Aircraft Maintenance Technician Study Guide - Vocabulary

A collection of vocabulary terms and definitions essential for aircraft maintenance technicians, covering general subjects, airframe structures, and powerplant systems as presented in the FAA study guide.

Ohm’s Law

The most important law applicable to the study of electricity, expressed by the formula I = E \bdiv R.

Inductance

An induced voltage in an AC circuit that is opposite in direction to the applied voltage and opposes any change in the alternating current.

Impedance

The combined effect of resistance, inductive reactance, and capacitive reactance in an AC circuit.

Specific Gravity

The measurement of the electrolyte in a lead acid battery, which should be between $1.275$ and $1.300$ in a fully charged battery.

Electromagnetic Induction

The transfer of electrical energy by means of a magnetic field, which is the principle of transformer operation.

Tolerance

The difference between the plus and the minus allowance figures when a dimension shows an allowable variation on an aircraft drawing.

Clearance

The dimension given for the space between moving parts in aircraft drawings.

Title Block

A section of a blueprint containing the drawing number, name of the part, scale, date, and names of the draftsman, checker, and approving official.

Bill of Material

A list of materials and parts necessary for the fabrication or assembly of a component or system.

Datum

An imaginary vertical line or plane used in weight and balance calculations from which all measurements are taken forward and aft.

Arm

The distance in inches an item is located either forward or aft of the datum line.

Moment

A force representing the tendency of an object to rotate about the center of gravity, obtained by multiplying weight by arm and expressed in $inch-pounds$.

Tare Weight

The weight of extra equipment used for weighing an aircraft (such as chocks or jacks) which must be subtracted from the scale readings.

Minimum Fuel

The amount of fuel necessary to operate engine(s) for one-half hour at maximum continuous power ($1/2 \text{ hour}$), used in weight and balance computations under FAR Part $23$.

Residual Fuel

Fuel remaining in the tanks, lines, and engine after draining; also known as unusable or undrainable fuel.

Identification Stripe

A stripe running along the length of a flexible hose used to determine if the hose has twisted during installation.

Quick Disconnect Couplings

Fittings installed where frequent uncoupling of lines is required, designed to prevent fluid loss or air entry when disconnected.

Grip Length

The unthreaded portion of a bolt shank, which should generally equal the total thickness of the material being bolted together.

Solution Heat Treating

The process of heating an alloy to a predetermined temperature, soaking it, and rapidly quenching it to a low temperature.

Hydraulic Lock

A condition where liquid is present in the cylinder of a reciprocating engine, detected by abnormal effort when pulling the propeller through by hand.

Octane Number

A system used to designate the performance rating of aviation gasoline for fuels below grade $100$.

Fretting Corrosion

Corrosion occurring between two mating surfaces subject to slight relative motion, characterized by pitting and fine debris.

Wet Wash Cleaning

A cleaning method used to remove oil, grease, and carbon deposits, excluding corrosion and oxide films.

Dry Wash Cleaning

A cleaning method used to remove film, dust, and small accumulations of dirt.

Time in Service

The time from the moment an aircraft leaves the surface of the earth until it touches it at the next point of landing.

FAA Form 337

The document used to record the description and approval of a major repair or major alteration.

Temperature Inversion

An atmospheric phenomenon where cool air is trapped near the earth's surface by a layer of warm air.

Absolute Zero

The temperature at which all molecular motion ceases, considered to be $-273^\text{o} C$.

Standard Atmospheric Pressure

Defined as $14.7 \text{ psi}$ or $29.92 \text{ inches of Hg}$ at sea level.

Speed of Sound

Under standard sea level conditions, this is $662 \text{ knots}$ or $761 \text{ mph}$.

Scarf Joint

A type of joint used in splicing structural wood members or plywood where the edges are beveled for maximum glue area.

Selvedge Edge

The edge of cloth, tape, or webbing woven to prevent raveling.

Blush

A milky white appearance on a wet dope or lacquer finish caused by the condensation of moisture due to rapid evaporation of thinners.

Neutral Axis

The space in a piece of sheet metal, located between the stretched outside and compressed inside of a curve, that is neither stretched nor compressed during bending.

Joggle

An offset formed on an angle strip to allow clearance for a sheet or extrusion.

Fairlead

A cable guide used to guide control cables in a straight line through structural members, not deflecting alignment by more than $3^\text{o}$.

Vortex Generators

Small, low-aspect-ratio airfoils mounted on the upper surface of wings to dampen shock-induced separation.

Servo Tab

An adjustable tab on the trailing edge of a control surface that moves opposite the control to aid the pilot in moving the surface.

Shimmy Damper

A hydraulic unit designed to prevent nose wheel vibration during taxiing, landing, or takeoff.

Fusible Plug

A plug in aircraft wheels designed to melt at specific elevated temperatures to relieve air pressure and prevent tire blowouts.

Unloading Valve

A valve designed to provide a low pressure path from the pump back to the reservoir when the system has no flow requirements, also acting as a pressure regulator.

Cabin Outflow Valve

The principal control element in a cabin pressurization system.

ELT

Emergency Locator Transmitter; a distress beacon activated by an impact force of $5G$ or more, transmitting on $121.5 \text{ MHz}$ and $243 \text{ MHz}$.

Detonation

The instantaneous explosive burning of the last portion of the fuel-air charge in a cylinder.

Nozzle Diaphragm

Also known as a turbine nozzle; it prepares combustion mass airflow to drive the turbine rotor by changing heat and pressure into velocity.

Augmentor System

A system using exhaust gas to draw additional cooling air over the engine and sometimes used for cabin heating or anti-icing.

Flash Point

The temperature at which oil will begin to give off ignitable vapors.

Fire Point

The temperature at which oil gives off sufficient vapors to support a continuous flame.

E-Gap Position

The point in magneto rotation when the poles of the rotating magnet are a few degrees past the neutral position, where the primary breaker points open.

Venturi

A component in a carburetor that proportions the fuel-air mixture, lowers pressure at the discharge nozzle, and limits airflow at full throttle.

Vapor Lock

A condition caused by low fuel pressure, high fuel temperatures, or excessive fuel turbulence that prevents fuel flow.

Slinger Ring

A U-shaped channel on a propeller assembly that uses centrifugal force to transfer deicing fluid to the propeller blades.