In addition to learning how to use the FD/autopilot, you must also learn when to use it. Since there are no definitive rules about when an FD/autopilot should or should not be used, you must learn to consider the benefits and disadvantages of using the FD/autopilot in any given situation.
One of the most valuable benefits of using the FD/autopilot is delegating the constant task of manipulating the aircraft’s controls to the equipment, which do nothing other than comply with the pilot’s programming. This allows you more time to manage and observe the entire flight situation. Managing the flight versus actually moving the controls allows more time for:
- Programming. Especially when flying under IFR, changes to a route are inevitable. Even when the pilot is proficient in using FMS/RNAV, this task requires focusing some attention on the programming task. The FD/autopilot keeps the aircraft on the programmed heading or course and altitude while the pilot makes the necessary changes to the flight plan. If programmed correctly, the aircraft maintains the correct track and altitude.
- Distracting tasks/workload. Similarly, the FD/ autopilot is used to control basic aircraft movement while the pilot focuses attention on tasks such as reviewing charts, briefing and configuring for an instrument approach, updating weather information, etc. The FD/autopilot can also be a great help in other high workload situations, such as flying in a busy terminal area or executing a missed approach in adverse weather conditions.
- Maintaining autopilot skills. The FD/autopilot’s ability to help manage pilot workload depends heavily on the pilot’s proficiency in using it. Regular practice with the various autopilot functions (especially the approach functions) is essential to develop and maintain the knowledge and skills necessary to maximize its utilization.
- Emergencies. The FD/autopilot can be extremely useful during an emergency. It can reduce pilot workload and facilitate efforts to troubleshoot the emergency.
Disadvantages of using the FD/autopilot include the following:
- Forgetting to maintain manual flying skills. It is important to practice flying without the FD/autopilot often enough to maintain proficiency in basic flying skills and the instrument cross-check and scan. One common pitfall of advanced avionics is the pilot’s tendency to forget to maintain hard-earned skills for instrument flight. All equipment will fail at some time. The competent pilot is ready and prepared to make a transition to aircraft piloting at any time.
- Turbulence. The pilot’s operating handbook (POH) and FD/autopilot flight manual supplements for many aircraft discourage or prohibit use of the autopilot’s altitude hold function during moderate or severe turbulence. Some FD/autopilot systems may default or disengage if certain trim or control limits are encountered during turbulent conditions. You should consult the flight manual to ensure the aircraft is not operated outside specified limits. The aircraft’s flightpath and mode indications should always be monitored to ensure what modes are active.
- Minimum altitude. Autopilots are certified for use above a specified minimum altitude above ground level (AGL). Some higher performance and higher service ceiling aircraft require autopilot control above certain airspeeds and altitudes. The flight manual and operations manual (if any) should be consulted to ensure that the pilot does not operate the aircraft outside specified limits. For higher safety standards, commercial operators must observe restrictions in Title 14 of the Code of Federal Regulations (14 CFR) sections 121.579, 125.328, and 135.93, according to their regulatory classification. Adoption of these limits by private operators would add a safety margin to flights conducted under 14 CFR part 91 regulations in many cases.
- Possible malfunction. If at any time the pilot observes unexpected or uncommanded behavior from the autopilot, he or she should disengage the autopilot until determination of the cause and its resolution. Most autopilot systems have multiple methods of disengagement; you should be immediately aware of all of them. Also be aware of the methods to cancel the FD display to avoid confusing information.