to use for message transmission. The user also can specify the set of VHF frequencies to use for that region. Figure 28 shows an example.
Figure 28 Regions
In this example, 5 regions are defined: Europe, US, Canada, Mexico, and Cuba. The OTHER region is used for all portions of the world not covered by the other
In this example if the aircraft is in the Mexico region, SATCOM would be the preferred subnetwork. However, if SATCOM is not available, VHF would be used with a frequency of 131.725. If that frequency is not available, then 131.550 would be used. If VHF is not available, then HF would be used.
This is a general algorithm based upon location within the world and is independent of message type. However, there may be cases where a user does not want certain messages to use certain subnetworks. For instance, the user may not wish to utilize HF for Divert Reports. The downlink message encoding property of the message allows the user to specify the set of allowable subnetworks.
Regions are defined to be the union of a set of areas with each area specified by a rectangle using latitude/longitude pairs. The capability to define areas within a region allows the user to more accurately define an irregularly shaped region. Using the map in Figure 29, the example USA region is comprised of three areas (Figure 30). Area 1 defines the continental US, area 2 defines Alaska, and area 3 Hawaii.
HONEYWELL Aerospace Electronic Systems | Page 44 |
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