0 WPT  KGNB  DIS  53.5NM  DTK  274° TRK  274° GPS AP YD VS ALT 800 FPM Armed functions are shown in white. WPT KGNB DIS 53 5 NM DTK 27 4 ° Engaged functions are shown in green. AP = autopilot engaged YD = yaw dampener VS = vertical speed engaged Awareness: Automatic Mode Changes Common Error: Failure To Arm the Altitude Mode Learning: The Importance of Understanding Awareness: Altitude Alerting Systems The indications on the autopilot in  Figure 4-11 do not  distinguish between functions that are armed or engaged. The more sophisticated annunciator shown in  Figure 4-12  uses  color coding to distinguish between armed and engaged  autopilot functions. alerting system, when the alerting system is missed, or you  are distracted, nothing is left to prevent an altitude deviation.  You must remember that the altitude alerting system is  designed as a backup, and be careful not to let the alerting  system become the primary means of monitoring altitude.  Most airline operators have a standard operating procedure  that requires pilots to call out approaching target altitudes  before the altitude alerting system gives the alert. Common  errors occur when setting 10,000 feet versus 11,000 feet.  Too many ones and zeros can confuse a fatigued, busy pilot,  resulting in setting an incorrect altitude. Distinguishing between “armed” and “engaged” adds  complexity to the process of maintaining mode awareness.  In addition to autopilot functions that are engaged by the  pilot, some autopilot functions engage and disengage  automatically. Automatic mode changes add to the challenge  of keeping track of which autopilot functions are currently  engaged and which functions are set to become engaged.  You can minimize confusion by always verifying the status  annunciations on the FMs, PFD/MFD, and the autopilot  mode annunciator after any change of heading, altitude,  or vertical speed. The verification process forces you to  carefully consider the configuration of the FMS and FD/ autopilot. Determine if engaging the autopilot cancels certain  FD modes. Some units interact, and when the autopilot is  engaged, some FD modes are automatically canceled, notably  altitude hold or selection. Figure 4-12. A mode annunciator showing armed and engaged  autopilot modes. The most common error made by pilots during climbs and  descents is failure to arm the altitude mode to capture the  assigned altitude. In many instances, this happens when the  crew does not correctly adjust the altitude selector or alerter.  Sometimes, this malfunction occurs when the altitude is  adjusted at the same time the system is attempting to go  into the capture mode. This situation typically results in the  aircraft climbing or descending beyond the assigned altitude,  which may result in an altitude deviation. Altitude deviations  are among the most common mishaps reported by pilots to  NASA’s Aviation Safety and Reporting System (ASRS). In  any event, always monitor the actions of the FD/autopilot  system and be prepared to fly the aircraft manually. One way to learn the steps required to use an autopilot is  simply to memorize them. This approach focuses solely on  the button and control manipulations required to perform each  procedure. Although this approach to learning may appear  to be the quickest, studies have shown that pilots who take  the time to develop a deeper understanding of how a system  works give themselves three important advantages. These  pilots are better able to: Altitude alerting systems were mandated for commercial  jet transports in the early 1970s in response to a growing  number of altitude deviations in airline operations. Although  they helped reduce the total number of altitude deviations,  altitude alerting systems also made possible a new kind of  error. Altitude deviation reports submitted to the Aviation  Safety and Reporting System (ASRS) indicate that pilots  sometimes rely too much on the altitude alerting system,  using it as a substitute for maintaining altitude awareness.  Instead of monitoring altitude, pilots sometimes simply listen  for the alert. This phenomenon is one instance of what human  factors experts call primary-secondary task inversion—when  an alert or alarm designed as a secondary backup becomes  the primary source of information. In the case of the altitude  Investing time to understand FD/autopilot functions pays off.  For example, in many systems, once the aircraft reaches the  selected altitude and levels off as indicated by the altitude  mode annunciator, the pilot can select the next altitude in  the window. Then, upon receiving the clearance to climb  1. Work through situations that differ from the ones they  learned and practiced during training, 2. Transition from one manufacturer’s system to another,  and 3. Recall procedures after not having practiced them for  some time. 4-10