060° Heading YD BARO ARM AP FD HDG NAV REV ALT APR A L T  S E L DN UP FT Press to engage the heading function. 60° Heading The autopilot maintains the heading until fuel starvation. HDG 06 SET Set the heading bug to the desired heading. ft 0 0 5 5 YD BARO ARM AP FD HDG NAV REV ALT APR A L T  S E L DN UP FT Press the altitude button when  aircraft reaches the desired altitude. LT The autopilot maintains the altitude until fuel starvation. ALT Figure 4-8. Flying an assigned heading using the heading mode. Figure 4-9. Maintaining an altitude using the altitude hold mode. Catching Errors: Armed Modes Help Prevent  Forgotten Mode Changes Vertical Speed Climbs and Descents Vertical Speed With Altitude Capture or the autopilot is disconnected. If an altitude selector is not  installed or functioning, the pilot has the task of leveling off  at the assigned altitude, which requires monitoring progress  and manually engaging the autopilot’s altitude hold function  once the aircraft reaches the desired altitude. You must be  very careful to specify an appropriate vertical speed, as the  aircraft will fly itself into a stall if you command the autopilot  to climb at a rate greater than the aircraft’s powerplant(s) is/ are capable of supporting. You also need to monitor descent  airspeeds diligently to ensure compliance with V$_{NE}$ /V$_{MO}$  and  V$_{A}$ or turbulence penetration speeds if there is doubt about  smooth air conditions. As discussed in the previous chapter,  you should be cognizant of the powerplant temperatures  reciprocating powered aircraft and bleed air requirements  for turbine‑powered aircraft. Some FD/autopilots have an altitude select/capture feature.  The altitude select/capture feature is illustrated in  Figure 4-11. The altitude select/capture feature combines use of the  activated vertical speed mode and an armed altitude hold  mode. To use this feature, the vertical speed function is  initially engaged. The altitude hold mode usually arms  automatically when a different altitude is selected for capture  and vertical speed is activated. With an altitude select/capture  option or feature, the altitude hold mode disengages the  vertical speed mode upon capture of the selected altitude once  the vertical speed function completes the necessary climb or  descent. Once the aircraft reaches the assigned altitude, the  vertical speed function automatically disengages, and the  altitude mode changes from armed to engaged. The change  from vertical speed mode to altitude hold mode is the capture  mode, or transition mode. Any changes made by the pilot  during this short phase usually result in a cancellation of the  capture action, allowing the aircraft to continue the climb or  descent past the selected altitude. Again, be familiar with the  aircraft’s equipment. Let the system complete programmed  tasks, and understand what it will do if interrupted. An autotrim system is capable of automatically making any  needed adjustments to the pitch trim to maintain the aircraft  at the desired altitude and in a properly trimmed condition.  Pitch control pressure applied with the altitude hold mode  engaged will cause the autopilot to trim against you. Many FD/autopilot altitude selectors include an altitude alert  feature, an auditory alert that sounds or chimes as the aircraft  approaches or departs the selected altitude. The autopilot’s vertical speed mode allows you to perform  constant‑rate climbs and descents.  Figure 4-10 illustrates  the use of the vertical speed mode for one autopilot that is  integrated with a PFD. When you engage the vertical speed mode, the FD/autopilot  will attempt to maintain the specified vertical speed until you  choose a different setting in autopilot, the aircraft reaches an  assigned altitude set into the assigned altitude selector/alerter,  You have already seen how remembering to make a needed  mode change in the future can be an error‑prone process. Not  canceling the armed function allows the altitude select mode  to relieve the pilot from needing to remember to engage the  function manually once the aircraft has reached the selected  altitude. Do not interrupt the altitude armed or capture mode,  unless prepared to manually control the process. 4-8