- FAA Federal Aviation Administration.
- FAC Forward air control (or controller).
- factored Multiplied by an agreed number to take account of extreme adverse conditions, errors, design deficiencies or other inaccuracies.
- FADEC Full-authority digital engine (or electronic) control.
- FAI Fédération Aéronautique Internationale.
- fail-operational System which continues to function after any single fault has occurred.
- fail-safe Structure or system which survives failure (in case of system, may no longer function normally).
- FAR Federal Aviation Regulations.
- FAR Pt 23 Defines the airworthiness of private and air taxi aeroplanes of 5,670 kg (12,500 lb) MTOW and below.
- FAR Pt 25 Defines the airworthiness of public transport aeroplanes exceeding 5,670 kg (12,500 lb) MTOW.
- FBL Fly-by-light (which see).
- FBW Fly-by-wire (which see).
- FCS Flight control system.
- FDR Flight data recorder (which see).
- FDS Flight director system.
- feathering Setting propeller blades at pitch aligned with slipstream to minimise drag.
- fence A chordwise projection on the surface of a wing, used to modify the distribution of pressure.
- Fenestron Helicopter tail rotor with many slender blades rotating in short duct (registered name).
- ferry range Extreme safe range with zero payload.
- FFAR Folding-fin (or free-flight) aircraft rocket.
- field length Measure of distance needed to land and/or take off; many different measures for particular purposes, each precisely defined.
- fixed-pitch Propeller with blades fixed to the hub.
- FL Flight level. National altitude for air traffic control purposes which assumes ISA pressure (1013.25 mb; 29.92 in Hg) at S/L. Expressed in hundreds of feet; thus FL255 indicates approximately 25,500 ft.
- flap A surface carried on the leading- or trailing-edge of a wing and able to move relative to it. The simplest leading-edge flap and so-called plain (trailing-edge) flap is formed by hinging the entire edge of the wing. The Krueger is a leading-edge flap forming part of the wing undersurface, swung down and forwards on arms to give a bluff leading-edge. A split flap is formed by hinging only the undersurface of the trailing-edge. A slotted flap ia a hinged trailing-edge which moves aft as well as down on tracks to leave a narrow slot ahead of it; hence double- and triple-slotted. A Fowler flap is a complete auxiliary aerofoil mounted on tracks under a fixed trailing-edge; initially it moves aft, to emerge behind the fixed part of the wing, and at the end of its travel it rotates down. A Gouge flap has an upper surface forming part of a cylinder, and rotates (on rails or brackets) about that cylinder's centre.
- flaperon Wing trailing-edge surface combining functions of flap and aileron.
- FLAR Federatsiya Lyubitelei Aviatsii Rossii, Russian PFA.
- flat-four Piston engine having four horizontally opposed cylinders; thus, flat-twin, flat-six and so on.
- flight-adjustable pitch Propeller with blades that can be changed in pitch during flight to a limited extent (eg one way only). Compare variable pitch.
- flat rated Propulsion engine capable of giving full thrust or power for take-off at an airfield well above S/L and/or at high ambient temperature (thus, probably derated at S/L).
- flight data recorder Crash-protected recorder of dynamic/static pressure, air temperature, control-surface and slat/flap positions, 3-axis accelerations, engine parameters and possibly other variables.
- FLIR Forward-looking infra-red.
- fly-by-light Flight control system in which signals pass between computers and actuators along fibre-optic leads.
- fly-by-wire Flight control system with electrical signalling, without mechanical interconnection between cockpit flying controls and control surfaces.
- FM Frequency modulation.
- FMS (1) Foreign military sales (US DoD); (2) Flight management system.
- footprint (1) A precisely delineated boundary on the surface around an airfield, inside which the perceived noise of an aircraft exceeds a specified level during take-off and/or landing; (2) Dispersion of weapon or submunition impact points.
- foreplanes Pivoted canard surfaces forming part of the primary flight control system with authority in pitch and possibly also in roll. See also canards.
- FOV Field of view.
- Fowler flap See flap.
- frequency See radar frequency.
- frequency agile (frequency hopping) Making a transmission harder to detect by switching automatically to a succession of frequencies.
- FSD Full-scale development.
- FSED Full-scale engineering development.
- FY Fiscal year; in US government affairs, runs from 1 October to 30 September (eg, FY05 begins 1 October 2004); in Japan, from 1 April (eg, FY04 began 1 April 2004).
