IRS PARAMETERS USED BY INTERFACES
A737-300/400/500MAINTENANCE MANUAL
Figure 20
A
737-300/400/500MAINTENANCE MANUAL
D. The three output buses from the IRU are all ARINC 429 high speed type. Digital data output bus No. 1 delivers the flight essential digital data and ground speed to the DAA. The data is received on this bus for digital-to-analog conversion in the DAA for analog output to the flight instruments.
E. Digital data output bus No. 2 is also a dedicated bus which delivers the digital IRU data directly to the flight control computer (FCC).
F. Digital data output bus No. 3 is a utility bus. This bus provides digital data from the IRU to the DAA for D/A conversion. This bus also provides IRU data to the FCC, FMC, ISDU, and the autothrottle computer.
G. Initialization of the IRU's from the FMC is accomplished on the FMC 1 and 2 output buses. Although not shown on Fig. 20, these buses also handle all the digital data from the FMC (Ref 34-62-00) to the DAA's, HSI's, FCC's and autothrottle.
16. Operation (Fig. 21)_________
A. IRS Alignment
(1)
The IRS can be initialized by the FMCS-CDU or ISDU whenever the IRU is in the alignment (ALIGN) mode. When a mode select switch on the MSU is switched to ALIGN or NAV from OFF, the respective IRU enters the alignment mode.
(2)
In the alignment mode, the IRU reference axis is aligned to the local vertical. The IRU calculates latitude by estimating the horizontal earth rate components. While in the alignment mode, the IRU outputs a discrete signal to light the ALIGN annunciator on the MSU. When the mode select switch is switched to ALIGN from OFF, present latitude and longitude (lat/long) must be entered to complete the alignment process. Present latitude and longitude are not required when switching from NAV to ALIGN.
(3)
Position initialization by the FMCS-CDU is accomplished by accessing the POS INIT 1/2 page on the FMCS-CDU by one of four methods:
(a)
Pressing the INIT/REF mode select key (when on the ground and when the IRS position has not been initialized).
(b)
Pressing the POS line select key when the INDEX page is displayed.
(c)
Pressing the POS INIT line select key when the IDENT page is displayed.
(d)
Pressing the PREV PAGE or NEXT PAGE key when the POS REF 2/2 page is displayed.
(4)
One of the following three methods is used to enter present position lat/long into the SET IRS POS line of the POS INIT page on the CDU.
(a)
LAT/LONG is entered into the scratch pad using the keyboard, then line selected into the SET IRS POS line.
(b)
LAT/LONG is transferred from the LAST POS line to the SET IRS POS line via the scratch pad.
(c)
REF AIRPORT or REF AIRPORT and GATE is entered, the resultant lat/long is line selected to the SET IRS POS line.
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A
737-300/400/500
MAINTENANCE MANUAL
IRS BITE INDEX PAGE MAINTENANCE INDEX PAGE
FMCS CDU - IRS Functions Figure 21
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(5)
(6)
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737-300/400/500MAINTENANCE MANUAL
Position initialization on the ISDU is done for both IRU's simultaneously. Initialization at the ISDU is done as follows:
(a)
Set SYS DSPL switch to either IRU (L or R).
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