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(d) The DME will tune and store station information in accordance with the FMC. The memory slot preference in which the station information will be stored is controlled by the FMC logic. This memory slot allocation logic is described as follows: 1) Memory slots 1 and 2 will always contain distance data from
autotuned stations making the best DME/DME pairing, which
will be used for VHF NAV radio position updating.
2) If there is a DME/DME pair in memory slots 1 and 2 and there is no manual, procedure or route tuned stations required, then the FMC will direct the second best DME/DME pair into memory slots 3 and 4. This second best DME/DME pair will be directed into memory slots 1 and 2 for VHF NAV radio position updating if the primary DME/DME pair previously in memory slots 1 and 2 become invalid.
3) If there is a manual, procedure or route tuned station required, this station will be directed into memory slot 3. The FMC will attempt to find a station which will create a DME/DME pair with this manual, procedure or route tuned station. If found, will direct this stations distance information into memory slot 4.
4) If there is a manual, procedure or route tuned station in which the FMC can create its only DME/DME pairing, then memory slots 3 and 4 will be used for VHF NAV radio position updating with memory slot 3 containing the manual, procedure or route tuned station.
(3) DME/VOR tuning
(a)
The VOR receivers will only be able to tune in one frequency corresponding to a station selected by the FMC. This VOR station, which is colocated with the DME station, will provide bearing information.
(b)
These DME/VOR colocated stations can be tuned by the FMC for VHF NAV radio position updating. The FMC will use this mode of radio position updating if no DME/DME pair is available and the airplane is not in the approach mode thereby using the ILS station for VHF NAV radio position updating.
(c)
The FMC will automatically down mode to DME/VOR VHF NAV radio positioning when the following occurs: 1) If no DME/DME pairing can be created and there is no
manual, procedure or route tuned stations. Then memory slot 2 will retain distance and bearing information for the closest DME/VOR station.
2) If there can be no DME/DME pair created and there is a manual, procedure or route tuned station, then the FMC will tune the closest DME/VOR station into channel 4 for radio position updating. If the manual, procedure or route tuned station in channel 3 is the closest then it will be used for radio position updating.
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(4)
Station allocation priority
(a) A procedure or route tuned station will go into memory slot 3 unless there is a manually tuned station, in which case, the procedure or route tuned station will be directed to memory slot 4. Manual will always take precedence over procedure and route tuned stations. Procedure will always take precedence over route tuned stations.
(5)
Station display priority
(a) In general all manual, procedure and route tuned stations will be displayed on the IDS map display. If there is only one manual, procedure or route tuned station, it will be the only one displayed, regardless of a paired autotuned station. These displays vary corresponding to the IDS CP configuration. These displays are explained further in chapter 31-61-00.
H. VHF NAV Radio Validation
(1)
The initial radio validation occurs in the input/output processor of the FMC. The activity of the bus is first checked. This check determines if the data being received has changed between two consecutive inputs. If the data from either the VOR, DME or ILS has not changed within two consecutive inputs, the data is considered invalid. If the data is determined active, the input/output processor determines the state of the sign signal matrix (SSM). If the SSM is not on normal configuration, then the data is considered invalid. If the SSM is normal then the data goes through further validation.
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