FHP.  Friction horsepower. The amount of horsepower  used to turn the crankshaft, pistons, gears, and accessories  in a reciprocating engine and to compress the air inside the  cylinders. Expansion wave.  The change in pressure and velocity of  supersonic air as it passes over a surface that drops away  from the flow. As the surface drops away, the air tries to  follow it, and in changing its direction, the air speeds up to  a higher supersonic speed, and its static pressure decreases.  There is no change in the total amount of energy as air passes  through an expansion wave. 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. External-combustion engine.  A form of heat engine in  which the fuel releases its energy outside of the engine.  This released heat expands air which is used to perform  useful work. Steam engines are a popular type of external  combustion engine. Fire sleeve.  A covering of fire-resistant fabric used to protect  flexible fluid lines that are routed through areas subject to  high temperature. Extreme pressure (EP) lubricant.  A lubricant that reacts  with iron to form iron chlorides, sulfides, or phosphides on  the surface of a steel part. These compounds reduce wear and  damage to surfaces in heavy rubbing contact. EP lubricants  are specially suited for lubricating gear trains. 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 fuel-air mixture  or interruption of the air flow through the engine can cause  a flameout. 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. 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. 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. 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. FADEC.  Full-authority digital electronic control. A digital  electronic fuel control for a gas turbine engine that is  functioning during all engine operations, hence full authority.  It includes the EEC (see EEC) and functions with the flight  management computer. FADEC schedules the fuel to the  nozzles in such a way that prevents overshooting power  changes and over-temperature conditions. FADEC furnishes  information to the EICAS (engine indication and crew  alerting system). 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. Fan pressure ratio.  The ratio of the fan-discharge pressure  to the fan inlet pressure. Flat-rated engine.  A turboprop engine whose allowable  output power is less than the engine is physically capable  of producing. Feathering propeller.  A controllable-pitch propeller whose  blades can be moved into a high pitch angle of approximately  90º. Feathering the propeller of an inoperative engine  prevents it from wind-milling and greatly decreases drag. 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. 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. 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.  G-12