747 Control Display Unit (CDU)|
by jerome meriweather
Inward to EICAS
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747 Photo and/or Graphic Element
The CDUs allow the flight crew to make inputs to, and control the FMS. FMC data and messages for the crew are displayed on the CDUs.
In addition to the graphic information displayed on the electronic flight instruments, CDU data is displayed in the form of pages relating
to the phases of flight or performance modes. Pages can be called up for display and the data manipulated by the various keys on the CDUs.
A CDU line containing boxes indicates an entry is required for FMS operation. A line containing dashes indicates an entry is optional for
FMS operation. The CDUs do not accept entries which are illogical, inappropriate, or beyond the capabilities of the airplane. In some cases
the entry produces no effect, and in others, generates a plain language message advising of the specific disparity. These messages are listed
under FMC Alerting Messages of this chapter.
The CDU can also operate as a control panel for other subsystems such as ACARS, SATCOM, central maintenance computers (CMCs), and aircraft
condition and monitoring system (ACMS). The CDU also provides backup functions for navigation, flight planning, radio tuning, and EFIS/EICAS
control. The CDU includes a system MENU display page from which systems other than the FMC can be chosen to control the display.
In the event of an EFIS or EICAS control panel failure, the MENU page will provide the capability to select a CDU backup of the EFIS or EICAS
control panel functions.
The CDU's capability for alternate navigation and radio tuning are only available after certain failures occur. The CDU automatically
activates its alternate navigation function (LEGS and PROGRESS pages) when it determines that the selected master FMC has failed. The CDU
automatically activates its alternate radio tuning capability (NAV RAD page) only when it determines that both FMCs have failed.
Alpha (Letter) Keys
- Alpha - Enter Alpha characters on scratch pad if scratch pad is blank.
- SP - Enters a space in the scratch pad when using the CDU for ACARS or SATCOM.
- DEL - Enters DELETE in the scratch pad if scratch pad is blank. Subsequent line selection deletes data on adjacent line
if the information is deletable. When information is removed, it is replaced by blanks, dashes, small font or boxes.
- CLR - Erases last character of scratch pad line or complete FMC message when pushed momentarily. Erases entire scratch
pad entry when held.
- / - Used to separate place bearing/distance, speed/altitude, wind direction/speed and similar type entries.
- Keys with white Border - North, South, East and West
Numeric (Number) Keys
Used to Enter Numeric characters on Scratch Pad.
Displays pages of FMC data containing up to 6 full or 12 half lines of data as selected with CDU keys, Line Select Keys or by FMC logic.
Line Select Keys (6 per side)
Transfer data from Scratch Pad to line next to key if acceptable to FMC or duplicate data from line next to key on Scratch Pad
if Scratch Pad is blank and data is acceptable to the FMC.
Call up first page in series corresponding to subject on line next to key if entry is preceded or followed by caret(< >).
Controls intensity of CDU display.
- DSPL Light - Indicates page displayed is not related to the active route leg or performance mode.
- FAIL Light - Indicates fault in the FMC.
- MSG Light - Indicates FMC generated message is displayed on scratch pad, or waiting to be displayed when scratch pad is clear.
Pushing CLR key extinguishes light and clears message.
- OFST Light - Indicates LNAV is based on a parallel route Offset from active route.
5 Page Buttons
- INIT / Reference Page - Calls up first uncompleted page of series used to initialize the FMC and IRS, plus various
pages of reference data.
- RTE Page - Calls up first page of series related to flight plan route on which data is displayed and entered.
- Departure / Arrivals Page - Calls up index page or pages listing all Departure or Arrival procedures in the database
for the Departure airport before traveling 400 miles or halfway to destination, whichever occurs first. After traveling 400 miles
or halfway to destination, the index or arrival procedures for destination will be displayed.
- ATC Page - Selects ATC/ADS status page.
- VNAV Page - Selects page for evaluating or modifying Vertical Navigation data.
5 Page Buttons
- FIX Page - Calls up first page of series used to establish bearings and distances from navaids as waypoints and to
display ETAs and distances.
- LEGS Page - Calls up first page of series displaying details of each Leg of route and list all route waypoints with
speed/altitude crossing restrictions. LEGS page controls route segment displayed on associated ND when ND is PLN mode.
- HOLD Page - Calls up page for entering or exiting Holding pattern, or for modifying a previously built Holding pattern.
- FMC COMM Page - Selects page which accepts datalink; provides datalink status.
- Progress Page - Calls up first page of series displaying dynamic flight and navigation data, including ETAs and fuel
remaining estimates for next two waypoints and destination or the entered waypoint.
4 Page Buttons
- MENU Page - Selects page to allow CDU interface with FMC, ACARS, SATCOM, ACMS, CMC and alternate control of EFIS and EICAS.
- NAV RAD Page - Selects page for monitoring or modifying Navigation Radio tuning.
- PREV Page - Changes display to Previous page number in multiple numbered page series.
- NEXT Page - Changes display to Next page number in multiple numbered page series.
Push Executes flight plan, or changes to the active flight plan including changes to the vertical profile.
Key is active when light bar is illuminated. Light bar indicates modification to active route or vertical profile has been entered but not executed.