Federal Communications Commission. See FCC.
feedback. A process in an electrical circuit or control system in which some energy from the output of the system or circuit is fed back into the input. If the energy being fed back is in phase with the input signal, the feedback is positive and the output is increased. But if it is fed back out of phase with the input signal, the feedback is negative and the output is decreased.
A control system using feedback is called a closed-loop system. The feedback closes the loop.
feeder fix (air traffic control). The fix depicted on instrument approach procedure charts which establishes the starting point of a feeder route.
feeder route (air traffic control). A route depicted on instrument approach procedure charts to designate routes for aircraft to proceed from the en route structure to the initial approach fix (IAF).
feedthrough capacitor. A capacitor used to carry a conductor through a panel or bulkhead. The outer conductor of the capacitor is connected to the case, and the inner conductor is connected to terminals that extend from both ends of the capacitor.
Feedthrough capacitors used in some aircraft magnetos minimize breaker point arcing and also decrease the radio interference caused by electrical energy radiated from the ignition switch lead.
feedthrough connector. A type of electrical connector used to carry a group of conductors through a bulkhead or panel. Feedthrough connectors do not have wires fastened to them, but rather they allow cables on both sides of the bulkhead to be connected through them.
 Sealed feedthrough connectors carry circuits through the bulkheads of pressurized aircraft.
feeler gage (precision tool). A type of measuring tool consisting of strips of precision-ground steel of accurately measured thickness. Feeler gages are used to measure the distance between close-fitting parts, such as the clearances in a mechanical system or the distance by which moving contacts are separated.
fence (aerodynamics). A stationary vane that extends chordwise, from the leading edge to the trailing edge, across upper surface of the wing of a high-speed airplane. Fences prevent the air from flowing spanwise along the wing.
Fenwal fire detection system. A patented spot-type fire detection system installed in an aircraft. This system uses individual thermal switches connected between two insulated conductors. An open circuit in either of the two conductors will not prevent the system from detecting a fire, but it will keep it from indicating good when the test switch is closed.