Ethylene glycol.  A form of alcohol used as a coolant for liquid-cooled engines and as an anti-icing agent. 

Eutectic material.  An alloy or solution that has the lowest possible melting point. 

Evacuation (air conditioning servicing procedure). A procedure in servicing vapor-cycle cooling systems. A vacuum pump removes all the air from the system. Evacuation removes all traces of water vapor that could condense out, freeze, and block the system. 

Evaporator (air conditioning component).  The component in a vapor-cycle cooling system in which heat from the aircraft cabin is absorbed into the refrigerant. As the heat is absorbed, the refrigerant evaporates, or changes from a liquid into a vapor. The function of the evaporator is to lower the cabin air temperature. 

Expander-tube brake.  A brake that uses hydraulic fluid inside a synthetic rubber tube around the brake hub to force rectangular blocks of brake-lining material against the rotating brake drum. Friction between the brake drum and the lining material slows the aircraft. 

Expansion wave.  The change in pressure and velocity of a supersonic flow of air as it passes over a surface which drops away from the flow. As the surface drops away, the air tries to follow it. In changing its direction, the air speeds up to a higher supersonic velocity and its static pressure decreases. There is no change in the total energy as the air passes through an expansion wave, and so there is no sound as there is when air passes through a shock wave. 

Extruded angle.  A structural angle formed by passing metal heated to its plastic state through specially shaped dies. 

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. 

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. 

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. 

FCC.  Federal Communications Commission. 

FCC.  Flight Control Computer. 

Feather (helicopter rotor blade movement).  Rotation of a helicopter rotor blade about its pitch-change axis. 

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. 

