Free Airframe Mechanic Aircraft Electrical Systems Questions and Answers

Question 1

An aircraft's electrical system is protected by 'trip-free' circuit breakers. What is the defining characteristic of this type of circuit breaker?

Accepted Answer

It will open the circuit to protect against overloads, even if the operating mechanism is held in the 'ON' position.

Answer

A 'trip-free' circuit breaker is a safety device designed to open and interrupt the current flow during an overload condition, regardless of the position of the operating handle. Even if a pilot or maintenance person tries to hold it in the closed ('ON') position, the internal mechanism will remain open as long as the fault exists, preventing damage to the circuit and reducing fire risk.

Question 2

A technician is troubleshooting a multi-engine aircraft's DC generation system where one generator is not sharing the load equally with the others. Which component is primarily responsible for ensuring all generators connected to a common bus share the electrical load proportionally?

Accepted Answer

The Generator Control Unit (GCU)

Answer

The Generator Control Unit (GCU) is responsible for multiple functions, including voltage regulation and load sharing in multi-generator systems. It senses the load on each generator and adjusts the field excitation to ensure each generator carries its proportional share of the total electrical load, a process often referred to as paralleling.

Question 3

Which of the following conditions is a primary cause of 'thermal runaway' in an aircraft's nickel-cadmium (Ni-Cad) battery?

Accepted Answer

High charging current combined with high battery temperature.

Answer

Thermal runaway in a Ni-Cad battery is a dangerous condition where high charging currents and high internal battery temperatures create a self-sustaining cycle. As the battery's temperature increases, its internal resistance drops, causing it to accept even more current from the charging system. This further increases the temperature, leading to an uncontrollable, rapid rise that can destroy the battery and create a fire hazard.

Question 4

What is the primary function of a static inverter in an aircraft electrical system?

Accepted Answer

To convert DC power from the aircraft battery or DC bus to AC power.

Answer

A static inverter is a solid-state electronic device that converts direct current (DC) into alternating current (AC). This allows DC power from sources like the aircraft's batteries or transformer-rectifier units to be used for instruments and avionics that require AC power, often as a primary or emergency backup source.

Question 5

During a pre-flight inspection, a pilot notices a frayed, flat, braided copper cable connecting the aircraft's elevator to the horizontal stabilizer. What is the primary purpose of this bonding strap?

Accepted Answer

To provide a low-resistance path for static electricity and fault currents.

Answer

Bonding straps (or jumpers) are used to create electrical continuity between all metallic components of the aircraft. Their primary purpose is to provide a path of least resistance for static electricity buildup and electrical fault currents, preventing arcing, sparks, and interference with radio and navigation equipment.

Airframe Mechanic Certification Practice Test

Airframe Mechanic Certification Practice Test

Free Airframe Mechanic Aircraft Electrical Systems Questions and Answers