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SACAA Aircraft Maintenance Engineer Electrical Equipment (CAT X & W) Theoretical Knowledge Examination practice questions are available now; exam metadata is being verified.
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Sample SACAA AME Electrical & Radio Practice Questions
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1How is the output voltage of a standard 28V DC aircraft generator regulated under varying engine speeds and electrical load conditions?
A.By adjusting the main armature rotational speed via a mechanical governor
B.By controlling the current flowing through the shunt field windings
C.By inserting variable series resistors in the main power output line
D.By altering the physical air gap between the field poles and the armature
Explanation: A DC generator's output voltage is proportional to rotational speed and magnetic field strength. Since engine speed varies, voltage regulators maintain a steady 28V output by controlling the current flowing through the generator's shunt field windings (varying field strength).
2In a standard 115V / 200V AC, 400Hz 3-phase Wye-connected aircraft electrical system, what is the line-to-line voltage?
A.115 V AC
B.163 V AC
C.200 V AC
D.345 V AC
Explanation: In a 3-phase Wye (Star) system, the line-to-line voltage (V_L-L) is equal to sqrt(3) times the phase (line-to-neutral) voltage (V_L-N). Therefore, 115V x sqrt(3) = 115 x 1.732 = 199.2V AC, which is conventionally designated as 200V AC.
3An aircraft AC alternator driven at 6000 RPM must produce power at a frequency of exactly 400 Hz. How many rotor poles must the alternator have?
A.4 poles
B.6 poles
C.8 poles
D.12 poles
Explanation: The frequency formula is f = (N x RPM) / 120, where N is the total number of poles. Rearranging gives N = (120 x f) / RPM = (120 x 400) / 6000 = 48,000 / 6000 = 8 poles.
4What is the primary function of an equalizing circuit in a multi-engine aircraft DC generator parallel distribution system?
A.To ensure equal rotational speed of engine-driven generators
B.To share electrical load current proportionally between parallel generators
C.To step down output voltage for emergency bus battery charging
D.To prevent high AC ripple voltage from entering the DC distribution bus
Explanation: Equalizing circuits compare the output current of parallel DC generators via sensing resistors or current transformers. Any imbalance creates a voltage across the equalizer coils in the voltage regulators, adjusting field excitation so generators share the electrical load current equally.
5How does a Constant Speed Drive (CSD) maintain a constant alternator output frequency despite varying jet engine speeds?
A.By varying the electrical frequency output electronically using a static inverter
B.By using a hydro-mechanical variable-displacement hydraulic pump and fixed motor differential gear system
C.By slipping an electromagnetic clutch between the engine accessory gearbox and alternator shaft
D.By altering the field pole excitation strength in proportion to rotor RPM changes
Explanation: A CSD uses a variable-displacement hydraulic pump driven by the engine gearbox combined with a hydraulic motor acting on a differential gear assembly. A speed governor adjusts pump displacement to speed up or slow down differential output, keeping the generator shaft speed constant (typically 6000 or 8000 RPM) to yield 400 Hz AC.
6If an Integrated Drive Generator (IDG) experiences a severe internal mechanical failure or high oil temperature in flight, what happens when the flight deck IDG disconnect switch is activated?
A.An electromechanical solenoid disengages the drive shaft, which can be reconnected in flight once the IDG cools
B.A spring-loaded jaw clutch disconnects the drive shaft electrically, and reconnection can only be performed manually on the ground
C.A hydraulic bypass valve redirects oil away from the CSD, allowing the generator to freewheel safely
D.The generator field circuit is opened, stopping current generation while maintaining mechanical shaft rotation
Explanation: Activating the flight deck IDG disconnect switch energizes a solenoid that releases a spring-loaded disconnect mechanism, unmeshing the drive jaw clutch from the engine accessory drive. Because of mechanical locking, an IDG disconnected in flight CANNOT be re-engaged in flight; it must be reset manually on the ground with the engine shut down.
7What is the mechanical purpose of the commutator in a DC generator?
A.To step up output voltage generated by the field coils
B.To convert alternating current (AC) induced in the armature coils into direct current (DC) at the output terminals
C.To eliminate electrical noise produced by radio frequency interference
D.To maintain constant armature rotational speed during varying electrical loads
Explanation: As the armature coils rotate in the magnetic field, an alternating voltage (AC) is induced in them. The mechanical commutator segments and stationary carbon brushes switch coil connections as polarity reverses, rectifying AC into pulsing DC output.
8What is the function of the Reverse Current Cutout Relay (RCCR) in a DC generator control system?
A.To disconnect the generator from the bus bar when generator output voltage falls below battery/bus voltage
B.To reverse generator armature polarity during engine starting
C.To open the shunt field circuit if generator current output exceeds rated limits
D.To equalize voltage differences between left and right engine main DC buses
Explanation: When generator output voltage drops below battery or bus voltage (such as during engine idle or shutdown), current would flow backwards from the battery into the generator, causing the generator to act as a motor and discharge the battery. The RCCR opens its contacts to disconnect the generator under reverse current conditions.
9A 115V/200V 3-phase AC aircraft alternator supplies a balanced load of 30 amperes per phase at a line-to-line voltage of 200V. What is the total apparent power supplied by the alternator?
A.6.0 kVA
B.10.39 kVA
C.12.0 kVA
D.18.0 kVA
Explanation: For a balanced 3-phase AC system, apparent power S = sqrt(3) x V_L-L x I_L = 1.732 x 200V x 30A = 10,392 VA = 10.39 kVA. Alternatively, using phase voltage: 3 x V_phase x I_phase = 3 x 115.47V x 30A = 10,392 VA = 10.39 kVA.
10During engine startup using a starter-generator, how are the internal field windings connected during the start phase compared to the generation phase?
A.Series-connected for high starting torque, then reconfigured to shunt-connected for voltage regulation
B.Shunt-connected for starting, then reconfigured to series-connected for power generation
C.Permanently connected in parallel for both start and generator operating modes
D.Separately excited by static inverter AC power during start, then self-excited during generation
Explanation: Starter-generators contain heavy series field windings to produce high starting torque needed to crank turbine engines. Once the engine reaches self-sustaining speed (starter cutout speed), internal relays reconfigure the field windings into a shunt circuit for stable voltage regulation during power generation.
About the SACAA AME Electrical & Radio Practice Questions
Verified exam format metadata for SACAA Aircraft Maintenance Engineer Electrical Equipment (CAT X & W) Theoretical Knowledge Examination is pending. The practice questions above remain available while official exam length, timing, passing score, fee, and administrator details are reviewed.