Flight instrument presentations on a PFD differ from conventional instrumentation not only in format, but sometimes in location as well. For example, the attitude indicator on the PFD in Figure 2-1 is larger than conventional round-dial presentations of an artificial horizon. Airspeed and altitude indications are presented on vertical tape displays that appear on the left and right sides of the primary flight display. The vertical speed indicator is depicted using conventional analog presentation. Turn coordination is shown using a segmented triangle near the top of the attitude indicator. The rate-of-turn indicator appears as a curved line display at the top of the heading/navigation instrument in the lower half of the PFD.
Cross-Checking the Primary Flight Instruments
The PFD is not intended to change the fundamental way in which you scan your instruments during attitude instrument flying. The PFD supports the same familiar control and performance, or primary and supporting methods you use with conventional flight instruments. For example, when using the primary and supporting method to maintain level flight, the altimeter is still the primary instrument for pitch, while the attitude indicator is a direct indicator and the vertical speed indicator provides supporting information. However, you need to train your eyes to find and interpret these instruments in their new formats and locations.
Common Errors: Altitude Excursions and Fixation
Pilots experienced in the use of conventional flight instruments tend to deviate from assigned altitudes during their initial experience with the PFD, while they adjust to the tape display presentation of altitude information. Another common error is the tendency to fixate and correct deviations as small as one to two feet at the expense of significant deviations on other parameters.
Enhancements to the Primary Flight Instruments
Some PFDs offer enhancements to the primary flight instruments. Figure 2-2 shows an airspeed indicator that displays reference speeds (V-speeds) and operating ranges for the aircraft. Operating ranges are depicted using familiar color coding on the airspeed indicator. One negative human factor concerning this type of presentation should be remembered: while most of the displays are intuitive in that a high indication (such as climb pitch or vertical speed) is corrected by lowering the nose of the aircraft, the situation with the usual airspeed vertical tape is the opposite. In most current displays, the lower speeds are at the lower side of the airspeed indicator, while the upper or higher speeds are in the top portion of the airspeed display area. Therefore, if a low airspeed is indicated, you must lower the nose of the aircraft to increase, which is counterintuitive to the other indications.
Figure 2-3 shows an attitude indicator that presents red symbols to assist in recovery from unusual attitudes. The symbols on the display recommend a lower pitch attitude.
Other valuable enhancements include trend indicators, which process data to predict and display future performance. For example, some systems generate “trend vectors” that predict the aircraft’s airspeed, altitude, and bank angle up to several seconds into the future.