Glossary

A soft silvery metal used for main bearing inserts in aircraft reciprocating engines. Babbitt is made of tin with small amounts of copper and antimony.

Aviation Maintenance Technician Handbook — Powerplant, p. G-3

The curved surface of a propeller blade. The back of a propeller blade corresponds to the upper surface of an airplane wing.

Aviation Maintenance Technician Handbook — Powerplant, p. G-3

The reciprocal of the localizer course for an ILS (Instrument Landing System). When flying a back-course approach, the aircraft approaches the instrument runway from the end on which the localizer antennas are installed.

Aviation Maintenance Technician Handbook — Airframe, p. G-4

A type of mixture control used in some float carburetors that regulates the air/fuel mixture by varying the air pressure above the fuel in the float bowl.

Aviation Maintenance Technician Handbook — Powerplant, p. G-3

Welding in which the torch is pointed away from the direction the weld is progressing.

Aviation Maintenance Technician Handbook — Airframe, p. G-4

A floating plate on which the wheel cylinder and the brake shoes attach on an energizing-type brake.

Aviation Maintenance Technician Handbook — Airframe, p. G-4

A flat leather or Teflon ring installed in the groove in which an O-ring or T-seal is placed. The backup ring is on the side of the seal away from the pressure, and it prevents the pressure extruding the seal between the piston and the cylinder wall.

Aviation Maintenance Technician Handbook — Airframe, p. G-4

A thin sheet metal shroud or bulkhead used to direct the flow of cooling air between and around the cylinder fins of an air-cooled reciprocating engine.

Aviation Maintenance Technician Handbook — Powerplant, p. G-3

A cable in the aileron system of an airplane that connects to one side of each aileron. When the control wheel is rotated, a cable from the flight deck pulls one aileron down and relaxes the cable going to the other aileron. The balance cable pulls the other aileron up.

Aviation Maintenance Technician Handbook — Airframe, p. G-4

A flat panel hinged to the leading edge of some ailerons that produces a force which assists the pilot in holding the ailerons deflected. The balance panel divides a chamber ahead of the aileron in such a way that when the aileron is deflected downward, for example, air flowing over its top surface produces a low pressure that acts on the balance panel and causes it to apply an upward force to the aileron leading edge.

Aviation Maintenance Technician Handbook — Airframe, p. G-4

An adjustable tab mounted on the trailing edge of a control surface to produce a force that aids the pilot in moving the surface. The tab is automatically actuated in such a way it moves in the direction opposite to the direction the control surface on which it is mounted moves.

Aviation Maintenance Technician Handbook — Airframe, p. G-4

A linear hydraulic or pneumatic actuator that has the same area on each side of the piston.

Aviation Maintenance Technician Handbook — Airframe, p. G-4

Being balanced in such a way that the aircraft wings tend to remain level.

Aircraft Weight and Balance Handbook, p. G-1

A weight installed or carried in an aircraft to move the center of gravity to a location within its allowable limits.

Aviation Maintenance Technician Handbook — General, p. G-2; Aircraft Weight and Balance Handbook, p. G-1

Nitrocellulose dissolved in amyl acetate, so named because it smells like bananas.

Aviation Maintenance Technician Handbook — Airframe, p. G-4

The act of rotating an aircraft about its longitudinal axis.

Aviation Maintenance Technician Handbook — Airframe, p. G-4

A method of augmenting the GPS integrity solution by using a nonsatellite input source. To ensure that baro-aiding is available, the current altimeter setting must be entered as described in the operating manual.

Pilot's Handbook of Aeronautical Knowledge, p. G-5

A small window in the dial of a sensitive altimeter in which the pilot sets the barometric pressure level from which the altitude shown on the altimeter is measured. This window is sometimes called the “Kollsman” window. base. The electrode of a bipolar transistor between the emitter and the collector. Varying a small flow of electrons moving into or out of the base controls a much larger flow of electron between the emitter and the collector.

Aviation Maintenance Technician Handbook — Airframe, p. G-4

In mathematics, used to refer to a particular mathematical object that is used as a building block. A base-a system is one that uses a as a new unit from which point counting starts again. (See decimal system.) In the mathematical expression an, read as “a to the nth power,” a is the base.

Aviation Maintenance Technician Handbook — General, p. G-2

Standard empty weight plus optional equipment.

Aviation Maintenance Technician Handbook — General, p. G-2

The moment of the airplane at its basic operating weight divided by the appropriate reduction factor.

Aircraft Weight and Balance Handbook, p. G-2

The empty weight of the aircraft plus the weight of the required crew, their baggage, and other standard items, such as meals and potable water.

Aircraft Weight and Balance Handbook, p. G-2

An exhaust stack with an elongated and flattened end. The gases leave the stack through a slot perpendicular to its length. Bayonet stacks decrease both exhaust back pressure and noise.

Aviation Maintenance Technician Handbook — Powerplant, p. G-3

See back course.

Pilot's Handbook of Aeronautical Knowledge, p. G-5

Bottom dead center. The position of a piston in a reciprocating engine when the piston is at the bottom of its stroke, and the wrist pin, crankpin, and center of the crankshaft are all in line.

Aviation Maintenance Technician Handbook — Powerplant, p. G-3

The high-strength carbon-steel wire bundles that give an aircraft tire its strength and stiffness where it mounts on the wheel.

Aviation Maintenance Technician Handbook — Airframe, p. G-4

The flat surface on the inside of the rim of an aircraft wheel on which the bead of the tire seats.

Aviation Maintenance Technician Handbook — Airframe, p. G-4

The amount of pull needed to cause a piece of sheet metal to tear at the points at which it is held together with rivets. The bearing strength of a material is affected by both its thickness and the diameter of the rivet.

Aviation Maintenance Technician Handbook — Airframe, p. G-4

A hardened-steel, coil-spring retainer used to hold a rivet set in a pneumatic rivet gun. This spring gets its name from its shape. It screws onto the end of the rivet gun and allows the set to move back and forth, but prevents it being driven from the gun.

Aviation Maintenance Technician Handbook — Airframe, p. G-5

The shape of the inlet of an augmentor tube that forms a smooth converging duct. The bell mouth shape allows the maximum amount of air to be drawn into the tube.

Aviation Maintenance Technician Handbook — Powerplant, p. G-3

A form of convergent inlet-air duct used to direct air into the compressor of a gas turbine engine. It is extremely efficient, and is used where there is little ram pressure available to force air into the engine. Bell mouth ducts are used in engine test cells and on engines installed in helicopters.

Aviation Maintenance Technician Handbook — Powerplant, p. G-3

The amount of material actually used to make a bend in a piece of sheet metal. Bend allowance depends upon the thickness of the metal and the radius of the bend, and is normally found in a bend allowance chart.

Aviation Maintenance Technician Handbook — Airframe, p. G-5

The radius of the inside of a bend.

Aviation Maintenance Technician Handbook — Airframe, p. G-5

A line made in a sheet metal layout that indicates the point at which the bend starts.

Aviation Maintenance Technician Handbook — Airframe, p. G-5

A colorless, volatile, flammable, aromatic hydrocarbon liquid which has the chemical formula C6H6. Benzene, which is sometimes called benzoil, is used as a solvent, a cleaning fluid, and a fuel for some special types of reciprocating engines.

Aviation Maintenance Technician Handbook — Powerplant, p. G-3

Equivalent to the principle of conservation of energy, this principle states that the static pressure of a fluid (liquid or gas) decreases at points where the velocity of the fluid increases, provided no energy is added to or taken away from the fluid.

Aviation Maintenance Technician Handbook — General, p. G-2

The range of operation of a turboprop powerplant used for in-flight approach and ground handling of the engine and aircraft. Typically, the Beta mode includes operations from 65% to 95% of the engine’s rated rpm.

Aviation Maintenance Technician Handbook — Powerplant, p. G-4

A tube in a Garrett TPE331 turboprop powerplant that extends into the propeller pitch control to act as a follow-up device. It provides movement of the propeller blades in proportion to movement of the power lever.

Aviation Maintenance Technician Handbook — Powerplant, p. G-4

The rim that holds the glass cover in the case of an aircraft instrument.

Aviation Maintenance Technician Handbook — Airframe, p. G-5

Brake horsepower. The actual horsepower delivered to the propeller shaft of a reciprocating or turboprop engine.

Aviation Maintenance Technician Handbook — Powerplant, p. G-4

A fabric tape in which the threads run at an angle of 45° to the length of the tape. Bias-cut tape may be stretched around a compound curve such as a wing tip bow without wrinkling.

Aviation Maintenance Technician Handbook — Airframe, p. G-5

Fibers in a piece of composite material arranged to sustain loads in two directions.

Aviation Maintenance Technician Handbook — Powerplant, p. G-4

A low portion in an aircraft structure in which water and contaminants collect. The area under the cabin floorboards is normally called the bilge.

Aviation Maintenance Technician Handbook — Airframe, p. G-5

A flat, spiral-wound spring made of two strips of metal laid side-by-side and welded together. The two metals have different coefficients of expansion, and as the temperature changes, the spiral either tightens or loosens. A bimetallic hair spring is used in a thermocouple temperature changes at the reference junction.

Aviation Maintenance Technician Handbook — Powerplant, p. G-4

A metal strip made of two different types of metal fastened together side by side. When heated, the two metals expand different amounts and the strip warps or bends.

Aviation Maintenance Technician Handbook — Powerplant, p. G-4

The binary number system is a number system that has only two digits, 0 (zero) and 1. Binary numbers are made from a series of zeros and ones. An example of an 8-bit binary number is 11010010. The prefix “bi” in the word binary is a Latin root for the word “two.”

Aviation Maintenance Technician Handbook — General, p. G-2

Airplanes with two sets of wings.

Pilot's Handbook of Aeronautical Knowledge, p. G-5

A solid-state component in which the flow of current between its emitter and collector is controlled by a much smaller flow of current into or out of its base. Bipolar transistors may be of either the NPN or PNP type.

Aviation Maintenance Technician Handbook — Airframe, p. G-5

Built-in test equipment.

Aviation Maintenance Technician Handbook — Airframe, p. G-5

A term used for any portion of an electrical or electronic system that can be removed as a unit. A black box does not have to be a physical box.

Aviation Maintenance Technician Handbook — Airframe, p. G-5

A plastic-impregnated fabric bag supported in a portion of an aircraft structure so that it forms a cell in which fuel is carried.

Aviation Maintenance Technician Handbook — Airframe, p. G-5

The component of a propeller that converts the rotation of the propeller shaft into thrust. The blade of a propeller corresponds to the wing of an airplane.

Aviation Maintenance Technician Handbook — Powerplant, p. G-4

An upward sweep of rotor blades as a result of lift and centrifugal force.

Helicopter Flying Handbook, p. G-1

A device attached to the drag hinge to restrain the fore and aft movement of the rotor blade.

Helicopter Flying Handbook, p. G-1

The rotation of the blade around the spanwise (pitch change) axis.

Helicopter Flying Handbook, p. G-1

The ability of the rotor blade to move in a vertical direction. Blades may flap independently or in unison.

Helicopter Flying Handbook, p. G-1

The part of the hub assembly to which the rotor blades are attached, sometimes referred to as blade forks.

Helicopter Flying Handbook, p. G-1

The fore and aft movement of the blade in the plane of rotation. It is sometimes called “hunting” or “dragging.”

Helicopter Flying Handbook, p. G-1

The load imposed on rotor blades, determined by dividing the total weight of the helicopter by the combined area of all the rotor blades.

Helicopter Flying Handbook, p. G-2

The part of the blade that attaches to the blade grip.

Helicopter Flying Handbook, p. G-2

The length of a blade from its tip to its root.

Helicopter Flying Handbook, p. G-2

The condition of the rotor blade when it is operating at an angle of attack greater than the maximum angle of lift.

Helicopter Flying Handbook, p. G-2

The furthermost part of the blade from the hub of the rotor.

Helicopter Flying Handbook, p. G-2

The condition of a helicopter rotor in which each blade follows the exact same path as the blade ahead of it.

Aviation Maintenance Technician Handbook — Airframe, p. G-5

The mechanical procedure used to bring the blades of the rotor into a satisfactory relationship with each other under dynamic conditions so that all blades rotate on a common plane.

Helicopter Flying Handbook, p. G-2

The variation in the angle of incidence of a blade between the root and the tip.

Helicopter Flying Handbook, p. G-2

A material such as glass cloth or mat that is placed over a composite lay-up to absorb the excess resin forced out of the ply fibers when pressure is applied.

Aviation Maintenance Technician Handbook — Airframe, p. G-5

Dope whose pigments are soluble in the solvents or thinners used in the finishing system. The color will bleed up through the finished coats.

Aviation Maintenance Technician Handbook — Airframe, p. G-5

The maintenance procedure of removing air entrapped in hydraulic fluid in the brakes. Fluid is bled from the brake system until fluid with no bubbles flows out. Blimp.A cigar-shaped, nonrigid lighter-than-air flying machine.

Aviation Maintenance Technician Handbook — Airframe, p. G-5

A method of repairing damaged compressor and turbine blades. The damage is removed and the area is cleaned out with a fine file to form a shallow depression with generous radii. The file marks are then removed with a fine abrasive stone so the surface of the repaired area will match the surface of the rest of the blade.

Aviation Maintenance Technician Handbook — Powerplant, p. G-4

A turbine wheel machined from a single slab of steel. The disc and blades are an integral unit.

Aviation Maintenance Technician Handbook — Powerplant, p. G-4

A block of altitudes assigned by ATC to allow altitude deviations; for example, “Maintain block altitude 9 to 11 thousand.”

Pilot's Handbook of Aeronautical Knowledge, p. G-5

Used to show a simplified relationship of a more complex system of components.

Aviation Maintenance Technician Handbook — General, p. G-2

Spring-loaded doors in the inlet duct of some turbojet or turbofan engine installations that are opened by differential air pressure when inlet air pressure drops below that of the ambient air. Air flowing through the doors adds to the normal inlet air passing through the engine and helps prevent compressor stall.

Aviation Maintenance Technician Handbook — Powerplant, p. G-4

The tendency of the rotor disk to tilt aft in transition to forward flight as a result of unequal airflow.

Helicopter Flying Handbook, p. G-2

A defect in a lacquer or dope finish caused by moisture condensing on the surface before the finish dries. If the humidity of the air is high, the evaporation of the solvents cools the air enough to cause the moisture to condense. The water condensed from the air mixes with the lacquer or dope and forms a dull, porous, chalky-looking finish called blush. A blushed finish is neither attractive nor protective.

Aviation Maintenance Technician Handbook — Airframe, p. G-5

Brake mean effective pressure. The average pressure inside the cylinder of a reciprocating engine during the power stroke. BMEP, measured in pounds per square inch, relates to the torque produced by the engine and can be calculated when you know the brake horsepower.

Aviation Maintenance Technician Handbook — Powerplant, p. G-4

The process of electrically connecting all isolated components to the aircraft structure. Bonding provides a path for return current from electrical components, and a low-impedance path to ground to minimize static electrical charges. Shock-mounted components have bonding braids connected across the shock mounts.

Aviation Maintenance Technician Handbook — Airframe, p. G-5

A term for manifold pressure that has been increased above the ambient atmospheric pressure by a supercharger.

Aviation Maintenance Technician Handbook — Powerplant, p. G-4

An electrically driven centrifugal pump mounted in the bottom of the fuel tanks in large aircraft. Boost pumps provide a positive flow of fuel under pressure to the engine for starting and serve as an emergency backup in the event an engine-driven pump should fail. They are also used to transfer fuel from one tank to another and to pump fuel overboard when it is being dumped. Boost pumps prevent vapor locks by holding pressure on the fuel in the line to the engine-driven pump. Centrifugal boost pumps have a small agitator propeller on top of the impeller to force vapors from the fuel before it leaves the tank.

Aviation Maintenance Technician Handbook — Airframe, p. G-5

An action that is self-initiating or self-sustaining. In a turbocharger system, bootstrapping describes a transient increase in engine power that causes the turbocharger to speed up, which in turn causes the engine to produce more power.

Aviation Maintenance Technician Handbook — Powerplant, p. G-4

The diameter of a reciprocating engine cylinder.

Aviation Maintenance Technician Handbook — Powerplant, p. G-4

A device that enables the inspector to see inside areas that could not otherwise be inspected without disassembly.

Aviation Maintenance Technician Handbook — General, p. G-2

An enlarged area in a casting or machined part. A boss provides additional strength to the part where holes for mounting or attaching parts are drilled.

Aviation Maintenance Technician Handbook — Powerplant, p. G-4

(verb) A condition in the installation of a propeller on a splined shaft when either the front or rear cone contacts an obstruction that prevents the cone from properly seating inside the propeller hub.

Aviation Maintenance Technician Handbook — Powerplant, p. G-4

The layer of air that flows next to an aerodynamic surface. Because of the design of the surface and local surface roughness, the boundary layer often has a random flow pattern, sometimes even flowing in a direction opposite to the direction of flight. A turbulent boundary layer causes a great deal of aerodynamic drag.

Aviation Maintenance Technician Handbook — Airframe, p. G-5

A pressure-indicating mechanism used in most oil pressure and hydraulic pressure gages. It consists of a sealed, curved tube with an elliptical cross section. Pressure inside the tube tries to straighten it, and as it straightens, it moves a pointer across a calibrated dial. Bourdon-tube pressure gauges are used to measure temperature by measuring the vapor pressure in a sealed container of a volatile liquid, such as methyl chloride, whose vapor pressure varies directly with its temperature.

Aviation Maintenance Technician Handbook — Airframe, p. G-5

States that the volume of an enclosed dry gas varies inversely with its absolute pressure, provided the temperature remains constant.

Aviation Maintenance Technician Handbook — General, p. G-2

The constant-pressure cycle of energy transformation used by gas turbine engines. Fuel is sprayed into the air passing through the engine and burned. Heat from the burning air/fuel mixture expands the air and accelerates it as it moves through the engine. The Brayton cycle is an open cycle in that the intake, compression, combustion, expansion, and exhaust events all take place at the same time, but in different locations within the engine.

Aviation Maintenance Technician Handbook — Powerplant, p. G-5

A method of thermally joining metal parts by wetting the surface with a molten nonferrous alloy. When the molten material cools and solidifies, it holds the pieces together. Brazing materials melt at a temperature higher than 800 °F, but lower than the melting temperature of the metal on which they are used.

Aviation Maintenance Technician Handbook — Airframe, p. G-6

Line on a drawing indicating that a portion of the object is not shown on the drawing.

Aviation Maintenance Technician Handbook — General, p. G-2

The amount of heat required to change the temperature of 1 pound of water by 1 degree Fahrenheit.

Aviation Maintenance Technician Handbook — General, p. G-2

Brake specific fuel consumption. A measure of the amount of fuel used for a given amount of power produced by a heat engine. BSFC is expressed in pounds of fuel burned per hour for each brake horse-power the engine is producing.

Aviation Maintenance Technician Handbook — Powerplant, p. G-5

The portions of aft-fan blades that are in the exhaust of the core engine. Buckets drive the fan from energy received from hot gases leaving the core engine.

Aviation Maintenance Technician Handbook — Powerplant, p. G-5

A heavy steel bar with smooth, hardened surfaces, or faces. The bucking bar is held against the end of the rivet shank when it is driven with a pneumatic rivet gun, and the shop head is formed against the bucking bar.

Aviation Maintenance Technician Handbook — Airframe, p. G-6

Turbulent movement of the air over an aerodynamic surface.

Aviation Maintenance Technician Handbook — Airframe, p. G-6

An L-shaped metal extrusion having an enlarged, rounded edge that resembles a bulb on one of its legs.

Aviation Maintenance Technician Handbook — Airframe, p. G-6

A structural partition that divides the fuselage of an aircraft into compartments, or bays.

Aviation Maintenance Technician Handbook — Airframe, p. G-6

An elastic cord made of small strips of rubber encased in a loosely braided cloth tube that holds and protects the rubber, yet allows it to stretch. The energy in a stretched bungee cord may be used to crank a large aircraft engine.

Aviation Maintenance Technician Handbook — Powerplant, p. G-5

A cushioning material used with the nonshock absorbing landing gears installed on older aircraft. Bungee cord is made up of many small rubber bands encased in a loose-woven cotton braid.

Aviation Maintenance Technician Handbook — Airframe, p. G-6

The upward force that any fluid exerts on a body submerged in it.

Aviation Maintenance Technician Handbook — General, p. G-2

See combustor.

Aviation Maintenance Technician Handbook — Powerplant, p. G-5

To smooth the surface of metal that has been damaged by a deep scratch or gouge. The metal piled up at the edge of the damage is pushed back into the damage with a smooth, hard steel burnishing tool.

Aviation Maintenance Technician Handbook — Airframe, p. G-6

A sharp rough edge of a piece of metal left when the metal was sheared, punched, or drilled.

Aviation Maintenance Technician Handbook — Airframe, p. G-6

A point within an electrical system from which the individual circuits get their power.

Aviation Maintenance Technician Handbook — Airframe, p. G-6

A line through the symmetrical center of an aircraft from nose to tail. It serves as the datum for measuring the arms used to determine the lateral CG. Lateral moments that cause the aircraft to rotate clockwise are positive (+) , and those that cause it to rotate counterclockwise are negative (–).

Aircraft Weight and Balance Handbook, p. G-2

A flat, disc-shaped valve used to control the flow of fluid in a round pipe or tube. When the butterfly valve is across the tube, the flow is shut off, and when it is parallel with the tube, the obstruction caused by the valve is minimum, and the flow is at its greatest. Butterfly-type throttle valves are used to control the airflow through the fuel metering system.

Aviation Maintenance Technician Handbook — Powerplant, p. G-5

The longitudinal axis of the aircraft that serves as the reference location for positions to the left and right of center. The positions are usually dimensioned in inches.

Aviation Maintenance Technician Handbook — General, p. G-2

Trade name for a synthetic rubber product made by the polymerization of isobutylene. Butyl withstands such potent chemicals as phosphate ester-base (Skydrol) hydraulic fluids.

Aviation Maintenance Technician Handbook — Airframe, p. G-6

Another name for a turbofan engine. See turbofan engine.

Aviation Maintenance Technician Handbook — Powerplant, p. G-5

The ratio of the mass of air moved by the fan to the mass of air moved by the core engine.

Aviation Maintenance Technician Handbook — Powerplant, p. G-5