Environmental systems.  In an aircraft, the systems,  including the supplemental oxygen systems, air conditioning  systems, heaters, and pressurization systems, which make it  possible for an occupant to function at high altitude.  Equilibrium.  A condition that exists within a body when the  sum of the moments of all of the forces acting on the body  is equal to zero. In aerodynamics, equilibrium is when all  opposing forces acting on an aircraft are balanced (steady,  unaccelerated flight conditions).  Equivalent shaft horsepower (ESHP).  A measurement of  the total horsepower of a turboprop engine, including that  provided by jet thrust.  Exhaust gas temperature (EGT).  The temperature of the  exhaust gases as they leave the cylinders of a reciprocating  engine or the turbine section of a turbine engine.  Exhaust manifold.  The part of the engine that collects  exhaust gases leaving the cylinders.  Exhaust.  The rear opening of a turbine engine exhaust duct.  The nozzle acts as an orifice, the size of which determines  the density and velocity of the gases as they emerge from  the engine.  False horizon.  An optical illusion where the pilot confuses a  row of lights along a road or other straight line as the horizon.  False start.  See hung start.  Feathering propeller (feathered).  A controllable pitch  propeller with a pitch range sufficient to allow the blades  to be turned parallel to the line of flight to reduce drag and  prevent further damage to an engine that has been shut down  after a malfunction.  Fixation.  A psychological condition where the pilot fixes  attention on a single source of information and ignores all  other sources.  Fixed shaft turboprop engine.  A turboprop engine where  the gas producer spool is directly connected to the output  shaft.  Fixed-pitch propellers.  Propellers with fixed blade angles.  Fixed-pitch propellers are designed as climb propellers,  cruise propellers, or standard propellers.  G-7 Frise-type aileron.  Aileron having the nose portion  projecting ahead of the hinge line. When the trailing edge  of the aileron moves up, the nose projects below the wing’s  lower surface and produces some parasite drag, decreasing  the amount of adverse yaw.  Friction drag.  The part of parasitic drag on a body resulting  from viscous shearing stresses over its wetted surface.  Free power turbine engine.  A turboprop engine where the  gas producer spool is on a separate shaft from the output  shaft. The free power turbine spins independently of the gas  producer and drives the output shaft.  Forward slip.  A slip in which the airplane’s direction of  motion continues the same as before the slip was begun. In  a forward slip, the airplane’s longitudinal axis is at an angle  to its flightpath.  Form drag.  The part of parasite drag on a body resulting  from the integrated effect of the static pressure acting normal  to its surface resolved in the drag direction.  Force (F).  The energy applied to an object that attempts to  cause the object to change its direction, speed, or motion.  In aerodynamics, it is expressed as F, T (thrust), L (lift), W  (weight), or D (drag), usually in pounds.  Floating.  A condition when landing where the airplane does  not settle to the runway due to excessive airspeed.  Flight idle.  Engine speed, usually in the 70-80 percent range,  for minimum flight thrust.  Flight director.  An automatic flight control system in which  the commands needed to fly the airplane are electronically  computed and displayed on a flight instrument. The  commands are followed by the human pilot with manual  control inputs or, in the case of an autopilot system, sent to  servos that move the flight controls.  Flicker vertigo.  A disorienting condition caused from  flickering light off the blades of the propeller.  Flat pitch.  A propeller configuration when the blade chord  is aligned with the direction of rotation.  Flaps.  Hinged portion of the trailing edge between the  ailerons and fuselage. In some aircraft, ailerons and flaps  are interconnected to produce full-span “flaperons.” In either  case, flaps change the lift and drag on the wing.  F