Free Airframe Mechanic Aircraft Electrical Systems Questions and Answers — 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?
- It can be manually reset only after the fault condition has been cleared.
- It will open the circuit to protect against overloads, even if the operating mechanism is held in the 'ON' position. (Correct answer)
- It automatically resets itself once the circuit has cooled down after an overload.
- It requires a special tool to be reset, preventing unauthorized reactivation of the circuit.
Correct answer: It will open the circuit to protect against overloads, even if the operating mechanism is held in the 'ON' position.
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?
- The static inverter
- The battery bus
- The Generator Control Unit (GCU) (Correct answer)
- The reverse current cutout relay
Correct answer: The Generator Control Unit (GCU)
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?
- Low electrolyte level causing increased internal resistance.
- Excessive discharge rates during engine start.
- High charging current combined with high battery temperature. (Correct answer)
- Operation in extremely low ambient temperatures.
Correct answer: High charging current combined with high battery temperature.
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?
- To convert AC power to DC power for battery charging.
- To regulate the voltage output of the main generators.
- To provide a stable source of DC power for emergency lighting.
- To convert DC power from the aircraft battery or DC bus to AC power. (Correct answer)
Correct answer: To convert DC power from the aircraft battery or DC bus to AC power.
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?
- To act as a secondary structural attachment for the control surface.
- To provide a low-resistance path for static electricity and fault currents. (Correct answer)
- To dampen high-frequency vibration of the control surface.
- To transmit control position data to the flight data recorder.
Correct answer: To provide a low-resistance path for static electricity and fault currents.
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.
Question 6: According to acceptable practices like those found in AC 43.13-1B, when routing a new wire bundle, what is a key requirement for the amount of slack provided in the bundle?
- The bundle must be routed with zero slack to prevent vibration.
- Sufficient slack must be provided to permit ease of maintenance and prevent mechanical strain. (Correct answer)
- A mandatory service loop of exactly 3 inches in diameter must be made at each end.
- Slack should be at least 50% of the total wire length for future repairs.
Correct answer: Sufficient slack must be provided to permit ease of maintenance and prevent mechanical strain.
AC 43.13-1B states that wires and cables should be provided with enough slack to permit ease of maintenance (like moving components without disconnecting them) and to prevent mechanical strain on the wires, connectors, and supports. Too much tension can damage connections, while too little can lead to chafing from excessive movement.
Free Airframe Mechanic Aircraft Electrical Systems Questions and Answers
An aircraft's electrical system is protected by 'trip-free' circuit breakers.
What is the defining characteristic of this type of circuit breaker?