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MULTI-MODE RECEIVER
Global Positioning System - Component Location
Figure 1 (Sheet 1)
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Global Positioning System - Component Location
Figure 1 (Sheet 2)
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EICAS
GPS Interface Schematic
Figure 2
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R IRS L IRS C IRS
IRS/FMC IRS/FMC DMU
MAWEA
GPSSU Schematic
Figure 3
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B. The MMR measures the time it takes for a radio signal to go from a satellite to the airplane. Since the MMR knows the location of the satellite, and that the radio signal travels at the speed of light, it can calculate the distance to the satellite.
C. However, since this is one-way ranging, the MMR must know precisely at what time the satellite sent the radio signal. The MMR compares the satellite signal to a signal the MMR generates at the same time as the satellite. The difference between the two signals is the time the signal took to get to the MMR.
D. The MMR assumes that its internal clock is off by some clock bias. This is an unknown that the MMR must calculate. This clock bias represents the difference between the MMR time and the GPS satellite time.
E. To calculate the airplane position (latitude, longitude, and altitude) and the clock bias, the MMR must use data from at least four satellites. The MMR measures the distances to all the satellites at the same time. It then solves for the four unknowns, latitude, longitude, altitude, and clock bias by the use of four equations.
4. GPS Displays
____________
A. Navigation Display (Fig. 4)
(1)
GPS position can be shown on the navigation display when the POS button is pushed and MAP mode is selected on the EFIS control panel. The IRU and VOR/DME positions are also shown.
(2)
When the distance between the two GPS positions is small enough for one GPS symbol circle to touch the other symbol circle, only one symbol is displayed.
B. FMCS CDU Displays (Fig. 5)
(1) The position initialization (POS INIT 1/3) page on the FMCS CDU shows data from GPS. GPS time is displayed from the left MMR, or from the right MMR if the left is not valid. GPS position from the left MMR is displayed if the horizontal integrity limit is 0.5 nm or less. If the left MMR exceeds this limit, position from the right MMR is displayed.
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