FMS - NAV Architecture
Figure 002
FMS - RAD NAV Architecture
Figure 003
FMS - Lateral Guidance Architecture
Figure 004
FMS - Weight Architecture
Figure 005
FMS - Predictions/Vertical Guidance Architecture
Figure 006
3. Operation
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A. Initialization and Flight Planning Due to the type of the various functions that the system is performing during the flight, the crew is required to initialize the system by inserting some data via the MCDU. To do so, the pilot must ensure that the MCDUs are correctly coupled to the FMGCs. The first page displayed by the FMGC, at power-up on the ground or after access through the MCDU MENU page, is the A/C status page which allows the crew to be aware of the status of the FMS. Then by selecting the INIT page, the pilot has the possibility to initialize the FMS (Ref. 22-71-00). The initialization consists of three main functions:
-Select a flight plan which will be the real basis for all computations and displays performed by the FMS
-Align the IRSs by using the position of the airport stored in the FMS data base and called by selection of the flight plan
-Enter the zero fuel weight (ZFW) and center of gravity for zero fuel weight (ZFWCG) which will be used for all the various performance computations.
The last two functions being self-explanatory, the following explains
what a flight plan consists of for the FMS.
A flight plan is composed of various elements which indicate the routes
the aircraft must follow and the limitations along these routes.
The lateral elements (Ref. 22-71-00) are:
-Origin airport and runway
-Departure procedure including optionally a RWY-SID transition, a SID and an En route transition. The procedures are defined by the various legs and the waypoints between these legs
-En route airways and waypoints
-Arrival procedure including optionally an En route transition, a STAR, a STAR-approach transition, an approach and a missed approach
-Alternate flight plan which is defined as the primary flight plan. The vertical elements are:
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The takeoff altitudes (Thrust reduction and acceleration altitudes) and the go around altitudes (1)
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The altitude and flight path angle constraints at the waypoints in all the procedures
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The time speed constraints also at the waypoints in all the procedures
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The climb and descent speed limits (e.g. 250 kts below 10,000 ft.)
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The cruise flight levels and possibly step climb/descent
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The cost index for this flight plan, which permits to translate the time cost and fuel cost in the same unit.
All these lateral and vertical elements are or may be defined during initialization. They may be included in the navigation data base which is resident in the FMS. They may also be contained in a specific record with a specific name (Company route) and therefore can be initialized by entering the company route number in the INIT page.
NOTE : The whole paragraph above does not apply to these elements.
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It has to be noted that the navigation data base (Ref. 22-71-00) includes therefore all the elements allowing the construction of company routes. In addition, to allow flight plan modifications by the crew, the data base contains also a set of waypoints, navaids and airports in the region covered by the data base. Together with the airports, the departure/arrival procedures are also defined even if not part of any company route. The file of navaids is also used for the navaid autotune function described later. Besides the nav data base, there is a performance data base containing various data corresponding to the aircraft and engine models. This performance data base is used for the performance functions (Ref. 22-71-00). Once introduced in the system, the flight plan may be displayed on the MCDU (F-PLN pages) and on the ND in the ARC, ROSE-NAV and PLAN modes. Flight plan modifications can then be performed by the crew. Two types of F-PLN revisions exist:
-Lateral revisions: an insertion or deletion of a waypoint in the F-PLN, an insertion of a leg to fly direct to a waypoint (2), an introduction or a modification of a departure procedure either partially or entirely, an introduction or a modification of an arrival procedure either partially or entirely, a modification of the destination, a modification of the alternate F-PLN, an activation of the alternate F-PLN, an insertion of an airway from a F-PLN waypoint down to a specific waypoint, a creation of an offset path, an insertion or a deletion of a Holding pattern, and an activation of the engine out SID.
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