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. 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. 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. FMC.  Flight Management Computer. 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. FPD.  Freezing point depressant.  G-16