Aviation Maintenance Terms beginning with F
FAA Form 337
The Major Repair and Alteration form that must be completed when an FAA-certificated aircraft or engine has been given a major repair or major alteration.
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.
Fan pressure ratio
The ratio of the fan-discharge pressure to the fan inlet pressure.
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.
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.
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.
Fire sleeve
A covering of fire-resistant fabric used to protect flexible fluid lines that are routed through areas subject to high temperature.
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.
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.
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-rated engine
A turboprop engine whose allowable output power is less than the engine is physically capable of producing.
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.
Four-stroke cycle
A constant-volume cycle of energy transformation that has separate strokes for intake, compression, power, and exhaust.
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.
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.
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