12.  System Operation (Fig. 4 and 5)
A.  There are eight flight modes selectable from the flight mode selector. TURB mode is selected by the TURB key. All modes are engageable, although STBY engages only self-test values to the EPR indicator and does not control the AFCS system (GJ B-2509 and B-2510). Performance functions are selectable with flight modes engaged or selected and do not alter command bug values.
NOTE:  During fueling operations the airplane gross weight is changing. PDCS data using airplane gross weight will be in error.
NOTE:  A "VALID USE EPR LIMIT" alert message will occur on PDCS CDU during flight modes of operation with less than 500 LBS of fuel in the fuel tanks.
(1)  
The standby (STBY) modes are used for data and automatic system checkout. Page 1-3, STANDBY, displays the program number. Page 2-3, CONFIG, indicates the airplane model, engine type, and units of weight (lbs or kg) used. Page 3-3, SELF TEST, displays VALID if the PDC system self-test is satisfactory and INVALID followed by a diagnostic message if the self-test is unsatisfactory. If the self-test is satisfactory, the ENGAGE key illuminates to indicate a test of the mode annunciator, and command bugs may be initiated. Pressing the minus key allows additional pages of self-tests to be displayed. The first page of TEST displays total air temperature (TAT), airspeed (IAS), altitude (ALT), and EPR values. The second page of TEST displays total fuel quantity, DME 1 and DME 2 distance, target EPR self-correction K-FACTOR and flight index value. The third page of TEST displays the status of system configuration interlocks and discrete input signals. The display consists of 6 rows of data with each row divided into 13 columns. The forth page of TEST displays drag performance modification factor plus OMEGA groundspeed and distance. Airplanes with PDCS-AFCS intertie have two additional test pages. The fourth and fifth pages of TEST provide displays for the A/T and AFCS BITE tests (Ref 22-11-00, 22-31-00). The sixth page of TEST displays the drag performance modification factor plus OMEGA groundspeed and distance.

(2)  
The takeoff (TO) modes display takeoff EPR limits, outside air temperature, and takeoff mode selected. The modes are displayed on 2 pages, FULL and REDUCED. When TO mode is engaged, only the EPR bugs are driven. The FULL page generates EPR guidance data using the actual OAT. With the REDUCED thrust takeoff mode, manually inserting an assumed temperature results in a computed thrust less than maximum climb thrust, causing the display to be limited to EPR values corresponding to maximum climb thrust.

(3)  
The climb (CLB) modes display climb EPR and speeds (IAS and MACH). Page 1-4, ECON, provides an economy schedule to minimize overall operating expense. ECON also displays wind component and an optimum altitude arrow, which indicates when current altitude is above or below optimum altitude by more than 2000 feet. With CLB engaged the EPR command bugs drive to the displayed value, and the EPR climb limits and target airspeed are sent to the AFCS. Page 2-4, RATE, displays EPR and speed for maximum rate of climb. Page 3-4, MANUAL, displays manually selected climb speed values. When ENGAGED, the speed value (IAS or MACH) controlling the mach/airspeed indicator command bugs is indicated by an underline on the display. Page 4-4, LIMIT, displays only the EPR limits.

NOTE:  The PDC constantly monitors the buffet margin and revises the targets airspeeds to maintain a buffet margin greater than 1.3g. in the CLB, CRZ, DES, and HOLD modes. If an airspeed is entered manually that is below 1.3g., an error message is displayed.

(4)  
The CRZ modes display the cruise EPR, speed and wind. With the CRZ engaged the target A/S drives the mach/airspeed indicator command bugs, and if the A/T is armed the EPR limit drives the EPR indicator command bugs. If the A/T is not armed the target EPR drives the command bugs. Page 1-4, ECON, displays the most economical cruise schedule based on atmospheric conditions and gross weight. An optimum altitude arrow is displayed when a 2000-foot difference between current and optimum altitude occurs. The optimum altitude can be displayed by selecting the FL function. Page 2-4, LRC, generates flight guidance information for best fuel mileage (long range cruise) and an optimum altitude arrow is displayed. Page 3-4, MANUAL, displays manual selected speed values. Page 4-4, LIMIT, displays only the maximum cruise EPR limit values.

(5)  
The DES modes display descent airspeed, destination elevation, wind, descent time, and horizontal descent distance. Engaging the DES mode causes the target A/S to drive the Mach/Airspeed indicator command bugs. If the A/T is armed the EPR bugs drive to the EPR limit, and if the A/T is not armed the EPR bugs drive to 1.00. Page 1-2 displays data for the most economical descent Page 2-2 displays data for manually selected speed descent.
　
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