NCATT AET cheat sheet

Four forces act on an aircraft: lift, weight, thrust, and drag; in steady, unaccelerated level flight, lift equals weight and thrust equals drag.

Roll is motion about the longitudinal axis and is controlled by ailerons; pitch is about the lateral axis and is controlled by the elevator; yaw is about the vertical axis and is controlled by the rudder.

Lift increases with angle of attack up to the critical angle, where airflow separates and the wing stalls; a stall can occur at any airspeed or attitude.

The ICAO standard atmosphere at sea level is 15 degrees Celsius, 29.92 inches of mercury or 1013.25 hectopascals, with a tropospheric lapse rate near 2 degrees Celsius per 1000 feet.

Pitot pressure is total pressure; static pressure is ambient pressure; the airspeed indicator uses the difference between them, while the altimeter and vertical speed indicator use static pressure.

Pascal's law states that pressure applied to a confined fluid is transmitted undiminished in all directions; hydraulic force equals pressure times piston area.

Semimonocoque structure uses stressed skin supported by stringers and frames; loads are carried by the skin, stringers, and frames together rather than by the skin alone.

A turbine engine has intake, compressor, combustor, turbine, and exhaust sections; a turbofan also has a bypass duct and is characterized by its bypass ratio.

Ohm's law: V = IR; power relationships include P = VI, P = I squared R, and P = V squared divided by R.

Series circuits have one current path: current is identical through all components, voltage divides, and total resistance is the sum of individual resistances.

Parallel circuits have multiple current paths: voltage is identical across each branch, current divides, and total resistance is found from the reciprocal sum of branch resistances.

Kirchhoff's current law states that the algebraic sum of currents entering a node is zero; Kirchhoff's voltage law states that the algebraic sum of voltages around a closed loop is zero.

For a sine wave, frequency equals one divided by period; RMS value equals peak value divided by the square root of two, about 0.707 times peak.

Capacitive reactance is XC = 1 divided by 2 pi f C; inductive reactance is XL = 2 pi f L; impedance magnitude is the square root of R squared plus the square of XL minus XC.

A capacitor stores energy in an electric field and blocks direct current while passing alternating current; an inductor stores energy in a magnetic field and opposes changes in current.

In an ideal transformer, primary-to-secondary voltage ratio equals the turns ratio, and power is conserved so current changes inversely with voltage.

Binary is base 2 and uses only 0 and 1; each bit position represents a power of two, and eight bits form one byte; hexadecimal is base 16.

In two's complement representation, a negative number is formed by inverting all bits of the positive value and adding one.

AND outputs 1 only when all inputs are 1; OR outputs 1 when any input is 1; NOT inverts; XOR outputs 1 only when inputs differ.

Combinational logic output depends only on present inputs; sequential logic uses memory elements such as flip-flops and changes state on a clock edge.

An analog-to-digital converter samples and quantizes an analog voltage into binary codes; resolution equals reference voltage divided by two raised to the number of bits.

ARINC 429 is a serial avionics bus using 32-bit words over twisted-pair wiring, commonly at 12.5 or 100 kilobits per second, with one transmitter per bus.

A line-replaceable unit is an avionics component designed for removal and replacement on the aircraft; built-in test equipment monitors its operation and reports faults.

RAM is volatile memory that loses data when power is removed; ROM and flash are nonvolatile and retain stored data without power.

American Wire Gauge numbers specify conductor size; a larger AWG number means a smaller conductor diameter and higher resistance per unit length.

A crimp termination is made by deforming a metal barrel around a conductor with a calibrated tool; correct wire gauge, insertion depth, and pull strength are required.

Cable shields are typically grounded at one end to provide electrostatic shielding while avoiding ground loops that can carry induced noise currents.

Coaxial cable has a center conductor, dielectric, metallic shield, and jacket; impedance is commonly 50 or 75 ohms, and minimum bend radius must be observed.

Connector keying and clocking prevent incorrect mating; keyways ensure pins engage only with their intended sockets.

Environmental splices use a crimp barrel with an adhesive-lined heat-shrink sleeve to exclude moisture and provide strain relief.

Twisted-pair wiring and shielded cables reduce electromagnetic interference; signal wires are routed separately from high-power and high-current cables.

Terminal lugs must be matched to stud size, installed with the specified torque, and checked for security; loose or over-torqued terminations cause high resistance or damage.

A multimeter measures voltage in parallel with the circuit, current in series with the circuit, and resistance only in a de-energized circuit.

An oscilloscope displays voltage versus time; volts per division sets vertical scale, time per division sets horizontal scale, and the ground clip provides the reference.

Probe compensation adjusts the probe's trimmer capacitor to match the oscilloscope input so a square wave displays flat tops and accurate amplitude.

A megohmmeter applies a high DC test voltage to measure insulation resistance; the circuit must be de-energized and isolated before testing.

A time-domain reflectometer sends pulses into a cable and analyzes reflections to locate opens, shorts, and impedance changes.

Voltage-drop testing measures voltage across a connection while current flows; excessive drop indicates high resistance such as a corroded or loose termination.

Half-split troubleshooting divides a system into sections, tests at the midpoint, and continues dividing the faulty section to isolate the fault efficiently.

Before working on avionics, discharge stored energy in capacitors, use lockout and tagout, and follow electrostatic discharge precautions for sensitive components.

Many transport aircraft use 28-volt DC and 115-volt 400-hertz AC electrical power; 400-hertz AC allows smaller transformers and motors than 60-hertz AC.

An antenna requires an adequate conductive ground plane and a good bond to the airframe; poor bonding or ground plane size affects radiation pattern and impedance.

Voltage standing wave ratio indicates impedance match in an antenna system; a value near 1:1 is ideal, and higher values indicate reflected power.

A line-replaceable unit installation requires correct part number and configuration, secure rack mounting, properly mated connectors, and adequate cooling airflow.

Aircraft bonding provides low-resistance electrical connections between structures and components for fault current return, static discharge control, and lightning protection.

Avionics cooling must maintain airflow and temperature limits; blocked filters, failed fans, or inadequate clearances can cause overheating and intermittent faults.

Wire bundles are routed with clamps and chafe protection, away from hot surfaces, fuel lines, and high-current cables, and must respect minimum bend radius.

Pitot and static systems require leak checks and correct port alignment; obstruction or leakage causes inaccurate airspeed, altitude, and vertical speed indications.