However, if a request is received from an active FM, the FM
annunciator comes on and a (REQ) indicator is inserted after
the FM menu text.
Likewise, if a request is received from an active non-FM
subsystem, the MCDU MENU annunciator comes on and a (REQ)
indicator is inserted after the subsystem menu text.
Communication with a subsystem is established by either
selecting the line select key (1L thru 6L) adjacent to a
subsystem menu text, selecting a FM mode key while the FM is
available, selecting an ATSU mode key while the ATSU is
available, selecting the RETURN key or through auto-return.
If the line key adjacent to a desired non-active subsystem is
selected, communication is terminated with any existing active
subsystem and established with the selected one. If the line
key corresponds to the currently active subsystem,
communication continues with that subsystem.
If any FM mode key is selected while the FM is available (i.e.
FM menu text exists), communications are established with the
FM. If a previous non FM subsystem is active at the time,
communications are terminated with it and the FM becomes the
active subsystem.
FM mode keys are: DIR, PROG, PERF, INIT, DATA, F-PLN, RAD NAV,
FUEL PRED, SEC F-PLN and AIRPORT. Upon mode key selection, the
page associated with the mode key is displayed, if
communications are successful.
If any ATSU mode key is selected while the ATSU is available
(ATSU menu text), communication is established with the ATSU.
If a previous non ATSU subsystem is active at the time,
communications are terminated with it and the ATSU becomes the
active subsystem.
The ATSU mode key is: ATC COMM. Upon mode key selection, the
page associated with the mode key is displayed , if
communications are successful. If the mode key is pressed
while the ATSU is not connected to the MCDU, the display will
revert to the MCDU MENU page with the scratchpad message
"SUBSYSTEM NOT AVAILABLE".
An auto-return occurs to the active subsystem if 60 seconds
elapse without any line select key selections. Auto-returns
are inoperable if no active subsystem exists.
Selection of the RETURN prompt returns display control to the active subsystem.
When the selected FM assumes control of the MCDU display via a line select key, a manual return or automatic return, the last known page displayed by the FM is redisplayed. If the page is unknown, the A/C Status page is displayed.
During the time between when a subsystem is selected and when the subsystem page is displayed, the MCDU MENU page remains displayed with the scratchpad message WAIT FOR SYSTEM RESPONSE. If communications are successfully established, the MCDU MENU page is replaced by the subsystem page display. If communications are unsuccessful, the MCDU MENU page remains displayed with a TIMEOUT indicator after the selected subsystem menu text.
4 Subsystem selected
_ The subsystem selected transitory state occurs after a subsystem has been selected to be given control of the MCDU display. At this time, a protocol dialog occurs between the MCDU and the selected subsystem. If the protocol is successful, the MCDU MENU page is replaced by the active subsystem page (B), if not the MCDU MENU page remains on display (A). If the protocol is unsuccessful, the MCDU MENU page is displayed with a TIMEOUT indication (B).
(b) MCDU MENU page The MCDU MENU page displays the subsystems available for communication (menu text displayed in 1L through 6L), indicates a subsystem status as to whether it is "active", "requesting service", "timed out" or "selected", provides a means of selecting an available subsystem for communication with the MCDU, allows the activation or deactivation of Standby Navigation. A figure illustrates an example of the menu page with the Standby Navigation function available. (Ref. Fig. 008)
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