Free Practice Questions for SACAA AME Electrical & Radio

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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 Exam

The SACAA AME Electrical & Radio examination tests DC and AC power generation, constant speed drives, integrated drive generators (IDGs), transformer rectifier units (TRUs), lead-acid and Ni-Cd batteries, EWIS wiring practices, and circuit protection devices for aircraft maintenance licensing (CAT X & W).

Exam sponsor: South African Civil Aviation Authority (SACAA). The requirements and fees below concern the certification or admission exam, separate from our free practice resources.

Assessment

Question count not published by the exam provider

Time Limit

75 minutes

Passing Score

75%

Exam / Certification Fees

~R425–R450 per subject (confirm current SACAA Part 187 fee)

Exam sponsor website

Fees, eligibility, and exam policies can change. Confirm them with the exam sponsor before applying or paying.

Official sources

Our practice resources: topics covered

We aim to reflect publicly available exam outlines and topic information in our study resources. Coverage, format, and difficulty may differ from the actual exam, and we cannot guarantee that every detail is accurate or current. Confirm exam requirements, fees, and policies with the official exam sponsor.

25%

Electrical Power Generation (DC & AC)

DC generators, alternators, starter-generators, AC alternators, brushless generators, constant speed drives (CSDs), and integrated drive generators (IDGs).

25%

Power Distribution & Bus Systems

Bus bar configuration, split-bus vs parallel bus, bus tie breakers (BTBs), static inverters, transformer rectifier units (TRUs), and essential bus power.

20%

Aircraft Batteries & Storage

Lead-acid and Nickel-Cadmium (Ni-Cd) aircraft batteries, electrolyte maintenance, thermal runaway precautions, battery capacity testing, and charging.

15%

EWIS & Circuit Protection

Electrical Wiring Interconnect System (EWIS), wire sizing, insulation types, crimping, connectors, relays, solenoids, circuit breakers, and fuses.

15%

Electric Motors, Actuators & Ignition

AC/DC electric motors, linear actuators, starter solenoids, high-energy turbine ignition units, and spark igniter lead testing.

Preparing for the SACAA AME Electrical & Radio Exam

What You Need to Know

Passing score: 75%
Assessment: Question count not published by the exam provider
Time limit: 75 minutes
Exam / certification fees: ~R425–R450 per subject (confirm current SACAA Part 187 fee) Official sources

Using Our Practice Resources

Work through all 100 available questions
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SACAA AME Electrical & Radio: Suggested Study Strategy

1Memorise standard aircraft AC frequency (400 Hz) and line-to-neutral (115V AC) vs line-to-line (200V AC) voltages.

2Understand TRU operation (steps down 115V AC and rectifies to 28V DC) and static inverter operation (converts 28V DC to 115V 400Hz AC).

3Know the difference between thermal circuit breakers (push-pull, trip-free) and magnetic circuit breakers.

4Review Ni-Cd battery electrolyte spill cleanup (use boric acid or vinegar) vs lead-acid (use sodium bicarbonate).

Frequently Asked Questions

What is the pass mark for SACAA AME Electrical & Radio?

The pass mark is 75%, tested centrally via SACAA PEXO multiple-choice exam.

What aircraft voltage standards are covered?

Standard 28V DC systems (generator/battery) and 115V AC / 400 Hz 3-phase AC systems (alternator/IDG/inverter).

What battery safety rules are tested?

Ni-Cd battery thermal runaway hazards, potassium hydroxide (KOH) electrolyte neutralisation, constant-current vs constant-voltage charging, and deep-cycling.

Free Practice Questions for SACAA AME Electrical & Radio

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