Circular Letter
COMSAR/Circ.28
INTERNATIONAL NAVTEX SERVICE
(of 12 June 2001)
1.
The Sub-Committee on Radiocommunications and Search and Rescue (COMSAR), at its
fifth session (11 to 15 December 2000), agreed to a number of recommendations
(reproduced at annex) aimed at reducing interference and volume of information
in the International NAVTEX service.
2.
In addition, COMSAR 5 agreed that it was important to encourage Administrations
to migrate non-English language broadcasts and broadcasts of information
provided specifically for non-SOLAS vessels from 518 kHz to 490 kHz or 4209.5
kHz, as appropriate.
3.
The Maritime Safety Committee, at its seventy-fourth session (30 May to 8 June
2001), approved the recommendations made by COMSAR 5 and urged Administrations
to complete this migration by 1 January 2005.
4.
Member Governments are invited to bring this circular to the attention of all
Maritime Safety Information (MSI) providers and National Telecommunication
Administrations for consideration and action as appropriate.
ANNEX.
Interference between stations and the use of 490 kHz
1.
Although NAVTEX continues to be generally reliable and an effective medium for
the promulgation of Maritime Safety Information, the world-wide infrastructure
continues to expand and the volume of information that each Administration
disseminates through a NAVTEX service on 518 kHz continues to increase. There
is now a real danger that in some geographical areas, without firm management,
both the system and system users may become overloaded with information on this
frequency.
2.
Many stations are filling their allotted 10 minute time slots and an increasing
number are over-running. Instances of interference with neighbouring stations,
as a result of over-running the time allocation, are also increasing. Where
adjacent stations have B1 characters which follow alphabetically
(i.e. time slots abut), if the first station over runs, it may mask the phasing
signal of the second station such that, to the user, it seems as if the second
station is off the air. Safety-critical information from the second station,
although broadcast, may not be received by the system users. Over-run is
usually caused by one or more of the following:
.1 a significant
increase in safety-critical activity such as cable laying. Navigational
warnings promulgating such activity often include numerous waypoints which are
listed by Latitude and Longitude;
.2
meteorological information provided in a manner which is not concise and easily
assimilated by the system user or for a much wider area than is covered by the
NAVTEX station;
.3 additional
information provided for non-SOLAS system users e.g. longer-range weather
forecasts for fishing and recreational vessels (see paragraph 3 below); and
.4 information
to meet specific national requirements. This includes national language
broadcasts and other information which is sometimes required to be broadcast by
national statute rather than IMO resolutions.
3.
As the GMDSS spreads to non-SOLAS mariners, their requirements for information
are often different from the SOLAS ships and may be determined at a national
level. SOLAS ships trading internationally usually pass through the area of
coverage of a NAVTEX transmitter in a day; for them a 24-hour weather forecast usually
suffices. However, fishing vessels and recreational vessels often remain in the
same vicinity for several days and may require much longer range forecasts
which take up more transmission time.
4.
In order to keep the quantity of information that is broadcast on 518 kHz to
manageable levels and to reduce avoidable interference on this frequency, it is
recommended that:
.1
Administrations monitor the volume of data broadcast and, together with
adjacent Administrations, actively manage the system to ensure that
interference caused by over-running allocated time slots is minimized; and
.2
Administrations migrate non-English language broadcasts, and broadcasts of
information provided specifically for non-SOLAS vessels from 518 kHz to a
national broadcast on 490 kHz or 4209.5 kHz as required. B1
characters for these frequencies will be allocated by the International NAVTEX
Co-ordinating Panel, on request.