230 23 AP YD FD HDG NAV APR ALT MENU VS NOSE UP FLC NOSE DOWN NAV1 10 NAV2  10 0 WPT  KGNB  DIS  53.5NM  DTK  274° TRK  360° GPS AP YD ALT KG N NB B GP P S S  I S  S P D A 5 N D D  5 53 .  Y DT K K  2 L T M AL Figure 4-3. An integrated avionics system with an autopilot. Figure 4-4. Engaged autopilot modes shown at the top of a PFD. 4-4 How Autopilot Functions Work Determination of Control Movements Required To  Achieve Goals Carrying Out Control Movements Flight Director Flight Director Functions profile. Every autopilot displays which autopilot modes are  currently engaged, and most indicate an armed mode that  activates when certain parameters are met, such as localizer  interception. The autopilot shown in  Figure 4-1  displays the  active modes on the front of the unit, just above the controls.  The integrated autopilot shown in  Figure 4-4  displays the  currently engaged autopilot mode along the top of the PFD. Once an autopilot mode has been engaged, the autopilot: Suppose you wish to use the autopilot/FD to turn to an  assigned heading of 270°. The heading knob is used to  select the new heading. Before any control movements are  made, the autopilot/FD must first determine which control  movements are necessary (e.g., left or right turn). To do so,  the FD/autopilot must first determine the aircraft’s current  heading and bank angle, determine amount and direction  of the turn, and then choose an appropriate bank angle,  usually up to 30° or less. To make these determinations, the  FD gathers and processes information from the aircraft’s  ADC (airspeed and altitude), magnetic heading reference  instrument, and navigation systems. Once the FD/autopilot has determined which control  movements are necessary to achieve the flight change,  the autopilot has the task of carrying out those control  movements. Every autopilot system features a collection of  electromechanical devices, called servos, that actuate the  aircraft control surfaces. These servos translate electrical  commands into motion, the “muscle” that actually moves  the control surfaces. An FD is an extremely useful aid that displays cues to guide  pilot or autopilot control inputs along a selected and computed  flightpath.  [Figure 4-5]  The flight director usually receives  input from an ADC and a flight data computer. The ADC  supplies altitude, airspeed and temperature data, heading  data from magnetic sources such as flux valves, heading  selected on the HSI (or PFD/multi-function display (MFD)/ electronic horizontal situation indicator (EHSI)), navigation  data from FMS, very high frequency omnidirectional range  (VOR)/distance measuring equipment (DME), and RNAV  sources. The flight data computer integrates all of the data  such as speed, position, closure, drift, track, desired course,  and altitude into a command signal.  The command signal is displayed on the attitude indicator  in the form of command bars, which show the pitch and roll  1. Determines which control movements are required to  follow the flight profile entered by the pilot, and  2. Moves the controls to affect tracking of the flight  profile.