Questions and Answers - Aircraft Electrical System

Study Aid Questions

Fill in the Blanks

1. Ohm’s Law describes the basic ___________________ relationships of ____________________.

2. Materials with a resistance to current flow halfway between the best conductor and the best insulators are called ____________________. Their application is in the field of ___________________.

3. Almost all mechanical devices, such as _______________________ and ______________________, use electromagnetic induction to produce electrical power.

4. According to Fleming’s left hand rule the thumb represents _______________________, the index finger represents _______________________, and the middle finger denotes _________________.

5. DC systems that require AC current use a(n) _____________________ to make the switch from 24‐volt DC to 400 _________________________ current in order to operate specialty equipment.

6. _____________________ reactance and ______________________ reactance oppose current flow in AC circuits. They may also create a ________________ shift between voltage and current.

7. Capacitance of parallel plates is ___________________ proportional to the distance between the plates. Therefore, if the distance doubles the capacitance is ________________ by __________________.

8. In an AC circuit where there is no inductance or capacitance, _____________________ is equal to the _____________________ of the circuit.

9. Two main types of batteries include _________________ and ___________________. They are identified by the material used for the ____________________.

10. The emergency rate is the total ___________________load required to support the essential bus for ________________________ minutes.

11. Unlike lead‐acid batteries, the state of charge of a Ni‐Cad battery cannot be determined by measuring the specific gravity of the ____________________________ electrolyte. State of charge is found by measuring the _________________________ with a Ni‐Cad battery charger and following the ______________________________.

12. In a series wound DC generator, when load increases, the voltage ________________________. This is because the greater the current through the field coils to the external circuit, the ____________________ the induced EMF and the _________________________ the output voltage.

13. DC generator control systems are often referred to as voltage regulators or ______________________ They are designed to keep the generator ____________________ within limits for all flight condition.

14. DC alternators contain two major components including the ____________________ winding and the _____________________ winding. Using the process of ____________________ induction, voltage is produced and fed to the aircraft electrical ________________________ and current is produced to power any electrical _______________________.

15. A solid state regulator monitors DC alternator output ____________________ and controls alternator ___________________________ current.

16. Inverters are __________________ devices that convert DC power to __________________.DC power feeds power to an AC distribution ___________________ that can be either 26 or 115 volts.

17. Constant speed drives can either be an independent unit or mounted within the _________________. A dual CSD and alternator is known as a(n) ________________________.

18. AC alternator controls that measure the integrity of the electrical system include the _________________ (BPCU) and the __________________________ (GCU).

19. A warning horn, with the gear switch in the up position, sounds when the _____________________ is reduced past a certain threshold and when the gear squat switch is ________________________.

20. Due to inflight vibration and _________________, conductor wire should be _______________ to minimize fatigue breakage.

21. Insulation resistance can be measured with a _____________________ or insulation tester, although it may not give a true picture of the _________________ of the insulation.

22. The amount of current ___________________ is a function of the number of wires in the bundle and the _________________ of the total wire bundle capacity that is being used.

23. Circuit resistance can be determined by checking the ______________________ across the circuit. As long as this value does not exceed the limit set down by the manufacturer, the resistance value for the circuit is considered ___________________________.

24. There should be no more than ______________ splice(s) in any one wire segment between two connectors. Splices in bundles must be _____________________ as to minimize any increase in bundle size.

25. ________________ are devices that open and close circuits and they consist of one or more pair of contacts. Current is permitted to flow when these contacts ____________________.

Matching Questions

1. Match these diagram types with their descriptions below

a. wiring diagrams      b. block diagrams      c. pictorial diagrams       d. schematic diagrams

_______ 1. Picture of the components used instead of conventional electrical symbols

_______ 2. Indicates the location of components with respect to each other

_______ 3. Consists of blocks that represent several components

_______ 4. Illustrates principle of operation

_______ 5. Identifies each component within a system by its part and serial number

_______ 6. Aid in troubleshooting complex electrical systems

2. Match these switch types with their descriptions below.

a. switches     b. electromagnetic switches     c. current limiters

_______ 1. Double‐pole single‐throw

_______ 2. Relay

_______ 3. Solenoid

_______ 4. Fuse

_______ 5. Toggle and rocker

_______ 6. Circuit breaker

3. Match these switch types with the description or diagram below.

a. SPST      b. DPST     c. SPDT     d. DPDT

_______ 1. Switch is on in both positions

_______ 2. Activates two separate circuits at the same time

_______ 3. Switch routes current through either of the two paths

_______ 4. Turns two circuits ON & OFF with one lever

_______ 5. Open and closes a single circuit

_______ 6. May have a center “OFF” position

_______ 7. 

_______ 8.

_______ 9


_______ 10.

4. Match these aircraft lighting types with the descriptions below.

a. anti‐collision lights       b. position lights          c. landing and taxi lights
d. wing                             e. inspection lights

_______ 1. Lights positioned in recessed areas of the wing designed to illuminate the ground

_______ 2. Rotating beam lights installed on the top of the fuselage or tail

_______ 3. Consists of one red, one green, and one white light

_______ 4. Lights that illuminate the leading edge of the wings

_______ 5. Has a white light located on the vertical stabilizer

_______ 6. Considered a safety light

_______ 7. Very powerful light directed by a parabolic reflector

5. Match these functions with their descriptions below.

a. Voltage Regulation                   b. Overvoltage Protection          c. Parallel Gen. Operations
d. Over‐excitation Protection        e. Differential Voltage                f. Reverse Current Sensing

_______ 1. Ensures all generator voltage values are w/in a close tolerance before load is brought online

_______ 2. Adjusts the voltage regulation circuit to ensure all generators operate w/in limits

_______ 3. Adjusts field current to control generator output

_______ 4. Disconnects a generator from a bus in the event it becomes inoperative

_______ 5. Controls a generator that is out of limits due to a paralleled system failure

_______ 6. Opens the relay that controls the field excitation current

6. Place the order of sequence of these events from start to finish. (from a – f)

_______ 1. pilot exciter field creates a magnetic field and induces power in the pilot exciter field

_______ 2. via EMF, main alternator field generates power in the main armature

_______ 3. output of exciter armature is rectified

_______ 4. ACU receives power output from 1 of the armatures and sends it to the exciter field

_______ 5. output of main AC armature is 3 phase AC

_______ 6. exciter permanent magnet and armature start process

Knowledge Application Questions

1. A circuit with a 10Ω lamp and a 24 V DC battery has a current of how many amps?

2. What is the resistance of a lamp in a circuit with a 12 V DC battery and a current value of 3 amps?

3. What is the system voltage of a circuit with a resistance of 3.5Ω and a total current of 6.85A?

4. What is the effective value of the voltage if the peak value is 24V?

5. What is the peak value of the voltage if the effective voltage is 112V?

6. Referring to the diagram below; in an AC circuit with an inductance value of .175 Henrys and voltage of 110V at 60 cycles per second, what is the inductive reactance?


7. Referring to the diagram below, what is the impedance of the following circuit?


8. Referring to the diagram below and the relationship between impedance, resistance, and reactance, find the total impedance of the following circuit.


9. Referring to the diagram below; find the total impedance of the following circuit.


10. What is the equation for true power? ______________________________________

11. What is the unit for T.P.? _______________________________________________

12. Referring to the diagram below, what is the total impedance of the following parallel AC circuit?


13. What is the equation for apparent power? __________________________________

14. What is the unit for A.P.? _______________________________________________

15. Referring to the circuit diagram below, find TP, AP, and PF. (RT=5.6Ω )


16. Using below chart ‐ fig. 1; determine the wire size for the following conditions:

‐voltage source 115 volt, continuous operation
‐wire run of 160ft
‐10A load capacity

Figure 1 Conductor Chart – continuous flow

17. Using above chart ‐ fig. 1; determine the wire size considering the following:

‐voltage source 14V, continuous operation
‐wire run length of 7ft
‐7A load capacity

18. Using the below chart – fig. 2; determine the wire size considering the following:

‐Voltage 28V, intermittent flow        ‐conduit
‐wire run of 24’                               ‐10A load

Figure 2 Conductor Chart – intermittent flow

19. Using below chart ‐ fig. 3; What is the free air rating of a size 18 wire at an ambient temperature of 70°C and rated at 195°C?
195‐70=125, wire size 18

Figure 3 single copper wire in free air

20. Using above chart ‐ fig. 3; What is the free air rating of a #22 wire at an ambient temperature of 40°C and rated at 200°C?
200‐40=160, wire size 22

Multiple Choices Questions

1. What does Ohm’s law state?

a. the current through a conductor is directly proportional to the voltage applied to that conductor, and inversely proportional to the resistance of the conductor.
b. the current through a conductor is inversely proportional to the voltage applied to that conductor, and directly proportional to the resistance of the conductor.
c. the current through a conductor is directly proportional to the voltage applied to that conductor and proportional to the resistance of the conductor.
d. the current through a conductor is inversely proportional to the voltage applied to that conductor and proportional to the resistance of the conductor.

2. What is voltage?

a. electrical pressure
b. force
c. both A &B
d. none of the above

3. Which of the following is a general rule regarding resistance in a circuit.

a. The lesser the resistance, the lesser the current flow.
b. The greater the resistance, the lesser the current flow.
c. The greater the resistance, the greater the current flow.
d. The resistance does not affect the current flow only voltage does.

4. What is the relationship between resistance and the length of a metallic conductor ?

a. directly proportional
b. indirectly proportional
c. no relationship

5. What determines the polarity within the conductor?

I. direction in which the wire is moved
II. position of the north and south poles of the field
III. the speed in which the conductor is moved through the magnets

a. only I
b. only II
c. both I & II
d. both II & III

6. The effective value in an AC system has the same value as which of the following.

a. DC voltage of the same value
b. peak values of the sine wave
c. the root mean square of the instantaneous voltage
d. 1.41 x peak voltage

7. What is the relationship between period and frequency?

a. P is inversely proportional to ƒ
b. ƒ is inversely proportional to P
c. P is equal to ƒ²
d. ƒ is equal to P²

8. What are the terms used to describe wave lengths that are out of phase with one another?

a. lead and lag
b. forward and aft
c. positive and negative
d. no terms, just denoted in degrees out of phase

9. What is resistance’s relationship to current and voltage, respectively?

a. inversely to current and inversely to voltage
b. inversely to current and directly to voltage
c. directly to current and inversely to voltage
d. directly to current and directly to voltage

10. What is inductance?

a. a coils ability to resist any change in current through it
b. a coils ability to hold an electric charge
c. the total opposition to current flow

11. What is the relationship of inductive reactance to inductance and frequency, respectively?

a. indirectly proportional, indirectly proportional
b. indirectly proportional, directly proportional
c. directly proportional, directly proportional
d. directly proportional, indirectly proportional

12. What is the purpose of a capacitor in an electric circuit?

a. reduces the inductive reactance
b. reservoir that stores electricity
c. opposes the flow of current
d. increases the voltage

13. What is capacitive reactance?

a. the opposition to current flow due to the rate of charge of the circuit
b. rate of charge of the circuit
c. the phase shift caused by the charging of a capacitor

14. Which of the following is NOT a part of impedance?

a. resistance
b. current
c. inductive reactance
d. capacitive reactance

15. What is a dry charged cell battery?

a. one that is known as flooded or wet
b. one that has been discharged before it was recharged
c. one that does not require an electrolyte
d. one that has 6 cells for an open circuit voltage of 24V

16. How much voltage does each cell in a Ni‐Cad battery deliver during discharge?

a. 1.2V
b. 1.4V
c. 2.0V
d. 2.4V

17. Ni‐Cad batteries typically have a fault protection system that monitors the condition of the battery, what does it monitor?

I. overheat condition        II. low heat condition
III. cell imbalance            IV. open and short circuit

a. I & II only
b. I & III only
c. III & IV only
d. all of the above

18. How can the overall battery condition be checked?

a. load check
b. closed circuit voltage
c. resistance check
d. opens circuit current rating

19. What charging method is preferred for lead‐acid batteries?

a. constant current
b. constant voltage
c. varying current
d. varying voltage

20. What is the benefit of the constant current charging method?

a. prolongs the life of the battery
b. there is no potential for the battery to overheat or gas excessively
c. fastest charging method for aircraft batteries
d. multiple batteries of varying voltages can be charged together

21. What charging method is preferred for Ni‐Cad batteries?

a. constant current
b. constant voltage
c. varying current
d. varying voltage

22. Where is the voltage induced in a DC generator?

a. armature
b. slip rings
c. stator
d. brushes

23. Which of these is NOT a major part of a DC generator?

a. field frame
b. field winding
c. rotating armature
d. brush assembly

24. Why are the poles laminated?

a. reduce eddy current loses
b. reduces arching
c. prolongs the life of poles

25. How is the compound DC generator connected?

a. field windings in series and in parallel
b. field winding in series, armature in parallel
c. armature in series, field winding in series

26. What is the downside to series generators?

a. difficult to troubleshoot
b. poor voltage regulation
c. they require a field rheostat
d. the “coming in” speed is higher than that of parallel or compound

27. How is the voltage in a shunt generator controlled?

a. rheostat
b. capacitor
c. resistor
d. rectifier

28. What is/are the advantage(s) of a starter‐generator?

a. saves space and weight
b. easier to start engine
c. unit is simplistic in design

29. Modern GCUs for high output generators use what type of electronic circuits to sense operations?

a. loop circuits
b. open circuits
c. closed circuits
d. solid state circuits

30. What voltage sensitive device is found in almost all voltage regulating circuitry?

a. zener diode
b. excitation relay
c. solenoid

31. What is/are the benefit(s) of DC alternators over DC generators?

a. lighter, more reliable
b. lighter, more efficient
c. less space, easier maintenance
d. easier maintenance

32. How many wire coils does a typical DC alternator have?

a. 1
b. 2
c. 3
d. 4

33. Why are ACU’s considered more reliable than vibrating‐type regulators?

a. no moving parts
b. do not require transistor circuitry to control current
c. provide addition protection like over‐ and under‐ current protection
d. more simplistic

34. Which of the following is the proper symbol for a diode?

35. How do zener diodes and regular diodes differ?

a. zener diodes can withstand higher voltage values
b. regular diodes have a breakdown value
c. zener diodes permit reverse current flow over a certain voltage
d. zener diodes permit reverse current flow over a certain current

36. The exciter generator in an AC alternator contains which of the following?

a. armature and permanent magnet
b. armature and field winding
c. armature and field windings

37. What is the frequency of an AC alternator?

a. 400 Hz ± 5%
b. 400 Hz ± 10%
c. 400 Hz ± 15%
d. 400 Hz ± 20%

38. How does the speed control unit of a CSD adjust the hydraulic pressure to control output speed?

a. piston pump
b. wobble plate
c. gear reduction
d. valve assembly

39. Why are starter motors controlled through a solenoid?

a. to prevent damage in case of starter malfunction
b. to prevent a reverse polarity connection
c. high voltage draw required for start
d. high amperage draw required for start

40. What is one of the most important pieces of information when analyzing/troubleshooting the landing gear via the electrical diagrams?

a. knowing the current value for each segment of the circuit
b. knowing the different circuits and how they relate to one another
c. knowing the gear position to ensure correct operation
d. determining whether there is a short or an open in the circuit

41. What is an LRU?

a. line replacement unit
b. line reverser unit
c. line redundant unit
d. line resistor unit

42. (Refer to figure 1) When the “gear up” switches are in the not up position where does current flow through?

a. though terminal 2, the squat switch, and the down solenoid
b. through terminal 1, the squat switch, and the up solenoid
c. through terminal 3 to the up motor
d. through terminal 2, the squat switch, and the up solenoid

Figure 1

43. (Refer to figure 1) What happens when the squat switch is activated (ground) and the gear switch is in the up position?

a. the gear will not retract
b. the gear will not retract and a warning horn will sound
c. the gear will retract

44. (Refer to figure 2) What contacts must be closed for the APU gen to power AC bus 1?

a. APB, GB2
b. APB, GB1
c. APB, BTB1
d. APB, BTB2

Figure 2

45. (Refer to figure 2) In the event that all generators fail, AC is available through which of the following?


46. What determines the size of an aluminum conductor wire?

a. current rating
b. contact current rating
c. brackets used to hold the wire in place
d. termination hardware rating

47. What is the maximum deflection between support points of wire bundles?

a. ¼”
b. ½”
c. ¾”
d. 1”

48. What is static bonding?

a. low‐impedance paths to the aircrafts structure for electrical equipment
b. conductive objects on the exterior of the airframe electrically connected through mechanical joints to the airframe
c. conductive parts subject to electrostatic charging mechanically secured through an electrical connection to the aircraft structure

49. Which type of switch is spring loaded?

a. rotary
b. toggle
c. micro
d. rocker

50. (Refer to figure 3) What bus powers the ESS AC BUS during normal operation?

a. Gen 1
b. Gen 2
c. Gen 3
d. APU Gen

Figure 3


Opposition to Current Flow of AC
Aircraft Batteries
Aircraft Battery Maintenance, Inspection, Installation Practices and Troubleshooting
DC Generators and controls
Generator Controls
DC Alternators and Controls
Power Systems and AC Alternators
Alternator Drive and AC Alternators Control Systems
Electrical System Components
Aircraft Lighting System
Small Single-Engine Aircraft Electrical System
Light Multiengine Aircraft Electrical System
Large Multiengine Aircraft Electrical System
Wiring Diagrams and Wire Types
Wire Size Selection
Wire Identification
Wire Installation and Routing and Lacing and Tying Wire Bundles
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