Flight Management, Navigation -Flight Management System Description
737 Operations Manual
When external position updating is not available, the FMC uses the IRS position as reference. When the IRS is the only position reference, the FMC applies an automatic correction to the IRS position to determine the most probable FMC position. This correction factor is developed by the FMC’s monitoring IRS performance during periods of normal position updating to determine the typical IRS error value. It is important to note that, when external position updating is not available, navigation accuracy may be less than required. Flight crews should closely monitor FMC navigation, especially when approaching the destination. The accuracy of the FMC navigation should be determined during descent phase by using radio navaids and radar information if available.
Note: Inaccurate position updating may cause the airplane to deviate from the desired track.
Control Display Units (CDUs)
Two identical, independent CDUs provide the means for the flight crew to communicate with the FMC. The crew may enter data into the FMC using either CDU, although simultaneous entries should be avoided. The same FMC data and computations are available on both CDUs; however, each pilot has control over what is displayed on an individual CDU.
On airplanes with ANCDUs, each CDU also has an alternate mode of operation using its own internal computer. This ANCDU capability is similar to an inertial navigation system and allows parallel operation independent of the FMC, or backup operation in the event of FMC failure. The ANCDU provides lateral navigation capability only. ANCDU navigation is always based on IRS position only.
Flight Management, Navigation -Flight Management System Description 737 Operations Manual
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Copyright . The Boeing Company. See title page for details.
11.30.4 December 1, 2000
737 Operations Manual
Introduction
When first powered, the FMS is in the preflight phase. As a phase is completed, the FMS automatically transitions to the next phase in this order:
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preflight . descent
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takeoff . approach
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climb . flight complete.
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cruise
Preflight
During preflight, flight plan and load sheet information are entered into the CDU. The flight plan defines the route of flight from the origin to the destination and initializes LNAV. Flight plan and load sheet information provide performance information to initialize VNAV.
Required preflight information consists of:
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initial position . performance data
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route of flight . takeoff data.
Optional preflight data includes:
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navigation database . RTA data (U4 and on)
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SID .cruise wind
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STAR . reduced takeoff and climb
limits.
Each required or optional data item is entered on specific preflight pages.
Preflight begins with the IDENT page. If the IDENT page is not displayed, it can be selected from the IDENT prompt on the INIT/REF INDEX page. Visual prompts provide assistance in selecting the appropriate CDU pages. Preflight pages can be manually selected in any order.
After entering and checking the necessary data on each preflight page, the lower right line select key is pushed to select the next page. When ACTIVATE is selected on the RTE page, the execute light illuminates. The EXEC key is then pushed to complete the task of making the route active before continuing with the preflight.
If a standard instrument departure (SID) is to be entered into the route, the departure/arrival (DEP/ARR) page is selected. After selecting the desired SID, the resulting modification must be appropriately linked to the existing route and executed. This can be accomplished on the RTE or RTE LEGS page.
When all required preflight entries are complete, the preflight status prompts on the TAKEOFF REF page are no longer displayed.
Flight Management, Navigation -Flight Management System Operation 737 Operations Manual
Takeoff
The takeoff phase begins with selection of TO/GA and extends to the thrust reduction altitude where climb thrust is normally selected.
Climb
The climb phase begins at the thrust reduction altitude and extends to the top of climb (T/C) point. The T/C point is where the airplane reaches the cruise altitude entered on the PERF INIT page.
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