Aviation Maintenance Terms beginning with F
FAA Form 337
The FAA form that must be filled in and submitted to the FAA when a major repair or major alteration has been completed.
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.
Feather (helicopter rotor blade movement)
Rotation of a helicopter rotor blade about its pitch-change axis.
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.
Ferrous metal
Any metal that contains iron and has magnetic characteristics.
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.
File
A hand-held cutting tool used to remove a small amount of metal with each stroke.
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.
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 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.
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.
Flameout
A condition in the operation of a gas turbine engine in which the fire in the engine unintentionally goes out.
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 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 material must be raised for it to ignite, but not continue to burn, when a flame is passed above it.
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.
Flight controller
The component in an autopilot system that allows the pilot to maneuver the aircraft manually when the autopilot is engaged.
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.
Flutter
Rapid and uncontrolled oscillation of a flight control surface on an aircraft that is caused by a dynamically unbalanced condition.
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
Energy brought to bear on an object that tends to cause motion or to change motion.
Forehand welding
Welding in which the torch is pointed in the direction the weld is progressing.
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.
Fractional distillation
A method of separating the various components from a physical mixture of liquids. The material to be separated is put into a container and its temperature is increased. The components having the lowest boiling points boil off first and are condensed. Then, as the temperature is further raised, other components are removed. Kerosene, gasoline, and other petroleum products are obtained by fractional distillation of crude oil.
Frangible
Breakable, or easily broken.
Freon
The registered trade name for a refrigerant used in a vapor-cycle air conditioning system.
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 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.
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.
Fungus (plural: fungi)
Any of several types of plant life that include yeasts, molds, and mildew.
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.
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