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the provisions of 4.1.8.1 with respect to the use of channels
based on 25 kHz channel spacing and, with regard to the
band 132 - 137 MHz, the provisions of the Radio Regulations
(see Introduction to 4.1). Although for Groups B, C, D and E
a preferred order of selection is not indicated, regional
planning may require a particular selection of frequencies
from these Groups in order to cater for specific regional
circumstances. This may apply particularly to the utilization
of frequencies from the band 132 - 137 MHz for reasons
of available airborne equipment andor availabiliry of
particular frequency channels for the aeronautical mobile (R)
service. It may also be found that, in a particular region, it is
desirable to select frequencies from Group B first, before
selecting frequencies from Groups C, D or E.
Chapter 4 Annex 10 - Aeronautical Telecommunications
Where all the channels of Groups A, B, C, D and E of the
list at 4.1.8.1.2 are insujicient to meet the requirements of a
region, a part or parts of the band may be designated as
containing 8.33 kHz width channels or designated as
supporting VDL Mode 3. For parts of the band containing
8.33 kHz width channels, the appropriate frequencies from
Group F should be used in accordance with 4.1.8.1.1.1 and
4.1.8.1.2. It should be noted that the designation offrequencies
in Group F differs from that of the corresponding frequencies
in Groups A to E to emphasize the difference in channel width.
For part of the bands supporting VDL Mode 3, frequencies
from Groups A, B, C, D and E are utilized on a time-division
basis. A single frequency supports multiple channels, each
utilizing the frequency in periodic time frames or time slots.
Specific time slots for VDL Mode 3 are identified using the
numeric designators of Table 4-1 (bis).
Although for Group F a preferred order of selection is not
indicated, regional planning may require a particular selection
of frequencies from this group in order to cater for specific
regional circumstances.
In many regions particular frequencies have already been
assigned for particular functions as, for instance, aerodrome
or approach control. The plan does not make such assignments
(except in respect to the emergency channel and ground
sewice frequencies), such action being taken regionally if
considered desirable.
4.1.8.1 The frequencies in the band 117.975 - 137 MHz
for use in the aeronautical mobile (R) service shall be selected
from the list in 4.1.8.1.2.
4.1.8.1.1 When the number of frequencies required in a
particular region does not exceed the number of frequencies
contained in Group A of 4.1.8.1.2, the frequencies to be used
shall be selected in sequence, in so far as practicable, from
those in Group A of 4.1.8.1.2.
4.1.8.1.1.1 When the number of frequencies required in a
particular region exceeds those available in Groups A to E of
4.1.8.1.2, parts of the band shall be designated as containing
8.33 kHz width channels (voice) or as containing VDL
Mode 3. Appropriate frequencies shall be selected from
Group F of 4.1.8.1.2 for 8.33 kHz channel assignments or
from Groups A to E in accordance with the time-slot
assignments in accordance with Table 4-1 (bis) for VDL
Mode 3. The remainder of the band shall continue to be used
for 25 kHz width channels selected from the appropriate parts
of Groups A to E.
Note 1.- The frequencies 121.425 - 121.575MHz inclusive,
123.075 - 123.125 MHz inclusive and 136.500 -
136.975 MHz inclusive are not available for assignment to
channels of less than 25 kHz width.
Note 2.- Services that continue operation using 25 kHz
assignments will be protected in regions implementing
8.33 kHz channel spacing.
4.1.8.1.2 List of assignable frequencies
The list of assignable frequencies is shown in the Appendix to
this chapter.
4.1.8.1.3 Recommendation.- Frequencies for operational
control communications may be required to enable
aircraji operating agencies to meet the obligations prescribed
in Annex 6, Part I, in which case they should be selected from
the bands 128.825 - 132.025 MHz. These frequencies should
be chosen, in so far as practicable, from the upper end of the
band and in sequential order:
Note.- It is recognized that the assignment of such
frequencies and the licensing of the operation of the related
facilities are matters for national determination. However; in
regions where a problem exists with respect to the provision of
frequencies for operational control purposes. it may be
advantageous if States endeavour to coordinate the requirements
of aircraft operating agencies for such channels prior to
　
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