Airframe Mechanic Aircraft Electrical Systems Questions and Answers

Question 1

An aircraft's electrical schematic shows a device that uses a small current flowing through a coil to electromagnetically close a set of contacts, allowing a much larger current to flow to a high-power component like a starter motor. Which device performs this function?

Accepted Answer

A relay

Answer

A relay is an electromechanical switch that uses a small control current to activate an electromagnet, which in turn closes contacts to control a separate, high-power circuit. This allows for remote switching and reduces the need for heavy-gauge wiring to the cockpit controls.

Question 2

Which of the following is the primary purpose of a Transformer Rectifier Unit (TRU) in an aircraft electrical system?

Accepted Answer

To convert 115V AC power to 28V DC power

Answer

A Transformer Rectifier Unit (TRU) is a standard component in aircraft with AC power generation. Its main function is to transform the high-voltage AC (typically 115V, 400Hz) and then rectify it into stable, low-voltage DC (typically 28V) for use by numerous aircraft systems.

Question 3

A technician is performing maintenance on a nickel-cadmium (Ni-Cad) battery and observes a white, powdery residue on the battery case near the cell vents. This is most often caused by:

Accepted Answer

Electrolyte spewage due to overcharging or excessive heat.

Answer

The white, powdery substance found on Ni-Cad batteries is potassium carbonate. It forms when the potassium hydroxide electrolyte is spewed from the cells, often due to overcharging or high temperatures, and subsequently reacts with carbon dioxide in the air.

Question 4

What is the primary function of a Constant Speed Drive (CSD) connected to an engine-driven AC generator?

Accepted Answer

To convert the variable engine RPM into a constant generator RPM.

Answer

AC generators must rotate at a precise, constant speed to produce alternating current at a stable frequency (typically 400 Hz). A Constant Speed Drive is a hydro-mechanical transmission that takes the variable RPM from the engine's accessory gearbox and outputs a constant RPM to drive the generator.

Question 5

In a brushed DC generator, what is the combined function of the commutator and brushes?

Accepted Answer

To provide a sliding electrical connection and convert the internal AC to external DC.

Answer

As the armature rotates, it generates AC internally. The commutator, consisting of segmented copper bars, rotates with the armature. The stationary carbon brushes ride on the commutator, acting as a mechanical rectifier to reverse the current direction every half-turn, resulting in a DC output to the external circuit.

Airframe Mechanic Certification Practice Test

Airframe Mechanic Certification Practice Test

Airframe Mechanic Aircraft Electrical Systems Questions and Answers