(2)
Ground Speed
(3)
Flight Path Angle (FPA)
(4)
Drift Angle (DA)
(5)
Track Angle
(6)
Wind Velocity and Direction
B. The basic navigational output data is computed using optimally mixed inputs of:
(1)
IRS position (latitude, longitude, and altitude)
(2)
Vertical Speed
(3)
Ground Speed Components (north/south, east/west)
(4)
Heading (magnetic and true)
(5)
Pressure Altitude
(6)
True Airspeed
(7)
DME Slant Range
C. Operation of the navigation function consists of the following processes:
(1) Compute Velocity
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M1162 IRU NO. 2
M1175 FLIGHT MANAGEMENT COMPUTERWORD DATA SHOWN ON DIGITAL BUSINTERFACESEE INTERFACE FOR SPECIFIC PINS
FMCS Navigation ComputationFigure 12
A 737-300/400/500MAINTENANCE MANUAL
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C95276
D.
E.
F.
A
737-300/400/500MAINTENANCE MANUAL
(2)
Compute Altitude
(3)
Compute Horizontal Position
(4)
Compute Position and Velocity corrections
(5)
Choose Navaids
(6)
Choose IRSThe navigation function will process measurements from two DME stations of acceptable geometry, or process measurements from a collocated VOR/DME facility. A reasonableness test is included to screen out any erroneous measurements. The FMC contains the systems navigation data base. This data base includes all of the enroute and terminal procedures required for flight in the area in which the airplane operates. The data base also includes navigation aid ground station information, stored company route structure, preplanned holding patterns, and preferred navaids.The primary mode of navigation in the horizontal plane uses two independent measurements of DME slant range. These measurements are optimally filtered with IRS position, heading, and velocity information to produce an accurate computation of the airplanes present position. There is also a secondary mode of navigation in the horizontal plane, based upon bearing and slant range data obtained from a single VOR/DME facility. Position is computed in terms of latitude and longitude for display on the CDU. The system also provides a variety of other navigation output variables. These navigation output variables include track angle, drift angle, ground speed, and wind information. The navigation outputs are available for display on the CDU, or on the electronic flight instruments.For vertical navigation, the navigation function provides computed values of altitude and flight path angle (FPA). Altitude computations operate upon input of inertially smoothed altitude from the IRS, corrected by barometric altitude and uncorrected pressure altitude from the DADS. Flight path angle is derived from IRS inputs of vertical speed, and north/south and east/west velocity components.
(1)
IRS Selection
(a) The preferred source of inertial reference data for the FMCS is defined as IRS No. 1, for either dual or triple IRS installations. The FMCS continuously monitors the IRS operating mode, and the IRS ARINC 429 output Sign/Status Matrix (SSM) indicators. The FMCS will attempt to use data from an IRS that provides fully valid SSM indications, when the IRS is in the NAV (navigate) mode. Data from the IRS in the ALIGN or ATT (attitude) modes is not acceptable for navigation.
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