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. 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. 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. 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. 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. 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. 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. 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. 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. G-15