A&P Aircraft Electrical Systems Questions and Answers — Questions and Answers
Question 1: An aircraft's 24-volt lead-acid battery has 12 cells. What is the approximate voltage of each cell when the battery is fully charged?
- 1.2 volts
- 1.5 volts
- 2.1 volts (Correct answer)
- 3.0 volts
Correct answer: 2.1 volts
A fully charged lead-acid battery cell has a nominal voltage of approximately 2.1 to 2.2 volts. In a 24-volt battery, there are 12 cells connected in series (12 cells x 2.1 volts/cell = 25.2 volts).
Question 2: During a pre-flight inspection, a pilot notices that a push-to-reset circuit breaker for the landing light circuit has 'popped.' What is the primary advantage of a circuit breaker over a fuse in this scenario?
- Circuit breakers react faster to overcurrent situations.
- Circuit breakers can be reset, while fuses must be replaced. (Correct answer)
- Circuit breakers are less susceptible to vibration.
- Circuit breakers provide both thermal and magnetic protection.
Correct answer: Circuit breakers can be reset, while fuses must be replaced.
The main advantage of a circuit breaker is its resettability. If a circuit breaker trips, it can be reset (after a cooling-off period and troubleshooting) without needing a replacement part, unlike a fuse which must be replaced once it blows.
Question 3: Which of the following is a primary advantage of an alternator over a generator in a light aircraft electrical system?
- Alternators are lighter and produce more stable voltage at low engine RPMs. (Correct answer)
- Alternators do not require a voltage regulator for operation.
- Alternators can produce AC power without the need for a rectifier.
- Alternators are self-exciting and can charge a completely dead battery.
Correct answer: Alternators are lighter and produce more stable voltage at low engine RPMs.
Alternators are generally lighter than generators of similar output and are capable of producing their rated power at lower engine speeds. This is a significant advantage during taxi and other low-RPM operations, preventing battery discharge.
Question 4: According to AC 43.13-1B, when routing electrical wiring, what is the maximum interval between support clamps for a wire bundle?
- 12 inches
- 18 inches
- 30 inches
- 24 inches (Correct answer)
Correct answer: 24 inches
FAA Advisory Circular AC 43.13-1B, Chapter 11, states that wires and cables should be supported by suitable clamps, grommets, or other devices at intervals of not more than 24 inches, except when contained in troughs, ducts, or conduits.
Question 5: A technician is troubleshooting an electrical issue and needs to distribute power from a single source to multiple circuits. What component is specifically designed for this purpose in an aircraft electrical system?
- A relay
- An inverter
- A bus bar (Correct answer)
- A transformer-rectifier unit
Correct answer: A bus bar
A bus bar is a metallic strip or bar that serves as a common connection point for multiple electrical circuits, distributing electricity from a single source (like a generator or battery) to various systems.
Question 6: What is the primary purpose of a voltage regulator in a DC generator or alternator system?
- To convert alternating current to direct current.
- To prevent the battery from overcharging by maintaining a constant system voltage. (Correct answer)
- To increase the output voltage as engine RPM increases.
- To act as a circuit breaker in case of a voltage spike.
Correct answer: To prevent the battery from overcharging by maintaining a constant system voltage.
The voltage regulator's main function is to monitor the aircraft's electrical system voltage and control the output of the generator or alternator to maintain a constant, predetermined voltage level, thus preventing battery overcharge and protecting electrical equipment.
