fatigue resistance (metal characteristic). The ability of a material to withstand vibration and repeated stress reversals without damage.
fault (electrical circuit defect). Typical faults are: an open circuit (a broken wire), a short circuit (an uninsulated portion of the wire making a connection it should not make), or a grounded circuit (a connection made to ground where there should be no connection).
faying surface (sheet metal structure). The portion of a lap joint in a sheet metal structure where two sheets of metal overlap. Moisture can be trapped in the faying surface, and it can cause corrosion if this area is not adequately protected.
FCC (Federal Communications Commission). A governmental board whose responsibility is the
regulation of all interstate electrical communications and all foreign electrical communications that originate in the United States. The FCC is made up of seven commissioners appointed by the President of the United States, under the Communications Act of 1934.
FCC (flight control computer). A portion of the automatic flight control system (See AFCS) that has inputs from the aircraft control surfaces and the engine controls, and outputs to the engine indicating and crew alerting system (See EICAS) and the flight management computer (See FMC).
FDR (flight data recorder). A sealed recording instrument installed in transport aircraft that makes a continuous record of the flight altitude, airspeed, heading, accelerations, and voices and noises heard on the flight deck.
The flight recorder, called a “black box,” is installed in a fireproof housing and is mounted in the tail of the aircraft where it is least likely to be destroyed in a crash.
feather (helicopter rotor blade movement). Rotation of a helicopter rotor blade about its pitch-change axis.
featheredge. A thin, sharp edge on a piece of material, left as the material is worn away by abrasion.
feathering (helicopter rotor blade). The action which changes the pitch angle of helicopter rotor blades by rotating them about their feathering axis.
feathering axis (helicopter rotor blade). The axis about which the pitch angle of a rotor blade is varied. The feathering axis is the same as the spanwise axis.
feathering propeller (aircraft propeller). A propeller whose blades can be moved to an extremely high pitch angle of approximately 90° so they face directly into the airstream and produce no aerodynamic forces. If an engine fails in flight, the aerodynamic forces acting on the propeller will cause it to continue to turn, or windmill.
A windmilling propeller produces enough drag on a multiengine aircraft to cause extreme control difficulties, and it can easily lead to a crash. To decrease the drag, the propeller blades can be feathered. Because a feathered propeller does not turn the engine, a damaged engine is prevented from destroying itself.
feathering switch (Hamilton Standard Hydromatic propeller component). A locking, solenoid-operated switch used in the feather-motor circuit for a Hydromatic propeller.
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