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of meteorological elements.
frontogenesis (meteorology). The initial formation of a front or frontal zone.
frontolysis (meteorology). The dissipation of a front or frontal zone.
front-surface mirror. A mirror with the reflective material on its front surface, rather than on the back.
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front-to-back ratio (semiconductor characteristic). A rough measurement of the condition of a
semiconductor diode. When the resistance of the diode is measured with an ohmmeter, it should have a
high resistance one way (the junction is reverse-biased), but when the leads are reversed, the resistance
should be low (the junction is forward-biased). A high front-to-back ratio normally indicates a good diode.
frost (meteorology). Ice crystal deposits formed by sublimation when the temperature and dew point are
below freezing.
frustrum. The portion of a cone or a cone-shaped solid from which the top has been removed. The top and
the bottom of the frustrum are parallel surfaces, with the top surface smaller than the bottom.
FSDO (Flight Standards District Office). 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 the certification and operation of air carrier and general aviation aircraft.
FSDO activities include general surveillance of operational safety, certification of airmen and
aircraft, accident prevention, investigation, enforcement, etc.
FSS (Flight Service Station). Air traffic control facilities which provide these services:
• Pilot briefing
• Enroute communications
• VFR search and rescue services
• Assistance to lost aircraft and aircraft in emergency situations
• Relay ATC clearances
• Originate Notices to Airmen
• Broadcast aviation weather and NAS information
• Receive and process IFR flight plans
• Monitor navaids
Some flight service stations perform these services in addition:
• Provide Enroute Flight Advisory Service (Flight Watch)
• Take weather observations
• Issue airport advisories
• Advise Customs and Immigration of transborder flights
fuel. Any material that can be burned to release its energy. Gasoline, kerosine, coal, wood, and natural gas
are all forms of fuel.
fuel-air mixture ratio. The ratio of the number of pounds of fuel to the number of pounds of air in the
mixture burned, in an internal combustion engine.
fuel boost pump (aircraft fuel system component). An auxiliary fuel pump used in an aircraft fuel system
to provide fuel pressure for starting the engine, for use as an emergency backup in case the fuel pump fails,
and to transfer fuel from one tank to another.
fuel control unit (gas turbine engine). The fuel metering device for a gas turbine engine that senses the
variables of power lever position, pressure, speed, and temperature in the engine. The fuel control unit then
meters the correct amount of fuel to be sent to the burners for the existing conditions.
fuel dump system (aircraft fuel system). See fuel jettison system.
fuel flowmeter (aircraft instrument). An instrument used to show the rate of fuel flowing to an engine.
Fuel flowmeters used with modern fuel-injected reciprocating engines are actually pressure gages that
measure the pressure drop across the injector nozzles.
A popular flowmeter for turbine engines uses a small turbine in the fuel line to the fuel control
unit that measures the rate of fuel flow. It converts this flow rate into an electrical signal and sends it to an
indicator in the instrument panel.
fuel flow transmitter (powerplant instrument). A device in the fuel line between the engine-driven fuel
pump and the carburetor that measures the rate of flow of the fuel. The flowmeter transmitter converts the
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flow rate into an electrical signal and sends it to an indicator in the instrument panel.
fuel heater (turbojet airplane fuel system component). A form of fuel-air heat exchanger in which heat
is taken from the compressor bleed air and put into the fuel before it flows through the fuel filter. At high
altitude, the temperature is so low that water entrained in the fuel precipitates out and freezes on the fuel
filter. The fuel heater warms the fuel enough to prevent the water freezing.
fuel injection manifold valve (reciprocating engine component). The valve used in a reciprocating
engine fuel injection system that takes fuel from the fuel control unit and distributes it to the various
injection nozzles. The manifold valve provides a metering force for conditions of low fuel flow, and also
　
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