AME - Aircraft Maintenance Engineer Aircraft Electrical Systems Questions and Answers — Questions and Answers
Question 1: What is the primary function of a Constant Speed Drive (CSD) unit in an aircraft's AC electrical system?
- To convert variable engine RPM into a constant generator RPM. (Correct answer)
- To rectify alternating current (AC) to direct current (DC).
- To regulate the voltage output of the generator.
- To act as a circuit breaker in case of an electrical fault.
Correct answer: To convert variable engine RPM into a constant generator RPM.
The primary purpose of a Constant Speed Drive (CSD) is to take the variable rotational speed from the engine's accessory gearbox and convert it into a constant speed for the AC generator. This ensures the generator produces a stable frequency (typically 400 Hz) required by aircraft systems, regardless of changes in engine thrust.
Question 2: During a routine inspection of a 24-volt lead-acid battery, an AME notices a significant difference in specific gravity readings between individual cells (e.g., one cell is 1.275 while another is 1.220). What is the most appropriate action?
- Top off the low cell with distilled water and return to service.
- Charge the battery and re-check the specific gravity.
- Replace the battery as it is likely nearing the end of its service life. (Correct answer)
- Add sulfuric acid to the low cell to equalize the specific gravity.
Correct answer: Replace the battery as it is likely nearing the end of its service life.
A specific gravity difference of 0.050 or more between cells in a lead-acid battery indicates that the battery is approaching the end of its useful life and should be considered for replacement. Topping off with water or simply recharging will not fix the underlying issue of a failing cell. Adding acid is never the correct procedure for adjusting specific gravity in the field.
Question 3: In accordance with 14 CFR Part 25, if a fuse is essential for safety in flight and is accessible to the flight crew, what is the minimum number of spare fuses that must be carried on board?
- One spare for each essential fuse.
- At least 25% of the number of fuses of each required rating.
- At least 50% of the number of fuses of each required rating. (Correct answer)
- A quantity sufficient to replace all essential fuses once.
Correct answer: At least 50% of the number of fuses of each required rating.
14 CFR § 25.1357(d) states: "Where fuses are used, there must be spare fuses for use in flight equal to at least 50% of the number of fuses of each rating required for complete circuit protection." This regulation ensures that sufficient spares are available for critical systems.
Question 4: Which of the following describes a 'trip-free' circuit breaker?
- A circuit breaker that can be reset remotely from the cockpit.
- A circuit breaker that requires a special tool to be reset.
- A circuit breaker that cannot be manually reset until it has cooled down.
- A circuit breaker that will open a circuit even if the operating control is held in the 'ON' position. (Correct answer)
Correct answer: A circuit breaker that will open a circuit even if the operating control is held in the 'ON' position.
A 'trip-free' circuit breaker is a safety feature designed to ensure that it will open the circuit during an overload or fault condition, regardless of whether the manual operating lever or button is held in the closed (ON) position. This prevents the crew from forcing a circuit to remain closed against a persistent fault.
Question 5: An aircraft is being prepared for flight at a remote station without ground power available. The AME needs to power the ground handling bus to operate the cargo bay lights and refueling system. Which power source would typically be used in this scenario?
- The main aircraft battery via an inverter.
- The Auxiliary Power Unit (APU) generator. (Correct answer)
- A Ram Air Turbine (RAT).
- The main engine-driven generators.
Correct answer: The Auxiliary Power Unit (APU) generator.
The ground handling bus is typically powered by the APU generator or an external power unit. Since external power is unavailable, the APU would be started to provide electrical power for ground operations like cargo lighting and refueling without needing to start the main engines.
Question 6: When selecting the proper wire size for an electrical installation in an aircraft, which of the following is a critical factor according to the American Wire Gauge (AWG) standard?
- The color of the wire insulation.
- The wire's flexibility rating.
- The wire's cross-sectional area. (Correct answer)
- The brand of the wire manufacturer.
Correct answer: The wire's cross-sectional area.
The American Wire Gauge (AWG) system sizes wires based on their diameter and corresponding cross-sectional area. A smaller AWG number indicates a larger wire diameter and greater current-carrying capacity. The cross-sectional area is the primary factor in determining the wire's resistance and ability to handle current without overheating.
AME - Aircraft Maintenance Engineer Aircraft Electrical Systems Questions and Answers
What is the primary function of a Constant Speed Drive (CSD) unit in an aircraft's AC electrical system?