Autopilot.  An aircraft flight control system that automatically  manipulates the roll, pitch, and, in some cases, the yaw  control surfaces of the airplane to capture and track the route  programmed into the FMS/RNAV, or altitudes, vertical  speeds, headings, and courses selected by the pilot. Desired track. The great circle course computed by the  FMS/RNAV, it goes from the past waypoint to the next  (active) waypoint. Distance measuring equipment (DME). Line‑of‑sight  limited airborne equipment (transceiver) using paired pulse  replies from ground‑based transponder to determine slant  range distance by time between airborne transmission of  pulses and return of pulses from the ground transponder. Autopilot flight mode annunciator.  A display that presents  the names of autopilot functions that are either armed or  engaged. It is the only reliable source of information about  what autopilot functions are in use. DME.  See distance measuring equipment. Autothrottle system. A system that automatically  manipulates the thrust setting of the airplane to help follow  the vertical trajectory portion or selected airspeed of the  planned flight route. EHSI.  See electronic horizontal situation indicator. Electronic flight instruments.  Flight instruments that use  electronic devices to prepare and/or present information such  as airspeed, attitude, altitude, and position. Autotrim system. The system that automatically adjusts  the pitch trim of the airplane in response to trim commands  generated by the autopilot. Electronic horizontal situation indicator (EHSI). Electronically generated HSI display, either CRT or LCD  type, indicating all standard HSI functions on a video screen  instead of using mechanical components. Bottom-of-descent point.  The end point of the descent, as  calculated by the FMS/RNAV. eLORAN.  See long range navigation. Engaged. A system mode or function that is actively  performing its function. Broadcast weather service.  A weather service that prepares  weather products and transmits them to participating aircraft,  also known as a data link weather service. Chapter. Associated group of electronic “pages” of  information from databases found in FMS and GPS RNAV  units similar in contents, such as airports, VORs, software/ unit settings, and feature selections. Error-evident display.  Any display that presents information  in a way that makes errors more obvious and detectable. 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. Command bars.  A flight director display that presents roll  and pitch instructions (generally, V‑shaped visual cues)  to help the pilot maintain the flightpath/flight track to the  selected point. The pilot keeps the airplane symbol aligned  with the command bars on the flight director, or centered on  the FD crossbars (e.g., older Cessna units). Crossing restriction. A directive issued or published by  air traffic control that instructs the pilot to cross a given  waypoint at a specified altitude, and sometimes at a specified  airspeed. 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. Cursor mode. The function offered by the FMS/RNAV  that allows data entry into an avionics unit such as the FMS  and RNAV. Data link weather service.  See broadcast weather service. 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. Deceleration segment. A planned portion of a descent  designed to permit the aircraft to slow to meet a terminal  area speed restriction, crossing restriction, or other speed  restriction.  G-2