faces and to excessive bend radius, both of which cause intermittent optical loss. These checks are unique to optical media and are the first things to inspect for intermittent data loss.

Question 33Digital Techniques / Electronic Instrument Systems

During a functional check, an EFIS display shows the horizon displaced and the pitch scale correct, but the roll pointer is steady while the aircraft is banked. Which conclusion is most defensible?

  1. The radio altimeter has failed and removed the roll reference
  2. The roll information path or the roll servo input to the display is faulty while pitch data remains valid Correct answer.
  3. The air data computer is supplying an incorrect barometric setting
  4. The display brightness control is set too low

Explanation

Pitch and roll are separate data channels, so correct pitch with a frozen roll pointer isolates the fault to the roll data path or its input rather than to the whole attitude source. Barometric setting and radio altitude do not generate the roll reference.

Question 34Digital Techniques / Electronic Instrument Systems

What is the primary purpose of the display controller or control panel in an EFIS installation?

  1. It selects display modes and ranges and provides the crew's interface to the symbol generators Correct answer.
  2. It converts analogue synchro signals into ARINC 429 words
  3. It stores the aircraft navigation database for the flight management system
  4. It supplies primary electrical power to the display units

Explanation

The display controller lets the crew choose modes, ranges and overlays, and passes those selections to the symbol generators that build the image. It is a control interface, not a power supply or a data converter.

Question 35Materials and Hardware

In aircraft hardware identification, what does the suffix marking on an AN bolt such as 'AN6-14A' primarily indicate about the fastener?

  1. The number after the dash gives the total bolt length in millimetres
  2. The bolt is made from corrosion-resistant steel and has a drilled head
  3. The dash number expresses the grip length in eighths of an inch beyond the shank Correct answer.
  4. The letter denotes the thread pitch series used on the shank

Explanation

In the AN bolt designation the first number gives the shank diameter in sixteenths of an inch, while the dash number gives the grip length in eighths of an inch. The grip length is the unthreaded portion that passes through the material, so it must match the stack being joined. The trailing letter indicates material or finish, not thread pitch or metric length.

Question 36Materials and Hardware

A maintenance engineer must select a locking method for a bolt that will be removed frequently during routine servicing. Which locking device is designed for repeated removal and refitting without renewal?

  1. Castellated nut with a split cotter pin Correct answer.
  2. Fibre-type self-locking nut
  3. Tab washer bent against a flat
  4. Stainless steel lockwire

Explanation

A castellated nut secured with a cotter pin can be repeatedly disassembled and reassembled, since the pin is simply withdrawn and a new one fitted. It provides a positive mechanical lock and is common on flight-control and frequently serviced joints. The other devices are either single-use or degrade with repeated reuse.

Question 37Materials and Hardware

Which aluminium alloy series is the primary heat-treatable type used for high-strength aircraft structural components such as wing skins?

  1. 5xxx series
  2. 7xxx series Correct answer.
  3. 3xxx series
  4. 1xxx series

Explanation

The 7xxx series, alloyed mainly with zinc and magnesium, is heat-treatable and develops very high strength, making it a standard choice for upper wing skins and other highly stressed structure. The 2xxx series is also heat-treatable but is used where its fatigue and damage-tolerance characteristics suit. The 1xxx, 3xxx and 5xxx series are essentially non-heat-treatable.

Question 38Materials and Hardware

During a check, a technician finds that the protective coating on a steel component has been breached and red-brown corrosion product is visible. What is the most appropriate first action?

  1. Paint over the area to seal it from further moisture ingress
  2. Apply a conversion coating directly over the corrosion product
  3. Remove the corrosion product and assess the remaining material thickness Correct answer.
  4. Reduce the component's inspection interval and leave the area untouched

Explanation

Corrosion product must be removed so the extent of the damage can be assessed against the permitted limits. Once cleaned, the remaining material thickness and any pitting are evaluated before deciding on rework, blending or replacement. Sealing over active corrosion traps moisture and allows it to continue undetected.

Question 39Materials and Hardware

A component is fabricated from a thermosetting composite. Which behaviour distinguishes it from a thermoplastic composite during a repair involving heat?

  1. It cures irreversibly and will char rather than melt when overheated Correct answer.
  2. It has a lower strength-to-weight ratio than thermoplastics
  3. It softens and can be reshaped repeatedly on reheating
  4. It cannot be bonded with adhesive systems

Explanation

Thermosetting resins cross-link during cure and form a rigid three-dimensional network that cannot be re-softened by reheating. Excessive heat therefore degrades or chars the resin instead of melting it. Thermoplastics, by contrast, can be softened and reshaped repeatedly, which is why the two families require different repair approaches.

Question 40Materials and Hardware

A bolt must be torqued to a specified value, and the maintenance data state that the torque figure assumes dry threads. If the threads are lubricated, what is the practical consequence for the clamp load achieved at the same applied torque?

  1. The clamp load becomes unpredictable and torque control is abandoned
  2. The clamp load decreases because lubricant reduces friction in the threads
  3. The clamp load increases because less torque is lost to friction Correct answer.
  4. The clamp load stays the same because torque and load are independent

Explanation

Applied torque is shared between producing clamp load and overcoming friction in the threads and under the head. Lubrication reduces friction, so a greater proportion of the same torque becomes preload, raising clamp load and risking overstress. This is why torque figures are always tied to a stated thread condition.

Question 41Materials and Hardware

In the unified thread system, what does the class designation such as '3A' on an external thread indicate?

  1. The length of thread engagement required
  2. The tolerance class, with 3 being a closer fit than 2 or 1 Correct answer.
  3. The direction of the thread helix
  4. The material grade of the bolt

Explanation

Unified thread classes indicate the fit or tolerance, with class 1 the loosest and class 3 the tightest; the letter A denotes an external thread and B an internal thread. A 3A thread therefore has a small tolerance band suited to applications needing minimal play and high strength. The class says nothing about material, engagement length or helix direction.

Question 42Materials and Hardware

Why is a close-tolerance or interference-fit fastener used in certain wing and fuselage joints rather than a standard clearance-fit bolt?

  1. It allows rapid disassembly during line maintenance
  2. It transfers shear load through bearing rather than relying on friction and bolt clearance Correct answer.
  3. It eliminates the need for any corrosion protection
  4. It permits the joint to accommodate larger manufacturing tolerances

Explanation

An interference-fit fastener fills the hole tightly, so shear loads are carried by bearing contact across the full hole surface, and the joint is less prone to slip and fretting. This improves fatigue life in highly loaded structure. It does, however, make assembly and removal more difficult and demands accurately reamed holes.

Question 43Materials and Hardware

A steel component is to be protected by sacrificial protection. Which coating works by this principle when applied to steel?

  1. Hard chromium plating
  2. Cadmium plating
  3. Zinc-rich coating Correct answer.
  4. Anodic coating of aluminium oxide

Explanation

Zinc is electrochemically more active than steel, so a zinc-rich coating corrodes preferentially and protects exposed steel at scratches and edges. This is sacrificial or cathodic protection. Chromium and cadmium platings act primarily as barrier layers and do not protect steel sacrificially in the same way.

Question 44Materials and Hardware

A sheet-metal part has been cold-worked heavily during forming. What is the purpose of a stress-relief heat treatment applied afterwards?

  1. To reduce internal residual stresses that could promote distortion or cracking Correct answer.
  2. To lower the melting point for subsequent welding
  3. To raise the electrical conductivity of the alloy
  4. To increase the alloy's hardness by precipitating coarse particles

Explanation

Cold working stores residual stresses in the material, which can cause distortion during later machining or promote stress-corrosion cracking in service. A controlled stress-relief treatment allows some stress relaxation without significantly changing the mechanical properties. It is not intended to harden, change conductivity or alter melting behaviour.

Question 45Materials and Hardware

An aircraft cable assembly terminates in a swaged terminal. Which inspection finding on the swage would require rejection of the assembly?

  1. A longitudinal crack running along the swaged area Correct answer.
  2. A slight polish mark on the terminal barrel from handling
  3. A small amount of protective compound at the cable entry
  4. Faint identification markings stamped on the terminal

Explanation

A longitudinal crack in a swaged terminal indicates that the swaging operation has overstressed or split the fitting, destroying its load-carrying capability, so the assembly must be rejected. Surface polish marks, identification markings and protective compound at the entry are normal and acceptable. Cracks are never blended out of a swaged terminal; the assembly is replaced.

Question 46Materials and Hardware

A composite laminate is found to have low-velocity impact damage that is barely visible on the external surface. Why is such damage a particular concern compared with a similar impact on aluminium sheet?

  1. Aluminium is always stronger than composite in every loading case
  2. Composites conduct impact energy away from the site, hiding the damage
  3. Composites recover their original strength automatically after impact
  4. Internal delamination and matrix cracking can reduce strength with little external evidence Correct answer.

Explanation

In laminated composites, impact energy can cause delamination between plies and matrix cracking beneath an apparently undamaged surface, so significant strength loss may exist with minimal visible indication. Aluminium tends to show visible dents and cracks that reveal the damage site. This is why defined inspection methods and damage-tolerance limits are applied to composite structure.

Question 47Maintenance Practices

When a torque wrench is being used to tighten a fastener to a specified value, what is the primary reason for applying the load smoothly and avoiding rapid jerking motion?

  1. To keep the socket from wearing out prematurely
  2. To guarantee the fastener reaches its yield point
  3. To prevent the wrench from over-reading due to dynamic (inertial) effects Correct answer.
  4. To make sure the fastener threads are lubricated evenly

Explanation

A torque wrench measures the applied moment, and sudden jerks add inertial and friction spikes that make the indicated value differ from the steady-state torque actually transmitted to the fastener. Smooth, steady loading gives a repeatable reading consistent with the calibration. Jerking can also damage the internal mechanism.

Question 48Maintenance Practices

In aircraft maintenance documentation, what does the term 'serviceable' indicate about a component?

  1. It has been repaired but not yet tested
  2. It is fit for return to service within its approved limits Correct answer.
  3. It is due for scheduled overhaul
  4. It is only approved for ground use

Explanation

A component certified as serviceable has been inspected or tested and found to meet its approved standards, so it may be returned to service. The term implies airworthiness within specified limits, not merely repair or ground-only use.

Question 49Maintenance Practices

Which practice best protects an aluminium alloy structure from galvanic corrosion when it must be joined to a stainless steel fitting?

  1. Install a compatible insulating barrier and seal the joint against moisture Correct answer.
  2. Coat both surfaces with conductive grease to equalise potential
  3. Weld the two materials directly to eliminate the joint gap
  4. Leave the joint dry so moisture can drain freely

Explanation

Galvanic corrosion needs an electrolyte path between dissimilar metals. Separating them with a compatible barrier (such as a sealant, primer, or isolating washer) and sealing against moisture interrupts that path. Direct contact in the presence of moisture accelerates attack on the less noble aluminium.

Question 50Maintenance Practices

A technician must remove a seized steel bolt from an aluminium alloy bracket. Which precaution most directly reduces the risk of damaging the bracket during removal?

  1. Applying heat until the aluminium glows visibly
  2. Drilling out the bolt immediately without penetrating oil
  3. Applying penetrating fluid and controlled heat while supporting the bracket Correct answer.
  4. Using an impact driver at maximum torque

Explanation

Penetrating fluid and controlled, moderate heat help break the seizure while supporting the bracket limits bending loads on the softer aluminium. Excessive heat or uncontrolled force risks distorting or cracking the alloy. The aim is to release the fastener without transferring damaging loads into the structure.