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C. The GPS receives position data from the inertial reference system (IRS) and altitude and true airspeed data from the air data computer system. The GPS supplies information to the flight management computer system (FMCS) and the master caution unit (MCU) (Fig. 2).
D. The GPS antennas receive position and time data from several satellites. The GPSSUs calculate the airplane position by determining the distance from the known location of the satellites in view. The GPS and other navigation systems send data to the FMCS for use in the FMCS calculation of airplane position.
2. Global Positioning System Sensor Unit (GPSSU) (Fig. 3)_____________________________________________
A. The GPSSU power supply uses 28v dc from the airplane buses. The GPSSU uses less than 20 watts of power during normal operation. It is an L-band receiver with internal data processing. It weighs 5 pounds, and is located above the ceiling close to the GPS antennas.
B. The RF section of the GPSSU receives the satellite signals from the GPS antenna. The signals are filtered, amplified, and sent to an analog to digital converter. After conversion the data is sent to the processor.
C. The processor controls satellite tracking, measures time from the satellite signals, determines signal validity, and decodes the satellite data. At least four satellites are tracked in the navigation mode. Navigation position calculations use position updates from a Kalman filter to determine the GPSSU location.
D. A Kalman filter is an algorithm (data processing scheme) used to make estimates of the performance of a system. It uses statistical techniques of estimating and weighting, and makes corrections. The filter continuously computes the difference between the current measurement and the current estimate (based on the last measurement). These differences are referred to as residuals.
E. Measurements obtained from the satellite signals are compared with estimates computed in a previous filter update. The resulting differences are used for subsequent updates.
F. ARINC 429 receivers in the GPSSU get position data from the IRUs. The GPSSU can locate and identify satellites much more quickly if the airplane position is known.
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
737-300/400/500
MAINTENANCE MANUAL
SCULPTURED
CEILING
PANEL GPSSU
(ABOVE STOWAGE BIN)
SEE A
CURVED
CEILING
PANEL
FWD PANEL TRANSITION
STOWAGE BIN PANEL CEILING LOWERED
PASSENGER CABIN
WASHER (TYPICAL) (TYPICAL) SCREW
FWD
GPSSU
A
Global Positioning System - Component Location
Figure 1 (Sheet 1)
F08890
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A 737-300/400/500MAINTENANCE MANUAL
GPS ANTENNA NO. 1
ANTENNA
GPS ANTENNA
Global Positioning System - Component Location
Figure 1 (Sheet 2)
EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. AIRPLANES WITH GPS ú
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
F08898
A 737-300/400/500MAINTENANCE MANUAL
FLIGHT COMPARTMENT
GPS ALERT ANNUNCIATION
IRS MODE SELECT UNIT (MSU)
Global Positioning System - Component Location
Figure 1 (Sheet 3)
EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. AIRPLANES WITH GPS ú
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737-300 400 500 AMM 飞机维护手册 导航 NAVIGATION 4(61)
