Glossary - F

FD.   See flight director.

Faildown.   The substitute display or backup instrument mode available if the primary component fails. In some systems, for example, the MFD can substitute for the PFD if the PFD fails. The PFD information “fails down” to the MFD. In other systems, the substitute for the PFD might be the conventional standby instruments and the standby or secondary navigation CDI.

Flight director.   Electronic flight calculator that analyzes the navigation selections, signals, and aircraft parameters. It presents steering instructions on the flight display as command bars or crossbars for the pilot to position the nose of the aircraft over or follow.

Flight management system (FMS).   A computer system containing a database to allow programming of routes, approaches, and departures that can supply navigation data to the flight director/autopilot from various sources, and can calculate flight data such as fuel consumption, time remaining, possible range, and other values.

Fly-by waypoint.   A waypoint designed to permit early turns, thus allowing the aircraft to roll out onto the center of the desired track to the next waypoint.

Fly-over waypoint.   A waypoint that precludes any turn until the waypoint is overflown, and is followed by either an intercept maneuver of the next flight segment or direct flight to the next waypoint.

FMS.   See flight management system.

Fuel management system or function.   An advanced avionics system that assists the pilot in managing fuel by considering fuel flow, airspeed, and winds to help predict fuel remaining at each waypoint along the programmed route, total endurance, and the viability of alternative routings or diversions. Stand-alone systems may integrate the output data into the FMS/RNAV or provide a discreet display, while the fuel management function is an integral portion of the FMS/ RNAV system. In either instance, the fuel data management goals are similar.

Fuel range ring.   A graphical depiction of the point at which an aircraft is predicted to exhaust its fuel reserves or reach a point at which only reserve fuel remains.

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