34-62-01

 ú CONFIG ú 04 Page 42 ú Nov 15/95
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
 B.
C.
D.
E.
A
737-300/400/500MAINTENANCE MANUAL
 (2)
Ground Speed

 (3)
Flight Path Angle (FPA)

 (4)
Drift Angle (DA)

 (5)
Track Angle

 (6)
Wind Velocity and Direction
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
Operation of the navigation function consists of the following processes:

 (1)
Compute Velocity

 (2)
Compute Altitude

 (3)
Compute Horizontal Position

 (4)
Compute Position and Velocity corrections

 (5)
Choose Navaids

 (6)
Choose IRS
The 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.

 EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. AIRPLANES WITH DUAL FMC ú

 34-62-01
 ú CONFIG ú 04 Page 43 ú Nov 15/95

BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A 737-300/400/500MAINTENANCE MANUAL
 F.  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.

 (b)  
The FMC applies a reasonableness test to the data received from each IRS. The reasonableness test is to ensure that the present position of each IRS is within 4 nautical miles of a position estimate determined solely from radio navigation systems.

 (c)  
If an IRS fails to agree with the radio position estimate for more than 70 seconds , it will not be used for FMCS navigation processing until such time as it recovers and passes the selection criteria .

 (2)  
　
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