A&P - Aircraft and Powerplant Aircraft Electrical Systems Questions and Answers — Questions and Answers
Question 1: In a typical light aircraft electrical system, what is the primary function of the voltage regulator?
- To convert alternating current (AC) to direct current (DC).
- To maintain a constant voltage output from the generator/alternator under varying engine speeds and electrical loads. (Correct answer)
- To prevent the battery from overcharging by disconnecting it from the bus bar.
- To step up the voltage for the ignition system.
Correct answer: To maintain a constant voltage output from the generator/alternator under varying engine speeds and electrical loads.
The voltage regulator's main purpose is to monitor the electrical system's voltage and adjust the field current of the alternator or generator to maintain a steady, predetermined voltage level. This ensures consistent power to all electrical components and proper battery charging, regardless of changes in engine RPM or the number of active electrical devices.
Question 2: A technician is troubleshooting a circuit where the circuit breaker trips immediately upon closing the switch, even with the electrical component disconnected. Which of the following is the MOST likely cause?
- A defective circuit breaker.
- An open circuit in the wiring.
- A short circuit to ground between the switch and the component. (Correct answer)
- The electrical component has an internal short.
Correct answer: A short circuit to ground between the switch and the component.
A direct short to ground provides a path of very low resistance for the current to flow, causing a very high current draw that trips the circuit breaker instantly. Since the component is disconnected, the fault must be in the wiring between the protective device and the point of disconnection.
Question 3: Which of the following is a key difference between a fuse and a circuit breaker in an aircraft electrical system?
- A fuse can be reset multiple times, whereas a circuit breaker must be replaced after tripping.
- A circuit breaker is designed to protect against over-voltage, while a fuse protects against over-current.
- A fuse must be replaced after it opens the circuit, while a circuit breaker can typically be reset. (Correct answer)
- A circuit breaker operates on thermal principles, while a fuse is electromagnetic.
Correct answer: A fuse must be replaced after it opens the circuit, while a circuit breaker can typically be reset.
The fundamental operational difference is that a fuse is a one-time use device containing a metal strip that melts to interrupt the circuit during an overcurrent event and must be replaced. A circuit breaker is a mechanical switch that automatically opens the circuit during an overcurrent and can be manually reset after the fault is cleared.
Question 4: According to 14 CFR Part 23, what is required for an aircraft's electrical system regarding its power sources?
- A single generator is sufficient for all flight operations, provided it has a backup battery.
- No failure or malfunction of any one power source may impair the ability of any remaining source to supply power to loads essential for safe operation. (Correct answer)
- The battery must be capable of powering all electrical equipment for at least 60 minutes.
- All power sources must be manually switchable by the flight crew.
Correct answer: No failure or malfunction of any one power source may impair the ability of any remaining source to supply power to loads essential for safe operation.
14 CFR 23.1351 states that electrical power sources must function properly when connected independently or in combination, and critically, that a failure of any single power source must not prevent the remaining sources from supplying power to essential loads required for safe flight.
Question 5: What is the purpose of a bus bar in an aircraft electrical system?
- To generate electrical power.
- To store electrical energy for emergency use.
- To serve as a common distribution point for electrical power to various circuits. (Correct answer)
- To regulate the current flowing to the battery.
Correct answer: To serve as a common distribution point for electrical power to various circuits.
A bus bar is a conductive metal strip or bar that serves as a centralized terminal for distributing electrical power from the sources (like the alternator and battery) to the individual circuits protected by fuses or circuit breakers.
Question 6: A technician measures the specific gravity of the electrolyte in a fully charged lead-acid battery. What reading would be considered normal?
- 1.100 to 1.150
- 1.200 to 1.250
- 1.325 to 1.350
- 1.275 to 1.300 (Correct answer)
Correct answer: 1.275 to 1.300
For a fully charged lead-acid battery, the specific gravity of the electrolyte is typically between 1.275 and 1.300. This measurement indicates the density of the sulfuric acid in the electrolyte, which is highest when the battery is fully charged.
A&P - Aircraft and Powerplant Aircraft Electrical Systems Questions and Answers
In a typical light aircraft electrical system, what is the primary function of the voltage regulator?