The link between the flight crew and the FMS is the multi-purpose control and display unit. It provides the crew with the means to make inputs to the system in order to obtain required displays, or information to assist with decision-making in respect of the aircraft's flight progress. The CDU display is in paged, digital format on a small, typically 2 6 3 inch, CRT screen.
The MCDU is primarily used for long-term actions, such as monitoring and revising the flight plan, selection of operating mode and insertion of data such as aircraft weight, wind speed and direction, various temperatures and performance data. It provides the flight management computer (FMC) with readout capability, together with verification of the data entered into the computer memory. Flight plan and advisory data are continuously available for display on the MCDU.
The MCDU panel has a full alpha-numeric keyboard, along with mode, function and data entry keys. The keyboard includes advisory annunciators, display light sensors and a manual brightness control. A typical multi- purpose control and display unit is illustrated in Figure 5.3.
flight management computer multipurpose control and display unit pilots electronic interface unit central maintenance computer flight director system inertial reference system integrated display system
ADF VOR DME ILS/MLS
autothrottle servo electronic engine controls fuel quantity indicating weight and balance computer air data computer flight control computer mode control panel digital clock GPWS EFIS
Display screen
The display screen of the MCDU shown in Figure 5.3 has 14 lines with a total of 24 characters per line. The page format of the screen is divided into four areas, these are:
. Title field, which contains the title of the page of subject data displayed and the page number (e.g.1/2, meaning page 1 of 2).
. Left and right fields, each containing six pairs of lines of 11 characters per line. The pilot has access to one line of each pair through the line select keys on either side of the unit.
. Scratchpad, which forms the bottom line of the display screen. Scratchpad entries may be pilot-inserted, unless an FMC originated message is dis- played in this field, and they are independent of the page displayed. Line select keys
Momentarily depressing a line select key affects the line adjacent to the key on the respective side of the MCDU for entry, selection or deletion of data. Brightness control
The light intensity of the MCDU display may be adjusted by rotating the BRT knob. Brightness of the illuminated keys is automatically adjusted by a remote flight deck control.
title field
scratchpad
left field right field
line select k e ys line select k e ys INIT REF RTE DEP
ARR ATC VNAV
BRT
FIX LEGS HOLD FMC COMM PROG
EXEC
MENU NAVRAD PREV PAGE NEXT PAGE 1 2 3 4 5 6 7 8 9 0
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+/- A B C D E F G H I J K L M N O P Q R S T U V W X Y Z SP DEL / CLR ann unciators ann unciatorsnumeric keys alpha keys function and
mode keys
brightness control
Annunciators
There are two annunciators on each side of the keyboard. These display the following messages when appropriate:
. DSPY. Display (upper left). The white display light illuminates when the active lateral or vertical leg performance mode is not displayed on the current MCDU page.
. FAIL. Fail (lower left). The amber light illuminates when there is a fault in the FMC.
. MSG. Message (upper right). The white light illuminates to indicate to the pilot that an FMC-generated message is displayed on the scratchpad, or is waiting to be displayed when the scratchpad is cleared.
. OFST. Offset (lower right). The white light is illuminated when lateral navigation (LNAV) is based on a route parallel to, but offset from, the active route.
Alpha-numeric keys
These keys allow the pilots to enter letters and numbers onto the scratchpad successively from left to right. They include space (SP), delete (DEL), slash (/), and plus/minus (+/7) keys.
Function keys
The function keys control the MCDU field displays, accomplished by the execution of pilot inputs and requests. The purpose of each of the function keys is briefly described below:
. EXEC. The execute key is the command key for the FMCS. Whenever a modification or activation is pending, a white light bar illuminates. Depressing the key will activate the flight plan, change the active flight plan or change the vertical profile, as appropriate.
. NEXT PAGE. Depressing this key causes the display to page on to the next higher page number in multi-page displays.
. PREV PAGE. Depressing this key causes the display to page back to the next lower page number in multi-page displays.
. CLR. The clear key extinguishes the MSG annunciator light and clears any message from the scratchpad. Where more than one message is displayed, each momentary push clears a single message; multiple messages are cleared by repetitive momentary pushes or a single long push.
. DEL. Pressing this key inserts the word DELETE onto the scratchpad, provided that the pad is clear. Line selection by means of a line selection key deletes the entered data on that line, but is only available for specific pages.
Mode keys
The mode keys control the type of page displayed on the MCDU and are therefore the means by which the pilots gain operational access to the flight management system. There are twelve keys, as described below:
. INIT REF. (Initialisation/reference.) The initialisation/reference key selects the first of a series of pages used to initialise the position of the FMCS and the inertial reference system (IRS).
. RTE. (Route.) The route key provides access to planned routes and selects the page for entering or changing the point of departure, destination or route.
. DEP ARR. (Departure/arrival.) Depressing this key calls up an index listing all terminal area procedures.
. ATC. (Air traffic control.) This key selects the ATC automatic dependent surveillance status page.
. VNAV. (Vertical navigation.) Depressing this key provides access to the climb (CLB), cruise (CRZ) and descent (DES) pages for evaluation and modification.
. FIX. The fix key provides access to the fix information pages, which are used for creation of waypoint fixes.
. LEGS. The legs key provides a page for evaluating or modifying lateral or vertical details of each route leg.
. HOLD. The hold key calls up the page for entering, exiting or amending a holding pattern.
. FMC COMM. (Flight management computer communications.) In most
current systems this key is non-operational.
. PROG. (Progress.) This key is used to select current dynamic flight and navigation data, such as ETAs and fuel remaining at a given point (e.g. next two waypoints, destination or alternate).
. MENU. The menu key provides access to other aircraft subsystems and to the alternate control for the EFIS and EICAS control panels in the event of failure.
. NAV RAD. (Navigational radio.) Depressing this key selects the page for monitoring or modifying navigational radio tuning.
Figure 5.4 shows a typical MCDU page display.
The MCDU is duplicated so that each pilot has access to the system and the two units are usually located on either side of the central console. Operation of the FMS is fully described in the Aircraft Operating Manual for each aircraft type.