CAA NZ AME Electrical flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Ohm's law

Voltage equals current multiplied by resistance (V = I × R). Combined with P = V × I it lets you solve for any unknown in a DC circuit from two known quantities.

Kirchhoff's voltage law

Around any closed loop, the algebraic sum of source EMFs and voltage drops is zero. Used to solve networks where simple series and parallel rules do not apply directly.

Capacitive reactance

X_C = 1/(2πfC), measured in ohms. It falls as frequency or capacitance rises, so a capacitor blocks DC and passes high frequencies more readily.

Inductive reactance

X_L = 2πfL, measured in ohms. It rises with frequency and inductance, so an inductor opposes changes in current and causes current to lag voltage.

Resonance in AC circuits

The frequency at which inductive and capacitive reactance are equal. At resonance impedance equals resistance, current is maximum, and the circuit is purely resistive.

RMS versus peak voltage

For a sine wave, RMS equals peak divided by the square root of two, about 0.707 times peak. RMS is the value that produces equivalent heating.

Transformer turns ratio

V1/V2 = N1/N2 = I2/I1 for an ideal transformer. Voltage steps down as current steps up, with power in equal to power out.

Relay operating principle

Coil current produces magnetic flux that pulls an armature, closing or opening load contacts. The coil circuit and load circuit are electrically separate.

Freewheel diode function

A diode connected across an inductive coil that provides a path for collapsing coil current, limiting the voltage spike when the coil is de-energised.

Generator frequency formula

Frequency in hertz equals poles multiplied by revolutions per minute, divided by 120. It shows that frequency depends on pole count and drive speed.

Starter-generator

A single machine that cranks the engine as a motor and then generates electrical power once the engine runs, with external contactors selecting each mode.

Voltage regulator role

Senses generator output voltage and modulates field current to hold output within limits as speed and load vary. Overvoltage protection protects the bus instead.

Aircraft AC system standard

Transport aircraft commonly use 115 V AC, 400 Hz, three-phase. The higher frequency reduces the weight of transformers and motors compared with 50 or 60 Hz.

Essential bus

A distribution bus that remains powered after loss of normal generation, feeding loads required for continued safe flight and landing.

External power interlock

A sensing circuit that prevents the external power contactor from closing if polarity is reversed or voltage is outside limits, protecting aircraft systems.

Constant speed drive

A unit between the engine and generator that holds generator speed constant as engine speed varies, keeping AC frequency stable. A disconnect is provided for failures.

Bus tie contactor

A contactor connecting two main buses so one source can feed both. It closes automatically on loss of a generator only if the remaining source has capacity.

Primary bonding limit

The maximum resistance permitted between structural members forming the primary return path, typically 0.0025 ohm, verified with a calibrated low-resistance meter.

Insulation resistance test

A megohmmeter applies a specified DC voltage to an isolated circuit and measures leakage resistance. Results are compared with the maintenance manual minimum.

Shield termination practice

Cable shields are normally grounded at one end to avoid ground loops, terminated to the connector backshell or a dedicated ground point per the wiring diagram.

Wire voltage drop

For a two-wire run, drop equals twice the length times current times resistance per unit length. Excessive drop causes equipment malfunction even when the wire is not overloaded.

Maintenance release

A certification that specified maintenance has been carried out and the aircraft is airworthy, issued by a person holding the appropriate licence and rating.

Airworthiness directive status

Airworthiness directives are mandatory and must be complied with within the stated period. Service bulletins are usually recommended unless made mandatory by an AD.

Authorised release certificate

Documentation accompanying a part that certifies its airworthiness status. A part without acceptable release documentation is not eligible for installation.

AME licence ratings

An aircraft maintenance engineer licence carries category and type ratings. Certification is only permitted for work within the holder's rating and currency.

Approved data revision control

Work must be performed to the current revision of the maintenance manual and approved data. Revision status is checked before the task begins, not after.

Dirty dozen

Twelve recognised human factors contributing to maintenance error, including complacency, fatigue, pressure, distraction, poor communication, lack of resources and lack of knowledge.

Independent inspection

A second qualified person inspects critical work without having performed it, providing a defence against complacency and confirmation bias in the original task.

Documentation correction rule

Errors in maintenance records are corrected with a single line through the entry, initialled and dated. Overwriting, erasing or correction fluid is not permitted.

Ammeter connection

An ammeter is connected in series with the load because it has very low resistance. Connecting it across a supply short-circuits the circuit and blows its fuse.

Lockout and prove dead

Isolate the electrical source, tag the isolation point, then verify the circuit is de-energised with a meter before touching conductors that could be energised remotely.

Diode forward drop

A silicon diode conducts with a forward drop of about 0.6 to 0.7 volt. A near-zero or infinite reading in both directions indicates a shorted or open diode.