FREE AMT Aircraft Electrical Systems Questions and Answers

Question 1

In a typical large transport aircraft AC electrical system, what is the primary purpose of a Constant Speed Drive (CSD) unit?

Accepted Answer

To convert variable engine RPM into a constant generator speed.

Answer

The AC generators on most large aircraft must turn at a constant speed to produce alternating current at a stable frequency, typically 400 Hz. [1, 2, 3] Since the engine's accessory gearbox speed varies with engine thrust settings, a Constant Speed Drive (CSD) is used as a hydro-mechanical transmission to ensure the generator rotates at a constant RPM, regardless of the engine's speed. [1, 4]

Question 2

A technician is troubleshooting a circuit that repeatedly trips its protective device shortly after being reset. The aircraft is in a high-vibration environment. Which of the following is the most likely cause?

Accepted Answer

An intermittent short to ground in the wiring.

Answer

An intermittent short to ground is a common cause for a circuit breaker to trip repeatedly. In a high-vibration environment, wiring insulation can chafe against the aircraft structure, creating a temporary path to ground that draws excessive current and trips the breaker. Once the vibration stops or changes, the contact may be broken, allowing the breaker to be reset, only for it to trip again when the fault reoccurs.

Question 3

When comparing a typical aircraft DC alternator to a DC generator, what is a significant advantage of the alternator?

Accepted Answer

It produces sufficient charging current at lower engine RPMs.

Answer

A key advantage of alternators is their ability to produce significant electrical output at low engine speeds, including idle. [12, 16, 27] This is crucial for modern aircraft with high electrical loads. Generators, in contrast, typically require higher RPM to produce adequate charging current, and can even drain the battery at idle. [24, 32]

Question 4

According to 14 CFR Part 25, if the ability to replace a fuse is essential to safety in flight, what is the minimum number of spare fuses that must be available?

Accepted Answer

At least 50% of the number of fuses of each rating.

Answer

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.' [11, 14] This regulation ensures that flight crews have sufficient spares for critical systems.

Question 5

While reviewing an aircraft wiring diagram, a technician notes a component symbol consisting of a coil and a set of contacts. When the coil is energized, it mechanically closes the contacts in a separate circuit. What does this symbol represent?

Accepted Answer

A relay.

Answer

This describes the function and schematic representation of a relay. A relay is an electromechanical switch that uses a small current in a control circuit (the coil) to control a larger current in a separate power circuit (the contacts). [9] This allows for remote switching and the control of high-power circuits with a low-power signal.

(AMT) Aviation Maintenance Technician Practice Test

(AMT) Aviation Maintenance Technician Practice Test

FREE AMT Aircraft Electrical Systems Questions and Answers