Home' RTCA Documents for Review : DO-343B Contents 56
© RTCA, 2018
that used to provide both DO-210D-compliant AMS(R)S/AMSS and SwiftBroadband-
based AMS(R)S/AMSS, thereby creating the potential for co-channel and adjacent
channel interference to these services in North American airspace. The FCC set limits
on ATCt to protect aeronautical communications and the FCC’s ATCt licensee in these
bands entered into a coordination agreement with Inmarsat that includes further limits
on co-channel and adjacent channel operations. In addition, the industry initiated work
to assess the impact of this decision and SC-222 was set up to address
SwiftBroadband Safety Services and Ancillary Terrestrial Component (ATCt).
The minimum performance standards contained in DO-210D and DO-262B are
intended to assure proper operation of Inmarsat AMS(R)S on all aircraft in FAA-
controlled procedural airspace beyond line of sight of any significant concentration of
ATCt base stations, and therefore well clear of any operationally significant ATCt-
induced interference. Procedural airspace is the only FAA-controlled airspace where
satellite services are currently utilized for AMS(R)S. For applications where AMS(R)S
or AMSS is used solely in procedural airspace, no ATCt-specific modifications are
required to an AES.
Aircraft seeking to use installed AMS(R)S equipment for provision of AMSS and aircraft
seeking to verify AMS(R)S communication capability within the continental United
States are cautioned that, as ATCt is deployed, additional resilience may be required
to avoid ATCt-induced interference when either in the air over a highly-dense
deployment of ATCt base stations or on the ground in close proximity to an ATCt base
station. This caution applies to both Classic Aero and SBB-based equipment.
Appendix B to this attachment provides the potential levels of such interference in these
environments together with the relevant ATCt interference models.
The analysis presented in Appendix B to this attachment is predicated upon
interference models that are limited to consideration of the impact of ATCt on Inmarsat
SBB and Classic Aero Services in the 1525 – 1559 MHz MSS band. These models do
not consider the impact of ATCt on adjacent-band airborne radionavigation satellite
services such as the Global Positioning System (GPS). Based on extensive RTCA and
government assessments [1 - 4], RTCA, FAA and others have determined that ATCt
operations per the transmission characteristics listed in this appendix are incompatible
with certified aviation GPS receivers. The assessments in [2, 3] also concluded that
ATCt operations per the transmission characteristics listed in this appendix are not
compatible with most other (non-aviation) GPS receiver types. Based on the
government assessments, the Chief of the FCC’s International Bureau has proposed
to suspend LightSquared’s ATCt authorization . LightSquared has disputed the
conclusiveness of the aviation analysis, among others, and has proposed various
alternatives that involve modified use of the ATCt frequencies.
continues to have an agreement with Inmarsat that would facilitate ATCt operation in
the band if and when ATCt compatibility issues with GPS are resolved by the FCC. The
FCC has not announced a final decision and it is considering options proposed by
LightSquared for a modified authorization that include a permanent relinquishing of
LightSquared’s authority to conduct terrestrial operations in its upper 10 MHz downlink
band at 1545-1555 MHz and a foregoing of terrestrial use of its lower 10 MHz downlink
band at 1526-1536 MHz pending the outcome of a separate rulemaking proceeding .
Thus, the interference modeling presented in Appendix B to this attachment does not
reflect a currently-authorized ATCt deployment model and is subject to future revisions.
Note: If and when ATCt is fully deployed, and depending on siting and transmitter
power of the ATCt base station, there is the possibility that ATCt interference may be
severe when the aircraft is at the gate. As indicated by the proximity model contained
in this appendix, such interference may make it impossible to verify either SBB or
Classic Aero satcom functionality prior to pushback. Operators are cautioned that such
interference may require a modification of operating procedures or AES equipment
exhibiting a greater resilience to interference.
3.6.2 Iridium AMS(R)S on the same aircraft
The minimum performance standards contained in this document are intended to
assure proper operation of Inmarsat safety services on all aircraft, and compatibility of
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