In every instance, you must be absolutely sure what modes the  FD/autopilot is in and include that indicator or annunciator  in the crosscheck. You must know what that particular  mode in that specific FD/autopilot system is programmed to  accomplish, and what actions will cancel those modes. Due to  numerous available options, two otherwise identical aircraft  can have very different avionics and autopilot functional  capabilities. You will learn how the autopilot and the flight management  system (FMS)/area navigation (RNAV) unit combine to  create a fairly automated form of flight that places you in  a managerial role. While the autopilot relieves you from  manually manipulating the flight controls, you must maintain  vigilance over the system to ensure that it performs the  intended functions and the aircraft remains within acceptable  parameters of altitudes, airspeeds, and airspace limits. An autopilot can be capable of many very time intensive  tasks, helping the pilot focus on the overall status of the  aircraft and flight. Good use of an autopilot helps automate  the process of guiding and controlling the aircraft. Autopilots  can automate tasks, such as maintaining an altitude,  climbing or descending to an assigned altitude, turning to  and maintaining an assigned heading, intercepting a course,  guiding the aircraft between waypoints that make up a  route programmed into an FMS, and flying a precision or  nonprecision approach. You must accurately determine the  installed options, type of installation, and basic and optional  functions available in your specific aircraft. Many advanced avionics installations really include two  different, but integrated, systems. One is the autopilot  system, which is the set of servo actuators that actually do  the control movement and the control circuits to make the  servo actuators move the correct amount for the selected  task. The second is the flight director (FD) component. The  FD is the brain of the autopilot system. Most autopilots can  fly straight and level. When there are additional tasks of  finding a selected course (intercepting), changing altitudes,  and tracking navigation sources with cross winds, higher  level calculations are required.  A track is a specific goal, such as a heading or course. A  goal can also be a level altitude, a selected airspeed, or a  selected vertical speed to be achieved with the power at  some setting. Every autopilot uses knobs, buttons, dials,  or other controls that allow the pilot to specify goals.  Figure 4-1  shows an autopilot combined with conventional  navigation instruments. Most autopilots have indicators for  the amount of servo travel or trim being used. These can be  early indicators of adverse conditions, such as icing or power  loss. Rarely will a trim indicator ever indicate full travel in  normal operation. Consistently full or nearly full travel of  the trim servos may be a sign of a trim servo failure, a shift  in weight resulting in a balance problem, or airfoil problems  such as icing or inadvertent control activation. The FD is designed with the computational power to  accomplish these tasks and usually displays the indications to  the pilot for guidance as well. Most flight directors accept data  input from the air data computer (ADC), Attitude Heading  Reference System (AHRS), navigation sources, the pilot’s  control panel, and the autopilot servo feedback, to name  some examples. The downside is that you must program the  FD to display what you are to do. If you do not preprogram  the FD in time, or correctly, FD guidance may be inaccurate. The programming of the FD increases the workload for the  pilot. If that increased workload is offset by allowing the  autopilot to control the aircraft, then the overall workload  is decreased. However, if you elect to use the FD display,  but manually fly the aircraft, then your workload is greatly  increased. 4-2 Specification of Track and Altitude Autopilot Concepts How To Use an Autopilot Function The following steps are required to use an autopilot function: 1. Specify desired track as defined by heading, course,  series of waypoints, altitude, airspeed, and/or vertical  speed. 2. Engage the desired autopilot function(s) and verify  that, in fact, the selected modes are engaged by  monitoring the annunciator panel. 3. Verify that desired track is being followed by the  aircraft. 4. Verify that the correct navigation source is selected  to guide the autopilot’s track. 5. Be ready to fly the aircraft manually to ensure proper  course/clearance tracking in case of autopilot failure  or misprogramming. 6. Allow the FD/autopilot to accomplish the modes  selected and programmed without interference, or  disengage the unit. Do not attempt to “help” the  autopilot perform a task. In some instances this has  caused the autopilot to falsely sense adverse conditions  and trim to the limit to accomplish its tasking. In more  than a few events, this has resulted in a total loss of  control and a crash.