The Primary Flight Display (PFD) gives a good representation of your aircraft's current flight state.  The PFD also provides some visual feedback regarding your aircraft's mode of operation and phase of flight.

Besides all the physical state information, the PFD provides the main source of information regarding your aircraft's mode of operation.  These modes fall into three categories:  Thrust, Lateral, and Pitch.  These categories are represented (from left to right) in your aircraft's PFD by the three green items at the top of the PFD display window.

The mode categories correlate closely with your aircraft's three MCP fields: speed, heading, and altitude respectively.  Just as the three fields of your aircraft's MCP are related, these mode categories are also closely related, but they can also vary independently of each other.  Examples of some of the modes are shown in the images on this page.

• The Thrust mode category can have any of four different modes:
          "HOLD" implies your aircraft is applying thrust to maintain a speed
          "SPD" implies your aircraft is applying thrust to meet a new speed
          "IDLE" implies your aircraft is not applying any thrust
          "THR" implies your aircraft is maintaining thrust (typically when climbing)
   

• The Lateral mode category can have any of three different modes:
          "LNAV" implies your aircraft's FMS is commanding the heading
          "HDG SEL" implies your aircraft's MCP is commanding the heading
          "HDG HOLD" implies your aircraft is maintaining the MCP heading
   

• The Pitch mode category can have any of five different modes:
          "VNAV PATH" implies your aircraft is pitching to meet a path
          "VNAV SPD" implies your aircraft is pitching to meet a speed
          "VNAV ALT" implies your aircraft is pitching to meet a new altitude (typically when leveling off)
          "FLCH SPD" implies your aircraft's MCP altitude is commanding the pitching to meet a speed
          "HOLD" implies your aircraft is maintaining the MCP altitude

In the bottom-right corner of the PFD, feedback concerning your control mode is displayed.  Either "ATC CTRL" or FREE FLIGHT" are displayed here.  The control mode determines the rules of operations for your flight, whether under the direction of the Air Traffic Controller (atc ctrl), or on your own preferences (free flight).  The control mode is assigned by your Air Traffic Controller. 

The PFD also indicates which phase of flight your aircraft is in.  This is displayed directly above the attitude indicator.  Your aircraft can be in either the Cruise, Descent, Approach, Final Approach, Landing, Initial Climb, Climb, or Unknown phase of flight.  The phase of flight is determined by considering three main factors:

• Your aircraft's current state relative to its trajectory profile:
              Top Of Descent (TOD), Top Of Climb (TOC), Bottom Of Descent (BOD), Bottom Of Climb (BOC), etc.

• Your aircraft's position relative to the runway (distance from, altitude above, etc.)

• Your aircraft's vertical speed

Examples of some of the phases of flight are shown in the images on this page.

Examples of some of the phases of flight are shown in the images on this page.