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.

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.

FLAT PITCH— A propeller configuration when the blade chord is aligned with the direction of rotation.

FLICKER VERTIGO— A disorientating condition caused from flickering light off the blades of the propeller.

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.

FLIGHT IDLE—Engine speed, usually in the 70-80 percent range, for minimum flight thrust.

FLOATING—A condition when landing where the airplane does not settle to the runway due to excessive airspeed.

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.

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.

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.

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.

FRICTION DRAG—The part of parasitic drag on a body resulting from viscous shearing stresses over its wetted surface.

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.

FUEL CONTROL UNIT— The fuel-metering device used on a turbine engine that meters the proper quantity of fuel to be fed into the burners of the engine. It integrates the parameters of inlet air temperature, compressor speed, compressor discharge pressure, and exhaust gas temperature with the position of the cockpit power control lever.

FUEL EFFICIENCY—Defined as the amount of fuel used to produce a specific thrust or horsepower divided by the total potential power contained in the same amount of fuel.

FUEL HEATERS—A radiator-like device which has fuel passing through the core. A heat exchange occurs to keep the fuel temperature above the freezing point of water so that entrained water does not form ice crystals, which could block fuel flow.

FUEL INJECTION— A fuel metering system used on some aircraft reciprocating engines in which a constant flow of fuel is fed to injection nozzles in the heads of all cylinders just outside of the intake valve. It differs from sequential fuel injection in which a timed charge of high-pressure fuel is sprayed directly into the combustion chamber of the cylinder.

FUEL LOAD—The expendable part of the load of the airplane. It includes only usable fuel, not fuel required to fill the lines or that which remains trapped in the tank sumps.

FUEL TANK SUMP—A sampling port in the lowest part of the fuel tank that the pilot can utilize to check for contaminants in the fuel.

FUSELAGE—The section of the airplane that consists of the cabin and/or cockpit, containing seats for the occupants and the controls for the airplane.