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CAA NZ AME Electrical study materials
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CAA NZ AME Electrical practice questions

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Question 1Electrical fundamentals

In an aircraft DC generation system, what is the primary function of the voltage regulator associated with a DC generator?

  1. To convert the generator AC ripple into usable DC
  2. To reverse the field polarity during engine start
  3. To control generator field current so terminal voltage stays within limits Correct answer.
  4. To limit the generator output current to a safe value

Explanation

A voltage regulator varies the field excitation current to hold generator terminal voltage at the design value as load and speed change. Current limiting and reverse-current protection are performed by separate protection devices, not by the regulator's voltage-sensing loop.

Question 2Electrical fundamentals

Which statement correctly describes the relationship between electrical power, voltage and current in a resistive aircraft circuit?

  1. Power equals voltage squared multiplied by current
  2. Power equals voltage multiplied by current Correct answer.
  3. Power equals current divided by voltage
  4. Power equals voltage divided by current

Explanation

By definition, electrical power in watts equals the potential difference in volts multiplied by the current in amperes. Combining this with Ohm's law gives the related forms P = I squared R and P = V squared / R, but the basic relationship is voltage times current.

Question 3Electrical fundamentals

A 28 V DC aircraft bus supplies a 56 W resistive load. What current flows in the circuit?

  1. 1568 A
  2. 2 A Correct answer.
  3. 56 A
  4. 0.5 A

Explanation

Current is found by rearranging P = V x I to give I = P / V. Substituting 56 W and 28 V gives 2 A. This current is what the protective device and wiring must be rated to carry.

Question 4Electrical fundamentals

What is the purpose of a freewheel (suppression) diode fitted across a DC relay coil?

  1. To increase the coil pull-in current
  2. To provide a path for the collapsing coil current when the supply is removed Correct answer.
  3. To reduce the coil resistance after energising
  4. To rectify the supply feeding the coil

Explanation

When the coil circuit is broken, the collapsing magnetic field induces a high voltage that can damage switching contacts or transistors. The freewheel diode provides a low-resistance path so the stored inductive energy circulates and dissipates safely.

Question 5Electrical fundamentals

In a series DC circuit, which quantity is the same through every component?

  1. Power
  2. Resistance
  3. Current Correct answer.
  4. Voltage

Explanation

In a series circuit there is only one path for current, so the same current flows through each component. The voltage divides across the components in proportion to their resistance, and power differs according to each component's resistance.

Question 6Electrical fundamentals

Two resistors of 6 ohms and 3 ohms are connected in parallel. What is the equivalent resistance?

  1. 9 ohms
  2. 2 ohms Correct answer.
  3. 4.5 ohms
  4. 18 ohms

Explanation

For two resistors in parallel the product-over-sum rule gives (6 x 3) / (6 + 3) = 18 / 9 = 2 ohms. The equivalent is always less than the smallest branch resistance, which confirms the result.

Question 7Electrical fundamentals

Which material property makes a conductor suitable for aircraft electrical wiring?

  1. High permeability with low conductivity
  2. High dielectric strength with low thermal conductivity
  3. High resistivity with low melting point
  4. Low resistance with good mechanical strength and corrosion resistance Correct answer.

Explanation

Aircraft wiring conductors must carry current with minimal voltage drop, so low resistance is essential. They must also withstand vibration, flexing and environmental attack, so mechanical strength and corrosion resistance matter.

Question 8Electrical fundamentals

What is the unit of electrical capacitance?

  1. Ohm
  2. Farad Correct answer.
  3. Weber
  4. Henry

Explanation

Capacitance is measured in farads, where one farad stores one coulomb per volt of potential difference. The henry measures inductance, the weber measures magnetic flux, and the ohm measures resistance.

Question 9Electrical fundamentals

A capacitor of 10 microfarads is charged to 50 V. How much charge is stored?

  1. 5 microcoulombs
  2. 0.2 microcoulombs
  3. 500 microcoulombs Correct answer.
  4. 5 millicoulombs

Explanation

Charge equals capacitance multiplied by voltage, so Q = 10 microfarads x 50 V = 500 microcoulombs. That is also 0.5 millicoulomb, so the answer must be read carefully against the stated units.

Question 10Electrical fundamentals

Why are capacitors sometimes fitted across the brushes of a DC motor in aircraft equipment?

  1. To provide additional field excitation
  2. To suppress radio frequency interference caused by brush arcing Correct answer.
  3. To increase the motor's starting torque
  4. To reduce the motor's back EMF

Explanation

Brush arcing generates broadband radio frequency noise that can interfere with communications and navigation receivers. Capacitors across the brushes provide a low-impedance path that bypasses this high-frequency energy.

Question 11Electrical fundamentals

A transformer has 200 turns on the primary and 50 turns on the secondary. If 115 V AC is applied to the primary, what is the secondary voltage?

  1. 57.5 V
  2. 11.5 V
  3. 28.75 V Correct answer.
  4. 460 V

Explanation

The voltage ratio equals the turns ratio, so secondary voltage is 115 V x (50 / 200) = 28.75 V. A step-down turns ratio produces a proportionally lower secondary voltage.

Question 12Electrical fundamentals

What does the term 'back EMF' refer to in a running DC motor?

  1. The voltage drop across the brush contacts
  2. The residual voltage remaining after shutdown
  3. The voltage induced in the armature that opposes the applied supply voltage Correct answer.
  4. The voltage produced by the field winding alone

Explanation

As the armature rotates in the magnetic field, it acts as a generator and produces a voltage that opposes the applied supply. This back EMF limits armature current, which is why a motor draws a large current at start and much less at speed.

Question 13Electrical fundamentals

An aircraft Ni-Cad battery is found to be suffering from thermal runaway. What is the most appropriate immediate action?

  1. Continue charging at a reduced rate to equalise the cells
  2. Disconnect the charging source and remove or isolate the battery Correct answer.
  3. Top up the electrolyte to cool the cells
  4. Increase ventilation only and leave the charger connected

Explanation

Thermal runaway is a self-accelerating rise in temperature and current that can lead to fire or explosion. The charging source must be removed promptly and the battery isolated and handled according to the approved procedure.

Question 14Electrical fundamentals

What is the main advantage of a lead-acid battery over a nickel-cadmium battery of similar capacity in aircraft use?

  1. It can deliver higher surge currents at low temperature
  2. It has a lower self-discharge rate and lower cost Correct answer.
  3. It requires no venting during charging
  4. It has a higher energy density per kilogram

Explanation

Lead-acid batteries have a lower self-discharge rate and are less expensive than nickel-cadmium types, which suits them to standby and emergency roles. Nickel-cadmium types offer better low-temperature performance and longer cycle life.

Question 15Electrical fundamentals

In a three-phase AC generator, what is the phase relationship between the three output voltages?

  1. They are displaced by 90 electrical degrees
  2. They are in phase with each other
  3. They are displaced by 180 electrical degrees
  4. They are displaced by 120 electrical degrees Correct answer.

Explanation

Three-phase generation produces three voltages of equal magnitude displaced by 120 electrical degrees, giving a constant total power transfer. The windings are physically spaced to achieve this displacement.

Question 16Electrical fundamentals

An AC generator's output frequency is 400 Hz at a rotor speed of 6000 rpm. How many pole pairs does the machine have?

  1. 4 pole pairs Correct answer.
  2. 2 pole pairs
  3. 8 pole pairs
  4. 1 pole pair

Explanation

Frequency equals (poles x rpm) / 120, so poles = (400 x 120) / 6000 = 8 poles, which is 4 pole pairs. Checking: 8 poles at 6000 rpm gives 400 Hz.

Question 17Electrical fundamentals

What is the purpose of a current transformer in an aircraft AC power indication circuit?

  1. To measure the phase angle between voltage and current directly
  2. To provide a scaled-down current signal proportional to the line current Correct answer.
  3. To convert AC to DC for the generator field
  4. To step up the bus voltage for the indicator lamps

Explanation

A current transformer reduces the high line current to a small, proportional value that instruments can safely measure. Its secondary is loaded by the indicator or protection circuit rather than being left open.

Question 18Electrical fundamentals

A wire of uniform material has its length doubled while its cross-sectional area is halved. How does its resistance change?

  1. It remains unchanged
  2. It doubles
  3. It halves
  4. It quadruples Correct answer.

Explanation

Resistance is proportional to length and inversely proportional to cross-sectional area. Doubling the length doubles the resistance, and halving the area doubles it again, giving four times the original value.

Question 19Electrical fundamentals

What is the function of a shunt in an ammeter circuit?

  1. To provide a parallel path for induced surges
  2. To carry most of the current so only a small fraction passes through the meter movement Correct answer.
  3. To convert the measured current into a voltage for the voltmeter
  4. To increase the meter's sensitivity by adding series resistance

Explanation

A shunt is a low-resistance element connected in parallel with the meter movement. It diverts most of the current so the delicate movement carries only a safe, calibrated fraction, extending the meter's range.

Question 20Electrical fundamentals

A 12 V battery is connected across a resistor and dissipates 24 W. What is the resistance?

  1. 6 ohms Correct answer.
  2. 288 ohms
  3. 2 ohms
  4. 0.5 ohms

Explanation

Using P = V squared / R rearranged to R = V squared / P gives 144 / 24 = 6 ohms. Checking with P = V x I, the current is 2 A, and 12 V / 2 A = 6 ohms.

Question 21Electrical fundamentals

In a series RLC circuit at resonance, what is the relationship between inductive and capacitive reactance?

  1. Capacitive reactance is greater than inductive reactance
  2. Inductive reactance is greater than capacitive reactance
  3. Both reactances fall to zero
  4. They are equal and cancel, leaving only resistance Correct answer.

Explanation

At resonance the inductive and capacitive reactances are equal in magnitude but opposite in effect, so they cancel. The circuit impedance then reduces to the resistance alone, and current is at its maximum for the applied voltage.

Question 22Electrical fundamentals

Aircraft wiring is required to be bundled and supported at specified intervals primarily to achieve which outcome?

  1. To improve the current-carrying capacity of each wire
  2. To reduce the total weight of the loom
  3. To allow the use of a smaller wire gauge
  4. To prevent chafing, vibration damage and excessive strain on terminations Correct answer.

Explanation

Regular supports and correct bundling limit movement so that insulation cannot chafe against structure or other wires. They also prevent mechanical strain being transferred to terminals and connectors, which is a common source of faults.

Question 23Electrical fundamentals

An aircraft 28 V DC circuit has a 10 m run of copper wire with a total loop resistance of 0.05 ohms carrying 20 A. What is the voltage drop, and why does it matter?

  1. 0.1 V, which is well within limits
  2. 0.5 V, which is negligible for any load
  3. 1 V, which is acceptable because it is below 10 percent of supply Correct answer.
  4. 4 V, which may cause equipment to operate below its minimum voltage

Explanation

Voltage drop is current times resistance, so 20 A x 0.05 ohms = 1 V. That is about 3.6 percent of 28 V, within the usual allowance, and the load still receives about 27 V.

Question 24Electrical fundamentals

A 24 V relay coil draws 0.2 A and must be operated from a 28 V bus through a series resistor. What resistor value brings the coil voltage to 24 V, and what power does it dissipate?

  1. 120 ohms, 0.8 W
  2. 20 ohms, 0.8 W Correct answer.
  3. 20 ohms, 4 W
  4. 4 ohms, 0.8 W

Explanation

The coil resistance is 24 V / 0.2 A = 120 ohms, and the series resistor must drop 4 V at 0.2 A, giving 20 ohms. The resistor dissipates 4 V x 0.2 A = 0.8 W, so a resistor rated above that value is required.

Question 25Electrical fundamentals

A technician finds that a generator control unit trips on overvoltage only when a particular high-current load is switched off. Which explanation best fits the observed behaviour?

  1. The bus tie contactor is stuck closed
  2. The voltage regulator has failed to a short circuit
  3. The load's inductive collapse causes a transient voltage spike detected by the control unit Correct answer.
  4. The generator field has lost residual magnetism

Explanation

Switching off an inductive load produces a transient overvoltage from the collapsing magnetic field. If suppression is missing or ineffective, the control unit's overvoltage sensor can respond to the spike, so the suppression and load switching circuit should be checked.

Question 26Electrical fundamentals

In an aircraft DC circuit, which quantity is defined as the rate of flow of electric charge past a point in the conductor?

  1. Power
  2. Resistance
  3. Current Correct answer.
  4. Voltage

Explanation

Current is defined as the rate of transfer of electric charge, one ampere being one coulomb per second. Voltage is the potential difference driving the charge, resistance opposes its flow, and power is the rate of energy transfer.

Question 27Electrical fundamentals

What is the standard unit of electrical resistance in the SI system used for aircraft maintenance calculations?

  1. The henry
  2. The ohm Correct answer.
  3. The siemens
  4. The farad

Explanation

Resistance is measured in ohms, where one ohm permits one ampere to flow when one volt is applied. The farad measures capacitance, the henry measures inductance, and the siemens measures conductance, which is the reciprocal of resistance.

Question 28Electrical fundamentals

An aircraft bonding lead carries a steady current of 4 A for 30 seconds. How much charge passes through the lead?

  1. 0.13 C
  2. 7.5 C
  3. 34 C
  4. 120 C Correct answer.

Explanation

Charge equals current multiplied by time, so 4 A times 30 s gives 120 coulombs. Dividing current by time or adding the two quantities does not give charge.

Question 29Electrical fundamentals

A 28 V DC bus supplies a 14 ohm resistive load. What current flows in the circuit?

  1. 42 A
  2. 0.5 A
  3. 2 A Correct answer.
  4. 392 A

Explanation

Ohm's law states that current equals voltage divided by resistance, so 28 V divided by 14 ohms gives 2 A. Multiplying or inverting the values gives results with no physical basis.

Question 30Electrical fundamentals

In an aircraft DC circuit, what happens to the total resistance when a second resistor is added in parallel with the first?

  1. The total resistance decreases. Correct answer.
  2. The total resistance stays the same.
  3. The total resistance increases.
  4. The total resistance becomes infinite.

Explanation

Adding a parallel path provides an additional route for current, so the equivalent resistance is always less than the smallest individual resistance. In series the resistances would add, but parallel connection divides the current between branches.

Question 31Electrical fundamentals

A 12 V aircraft battery is connected to a 3 ohm resistor. What power is dissipated in the resistor?

  1. 0.25 W
  2. 36 W Correct answer.
  3. 4 W
  4. 48 W

Explanation

Power equals voltage squared divided by resistance, so 144 divided by 3 gives 48 W, which is also the product of 12 V and 4 A. The other values arise from incorrect formulas.

Question 32Electrical fundamentals

A maintenance technician measures 0.6 A through a 50 ohm resistor in a test circuit. What voltage appears across the resistor?

  1. 50.6 V
  2. 30 V Correct answer.
  3. 0.012 V
  4. 83 V

Explanation

Ohm's law gives voltage as current times resistance, so 0.6 A times 50 ohms equals 30 V. Dividing or adding the values does not produce a valid voltage.

Question 33Electrical fundamentals

What is the principal effect of connecting a resistor in series with an aircraft indicator lamp?

  1. It limits the current through the lamp. Correct answer.
  2. It increases the current through the lamp.
  3. It increases the lamp's brightness.
  4. It reverses the polarity of the lamp.

Explanation

A series resistor adds resistance to the circuit, reducing the current for a given supply voltage and thereby limiting lamp current. It does not reverse polarity or increase brightness.

Question 34Electrical fundamentals

An aircraft alternator produces an AC waveform. What does the term 'frequency' describe in this context?

  1. The average value of the waveform.
  2. The number of complete cycles per second. Correct answer.
  3. The phase difference between two waveforms.
  4. The peak voltage of the waveform.

Explanation

Frequency is the number of complete alternating cycles occurring each second, measured in hertz. Peak voltage, phase difference and average value are separate waveform characteristics.

Question 35Electrical fundamentals

What is the primary function of a diode in an aircraft DC electrical circuit?

  1. To store electrical charge.
  2. To amplify a small signal.
  3. To allow current in one direction only. Correct answer.
  4. To convert AC to DC by mechanical means.

Explanation

A diode is a semiconductor device that conducts readily in one direction and blocks current in the reverse direction, making it useful for suppression and rectification. Charge storage, amplification and mechanical conversion are functions of other devices.

Question 36Electrical fundamentals

A 28 V DC circuit has a total resistance of 7 ohms. What is the power dissipated in the circuit?

  1. 0.25 W
  2. 4 W
  3. 112 W Correct answer.
  4. 196 W

Explanation

Power equals voltage squared divided by resistance, so 784 divided by 7 gives 112 W, which is also 28 V times 4 A. This confirms the result by two consistent routes.

Question 37Electrical fundamentals

A 28 V DC bus supplies a 10 ohm resistive load through a cable with a total loop resistance of 2 ohms. What is the current in the circuit?

  1. 14 A
  2. 2.8 A
  3. 3.11 A
  4. 2.33 A Correct answer.

Explanation

The total circuit resistance is the sum of the load and cable resistances, giving 12 ohms. Dividing 28 V by 12 ohms gives approximately 2.33 A, so the cable drop must be included.

Question 38Electrical fundamentals

A technician needs a 5 ohm resistor to carry 0.4 A. Which resistor power rating is the minimum suitable choice from the standard values given?

  1. 5 W
  2. 2 W
  3. 0.5 W
  4. 1 W Correct answer.

Explanation

Power equals current squared times resistance, so 0.16 times 5 gives 0.8 W. The rating must exceed this value, so a 1 W resistor is the minimum suitable standard choice; 0.5 W would be overloaded.

Question 39Electrical fundamentals

An aircraft 28 V DC circuit uses a cable whose resistance causes a 1.4 V drop at 10 A. What is the cable resistance?

  1. 0.14 ohm Correct answer.
  2. 0.014 ohm
  3. 14 ohm
  4. 1.4 ohm

Explanation

Resistance equals voltage drop divided by current, so 1.4 V divided by 10 A gives 0.14 ohm. This value can then be compared with the cable's permitted voltage drop for the installation.

Question 40Electrical fundamentals

An aircraft 28 V DC bus feeds a 6 ohm resistive heater through a cable whose total loop resistance is 1 ohm. What is the current in the circuit?

  1. 4.7 A
  2. 4.0 A Correct answer.
  3. 0.25 A
  4. 3.5 A

Explanation

The cable resistance is in series with the heater, so the total circuit resistance is 6 + 1 = 7 ohms. Applying Ohm's law to the whole circuit, the current is 28 V divided by 7 ohms, which equals 4.0 A. The cable drop is then 4 A x 1 ohm = 4 V, leaving 24 V across the heater, consistent with 24 V / 6 ohms = 4 A.

Question 41Electrical systems and components

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

  1. To provide overvoltage protection for the avionics bus
  2. To connect and disconnect the battery from the main DC bus Correct answer.
  3. To limit the charging current from the alternator
  4. To convert 28 V DC into 115 V AC for instruments

Explanation

The battery contactor is a heavy-duty relay controlled from the flight deck that connects or isolates the battery from the main bus, allowing the battery to supply or receive charge current. It does not perform voltage conversion, current limiting, or overvoltage protection; those functions belong to other components.

Question 42Electrical systems and components

What is the purpose of the voltage regulator in a light aircraft DC charging system?

  1. To limit generator or alternator output voltage to a safe value Correct answer.
  2. To reverse the polarity of the battery during starting
  3. To disconnect the starter motor after engine start
  4. To step 28 V DC up to 115 V AC

Explanation

The voltage regulator controls the field current so the generator or alternator output is held near the design voltage, protecting the battery and equipment from overvoltage. The other functions listed belong to inverters, starters, or starter relays.

Question 43Electrical systems and components

On an aircraft with a 28 V DC system, a 5 A circuit breaker protecting a wire run should be selected so that the continuous current rating of the wire is:

  1. Always exactly 5 A regardless of length
  2. Independent of the breaker rating
  3. Equal to or greater than the breaker rating Correct answer.
  4. At least half the breaker rating

Explanation

Protection is coordinated so the wire can carry the breaker's rated current continuously without overheating; the wire's continuous rating must equal or exceed the breaker rating. This ensures the breaker opens before the wire is damaged.

Question 44Electrical systems and components

What does a red (or amber, depending on type) annunciator indicating a generator or alternator failure typically require the pilot to do?

  1. Reset the fuel pump circuit
  2. Immediately shut down the engine
  3. Reduce electrical load and check the charging system Correct answer.
  4. Increase electrical load to test the system

Explanation

A charging-system failure warning alerts the crew that the source is offline, so non-essential loads are shed to conserve battery power while the fault is investigated. Engine shutdown or deliberate load increase is not the correct response.

Question 45Electrical systems and components

Which component converts 28 V DC from the aircraft bus into 115 V AC for instruments?

  1. Transformer rectifier unit
  2. Voltage regulator
  3. Inverter Correct answer.
  4. Current transformer

Explanation

An inverter produces AC from a DC source, which is the standard way to supply 115 V AC instruments in a DC-equipped aircraft. A transformer rectifier unit does the opposite, converting AC to DC.

Question 46Electrical systems and components

In aircraft bonding, what is the purpose of connecting major metallic structures together with low-resistance bonds?

  1. To provide structural stiffness to the fuselage
  2. To increase the aircraft's radar cross-section
  3. To provide a return path for current and equalise potential across the airframe Correct answer.
  4. To reduce the weight of the electrical system

Explanation

Bonding ensures a low-impedance return path for electrical current and keeps all structure at a common potential, which is essential for fault current return and lightning protection. It does not serve structural or radar purposes.

Question 47Electrical systems and components

What is the function of a starter relay (starter contactor) in an aircraft starting circuit?

  1. To charge the battery during engine start
  2. To switch the high starter current using a low-current control circuit Correct answer.
  3. To convert battery DC into AC for the starter
  4. To regulate the starter motor speed

Explanation

The starter relay is a heavy-duty switch operated by a low-current circuit from the starter button, allowing the large starter current to be controlled safely. It does not regulate speed, convert power, or charge the battery.

Question 48Electrical systems and components

Which of the following best describes the purpose of a shunt in an aircraft DC ammeter circuit?

  1. To protect the ammeter from overvoltage
  2. To convert AC to DC for the ammeter
  3. To develop a small voltage drop proportional to current for measurement Correct answer.
  4. To store charge for emergency use

Explanation

A shunt is a low-resistance element that produces a small voltage proportional to the current flowing through it, which the ammeter measures. It does not store energy, protect against overvoltage, or rectify AC.

Question 49Electrical systems and components

A 28 V DC system has a 10 A load connected through 20 m of wire with a total loop resistance of 0.05 ohm. What is the approximate voltage drop in the wiring?

  1. 0.5 V Correct answer.
  2. 5.0 V
  3. 2.0 V
  4. 0.05 V

Explanation

Voltage drop equals current times resistance, so 10 A times 0.05 ohm gives 0.5 V. This drop must be accounted for so equipment at the far end still receives adequate voltage.

Question 50Electrical systems and components

An aircraft alternator is rated at 28 V and 60 A. What is its approximate maximum continuous output power?

  1. 28 W
  2. 0.47 kW
  3. 168 W
  4. 1.68 kW Correct answer.

Explanation

Power equals voltage times current, so 28 V times 60 A equals 1680 W, or about 1.68 kW. This figure represents the maximum continuous electrical power the alternator can supply.