Aviation Maintenance Terms beginning with F

FAA Form 337

This form must be completed when a major repair or alteration is accomplished.

Face (propeller nomenclature)

The flat surface of a propeller that strikes the air as the propeller rotates. The face of a propeller corresponds to the bottom of an airplane wing.

Face surface

Flat, or very slightly curved, side of the propeller blade against which the relatively higher pressure acts to produce thrust when the propeller is rotated.

Fading of brakes

The decrease in the amount of braking action that occurs with some types of brakes that are applied for a long period of time. True fading occurs with overheated drum-type brakes. As the drum is heated, it expands in a bell-mouthed fashion. This decreases the amount of drum in contact with the brake shoes and decreases the braking action. A condition similar to brake fading occurs when there is an internal leak in the brake master cylinder. The brakes are applied, but as the pedal is held down, fluid leaks past the piston, and the brakes slowly release.

Fairing

A part of a structure whose primary purpose is to produce a smooth surface or a smooth junction where two surfaces join.

Fairlead

A plastic or wooden guide used to prevent a steel control cable rubbing against an aircraft structure.

Fan pressure ratio

The ratio of the fan-discharge pressure to the fan inlet pressure.

Feather (helicopter rotor blade movement)

Rotation of a helicopter rotor blade about its pitch-change axis.

Feathering propeller

A controllable-pitch propeller whose blades can be moved into a high pitch angle of approximately 90°. Feathering the propeller of an inoperative engine prevents it from wind-milling and greatly decreases drag.

Federal Aviation Administration Flight Standards District Office (FAA FSDO)

An FAA field office serving an assigned geographical area staffed with Flight Standards personnel who serve the aviation industry and the general public on matters relating to certification and operation of air carrier and general aviation aircraft.

Feeler gages

A type of measuring tool consisting of strips of precision-ground steel of accurately measured thickness. Feeler gages are used to measure the distance between close- fitting parts, such as the clearances of a mechanical system or the distance by which moving contacts are separated.

Ferrous metal

Any metal that contains iron and has magnetic characteristics.

Ferrous metals

Metals having iron as their principal constituent.

Fiber optics

The technique of transmitting light or images through long, thin, flexible fibers of plastic or glass. Bundles of fibers are used to transmit complete images.

Fiber stop nut

A form of a self-locking nut that has a fiber insert crimped into a recess above the threads. The hole in the insert is slightly smaller than the minor diameter of the threads. When the nut is screwed down over the bolt threads, the opposition caused by the fiber insert produces a force that prevents vibration loosening the nut.

Fiberglass

The most common material used to reinforce structures in home-built and experimental aircraft. Available as mat, roving, fabric, etc. It is incorporated into both thermoset and thermoplastic resins. The glass fibers increase mechanical strength, impact resistance, stiffness, and dimensional stability of the matrix.

Field of View

The field of view of a CDTI is the geographical region within which the CDTI shows traffic. Some documents call this the field of regard.

File

A hand-held cutting tool used to remove a small amount of metal with each stroke.

Filiform corrosion

A thread, or filament-like corrosion which forms on aluminum skins beneath the finish.

Fill

Threads in a fabric that run crosswise of the woven material.

Fill threads

Threads in a piece of fabric that run across the width of the fabric, interweaving with the warp threads. Fill threads are often called woof, or weft, threads.

Fillet

A fairing used to give shape but not strength to an object. A fillet produces a smooth junction where two surfaces meet.

Finish

External coating or covering of an aircraft or part.

Finishing tape

Another name for surface tape. See surface tape.

Fire pull handle

The handle in an aircraft flight deck that is pulled at the first indication of an engine fire. Pulling this handle removes the generator from the electrical system, shuts off the fuel and hydraulic fluid to the engine, and closes the compressor bleed air valve. The fire extinguisher agent discharge switch is uncovered, but it is not automatically closed.

Fire resistant

(1) With respect to sheet or structural members the capacity to withstand the heat associated with fire at least as well as aluminum alloy in dimensions appropriate for the purpose for which they are used; and (2) With respect to fluid-carrying lines, fluid system parts, wiring, air ducts, fittings, and powerplant controls, means the capacity to perform the intended functions under the heat and other conditions likely to occur when there is a fire at the place concerned.

Fire sleeve

A covering of fire-resistant fabric used to protect flexible fluid lines that are routed through areas subject to high temperature.

Fire zone

A portion of an aircraft designated by the manufacturer to require fire-detection and/or fire-extinguishing equipment and a high degree of inherent fire resistance.

Fireproof

(1) With respect to materials and parts used to confine fire in a designated fire zone, the capacity to withstand at least as well as steel in dimensions appropriate for the purpose for which they are used, the heat produced when there is a severe fire of extended duration in that zone; and (2) With respect to other materials and parts, means the capacity to withstand the heat associated with fire at least as well as steel in dimensions appropriate for the purpose for which they are used.

Fishmouth splice

A type of splice used in a welded tubular structure in which the end of the tube whose inside diameter is the same as the outside diameter of the tube being spliced is cut in the shape of a V, or a fishmouth, and is slipped over the smaller tube welded. A fishmouth splice has more weld area than a butt splice and allows the stresses from one tube to transfer into the other tube gradually.

Fitting

An attachment device that is used to connect components to an aircraft structure.

Fixed fire-extinguishing system

A fire-extinguishing system installed in an aircraft.

Flame resistant

Not susceptible to combustion to the point of propagating a flame, beyond safe limits, after the ignition source is removed.

Flame tubes

Small-diameter metal tubes that connect can- type combustors in a turbine engine to carry the ignition flame to all of the combustion chambers. The British call combustion liners flame tubes.

Flameout

A condition of turbine engine operation when the fire unintentionally goes out. Improper air/fuel mixture or interruption of the air flow through the engine can cause a flameout.

Flammable

With respect to a fluid or gas, susceptible to igniting readily or to exploding.

Flap (aircraft control)

A secondary control on an airplane wing that changes its camber to increase both its lift and its drag.

Flap (helicopter rotor blade movement)

Up-and-down movement of the tip of a helicopter rotor blade.

Flap extended speed

The highest speed permissible with wing flaps in a prescribed extended position.

Flap overload valve

A valve in the flap system of an airplane that prevents the flaps being lowered at an airspeed which could cause structural damage. If the pilot tries to extend the flaps when the airspeed is too high, the opposition caused by the air flow will open the overload valve and return the fluid to the reservoir.

Flash point

The temperature to which a liquid must be raised for it to ignite, but not continue to burn when a flame is passed above it.

Flash resistant

Not susceptible to burning violently when ignited.

Flashing the field

A maintenance procedure for a DC generator that restores residual magnetism to the field frame, A pulse of current from a battery is sent through the field coils in the direction in which current normally flows. The magnetic field produced by this current magnetizes the steel frame of the generator.

Flashover

An ignition system malfunction in which the high voltage in the magneto distributor jumps to the wrong terminal. Flashover causes the wrong spark plug to fire. This reduces the engine power and produces vibration and excessive heat.

Flat grain

Lumber has been sawed parallel with the pith of the log and approximately tangent to the growth rings; that is, the rings form an angle of less than 45 degrees with the surface of the piece.

Flat pattern layout

The pattern for a sheet metal part that has the material used for each flat surface, and for all of the bends, marked out with bend-tangent lines drawn between the flats and bend allowances.

Flat-rated engine

A turboprop engine whose allowable output power is less than the engine is physically capable of producing.

Flatspotting

A localized accelerated wear condition associated with landings; A temporary or permanent “out-of-round” condition resulting from a loaded hot tire having not rotated while cooling to the ambient temperature. This condition is most prevalent on bias nylon tires due to the “plastic memory” of the nylon cords.

Flight controller

The component in an autopilot system that allows the pilot to maneuver the aircraft manually when the autopilot is engaged.

Flight Crew

One or more cockpit crew members required for the operation of the aircraft.

Flight Information Service Broadcast (FIS-B)

FIS-B is a ground broadcast service provided over the UAT data link. The FAA FIS-B system provides pilots and flight crews of properly equipped aircraft with a cockpit display of certain aviation weather and aeronautical information.

Flight Information System - Broadcast (FIS-B)

A ground broadcast service provided over the UAT data link. The FAA FIS-B system provides pilots and flightcrews of properly equipped aircraft with a cockpit display of certain aviation weather and aeronautical information.

Flight Manual

A generic term used throughout this AC to represent the AFM, RFM, AFM supplement, or RFM supplement.

Flightcrew member

A pilot, flight engineer, or flight navigator assigned to duty in an aircraft during flight time.

Float carburetor

A fuel metering device that uses a float- actuated needle valve to maintain fuel level slightly below the edge of the discharge nozzle.

Flock

Pulverized wood or cotton fibers mixed with an adhesive. Flock, attached to a wire screen, acts as an effective induction air filter for small reciprocating engines.

Flow divider (reciprocating engine)

The valve in an RSA fuel injection system that divides the fuel from the fuel control unit and distributes it to all of the cylinders. It compares with the manifold valve in a Teledyne-Continental fuel injection system.

Flow divider (turbine engine)

A component in a turbine engine fuel system that routes all of the fuel to the primary nozzles or primary orifices when starting the engine or when the rpm is low. When the engine speed builds up, the flow divider shifts and opens a passage to send the majority of the fuel to the secondary nozzles or orifices.

Fluid

A form of material whose molecules are able to flow past one another without destroying the material. Gases and liquids are both fluids.

Fluid power

The transmission of force by the movement of a fluid. The most familiar examples of fluid power systems are hydraulic and pneumatic systems.

Fluorescent

A substance is said to be fluorescent when it will glow or fluoresce when excited by ultraviolet light. Some types of dye-penetrant material use fluorescent dyes which are pulled from the cracks by a developer and observed under “black” ultraviolet light.

Flutter

Rapid and uncontrolled oscillation of a flight control surface on an aircraft that is caused by a dynamically unbalanced condition.

Flux

Materials used to prevent, dissolve, or facilitate removal of oxides and other undesirable surface substances. Also, the name for magnetic fields.

Fly-by-wire

A method of control used by some modern aircraft in which control movement or pressures exerted by the pilot are directed into a digital computer where they are input into a program tailored to the flight characteristics of the aircraft. The computer output signal is sent to actuators at the control surfaces to move them the optimum amount for the desired maneuver.

Flying boat

An airplane whose fuselage is built in the form of a boat hull to allow it to land and takeoff from water. In the past, flying boats were a popular form of large airplane.

Flying wing

A type of heavier-than-air aircraft that has no fuselage or separate tail surfaces. The engines and useful load are carried inside the wing, and movable control surfaces on the trailing edge provide both pitch and roll control.

Foot-pound

A measure of work accomplished when a force of 1 pound moves an object a distance of 1 foot.

Force

The intensity of an impetus, or the intensity of an input.

Forehand welding

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

Foreign object damage (FOD)

Any damage caused by any loose object to aircraft, personnel, or equipment. These loose objects can be anything from broken runway concrete to shop towels and safety wire.

Form drag

Parasite drag caused by the form of the object passing through the air.

Former

An aircraft structural member used to give a fuselage its shape.

Forward bias

A condition of operation of a semiconductor device such as a diode or transistor in which a positive voltage is connected to the P-type material and a negative voltage to the N-type material.

Forward wing

A forward lifting surface of a canard configuration or tandem-wing configuration airplane. The surface may be a fixed, movable, or variable geometry surface, with or without control surfaces.

Four-stroke cycle

A constant-volume cycle of energy transformation that has separate strokes for intake, compression, power, and exhaust.

Fraction

A number written in the form N⁄D in which N is the numerator and D is the denominator. For example, 5⁄16 is a fraction.

Fractional distillation

Procedure used for separating various components from a physical mixture of liquids. Crude oil is a mixture of many different types of hydrocarbon fuels which can be separated by carefully raising its temperature. The first products to be released, those having the lowest boiling points, are some of the gaseous fuels; next are gasoline, kerosene, diesel fuel, heavy fuel oils, lubricating oils, and finally, tar and asphalt.

Frangible

Capable of being broken.

Free-turbine engine

A gas turbine engine with a turbine stage on a shaft independent of the shaft used to drive the compressor. Free turbines are used to drive the propeller reduction gear in a turboprop engine and the rotor transmission in a helicopter.

Freezing point

The temperature at which solids, such as wax crystals, separate from a hydrocarbon fuel as it is cooled.

Freon

The registered trade name for a refrigerant used in a vapor-cycle air conditioning system.

Frequency

The number of cycles (on/off) completed per unit of time. Usually expressed in Hertz.

Fretting corrosion

Occurs when two mating surfaces, normally at rest with respect to one another, are subject to slight relative motion.

Friction

The opposition to movement between objects.

Frise aileron

An aileron with its hinge line set back from the leading edge so that when it is deflected upward, part of the leading edge projects below the wing and produces parasite drag to help overcome adverse yaw.

Frost

Ice crystal deposits formed by sublimation when the temperature and dew point are below freezing.

Fuel grade

The rating system used for aviation gasoline. It rates fuel according to its antidetonation characteristics.

Fuel jettison system

A system installed in most large aircraft that allows the flight crew to jettison, or dump, fuel to lower the gross weight of the aircraft to its allowable landing weight. Boost pumps in the fuel tanks move the fuel from the tank into a fuel manifold. From the fuel manifold, it flows away from the aircraft through dump chutes is each wing tip. The fuel jettison system must be so designed and constructed that it is free from fire hazards.

Fuel totalizer

A fuel quantity indicator that gives the total amount of fuel remaining on board the aircraft on one instrument. The totalizer adds the quantities of fuel in all of the tanks.

Fuel-flow transmitter

A device in the fuel line between the engine-driven fuel pump and the carburetor that measures the rate of flow of the fuel. It converts this flow rate into an electrical signal and sends it to an indicator in the instrument panel.

Full-bodied

Not thinned.

Full-register position

The position of a magnet in a magneto when its poles are aligned with the pole shoes and the maximum amount of magnetic flux is flowing through the magnetic circuit.

Fully articulated rotor

A helicopter rotor whose blades are attached to the hub in such a way that they are free to flap, drag, and feather. See each of these terms.

Functional check

This test may require the use of appropriate test equipment.

Fungus (plural: fungi)

Any of several types of plant life that include yeasts, molds, and mildew.

Fuse

A protective device containing a special wire that melts when current exceeds the rated value for a definite period.

Fuselage stations (FS)

Reference locations, usually given in inches, used to determine forward and aft positions on an aircraft. FS − 0 is the datum

Fusible plugs

Plugs in the wheels of high-performance airplanes that use tubeless tires. The centers of the plugs are filled with a metal that melts at a relatively low temperature. If a takeoff is aborted and the pilot uses the brakes excessively, the heat transferred into the wheel will melt the center of the fusible plugs and allow the air to escape from the tire before it builds up enough pressure to cause an explosion.