Aircraft Electrical Fundamentals and Maintenance Regulations

Comprehensive practice flashcards covering basic electrical theory, DC circuits, electromagnetic induction, aircraft maintenance legislation (Part 43/SACAA), aircraft power generation, and lighting systems.

How is matter defined, and how does mass differ from weight?

Matter is anything that occupies space and has mass. Mass is the actual amount of matter in an object, whereas weight is the force exerted on that mass by gravity.

What formula defines the maximum electron capacity of an energy shell?

$\text{Capacity} = 2n^2$, where $n$ represents the shell number.

What are valence electrons, and why are they significant in electrical theory?

Valence electrons are electrons located in an atom's outermost shell. They govern electrical conductivity, valence, and the ability of an atom to participate in chemical bonding.

What is the distinction between a positive ion (cation) and a negative ion (anion)?

A cation is a positively charged ion formed when an atom loses one or more electrons; an anion is a negatively charged ion formed when an atom gains extra electrons.

How do conductors, semiconductors, and insulators differ in terms of free electron mobility?

Conductors have abundant free electrons that move easily under applied voltage (e.g., copper). Insulators hold electrons tightly with few or no free electrons under normal conditions (e.g., glass). Semiconductors possess electrical properties intermediate between conductors and insulators (e.g., silicon).

What causes static electricity, and why is it dangerous in aviation?

Static electricity is caused by friction between materials transferring electrons, creating a charge imbalance where no current flows. In aviation, friction between the outer airframe and the air can interfere with radio communication systems and damage sensitive equipment.

What is Coulomb's Law, and what is its mathematical expression?

Coulomb's Law states that the electrostatic force between two point charges is directly proportional to the product of their charges and inversely proportional to the square of the distance between them: $F = k \frac{q_1 q_2}{r^2}$, where Coulomb's constant $k = 8.99 \times 10^9\,N\cdot m^2/C^2$.

How many electrons make up one ampere of current flowing for one second?

$6.241 \times 10^{18}$ electrons, which equals $1\,C$ of electrical charge.

What are the three methods by which an object can acquire an electrostatic charge?

Friction (rubbing materials together), contact (touching an uncharged object with a charged object), and induction (bringing a charged object near a neutral object without physical contact).

What is electrical conductance, and what is its relationship to resistance?

Conductance ($G$) measures how easily a material permits electric current to flow and is the mathematical reciprocal of resistance: $G = \frac{1}{R}$. Its SI unit is the Siemens ($S$), previously termed mho.

How does conventional current flow compare to actual electron flow?

Conventional current flow assumes current moves from positive (+$) to negative (-$). Electron flow is the physical motion of negatively charged electrons travelling from the negative ($-$) terminal to the positive ($+$$) terminal.

What does Ohm's Law state in words and mathematical formula?

The voltage across a conductor is directly proportional to the current flowing through it, provided physical conditions and temperature remain constant: $V = I \times R$.

Which three physical factors govern the electrical resistance of a conductor?

Material resistivity, length (directly proportional), and cross-sectional area (inversely proportional).

What is the structural and functional difference between a rheostat and a potentiometer?

A rheostat has two terminals and regulates circuit current with a sliding contact; a potentiometer has three terminals and operates as an adjustable potential divider to regulate voltage.

What are Kirchhoff's First and Second Laws?

Kirchhoff's Current Law (KCL) states that the sum of currents entering a junction equals the sum of currents leaving that junction. Kirchhoff's Voltage Law (KVL) states that the algebraic sum of potential differences around any closed circuit loop is zero.

Why is the terminal potential difference of a battery lower than its electromotive force (EMF) when a load is applied?

When current flows through a completed circuit, internal resistance inside the battery creates an internal voltage drop ($I \times r$), resulting in a measured terminal voltage of $V = E - (I \times r)$.

What are the six primary methods used to generate electromotive force (EMF)?

Friction (static electricity), pressure (piezoelectricity), heat (thermoelectricity), light (photoelectricity), chemical action (batteries), and magnetism (electromagnetic induction).

How does a thermocouple generate voltage, and where is it applied in aviation?

It joins two dissimilar metals at two junctions; heating one junction relative to the other drives electron movement, producing a small voltage. Aviation uses thermocouples to measure exhaust gas temperature (EGT) and cylinder head temperature (CHT).

What do Faraday's Law and Lenz's Law establish regarding electromagnetic induction?

Faraday's Law establishes that a voltage is induced whenever there is relative motion or change in a magnetic field relative to a conductor. Lenz's Law states that the induced current flows in a direction that opposes the change producing it.

What is thermal runaway in aircraft batteries, and why is it dangerous?

Thermal runaway is an uncontrolled condition where elevated battery temperatures decrease internal resistance, drawing higher current and generating more heat. It can cause violent fire, explosions, structural component damage, and complete loss of electrical systems.

Why must aircraft battery compartments be well ventilated?

To ensure proper heat dissipation and prevent the hazardous accumulation of explosive hydrogen gas generated during the charging cycle.

What is the primary role of the International Civil Aviation Organization (ICAO)?

ICAO is a United Nations agency that establishes international Standards and Recommended Practices (SARPs) to promote safe, orderly, and compatible civil aviation across member states.

How do SACAA, SACAR, and SA-CATS interrelate within South African aviation law?

The South African Civil Aviation Authority (SACAA) is the regulatory body; the South African Civil Aviation Regulations (SACAR) represent the legal mandates; and the South African Civil Aviation Technical Standards (SA-CATS) supply the technical details explaining how to meet SACAR.

What do the aviation abbreviations AME, AMO, ATO, and AMTO stand for?

AME: Aircraft Maintenance Engineer; AMO: Aircraft Maintenance Organisation; ATO: Aviation Training Organisation (for flight crew); AMTO: Aircraft Maintenance Training Organisation.

How does SACAR Part 43 define an aircraft modification versus a repair?

A repair restores an unserviceable or damaged aircraft structure/component to an acceptable original configuration, whereas a modification is an approved change to the aircraft's original design, structure, or equipment.

What are the specific scopes of an AMM, CMM, and SRM?

An Aircraft Maintenance Manual (AMM) covers servicing and procedures for the entire aircraft type; a Component Maintenance Manual (CMM) provides detailed bench instructions for a specific off-wing component; and a Structural Repair Manual (SRM) covers allowable damage limits and structural repairs.

What do the Aircraft Logbook, Engine Logbook, and Propeller Logbook each record?

The Aircraft Logbook tracks airframe maintenance history, inspections, and defect rectifications; the Engine Logbook tracks engine maintenance, overhauls, and time-in-service; the Propeller Logbook tracks propeller inspections, repairs, and component replacements.

What does a maintenance Release to Service legally certify?

It certifies that all specified maintenance was completed in accordance with applicable technical procedures, approved data, and regulatory standards. It does not certify that the aircraft is free of every potential hidden defect.

Which ATA chapters govern Electrical Power and Aircraft Lighting respectively?

ATA Chapter 24 governs Electrical Power, and ATA Chapter 33 governs Aircraft Lighting.

What proportion of total aircraft cost can avionics represent in AWACS aircraft?

Over $75\%$ of the total aircraft cost (compared to approximately $30\%$ in general aircraft and $40\%$ in maritime patrol aircraft).

What are standard operating voltages and frequencies for aircraft DC and AC systems?

DC systems typically operate at $14\,V$ or $28\,V$. AC systems operate at $115\,V$ or $230\,V$ at a frequency of $400\,Hz$.

What is the function of a bus bar in an aircraft electrical system?

A bus bar acts as a common distribution point that receives power from generators or batteries and distributes electrical energy to specific circuit breakers and system loads.

What is the primary difference in function between an inverter and a transformer?

An inverter converts Direct Current (DC) into Alternating Current (AC), whereas a transformer steps an existing AC voltage up or down.

How does a DC generator convert internally induced AC into DC output?

It uses a mechanical commutator and carbon brushes to mechanically switch connections as the armature rotates through the magnetic field, rectifying the internal AC into DC.

What are the three functional sections of an electromagnetic generator voltage regulator?

A voltage regulator (maintains steady output voltage), a current limiter (limits maximum current to prevent overload), and a reverse-current cutout relay (disconnects the generator when output drops below battery voltage).

What are three advantages of aircraft alternators over DC generators?

Alternators are lighter, produce electrical power efficiently at low RPM, require less maintenance because they use solid-state diodes rather than commutators, and have a stationary stator where high currents are generated.

How does an Integrated Drive Generator (IDG) ensure a constant frequency output?

The IDG uses an internal constant speed drive to convert variable engine input speeds ($4{,}500\text{--}9{,}120\,\text{RPM}$) to a stabilized $12{,}000 \pm 120\,\text{RPM}$, delivering a steady $400 \pm 4\,Hz$ AC output.

What is the function of an aircraft Ram Air Turbine (RAT)?

The RAT is an emergency power source that deploys into the airstream to drive a turbine, generating hydraulic or electrical power during catastrophic dual-generator or engine loss.

What are the standard colors and airframe locations for aircraft navigation lights?

Red on the left wingtip (port), green on the right wingtip (starboard), and white on the tail/rear.

When must aircraft beacon lights and strobe lights be operated?

Anti-collision beacon lights (flashing red) must operate whenever the engines are running. High-intensity strobe lights (flashing white) operate during takeoff, flight, and landing, but should be turned off when taxiing or inside cloud/fog.

If a pilot at night sees only a steady red light from another aircraft, what does this indicate?

The other aircraft is crossing from right to left in front of the observer, showing its left (port) wingtip.

If a pilot at night sees both red and green lights on another aircraft simultaneously, what does this indicate?

The other aircraft is approaching directly head-on.

Under what conditions does aircraft emergency lighting automatically activate, and for how long does it operate?

Emergency lighting illuminates automatically when the flight deck control switch is set to 'ARM' and both AC and DC main electrical power fail. It runs on independent emergency batteries for approximately $15\,\text{minutes}$.

What safety precautions must be followed when maintaining high-intensity strobe lighting systems?

The power supply must be switched off and technicians must wait at least $5\,\text{minutes}$ for internal capacitors to discharge high voltages before handling. Strobe/halogen bulbs must never be touched with bare fingers because skin oils cause uneven heating and cracking.