(2)
The FMCs receive data from various airplane systems, crew input data through the CDU and data stored in the navigation and performance data bases. This data is then used to compute the optimal flight path plan, accurate airplane present position and thrust commands.
B. Physical description (Fig. 1)
(1)
The FMC is housed in a 10.25 x 15.02 x 7.64-inch chassis with mounting and cooling requirements of ARINC specification 600-5. The front panel of the FMC contains the identification plate, carrying handle, hold down hooks, test connector with access cover, operational status indicator lights, test switch, and unit marking. The top and bottom covers are all held in place with captive screws.
(2)
The FMC is hard mounted in the avionics rack with front support provided by the hold down hooks and rear support provided by the ARINC 600 style unit connector. The rear connector is mechanically keyed to prevent incorrect mating.
C. FMC Functions (Fig. 2)
(1) The FMC performs the following major functions:
(a)
Navigation
(b)
Peformance
(c)
Guidance
(d)
Thrust management
(e)
EFIS display processing
(f)
CDU display processing
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(2) The navigation function is primarily responsible for calculations of airplane velocity, position and altitude. Using the navigational data base, the FMC selects the best available navaids (based on geometry) and issues tuning commands to the VHF NAV radios. It uses data from these VHF NAV radios along with data from the navigation data base, inertial reference system, and the air data computers to calculate airplane position, lateral velocity, wind vector data, altitude, flight path angle and local earth radius. The FMC also contains software for Future Air Navigation System (FANS 1) which includes these functions:
(a) Two-Way Oceanic ATC Data Link (ATC DL)
1) The FMC allows the flight crew to initiate requests to ATC for route changes, lateral offsets, speed and vertical clearances, and for voice contact. The FMC can receive and display the corresponding clearances, as well as report requests and advisories. The FMC displays the message to the flight crew on the CDU, and sends the decision to the originator of the message. An adequate number of received and sent messages can be stored and retrieved.
2) When an ATC message is received, the flight crew is alerted by a message on EICAS and a low-level aural chime.
3) The ATC DL function is enabled by an option code in the Airline Policy File (APF) and a hardware program pin.
4) ATC DL messages can be printed on a flight deck printer. These messages will include the time and date of the message, the flight number, and the airplane registration number. The printer interface function is selected through an option code in the APF.
(b) Automatic Dependent Surveillance (ADS)
1) The FMC is capable of automatically sending periodic, event, and on-demand ADS reports. These reports are sent through the ACARS network.
2) The ADS function is enabled by an option code in the APF and a hardware program pin. It is enabled with ATC DL.
(c) Air Traffic Services Facilities Notification (ATS)
1) The FMC can initiate notification both manually through flight crew action and automatically by uplink. The flight crew must perform a successful logon through the AFN before ATC DL communication may be conducted.
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