R **ON A/C 106-149, 151-199, 211-299, 301-399, 401-499,
 Post SB 22-1089 For A/C 151-199,211-212,
 NAVIGATION/LATERAL FUNCTIONS - DESCRIPTION AND OPERATION
________________________________________________________
 1. General
_______
 The lateral functions of the Flight Management (FM) system consist of:

 -
the navigation function:
 . Navigation modes
 . Navigation mode selection and class of navigation
 . Radio navigation tuning
 . Inertial Reference System (IRS) alignment
 . IRS Heading (HDG) initialization
 . IRS average drift computation
 . Global Positioning System (GPS) initialization

 -
the guidance function:
 . Leg transition
 . Displayed parameters-path errors
 . Nav guidance mode
 . Flight plan sequencing.

 2. System Description
__________________
 A. Navigation Modes
 (1) General Although the navigation modes are named DME/DME/INERTIAL or VOR/DME/INERTIAL, these words are just used for clarification of the
R  text and the display on the Multipurpose Control and Display Unit
R  (MCDU). The Navigation function computes the aircraft position using information from the following systems:
 -Air Data and Inertial Reference (ADIRS)
 -VHF Omnidirectional Radio Range (VOR)
 -Distance Measuring Equipment (DME)
 -Global Positioning System (GPS) if installed (realized via OPC
 software option)
R  - Instrument Landing System (ILS)
R  - Microwave Landing System (MLS) if installed.
 The position computation algorithms take into account polar
 navigation.
 In addition to the present position, the Flight Management and
 Guidance Computer (FMGC) computes other signals for use and display
 on MCDU or Electronic Instrument System (EIS) such as wind, track,
 ground speed, bearing/distance to a fix.
 The aircraft position can be updated either manually or
 automatically.

 (2)
 Inertial position IRS signals yield to compute inertial position. If 3 IRS are available, the inertial position is an optimal mixed position based on the 3 IRS positions and speeds. If mixed inertial position becomes invalid, the FM position also goes invalid. When at least one inertial position becomes valid, the FM position becomes valid and is initialized to mixed IRS position. As a consequence IRS bias are zeroed. Hybrid signals from IRS/GPS (when GPS is installed and hybrid configuration is selected via OPC software) yield to compute GPS/INERTIAL position.

 (3)
 Radio position Signals from VOR and DME yield to compute various radio positions. If at least two DME stations are available and their geometry is such that error is minimized then radio position is called rho/rho or DME/DME position. If only one VOR/DME collocated station is available, the radio position is called rho/theta or VOR/DME position.

 (4)
 FMGC position (Ref. Fig. 001) When a mixed IRS position is computed, the FMGC computes a GPS inertial or a radio inertial position by mixing both the IRS position and the GPIRS or radio position (if any). When a GPIRS or radio position becomes available, the GPIRS or radio inertial position is filtered to become almost equal to that GPIRS or radio position. Thus, a bias between IRS and FMGC positions is then computed.

 NOTE : When the GPIRS or radio mode is lost (no more radio position),
____ the last computed bias is memorized and used for FMGC position computation.
 (5) Radio-inertial position If both inertial position and radio position are valid, and IRS/GPS hybrid position is not valid or GPS not installed, the FM computes mixed radio-inertial position as the best estimated aircraft position (either IRS/DME/DME or IRS/VOR/DME with or without LOC update).
R
 (6) Position and navigation mode display
 (a) POSITION MONITOR page (Ref. Fig. 002) The POSITION MONITOR page displays general navigation information. This function allows the crew to display, on a single page, the basic navigation data which represent the aircraft position as computed from various functions:
 -
FMGC 1 and 2 positions

 -
FMGC 1 and 2 navigation modes

 -radio position or GPS position
 -mixed IRS position
 -IRS deviations and modes.
 1 Access
_
 -Line select (LS) key from DATA INDEX A page.
 -6L LS key on SELECTED NAVAIDS page (RETURN).
 2 Purpose
_
 -Displays aircraft position information.

 FMGC Position
 Figure 001