Chapter 16

Flight Management Computer

Main Menu

SYSTEM DESCRIPTION

MULTIPURPOSE CONTROL DISPLAY UNIT (MCDU)

 

The Multipurpose Control Display Unit (MCDU) is the interface between the pilot and the FMC. It provides the means to for manually inserting system control parameters and selecting modes of operation. 

 

MCDU Functional Areas

 

The Flight Deck: MD-80 FMC has 5 functional areas.

 

 

LOCATION: FMC Panel

 

1. DISPLAY. 

 

The cathode ray tube displays all selected [age formats and is partitioned in four area:

 

    Title Line - The title line is located at the top of the CRT display.

 

    Left Field - The left field is divided vertically into six lines of information that extend from the left side of the display to the center of the display.

 

    Right Field -  Similar to the left field, the right field is divided vertically into six lines of information that extend from the center of the display to 

                           the right side of the display. 

 

    Scratch Pad Line - The scratch pad line is located at the bottom of the CRT display. Typed numeric characters an FMC generated messages

                                    are displayed on this line. 

 

 

2. LINE SELECT KEYS.

 

There are 6 line select keys (LSKs) on each side of the CRT display. The left set of keys is identified as 1L, 2L, 3L, 4L, 5L, and 6L, while the right set of keys is identified as 1R, 2R, 3R, 4R, 5R, and 6R. They are used for the following functions.

 

    a. To allow entry of data from the Scratch Pad into the selected line and field. 

 

    b. If a LSK is pressed with the Scratch Pad empty, it enters the contents of that line into the Scratch Pad, if applicable.

 

    c. To provide access to the data or function identified with that field. 

 

 

3. CLR (Clear).

 

Pressing will cause the last number in the scratch pad to be erased. Holding down will erase the entire line.

 

 

4. NUMERIC KEYS (circular).

 

Pressing these keys enters the selected number in the Scratch Pad.

 

 

5. MODE SELECT AND FUNCTION KEYS (Rectangular).

 

    INIT/REF Key - The INIT/REF key provides access to pages of data required for initialization of the FMC and IRS for flight, plus various

                               categories of reference data.

 

    DIR/INTC (direct) - Used for selecting direct to an altitude when using VNAV.

 

    LEGS Key - The LEGS page provides access to the active leg of the flight plan. 

 

    CLB key - The CLB key provides access to the climb page. It allows the pilot to add climb airspeed/altitude restrictions.

 

    CRZ key - The CRZ key provides access to the cruise page and allows the pilot to change the cruise altitude and airspeed.

 

    DES Key - The DES key provides access to the descent page. The Key allows the pilot to change the descent profile, and displays the vertical

                       path error when in the descent phase of flight.

 

    PROG Key - The PROG key provides access to the PROGRESS pages that display dynamic information for the next waypoint. 

 

 

PAGE SELECTION/EXECUTION

 

Data is organized in a multi-level format. Multiple prompted page selections may be required to reach the appropriate sub-page level of information.

 

The INIT/REF selection has a dedicated index page. These pages are displayed by pushing the INIT/REF Key. Once the index is displayed, pushing the Line Select Key adjacent  to the desired prompt causes the MCDU to display the selected sub-page of information.

 

 

As an example, selecting <POS wiht LSK 2 on the INIT/REF INDEX 1/1 page changes the display to appear as below:

 

 

Sometimes there is so much information that is cannot be displayed on one page. Consequently, the information is continued on additional pages. Page numbers are located in the upper right corner of each page. The 1/2 indicates that the first page of two pages is currently displayed. Page 2/2 is displayed by pressing the NEXT PAGE key. The PREV PAGE is used in a similar way.

 

Occasionally, a page of information is made available by pushing a Line Select Key. In the display shown below, selecting TAKEOFF> with LSK 6R. This is convenient in suggesting a logical next step, or information should be confirmed on another page.

 

 

 

INDEX/MENU PAGES

 

INIT/REF INDEX

 

 

The INIT REF 1/1 page provides prompts for selection of sub-pages for initialization, and reference information. 

 

    <IDNET - selects the IDENT 1/1 page for program identification database selection, and display of drag and fuel-flow factors.

 

    <POS - selects the POS 1/2 page for normal position for initialization. The NEXT PAGE Function Key will then select POS REF 2/2 

                 for reference data.

 

    <PERF - selects the PERF INIT 1/1 page for entry of performance initialization data.

 

    <TAKEOFF - selects the TAKEOFF REF 1/1 page for display of takeoff EPR, performance status, and takeoff speed entry.

 

    <APPROACH - selects the APPROACH REF 1/1 page for reference speeds at current selected gross weight.

 

 

MCDU MODES AND OPERATION

 

MCDU DATA ENTRY

 

Data is entered into the scratchpad from left to right using the numeric keys. Often, the display field acts as an example format for the data entry to be made. After scratchpad entry and confirming that the data is correct, pressing a LSK transfers the data from the scratchpad to the data field. For some specific formats, data can also be entered from the MCDU screen into a blank scratchpad by pressing the LSK adjacent to the desired data ("line Selecting"). The data can then be transferred to another data field by pressing its associated LSK, or cleared from the scratchpad by pressing the CLR key.

 

INITIALIZATION AND REFERENCE MODE

 

The INIT/REF INDEX 1/1 page is selected by pressing the INIT/REF Mode Select Key. The IDENT page is displayed by selecting <IDENT with LSK 1L on the INIT/REF INDEX 1/1 page.

 

 

The IDENT page nromally appears on the MCDU when power is first applied to the aircraft. The NAV DATA shows the data base code. DRAG and F - F (fuel fow) FACTORS are stored in the computer for performance calculations and may not be altered by the crew. 

 

Selecting POS INIT> with the LSK 6R on the IDENT page performs the same function as selecting <POS with LSK 2L on the INIT/REF index page. The POS 1/2 appears in both cases.

 

 

Position Pages

 

POS 1/2 is used to enter aircraft position for FMC and IRU alignment.

 

 

The aircraft position must be entered for the IRUs to complete their alignment phase. (refer to chapter 12 for more on IRU alignment) To enter the aircraft position press LSK 1R to bring the LAST POS lat long down to the scratchpad. Then press LSK 4R to enter that value into the SET IRS POS data field. Once the IRS position has been set, pressing the NEXT PAGE key allows you to view the current lat long position, ground speed, UTC time, and the date.

 

 

 

LEGS MODE

 

The flight plan must be entered using the FS GPS. Pressing the LEGS Mode Select Key displays more detailed information on the active waypoint. The active waypoint is always at the top of the page. 

 

 

The waypoint ID is located on the left side. Above the waypoint ID, the current Track to the waypoint is displayed. Just to the right of the ID, is the distance to the waypoint. To the right is the angle of decent and the VNAV altitude (described later).

 

 

PERFORMANCE INITIALIZATION

 

After the flight plan has been activated select PERF INIT> with LSK 6R or the index menu to access the PERF INIT page. On this page performance items are entered such as weights, fuel, cost index, and cruise altitude. Entries are typed into the Scratch Pad and then entered with the appropriate LSK.  

 

The PERF INIT page may be accessed as any time by first pressing the INIT/REF Mode Select Key. An additional selection of <PERF with LSK 3L. Pressing the INIT/REF key on the ground after the aircraft position has been initiated automatically displays the PERF INIT page. This provides quick access to the PERF INIT page to change the ZFW for final closeout or change CRZ ALT for an ATC clearance change before takeoff.

 

 

Boxed prompts indicate data entries required for FMC initialization. Make all entries by first typing the required item in the Scratch Pad. Then line selecting the item to its proper location by pressing the appropriate LSK.

 

GROSS WT - displays the FMC computed. When the ZFW and fuel load are entered, the FMC automatically adds fuel to ZFW and displays 

                        gross weight.

 

FUEL - fuel must be entered using the full amount. Example, 23000. The FMC will automatically adjust the value to display in thousands of pounds.

             Example 23.0.

 

On the PROGRESS 2/2 page, CALC follows the fuel weight since, after engine start, the FMC uses fuel flow to calculate the current fuel weight. The crew can change the fuel quantity on the PERF page at any time during flight. 

 

ZFW - entered at LSK 3L. It is initially taken from the TPS report. When the sim loads, it will show empty weight. Complete the initial gross weight

            calculations on the TPS report (See performance section) and then enter the new ZFW here. 

 

RESERVES - entered as the total of FAA reserve fuel and alternate fuel only. It is entered at LSK 4L. For the MD-80, the standard reserve 

                       is 4,500 lbs.

 

COST INDEX - Entered at LSK 5L. It is the ratio of the hourly cost of aircraft operation to the cost of fuel and is found on the computer flight plan.

                           The normal value for this is 20.

 

CRZ ALT - entered as LSK 1R and is the initial cruise altitude for the flight.

 

TRANS ALT - automatically defaults to 18,000 feet. It is used for the Virtual First Officer callouts. The value can be changes using LSK 5R. 

 

 

TAKEOFF REFERENCE

 

When the PERF INIT page is complete, select TAKEOFF> with LSK 6R to access the TAKEOFF REF page. This page displays takeoff EPR, crew-entered takeoff speeds, and confirms FMC preflight status. If all preflight steps have been successfully complete, PRE-FLT COMPLETE appears. If the preflight is incomplete, PRE-FLIGHT STATUS appears with prompts to return to the incomplete page by pressing the associated LSK.

 

 

Total air temperature (TAT) from the DFGC is displayed in the data field next to LSK 1L. The field at LSK 2L displays the takeoff thrust setting as calculated by the DFGC. Aircraft gross weight is displayed at LSK 3L

 

 

For Standard Thrust Takeoff, the assumed temperature selected on the Thrust Rating Panel is displayed on the central data field between LSK 1L and LSK 1R with FLEX on the header line. As above, the data field next to LSK 2L is the takeoff thrust setting as calculated by the DFGC. The heading line of this field is FLX EPR when the takeoff mode is in TO FLX is selected on the TRP.

 

 

Values for V1, VR, and V2 may be entered on the right side of the page for crew reference at LSK 1R, 2R, and 3R respectively. All values blank after takeoff. These values are contained on the TPS sheet in the Performance Data.

 

 

APPROACH REFERENCE

 

APPROACH REF 1/1, when airborne, is accessed directly by pressing the INIT/REF Mode Select Key, and may be selected in the ground from the INIT/REF INDEX 1/1. It displays reference data relating to the approach. 

 

 

Approach speeds are displayed for various landing flap configurations and gross weight. The displayed gross weight is the current aircraft gross weight. GROSS WT may temporarily be changed by entering the proposed weight in the Scratch Pad and line selecting it with LSK 1L. When you exit the APPROACH REF page, the GROSS WT is reset to the current gross weight.

 

 

PERFORMANCE MODES

 

The performance Mode Select Keys are CLB, CRZ, and DES. Performance data is derived from the required preflight entries on the PERF INIT page and the stored aircraft performance information.

 

 

CLIMB MODE

 

The CLB Mode Select Key displays the climb speed and altitude targets. The speed/altitude restriction defaults to 250kts and 10,000 feet. This field is used for the CHECK SPEED warning. If the aircraft accelerates beyond the speed in this field and is below the altitude in this field, the CHECK SPEED will appear. The message can be cleared by pressing the CLR key. This field is also displayed on the descent page. The CRZ ALT is the altitude that was entered in the performance page. The value can also be entered or changed from the CLB page. The ECON SPD is the speeds that are set in the flight guidance computer. The MAX ANGLE is the default speed for maximum angle climb and cannot be modified. 

 

 

 

CRUISE MODE

 

The CRZ Mode Select Key displays the cruise page. The CRZ ALT is the altitude that was entered in the performance page. The value can also be entered or changed from the CRZ page. The OPT field contains the optimum cruise altitude based on the weight of the aircraft. The ECON SPD is the mach speed in the flight guidance computer. The lower right side field displays the wind readout. The middle right field displays the ETA and distance to the top of descent point. This is only avialible when you have a VNAV descent programmed. This is described in the VNAV section.

 

 

 

DESCENT MODE

 

The DES Mode Select Key displays the descent performance page. The aircraft starts a descent only if the Digital Flight Guidance System (DFGS) is engaged in VNAV and a lower altitude has been set in the altitude select window of the FGCP. The E/D AT is the current waypoint in the flight plan and is the waypoint that is available for VNAV and is only displayed if a VNAV altitude has been entered in the LEGS page. The AT field is the altitude at which the VNAV will descend to cross the VNAV waypoint. The SEL SPD is the speed in the FGCP. The PATH ERROR is the deviation from the VNAV descent path. The error will display how many feet above or below the VNAV path by displaying HI or LOW following the number. The path error is accompanied by a path deviation indicator on the nav display. The speed/altitude restriction defaults to 250kts and 10,000 feet. This field is used for the CHECK SPEED warning. If the aircraft accelerates beyond the speed in this field and is below the altitude in this field, the CHECK SPEED will appear. The message can be cleared by pressing the CLR key. This field is also displayed on the climb page.

 

 

 

VNAV

 

The Flight Deck: MD-80 is equipped with a single segment VNAV. The VNAV system will let you cross the active waypoint at a programmed altitude. When programmed and the VNAV is selected on the FGCP, the autopilot will fly the VNAV descent and level off at the active waypoint at the programmed altitude. The angle of descent can also be programmed so a steeper or shallower descent can be used. Angles from 1 to 6 degrees can be used. 

 

VNAV PROCEDURES

 

VNAV will only work is their is a active GPS waypoint. To initiate VNAV go to the LEGS page and the active waypoint will be displayed. Enter the altitude that you want to cross that waypoint in the Scratch Pad and then load it into the VNAV altitude field using LSK 1R. Valid values for altitude are greater than 100 feet. The default angle is 3.0 degrees. If you want to change the angle, enter a value from 1-6 in the Scratch Pad and enter it into VNAV field using the LSK 1R. 

 

 

 

VNAV MODE 1 - PROGRAMMED MODE

 

In this mode, the VNAV altitude and angle is programmed and then the aircraft is left alone to intercept the VNAV path and descend to the final VNAV altitude. After the altitude has been entered, the time and distance to the top of descent is displayed on the cruise page.

 

 

To arm the VNAV function of the autopilot, press the VNAV button on the FGCP. The autopilot mode panel will indicate VNAV LVL. Next, select the altitude in the autopilot altitude window. The VNAV is now armed to descend when the aircraft reaches the path angle entered in the LEGS page. 

 

 

If you have not selected the new altitude in the altitude window within 5 miles of the top of descent, a CHECK ALT SELECT will display in the Scratch Pad. When the altitude is selected in the altitude select window, the message will disappear. 

 

When the aircraft reaches the top of descent, the VNAV enters the descent mode and that is annunciated on the autopilot mode annunciator panel with VNAV DES. This also activates the PATH ERROR on the descent page. The PATH ERROR is the deviation from the VNAV descent path. The error will display how many feet above or below the VNAV path by displaying HI or LOW following the number. The path error is accompanied by a path deviation indicator on the nav display.

 

 

The autopilot will fly the VNAV descent profile making adjustments to stay on the path. At the end of the descent the autopilot will revert back to the standard altitude hold mode. 

 

 

VNAV MODE 2 - DIRECT MODE

 

This mode allows you to go direct to the final VNAV altitude. To do this, press the DIR/INTC Key. The word DIRECT will be displayed in the Scratch Pad and a carrot (>) will be displayed next to the VNAV altitude. Next, press the LSK 1R next to the carrot. The computer figures out what angle will take you directly from your present altitude to the VNAV altitude and will display it in the VNAV angle field. As long as the altitude select window altitude is lower than the present altitude, the aircraft will start an immediate descent along the computed VNAV path. 

 

 

Both the programmed and direct modes can be used interchangeably during a single descent. For example; if you are at 29,000 feet and you have a VNAV programmed to cross the active waypoint at 10,000 feet using an angle of 3.0 degrees. You get a clearance to descend at pilots discretion to 20,000 feet. You set 20,000 feet in the altitude select window and wait for the aircraft to reach the top of descent. At he top of descent the aircraft will begin a VNAV descent but will enter the VNAV LVL mode when the aircraft reaches 20,000 feet. You will see the PATH ERROR start to increase and the path deviation indicator go down signifying that the aircraft is above the VNAV path. When ATC gives you the clearance to cross the waypoint at the VNAV altitude, you will see that you are way above the path so you can set the new altitude in the altitude select window and then press the DIR/INTC and then the LSK 1R to activate the DIRECT mode and the aircraft will start a direct descent to the VNAV altitude. If the angle is greater than 6 degrees, then 6 degrees will be entered and you may or may not be able to catch up to the 6 degree path. Upon reaching the VNAV altitude, the aircraft will enter the standard altitude hold mode.

 

 

PROGRESS MODE

 

The PROG Mode Select Key displays two pages of data concerning the progress of the flight along the active route. Data includes:

 

    PROGRESS 1/1

 

        Current waypoint Distance, ETA, and Fuel Remaining.

 

        User entered Distance, ETA, and Fuel Remaining. 

 

        Active Speed and next vertical Event.

 

    PROGRESS 2/2

 

        Existing Wind/SAT/TAS

 

        Tracking Errors

 

        Fuel Monitoring

 

Pressing the PROG Mode Select Key displays PROGRESS 1/1.

 

 

The distance to go (DTG), ETA and FMC predicted fuel is displayed for the active waypoint. The crew can also enter another distance into field L4 to get DTG, ETA, and fuel remaining for that distance. This can be done by entering a distance into the Scratch Pad and then line selecting using LSK 4L. This can be useful for a quick check of an alternate airport. Leaving the PROGRESS 1/1 page will erase this value. Fuel remaining at these two locations is based on the CALCULATED fuel quantity shown in PROGRESS 2/2. 

 

 

SEL SPD is the current mode from the active speed mode in the FGCP. 

 

Adjacent to the active speed is the EAT and distance to go to the next significant VNAV vertical event along the active route. 

 

 

Pushing the NEXT PAGE displays PROGRESS 2/2.

 

 

The top of the page has the headwind/tailwind at LSK 1L, the crosswind component at LSK 1R, and the present calculated wind centered between them. WIND is the present wind direction. The wind is also depicted on all ND displays as a vector/speed symbol. 

 

XTK (cross track) ERROR is a continuous update of the aircraft lateral position error related to the active route.

 

VTK (vertical track) ERROR appears after the Top of Descent is passed and displays airplane altitude error relative to the optimum descent path.

 

Vertical deviation is also displayed on the ND vertical deviation scale and pointer when in map mode. This scale is only present during the descent phase of flight with VNAV engaged. Full deflection represents +/- 1000 feet.

 

TAS and SAT are derived from the Central Air Data Computer. 

 

Fuel information at the bottom of the page displays FUEL USED by each engine and total fuel used (TOT) all based on the engine fuel flow sensing system. The CALCULATED FUEL QTY is the fuel quantity at engine start minus fuel flow sensed to the engines.

 

The Left and Right can be reset on the ground by pressing the LSK 4L and LSK 4R. 

 

NOTE - FS does not do a good job of keeping track of fuel when in acceleration mode. For this reason, the fuel used numbers will not be accurate

              when the sim acceleration is above 4X.

 

 

MCDU ALERT MESSAGES

 

CHECK ALT SELECT - The aircraft is within 5 miles of the top of descent and the altitude select window is set at current altitude. 

 

CHECK SPEED - If the aircraft accelerates beyond the speed and is below the altitude on the CLB or DES page. The message can be cleared 

                               by pressing the CLR key.

 

INSUFFICIENT FUEL - Estimated fuel at current waypoint or user entered distance is less than RESERVES value displayed on the

                                          PERF INIT 1/1 page.