-IR
-VOR
-DME
-ILS
-GPS (optional) (Ref. Fig. 001) In addition to the present position, the FMGC computes other signals for use and display on MCDU or EIS such as wind, track, ground speed, bearing/distance to a fix (Ref. Para. (8)). At last, the aircraft position may be updated either manually or automatically (Ref. Para. (6)).
(2)
Inertial position The FMGC computes an inertial position with data coming from the three IRS sensors. If the three IR positions are available and valid, the system computes a weighted mixed IR position using all three IR positions.
General Navigation Computation Organization
Figure 001
If one of the IR positions is not available or if any IR drift is too large (greater than 30 NM compared to the previous mixed IR position), the system computes an IR position using only one IRS. Each FM chooses one IRS with the following priority:
-1st - IRS OWN
-2nd - IRS 3
-3rd - IRS OPP
If no IRS is available, no IRS position is computed.
(3)
Radio positions The FMGC can compute a radio position using VOR and DME/TACAN signals. There are two modes available: (Ref. Fig. 002)
-DME/DME: The ambiguity is eliminated by knowing the previous position and by limiting the geometry of the navaids to an angle (DME 1, A/C, DME 2) of between 30 and 150 degrees.
-VOR/DME: The position is computed using the radial and the DME distance coming from a collocated VOR/DME or VORTAC.
(4)
FMGC position (Ref. Fig. 003) When a mixed IR position is computed, the FMGC computes a GPS inertial or a radio inertial position mixing both the IR position and the GPIRS or radio position (if any). In fact, when a GPIRS or radio position becomes available, the GPIRS or radio inertial position is filtered to become almost equal to that GPIRS or radio position. Thus, a bias between IR and FMGC position is then computed.
NOTE : When the GPIRS or radio mode is lost (no more radio position),
____ the last computed bias is memorized and used for FMGC position computation.
(5) Localizer updating (Ref. Fig. 004) In ILS or LOC approach mode, with the AP/FD engaged, the localizer signal is used to update the FMGC position. The update position is the intersection of the projection of the previous computed position onto the LOC center beam with the LOC deviation.
Radio Positions
Figure 002
FMGC Position
Figure 003
Localizer Updating
Figure 004
(6)
Position updating In some conditions the FM position is updated, either automatically or on pilot demand. The updating modifies the bias between the mixed IR position and the FM position. The new bias is then used in the navigation algorithms. The manual updatings are performed:
-
at IR alignment (Ref. Para. D.)
(Ref. Fig. 005)
- on pilot demand on PROG page (UPDATE AT prompt)
(Ref. Fig. 005) The position can be updated on a LAT/LONG, a PLACE/BEARING/DISTANCE, a PLACE/BEARING-PLACE/BEARING or waypoint, navaid, airport ident. The automatic updatings are provided:
-
at takeoff when takeoff thrust is applied. The FM position is updated at the runway threshold position (modified by the takeoff shift entered by the pilot on the TAKEOFF page). (Ref. Fig. 006)
(7)
Position and navigation mode display
-General navigation information is displayed on the POSITION MONITOR page which is accessed from the DATA MENU page. (Ref. Fig. 007) This page displays on the first two lines, the FMGC1 and 2 aircraft position and the navigation mode active on each FMGC. On the third line, the own FMGC GPIRS or RADIO position (depending on the navigation mode) is displayed, followed on the fourth line by the MIXED IRS position. The fifth line displays the IRS status (INVAL, ALIGN, NAV or ATT) and the deviation of each IRS position versus the own FMGC position (if IRS status is NAV). When the 6L line select key is pushed, this allows to freeze the data displayed this page. A second push reactivates the page data. The 6R line select key gives access to the SELECTED NAVAIDS pages which display the features of the selected VOR, DME and/or ILS. (Ref. Fig. 008)
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