(a) Scratchpad. The scratchpad is a
buffer to hold all data for review prior to executing the
input. As data is keyed into the CDU with the keypad,
the entered values are displayed within the scratchpad
field at the bottom of the display. Incorrect entries are
cleared with the CLR key. A single press clears the
last character on the right. Holding the CLR key down
clears the entire scratchpad. The scratchpad is
cleared automatically when the system accepts valid
(b) Function Keys. The labeled function
keys are used to call up specific top-level pages of the
CDU and to simultaneously dedicate the line select
keys to the functions indicated on that page.
Exceptions are the MARK, DATA, and M3 keys that
do not change the page but do initiate their respective
functions. Some functions, which are less frequently
used in flight, are accessed through the index (IDX)
and flight plan edit (EDIT) function keys and then via
line select keys on the respective menu page. The
Index and Flight Plan Edit pages are shown in
Figure 3C-24 and Table 3C-14.
(c) Line Select Keys. Line select keys
can be used to access lower level pages, toggle
modes of the function, enter data in the associated
field, or copy data in the scratchpad. When undefined
line select keys are pressed, no operation is performed
and no annunciation is displayed.
When a label next to the line select displays an
outward pointing arrow, selecting the line select will
access the page identified by the line select label.
When a colon is displayed next to a line select
label, selecting the line select will toggle the label
value to a different state. When two labels are shown,
the toggled value is the innermost label or value.
When brackets ([ ]) are displayed next to a line
select, selection of the line select with valid data in the
scratchpad will enter the data into the bracketed field
and enable use of that data by the FMS. When the
scratchpad is blank, selection of the line select next to
the bracketed data will copy that data to the
When a label next to a line select displays an
inward pointing arrow, selecting this line select will
either select, enable, or disable the indicated function
or item. For single step functions, an asterisk to
identify the function as enabled will replace the arrow.
When multiple selections are needed prior to activation
of the function, a "fat" arrow to highlight the selection
will replace the arrow. When all selections are made,
an asterisk will replace the fat arrow when the function
Symbolic aids are used to indicate what entries
can be made, what functions are on or engaged, and
what selections are possible. Refer to Figure 3C-25
for a summary of these symbols.
The lateral and vertical scroll arrows are
located next to the scratchpad on the
(d) Display Scrolling. Often more data
is available than what fits on a single display page. In
these cases display scrolling is used to access all the
Two types of scrolling are page scrolling and line
scrolling. Vertical scrolling with up (- ) and down (¯ )
arrows either accesses additional pages of the
information shown or scrolls through lists of data.
Horizontal scrolling with left (¬ ) or right (® ) arrows
accesses additional pages of similar information.
Holding the arrow keys causes the scrolling to
continue until the key is released. Special characters
(horizontal double-headed arrow, vertical double-
headed arrow, and multi-headed arrow) are displayed
next to the scratchpad to indicate the type of scrolling.
(e) Confirmation Function. Functions
that involve destruction of significant internal data
require confirmation before execution. A message,
CONFIRM XXX, will appear in the scratchpad, where
XXX is a message unique to the item requiring
confirmation. The scratchpad message is cleared by
either reselecting the appropriate line select key to
confirm the selection or by pressing the CLR key if the
function is not desired.
Most data to be entered on the CDU can be copied
into the scratchpad in its original form by pressing the
operations are performed which take precedence.
Once copied into the scratchpad, this data may be
transferred elsewhere in the FMS-800. For example, a
waypoint may be transferred from the mark point list to
the flight plan, or the flight plan waypoint sequence
may be reordered without having to re-enter the