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NCAA AME Avionics study materials
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NCAA AME Avionics practice questions

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Question 1Avionics systems and aircraft electrical/electronic maintenance (subject area not enumerated by the source)

In a 28 VDC aircraft electrical system, what is the primary purpose of the master battery relay (battery contactor)?

  1. To regulate generator output voltage to 28 V
  2. To provide overvoltage protection for the alternator
  3. To convert AC to DC for the avionics bus
  4. To connect and disconnect battery power to the main DC bus Correct answer.

Explanation

The battery relay (contactor) is the heavy-duty switch that ties the battery to the main distribution bus and lets the pilot isolate battery power. Voltage regulation is handled by the regulator, not the contactor.

Question 2Avionics systems and aircraft electrical/electronic maintenance (subject area not enumerated by the source)

Aircraft wiring is commonly identified by printed or stamped markings on the wire insulation. What does the wire identification number typically indicate?

  1. The wire's current-carrying capacity in amperes
  2. The circuit function and routing segment of that wire Correct answer.
  3. The insulation temperature rating in degrees Celsius
  4. The gauge size expressed in circular mils

Explanation

Wire identification numbers encode the circuit function and the location of the wire within a harness, allowing technicians to trace circuits through connectors and bundles. Gauge and current capacity are separate characteristics.

Question 3Avionics systems and aircraft electrical/electronic maintenance (subject area not enumerated by the source)

Which instrument is used to measure the insulation resistance of an aircraft electrical cable to detect degraded dielectric?

  1. Oscilloscope
  2. Clamp-on ammeter
  3. Megohmmeter Correct answer.
  4. Wheatstone bridge

Explanation

A megohmmeter applies a high test voltage to measure insulation resistance and reveal moisture, cracks, or contamination in the dielectric. It is the standard tool for insulation checks on aircraft wiring.

Question 4Avionics systems and aircraft electrical/electronic maintenance (subject area not enumerated by the source)

What is the standard nominal voltage of a lead-acid aircraft battery used in a 28 VDC system?

  1. 48 V
  2. 24 V Correct answer.
  3. 12 V
  4. 28 V

Explanation

A 28 VDC aircraft system uses a 24 V lead-acid battery, typically 12 cells at about 2 V each. The system bus is regulated near 28 V by the generator or alternator.

Question 5Avionics systems and aircraft electrical/electronic maintenance (subject area not enumerated by the source)

In an aircraft AC power system, what component converts variable-frequency alternator output into constant-frequency 400 Hz power?

  1. Static exciter
  2. Transformer-rectifier
  3. Constant-speed drive Correct answer.
  4. Inverter

Explanation

A constant-speed drive (CSD) maintains a fixed alternator shaft speed so the generated frequency stays at 400 Hz. Inverter-driven or variable-frequency systems achieve constant frequency by other means, but the CSD is the classic mechanical solution.

Question 6Avionics systems and aircraft electrical/electronic maintenance (subject area not enumerated by the source)

A technician finds that an avionics unit loses power only when the aircraft is in a steep climb. Which fault is most consistent with this symptom?

  1. A failed voltage regulator
  2. A discharged battery
  3. An intermittent open in a connector pin or wire harness Correct answer.
  4. A shorted suppression capacitor

Explanation

A fault that appears only under specific attitude or vibration points to a mechanical intermittent, such as a loose connector pin or chafed wire. Electrical component failures generally produce symptoms independent of aircraft attitude.

Question 7Avionics systems and aircraft electrical/electronic maintenance (subject area not enumerated by the source)

What is the purpose of a current limiter in an aircraft DC generation system?

  1. To filter electrical noise from the generator
  2. To open the generator output circuit on reverse current
  3. To step down bus voltage for avionics
  4. To limit generator output current to a safe value during high loads Correct answer.

Explanation

A current limiter protects the generator and wiring by restricting output current to a design maximum during heavy loads. Reverse-current protection is a separate function performed by a reverse-current cutout or relay.

Question 8Avionics systems and aircraft electrical/electronic maintenance (subject area not enumerated by the source)

Why is shielded wire used for certain avionics signal circuits?

  1. To reduce electromagnetic interference coupling into the signal Correct answer.
  2. To raise the dielectric withstand voltage
  3. To increase current-carrying capacity
  4. To provide mechanical support for the harness

Explanation

A shield around a signal wire intercepts and drains electromagnetic fields, reducing interference coupling into sensitive circuits. Shielding does not change current capacity or dielectric rating.

Question 9Avionics systems and aircraft electrical/electronic maintenance (subject area not enumerated by the source)

When performing a continuity check on a wire that terminates at both ends in a connector, what must be done before connecting the ohmmeter?

  1. Disconnect the wire from the circuit to isolate it Correct answer.
  2. Install a shunt across the connector
  3. Energize the circuit to verify operation
  4. Set the aircraft battery to the on position

Explanation

Continuity testing requires the wire to be isolated so parallel paths do not give false readings and so test current does not damage components. The circuit must be de-energized and disconnected at the ends.

Question 10Avionics systems and aircraft electrical/electronic maintenance (subject area not enumerated by the source)

What does a bonding jumper accomplish on an aircraft structure?

  1. It carries the full generator output current
  2. It isolates the component from the airframe ground
  3. It supplies primary operating power to the component
  4. It provides a low-resistance path to equalize static potential between components Correct answer.

Explanation

Bonding jumpers connect metallic parts with low resistance so static charges and fault currents equalize without arcing. This protects against static discharge and provides a reliable ground return.

Question 11Avionics systems and aircraft electrical/electronic maintenance (subject area not enumerated by the source)

An aircraft's 28 VDC bus reads 24 V with the generator online and the battery disconnected. Which condition is most likely?

  1. The voltage regulator is commanding low output Correct answer.
  2. The generator is producing excessive voltage
  3. The bus tie is open
  4. The battery relay is stuck closed

Explanation

With the generator online and no battery to mask the reading, a low bus voltage indicates the regulator is not commanding the correct field. Excessive voltage would read above 28 V, and a stuck battery relay would show battery influence.

Question 12Avionics systems and aircraft electrical/electronic maintenance (subject area not enumerated by the source)

What is the function of a transformer-rectifier unit (TRU) in an aircraft electrical system?

  1. Convert AC generator power to DC for the DC bus Correct answer.
  2. Regulate alternator field current
  3. Convert DC bus power to AC for instruments
  4. Provide backup power during engine start

Explanation

A TRU steps down AC and rectifies it to supply the DC bus in aircraft that use AC as primary power. It is a power conversion device, not a regulator or inverter.

Question 13Avionics systems and aircraft electrical/electronic maintenance (subject area not enumerated by the source)

A pitot-static system's air data computer reports erratic altitude readings that correlate with electrical load changes. Which action is the most appropriate first step?

  1. Recalibrate the altimeter
  2. Check the pitot-static plumbing for leaks
  3. Inspect the air data computer's power and ground connections for voltage drops Correct answer.
  4. Replace the air data computer

Explanation

A symptom tied to electrical load changes points to a power or ground integrity problem rather than a pneumatic fault. Verifying supply voltage and ground returns at the unit is the logical first step before replacing hardware.

Question 14Avionics systems and aircraft electrical/electronic maintenance (subject area not enumerated by the source)

Which practice is required when routing new avionics wire near a fuel line?

  1. Use uninsulated wire to improve heat dissipation
  2. Route the wire in direct contact to save space
  3. Bundle the wire with the fuel line using a single clamp
  4. Maintain separation and secure the wire to prevent chafing Correct answer.

Explanation

Wiring must be separated from fuel lines and secured to prevent chafing, arcing, or heat damage that could ignite fuel vapors. Direct contact or shared clamping is prohibited.

Question 15Avionics systems and aircraft electrical/electronic maintenance (subject area not enumerated by the source)

What does the term 'avionics bus' refer to in an aircraft electrical distribution system?

  1. The battery charging circuit
  2. The main generator output terminal
  3. A dedicated bus that supplies power to electronic communication, navigation, and display equipment Correct answer.
  4. The engine ignition circuit

Explanation

The avionics bus is a dedicated distribution bus that feeds sensitive electronic equipment, often through its own switch and protection. This separation allows avionics to be controlled independently of other loads.

Question 16Avionics systems and aircraft electrical/electronic maintenance (subject area not enumerated by the source)

A 400 Hz aircraft AC system uses a frequency of 400 Hz rather than 60 Hz primarily because:

  1. Higher frequency increases generator efficiency at low rpm
  2. Lower frequency reduces wire weight
  3. Higher frequency allows smaller, lighter transformers and motors Correct answer.
  4. Lower frequency reduces radio interference

Explanation

At higher frequency, magnetic components such as transformers and motors can be built smaller and lighter for the same power, which is a key advantage in aircraft. The tradeoff is increased reactance and interference concerns.

Question 17Avionics systems and aircraft electrical/electronic maintenance (subject area not enumerated by the source)

What is the purpose of a reverse-current relay in a DC generator circuit?

  1. To convert AC ripple to smooth DC
  2. To limit generator output current to a maximum value
  3. To prevent the battery from discharging through the generator when generator output falls below battery voltage Correct answer.
  4. To regulate the generator field current

Explanation

A reverse-current relay opens the generator-to-bus connection when current flows backward, protecting the generator from being driven as a motor by the battery. Current limiting and voltage regulation are separate functions.

Question 18Avionics systems and aircraft electrical/electronic maintenance (subject area not enumerated by the source)

An avionics technician measures 0.6 V drop across a ground return path that should be near 0 V. What is the most likely consequence?

  1. The unit sees a reduced supply voltage and may malfunction intermittently Correct answer.
  2. The generator will overvoltage
  3. The circuit breaker will trip immediately
  4. The unit receives excessive voltage and may overheat

Explanation

A significant voltage drop in the ground return reduces the voltage actually available at the unit and can cause erratic or intermittent operation. Excessive drop indicates a poor bond or corroded connection that must be corrected.

Question 19Avionics systems and aircraft electrical/electronic maintenance (subject area not enumerated by the source)

Which condition would cause a generator control unit (GCU) to trip the generator offline?

  1. A normal battery charge cycle
  2. An overvoltage or overfrequency condition Correct answer.
  3. A bus voltage within normal limits
  4. A closed bus tie

Explanation

The GCU monitors generator output and trips the generator offline for faults such as overvoltage, undervoltage, or overfrequency to protect the bus and equipment. Normal operating conditions do not cause a trip.

Question 20Avionics systems and aircraft electrical/electronic maintenance (subject area not enumerated by the source)

What is the primary reason for using twisted pairs in avionics signal wiring?

  1. To cancel magnetically induced noise in balanced signal circuits Correct answer.
  2. To increase the wire's current rating
  3. To reduce the wire's capacitance to the airframe
  4. To provide a redundant ground path

Explanation

Twisting the two conductors of a balanced pair causes induced noise to cancel because the loops couple equal and opposite voltages. This improves signal integrity in low-level avionics circuits.

Question 21Avionics systems and aircraft electrical/electronic maintenance (subject area not enumerated by the source)

What does a circuit breaker's trip-free feature ensure in aircraft electrical systems?

  1. The breaker opens only on overvoltage
  2. The breaker automatically resets after cooling
  3. The breaker can be reset while the fault is still present
  4. The breaker will not hold closed against a fault even if the handle is held Correct answer.

Explanation

A trip-free breaker opens the circuit on fault current even if the handle is held in the closed position, preventing the fault from being sustained. This protects wiring from overheating.

Question 22Avionics systems and aircraft electrical/electronic maintenance (subject area not enumerated by the source)

What is the purpose of a static discharge wick on an aircraft?

  1. To provide a controlled path for static electricity to dissipate into the air Correct answer.
  2. To supply backup electrical power
  3. To reduce the aircraft's radar cross section
  4. To ground the aircraft during maintenance

Explanation

Static dischargers (wicks) provide a high-resistance path that bleeds accumulated static charge into the atmosphere, reducing radio interference. They are not power sources or maintenance grounds.

Question 23Avionics systems and aircraft electrical/electronic maintenance (subject area not enumerated by the source)

Which document would a technician consult to find the approved wire gauge and terminal for a specific avionics installation?

  1. The weight and balance report
  2. The aircraft's flight manual
  3. The airworthiness directive summary
  4. The manufacturer's maintenance or standard wiring practices manual Correct answer.

Explanation

Standard wiring practices and manufacturer maintenance manuals specify approved wire gauges, terminals, and installation methods. The flight manual and weight and balance report do not contain wiring specifications.

Question 24Avionics systems and aircraft electrical/electronic maintenance (subject area not enumerated by the source)

An aircraft battery is being charged and the technician notices the electrolyte level is below the plates. What is the correct action?

  1. Add electrolyte acid to raise the level
  2. Replace the battery immediately
  3. Continue charging until the level rises
  4. Add distilled water to bring the level above the plates Correct answer.

Explanation

Only distilled water should be added to a lead-acid battery to restore electrolyte level; the acid does not evaporate. Adding acid changes the electrolyte concentration and can damage the battery.

Question 25Avionics systems and aircraft electrical/electronic maintenance (subject area not enumerated by the source)

In a multi-engine aircraft, what is the purpose of a bus tie breaker?

  1. To protect the avionics bus from overvoltage
  2. To charge the battery from either generator
  3. To connect or isolate the two main DC buses so either generator can supply both Correct answer.
  4. To disconnect the battery during engine start

Explanation

A bus tie allows the left and right DC buses to be connected so one generator can feed both buses in the event of a generator failure, or isolated for independent operation. It is a distribution control device.

Question 26Avionics systems and aircraft electrical/electronic maintenance (subject area not enumerated by the source)

An avionics technician is preparing to install a new radio in a pressurized aircraft. Which document type normally provides the approved wiring practices, including crimp tool selection and terminal part numbers, for that installation?

  1. The manufacturer's maintenance manual chapter for electrical wiring Correct answer.
  2. The aircraft's weight and balance report
  3. A standard aviation handbooks on sheet metal repair
  4. The aircraft's illustrated parts catalog

Explanation

Approved wiring practices for a specific aircraft are published in the manufacturer's maintenance or wiring practices documentation, which lists acceptable tools, terminals, and splices. The parts catalog only identifies part numbers for procurement and does not define workmanship standards.

Question 27Avionics systems and aircraft electrical/electronic maintenance (subject area not enumerated by the source)

When a technician squeezes a crimp terminal onto a wire, the terminal's insulation support must grip which portion of the wire?

  1. Neither, since insulation support is optional on avionics wiring
  2. The wire insulation, with the conductor barrel gripping the stripped strands Correct answer.
  3. Both the insulation and the conductor in a single crimp barrel
  4. The bare conductor strands only

Explanation

A proper crimp has two zones: the conductor barrel captures the stripped strands, and the separate insulation support grips the wire jacket to provide strain relief. Allowing the insulation into the conductor barrel prevents metal-to-metal contact and creates a high-resistance joint.

Question 28Avionics systems and aircraft electrical/electronic maintenance (subject area not enumerated by the source)

An avionics LRU is mounted on shock mounts in a rack. Which bonding requirement applies to the unit's chassis?

  1. The chassis must be isolated from structure and grounded through the signal return only
  2. The chassis must be bonded to the aircraft structure with a low-resistance path Correct answer.
  3. The chassis must be left floating to prevent ground loops
  4. The chassis must be bonded only through the mounting bolts' paint

Explanation

Equipment cases are bonded to structure so fault current and static charges have a defined low-impedance path, and so shielding is effective. A deliberate low-resistance bond is required rather than reliance on painted interfaces or signal returns.

Question 29Avionics systems and aircraft electrical/electronic maintenance (subject area not enumerated by the source)

What is indicated when an insulation resistance test between a wire conductor and aircraft structure reads a very low resistance?

  1. The wire is properly shielded
  2. The insulation is degraded and provides a leakage path Correct answer.
  3. The conductor gauge is larger than required
  4. The circuit is correctly bonded at both ends

Explanation

An insulation resistance check applies a test voltage between the conductor and structure; a low reading means current leaks through damaged or contaminated insulation. Acceptable values are high, typically in the megohm range, so a low value signals a defect to be corrected.

Question 30Avionics systems and aircraft electrical/electronic maintenance (subject area not enumerated by the source)

Why are avionics line-replaceable units typically connected to the aircraft wiring through connectors with keyed shells?

  1. To allow any unit to be installed in any rack position
  2. To prevent mating the wrong connector or inserting it in the wrong orientation Correct answer.
  3. To increase the current rating of the contacts
  4. To eliminate the need for a bonding jumper

Explanation

Keying and polarization features make a connector physically compatible only with its intended mate, preventing crossed connections and bent pins. This protects equipment from misapplication during maintenance.

Question 31Avionics systems and aircraft electrical/electronic maintenance (subject area not enumerated by the source)

A technician must identify the specific wire in a bundle that feeds a particular avionics circuit breaker. Which marking scheme is normally used for this purpose?

  1. Color of the circuit breaker collar
  2. Position of the wire within the bundle
  3. Wire identification code stamped on the terminal lug only
  4. Wire identification markings printed at intervals along the wire insulation Correct answer.

Explanation

Aircraft wiring is identified by markings printed along the insulation at regular intervals so a wire can be traced anywhere in the run. Terminal-only marking is insufficient because it is lost once the lug is removed or hidden in a bundle.

Question 32Avionics systems and aircraft electrical/electronic maintenance (subject area not enumerated by the source)

What is the primary hazard of using a soldering iron with an ungrounded tip near a static-sensitive avionics circuit card?

  1. It may change the card's weight and balance
  2. It may inject damaging leakage voltage into the circuitry Correct answer.
  3. It may overheat the card's heat sink
  4. It may demagnetize the card's transformers

Explanation

An ungrounded soldering iron tip can couple line voltage or leakage onto the workpiece, damaging sensitive semiconductors. Irons used on avionics assemblies are grounded and often temperature-controlled to protect the hardware.

Question 33Avionics systems and aircraft electrical/electronic maintenance (subject area not enumerated by the source)

What does a built-in test equipment (BITE) fault code reported by an avionics unit typically indicate?

  1. The airworthiness directive status of the unit
  2. The system or line-replaceable unit the maintenance action should address Correct answer.
  3. The exact failed component inside the unit
  4. The aircraft's next scheduled inspection date

Explanation

BITE codes are designed to direct maintenance to the affected system or unit, often with a confidence level, rather than to identify an internal component. Technicians use the code with fault isolation manuals to decide the removal action.

Question 34Avionics systems and aircraft electrical/electronic maintenance (subject area not enumerated by the source)

An avionics technician replaces a damaged antenna coaxial cable with a cable of the same type but shorter length. What effect does the shorter cable have on the system?

  1. It eliminates the need for the antenna's bonding
  2. It changes the antenna's resonant frequency to a new band
  3. It reduces signal loss in the cable, generally improving performance Correct answer.
  4. It doubles the transmitter output power

Explanation

Coaxial cable loss is proportional to length, so a shorter run of the same cable type attenuates the signal less. The antenna's tuning and the transmitter's output are set by their own design and are not changed by shortening the feed line.

Question 35Avionics systems and aircraft electrical/electronic maintenance (subject area not enumerated by the source)

A technician is asked to verify the integrity of a shielded avionics cable's shield. Where should the shield normally be terminated?

  1. To the center conductor at the antenna
  2. To the aircraft structure at both ends of the run
  3. At one end only, to a connector shell or ground point as specified in the installation data Correct answer.
  4. To the circuit breaker bus bar

Explanation

Shield termination practice depends on the design, but the shield is grounded to a connector shell or specified ground point rather than arbitrarily to structure. Following the installation data prevents ground loops and preserves shielding effectiveness.

Question 36Avionics systems and aircraft electrical/electronic maintenance (subject area not enumerated by the source)

During a functional check, a VHF communication radio transmits but receives poorly, and the problem disappears when the aircraft's battery charger is turned off. Which condition best explains this?

  1. The receiver's antenna is physically disconnected
  2. The radio's frequency synthesizer has failed
  3. Electrical noise from the charger is being coupled into the receiver Correct answer.
  4. The transmitter's output power is too low

Explanation

A fault that tracks the operation of another electrical device indicates conducted or radiated interference from that device. Turning off the charger removes the noise source, confirming interference coupling rather than a hard receiver failure.

Question 37Avionics systems and aircraft electrical/electronic maintenance (subject area not enumerated by the source)

An avionics unit draws 5 A from a 28 VDC bus through a wire run with 0.4 ohm total resistance. What voltage is actually delivered to the unit?

  1. 23 V
  2. 26 V Correct answer.
  3. 30 V
  4. 28 V

Explanation

The voltage drop is I times R, or 5 A times 0.4 ohm, which equals 2 V. Subtracting that drop from the 28 V bus leaves 26 V at the unit terminals.

Question 38Avionics systems and aircraft electrical/electronic maintenance (subject area not enumerated by the source)

An avionics technician finds that a connector pin is pushed back (recessed) in its shell after mating. What is the most appropriate corrective action?

  1. Increase the torque on the connector coupling nut
  2. Replace or re-terminate the affected contact using the approved extraction and insertion tools Correct answer.
  3. Bend the mating pin outward to restore contact
  4. Add a jumper wire across the affected circuit

Explanation

A recessed contact indicates the contact is not properly locked in the connector, which can cause intermittent or open circuits. The correct repair is to remove and re-terminate or replace the contact with the specified tools so it locks in place.

Question 39Avionics systems and aircraft electrical/electronic maintenance (subject area not enumerated by the source)

What is the purpose of a ground power receptacle interlock on an aircraft?

  1. To charge the aircraft battery during ground operations
  2. To measure the external power source's frequency
  3. To prevent the aircraft's generators from being connected to the external source at the same time Correct answer.
  4. To disconnect the aircraft's avionics buses automatically

Explanation

The interlock ensures external power and aircraft generators are not paralleled inadvertently, protecting equipment and personnel. It enforces the correct sequence of connecting and disconnecting ground power.

Question 40Avionics systems and aircraft electrical/electronic maintenance (subject area not enumerated by the source)

An avionics technician notices that a wire bundle is routed tightly against a hydraulic line that vibrates in flight. What is the concern?

  1. Change in the aircraft's center of gravity
  2. Reduction of the hydraulic line's burst pressure
  3. Chafing of wire insulation leading to arcing or short circuits Correct answer.
  4. Loss of hydraulic fluid pressure due to the wire's weight

Explanation

Relative motion between a wire bundle and a vibrating line causes abrasion of the insulation, which can expose conductors and produce shorts or arcing. Proper standoff and clamping with adequate clearance prevent chafing.

Question 41Avionics systems and aircraft electrical/electronic maintenance (subject area not enumerated by the source)

What does a time-delay circuit breaker characteristic provide compared with an instantaneous-trip breaker of the same rating?

  1. It allows continuous current above its rating
  2. It tolerates brief inrush currents without tripping Correct answer.
  3. It eliminates the need for a bus tie
  4. It trips faster on all overloads

Explanation

Time-delay breakers are designed to ride through short-duration inrush, such as motor starting, while still protecting against sustained overloads. Instantaneous types respond immediately and may nuisance-trip on such inrush.

Question 42Avionics systems and aircraft electrical/electronic maintenance (subject area not enumerated by the source)

An avionics technician is performing a pitot-static leak check and observes that the indicated airspeed slowly decreases while the system is capped. What does this indicate?

  1. A leak in the static portion of the system
  2. A correctly sealed system
  3. A leak in the pitot (impact pressure) portion of the system Correct answer.
  4. A failed air data computer only

Explanation

With the system capped and pressure applied to the pitot side, a slowly decaying differential pressure indicates leakage from the impact side. A static-side leak would produce a different signature, so isolating each side is part of the test procedure.

Question 43Avionics systems and aircraft electrical/electronic maintenance (subject area not enumerated by the source)

When replacing a static discharge wick, what installation condition most affects its effectiveness?

  1. The wick must be longer than the trailing edge
  2. The wick must make firm electrical contact with the structure Correct answer.
  3. The wick must be painted to match the airframe
  4. The wick must be mounted only on the fuselage centerline

Explanation

A static wick works by providing a conductive path that bleeds accumulated charge into the air stream. Poor bonding at its base leaves the charge trapped and defeats the purpose of the installation.

Question 44Avionics systems and aircraft electrical/electronic maintenance (subject area not enumerated by the source)

An avionics technician is troubleshooting an intermittent fault and finds that wiggling a specific wire bundle reproduces the failure. What is the best next step?

  1. Reset the circuit breaker and release the aircraft
  2. Isolate and inspect the affected bundle for chafing, loose contacts, or broken strands Correct answer.
  3. Replace the LRU and return it to service
  4. Increase the torque on all nearby fasteners

Explanation

A fault reproduced by flexing a bundle localizes the problem to that wiring, so the bundle should be opened and inspected for damage or loose terminations. Replacing unrelated hardware would not address the confirmed fault location.

Question 45Avionics systems and aircraft electrical/electronic maintenance (subject area not enumerated by the source)

Which practice best protects an avionics line-replaceable unit during removal from an aircraft?

  1. Remove the unit while power is applied to verify the fault
  2. Store the unit on a metal shelf without a protective cover
  3. Handle the unit by its connector pins
  4. Disconnect electrical power and observe anti-static precautions before handling the unit Correct answer.

Explanation

Removing power before disconnecting the unit prevents arcing and accidental damage, and static precautions protect sensitive electronics. Connectors and pins should be protected with covers during handling and storage.

Question 46Avionics systems and aircraft electrical/electronic maintenance (subject area not enumerated by the source)

An aircraft has two avionics buses fed from separate generator channels, with a normally open bus tie. If one generator channel fails, what is the expected result when the bus tie is closed?

  1. Both avionics buses lose power
  2. The battery is disconnected from the essential bus
  3. The failed generator is automatically restarted
  4. Both avionics buses are fed from the remaining generator channel Correct answer.

Explanation

Closing the bus tie parallels the distribution buses so the surviving source can supply both loads, subject to load capacity. This preserves avionics operation after a single-channel failure.

Question 47Avionics systems and aircraft electrical/electronic maintenance (subject area not enumerated by the source)

An avionics technician measures the resistance of a bonding strap from an equipment rack to structure and obtains 0.5 ohm. The maintenance data specifies a maximum of 0.0025 ohm. What is the correct interpretation?

  1. The bond is acceptable because any reading below 1 ohm is adequate
  2. The meter is reading in kilohms and the bond is acceptable
  3. The bond exceeds the limit and must be corrected Correct answer.
  4. The bond should be left as is because racks are not bonded

Explanation

The measured value is far above the specified maximum, so the bond does not meet the low-impedance requirement. The connection must be cleaned, re-terminated, or replaced until the reading is within the published limit.

Question 48Avionics systems and aircraft electrical/electronic maintenance (subject area not enumerated by the source)

A 400 Hz AC avionics bus is supplied by an inverter, and a technician observes that the frequency drifts as the connected load increases. Which explanation is most consistent with this symptom?

  1. The battery is fully charged
  2. The inverter's regulation is degrading under load Correct answer.
  3. The static wicks are worn
  4. The bus tie breaker is open

Explanation

An inverter regulates output voltage and frequency; drift that tracks load indicates the regulation loop or its components are degrading. The other listed items do not control inverter frequency.

Question 49Avionics systems and aircraft electrical/electronic maintenance (subject area not enumerated by the source)

An avionics technician is asked to explain why a fault-isolation manual directs a check of connector pin retention before replacing a suspected LRU. What is the reasoning?

  1. Pin retention checks are required only for new installations
  2. A recessed or loose contact can mimic a failed unit and would recur after replacement Correct answer.
  3. Replacing the LRU always corrects connector faults
  4. Pin retention affects only the unit's weight

Explanation

Intermittent or open circuits caused by poor contact retention look identical to unit failures, so verifying the connector prevents unnecessary removals and repeat write-ups. Fault isolation proceeds from the most likely and least costly causes.

Question 50Avionics systems and aircraft electrical/electronic maintenance (subject area not enumerated by the source)

A technician is evaluating a proposed repair that would splice an avionics signal wire inside a bundle using a solder joint covered with tape. Why is this repair generally unacceptable?

  1. Solder joints are prohibited everywhere on aircraft
  2. The splice would change the wire's color code
  3. The splice lacks an approved mechanical support and environmental seal required by wiring practices Correct answer.
  4. Tape adds too much weight to the bundle

Explanation

Approved wiring practice requires splices to be made with specified splice connectors or approved solder techniques, with proper strain relief and insulation sealing. A taped solder joint provides neither reliable mechanical support nor environmental protection.