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Parameter Value Notes
Frequency availability
(allocation status)
Available Band globally available.
Dependencies Time-source Each ground station needs a time reference for the
proper working of its squitter. The access to the
physical medium is a random access to avoid the
collision as far as possible, and there is a need for
temporal co-ordination in this procedure.
Power Ground – 6kW or less
Air – 400W or less
This is the transmitter peak envelope power [ref ICAO
SARPS – Annex 10].
Table 5- 1 HFDL Characteristics
5.3.3.3 AMSS
The AMSS is a mobile communications system intended for provision of digital voice and
data communications services to and from aircraft. The range of possible applications for
these services includes airline passenger communications (public correspondence),
airline operations communications and air traffic control services.
The major elements of AMSS are:
• Space Segment: in particular the satellite communications transponders and
associated frequency bands assigned for use by the Aeronautical Mobile
Satellite System. The space segment uses transparent payloads.
• Aircraft Earth Stations (AES) which interface with the space segment (at L-band)
for communications with Ground Earth Stations, and which interface in the
aircraft with ACARS and other data equipment, and with crew and passenger
voice equipment, in accordance with the relevant technical and operational
requirements;
• Ground Earth Stations (GES): Which interface with the space segment (at Cband
and L-band) and with the fixed networks, and which are operated in
accordance with the relevant technical and operational requirements for
communications with AESs; GESs operate to their own essentially independent
but interlinked networks; and
• Network Coordination Stations (NCS): Located at designated earth stations,
which interface via the space segment (at C-band and L-band) with the GESs for
the purpose of allocating satellite channels.
AESs supporting circuit-mode voice services (Classes 2 and 3) are classified according to
the type of voice services that they can support; that is safety or non-safety. The Inmarsat
safety/non-safety classification concerns only the minimum EIRP supported by the AES
installation. This in turn reflects a theoretical voice channel return link availability that is
expected for a particular AES.
It should be noted that AESs which do not meet the minimum EIRP for the safety
classification will not comply with the existing minimum EIRP requirements of ICAO
SARPs or RTCA MOPS for voice services. The relaxed EIRP requirements for the nonsafety
classification are intended to meet the needs of those AES users wishing to carry
aeronautical public correspondence circuit-mode traffic only, at the lower channel
availability figure.
Both safety and non-safety AESs are fully compliant with the ITU International Radio
Regulations criteria for the use of the AMSS band and provide for strict observance of the
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