(b)
DME/DME/INERTIAL If a valid and reasonable radio combination allows the computation of a radio position, the DME/DME/INERTIAL mode is chosen. if it provides the best accuracy solution than any other sensor (based on sensor EPE). The logic to determine the availability of a radio position takes the DMEs of both sides into account. In particular, if one DME receiver is not working, the onside FMGC uses information of the offside DME receiver. The DME ident signal from the DMEs is used to avoid selection mistakes in the position computation and to recognize the DME station. The navigation mode as displayed on the POSITION MONITOR page is N IRS/DME/DME, where N is the number of IRS used to compute mixed IRS position (either 3 or 1).
(c)
VOR/DME/INERTIAL In all cases, VOR/DME/INERTIAL position mode is chosen only if no DME/DME pair can be found. And if it provides the best accuracy position than any other sensor (based on sensor EPE). The logic to determine the availability of a radio position takes the VORs and DMEs of both sides into account. In particular, if one VOR or DME receiver is not working, the onside FMGC uses information of the offside VOR and DME receivers. The navigation mode as displayed on the POSITION MONITOR page is N IRS/VOR/DME, where N is the number of IRs used to compute mixed IRS position (either 3 or 1). VOR/DME/INERTIAL mode remains selected when flying away from the VOR/DME navaid as long as the EPE does not increase at a higher rate than the EPE which is provided by the selection of INERTIAL ONLY mode. If the EPE does increase at a higher rate during fly away, then the navigation mode changes to INERTIAL ONLY. An exception to the above rule is when the VOR/DME navaid is a procedure specified navaid in approach. In this case, the navigation mode does not change to INERTIAL ONLY mode until the approach area is left. The VOR and DME ident signals from the VORs and DMEs are used to avoid selection mistakes in the position computation and to recognize the DME/VOR station.
1_ En route and terminal area
If the estimated error for the chosen rho/theta station is
less than the estimated error for the INERTIAL ONLY mode and
If the DME/DME/INERTIAL mode was not chosen, then the mode of navigation will be the VOR/DME/INERTIAL; else the INERTIAL ONLY mode is chosen.
2 Approach Area termination
_ The priority depends upon the approach type as follows:
-ILS/MLS, LOC, and Backcourse approaches If the DME/DME/INERTIAL mode was not chosen then the VOR/DME/INERTIAL mode is used if the error is less than the estimated error for the INERTIAL ONLY mode. The system tunes by priority the VOR/DME (if any) within 5 NM of the AIRPORT or the closest station to the aircraft.
-RNAV, VOR/DME and VOR approaches If the DME/DME/INERTIAL mode could not be chosen, the system uses the specified VOR/DME. If available, the VOR/DME/INERTIAL mode is selected. Otherwise, the system searches for another VOR/DME to be tuned (if possible) by priority within 5 NM of the ARPT or the closest station to the aircraft;
then, if the estimated error with this station is less than
the estimated error in INERTIAL ONLY mode then the
VOR/DME/INERTIAL mode is selected.
Else, the INERTIAL ONLY mode is selected.
-NDB or pilot-created approach Same as VOR approach except that there is no specified VOR.
(d)
Localizer updating When an ILS, LOC, or Backcourse approach is selected and LOC signals are available, the system, using the LOC information, laterally updates the current position computed with GPS/INERTIAL or DME/DME/INERTIAL or VOR/DME/INERTIAL or INERTIAL ONLY mode. The LOC updating does not change the calculation of radio position.
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